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Polymers
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Development in Fiber-Reinforced Polymer Composites
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Development in Fiber-Reinforced Polymer Composites

A special issue of Polymers (ISSN 2073-4360). This special issue belongs to the section "Polymer Composites and Nanocomposites".

Deadline for manuscript submissions: 31 May 2024 | Viewed by 85355

Special Issue Editors

Prof. Dr. Juan Carlos Merino

E-Mail Website
Guest Editor
1. Department of Condensed Matter Physics, Escuela de Ingenierías Industriales, University of Valladolid, Paseo del Cauce, 59, 47011 Valladolid, Spain
2. Department of Materials-Process-Product, Foundation for Research and Development in Transport and Energy (CIDAUT) <<Centro de Excelencia Cervera>>, Parque Tecnológico de Boecillo, 47051 Valladolid, Spain
Interests: thermoset polymers; thermoplastic polymers; polymer composites; in-situ polymerization; biopolymers; reinfocements; recyclability; sustanability; circular economy
Dr. Mercedes Santiago-Calvo

E-Mail Website
Guest Editor
Department of Materials-Process-Product, Foundation for Research and Development in Transport and Energy (CIDAUT) <<Centro de Excelencia Cervera>>, Parque Tecnológico de Boecillo, 47051 Valladolid, Spain
Interests: thermoset polymers; thermopalstic polymers; polymer composites; in-situ polymerization; biopolymers; reinfocements; recyclability; sustanability; circular economy
Dr. María Asensio-Valentin

E-Mail Website
Guest Editor
Department of Materials-Process-Product, Foundation for Research and Development in Transport and Energy (CIDAUT) <<Centro de Excelencia Cervera>>, Parque Tecnológico de Boecillo, 47051 Valladolid, Spain
Interests: nanocomposites; thermoplastic resin; recycled; glass fibers; sepiolite nanoparticles; pultrusion; in-situ polymerization; reactive extrusion; mechanical recycling
Dr. Karina Nuñez

E-Mail Website
Guest Editor
Department of Materials-Process-Product, Foundation for Research and Development in Transport and Energy (CIDAUT) <<Centro de Excelencia Cervera>>, Parque Tecnológico de Boecillo, 47051 Valladolid, Spain
Interests: biomaterials; nano & composites; circular economy; recycling; polymer blends; synthesis; microstructural

Special Issue Information

Dear Colleagues,

Fiber-reinforced polymer (FRP) composites, constituted by a polymer matrix and fibers, are known as high-performance composite materials due to the combination of the advanced properties such as extremely high strength, high stiffness, and lightweight. The fibers incorporated in polymer composite can be natural or synthetic and are applied in the fabrication of advanced engineering structures for many sectors for instance construction, automotive, aerospace and maritime, among others. At the industrial level, carbon, glass and polymer fibers are one of the most common reinforcement in matrices mainly based on thermosetting polymers, such as epoxy or polyester resins, as well as on thermoplastic polymers. However, these composite materials based on synthetic fibers have significant drawbacks related to the environmentally pollution caused by their residues and also their source from non-renewable recourses. Due to these previous concerns, much of the researcher efforts in the field of FRP composites are focusing on the new developments in recycling processes that allow recovering the fibers with good qualities and also the corresponding monomers of the polymer matrices, and on the replacement of both synthetic fibers by natural fibers and polymer matrixes synthesized from petroleum by biopolymers which allow obtaining more renewable and eco-friendly products.

This Special Issue on “Development in Fiber-reinforced Polymer Composites” supposes an opportunity to submit research and review manuscripts associated to polymeric composites containing fibers and also to polymeric materials from renewable or recycling resources. It covers all types of polymeric matrices (thermoplastics, thermosets, biopolymers, etc) and fibers (synthetic, natural, recycled fibers, etc), and involves novel developments, innovations and applications in the field of the FRP composites, with special emphasis on the waste recycling and the manufacturing of bio-based products.

Prof. Dr. Juan Carlos Merino
Dr. Mercedes Santiago-Calvo
Dr. María Asensio Valentin
Dr. Karina Nuñez
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Polymers is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • polymer composites
  • natural fibers
  • synthetic fibers
  • recycled fibers
  • thermoset polymers
  • thermoplastic polymers
  • recycling
  • renewable recourses
  • biopolymers
  • properties

Published Papers (40 papers)

