A Review on Mechanical Properties of Natural Fibre Reinforced Polymer Composites under Various Strain Rates

Round 1

Reviewer 1 Report

Comments

This paper studied the mechanical properties of 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. How Fig. 4 was developed. Is it the results of the previous study? Is it the normalised pattern of the stress strain curve obtained from literature?
2. The stress strain curve for compressive strain rate is provided. However, no such plots are provided for tensile strain rate and flexural strain rate. Why it is not provided?
3. Generally FRP is a linear elastic material. Why a nonlinear stress-strain curve was obtained in Fig. 4?
4. The failure mechanism of the specimen should be discussed more clearly.
5. The novelty of the study should be highlighted more clearly at the end of introduction section. How this study is different from the published study in literature?
6. How the outcome of this study will benefit researchers and end users? This need to be highlighted in introduction or end of conclusion.
7. Few important properties are missing for FRP laminates. The recent findings on the dynamic properties of laminates should be highlighted in introduction section to improve the background study. For example, FRP laminates failed in brittle manner under fatigue loading [Ref: Testing and modelling the fatigue behaviour of GFRP composites–Effect of stress level, stress concentration and frequency] and they are now used in manufacturing railway sleepers [Ref: Static behaviour of glass fibre reinforced novel composite sleepers for mainline railway track] and fire resistant structural components [Ref: Effect of fire-retardant ceram powder on the properties of phenolic-based GFRP composites]. 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

1. How Fig. 4 was developed. Is it the results of the previous study? Is it the normalised pattern of the stress strain curve obtained from literature?

• Yes, it is a general pattern concluded from literature. The sentence has rephrased for better clarity of the statement.

1. The stress strain curve for compressive strain rate is provided. However, no such plots are provided for tensile strain rate and flexural strain rate. Why it is not provided?

• The normalised curves for tensile behaviour were added in the manuscript and as the flexural was similar to that of tensile behaviour, hence a declaration regarding that was added in the revised manuscript.

1. Generally FRP is a linear elastic material. Why a nonlinear stress-strain curve was obtained in Fig. 4?

• Ideally, it was linear due to negligible plastic deformation. However, published results shows that it is not linear especially for the cases in compression and the non-linear behaviour of polymer/NFPCs is due to their viscoelastic behaviour. This non-linear behaviour become more obvious under varying strain rates, which leads to further investigation in this area.

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

• Due to the limited availability of data in this particular topic in literature, it was beyond the scope for further investigation on failure mechanism. This also implies that, more work in that is foreseen to clarify the failure mechanisms.

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

• There is hardly any review paper on NFPCs under different strain rates loadings, which makes it more challenging to collect more information on that. And the few published experimental papers conclude some patterns. Hence, further reports are foreseen in the areas of research.

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

• Based on reviewers’ suggestion, the manuscript was revised (highlighted in yellow in revised manuscript) accordingly: “The polymeric composite was viscoelastic in nature and the real application such as automotive, aerospace and any machines were not operated in constant quasistatic conditions. Hence, this review would benefits researchers to further understand the NFPCs mechanical behaviours by simulating real application that involve varying strain rates.”

1. Few important properties are missing for FRP laminates. The recent findings on the dynamic properties of laminates should be highlighted in introduction section to improve the background study. For example, FRP laminates failed in brittle manner under fatigue loading [Ref: Testing and modelling the fatigue behaviour of GFRP composites–Effect of stress level, stress concentration and frequency] and they are now used in manufacturing railway sleepers [Ref: Static behaviour of glass fibre reinforced novel composite sleepers for mainline railway track] and fire resistant structural components [Ref: Effect of fire-retardant ceram powder on the properties of phenolic-based GFRP composites]. Suggest to include them in introduction section with proper citations to improve the background study.

• Some additional info was added in the introduction section as highlighted in yellow.

Reviewer 2 Report

A Review on Mechanical Properties of Natural Fibre Reinforced Polymer Composites under Various Strain Rates – Khieng et al.

This review paper does a literature review on NFPC’s under various strain rates. The work is related only to tensile, compressive and flexural mechanical properties. This work appears to be limited in scope in that, they only consider NFPC’s performance under various strain rates. Nonetheless, the authors must clean up the draft and conform to the journal formatting guidelines. There are indentation issues and spelling errors which must be addressed before this draft can be accepted.

Author Response

This review paper does a literature review on NFPC’s under various strain rates. The work is related only to tensile, compressive and flexural mechanical properties. This work appears to be limited in scope in that, they only consider NFPC’s performance under various strain rates. Nonetheless, the authors must clean up the draft and conform to the journal formatting guidelines. There are indentation issues and spelling errors which must be addressed before this draft can be accepted.

- Based on reviewers’ suggestions, formatting was carried out as per journal’s guidelines. The manuscript was revised accordingly, and care has been taken to minimise the errors as much as feasible.

- As for the scope, the paper was focused on NFPCs mechanical performance/properties under various/varying strain rates. The authors tried to understand how the strain rate affect the performance/properties in term of some basic deformations that can be found in the literature which are tension, compression and bending. Having said that, there is very limited information is available in literature which makes this review work changeling. Thus, more work in this area is foreseen.

