Review Reports - Study on the Dynamic Mechanical Behavior of 2D C/SiC Composites at Medium Strain Rates

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript refers to the material as “2D C/SiC composites.” However, the definition of “2D” is not explicitly provided. Please clarify what is meant by “2D” in this context and why this terminology is appropriate. In addition, the thickness of the tensile, compressive, and shear specimens are not reported.

In the present work, the authors report an approximately linear compressive stress–strain response up to failure (Figure 3c), whereas Liu et al. [12] reported a pronounced nonlinear compressive behavior for similar 2D C/SiC composites. Please clarify or discuss the possible reasons for this discrepancy.

Equations (2) and (3) are introduced with limited explanation. Please clarify whether these equations are simplified forms of Liu et al. [12]’s constitutive model. In addition, the physical meaning and significance of each parameter, including B, A, a1, a2, a3, etc. should be explained.

The introduction states that the main contribution of this work is the investigation of mechanical properties and failure mechanisms at medium strain rates. Please clarify the unique findings and contributions of the present work compared with prior studies including both low strain rate and high strain rate.

Author Response

Comment (1): The manuscript refers to the material as “2D C/SiC composites.” However, the definition of “2D” is not explicitly provided. Please clarify what is meant by “2D” in this context and why this terminology is appropriate. In addition, the thickness of the tensile, compressive, and shear specimens are not reported.

Response: Thank you for pointing this out. The material used in this investigation was a cross-woven C/SiC composite fabricated by isothermal CVI technique. As seen in Figure 1, plain weave carbon fiber cloths were laminated. This laminated structure of C/SiC is usually referred to as 2D C/SiC in reported the literatures. In the revised paper, a schematic diagram of 2D C/SiC was added.

The thickness of the specimens for the tensile, compressive and shear tests was all 3mm. This thickness is indicated in Figure 2 and has been supplemented in the revised text.

Comment (2): In the present work, the authors report an approximately linear compressive stress–strain response up to failure (Figure 3c), whereas Liu et al. [12] reported a pronounced nonlinear compressive behavior for similar 2D C/SiC composites. Please clarify or discuss the possible reasons for this discrepancy.

Response: Thank you for pointing this out. Liu et al. examined the layer-directional compression of 2D C/SiC composites, whereas in-plane compression tests were performed in this work. The differing loading conditions result in separate damage modes, which leads to different stress–strain behaviors.

Comment (3): Equations (2) and (3) are introduced with limited explanation. Please clarify whether these equations are simplified forms of Liu et al. [12]’s constitutive model. In addition, the physical meaning and significance of each parameter, including B, A, a1, a2, a3, etc. should be explained.

Response: Thank you for pointing this out. This paper applies the constitutive model proposed by Liu et al. to describe the stress-strain curves for in-plane tensile and shear of 2D C/SiC. The constitutive model describing nonlinearity and strain rate correlation behavior of the material. The introduced equations are the complete form presented in the paper by Liu. In this study, since the stress-strain curve of in-plane compression is in a linear form, the nonlinear term in the equation was not included. But, the effect of strain rate was still taken into account. In the revised text, additional explanation for the constitutive model was provided. m is a rate-dependent parameter. D is the damage parameter, which is assumed to follow a Weibull distribution. The parameter n defines the shape of the damage growth curve. a1, a2 and a3 are parameters to be determined from test data. A represents the trend of the elastic modulus changing with the strain rate.

Comment (4): The introduction states that the main contribution of this work is the investigation of mechanical properties and failure mechanisms at medium strain rates. Please clarify the unique findings and contributions of the present work compared with prior studies including both low strain rate and high strain rate.

In this paper, the strain rate sensitivity of the in-plane tensile, compressive and shear strengths of the material was discussed within the medium strain rate range. The strain rate strengthening effect is most pronounced under compression, while the effect under tensile loading is less significant within the strain rate range from quasi-static to 10s-1. In the prior studies including both low strain rate and high strain rate, the trend of material strength changing with strain rate is unknown within the range of medium strain rates. The strain rate sensitivity of the tensile strength within the intermediate strain rate range is different from the conclusions obtained from the studies including both low strain rate and high strain rate.

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript presents an experimental and modeling study on the in plane tensile, compressive and shear behavior of 2D C/SiC composites over quasistatic to medium strain rate regimes.However, major revisions are required.

The novelty of the study should be emphasized.
The manuscript does not report the number of specimens.
The discussion of energy consumption for multiple crack initiation remains qualitative.
The model is not validated for compression beyond linear elastic.

Author Response

Comment (1): The manuscript presents an experimental and modeling study on the in plane tensile, compressive and shear behavior of 2D C/SiC composites over quasistatic to medium strain rate regimes. However, major revisions are required.

The novelty of the study should be emphasized.