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12 pages, 1624 KiB  
Article
Mechanical Properties and Ion Release from Fibre-Reinforced Glass Ionomer Cement
by Anja Ivica, Ivan Šalinović, Silvana Jukić Krmek, Sufyan Garoushi, Lippo Lassila, Eija Säilynoja and Ivana Miletić
Polymers 2024, 16(5), 607; https://0-doi-org.brum.beds.ac.uk/10.3390/polym16050607 - 23 Feb 2024
Viewed by 554
Abstract
The aim of this study was to compare the mechanical properties and ion release from a commercially available resin-modified glass ionomer cement to a formulation reinforced by the addition of short glass fibres at various percentages. Methods: Three experimental groups were prepared by [...] Read more.
The aim of this study was to compare the mechanical properties and ion release from a commercially available resin-modified glass ionomer cement to a formulation reinforced by the addition of short glass fibres at various percentages. Methods: Three experimental groups were prepared by adding a mass ratio of 10%, 15% and 20% of short glass fibres to the powder portion of the cement from a capsule (GC Fuji II LC), while the control group contained no fibres. Microhardness (n = 12), fracture toughness, and flexural, compressive and diametral tensile strength (n = 8) were evaluated. To study ion release, readings were obtained utilising fluoro-selective and calcium-selective electrodes after 24 h, 7 days and 30 days (n = 12). The spatial distribution of fibres within the material was evaluated through scanning electron microscopy. The data were analysed using one-way ANOVA with a Bonferroni adjustment. Results: The findings suggest that elevating fibre weight ratios to 20 wt% results in improved mechanical properties (p < 0.05) in microhardness, flexural strength, diametral tensile strength and fracture toughness. In terms of ion release, a statistically significant difference (p < 0.001) was observed between the groups at the conclusion of 24 h and 7 days, when the fluoride release was much higher in the control group. However, after 30 days, no significant distinction among the groups was identified (p > 0.05). Regarding calcium release, no statistically significant differences were observed among the groups at any of the evaluated time points (p > 0.05). SEM showed the fibres were homogeneously incorporated into the cement in all experimental groups. Conclusions: Resin-modified glass ionomer enhanced with short glass fibres at a weight loading of 20% showcased the most favourable mechanical properties while concurrently maintaining the ability to release fluoride and calcium after a 30-day period. Full article
(This article belongs to the Special Issue Development in Fiber-Reinforced Polymer Composites)
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13 pages, 4871 KiB  
Article
Effect of Hydrothermal Aging on Damping Properties in Sisal Mat-Reinforced Polyester Composites
by Moisés F. E. Silva, Beatriz R. Silva, Adrielle N. Marques, Silvana Mattedi and Ricardo F. Carvalho
Polymers 2024, 16(2), 166; https://0-doi-org.brum.beds.ac.uk/10.3390/polym16020166 - 05 Jan 2024
Viewed by 676
Abstract
Hydrothermal aging is a matter of considerable concern for natural fiber-reinforced polymers; it can alter dimensional stability and induce microcracks and macro strain on the composite structure. This study applied a sorption kinetic model and examined the effects of water on the damping [...] Read more.
Hydrothermal aging is a matter of considerable concern for natural fiber-reinforced polymers; it can alter dimensional stability and induce microcracks and macro strain on the composite structure. This study applied a sorption kinetic model and examined the effects of water on the damping factor of sisal mat-reinforced polyester composites. The experimental data were fitted well using a Boltzmann sigmoid function, suggesting a promising first step toward kinetic water sorption modeling. Additionally, a damping test was carried out using the impulse excitation technique, highlighting the composite material’s dynamic response under varying water absorption conditions. The result showed that damping exhibited sensitivity to water absorption, increasing significantly during the first 24 h of immersion in water, then remained steady over time, inferring a critical time interval. An empirical model proved satisfactory with the correlation coefficient for sorption rates and damping of sisal mat polymeric composites. Full article
(This article belongs to the Special Issue Development in Fiber-Reinforced Polymer Composites)
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18 pages, 40551 KiB  
Article
Optimization of Thermoplastic Pultrusion Parameters of Jute and Glass Fiber-Reinforced Polypropylene Composite
by Ponlapath Tipboonsri, Supaaek Pramoonmak, Putinun Uawongsuwan and Anin Memon
Polymers 2024, 16(1), 83; https://0-doi-org.brum.beds.ac.uk/10.3390/polym16010083 - 27 Dec 2023
Viewed by 691
Abstract
Thermoplastic pultrusion is a suitable process for fabricating continuous unidirectional thermoplastics with a uniform cross-section, high mechanical properties due to continuous fiber reinforcement, low cost, and suitability for mass production. In this paper, jute and glass fibers were reinforced with a polypropylene matrix [...] Read more.
Thermoplastic pultrusion is a suitable process for fabricating continuous unidirectional thermoplastics with a uniform cross-section, high mechanical properties due to continuous fiber reinforcement, low cost, and suitability for mass production. In this paper, jute and glass fibers were reinforced with a polypropylene matrix and fabricated using the thermoplastic pultrusion process. The volumetric fraction of the composite was designed by controlling the filling ratio of the reinforcing fiber and matrix. The effects of molding parameters were investigated, such as pulling speed and molding temperature, on the mechanical properties and microstructure of the final rectangular profile composite. The pulling speed and molding temperature varied from 40 to 140 mm/min and 190 to 220 °C, respectively. The results showed that an increase in molding temperature initially led to an increase in mechanical properties, up to a certain point. Beyond that point, they started to decrease. The resin can be easily impregnated into the fiber due to the low viscosity of thermoplastic at high temperatures, resulting in increased mechanical properties. However, the increase in molding temperature also led to a rise in void content due to moisture in jute fiber, resulting in decreased mechanical properties at 210 °C. Meanwhile, un-impregnation decreased with the increase in molding temperature, and the jute fiber began to degrade at high temperatures. In the next step, with varying pulling speed, the mechanical properties decreased as the pulling speed increased, with a corresponding increase in void content and un-impregnation. This effect occurred because the resin had a shorter time to impregnate the fiber at a higher pulling speed. The decrease in mechanical properties was influenced by the increase in void content and un-impregnation, as the jute fiber degraded at higher temperatures. Full article
(This article belongs to the Special Issue Development in Fiber-Reinforced Polymer Composites)
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13 pages, 4279 KiB  
Article
Enhancing Stiffness and Oil Resistance of Fluorosilicone Rubber Composites through Untreated Cellulose Reinforcement
by Ye-Won Park, Jeong-Hwan Yoon, Kyoung-Ho Shin, Yeon-Jee Cho, Ju-Ho Yun, Won-Hee Han, Min-Hyuk Hong, Dong-Gug Kang and Hye-Young Kim
Polymers 2023, 15(23), 4489; https://0-doi-org.brum.beds.ac.uk/10.3390/polym15234489 - 22 Nov 2023
Viewed by 749
Abstract
Fluorosilicone rubber, essential in automotive and aerospace owing to its excellent chemical resistance, plays a pivotal role in sealing technology, addressing the industry’s evolving demands. This study explores the preparation and properties of fibrillated cellulose-reinforced fluorosilicone rubber composites to enhance their stiffness and [...] Read more.
Fluorosilicone rubber, essential in automotive and aerospace owing to its excellent chemical resistance, plays a pivotal role in sealing technology, addressing the industry’s evolving demands. This study explores the preparation and properties of fibrillated cellulose-reinforced fluorosilicone rubber composites to enhance their stiffness and oil resistance. Fibrillated cellulose sourced as a wet cake and subjected to processing and modification is incorporated into a fluorosilicone rubber matrix. The resulting composites are analysed by tensile and compression tests, along with compressive stress-relaxation testing in air and in an oil-immersed environment. The findings demonstrate significant improvements in the mechanical properties, including an increased Young’s modulus and elongation at break, whereas the tensile strength remained uncompromised throughout the testing procedures. Morphological analysis of the fracture surfaces revealed a remarkable interfacial affinity between the fibrillated cellulose and rubber matrix, which was attributed in part to the modified fatty acids and inorganic nanoparticles. The presence of fibrillated cellulose enhanced the stress-relaxation characteristics under oil-immersion conditions. These results contribute to the domain of advanced elastomer materials, with potential for applications requiring enhanced mechanical properties and superior oil resistance. Full article
(This article belongs to the Special Issue Development in Fiber-Reinforced Polymer Composites)
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15 pages, 15192 KiB  
Article
Hair-Reinforced Elastomer Matrix Composites: Formulation, Mechanical Testing, and Advanced Microstructural Characterization
by Eugene S. Statnik, Julijana Cvjetinovic, Semen D. Ignatyev, Loujain Wassouf, Alexey I. Salimon and Alexander M. Korsunsky
Polymers 2023, 15(22), 4448; https://0-doi-org.brum.beds.ac.uk/10.3390/polym15224448 - 17 Nov 2023
Viewed by 863
Abstract
Epoxy matrix composites reinforced with high-performance fibers, such as carbon, Kevlar, and glass, exhibit excellent specific stiffness and strength in many mechanical applications. However, these composites are disappointingly non-recyclable and are usually disposed of in landfill sites, with no realistic prospect for biodegradation [...] Read more.
Epoxy matrix composites reinforced with high-performance fibers, such as carbon, Kevlar, and glass, exhibit excellent specific stiffness and strength in many mechanical applications. However, these composites are disappointingly non-recyclable and are usually disposed of in landfill sites, with no realistic prospect for biodegradation in a reasonable time. In contrast, moldable composites with carbonized elastomeric matrices developed in the last decades possess attractive mechanical properties in final net-shape products and can also be incinerated or recycled. Many carbon and inorganic fillers have recently been evaluated to adjust the properties of carbonized elastomeric composites. Renewable organic fillers, such as human or animal hair, offer an attractive fibrous material with substantial potential for reinforcing composites with elastomeric matrices. Samples of unidirectional fiber composites (with hair volume fractions up to 7%) and quasi-isotropic short fiber composites (with hair volume fractions up to 20%) of human hair-reinforced nitrile butadiene rubbers (HH-NBRs) were produced in the peroxide-cured and carbonized states. The samples were characterized using scanning electron microscopy (SEM), Raman spectroscopy, and photoacoustic microscopy. Mechanical tests were performed under tension using a miniature universal testing machine. The expected effect of fiber reinforcement on the overall mechanical performance was demonstrated for both cured and carbonized composites. Considerable enhancement of the elastic modulus (up to ten times), ultimate tensile strength (up to three times), and damage tolerance was achieved. The evidence of satisfactory interfacial bonding between hair and rubber was confirmed via SEM imaging of fracture surfaces. The suitability of photoacoustic microscopy was assessed for 3D reconstructions of the fiber sub-system’s spatial distribution and non-destructive testing. Full article
(This article belongs to the Special Issue Development in Fiber-Reinforced Polymer Composites)
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18 pages, 8518 KiB  
Article
Cognizant Fiber-Reinforced Polymer Composites Incorporating Seamlessly Integrated Sensing and Computing Circuitry
by Mohammed Jaradat, Jorge Loredo Duran, Daniel Heras Murcia, Leah Buechley, Yu-Lin Shen, Christos Christodoulou and Mahmoud Reda Taha
Polymers 2023, 15(22), 4401; https://0-doi-org.brum.beds.ac.uk/10.3390/polym15224401 - 14 Nov 2023
Viewed by 806
Abstract
Structural fiber-reinforced polymer (FRP) composite materials consisting of a polymer matrix reinforced with layers of high-strength fibers are used in numerous applications, including but not limited to spacecraft, vehicles, buildings, and bridges. Researchers in the past few decades have suggested the necessary integration [...] Read more.
Structural fiber-reinforced polymer (FRP) composite materials consisting of a polymer matrix reinforced with layers of high-strength fibers are used in numerous applications, including but not limited to spacecraft, vehicles, buildings, and bridges. Researchers in the past few decades have suggested the necessary integration of sensors (e.g., fiber optic sensors) in polymer composites to enable health monitoring of composites’ performance over their service lives. This work introduces an innovative cognizant composite that can self-sense, compute, and implement decisions based on sensed values. It is a critical step towards smart, resilient infrastructure. We describe a method to fabricate textile sensors with flexible circuitry and a microcontroller within the polymer composite, enabling computational operations to take place in the composite without impacting its integrity. A microstructural investigation of the sensors showed that the amount of oxidative agent and soaking time of the fabric play a major role in the adsorption of polypyrrole (PPy) on fiberglass (FG). XPS results showed that the 10 g ferric chloride solution with 6 h of soaking time had the highest degree of protonation (28%) and, therefore, higher adsorption of PPy on FG. A strain range of 30% was achieved by examining different circuitry and sensor designs for their resistance and strain resolution under mechanical loading. A microcontroller was added to the circuit and then embedded within a composite material. This composite system was tested under flexural loading to demonstrate its self-sensing, computing, and actuation capabilities. The resulting cognizant composite demonstrated the ability to read resistance values and measure strain using the embedded microcontroller and autonomously actuate an LED light when the strain exceeds a predefined limit of 2000 µε. The application of the proposed FRP system would provide in situ monitoring of structural composite components with autonomous response capabilities, as well as reduce manufacturing, production, and maintenance costs. Full article
