Ballistic Impact and Virtual Testing of Woven FRP Laminates

Round 1

Reviewer 1 Report

Comments

This paper studied the ballistic impact and virtual testing of woven FRP laminates. The outcome is interesting for readers. However, there are several aspects that need to be improved. The reviewer can only recommend for publication if the author satisfactorily address the following comments in the revised version.

1. The parameters investigated in this study should be clearly highlighted. What are the effect of this parameter on the properties of composites?
2. Which test standard was considered? How many replicate samples were tested in each category?
3. The failure mechanism of the specimen should be discussed more clearly.
4. The impact damage observed in this study is quite similar to other study in literature [Ref: A novel hybridised composite sandwich core with Glass, Kevlar and Zylon fibres–Investigation under low-velocity impact]. Suggest to cite this paper in Section 4 to enhance discussion.
5. How many samples were tested in each category?
6. The novelty of the study should be highlighted at the end of introduction section. How this study is different from the published study in literature?
7. How the outcome of this study will benefit researchers and end users? This need to be highlighted in introduction or end of conclusion.
8. The literature on the other dynamic properties such as fatigue of composites need to be reviewed. Recent study shows that the laminated composites can offer good fatigue life [Ref: Testing and modelling the fatigue behaviour of GFRP composites – Effect of stress level, stress concentration and frequency]. Moreover, the laminated composites are used in structural application where high impact force is desirable [Ref: Static behaviour of glass fibre reinforced novel composite sleepers for mainline railway track]. Suggest to include them in introduction section with proper citations to improve the background study.

I would be happy to see the revised version to understand how these comments are being addressed.

Author Response

Response to Reviewer 1:

1. The parameters investigated in this study should be clearly highlighted. What are the effect of this parameter on the properties of composites?

For the woven CFRP composite ply used in this study, the strength and stiffness material property has been given Table 1 with sources cited in the caption. The Mode I and Mode II fracture toughness property is given in Table 4 with sources cited in the caption. Page 6 describes the calibration process of these properties in the FE using data from the sources above. The calibrated modelling parameters are given in Table 3 for laminate failure and in Table 4 for the cohesive zone model. For interest of page limit, we have not included all these calibrations as the process is rather routine. We agree we did not discuss how the changes of these parameters may affect response.

Modification 1: Added Figure 4 and description on page 6 to show the calibration results of material model MAT_54. Added Figure 5 and description on page 7 to show calibration results for cohesive zone delamination model.

1. Which test standard was considered? How many replicate samples were tested in each category?

The primary aim of this investigation was to understand if low fidelity models are capable to capture complex failure mechanisms of an impacted composite plate. For the experimental portion the aim was to collect some empirical data to assist with the modelling. Limitations in sample numbers meant we could conduct four test on 0/90 and four tests on QI laminates to give general trend.  Looking at standards available, the projectiles they incorporate are often specialised in form of bullets or blunt objects. Since we wanted to maintain a simple test using a spherical steel projectile we did not consider the available standards. In fact many experimental work on this topic do not follow standards for the impact tests.  

Modification 2: Descriptions have been added to page 3 to explain this justification.

1. The failure mechanism of the specimen should be discussed more clearly.

Some failure description has been given on page 9. However, we agree we can add more clear descriptions as well.

Modification 3: Extra description of failure mechanisms of woven composite plate has been added on page 8.

1. The impact damage observed in this study is quite similar to other study in literature [Ref: A novel hybridised composite sandwich core with Glass, Kevlar and Zylon fibres–Investigation under low-velocity impact]. Suggest to cite this paper in Section 4 to enhance discussion.

Modification 4: Thank you for the suggestion. This is added in section 4, page 8 to supplement modification 3.

1. How many samples were tested in each category?

Already addressed in comment 2, four samples were tested for each category, see Modification 2.

1. The novelty of the study should be highlighted at the end of introduction section. How this study is different from the published study in literature?

We agree the novelty was not clearly highlighted. The key novelty of this work is the comparison of the two low-fidelity and high-fidelity schemes in terms of computational speeds and accuracy in damage prediction. This type of comparison is not available in literature under a single investigation, since most research employ a single detailed modelling procedure often with bespoke user materials specifically written for it.

Modification 5: The motivation and key novelty of the work has been added on page 2, to highlight the benefits of this work for the community.

1. How the outcome of this study will benefit researchers and end users? This need to be highlighted in introduction or end of conclusion.

Modification 6: Extra description of the highlighted benefits of this work have been added in page 17.

1. The literature on the other dynamic properties such as fatigue of composites need to be reviewed. Recent study shows that the laminated composites can offer good fatigue life [Ref: Testing and modelling the fatigue behaviour of GFRP composites – Effect of stress level, stress concentration and frequency]. Moreover, the laminated composites are used in structural application where high impact force is desirable [Ref: Static behaviour of glass fibre reinforced novel composite sleepers for mainline railway track]. Suggest to include them in introduction section with proper citations to improve the background study.

Modification 6: Thank you for these suggestions. Relevant citations have been added to introduction (page 1) to supplement the literature review on composite material usage benefits in industry.