Round 2

Reviewer 1 Report

The author attempted to address the comments. However, the below four comments are not properly addressed. The reviewer would not recommend to accept this paper unless the below comments are addressed properly.

1. The stress strain curve for compressive strain rate is provided. However, no such plots are provided for tensile strain rate and flexural strain rate. Why it is not provided?

• The normalised curves for tensile behaviour were added in the manuscript and as the flexural was similar to that of tensile behaviour, hence a declaration regarding that was added in the revised manuscript.

Reviewer’s comment: Fig.5 is provided in Section 3.2. I have not found similar photo in Section 3.3

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

• Due to the limited availability of data in this particular topic in literature, it was beyond the scope for further investigation on failure mechanism. This also implies that, more work in that is foreseen to clarify the failure mechanisms.

Reviewer’s comment: The author need to provide his own interpretation about failure mode.

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

• There is hardly any review paper on NFPCs under different strain rates loadings, which makes it more challenging to collect more information on that. And the few published experimental papers conclude some patterns. Hence, further reports are foreseen in the areas of research.

Reviewer’s comment: Every research should have novelty. Otherwise this paper is not publishable. Suggest to highlight the novelty very clearly.

1. Few important properties are missing for FRP laminates. The recent findings on the dynamic properties of laminates should be highlighted in introduction section to improve the background study. For example, FRP laminates failed in brittle manner under fatigue loading [Ref: Testing and modelling the fatigue behaviour of GFRP composites–Effect of stress level, stress concentration and frequency] and they are now used in manufacturing railway sleepers [Ref: Static behaviour of glass fibre reinforced novel composite sleepers for mainline railway track] and fire resistant structural components [Ref: Effect of fire-retardant ceram powder on the properties of phenolic-based GFRP composites]. Suggest to include them in introduction section with proper citations to improve the background study.

• Some additional info was added in the introduction section as highlighted in yellow.

Reviewer’s comment: Not properly addressed this comment. Suggest to improve background study by including findings from the suggested papers.

I would be happy to see the revised version of the manuscript to understand who these comments were being addressed.

Author Response

The author attempted to address the comments. However, the below four comments are not properly addressed. The reviewer would not recommend to accept this paper unless the below comments are addressed properly.

1. The stress strain curve for compressive strain rate is provided. However, no such plots are provided for tensile strain rate and flexural strain rate. Why it is not provided?

• The normalised curves for tensile behaviour were added in the manuscript and as the flexural was similar to that of tensile behaviour, hence a declaration regarding that was added in the revised manuscript.

Reviewer’s comment: Fig.5 is provided in Section 3.2. I have not found similar photo in Section 3.3

 Reply: As per reviewers’ suggestion, normalised curves for flexural strain has included in the revised manuscript (please see the Fig. 6 in the revised manuscript).

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

• Due to the limited availability of data in this particular topic in literature, it was beyond the scope for further investigation on failure mechanism. This also implies that, more work in that is foreseen to clarify the failure mechanisms.

Reviewer’s comment: The author need to provide his own interpretation about failure mode.

Reply: Interpretation of failure mechanism behaviour has been given in literature summary part.

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

Reviewer’s comment: Every research should have novelty. Otherwise this paper is not publishable. Suggest to highlight the novelty very clearly.

Reply: The authors tried to make the novelty statement of the present work evident as follows:

- The novelty is that there are already numerous literatures established on the strain rate sensitivity of NFPCs, their limitations and factors affecting it, but limited relevant review articles are available. Many studies often found embrittlement and fillers debonding as the primary issues in most of the NFPCs under higher strain rates loading. Nonetheless, there are still many other critical issues that need to be addressed to produce a mechanically competent NFPCs under diverse loading conditions in order for them to be utilized in high performance industries such as automotive and aerospace. Hence, this article aims to provide a summary for current studies of NFPCs under various strain rates conditions, the challenges remain and also discuss the possible future research directions.

1. Few important properties are missing for FRP laminates. The recent findings on the dynamic properties of laminates should be highlighted in introduction section to improve the background study. For example, FRP laminates failed in brittle manner under fatigue loading [Ref: Testing and modelling the fatigue behaviour of GFRP composites–Effect of stress level, stress concentration and frequency] and they are now used in manufacturing railway sleepers [Ref: Static behaviour of glass fibre reinforced novel composite sleepers for mainline railway track] and fire resistant structural components [Ref: Effect of fire-retardant ceram powder on the properties of phenolic-based GFRP composites]. Suggest to include them in introduction section with proper citations to improve the background study.

• Some additional info was added in the introduction section as highlighted in yellow.

Reviewer’s comment: Not properly addressed this comment. Suggest to improve background study by including findings from the suggested papers.

Reply: Suggested references has included in the revised version of the manuscript and the background study was also revised in view of that.

I would be happy to see the revised version of the manuscript to understand who these comments were being addressed.

Reviewer 2 Report

The revised paper may be accepted in its current form. 

Author Response

Thanks for reviewers' valuable comments and based on that, the quality of the manuscript was improved further.

Round 3

Reviewer 1 Report

I have no further comments