(This article belongs to the Special Issue Development in Fiber-Reinforced Polymer Composites)
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16 pages, 15448 KiB  
Article
Effects of Melt-Blown Processing Conditions on Nonwoven Polylactic Acid and Polybutylene Succinate
by Patcharee Pratumpong, Thananya Cholprecha, Nanjaporn Roungpaisan, Natee Srisawat, Surachet Toommee, Chiravoot Pechyen and Yardnapar Parcharoen
Polymers 2023, 15(20), 4189; https://0-doi-org.brum.beds.ac.uk/10.3390/polym15204189 - 23 Oct 2023
Cited by 1 | Viewed by 1349
Abstract
This research aimed to prepare nonwovens from polylactic acid and polybutylene succinate using the melt-blown process while varying the melt-blown process parameters, including air pressure (0.2 and 0.4 MPa) and die-to-collector distance (15, 30, and 45 cm). Increasing the air pressure and die-to-collector [...] Read more.
This research aimed to prepare nonwovens from polylactic acid and polybutylene succinate using the melt-blown process while varying the melt-blown process parameters, including air pressure (0.2 and 0.4 MPa) and die-to-collector distance (15, 30, and 45 cm). Increasing the air pressure and die-to-collector distance resulted in the production of smaller fibers. Simultaneously, the tensile strength was dependent on the polymer, air pressure, and die-to-collector distance used, and the percentage elongation at the break tended to increase with an increasing die-to-collector distance. Regarding thermal properties, the PBS nonwovens exhibited an increased level of crystallinity when the die-to-collector distance was raised, consistent with the degree of crystallinity obtained from X-ray diffraction analysis. Polylactic acid could be successfully processed into nonwovens under all six investigated conditions, whereas nonwoven polybutylene succinate could not be formed at a die-to-collector distance of 15 cm. However, both polymers demonstrated the feasibility of being processed into nonwovens using the melt-blown technique, showing potential for applications in the textile industry. Full article
(This article belongs to the Special Issue Development in Fiber-Reinforced Polymer Composites)
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16 pages, 3725 KiB  
Article
Characterisation of Curing of Vinyl Ester Resin in an Industrial Pultrusion Process: Influence of Die Temperature
by Sai Ajay Chandra Chaparala, Omar Alajarmeh, Tristan Shelley, Xuesen Zeng, Kendric Rendle-Short, Dean Voice and Peter Schubel
Polymers 2023, 15(18), 3808; https://0-doi-org.brum.beds.ac.uk/10.3390/polym15183808 - 18 Sep 2023
Viewed by 1043
Abstract
Pultrusion is a high-volume manufacturing process for Fibre-Reinforced Polymer (FRP) composites. It requires careful tuning and optimisation of process parameters to obtain the maximum production rate. The present work focuses on the correlation between the set die temperatures of 80 °C, 100 °C, [...] Read more.
Pultrusion is a high-volume manufacturing process for Fibre-Reinforced Polymer (FRP) composites. It requires careful tuning and optimisation of process parameters to obtain the maximum production rate. The present work focuses on the correlation between the set die temperatures of 80 °C, 100 °C, 120 °C, and 140 °C and the resin cure state at constant pull speeds. Lab-scale oven trials were conducted to understand the thermal behaviour of the resin system and to provide a temperature range for the pultrusion trials. Dielectric Analysis (DEA) was used during pultrusion trials to monitor the effect of die temperature on the cure progression. The DEA results showed that, by increasing die temperature, the exothermic peak shifts closer towards the die entry. Moreover, the degree of cure for samples processed at 140 °C was 97.7%, in comparison to 86.2% for those cured at 100 °C. The rate of conversion and the degree of cure correspond directly to the set die temperatures of the pultrusion trials, contributing to understanding the effect of die temperature on cure progression. Mechanical and thermal material properties were measured. Samples cured at 120 °C showed the highest mechanical performance, exceeding those cured at 140 °C, linked to the generation of higher internal stress due to the higher rate of conversion. This work can be used as a guide for pultruded composite sections, to understand the cure behaviour of resin systems under various applied temperatures and the impact of the die temperature conditions on thermal and mechanical properties. Full article
(This article belongs to the Special Issue Development in Fiber-Reinforced Polymer Composites)
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16 pages, 7688 KiB  
Article
Synchronous Improvement of Mechanical and Damping Properties of Structural Damping Composites with Polyetherimide Non-Woven Fabric Interlayers Loaded with Polydopamine and Carbon Nanotubes
by Shihao Zhou, Yuanchang Lai, Junchi Ma, Bin Liu, Nannan Ni, Feng Dai, Yahong Xu, Zhaodi Wang and Xin Yang
Polymers 2023, 15(14), 3117; https://0-doi-org.brum.beds.ac.uk/10.3390/polym15143117 - 21 Jul 2023
Viewed by 990
Abstract
Structural damping composites exhibit considerable potential in aerospace and other fields due to their excellent damping and vibration reduction performance, as well as their structural carrying capacity. However, conventional structural damping composite materials generally do not combine excellent mechanical and damping properties at [...] Read more.
Structural damping composites exhibit considerable potential in aerospace and other fields due to their excellent damping and vibration reduction performance, as well as their structural carrying capacity. However, conventional structural damping composite materials generally do not combine excellent mechanical and damping properties at the same time, which makes it difficult for them to meet the practical demand in engineering. In this paper, polyetherimide (PEI) non-woven fabric interlayer materials loaded with quantified polydopamine (PDA) and carboxylated multi-walled carbon nanotubes (MWCNTs-COOH) were used to prepare carbon fiber-reinforced bismaleimide composites through the co-curing process. The mechanical and damping properties of the composites were systematically studied. The results demonstrate that PEI non-woven fabric interlayers loaded with PDA and MWCNTs-COOH can synchronously improve the mechanical and damping properties of the co-cured composites. The incorporation of carbon nanotubes and polydopamine during the co-curing process synergistically improves the flexural strength, flexural modulus, interlaminar shear strength, and impact fracture toughness of the composites. Most importantly, damping properties show an increase of 45.0% in the loss factor of the co-cured composites. Moreover, the reinforcement mechanism was investigated using the optical microscopy and scanning electron microscopy, which indicated that the PEI interlayers loaded with carbon nanotubes and polydopamine form a rich resin area between the layers of the composites. Full article
(This article belongs to the Special Issue Development in Fiber-Reinforced Polymer Composites)
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24 pages, 5695 KiB  
Article
Characterization of Hybrid FRP Composite Produced from Recycled PET and CFRP
by Ghdayra Almahri, Kaouthar Madi, Fatima Alkaabi, Yahia Badran, Khaled Shehadeh, Amged ElHassan, Waleed Ahmed and Salem Alzahmi
Polymers 2023, 15(13), 2946; https://0-doi-org.brum.beds.ac.uk/10.3390/polym15132946 - 04 Jul 2023
Cited by 3 | Viewed by 1112
Abstract
In recent years, carbon fiber has experienced a significant surge in popularity attributed to its exceptional properties, including its high-temperature resistance, mechanical strength, and cost-effectiveness. Many industries have been attracted to the prevalent use of carbon-fiber-reinforced polymers or plastics (CFRP). However, the increasing [...] Read more.
In recent years, carbon fiber has experienced a significant surge in popularity attributed to its exceptional properties, including its high-temperature resistance, mechanical strength, and cost-effectiveness. Many industries have been attracted to the prevalent use of carbon-fiber-reinforced polymers or plastics (CFRP). However, the increasing demand for carbon fiber has created a waste recycling problem that needs to be addressed. This research aimed to develop a recycled composite using PET waste as a solution to the growing demand for both materials. The recycled carbon fibers were processed chemically and mechanically to generate power for this process. Various samples were tested with different proportions of CF (10%, 20%, 30%, and 40%) to analyze their mechanical properties. The recycled composites are examined under tensile test conditions to further explore the waste carbon reinforcement’s effect on polymers’ characteristics. Scanning electron microscopy was also utilized for mechanical morphology evaluations. After analyzing the data, it was found that samples containing 20% CF had the highest elastic modulus value among all the mixes. This is attributed to the reinforcing effect of the fibers. The Elasticity Modulus of the filaments increased with the concentration of CF, reaching its peak at 20% before decreasing. This trend is also apparent in the visual representations. When compared to recycling, the Elasticity Modulus value of 20% CF filament increased by 97.5%. The precise value for CF with a 20% filament is 4719.3 MPa. Moreover, the composite samples were analyzed using SEM to characterize them, and it was discovered that the incorporation of 20% CF/PET filler produced the composition with the highest strength. Full article
(This article belongs to the Special Issue Development in Fiber-Reinforced Polymer Composites)
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13 pages, 16697 KiB  
Article
Effect of Strain Rate on Tensile Properties of Carbon Fiber-Reinforced Epoxy Laminates with Different Stacking Sequences and Ply Orientations
by Donglin Gao, Zuguo Bao, Weijian Han, Xianpeng Wang, Shiyao Huang, Li Huang, Qiuren Chen, Hailong Zhao and Yahong Xu
Polymers 2023, 15(12), 2711; https://0-doi-org.brum.beds.ac.uk/10.3390/polym15122711 - 17 Jun 2023
Cited by 3 | Viewed by 1426
Abstract
In practical application situations, a carbon fiber-reinforced polymer (CFRP) is often subjected to complex dynamic loadings. The effect of the strain rate on mechanical properties is very important for the CFRP design and product development. In this work, static and dynamic tensile properties [...] Read more.
In practical application situations, a carbon fiber-reinforced polymer (CFRP) is often subjected to complex dynamic loadings. The effect of the strain rate on mechanical properties is very important for the CFRP design and product development. In this work, static and dynamic tensile properties of CFRP with different stacking sequences and ply orientations were investigated. The results showed that the tensile strengths of CFRP laminates were sensitive to the strain rate, while Young’s modulus was independent of the strain rate. Moreover, the strain rate effect was related to the stacking sequences and ply orientations. The experimental results showed that the strain rate effects of the cross-ply laminates and quasi-isotropic-ply laminates were lower than that of the unidirectional-ply laminates. Finally, the failure modes of CFRP laminates were investigated. Failure morphology demonstrated that the differences in strain rate effects among cross-ply laminates, quasi-isotropic-ply laminates, and unidirectional-ply laminates were caused by the mismatch between the fiber and the matrix when the strain rate increased. Full article
(This article belongs to the Special Issue Development in Fiber-Reinforced Polymer Composites)
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20 pages, 8445 KiB  
Article
Sustainability Assessment of the End-of-Life Technologies for Biocomposite Waste in the Aviation Industry
by Špela Ferjan, Milkica Jovičić, Nora Lardiés Miazza, Tom Ligthart, Clare Harvey, Sergio Fita, Rajesh Mehta and Pouya Samani
Polymers 2023, 15(12), 2689; https://0-doi-org.brum.beds.ac.uk/10.3390/polym15122689 - 15 Jun 2023
Cited by 2 | Viewed by 1331
Abstract
Biocomposites have emerged as promising alternative materials for the aviation industry. However, there is a limited body of scientific literature addressing the end-of-life management of biocomposites. This article evaluated different end-of-life technologies for biocomposite recycling in a structured, five-step approach applying the innovation [...] Read more.
Biocomposites have emerged as promising alternative materials for the aviation industry. However, there is a limited body of scientific literature addressing the end-of-life management of biocomposites. This article evaluated different end-of-life technologies for biocomposite recycling in a structured, five-step approach applying the innovation funnel principle. First, ten end-of-life (EoL) technologies were compared in terms of their circularity potential and technology readiness levels (TRL). Second, a multi-criteria decision analysis (MCDA) was carried out to find out the top four most promising technologies. Afterwards, experimental tests were conducted at a laboratory scale to evaluate the top three technologies for recycling biocomposites by analysing (1) three types of fibres (basalt, flax, carbon) and (2) two types of resins (bioepoxy and Polyfurfuryl Alcohol (PFA) resins). Subsequently, further experimental tests were performed to identify the top two recycling technologies for the EoL treatment of biocomposite waste from the aviation industry. Finally, the sustainability and economic performance of the top two identified EoL recycling technologies were evaluated through life cycle assessment (LCA) and techno-economic analysis (TEA). The experimental results, performed via the LCA and TEA assessments, demonstrated that both solvolysis and pyrolysis are technically, economically, and environmentally viable options for the EoL treatment of biocomposite waste from the aviation industry. Full article
(This article belongs to the Special Issue Development in Fiber-Reinforced Polymer Composites)
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17 pages, 3379 KiB  
Article
Cooperative Effect of Chemical and Physical Processes for Flame Retardant Additives in Recycled ABS
by Alicia Rodriguez, Manuel Herrero, Maria Asensio, Mercedes Santiago-Calvo, Julia Guerrero, Esteban Cañibano, Maria Teresa Fernández and Karina Nuñez
Polymers 2023, 15(11), 2431; https://0-doi-org.brum.beds.ac.uk/10.3390/polym15112431 - 24 May 2023
Cited by 1 | Viewed by 1248
Abstract
In the present work, the effectiveness of four non-halogenated flame retardants (FR) (aluminium trihydroxide (ATH), magnesium hydroxide (MDH), Sepiolite (SEP) and a mix of metallic oxides and hydroxides (PAVAL)) in blends with recycled acrylonitrile-butadiene-styrene (rABS) was studied in order to develop a more [...] Read more.
