Temperature-Dependent Elastic and Damping Properties of Basalt- and Glass-Fabric-Reinforced Composites: A Comparative Study

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

• Which is the melting temperature of rocks used to produce basalt fibers and how do you explain the fact that environmental impact of them is lower than that of synthetic fibers? Can you give a comparative quantitative value to support this statement (section 1.2, lines 42-44)?
• It is needed to insert the number for all equations presented in sections 1.3 and 6.
• Please insert labels (a) and (b) on figure 3 instead of (left) and (right).
• Please specify how the dimensions of beams and plates from Table 1 were determined.
• Some figures with the experimental setup, beams and plates of GFRP and BFRP are needed in section 4. It is not clear how the sample was measured.
• In figs. 9-13 please keep the same notation on figures title (GFRP/BFRP) and labels (basalt and glass composite).
• In discussion, please provide more comparative data about the results obtained for both composites. Also, results obtained in this experimental study are recommended to be compared with results obtained by other researchers on similar materials proposed for the same applications. This analysis will be useful to highlight better the novelty of this article.
• The number of self-citations is high (8/45). If it is possible please try to reduce them.

Author Response

Answers to questions and remarks of reviewer 1

Which is the melting temperature of rocks used to produce basalt fibers and how do you explain the fact that environmental impact of them is lower than that of synthetic fibers? Can you give a comparative quantitative value to support this statement (section 1.2, lines 42-44)?

Indeed, the indicated sentence is not clear and even not correct. We will replace it in the revised document with the following sentences:

Basalt fibers are produced by melting crushed basalt rock at temperatures around 1200–1600°C. This process does not require the addition of other materials and produces no toxic emissions. The melting temperature of silica sand for the production of synthetic fibers like glass fibers is higher than 1700°C. Individual studies of basalt producers claim 20% lower energy consumption as compared to glass fiber production.

It is needed to insert the number for all equations presented in sections 1.3 and 6.

In the revised document, we inserted a number for each equation through the whole document

Please insert labels (a) and (b) on figure 3 instead of (left) and (right).

We added labels (a) and (b) in figure 3

Please specify how the dimensions of beams and plates from Table 1 were determined.

The widths and lengths of beams and plates are now explicitly marked in figure 4

Some figures with the experimental setup, beams and plates of GFRP and BFRP are needed in section 4. It is not clear how the sample was measured.

An additional figure 8 (a) and (b) is added in section 4 in the revised document to supply more details about the setup and the measured samples.

In figs. 9-13 please keep the same notation on figures title (GFRP/BFRP) and labels (basalt and glass composite).

We made the notations more uniform in the revised document

In discussion, please provide more comparative data about the results obtained for both composites. Also, results obtained in this experimental study are recommended to be compared with results obtained by other researchers on similar materials proposed for the same applications. This analysis will be useful to highlight better the novelty of this article.

The discussion has been extended with more comparative data about the results. The authors will add results of some tests on the same material by the SHD laboratory (Sleaford, U.K.) in section 5.

 

 

The number of self-citations is high (8/45). If it is possible please try to reduce them.

Only the self-citations with more details about the Resonalyser method, damping measurements, temperature control and automated excitations are kept because this information is dedicated to the new method and can be useful for interested readers. We will replace the self-citation reference [37] (proceedings of Euromech  357 in Kerkrade Holland) by an interesting review paper about material identification using parameter estimations methods ( A. Aguilo et al. “An overview of material identification within the frameworks of deterministic and stochastic parameter estimation methods”)

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

General comments:

The article investigates the behaviour of glass and basalt reinforced composites. A few considerations shall be made.

References and citations should be checked for consistency. The bibliography adopts several different styles, some information is missing, and several typos are present. Moreover, when citing a work using the names of the authors “et al.” is sometimes missing (see for example citations 20 and 21 where only the names of Lauwagie and Pierron are reported, but there are more). Also, the name or names of the authors shoudn’t be simply placed after a comma but properly introduced in a way such as “as proposed by…”, “see the work of…”.

Although the work where Resonalyser method can be found in reference 27, a brief summary shall be proposed before showing the results in section 5. The authors have the tendency to suddenly show results without proper introduction to them.

The discussion and conclusions sections are very short and perhaps a more detailed discussion of the results obtained is desirable and could help readers. Comment on the fact that basalt and glass give very similar properties.