Response: Thanks for your carefulness and suggestion. For most materials, the rate sensitivity varies across different strain rate ranges. If only the rules obtained under high strain rates are used to analyze the structure, there will be significant deviations in the strength analysis. Therefore, the work in this paper can provide data support for the analysis and design of the mechanical behavior of C/SiC structures within the medium strain rate range. Besides, this paper compares the strain rate sensitivity of the in-plane tensile, compressive and shear strengths of the material within the medium strain rate range. The research finds that the strain rate sensitivity of the tensile strength within the intermediate strain rate range is different from the conclusions obtained from the studies including both low strain rate and high strain rate. Furthermore, this work proved that this constitutive model proposed by Liu was also applicable to the in-plane tensile and shear loading mechanical behaviors of C/SiC materials within the medium strain rate range.

Comment (2): The manuscript does not report the number of specimens.

Response: Thanks for your carefulness and suggestion. For each loading condition, three to five specimens were tested. This has been added in the revised text.

Comment (3): The discussion of energy consumption for multiple crack initiation remains qualitative.

Response: Thank you for pointing this out. Energy absorption can generally be quantitatively measured by acoustic emission in quasi-static and fatigue tests. But, in dynamic test, the response time is too short to accurately obtain the number of acoustic emission response events, making it difficult to quantitatively compare the damage energy. Moreover, since cracks can only be observed on the fracture surfaces and the surface of the test piece, and cracks generated within the material cannot be observed, it is impossible to quantitatively compare the number of cracks.

Comment (4): The model is not validated for compression beyond linear elastic.

Response: Thank you for pointing this out. The comparison between the constitutive model and the in-plane compressive experimental data at different strain rates has been added in Figure 16 in the revised text. The constitutive model agrees well with the experimental data under in compression loading conditions.


(a)	(b)

(c)	(d)

Figure 16. The comparison between the constitutive model and the in-plane compressive experimental data at strain rates of 0.00003s^-1(a) 0.0003s^-1(b) 0.2s^-1(c) and 2s^-1(d)

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript is clearly written and addresses a timely topic. However, the purpose, motivation, and practical relevance of the study are not sufficiently clarified. Several conceptual and methodological issues must be addressed.

The manuscript emphasizes the suitability of 2D C/SiC composites for high-temperature applications, yet all experiments are conducted at room temperature. The authors should justify the relevance of room-temperature testing or clarify that the results serve only as baseline data.
The practical relevance of impact loading for high-temperature C/SiC components is not clearly discussed. The authors should identify realistic service scenarios where such materials experience impact loading and explain why impact resistance is a critical design concern. The absence of temperature effects further limits applicability.
The objectives and research gap are not explicitly stated. Studying medium strain rates requires clear justification beyond the existence of prior high strain-rate studies.
The rationale for selecting 2D C/SiC architecture is unclear, particularly since 3D C/SiC is more commonly used for high-temperature structural applications due to improved delamination resistance.
The manuscript lacks analysis of damage mechanisms. Microstructural or fractographic evidence is needed to correlate mechanical response with failure modes.
Comparison with existing literature is limited, making it difficult to assess the novelty of the work.
Experimental scatter and statistical reliability are not adequately reported. The number of specimens tested and data variability should be clearly stated.
The conclusions overgeneralize the applicability of the results. Limitations related to room-temperature testing and absence of fatigue considerations should be clearly acknowledged.

Author Response

Comment (1): The manuscript emphasizes the suitability of 2D C/SiC composites for high-temperature applications, yet all experiments are conducted at room temperature. The authors should justify the relevance of room-temperature testing or clarify that the results serve only as baseline data.

Response: Thank you for pointing this out. Temperature, strain rate and loading conditions are all important factors influencing the mechanical properties of this material, and these factors interact with each other. This paper mainly studies the mechanical properties of the material under different loading conditions and strain rates during its service to support the simulation of the C/SiC structure at room temperature. This research work also provides a fundamental support for the subsequent studies on the high-temperature mechanical properties and coupling effects of the C/SiC within medium strain rate range. In the revised version, the research purpose was further elaborated.

Comment (2): The practical relevance of impact loading for high-temperature C/SiC components is not clearly discussed. The authors should identify realistic service scenarios where such materials experience impact loading and explain why impact resistance is a critical design concern. The absence of temperature effects further limits applicability.

Response: Thank you for pointing this out. In general, engineering applications will be subjected to loads in various directions during service. In addition to static loads, these aeroengines and thermal protection systems are sometimes exposed to the threat of impact loads. High-speed destructive impacts such as those caused by foreign objects usually fall within the high strain rate range. However, scenarios involving high pulse pressure, high overload, or sudden pressure changes, such as nozzle ignition or rocket separation, generally exhibit strain rates not exceeding 100 s-1, falling within the range of medium strain rate. Existing research efforts mainly focus on quasi-static and high strain rate intervals, lacking results from medium strain rate experiments. Besides, temperature, strain rate and loading conditions are all important factors influencing the mechanical properties of this material, and these factors interact with each other. Therefore, the purpose of this paper is to study the mechanical properties of the material under different loading conditions and strain rates during its service to support the simulation of the C/SiC structure at room temperature. The work can provide a fundamental support for the subsequent studies on the high-temperature mechanical properties and coupling effects of the C/SiC in the medium strain rate range.