In the present work, the effectiveness of four non-halogenated flame retardants (FR) (aluminium trihydroxide (ATH), magnesium hydroxide (MDH), Sepiolite (SEP) and a mix of metallic oxides and hydroxides (PAVAL)) in blends with recycled acrylonitrile-butadiene-styrene (rABS) was studied in order to develop a more environmentally friendly flame-retardant composite alternative. The mechanical and thermo-mechanical properties of the obtained composites as well as their flame-retardant mechanism were evaluated by UL-94 and cone calorimetric tests. As expected, these particles modified the mechanical performance of the rABS, increasing its stiffness at the expense of reducing its toughness and impact behavior. Regarding the fire behavior, the experimentation showed that there is an important synergy between the chemical mechanism provided by MDH (decomposition into oxides and water) and the physical mechanism provided by SEP (oxygen barrier), which means that mixed composites (rABS/MDH/SEP) can be obtained with a flame behavior superior to that of the composites studied with only one type of FR. In order to find a balance between mechanical properties, composites with different amounts of SEP and MDH were evaluated. The results showed that composites with the composition rABS/MDH/SEP: 70/15/15 wt.% increase the time to ignition (TTI) by 75% and the resulting mass after ignition by more than 600%. Furthermore, they decrease the heat release rate (HRR) by 62.9%, the total smoke production (TSP) by 19.04% and the total heat release rate (THHR) by 13.77% compared to unadditivated rABS; without compromising the mechanical behavior of the original material. These results are promising and potentially represent a greener alternative for the manufacture of flame-retardant composites. Full article
(This article belongs to the Special Issue Development in Fiber-Reinforced Polymer Composites)
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16 pages, 6402 KiB  
Article
Anti-Ballistic Performance of PPTA/UHMWPE Laminates
by Long Zhu, Weixiao Gao, Dmitriy A. Dikin, Simona Percec and Fei Ren
Polymers 2023, 15(10), 2281; https://0-doi-org.brum.beds.ac.uk/10.3390/polym15102281 - 12 May 2023
Viewed by 2085
Abstract
Poly(p-phenylene terephthalamide) (PPTA) and ultra-high-molecular-weight polyethylene (UHMWPE) are high-performance polymer materials largely used for body armor applications. Although composite structures from a combination of PPTA and UHMWPE have been created and described in the literature, the manufacture of layered composites from [...] Read more.
Poly(p-phenylene terephthalamide) (PPTA) and ultra-high-molecular-weight polyethylene (UHMWPE) are high-performance polymer materials largely used for body armor applications. Although composite structures from a combination of PPTA and UHMWPE have been created and described in the literature, the manufacture of layered composites from PPTA fabrics and UHMWPE films with UHMWPE film as an adhesive layer has not been reported. Such a new design can provide the obvious advantage of simple manufacturing technology. In this study, for the first time, we prepared PPTA fabrics/UHMWPE films laminate panels using plasma treatment and hot-pressing and examined their ballistic performance. Ballistic testing results indicated that samples with moderate interlayer adhesion between PPTA and UHMWPE layers exhibited enhanced performance. A further increase in interlayer adhesion showed a reverse effect. This finding implies that optimization of interface adhesion is essential to achieve maximum impact energy absorption through the delamination process. In addition, it was found that the stacking sequence of the PPTA and UHMWPE layers affected ballistic performance. Samples with PPTA as the outermost layer performed better than those with UHMWPE as the outermost layer. Furthermore, microscopy of the tested laminate samples showed that PPTA fibers exhibited shear cutting failure on the entrance side and tensile failure on the exit side of the panel. UHMWPE films exhibited brittle failure and thermal damage at high compression strain rate on the entrance side and tensile fracture on the exit side. For the first time, findings from this study reported in-field bullet testing results of PPTA/UHMWPE composite panels, which can provide important insights for designing, fabricating, and failure analysis of such composite structures for body armors. Full article
(This article belongs to the Special Issue Development in Fiber-Reinforced Polymer Composites)
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22 pages, 6174 KiB  
Article
Polymer Waste-Based Highly Efficient Maleated Interfacial Modifier in iPP/SCF Composites—Some Notes on the Role of Processing in Their Thermal and Dynamic Mechanical Properties
by Jesús-María García-Martínez and Emilia P. Collar
Polymers 2023, 15(6), 1527; https://0-doi-org.brum.beds.ac.uk/10.3390/polym15061527 - 20 Mar 2023
Viewed by 1209
Abstract
This work has a two-fold objective. First, it attempts to present the excellent efficiency of a maleated interfacial agent (obtained by the authors by using atactic polypropylene industrial waste) when used as interfacial additive in polypropylene/short carbon fiber composites (iPP/SCF). Second, in this [...] Read more.
This work has a two-fold objective. First, it attempts to present the excellent efficiency of a maleated interfacial agent (obtained by the authors by using atactic polypropylene industrial waste) when used as interfacial additive in polypropylene/short carbon fiber composites (iPP/SCF). Second, in this paper, we pay attention to the role played by processing in the final properties of the composite. This work has been performed by considering the emerging crystalline morphologies generated by the different shear forces that the molten material suffers depending on the molding method employed. The interfacial agent analyzed here consists of an atactic polypropylene containing succinic anhydride grafts obtained through a chemical modification process performed in solution. It incorporates different types of succinic grafts, such as succinic bridges between aPP chains and backbone and terminal grafts (aPP-SASA) in its structure, and contains 5.6% (5.6 × 10−4 g/mol) of grafted polar groups in total. The adhesion of the polyamide SCF sizing and the succinic units is followed by Field Emission Scanning Electronic Microscopy (FESEM) and Synchrotron Infrared Microscopy (SIRM). However, the main objective of this work is the study of the thermal and the dynamic mechanical behavior of the materials of a series of both compression- and injection-molded samples to ascertain the enhanced interfacial interactions in the material and further comparison between the results obtained by both processing operations. Therefore, we detect improvements of 200% in stiffness and 400% in the viscous response of the same SCF content composites caused by aPP-SASA, depending on the processing method used. Full article
(This article belongs to the Special Issue Development in Fiber-Reinforced Polymer Composites)
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27 pages, 5981 KiB  
Article
Transfer Length vs. Slip of Prestressed Fiber-Reinforced Polymer Reinforcement
by Aidas Jokūbaitis and Juozas Valivonis
Polymers 2023, 15(5), 1190; https://0-doi-org.brum.beds.ac.uk/10.3390/polym15051190 - 27 Feb 2023
Cited by 2 | Viewed by 1606
Abstract
A comprehensive analysis of the relationship between transfer length and slip of different types of prestressed fiber reinforced polymer (FRP) reinforcement is provided. The results of the transfer length and slip together with the main influencing parameters of approximately 170 specimens prestressed with [...] Read more.
A comprehensive analysis of the relationship between transfer length and slip of different types of prestressed fiber reinforced polymer (FRP) reinforcement is provided. The results of the transfer length and slip together with the main influencing parameters of approximately 170 specimens prestressed with different FRP reinforcement were collected. After the analysis of a larger database of transfer length versus slip, new bond shape factors were proposed for carbon fiber composite cable (CFCC) strands (α = 3.5) and carbon fiber reinforced polymer (CFRP) bars (α = 2.5). It was also determined that the type of prestressed reinforcement has an influence on the transfer length of the aramid fiber reinforced polymer (AFRP) bars. Therefore, α = 4.0 and α = 2.1 were proposed for AFRP Arapree bars and AFRP FiBRA and Technora bars, respectively. Moreover, the main theoretical models are discussed together with the comparison of theoretical and experimental transfer length results based on the slip of reinforcement. Additionally, the analysis of the relationship between transfer length and slip and the proposed new values of the bond shape factor α have the potential to be introduced in the production and quality control processes of precast prestressed concrete members and to stimulate additional research that increases the understanding of the transfer length of FRP reinforcement. Full article
(This article belongs to the Special Issue Development in Fiber-Reinforced Polymer Composites)
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30 pages, 12420 KiB  
Article
Damping under Varying Frequencies, Mechanical Properties, and Failure Modes of Flax/Polypropylene Composites
by Md Zillur Rahman and Huaizhong Xu
Polymers 2023, 15(4), 1042; https://0-doi-org.brum.beds.ac.uk/10.3390/polym15041042 - 19 Feb 2023
Cited by 3 | Viewed by 2040
Abstract
This work investigates the effects of fibre content, fibre orientation, and frequency on the dynamic behaviour of flax fibre-reinforced polypropylene composites (FFPCs) to improve understanding of the parameters affecting vibration damping in FFPCs. The effects of fibre content and fibre orientation on the [...] Read more.
This work investigates the effects of fibre content, fibre orientation, and frequency on the dynamic behaviour of flax fibre-reinforced polypropylene composites (FFPCs) to improve understanding of the parameters affecting vibration damping in FFPCs. The effects of fibre content and fibre orientation on the mechanical performances of FFPCs, along with fracture characteristics, are also investigated in this study. Laminates of various fibre contents and orientations were manufactured by a vacuum bagging process, and their dynamic and static properties were then obtained using dynamic (dynamic mechanical analysis (DMA) to frequencies of 100 Hz) and various mechanical (tensile and flexural) analyses, respectively. The findings suggest that of all the parameters, fibre orientation has the most significant impact on the damping, and the maximum loss factor (i.e., 4.3–5.5%) is obtained for 45° and 60° fibre orientations. However, there is no significant difference in loss factors among the composites with different fibre contents. The loss factors lie mainly in the range of 4–5.5%, irrespective of the fibre volume fraction, fibre orientation, and frequency. A significant improvement (281 to 953%) in damping is feasible in flax fibre/polypropylene composites relative to more widespread glass/epoxy composites. The mechanical properties of composites are also strongly affected by fibre orientation with respect to the loading direction; for example, the tensile modulus decreases from 20 GPa to 3.45 GPa at an off-axis angle of 30° for a fibre volume fraction of 0.40. The largest mechanical properties (tensile and flexural) are found in the case of 0° fibre orientation. For composites with fibre volume fractions in the range 0.31–0.50, tensile moduli are in the range 16–21 GPa, and tensile strengths are in the range 125–173 MPa, while flexural moduli and strengths are in the ranges 12–15 GPa and 96–121 MPa, respectively, making them suitable for structural applications. The obtained results also suggest that flax fibre composites are comparable to glass fibre composites, especially in terms of specific stiffness. The ESEM analysis confirms the tensile failures of specimens due to fibre debonding, fibre pull-out and breakage, matrix cracking, and inadequate fibre/matrix adhesion. The outcomes from this study indicate that flax fibre-reinforced composite could be a commercially viable material for applications in which noise and vibration are significant issues and where a significant amount of damping is required with a combination of high stiffness and low weight. Full article
(This article belongs to the Special Issue Development in Fiber-Reinforced Polymer Composites)
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23 pages, 24016 KiB  
Article
Development of a Pretensioning Anchorage for Sand-Coated CFRP Tendons: Modeling and Validation
by Gian-Luca Züst, Valentin Ott and Giovanni Pietro Terrasi
Polymers 2022, 14(24), 5531; https://0-doi-org.brum.beds.ac.uk/10.3390/polym14245531 - 17 Dec 2022
Viewed by 1521
Abstract
This paper presents a finite element (FE) analysis of an anchor for prestressing of sand-coated carbon-fiber-reinforced polymer (CFRP) tendons during the manufacturing of precast elements. This anchorage is temporary and removed after 2 to 7 days, when the pretensioning is released and the [...] Read more.
This paper presents a finite element (FE) analysis of an anchor for prestressing of sand-coated carbon-fiber-reinforced polymer (CFRP) tendons during the manufacturing of precast elements. This anchorage is temporary and removed after 2 to 7 days, when the pretensioning is released and the concrete is finally compressed. The investigated anchor consists of a conical metal barrel and three polymer wedges. The main tendon material properties are measured, compared with theoretical values and define the basis for the FE model. The latter considers both steps, pressing-in of the wedges and the subsequent loading of the tendon (diameter 7.5 mm). The relatively soft contact between polymer wedge and sand-coating is characterized experimentally and implemented with a pressure-overclosure condition. For the validation of the FE model, the strain distribution in the tendon is measured using fiber optical sensing. The therefore crucial process of fiber integration is described, and a novel approach is presented to uncover the optical fiber. The strain distribution of a sample with two anchors loaded in tension up to 80 kN is presented. The stress concentration at the front of the anchorage is highlighted. In addition, the finite element model is compared with the experiment, showing a good agreement of the strain distribution. A failure criterion according to Puck is finally implemented, which allows to assess potential fiber or interfiber failure. Full article
(This article belongs to the Special Issue Development in Fiber-Reinforced Polymer Composites)
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13 pages, 5213 KiB  
Article
On the Resin Transfer Molding (RTM) Infiltration of Fiber-Reinforced Composites Made by Tailored Fiber Placement
by Lars Bittrich, Julian Seuffert, Sarah Dietrich, Kai Uhlig, Tales de Vargas Lisboa, Luise Kärger and Axel Spickenheuer
Polymers 2022, 14(22), 4873; https://0-doi-org.brum.beds.ac.uk/10.3390/polym14224873 - 12 Nov 2022
Cited by 4 | Viewed by 1812
Abstract
Tailored fiber placement (TFP) is a preform manufacturing process in which rovings made of fibrous material are stitched onto a base material, increasing the freedom for the placement of fibers. Due to the particular kinematics of the process, the infiltration of TFP preforms [...] Read more.