 

Specific Remarks:

Row 185 / Figure 5: Please further comment on how the modal shapes are obtained. Add some references as well

Row 236: chapter instead of paragraph.

Table 1: use mm and grams as measurement units to reduce decimal places

Row 264: “free-free”?

Row 271: 80 mm instead of 8 cm

Row 284: Equation (5) instead of 5. Moreover, the slope of the fitted curve is the stiffness value (F/u). Is that the value used in equation (5) in combination with geometric parameters? The text is not very clear on the procedure

Row 329: is a polynomial the best solution? Raw data appear to have a certain trend overlapped with a periodic signal. Perhaps a frequency-based filter method would be a better solution.

Rows 374-377: use “larger” instead of “bigger”.

Author Response

Answers to questions and remarks of reviewer 2

General comments:

The article investigates the behaviour of glass and basalt reinforced composites. A few considerations shall be made.

References and citations should be checked for consistency. The bibliography adopts several different styles, some information is missing, and several typos are present. Moreover, when citing a work using the names of the authors “et al.” is sometimes missing (see for example citations 20 and 21 where only the names of Lauwagie and Pierron are reported, but there are more). Also, the name or names of the authors shoudn’t be simply placed after a comma but properly introduced in a way such as “as proposed by…”, “see the work of…”.

Thank you for this remark. We will eliminate the inconsistencies and introduce the reference to authors more in the suggested way.

Although the work where Resonalyser method can be found in reference 27, a brief summary shall be proposed before showing the results in section 5. The authors have the tendency to suddenly show results without proper introduction to them.

We agree and we added a brief introduction of the Resonalyser method in section 5 of the new document before showing the results. The added text at the beginning of 5.1 is the following:

The Resonalyser is a multi sample mixed numerical experimental technique based on the measurement of the first resonance frequencies and damping ratios associated with the fundamental flexural modal shape of two beams and two resonance frequencies and damping ratios of the test plate associated with the torsion and breathing modal shapes.

The added text at the beginning of 5.2 is the following:

In the Resonalyser procedure, the complex engineering constants in the numerical models of the two test beams and the test plate are iteratively updated till the computed resonance frequencies and damping ratios match the measured values.

The discussion and conclusions sections are very short and perhaps a more detailed discussion of the results obtained is desirable and could help readers. Comment on the fact that basalt and glass give very similar properties.

The discussion part in the updated new document is extended with a more detailed discussion about similarities and deviations of the properties of glass and basalt. Also comparative data from another test laboratory is added as validation

 

 

Specific Remarks:

Row 185 / Figure 5: Please further comment on how the modal shapes are obtained. Add some references as well

OK done

Row 236: chapter instead of paragraph.

OK done

Table 1: use mm and grams as measurement units to reduce decimal places

OK done

Row 264: “free-free”?

We added an explanation for “free-free”. It was replaced by “freely suspended” with an additional figure and some additional comments

Row 271: 80 mm instead of 8 cm

OK done

Row 284: Equation (5) instead of 5. Moreover, the slope of the fitted curve is the stiffness value (F/u). Is that the value used in equation (5) in combination with geometric parameters? The text is not very clear on the procedure

An extra figure 8 is added together with some more detailed explanation on the setup for 3 point bending and formula (5).

Row 329: is a polynomial the best solution? Raw data appear to have a certain trend overlapped with a periodic signal. Perhaps a frequency-based filter method would be a better solution.

The authors themselves are not completely satisfied with the current curve fitting method. But it remains a difficult problem (too fine or too rough and everything between). We will study new methods for our future publications.

Rows 374-377: use “larger” instead of “bigger”.

OK done.

Author Response File: Author Response.docx

Reviewer 3 Report

Comments and Suggestions for Authors

1. Material Preparation and Characterization

1. Omission of Fiber-Matrix Interface Properties

The paper does not specify fiber surface treatments (e.g., silane coupling agents) or interface morphology characterization (SEM). Does the interfacial compatibility between basalt fibers and epoxy resin significantly differ from that of glass fibers? Interfacial property variations may affect damping behavior (Fig. 13). Interfacial shear strength (IFSS) test data should be supplemented.

