Experimental Study on the Static Behavior and Recovery Properties of CFRP/SMA Composites
Round 1
Reviewer 1 Report (Previous Reviewer 2)
The authors have diligently addressed the reviewer's comments and incorporated necessary corrections into their paper. Based on the revisions made, the paper is now in a state that meets the standards for publication. Therefore, I recommend accepting the paper for publication in its present form.
Author Response
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Reviewer 2 Report (Previous Reviewer 1)
Authors need to address the following points to improve the quality of the article.
Abstract can be improved adding the quantitative data.
The research gap is not properly captured. Give detailed literature review support for the found research gap.
“According to Article 8.3.2 of the standard, the standard displacement rate was set at 2 mm/min” Which is the article 8.3.2 to refers too?
In the results, the author(s) is expected to try as much as possible to compare their results obtained with the existing or similar studies.
The article must undergo language proofreading, as I found grammatical and typo errors.
The article must undergo language proofreading, as I found grammatical and typo errors.
Author Response
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Reviewer 3 Report (New Reviewer)
In this paper, the properties of shape memory alloys (SMA) were studied in detail, considering the effects of cycle times, strain amplitude, loading rate, wire diameter, and temperature on the uniaxial tensile properties of SMA. Results show that when the loading rate is 1mm/min, the stress cycle within ten times of SMA is relatively stable, the strain amplitude within 1.5% is the linear elasticity, within 1.5%-6% is the yield stage, and above 6% is the strengthening stage. Increasing the loading rate will advance the SMA into the yield and strengthening stage.
However, the experimental setting of SMA composites in this paper is unreasonable, and the conclusion is not convincing because of the lack of sufficient experimental support. It is suggested to add the relevant experiments on SMA composites. Otherwise, this paper only studies the SMA properties under the research skin of SMA composites. Several other drawbacks that the manuscript suffers from are given below.
1. It is suggested that the sample preparation and testing process should be expressed in figures.
(1) This paper tests the mechanical properties of 300mm long SMA steel wire and 250mm long SMA composite material. The standard distance between the two is 200mm and 150mm, respectively, which can easily cause misunderstanding. It is recommended to set up a diagram showing sample sizes for both tests and the preparation process of SMA composites. The 9 sample preparation steps of SMA composites take much work to read.
(2) The physical diagram of the test of SMA in Fig.1 cannot be seen clearly because the wire is too thin, so adding a test schematic diagram is suggested.
(3) Section 2.2 describes a study on the effect of temperature on SMA properties, but the test objects and parameters need to be clarified. Were temperature tests performed on all samples in Table 1 or some? What temperatures or temperature ranges were tested? Expressing the experimental parameters as a figure or table is suggested.
(4) How are the maximum tensile strain and tensile modulus measured in Section 3.1.1? Is an extensometer or strain gauge attached to the sample? Adding figures to show the SMA composite’s test principle or physical diagram is suggested.
2. The setting of experimental parameters needs more explanation and explanation
(1) In Section 2.3.1, why is a 4% pre-strain level selected for straightening SMA wire instead of 3% or 5%?
(2) In Section 2.3.1, how is the spacing or number of SMA selected?
Why choose a 0.5mm-5/10/15 arrangement? Is it hoped to obtain the conclusion that "the more steel wire, the better performance"? Within the 25mm width of CFRP, up to 50 0.5mm diameter SMA can be densely arranged. Because the resin between the SMA cannot provide perfect wrapping conditions, the performance will degrade, so how many 0.5mm SMA can be arranged to achieve optimal performance? Since the experimental result of setting 5/10/15 0.5mm steel wire is obvious, what is the significance of comparing?
(3) In Section 2.3.1, why are the parameters set as FRP/SMA-I-0.5-5/10/15 and FRP/SMA-I-1-10? The cross-sectional area and the provided incremental tensile load of 10 SMA of diameter 1mm equal that of 40 SMA of diameter 0.5mm. How do test results compare for different diameters?