Tailored fiber placement (TFP) is a preform manufacturing process in which rovings made of fibrous material are stitched onto a base material, increasing the freedom for the placement of fibers. Due to the particular kinematics of the process, the infiltration of TFP preforms with resin transfer molding (RTM) is sensitive to multiple processes and material parameters, such as injection pressure, resin viscosity, and fiber architecture. An experimental study is conducted to investigate the influence of TFP manufacturing parameters on the infiltration process. A transparent RTM tool that enables visual tracking of the resin flow front was developed and constructed. Microsection evaluations were produced to observe the thickness of each part of the composite and evaluate the fiber volume content of that part. Qualitative results have shown that the infiltration process in TFP structures is strongly influenced by a top and bottom flow layer. The stitching points and the yarn also create channels for the resin to flow. Furthermore, the stitching creates some eye-like regions, which are resin-rich zones and are normally not taken into account during the infusion of TFP parts. Full article
(This article belongs to the Special Issue Development in Fiber-Reinforced Polymer Composites)
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9 pages, 1647 KiB  
Article
The Effect of Glass Fiber Storage Time on the Mechanical Response of Polymer Composite
by Michal Jurko, Lenka Souckova, Jan Prokes and Vladimir Cech
Polymers 2022, 14(21), 4633; https://0-doi-org.brum.beds.ac.uk/10.3390/polym14214633 - 31 Oct 2022
Cited by 4 | Viewed by 2112
Abstract
The growing demand for polymer composites and their widespread use is inevitably accompanied by the need to know their degradation behavior over a sufficiently long period of time. This study focuses on commercial glass fiber rovings, which were stored in the indoor environment [...] Read more.
The growing demand for polymer composites and their widespread use is inevitably accompanied by the need to know their degradation behavior over a sufficiently long period of time. This study focuses on commercial glass fiber rovings, which were stored in the indoor environment for up to 11 years. Fibers with different storage times, from fresh up to the oldest, were used to produce unidirectional fiber-reinforced polyester composites that were characterized to determine their shear and flexural properties dependent on fiber storage time. A significant decrease in shear strength was observed throughout the aging of the fibers, down to a decrease of 33% for the oldest fibers. An important finding, however, was that the significant decrease in shear strength was only partially reflected in the flexural strength, which corresponded to a decrease of 18% for the oldest fibers at consistent flexural modulus. Full article
(This article belongs to the Special Issue Development in Fiber-Reinforced Polymer Composites)
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19 pages, 4810 KiB  
Article
Thermal, Mechanical, and Morphological Characterisations of Graphene Nanoplatelet/Graphene Oxide/High-Hard-Segment Polyurethane Nanocomposite: A Comparative Study
by Muayad Albozahid, Haneen Zuhair Naji, Zoalfokkar Kareem Alobad, Jacek K. Wychowaniec and Alberto Saiani
Polymers 2022, 14(19), 4224; https://0-doi-org.brum.beds.ac.uk/10.3390/polym14194224 - 09 Oct 2022
Cited by 10 | Viewed by 2344
Abstract
The current work investigates the effect of the addition of graphene nanoplatelets (GNPs) and graphene oxide (GO) to high hard-segment polyurethane (75% HS) on its thermal, morphological, and mechanical properties. Polyurethane (PU) and its nanocomposites were prepared with different ratios of GNP and [...] Read more.
The current work investigates the effect of the addition of graphene nanoplatelets (GNPs) and graphene oxide (GO) to high hard-segment polyurethane (75% HS) on its thermal, morphological, and mechanical properties. Polyurethane (PU) and its nanocomposites were prepared with different ratios of GNP and GO (0.25, 0.5, and 0.75 wt.%). A thermal stability analysis demonstrated an enhancement in the thermal stability of PU with GNP and GO incorporated compared to pure PU. Differential Scanning Calorimetry (DSC) showed that both GNP and GO act as heterogeneous nucleation agents within a PU matrix, leading to an increase in the crystallinity of PU. The uniform dispersion and distribution of GNP and GO flakes in the PU matrix were confirmed by SEM and TEM. In terms of the mechanical properties of the PU nanocomposites, it was found that the interaction between PU and GO was better than that of GNP due to the functional groups on the GO’s surface. This leads to a significant increase in tensile strength for 0.5 wt.% GNP and GO compared with pure PU. This can be attributed to interfacial interaction between the GO and PU chains, resulting in an improvement in stress transferring from the matrix to the filler and vice versa. This work sheds light on the understanding of the interactions between graphene-based fillers and their influence on the mechanical properties of PU nanocomposites. Full article
(This article belongs to the Special Issue Development in Fiber-Reinforced Polymer Composites)
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19 pages, 11762 KiB  
Article
Experimental, Analytical, and Numerical Assessments for the Controversial Elastic Stiffness Enhancement of CFRP-Strengthened Timber Beams
by Khaled Saad and András Lengyel
Polymers 2022, 14(19), 4222; https://0-doi-org.brum.beds.ac.uk/10.3390/polym14194222 - 08 Oct 2022
Cited by 3 | Viewed by 1617
Abstract
The strengthening of timber beams with carbon-fibre-reinforced polymers (CFRP) has been widely used in the last decades to enhance the behaviour of historical or new timber structures, usually for bending. While considerable improvement in capacity and ductility is typically achieved, the increase in [...] Read more.
The strengthening of timber beams with carbon-fibre-reinforced polymers (CFRP) has been widely used in the last decades to enhance the behaviour of historical or new timber structures, usually for bending. While considerable improvement in capacity and ductility is typically achieved, the increase in stiffness was, in many cases, well short of analytical expectations, which tend to overestimate stiffness. This study addresses the problem by investigating the underlying mechanical behaviour using experimental, analytical, and numerical tools on a sample of Norway spruce (Picea abies) beams reinforced with carbon-fibre fabric. In the experimental program, each beam is tested for bending with and without CFRP reinforcement in order to determine specimen-specific stiffness increase on an individual basis. The reinforcement yielded an increase of 27% in capacity, 53% in ultimate displacement, and 133% in compliance, verifying its efficiency. Axial compression tests on an independent sample are also performed to verify modulus of elasticity in compression. Numerical computations based on a beam model and a three-dimensional finite element model are performed with the introduction of separate moduli of elasticity for tension and compression in timber. Inverse computation using the experimental load–deflection curves yielded the moduli and the compression yield stress of timber to provide the best match between tests and simulations. The mean difference of only 6% in stiffness between FEM and the tests is obtained. The dominance of normal stresses in the longitudinal direction is found, in correspondence with the experimentally observed tensile failure of timber (apart from a few defected specimens). Compression yield stresses are within 7% (beam model) and 2% (FEM) error compared with the control axial tests. The differences between FE simulations and tests in ultimate load and compliance are within 1%. This study concludes that the application of CFRP in the composite beams enables the determination of timber material properties opposed to pure timber beams without reinforcement, and the adoption of separate moduli of elasticity for tension and compression leads to adequate modelling of reinforced timber beams. Full article
(This article belongs to the Special Issue Development in Fiber-Reinforced Polymer Composites)
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18 pages, 5521 KiB  
Article
Numerical Studies on Failure Mechanisms of All-Composite Sandwich Structure with Honeycomb Core under Compression and Impact Loading Conditions
by Xuecheng Han, Hongneng Cai, Jie Sun, Zhiyuan Wei, Yaping Huang and Ang Wang
Polymers 2022, 14(19), 4047; https://0-doi-org.brum.beds.ac.uk/10.3390/polym14194047 - 27 Sep 2022
Cited by 6 | Viewed by 3778
Abstract
The all-composite sandwich structure with the honeycomb core is a lightweight and high-strength structure with broad application scenarios. The face sheet and honeycomb core of the proposed all-composite sandwich structure in this work are composed of carbon-fiber-reinforced polymer (CFRP) composites. The mechanical response [...] Read more.
The all-composite sandwich structure with the honeycomb core is a lightweight and high-strength structure with broad application scenarios. The face sheet and honeycomb core of the proposed all-composite sandwich structure in this work are composed of carbon-fiber-reinforced polymer (CFRP) composites. The mechanical response and damage mechanism of the all-composite sandwich structure under out-of-plane quasi-static compression and out-of-plane impact are studied by numerical methods. The refined finite element models of the sandwich structures are built on the ABAQUS/Explicit platform. The micromechanics of failure (MMF) theory based on physical component failure is used to describe the intralaminar damage mechanism of the face sheet and honeycomb core, and the mixed-mode exponential cohesive zone model (ECZM) is utilized to simulate the initiation and evolution of interlayer damage. In addition, the cohesive contact approach is adopted to capture the debonding failure at the face-sheet/core. The numerical results show that the all-composite sandwich structure has the characteristics of large structural stiffness and strong energy absorption ability. The failure mechanism of the all-composite sandwich structure under compression is mainly matrix damage and delamination of the honeycomb core, with buckling and folding in appearance. Under out-of-plane impact, matrix damage and delamination arise on the upper sheet, little damage is observed on the lower sheet, and the delamination damage morphology tends to be circular with increasing impact energy. In addition, the interface failure of the upper-sheet/core is more than that of the lower-sheet/core. In addition, the matrix damage near the impact center of the honeycomb core tends to be consistent with the delamination contour, and a small amount of fiber failure is also observed, which manifests as a collapse morphology of the impact area. The research results enrich the understanding of the mechanical behavior of all-composite sandwich structures with honeycomb cores and provide theoretical support for their potential applications. Full article
(This article belongs to the Special Issue Development in Fiber-Reinforced Polymer Composites)
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19 pages, 9810 KiB  
Article
Novel Thermoplastic Composites Strengthened with Carbon Fiber-Reinforced Epoxy Composite Waste Rods: Development and Characterization
by José Antonio Butenegro, Mohsen Bahrami, Yentl Swolfs, Jan Ivens, Miguel Ángel Martínez and Juana Abenojar
Polymers 2022, 14(19), 3951; https://0-doi-org.brum.beds.ac.uk/10.3390/polym14193951 - 21 Sep 2022
Cited by 9 | Viewed by 2862
Abstract
The increasing use of carbon fiber and epoxy resin composite materials yields an increase in the amount of waste. Therefore, we present a solution consisting of composites manufactured by hot pressing, employing polyamides (either PA11 or PA12) and a mechanically recycled carbon fiber-reinforced [...] Read more.
The increasing use of carbon fiber and epoxy resin composite materials yields an increase in the amount of waste. Therefore, we present a solution consisting of composites manufactured by hot pressing, employing polyamides (either PA11 or PA12) and a mechanically recycled carbon fiber-reinforced polymer (CFRP) as reinforcement. The main objectives are to study the manufacturing of those composites, to evaluate the fiber distribution, and to perform a mechanical, dynamical, and thermomechanical characterizations. The X-ray micro-computed tomography (μCT) shows that the fibers are well-distributed, maintaining a homogeneous fiber volume fraction across the material. The variability in the results is typical of discontinuous fiber composites in which the fibers, although oriented, are not as homogeneously distributed as in a continuous fiber composite. The mechanical and dynamic properties barely differ between the two sets of composites. A dynamic-mechanical analysis revealed that the glass transition temperature (Tg) increases slightly for both composites, compared to the polymers. These results illustrate the viability of the recycling and reuse route for preventing the deterioration of carbon fibers and promoting the subsequent reduction in the environmental impact by employing a thermoplastic matrix. Full article
(This article belongs to the Special Issue Development in Fiber-Reinforced Polymer Composites)
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18 pages, 5698 KiB  
Article
Flexural Fatigue in a Polymer Matrix Composite Material Reinforced with Continuous Kevlar Fibers Fabricated by Additive Manufacturing
by Alberto David Pertuz-Comas, Jorge G. Díaz, Oscar Javier Meneses-Duran, Nixon Yesid Niño-Álvarez and Juan León-Becerra
Polymers 2022, 14(17), 3586; https://0-doi-org.brum.beds.ac.uk/10.3390/polym14173586 - 30 Aug 2022
Cited by 17 | Viewed by 2131
Abstract
Fatigue bending tests, under controlled displacement, were performed on a polymer matrix composite material reinforced with continuous Kevlar fibers. The samples were fabricated using the Fused Filament Fabrication (FFF) technique in a Markforged Two® 3D printer. The static characterization delivered a flexural [...] Read more.
Fatigue bending tests, under controlled displacement, were performed on a polymer matrix composite material reinforced with continuous Kevlar fibers. The samples were fabricated using the Fused Filament Fabrication (FFF) technique in a Markforged Two® 3D printer. The static characterization delivered a flexural modulus of elasticity of 4.73 GPa and flexural strength of 110 MPa. The applied loading corresponded to 92.3, 88.5, 86.2, and 84.7% of the static flexural displacement, giving 15, 248, 460, and 711 cycles for failure. Additionally, two numerical models were created: one using orthotropic properties for static loading conditions; and a second one using isotropic in-bulk properties for fatigue modeling. The second model was able to reproduce the experimental fatigue results. Finally, morphological analysis of the fractured surface revealed fiber breakage, fiber tearing, fiber buckling, matrix cracking, and matrix porosity. Full article
(This article belongs to the Special Issue Development in Fiber-Reinforced Polymer Composites)
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24 pages, 7794 KiB  
Article
Mask-Point: Automatic 3D Surface Defects Detection Network for Fiber-Reinforced Resin Matrix Composites
