Editorial

4 pages, 182 KiB

Open AccessEditorial

Fatigue and Fracture Behavior of Composite Materials

by Davide Palumbo and Rosa De Finis

Materials 2023, 16(23), 7292; https://0-doi-org.brum.beds.ac.uk/10.3390/ma16237292 - 23 Nov 2023

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Presently, composites are one of the top-of-the-range materials used in different industrial sectors and represent the best alternative to metal alloys in those applications where higher mechanical properties and lower weights are required [...] Full article

(This article belongs to the Special Issue Fatigue and Fracture Behavior of Composite Materials)

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24 pages, 6781 KiB

Open AccessEditor’s ChoiceArticle

Effect of Carbon Nanofibers on the Strain Rate and Interlaminar Shear Strength of Carbon/Epoxy Composites

by Paulo Santos, Abílio P. Silva and Paulo N. B. Reis

Materials 2023, 16(12), 4332; https://0-doi-org.brum.beds.ac.uk/10.3390/ma16124332 - 12 Jun 2023

Cited by 3 | Viewed by 929

Abstract

The static bending properties, different strain rates and interlaminar shear strength (ILSS) of carbon-fiber-reinforced polymers (CFRP) with two epoxy resins nano-enhanced with carbon nanofibers (CNFs) are studied. The effect on ILSS behavior from aggressive environments, such as hydrochloric acid (HCl), sodium hydroxide (NaOH), [...] Read more.

The static bending properties, different strain rates and interlaminar shear strength (ILSS) of carbon-fiber-reinforced polymers (CFRP) with two epoxy resins nano-enhanced with carbon nanofibers (CNFs) are studied. The effect on ILSS behavior from aggressive environments, such as hydrochloric acid (HCl), sodium hydroxide (NaOH), water and temperature, are also analyzed. The laminates with Sicomin resin and 0.75 wt.% CNFs and with Ebalta resin with 0.5 wt.% CNFs show significant improvements in terms of bending stress and bending stiffness, up to 10%. The values of ILLS increase for higher values of strain rate, and in both resins, the nano-enhanced laminates with CNFs show better results to strain-rate sensitivity. A linear relationship between the logarithm of the strain rate was determined to predict the bending stress, bending stiffness, bending strain and ILSS for all laminates. The aggressive solutions significantly affect the ILSS, and their effects are strongly dependent on the concentration. Nevertheless, the alkaline solution promotes higher decreases in ILSS and the addition of CNFs is not beneficial. Regardless of the immersion in water or exposure to high temperatures a decrease in ILSS is observed, but, in this case, CNF content reduces the degradation of the laminates. Full article

(This article belongs to the Special Issue Fatigue and Fracture Behavior of Composite Materials)

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34 pages, 13301 KiB

Open AccessArticle

An Extended Hydro-Mechanical Coupling Model Based on Smoothed Particle Hydrodynamics for Simulating Crack Propagation in Rocks under Hydraulic and Compressive Loads

by Dianrui Mu, Aiping Tang, Haigang Qu and Junjie Wang

Materials 2023, 16(4), 1572; https://0-doi-org.brum.beds.ac.uk/10.3390/ma16041572 - 13 Feb 2023

Cited by 3 | Viewed by 1315

Abstract

A seepage model based on smoothed particle hydrodynamics (SPH) was developed for the seepage simulation of pore water in porous rock mass media. Then, the effectiveness of the seepage model was proved by a two-dimensional seepage benchmark example. Under the framework of SPH [...] Read more.

A seepage model based on smoothed particle hydrodynamics (SPH) was developed for the seepage simulation of pore water in porous rock mass media. Then, the effectiveness of the seepage model was proved by a two-dimensional seepage benchmark example. Under the framework of SPH based on the total Lagrangian formula, an extended hydro-mechanical coupling model (EHM-TLF-SPH) was proposed to simulate the crack propagation and coalescence process of rock samples with prefabricated flaws under hydraulic and compressive loads. In the SPH program, the Lagrangian kernel was used to approximate the equations of motion of particles. Then, the influence of flaw water pressure on crack propagation and coalescence models of rock samples with single or two parallel prefabricated flaws was studied by two numerical examples. The simulation results agreed well with the test results, verifying the validity and accuracy of the EHM-TLF-SPH model. The results showed that with the increase in flaw water pressure, the crack initiation angle and stress of the wing crack decreased gradually. The crack initiation location of the wing crack moved to the prefabricated flaw tip, while the crack initiation location of the shear crack was far away from the prefabricated flaw tip. In addition, the influence of the permeability coefficient and flaw water pressure on the osmotic pressure was also investigated, which revealed the fracturing mechanism of hydraulic cracking engineering. Full article

(This article belongs to the Special Issue Fatigue and Fracture Behavior of Composite Materials)

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18 pages, 5766 KiB

Open AccessArticle

Modeling of Internal Geometric Variability and Statistical Property Prediction of Braided Composites

by Wenli Li, Donghui Zhu, Wenqi Shao and Dong Jiang

Materials 2022, 15(15), 5332; https://0-doi-org.brum.beds.ac.uk/10.3390/ma15155332 - 03 Aug 2022

Cited by 6 | Viewed by 1319

Abstract

Due to the advantages of high specific strength, specific stiffness, and excellent fatigue resistance, carbon fiber reinforced braided composites have been widely applied in engineering. Since the molding process of braided composites is complex and immature, substantial variability of the internal geometry exists [...] Read more.