3. The presentation and interpretation of experimental results need improvement
(1) In Fig. 6(d), compared with the other five subgraphs, the stress-strain curves of the two samples are so different that why no third sample is added. Sample 1, represented by the blue line in Fig. 6(d), has a completely different strain-strain morphology from the other 11 samples. Is it due to operational errors caused by inadequate tensioning?
(2) Part of the figures lack self-illumination.
In this paper, the effects of cycle times, strain amplitude, loading rate, wire diameter, and temperature on the mechanical properties of SMA are studied. However, when describing the influence of each variable in Chapter 3, the values of several other parameters are not mentioned, so it is necessary to return to Table 1,2.
For example, the loading rate is not mentioned in Fig. 6 and Fig. 7, and a complete graphical representation is adopted in Fig.8. Although the loading rate of 1mm/min is mentioned in Section 3.2.4 of Fig. 9, this parameter is still not reflected in the figure and the figure caption. There are many similar problems in the subsequent figures.
(3) The discussion of coupling analysis using the Lorentz function in section 3.3.2 needs to be clarified.
Firstly, what is the reason for choosing the Lorentz function? Quotations are missing here. Secondly, Fig. 12(a) is difficult to read, and it is recommended to set the ordinate to 450-550 to enlarge the details of the curve.
Finally, Fig. 12(a) and Table 3 show that the maximum absolute error between the predictive model and the test data at 11 points in 0-10 cycles is only 1.005, and the error is stable between 0.995 and 1.005. The data is too perfect to be convincing. It is suggested to add detailed original data and the fitting process of parameters in the Lorentz function in the appendix to avoid the suspicion of data fraud.
(4) Fig. 13 is hard to read.
As described in section 3.4.1, when the number of SMA wires (5) was relatively small, the failure of the specimen was represented by the bursting failure of the middle part of the CFRP sheet. However, in Fig. 13(a), the specimen with 5 SMA also seems to suffer from bursting failure of the middle part. As Fig. 13 is not clear, the failure mode of the sample is difficult to determine. It is recommended to arrange the damaged samples with a certain gap and not put the sample together to form an undamaged appearance.
(5) Section 3.4.1 describe the reason for failure mode as ‘the bonding interface between SMA wires and CFRP increases, and an obvious weak layer appeared.’
However, it is well known that increasing the bonding interface will increase the strength of the composite. Does the sample preparation defect cause the bursting failure of the middle part? Was metallographic analysis performed on the control group? Does the resin applied between the CFRP layers completely cover the SMA? Or is the resin not filled between the CFRP layers, which contain many cavities? The metallographic analysis is recommended to eliminate the problem of sample preparation.
(6) In Section 3.4.2, how is the stress of the composite sample obtained? No metallographic analysis has been performed on the specimen, and the thickness of the specimen has not been measured. How was the cross-sectional area obtained? Is it directly considered that the thickness of the sample is 0.667*2+0.5 or 0.667*2+1?
(7) Based on the same reason described in (6), the average tensile strength of FRP/SMA-0.5-5/10/15 group are 2496, 2568, and 2989MPa, respectively, which is a large deviation from the ideal linear relationship. Is it due to a sample preparation error?
Does the increase in tensile strength caused by replacing the resin between the CFRPS with more SMA? Whether or not the conclusion that the increase of SMA wire diameter reduces the fracture strain and tensile strength caused by too much resin between CFRP? Since the steel wire volume fraction of the 1mm steel wire group and the 0.5mm steel wire group is inconsistent, how can the effect of diameter on the performance be compared?
The Quality of English Language can be improved.
Author Response
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Reviewer 4 Report (New Reviewer)
The manuscript deals with the Static Behavior and Recovery Properties of CFRP/SMA Composites. The research is simple but it is useful. The structure of the manuscript can be improved. The experimental program is limited. The results discussion is well explained. Some detailed issues:
1. I suggest the authors modify the manuscript’s topic.
2. The abstract should briefly state the research's purpose, principal results, and major conclusions. An abstract is often presented separately from the article, so it must be able to stand alone. The abstract structure should be as follows: (introduction, problem of statement, materials, methods, results, and recommendations). Please revise your abstract.