by Helin Li, Bin Lin, Chen Zhang, Liang Xu, Tianyi Sui, Yang Wang, Xinquan Hao, Deyu Lou and Hongyu Li
Polymers 2022, 14(16), 3390; https://0-doi-org.brum.beds.ac.uk/10.3390/polym14163390 - 19 Aug 2022
Cited by 2 | Viewed by 2146
Abstract
Surface defects of fiber-reinforced resin matrix composites (FRRMCs) adversely affect their appearance and performance. To accurately and efficiently detect the three-dimensional (3D) surface defects of FRRMCs, a novel lightweight and two-stage semantic segmentation network, i.e., Mask-Point, is proposed. Stage 1 of Mask-Point is [...] Read more.
Surface defects of fiber-reinforced resin matrix composites (FRRMCs) adversely affect their appearance and performance. To accurately and efficiently detect the three-dimensional (3D) surface defects of FRRMCs, a novel lightweight and two-stage semantic segmentation network, i.e., Mask-Point, is proposed. Stage 1 of Mask-Point is the multi-head 3D region proposal extractors (RPEs), generating several 3D regions of interest (ROIs). Stage 2 is the 3D aggregation stage composed of the shared classifier, shared filter, and non-maximum suppression (NMS). The two stages work together to detect the surface defects. To evaluate the performance of Mask-Point, a new 3D surface defects dataset of FRRMCs containing about 120 million points is produced. Training and test experiments show that the accuracy and the mean intersection of union (mIoU) increase as the number of different 3D RPEs increases in Stage 1, but the inference speed becomes slower when the number of different 3D RPEs increases. The best accuracy, mIoU, and inference speed of the Mask-Point model could reach 0.9997, 0.9402, and 320,000 points/s, respectively. Moreover, comparison experiments also show that Mask-Point offers relatively the best segmentation performance compared with several other typical 3D semantic segmentation networks. The mIoU of Mask-Point is about 30% ahead of the sub-optimal 3D semantic segmentation network PointNet. In addition, a distributed surface defects detection system based on Mask-Point is developed. The system is applied to scan real FRRMC products and detect their surface defects, and it achieves the relatively best detection performance in competition with skilled human workers. The above experiments demonstrate that the proposed Mask-Point could accurately and efficiently detect 3D surface defects of FRRMCs, and the Mask-Point also provides a new potential solution for the 3D surface defects detection of other similar materials Full article
(This article belongs to the Special Issue Development in Fiber-Reinforced Polymer Composites)
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20 pages, 3434 KiB  
Article
Recovery of Green Polyols from Rigid Polyurethane Waste by Catalytic Depolymerization
by Rafael Miguel-Fernández, Izotz Amundarain, Asier Asueta, Sara García-Fernández, Sixto Arnaiz, Nora Lardiés Miazza, Ernesto Montón, Bárbara Rodríguez-García and Elena Bianca-Benchea
Polymers 2022, 14(14), 2936; https://0-doi-org.brum.beds.ac.uk/10.3390/polym14142936 - 20 Jul 2022
Cited by 5 | Viewed by 3102
Abstract
Polyurethane (PU) is one of the most versatile polymers available and can be found in an infinite number of formats ranging from rigid or flexible foams to elastomers. Currently, most Rigid PU Foam (RPUF) waste is landfilled, even though a small amount is [...] Read more.
Polyurethane (PU) is one of the most versatile polymers available and can be found in an infinite number of formats ranging from rigid or flexible foams to elastomers. Currently, most Rigid PU Foam (RPUF) waste is landfilled, even though a small amount is mechanically recycled, in which the material is conditioned in size to a very fine powder, which is introduced as a filler. In this work, chemical recycling of two types of rigid PU foams is studied, the major difference being the aliphatic or aromatic nature of the isocyanate used in the synthesis. A solvolysis process is developed, a chemical depolymerization that breaks the chains by means of a chemical agent, a solvent, in the presence of a catalyst and under controlled process conditions. The glycolysis products are purified by vacuum distillation, centrifugation, and acid water treatment, depending on the most suitable process for each waste type. Optimal process conditions are established to obtain high-purity green polyols by performing a set of catalytic glycolysis reactions at laboratory scale with the previously conditioned RPUF waste samples. The physicochemical properties of the polyols, such as hydroxyl value, acid value, average molecular weight (Mn), and viscosity, are analyzed. The chemical structure and thermal stability of the polyols are studied by means of FTIR and TGA, respectively. Partial substitution of the commercial polyol (up to 15 wt.%) by the recycled polyols for RPUF synthesis is studied and characterized. Full article
(This article belongs to the Special Issue Development in Fiber-Reinforced Polymer Composites)
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23 pages, 6466 KiB  
Article
Three-Dimensional Boundary Element Strategy for Stress Sensitivity of Fractional-Order Thermo-Elastoplastic Ultrasonic Wave Propagation Problems of Anisotropic Fiber-Reinforced Polymer Composite Material
by Mohamed Abdelsabour Fahmy
Polymers 2022, 14(14), 2883; https://0-doi-org.brum.beds.ac.uk/10.3390/polym14142883 - 16 Jul 2022
Cited by 4 | Viewed by 1152
Abstract
A new three-dimensional (3D) boundary element method (BEM) strategy was developed to solve fractional-order thermo-elastoplastic ultrasonic wave propagation problems based on the meshless moving least squares (MLS) method. The temperature problem domain was divided into a number of circular sub-domains. Each node was [...] Read more.
A new three-dimensional (3D) boundary element method (BEM) strategy was developed to solve fractional-order thermo-elastoplastic ultrasonic wave propagation problems based on the meshless moving least squares (MLS) method. The temperature problem domain was divided into a number of circular sub-domains. Each node was the center of the circular sub-domain surrounding it. The Laplace transform method was used to solve the temperature problem. A unit test function was used in the local weak-form formulation to generate the local boundary integral equations, and the inverse Laplace transformation method was used to find the transient temperature solutions. Then, the three-dimensional elastoplastic problems could be solved using the boundary element method (BEM). Initial stress and strain formulations are adopted, and their distributions are interpolated using boundary integral equations. The effects of the fractional-order parameter and anisotropy are investigated. The proposed method’s validity and performance are demonstrated for a two-dimensional problem with excellent agreement with other experimental and numerical results. Full article
(This article belongs to the Special Issue Development in Fiber-Reinforced Polymer Composites)
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18 pages, 6870 KiB  
Article
Numerical and Experimental Analysis of Mechanical Properties of Natural-Fiber-Reinforced Hybrid Polymer Composites and the Effect on Matrix Material
by Ayyappa Atmakuri, Arvydas Palevicius, Andrius Vilkauskas and Giedrius Janusas
Polymers 2022, 14(13), 2612; https://0-doi-org.brum.beds.ac.uk/10.3390/polym14132612 - 27 Jun 2022
Cited by 16 | Viewed by 3075
Abstract
The impact of matrix material on the mechanical properties of natural-fiber-reinforced hybrid composites was studied by comparing their experimental, and numerical analysis results. In the present work hemp and flax fibers were used as reinforcement and epoxy resin and ecopoxy resin along with [...] Read more.
The impact of matrix material on the mechanical properties of natural-fiber-reinforced hybrid composites was studied by comparing their experimental, and numerical analysis results. In the present work hemp and flax fibers were used as reinforcement and epoxy resin and ecopoxy resin along with hardener were used as matrix materials. To study the influence of the matrix material, two sets of hybrid composites were fabricated by varying the matrix material. The composite samples were fabricated by using the compression-molding technique followed by a hand layup process. A total of five different composites were fabricated by varying the weight fraction of fiber material in each set based on the rule of the hybridization process. After fabrication, the mechanical properties of the composite samples were tested and morphological studies were analyzed by using SEM-EDX analysis. The flexural-test fractured specimens were analyzed by using a scanning electron microscope (SEM). In addition, theoretical analysis of the elastic properties of hybrid composites was carried out by using the Halpin–Tsai approach. The results showed that the hybrid composites had superior properties to individual fiber composites. Overall, epoxy resin matrix composites exhibited superior properties to ecopoxy matrix composites. Full article
(This article belongs to the Special Issue Development in Fiber-Reinforced Polymer Composites)
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20 pages, 3852 KiB  
Article
Simplified Rules for Serviceability Control of FRPRC Elements
by Tomislav Kišiček, Tvrtko Renić, Ivan Hafner and Mislav Stepinac
Polymers 2022, 14(12), 2513; https://0-doi-org.brum.beds.ac.uk/10.3390/polym14122513 - 20 Jun 2022
Cited by 2 | Viewed by 1354
Abstract
Serviceability limit states are very important in the design of reinforced concrete elements but they are complex to calculate. Simplified serviceability calculations are provided in EN 1992-1-1 (2013) for steel reinforced elements. The crack widths are assumed to be acceptable if the bar [...] Read more.
Serviceability limit states are very important in the design of reinforced concrete elements but they are complex to calculate. Simplified serviceability calculations are provided in EN 1992-1-1 (2013) for steel reinforced elements. The crack widths are assumed to be acceptable if the bar diameters or bar spacings are not too large, while deflections are acceptable if the slenderness is not too large. In recent decades, FRP bars have become an adequate replacement for steel bars, especially in aggressive environments. The calculation procedures for FRP-reinforced concrete elements (FRPRC) were developed from calculation methods for steel reinforced elements. The first part of this paper demonstrates the procedures and parametric investigation for calculating the maximum bar diameter and bar spacing for the purpose of controlling the crack width, focusing on calculations for the maximum bar diameter for which cracks widths are acceptable. The second part of the paper demonstrates the procedures and parametric calculations for the slenderness limits for concrete elements reinforced with FRP bars in order to satisfy the usual deflection limits. Due to the different modulus of elasticity values of FRP and steel, the tables used for steel cannot be used for concrete beams reinforced with FRP bars. Therefore, new tables and diagrams are proposed in the paper. The new tables and diagrams for the maximum allowable bar diameters for the different modulus of elasticity values of FRP can be useful for the rapid control of the crack width in FRPRC elements. They are conservative compared to the exact calculations because some assumptions taken in the calculations are different to those taken in the exact calculation procedure for the crack width. The results of parametric calculations for the slenderness limits for FRPRC elements are provided in the form of a diagram for different concrete classes. Satisfying the slenderness from these curves will result in a smaller deflection than that allowed for each parameter related to that class of concrete. Full article
(This article belongs to the Special Issue Development in Fiber-Reinforced Polymer Composites)
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13 pages, 5735 KiB  
Article
Anchoring Issues of CFRP Laminates to Concrete Members
by Justas Slaitas, Remigijus Šalna and Juozas Valivonis
Polymers 2022, 14(12), 2338; https://0-doi-org.brum.beds.ac.uk/10.3390/polym14122338 - 09 Jun 2022
Cited by 2 | Viewed by 1786
Abstract
In recent years, carbon fibre reinforced polymer (CFRP) laminates have conquered the structural rehabilitation market due to their ease and quick installation, high strength, anticorrosion properties, and other properties often repeated in the literature. The full potential of these high-strength elements can only [...] Read more.
In recent years, carbon fibre reinforced polymer (CFRP) laminates have conquered the structural rehabilitation market due to their ease and quick installation, high strength, anticorrosion properties, and other properties often repeated in the literature. The full potential of these high-strength elements can only be exploited by prestressing. However, the glued laminate joint is partially rigid, resulting in slippage that leads to premature debonding and failure. Therefore, anchoring of the laminate ends is required to stop or delay premature failure and/or perform prestressing. This article discusses the anchoring issues of CFRP laminates and guidelines for the development of anchoring systems. To achieve this goal, the laminate strip was bent, the required clamping forces were determined, possible cases of damage were identified, and individual stress concentrations were modelled. The methodology for calculating the anchor length and the pull-off force is also presented. Full article
(This article belongs to the Special Issue Development in Fiber-Reinforced Polymer Composites)
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25 pages, 12699 KiB  
Article
Analysis of Sheep Wool-Based Composites for Building Insulation
by Tünde-Orsolya Dénes, Raluca Iştoan, Daniela Roxana Tǎmaş-Gavrea, Daniela Lucia Manea, Andreea Hegyi, Florin Popa and Ovidiu Vasile
Polymers 2022, 14(10), 2109; https://0-doi-org.brum.beds.ac.uk/10.3390/polym14102109 - 22 May 2022
Cited by 11 | Viewed by 5344
Abstract
The aim of this paper is to propose ecological thermal insulation materials that meet the goals of sustainability but also fulfill the imposed thermal performance requirements. This paper studies new composite materials based on sheep wool from the perspective of thermal conductivity. The [...] Read more.
The aim of this paper is to propose ecological thermal insulation materials that meet the goals of sustainability but also fulfill the imposed thermal performance requirements. This paper studies new composite materials based on sheep wool from the perspective of thermal conductivity. The composites were prepared using two types of binder: acrylic-polyurethane resin and natural rubber latex, which were applied to the wool fibres through different methods and percentages. Based on the obtained results of thermal conductivity, two types of samples were selected for further analysis, which aimed to determine the microstructure, chemical composition, water absorption, attack of microorganisms, water vapour permeability, hygrothermal adsorption characteristics and sound absorption of the samples. In order to analyse the variation of thermal conductivity, the following parameters were taken into account: thickness, density, type of binder and percentage of binder. Following the obtained results, it was observed that the value of the thermal conductivity of the samples varies between 0.0324 and 0.0436 W/mK. It was found that all the samples prepared and analysed in this study fulfil the national criteria for the thermal performance of thermal insulation material. After conducting the in-depth analysis of the two selected sample types, it was concluded that both materials have good sound absorption characteristics over the considered frequency range. In addition, as it was expected from the natural fibres, the samples had low resistance against the attack of microorganisms and water-related tests. Full article