Due to the advantages of high specific strength, specific stiffness, and excellent fatigue resistance, carbon fiber reinforced braided composites have been widely applied in engineering. Since the molding process of braided composites is complex and immature, substantial variability of the internal geometry exists in composites, in which the yarn path with uncertainty is a main factor, so it is necessary to establish an uncertainty model to study the influence of randomness of the yarn path on mechanical properties, which is significantly related to the fatigue resistance properties of composite. An uncertain mesoscopic model with uniform distribution of yarn paths is proposed. Assuming the yarn path is spatially varying in interval range, the variability of yarn path is represented geometrically in the unit cell of composite. The three-dimensional coordinates of the yarn trajectory are calculated, the meso-uncertainty models of 2-D and 2.5-D braided composites are established. The equivalent elastic parameters and the thermal expansion coefficients are obtained by applying homogenization method and temperature field boundary conditions to the mesoscopic model. The effect of yarn path uncertainty on the statistical characteristics of elastic and thermal parameters of braided composites was studied by using Monte-Carlo simulation. A simulation method for modeling yarn path uncertainty of braided composites is provided in this paper for predicting the statistical characteristics of the equivalent elastic and thermal parameters. Full article

(This article belongs to the Special Issue Fatigue and Fracture Behavior of Composite Materials)

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13 pages, 5188 KiB

Open AccessArticle

CFRP Fatigue Damage Detection by Thermal Methods

by Marta De Giorgi, Riccardo Nobile and Fania Palano

Materials 2022, 15(11), 3787; https://0-doi-org.brum.beds.ac.uk/10.3390/ma15113787 - 26 May 2022

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Abstract

In this work, the fatigue damage of CFRP uniaxial composite specimens were studied using thermal methods to determine the fatigue behavior. The aim was to evaluate the fatigue damage as a function of the number of cycles. Consequently, the damage process was studied [...] Read more.

In this work, the fatigue damage of CFRP uniaxial composite specimens were studied using thermal methods to determine the fatigue behavior. The aim was to evaluate the fatigue damage as a function of the number of cycles. Consequently, the damage process was studied in terms of a global indicator, considering the stiffness decay, and in terms of local parameters, considering the evolution of temperature maps acquired during the fatigue tests. A direct correlation between the damage index, corresponding to 90% of the fatigue life, and the temperature variation of the most stressed area was found. Another parameter taken into consideration was the heating rate during the application of the first thousands cycles. This parameter was proportional to the stress amplitude, making it a useful parameter since it refers to the initial part of the specimen fatigue life. Full article

(This article belongs to the Special Issue Fatigue and Fracture Behavior of Composite Materials)

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15 pages, 2775 KiB

Open AccessArticle

Low- and High-Cycle Fatigue Behavior of FRCM Composites

by Angelo Savio Calabrese, Tommaso D’Antino, Pierluigi Colombi and Carlo Poggi

Materials 2021, 14(18), 5412; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14185412 - 18 Sep 2021

Cited by 11 | Viewed by 1975

Abstract

This paper describes methods, procedures, and results of cyclic loading tensile tests of a PBO FRCM composite. The main objective of the research is the evaluation of the effect of low- and high-cycle fatigue on the composite tensile properties, namely the tensile strength, [...] Read more.

This paper describes methods, procedures, and results of cyclic loading tensile tests of a PBO FRCM composite. The main objective of the research is the evaluation of the effect of low- and high-cycle fatigue on the composite tensile properties, namely the tensile strength, ultimate tensile strain, and slope of the stress–strain curve. To this end, low- and high-cycle fatigue tests and post-fatigue tests were performed to study the composite behavior when subjected to cyclic loading and after being subjected to a different number of cycles. The results showed that the mean stress and amplitude of fatigue cycles affect the specimen behavior and mode of failure. In high-cycle fatigue tests, failure occurred due to progressive fiber filaments rupture. In low-cycle fatigue, the stress–strain response and failure mode were similar to those observed in quasi-static tensile tests. The results obtained provide important information on the fatigue behavior of PBO FRCM coupons, showing the need for further studies to better understand the behavior of existing concrete and masonry members strengthened with FRCM composites and subjected to cyclic loading. Full article

(This article belongs to the Special Issue Fatigue and Fracture Behavior of Composite Materials)

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16 pages, 16156 KiB

Open AccessArticle

Fatigue Damage Evaluation of Short Carbon Fiber Reinforced Plastics Based on Thermoelastic Temperature Change and Second Harmonic Components of Thermal Signal

by Daiki Shiozawa, Takahide Sakagami, Yu Nakamura, Takato Tamashiro, Shinichi Nonaka, Kenichi Hamada and Tomoaki Shinchi

Materials 2021, 14(17), 4941; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14174941 - 30 Aug 2021

Cited by 3 | Viewed by 1472

Abstract

Short fiber reinforced plastics (SFRPs) have excellent moldability and productivity compared to continuous fiber composites. In this study, thermoelastic stress analysis (TSA) was applied to detect delamination defects in short carbon fiber reinforced plastics (SCFRPs). The thermoelastic temperature change ΔT_E, [...] Read more.