3. I suggest the authors to conduct a more in-depth review and summarize in section 1.
4. I suggest the authors to add a flowchart.
5. I suggest the authors to modify the name of section 2 to “Materials and test program”.
6. Figs 4 and 5 are not clear.
7. The points presented in the conclusion section are not up to the mark. The authors are advised to revise it completely and try to present information, which is a summary of the important aspects discussed in the preceding sections. It certainly lacks in its current form.
- Change the name of section 4 to “Conclusion and Recommendations”.
- Add Recommendations.
- Add more critical points.
Author Response
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Reviewer 5 Report (New Reviewer)
This paper investigated the mechanical properties and Recovery Properties of CFRP/SMA Composites. A new type of composite material has been designed and the related properties has been systematically evaluated. The research results are significant to advance the strengthening of engineering structures through prestressed CFRP. The authors are encouraged to consider the following comments and make further additions and improvements.
1. In the title, it is suggested to change the static behavior to mechanical properties.
2. This paper mainly uses CFRP as the prestressed reinforcement material. Therefore, the related summary on the performance and advantages are directly targeted at CFRP, such as its high tensile performance, excellent fatigue resistance, corrosion resistance, and creep resistance compared to other FRPs. The following research on the mechanics and long-term performance of CFRP can be reviewed to enrich and supplement the introduction, Polymers, 2023, 15: 2483. Composite Structures, 2021, 256: 113058. Composite Structures, 2022, 293, 115719.
3. For FRP/SMA composites in this paper, how to ensure the synergistic load bearing of the two materials mentioned above due to different thermal expansion coefficient and stiffness? Suggest adding relevant explanations.
4. For the prestressed FRP sheets, the anchorage system may play an important role in strengthening structures. Please add the research summary and analysis on the anchoring of CFRP sheets.
5. Please highlight some important research findings and innovative points in this article, which are different from existing research [15].
6. Please provide some basic mechanical and physical performance parameters related to raw materials in section 2.1.
7. In section 2.3, if the relevant descriptions and data in the table derived from previous research, it should be added with relevant literature sources and citations.
8. The uniaxial tensile stress-strain curve of CFRP has been shown in the figure 4, please explain why the curves exhibit some fluctuations. In addition, it is recommended that the authors check the images in the paper and replace them with high-definition images.
9. It is recommended to mark the different stages of destruction in figure 5.
10. Why does the effects of loading rate on the stress-strain of SMA studied in this article? Does the loading rate have relevant application backgrounds or operating conditions?
11. The Figure 13 shows the typical tensile failure mode of CFRP/SMA composites. It can be observed that CFRP did not present the typical bursting failure. Is this related to the inconsistent stress state of the two materials? It is recommended to add relevant explanations.
Author Response
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Reviewer 6 Report (New Reviewer)
Dear Authors,
Thank you for the manuscript. this is a good study; not entirely novel but good to understand the CFRP and SMA behavior. The quality of almost all figures is poor and needs to be revised. There are some equations and expressions that need to be explained better. Please find my review to improve the manuscript.
Thanks!
Comments for author File: Comments.docx
moderate English editing is required.
Author Response
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Author Response File: Author Response.docx
Round 2
Reviewer 2 Report (Previous Reviewer 1)
The authors have addressed all the queries. The article may be accepted in its present form.
Reviewer 3 Report (New Reviewer)
In this paper, the properties of shape memory alloys (SMA) were studied in detail, considering the effects of cycle times, strain amplitude, loading rate, wire diameter, and temperature on the uniaxial tensile properties of SMA. Results show that when the loading rate is 1mm/min, the stress cycle within ten times of SMA is relatively stable, the strain amplitude within 1.5% is the linear elasticity, within 1.5%-6% is the yield stage, and above 6% is the strengthening stage. Increasing the loading rate will advance the SMA into the yield and strengthening stage. This article has been suitably revised for publication.
Reviewer 5 Report (New Reviewer)
The revised manuscript can be accepted in its current form.
Reviewer 6 Report (New Reviewer)
Dear Authors,
Thank you for revising the manuscript. I would recommend this manuscript for publication.