(This article belongs to the Special Issue Development in Fiber-Reinforced Polymer Composites)
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19 pages, 11533 KiB  
Article
Mechanical and Tribological Behavior of Functionally Graded Unidirectional Glass Fiber-Reinforced Epoxy Composites
by Waleed Alhazmi, Yosef Jazaa, Sultan Althahban, Saeed Mousa, Ahmed Abu-Sinna, Amr Abd-Elhady, Hossam El-Din Sallam and Mahmoud Atta
Polymers 2022, 14(10), 2057; https://0-doi-org.brum.beds.ac.uk/10.3390/polym14102057 - 18 May 2022
Cited by 7 | Viewed by 2186
Abstract
This paper aims to assess experimentally the mechanical and tribological behavior of conventional and functionally graded (FG) polymeric matrix composites reinforced with continuous glass fibers. The small punch test (SPT) and a pin-on-disc device were used in the present work to examine the [...] Read more.
This paper aims to assess experimentally the mechanical and tribological behavior of conventional and functionally graded (FG) polymeric matrix composites reinforced with continuous glass fibers. The small punch test (SPT) and a pin-on-disc device were used in the present work to examine the mechanical and wear behavior, respectively. The hand lay-up technique was used in the present investigation to manufacture the conventional and FG composites. Various wooden looms with different nailed spacing were employed to manufacture the FG composites. According to test type, the FG composite is composed of four and ten layers, with a different glass fiber volume of fraction (Vf%) for each layer. In addition, the finite element simulation based on Hashin’s failure criterion and cohesive zone modeling was used to show the progressive failure and give more explanation regarding the flexural behavior of such composites. The present results indicate that the wear rate of an FG composite could be affected by many factors, including the disk speed, applied load, the composite layers number, and average glass fiber volume fraction. On the other hand, the arrangement of layers in the composite materials by variation of Vf% for each layer can improve the wear rate and value of the ultimate load before the fracture of the composite material when subjected to SPT. The experimental and numerical results for all SPT specimens showed that the fracture of the SPT specimens began beneath the punch tip and grew along the fiber direction. The ultimate flexural capacity of FG composites increased by 30% compared with the conventional composites. Full article
(This article belongs to the Special Issue Development in Fiber-Reinforced Polymer Composites)
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19 pages, 9541 KiB  
Article
Structural Behavior of RC Beams Containing Unreinforced Drilled Openings with and without CFRP Strengthening
by Alaa A. El-Sisi, Hesham M. El-Emam, Abd El-Monem I. El-Kholy, Seleem S. Ahmad, Hossam M. Sallam and Hani A. Salim
Polymers 2022, 14(10), 2034; https://0-doi-org.brum.beds.ac.uk/10.3390/polym14102034 - 16 May 2022
Cited by 7 | Viewed by 2128
Abstract
Construction deficiencies can cause serious problems that significantly decrease the design strength of concrete structures, such as the unreinforced drilled openings. With the absence of sufficient reinforcement, the stress concentrations generated around the opening corners produce cracks in the beams. The size and [...] Read more.
Construction deficiencies can cause serious problems that significantly decrease the design strength of concrete structures, such as the unreinforced drilled openings. With the absence of sufficient reinforcement, the stress concentrations generated around the opening corners produce cracks in the beams. The size and location of the opening significantly affect the behavior of the beam under static and dynamic load. In this work, an experimental and numerical program was performed to investigate the behavior of drilled reinforced concrete beams with and without strengthening using CFRP sheets. Energy absorption and SDOF analyses were performed to preliminary assess the behavior of the beams under the dynamic load, such as blast. One control beam without any openings, six beams with tension-zone openings, and six beams with shear-zone openings were tested. It was found that the samples with tension-zone openings were slightly affected by the opening, where the reduction in the ultimate strength was approximately 7 to 14%. The beams were able to recover up to 46% of the lost strength by CFRP strengthening. On the other hand, the shear-zone opening significantly decreased the strength and energy absorption and increased the blast response. It can be concluded that it is not recommended to drill any opening at the shear zone as strength loss can reach 57% even with the strengthening, especially for blast resisting structure; in addition, the strength recovered from approximately 11.95 to 32.46% only. The finite element model was able to predict the strength of the beams. The results were closer in the case of tension-zone opening than those in the case of the shear-zone opening. Shear cracks were observed at the corners of the openings even if the opening exists at the tension zone. A reduction in the density of cracks can be observed after the strengthening, where the FRP sheet decreases the stress in the concrete. Full article
(This article belongs to the Special Issue Development in Fiber-Reinforced Polymer Composites)
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18 pages, 2008 KiB  
Article
Development and Characterisation of Sustainable Prepregs with Improved Fire Behaviour Based on Furan Resin and Basalt Fibre Reinforcement
by Patricia Ares Elejoste, Alexandra Allue, Jesus Ballestero, Santiago Neira, José Luis Gómez-Alonso and Koldo Gondra
Polymers 2022, 14(9), 1864; https://0-doi-org.brum.beds.ac.uk/10.3390/polym14091864 - 02 May 2022
Cited by 5 | Viewed by 2447
Abstract
In recent years, the need to minimise environmental impact has led to the exploration of sustainable materials, avoiding those derived from petroleum, considering that these materials should proceed from nature and be harmless and durable. Therefore, throughout this work, the following raw materials [...] Read more.
In recent years, the need to minimise environmental impact has led to the exploration of sustainable materials, avoiding those derived from petroleum, considering that these materials should proceed from nature and be harmless and durable. Therefore, throughout this work, the following raw materials were used: furan resin, which comes from agricultural by-products, and basalt fibre, obtained by melting basaltic volcanic rock. Specifically, this work studies the development of a flame-retarded furan prepreg manufactured by means of a continuous process combining a double-belt lamination equipment with an impregnation system. Once the prepregs (flame- and non-flame-retarded) were obtained, they were subjected to various tests to analyse their fire behaviour, with both showing an adequate performance. However, comparing both, concerning the toxicity index (CITG), the flame-retarded prepreg generated fewer toxic gases during combustion than the non-flame-retarded one, although the latter showed a lower smoke density. In short, the developed flame-retarded material falls into the R1HL3 (Requirement 1 and Hazard Level 3) classification demanded by products with large areas in railway vehicle interiors, which is the maximum safety level according to the risk index established in applicable regulations. Therefore, this material could be used in any railway vehicle for indoor applications. Full article
(This article belongs to the Special Issue Development in Fiber-Reinforced Polymer Composites)
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26 pages, 11551 KiB  
Article
The Effectiveness of CFRP- and Auxetic Fabric-Strengthened Brick Masonry under Axial Compression: A Numerical Investigation
by Mohammad Asad, Tatheer Zahra and Julian Thamboo
Polymers 2022, 14(9), 1800; https://0-doi-org.brum.beds.ac.uk/10.3390/polym14091800 - 28 Apr 2022
Cited by 3 | Viewed by 2462
Abstract
Bonded brickwork used for loadbearing walls is widely found in heritage structures worldwide. The evaluation of bonded masonry structures and their strengthening strategies against dynamic actions require appropriate understanding under cyclic loading. Subsequently, a simplified 3D microscale numerical model is developed in this [...] Read more.
Bonded brickwork used for loadbearing walls is widely found in heritage structures worldwide. The evaluation of bonded masonry structures and their strengthening strategies against dynamic actions require appropriate understanding under cyclic loading. Subsequently, a simplified 3D microscale numerical model is developed in this paper to analyse bonded brickwork under cyclic compression. A plasticity-based damage constitutive model to represent damage in masonry bricks under cyclic compression loading was employed, and zero-thickness interfaces were considered with non-linear damage properties to simulate the mechanical behaviour of masonry. A threshold strain level was used to enact the element deletion technique for initiating brittle crack opening in the masonry units. The developed model was validated against the experimental results published by the authors in the past. The models were able to accurately predict the experimental results with an error limit of 10% maximum. Mainly, two types of strengthening materials, possessing (1) high energy absorption characteristics (auxetic fabric) and (2) high strength properties (carbon fibre reinforced polymer composites/CFRP) were employed for damage mitigation under cyclic compression. Results show that the CFRP-strengthened masonry failure was mainly attributed to de-bonding of the CFRP and crushing under compression. However, the auxetic strengthening is shown to significantly minimise the de-bonding phenomenon. Enhanced energy dissipation characteristics with relatively higher ductility (up to ~50%) and reduced damages on the bonded brickwork were observed as compared to the CFRP-strengthened brickwork under cyclic compression loading. Additionally, the auxetic fabric application also increased the compressive resistance of brickwork by 38–60% under monotonic loading, which is comparably higher than with the CFRP strengthening technique. Full article
(This article belongs to the Special Issue Development in Fiber-Reinforced Polymer Composites)
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12 pages, 1666 KiB  
Article
Synthesis of Rigid Polyurethane Foams Incorporating Polyols from Chemical Recycling of Post-Industrial Waste Polyurethane Foams
by Izotz Amundarain, Rafael Miguel-Fernández, Asier Asueta, Sara García-Fernández and Sixto Arnaiz
Polymers 2022, 14(6), 1157; https://0-doi-org.brum.beds.ac.uk/10.3390/polym14061157 - 14 Mar 2022
Cited by 10 | Viewed by 5579
Abstract
The preparation and characteristics of rigid polyurethane foams (RPUFs) synthesized from polyols obtained by glycolysis of post-industrial waste RPUFs have been studied. More precisely, waste rigid foams that have been chemically recycled by glycolysis in this work are industrially produced pieces for housing [...] Read more.
The preparation and characteristics of rigid polyurethane foams (RPUFs) synthesized from polyols obtained by glycolysis of post-industrial waste RPUFs have been studied. More precisely, waste rigid foams that have been chemically recycled by glycolysis in this work are industrially produced pieces for housing and bracket applications. The glycolysis products have been purified by vacuum distillation. The physicochemical properties of the polyols, such as hydroxyl value, acid value, average molecular weight (Mn) and viscosity have been analyzed. The chemical structure and thermal stability of the polyols have been studied by means of FTIR and TGA, respectively. Partial substitution of the commercial polyol (up to 15 wt.%) by the recycled polyols increases the reactivity of the RPUFs synthesis, according to short characteristic times during the foaming process along with more exothermic temperature profiles. Foams formulated with recycled polyols have a lower bulk density (88.3–96.9 kg m−3) and smaller cell sizes compared to a conventional reference RPUF. The addition of recycled polyols (up to 10 wt.%) into the formulation causes a slight decrease in compressive properties, whereas tensile strength and modulus values increase remarkably. Full article
(This article belongs to the Special Issue Development in Fiber-Reinforced Polymer Composites)
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18 pages, 4179 KiB  
Article
Star-Branched Polyamides as the Matrix in Thermoplastic Composites
by Karina C. Núñez Carrero, Manuel Herrero, María Asensio, Julia Guerrero, Juan Carlos Merino and José María Pastor
Polymers 2022, 14(5), 942; https://0-doi-org.brum.beds.ac.uk/10.3390/polym14050942 - 26 Feb 2022
Cited by 1 | Viewed by 2112
Abstract
The aim of this study is the preparation of star-shaped branched polyamides (sPA6) with low melt viscosity, but also with improved mechanical properties by reactive extrusion. This configuration has been obtained by grafting a tri-functional, three-armed molecule: 5-aminoisophthalic-acid, used as a linking agent [...] Read more.
The aim of this study is the preparation of star-shaped branched polyamides (sPA6) with low melt viscosity, but also with improved mechanical properties by reactive extrusion. This configuration has been obtained by grafting a tri-functional, three-armed molecule: 5-aminoisophthalic-acid, used as a linking agent (LA). The balance between the fluidity, polarity and mechanical properties of sPA6s is the reason why these materials have been investigated for the impregnation of fabrics in the manufacture of thermoplastic composites. For these impregnation processes, the low viscosity of the melt has allowed the processing parameters (temperature, pressure and time) to be reduced, and its new microstructure has allowed the mechanical properties of virgin thermoplastic resins to be maintained. A significant improvement in the ultrasonic welding processes of the composites was also found when an energy director based on these materials was applied at the interface. In this work, an exhaustive microstructural characterization of the obtained sPAs is presented and related to the final properties of the composites obtained by film stacking. Full article
(This article belongs to the Special Issue Development in Fiber-Reinforced Polymer Composites)
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Review