Short fiber reinforced plastics (SFRPs) have excellent moldability and productivity compared to continuous fiber composites. In this study, thermoelastic stress analysis (TSA) was applied to detect delamination defects in short carbon fiber reinforced plastics (SCFRPs). The thermoelastic temperature change ΔT_E, phase of thermal signal θ_E, and second harmonic temperature component ΔT_D were measured. In the fatigue test of SCFRP, it was confirmed that changes in ΔT_E, θ_E, and ΔT_D appeared in the damaged regions. A staircase-like stress level test for a SCFRP specimen was conducted to investigate the generation mechanism of the ΔT_D. The distortion of the temperature change appeared at the maximum tension stress of the sinusoidal load—and when the stress level decreased, the temperature change returned to the original sinusoidal waveform. ΔT_D changed according to the change in the maximum stress during the staircase-like stress level test, and a large value of ΔT_D was observed in the final ruptured region. A distortion of the temperature change and ΔT_D was considered to be caused by the change in stress sharing condition between the fiber and resin due to delamination damage. Therefore, ΔT_D can be applied to the detection of delamination defects and the evaluation of damage propagation. Full article

(This article belongs to the Special Issue Fatigue and Fracture Behavior of Composite Materials)

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11 pages, 3156 KiB

Open AccessArticle

Fatigue Life Improvement of Cracked Aluminum 6061-T6 Plates Repaired by Composite Patches

by Armin Yousefi, Saman Jolaiy, Reza Hedayati, Ahmad Serjouei and Mahdi Bodaghi

Materials 2021, 14(6), 1421; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14061421 - 15 Mar 2021

Cited by 10 | Viewed by 2750

Abstract

Bonded patches are widely used in several industry sectors for repairing damaged plates, cracks in metallic structures, and reinforcement of damaged structures. Composite patches have optimal properties such as high strength-to-weight ratio, easiness in being applied, and high flexibility. Due to recent rapid [...] Read more.

Bonded patches are widely used in several industry sectors for repairing damaged plates, cracks in metallic structures, and reinforcement of damaged structures. Composite patches have optimal properties such as high strength-to-weight ratio, easiness in being applied, and high flexibility. Due to recent rapid growth in the aerospace industry, analyses of adhesively bonded patches applicable to repairing cracked structures have become of great significance. In the present study, the fatigue behavior of the aluminum alloy, repaired by a double-sided glass/epoxy composite patch, is studied numerically. More specifically, the effect of applying a double-sided composite patch on the fatigue life improvement of a damaged aluminum 6061-T6 is analyzed. 3D finite element numerical modeling is performed to analyze the fatigue performance of both repaired and unrepaired aluminum plates using the Abaqus package. To determine the fatigue life of the aluminum 6061-T6 plate, first, the hysteresis loop is determined, and afterward, the plastic strain amplitude is calculated. Finally, by using the Coffin-Manson equation, fatigue life is predicted and validated against the available experimental data from the literature. Results reveal that composite patches increase the fatigue life of cracked structures significantly, ranging from 55% to 100% for different applied stresses. Full article

(This article belongs to the Special Issue Fatigue and Fracture Behavior of Composite Materials)

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18 pages, 5214 KiB

Open AccessArticle

Estimation of the Dissipative Heat Sources Related to the Total Energy Input of a CFRP Composite by Using the Second Amplitude Harmonic of the Thermal Signal

by Rosa De Finis and Davide Palumbo

Materials 2020, 13(12), 2820; https://0-doi-org.brum.beds.ac.uk/10.3390/ma13122820 - 23 Jun 2020

Cited by 10 | Viewed by 1707

Abstract

Theories for predicting the fatigue behaviour of composite laminates often make strong assumptions on the damage mechanisms that strongly depend on the designed laminate lay-up. In this regard, several physical and empirical models were proposed in the literature that generally require experimental validations. [...] Read more.

Theories for predicting the fatigue behaviour of composite laminates often make strong assumptions on the damage mechanisms that strongly depend on the designed laminate lay-up. In this regard, several physical and empirical models were proposed in the literature that generally require experimental validations. The experimental techniques, such as thermography, also provide useful tools for monitoring the behaviour of the specific material so, that they can be used to support the study of the damage mechanisms of materials. In this research, the second amplitude harmonic of the thermal signal has been investigated and used to assess the relationship with the total energy input in order to estimate the fatigue strength of the material. A thermal index was assessed by monitoring the constant amplitude tests (S/N curve) that were performed on a quasi-isotropic carbon fibre reinforced polymer (CFRP) laminate obtained by the automated fibre placement process. The obtained results demonstrated the capability of the second amplitude harmonic of the thermal signal to describe and monitor the fatigue damage. Full article

(This article belongs to the Special Issue Fatigue and Fracture Behavior of Composite Materials)

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