I would be happy to see the revised version to understand how these comments are being addressed.

Reviewer 2 Report

This paper has been dedicated to experimentally and numerically investigate the behavior of woven FRP laminates under impact loading. The novelty of the paper is good. The subject of the research is interesting. Therefore, the paper can be recommended for publication in this journal after minor revision:

1. The literature review of this article should be improved by adding some recent and relevant papers in the introduction.
2. The main contribution and highlights of the research should be clarified.
3. The verification study of the numerical simulation is missing. It is better that the authors explain more about the details of simulation.
4. In figure 13, the results have not been depicted clearly. The experimental results related to /-45 and (0/90) cannot be distinguished.
5. In figure 12, why the results of simulation study associated to the velocity of 54 m/s are missing?
6. The conclusion part should be re-written. At the first of this section, the authors should provide a summary of the research work which they have done.

Author Response

Response to Reviewer 2:

The authors would like to thank the reviewer for taking the time to review their work and for the invaluable comments offered. Below, the authors responses:

This paper has been dedicated to experimentally and numerically investigate the behaviour of woven FRP laminates under impact loading. The novelty of the paper is good. The subject of the research is interesting. Therefore, the paper can be recommended for publication in this journal after minor revision:

1. The literature review of this article should be improved by adding some recent and relevant papers in the introduction.

Response: Three more additional papers have been added

1. The main contribution and highlights of the research should be clarified.

Response: The motivation and key novelty of the work has been added on page 2, to highlight the benefits of this work for the community

1. The verification study of the numerical simulation is missing. It is better that the authors explain more about the details of simulation.

Response: According to the authors opinion, the pictorial benchmarking of the damage at various impact speeds, is the proposed format of modelling verification

1. In figure 13, the results have not been depicted clearly. The experimental results related to /-45 and (0/90) cannot be distinguished.

Response: the authors agree with the comment from the reviewer, but since the results are very close, it is difficult to clearly depict them as non-overlapping

1. In figure 12, why the results of simulation study associated to the velocity of 54 m/s are missing?

Response: As mentioned in the main text, the results at 54m/s where not plotted since the impact and subsequent damage location was off-target

1. The conclusion part should be re-written. At the first of this section, the authors should provide a summary of the research work which they have done.

Response: According to the authors opinion, the conclusions section, although sort, it does present with the study’s major findings. Nevertheless, as an addition, the motivation and key novelty of the work has been added on page 2, to highlight the benefits of this work for the community.

Reviewer 3 Report

The submitted manuscript addressed the computational study of ballistic impact test on the CFRP specimen. 

It is well matched with the experimental result but requires several points to be improved.

1. The literature survey is not enough, please provide more than 30 paper to catch the recent trend of the topic.

2. It is well known that aramid fiber rather than carbon fiber is used for bullet proof material. Please address why CFRP have used in this study.

3. More results should support the main theme of this study. For example, threshold speed (or impact energy) to perforate the substrate respect to the number of plys.

Please revise the manuscript for possible publication in J. Compos. Sci.

Author Response

Reviewer 3:

The authors would like to thank the reviewer for taking the time to review their work and for the invaluable comments offered. Below, the authors responses:

The literature survey is not enough, please provide more than 30 paper to catch the recent trend of the topic.

Response: We agree with the reviewer’s opinion that there are many publications in the open domain in relation to ballistic impacts The cited publications we cited which were less than 30, were the ones we used and draw information from. The work has been completed using these references. In any case, three additional publications that were found relevant were added

It is well known that aramid fiber rather than carbon fiber is used for bullet proof material. Please address why CFRP have used in this study.

Response: In this study, we wanted to examine the correlation with numerical modelling of ballistic impact on the mentioned carbon fibre fabric. We do know that aramid fibres are better, but our study focuses on a different material, because our aim was to examine that material's behaviour under ballistic impact

More results should support the main theme of this study. For example, threshold speed (or impact energy) to perforate the substrate respect to the number of plys.

Response: Our experimental resources were limited to a fixed number of specimens. It is true that a better representation and correlation would results from more experimental results but unfortunately, we had available resources for this limited number of specimens. In any case, the study was on the modelling correlation with experiments and not in the actual full velocity spectrum perforation response

Round 2

Reviewer 1 Report

I have no further comments

Author Response

The authors would like to thank the reviewer for the feedback. The manuscript has been checked for possible spelling errors

Reviewer 3 Report

Dear Author, 

your response doesn't provide any sound resolution even one of my three questions. 

I'd like to give same request again. Please show me reasonable answer to each question.

Author Response

Dear respectable reviewer,

According to the authors, a response has been provided, it is just that your demands have not been met. To re-iterate:

• It is the author’s belief that the quality of the content of a manuscript is not directly related to the number of references referred to in the work. It is true that more references provide the reader with a somewhat false impression of a work being more thorough. We are at the age of big data and infinite access to information. We have to be selective and distil the references that are more important to each work. We read a lot of papers to undertake our work but we made use of just 15 of them to compile it. We added 3 more references, found to be relevant.
• The woven fabric used, was the one we wanted to draw some results on.
• We had limited access to resources, so the study was tailored to al limited number of tests