Comment (3): The objectives and research gap are not explicitly stated. Studying medium strain rates requires clear justification beyond the existence of prior high strain-rate studies.

Response: Thank you for pointing this out. For most materials, the rate sensitivity varies across different strain rate ranges. However, for ceramic matrix composites, if a structure is designed based on the high strain rate rule within the medium strain rate range, it will affect the analysis of structural strength. In addition to static loads, the aeroengines and thermal protection systems are sometimes exposed to the threat of impact loads. High-speed destructive impacts such as those caused by foreign objects usually fall within the high strain rate range. However, scenarios like nozzle ignition and rocket separation, which involve high pulse pressure, high overload, and sudden pressure changes, typically have strain rates of no more than 100s-1, falling within the range of medium strain rate studies. Existing research efforts mainly focus on quasi-static and high strain rate intervals, lacking results from medium strain rate experiments. Therefore, further research is needed on the mechanical properties and failure mechanisms of the material in the range of medium strain rates. These are of great significance for a comprehensive understanding of the mechanical behavior of the material. The above content has been supplemented in the revised article.

Comment (4): The rationale for selecting 2D C/SiC architecture is unclear, particularly since 3D C/SiC is more commonly used for high-temperature structural applications due to improved delamination resistance.

Response: Thank you for pointing this out. 2D C/SiC is the representatives amongst C/SiC. In large thin-walled structures, the 2D woven structure is widely used to meet the design requirements of different configurations. Due to its weaving method, the 2D structure offers excellent in-plane mechanical properties in all directions. Additionally, its preform fabrication process is relatively mature, enabling the controlled manufacturing of complex components. Therefore, it has become the most representative structural form in the application of high-temperature structures in aeroengines and thermal protection systems.

Comment (5): The manuscript lacks analysis of damage mechanisms. Microstructural or fractographic evidence is needed to correlate mechanical response with failure modes.

Response: Thank you for pointing this out. In Section 3.3 of this paper, the fracture surfaces of the specimens after the tests were analyzed, and the differences in failure patterns under quasi-static and dynamic loading conditions were compared. Further analysis may require the use of in-situ CT, but currently this method is mainly applicable to quasi-static loading. For dynamic loading, as the measurement response time is insufficient, it is difficult to conduct further analysis.

Comment (6): Comparison with existing literature is limited, making it difficult to assess the novelty of the work.

Response: Thank you for pointing this out. In this paper, the strain rate sensitivity of the in-plane tensile, compressive and shear strengths of the material within the medium strain rate range was compared. The research finds that the strain rate sensitivity of the tensile strength within the intermediate strain rate range is different from the conclusions obtained from the studies including both low strain rate and high strain rate[1][2]. It demonstrates the differences in the mechanical properties of this material within the medium strain rate range compared to those within the quasi-static and high strain rate ranges. Besides, the stress-strain curve characteristics and strain rate sensitivity laws of the material under in-plane compression are the same as those obtained in [3]. However, as limited research has been conducted on the dynamic in-plane shear mechanical behavior of the C/SiC, it is difficult to compare the differences in the strain rate sensitivity of this material in this loading condition. Furthermore, this work proves that this constitutive model proposed by Liu was also applicable to the in-plane tensile and shear loading mechanical behaviors of C/SiC materials within the medium strain rate range, which will support the simulation of the C/SiC structure under wide strain rate range and different loading directions.

Chen X, Li Y. Dynamic tensile behavior of two-dimensional carbon fiber reinforced silicon carbide matrix composites. Materials Science Engineering Analysis with Boundary Elements 2011, 528, 6998-7004.

Zhang C , Guan T , Zhang X ,et al.Tensile properties of 2D-C/SiC composites at temperatures up to 1873 K at wide-ranging strain rates. Composite Structures 2023.

Guan T , Li Y , Zhang C ,et al.Transition of in-plane compressive strength and failure mechanism of 2D-C/SiC: Influence of off-axis loading angle and loading rate[J].Composite Structures, 2023, 324(000):15.

Comment (7): Experimental scatter and statistical reliability are not adequately reported. The number of specimens tested and data variability should be clearly stated.

Response: Thank you for pointing this out. For each loading condition, three to five specimens were tested. This has been added in the revised text. In Figure 5 of the text, error bars are marked to illustrate the dispersion of the data.

Comment (8): The conclusions overgeneralize the applicability of the results. Limitations related to room-temperature testing and absence of fatigue considerations should be clearly acknowledged.

Response: Thank you for pointing this out. The limitation and subsequent work the has been added in the revised text after the conclusion.

The results obtained in this study suggest further investigations. Further research on the mechanical properties under the coupling of multiple factors such as temperature and strain rate should be conducted in medium strain rate. And the constitutive model considering the temperature influence factor need to be established to support the impact design of C/SiC structure under high temperatures.