Jump to: Research

20 pages, 4249 KiB  
Review
An Overview of the Measurement of Permeability of Composite Reinforcements
by Andrea Dei Sommi, Francesca Lionetto and Alfonso Maffezzoli
Polymers 2023, 15(3), 728; https://0-doi-org.brum.beds.ac.uk/10.3390/polym15030728 - 31 Jan 2023
Cited by 4 | Viewed by 3096
Abstract
Liquid composite molding (LCM) is a class of fast and cheap processes suitable for the fabrication of large parts with good geometrical and mechanical properties. One of the main steps in an LCM process is represented by the filling stage, during which a [...] Read more.
Liquid composite molding (LCM) is a class of fast and cheap processes suitable for the fabrication of large parts with good geometrical and mechanical properties. One of the main steps in an LCM process is represented by the filling stage, during which a reinforcing fiber preform is impregnated with a low-viscosity resin. Darcy’s permeability is the key property for the filling stage, not usually available and depending on several factors. Permeability is also essential in computational modeling to reduce costly trial-and-error procedures during composite manufacturing. This review aims to present the most used and recent methods for permeability measurement. Several solutions, introduced to monitor resin flow within the preform and to calculate the in-plane and out-of-plane permeability, will be presented. Finally, the new trends toward reliable methods based mainly on non-invasive and possibly integrated sensors will be described. Full article
(This article belongs to the Special Issue Development in Fiber-Reinforced Polymer Composites)
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32 pages, 1860 KiB  
Review
Strengthening Timber Structural Members with CFRP and GFRP: A State-of-the-Art Review
by Khaled Saad and András Lengyel
Polymers 2022, 14(12), 2381; https://0-doi-org.brum.beds.ac.uk/10.3390/polym14122381 - 12 Jun 2022
Cited by 17 | Viewed by 5307
Abstract
The application of fibre-reinforced polymers (FRP) for strengthening timber structures has proven its efficiency in enhancing load-bearing capacity and, in some cases, the stiffness of structural elements, thus providing cost-effective and competitive alternatives both in new design and retrofitting existing historical buildings. Over [...] Read more.
The application of fibre-reinforced polymers (FRP) for strengthening timber structures has proven its efficiency in enhancing load-bearing capacity and, in some cases, the stiffness of structural elements, thus providing cost-effective and competitive alternatives both in new design and retrofitting existing historical buildings. Over the last few decades, several reinforcing materials and techniques evolved, and considerable progress was made in numerical modelling, especially using the finite element method. As this field of research has become extensive and diversified, as well as numerous contradicting results have emerged, a thorough review is necessary. This manuscript covers the topics of historical preliminaries, reinforcing with carbon and glass fibre composites, bond characteristics, main reinforcing techniques, modelling of knots, and the effects of the fibre waviness on the composite behaviour. A detailed overview is given on the experimental and numerical investigation of mechanics of strengthened beams. A one-of-a-kind table is presented that compares the stiffness improvement observed in several studies with analytical estimates. Attention is drawn to a number of challenges that have arisen, e.g., the moderate stiffness enhancement, composite-to-wood interface, modelling of knots, and strengthening of defected timber members. This paper can be used as a starting point for future research and engineering projects. Full article
(This article belongs to the Special Issue Development in Fiber-Reinforced Polymer Composites)
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