Moderate editing of English language required.
This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.
Round 1
Reviewer 1 Report
The authors need to address the following queries.
· The abstract is a summary of the introduction, materials and method, results, and conclusion. This order needs to be followed. The methodology, results (quantifying data), and conclusion component of the abstract should be properly captured.
· Introduction doesn’t give the background of the study. It is advised to improve the introduction significantly. The literature review looks shallow.
· Highlight the contribution of the study to the knowledge gap/specific problem.
· What is the curing agent used along epoxy resin?
· How many specimens are tested for each condition?
· The quality of the graphs is very poor. It is advised to improve the same.
· “The tensile strength was about 3000 MPa,” is it the maximum tensile strength? From figure 3, it can be observed that some specimens failed below 3000 MPa stress. What is average tensile strength?
· Why did the loading rate of 1mm/min for SMA wire and 2mm/min for CFRP?
· Failure mode is not explained in detail.
· “Figure 12. Failure mode of FRP/SMA composite specimens” Mark the point of observation.
· “Figure 19. Effect of reciprocating temperature cycles on maximum resilience.” It is figure 10.
· For figures 9 and 10. Write the SI unit of x – axis in brackets to maintain uniformity.
· In table 4 - Add the error value. Have authors used mean value or maximum value?
· Results and discussion part look shallow. Add more reasoning and explanations
· Kindly reconcile the conclusion with the study objectives.
· What are the practical implications of this study and the future directions? kindly state
Reviewer 2 Report
In this paper, the authors investigate the mechanical properties of Fiber Reinforced Polymer and Shape Memory Alloy composites. The problem that solves the proposed composite material for a prestressed material is not described and presents a lack of rigorous study. Therefore, the experiment results presented in the paper show a lack of scientific relevance. Also, their presentation effectively disrupts their reception.
In the introduction section, the authors poorly review the state of knowledge, the selection of references is appropriate, but the review of FRF materials and its application need to be completed. It is not clear to the reviewer what research gap did you find from other researchers. Also, since this journal's scope is about sustainability, a deeper discussion is necessary regarding how the results of this work impact global change and development related to sustainability. This is the key part of the article.
Major comments
1. Consider changing the title of the papers taking into consideration the application of the presented experimental study.
2. The authors are required to explain in detail the manufacturing process used to fabricate the CFRP/SMA composite and what process parameters were used. How were the SMA wires positioned and aligned repetitively?
3. How was Equation 1 established? If a mathematical was used according to other studies, should be cited. Otherwise, the authors should explain how this equation was validated.
4. There is plenty of stress vs strain plots, that show the experimental data and help to understand the mechanical properties of the CFRP Sheet and SMA wires. However, the authors should study and process all this information to be present from the point of view of mechanical properties. The reader needs to understand what insightful information was obtained regarding the development of new material.
5. Then, using the experimental data a mathematical model must be proposed to predict the mechanical properties of the proposed composite material, understanding the influence of the diameter, pre-strain of the SMA as well the number of wires in the CFRP/SMA material.
6. Describe the concept of reciprocation on resilience for the SMA wire. Again, it seems that Equation 2 was proposed by the authors. Please explain in detail how this mathematical model was formulated.
7. The authors are required to compare the mechanical properties of the CFRP and the CFRP/SMA composites since the main contribution of this study is the new composite material. Additional data should be included to provide how fracture strain and ultima tensile strength are improved.
Minor comments
8. The optical photograph provided in Figure 1 doesn’t provide precise information on the experimental setup. It can be improved if replaced with a scheme.
9. Include a scheme for the steps followed in the process to manufacture composite materials.
10. Figure 9a and figure 9b are very similar that should be merged. 9
11. Include optical photographs with higher quality and with a zoom detail view so the failure can be observed.
The idea presented about the use of CFRP/SMA composite seems to be promising and interesting, but due to the above concerns, at this moment I do not recommend the paper for publication. There are several points in the article that require further explanation and experimental data. In particular, a mathematical model to predict the mechanical properties of the materials is required.