1. Quantification of Fabric Structure Influence

GFRP uses 8HS weave while BFRP uses 7HS weave (p.7), leading to differing warp/weft stiffness ratios. Was Classical Lamination Theory (CLT) applied to decouple weaving structure effects on engineering constants? Direct comparison of fiber-type effects remains questionable without this clarification.

 

1. Methodological Rigor

1. Lack of Empirical Validation for Temperature Uniformity

Only theoretical heat transfer parameters are mentioned (p.7). Were internal temperature gradients experimentally measured (e.g., embedded thermocouples)? Non-uniform thermal fields may cause damping ratio noise (Fig. 11). Compliance with ASTM E289 (<1°C variation) must be verified.

1. Unaddressed Frequency Dependence in Dynamic Testing

Complex modulus theory emphasizes frequency dependence (p.3, Eq.(2)), yet the IET excitation frequency range is unspecified. Was frequency insensitivity validated across the test band (e.g., 1-10 kHz)? Dispersion effects could limit conclusion generalizability.

1. Theoretical Basis for Poisson Plate Aspect Ratio

Eq.(3) defines L/W=f1L2/f2L12L/W=2f1​L2​/f2​L1​​ without citing derivation sources. Is this formula applicable to damped materials? FE modal analysis comparisons should validate this assumption.

 

III. Data Interpretation and Statistics

1. Inadequate Mechanistic Explanation for Static/Dynamic Modulus Discrepancy

Fig.9 shows lower static moduli (especially for BFRP), attributed vaguely to "viscoelasticity." Was strain rate disparity quantified (static: 1 mm/min vs. dynamic: impact)? Time-temperature superposition (WLF equation) analysis is recommended.

1. Scientific Justification for Damping Data Smoothing

Damping curves were polynomial-smoothed (p.11), but selection criteria and residual analysis are absent. Could smoothing obscure glass transition onset (e.g., tanδ(G12)tanδ(G12​) rise post-40°C)? Confidence intervals for raw data are needed.

 

1. Engineering Applicability

1. Limitations in Simulating Real-World Conditions

Tests used free vibration (unconstrained), whereas automotive components experience preload. Do boundary conditions significantly alter engineering constants? Clamping effects should be discussed (e.g., using Reference 41 methodology).

1. Neglect of Hygrothermal Coupling Effects

Epoxy resins are hygroscopic (e.g., MTB350 moisture absorption ≈1.5%). Was humidity controlled or its impact assessed within -20°C–60°C? Automotive environments require humidity cycling validation (SAE J2522).

 

1. Conclusion Extrapolation Risks

1. Unsubstantiated High-Temperature Performance Claims

The assertion "60°C is far below TgTg​" (p.14) lacks DMA-derived TgTg​ data. Does basalt fiber’s thermal resistance advantage (Ref.6) only manifest >100°C? High-temperature pilot data must support conclusion boundaries.

 

Recommended Supplementary Analyses

• Interface characterization: Fiber pull-out tests (ISO 13480) or nanoindentation for interfacial modulus.
• Frequency-sweep DMA: Verify complex modulus dispersion (1–100 Hz).
• Hygrothermal aging: Post-48h water immersion testing to assess real-world applicability.

These questions address critical reliability boundaries of the conclusions. Authors should either supplement data or explicitly limit claims (e.g., "Conclusions valid only for dry, low-frequency, unconstrained conditions").

 

Author Response

Answers to questions and remarks of reviewer 3

General

Omission of Fiber-Matrix Interface Properties

The paper does not specify fiber surface treatments (e.g., silane coupling agents) or interface morphology characterization (SEM). Does the interfacial compatibility between basalt fibers and epoxy resin significantly differ from that of glass fibers? Interfacial property variations may affect damping behavior (Fig. 13). Interfacial shear strength (IFSS) test data should be supplemented.

According to our material supplier, both the basalt and glass fiber were treated with the same silane coupling agent. The interfacial shear strength of the BFRC and GFRC samples was measured by the SHD composites laboratory (Sleaford, U.K):

0° direction glass:  63.0 MPa, basalt 69.8 MPa

90° direction glass: 58.7 MPa, basalt 58.4 MPa

We added this information in the revised document in chapter 3.

Quantification of Fabric Structure Influence

GFRP uses 8HS weave while BFRP uses 7HS weave (p.7), leading to differing warp/weft stiffness ratios. Was Classical Lamination Theory (CLT) applied to decouple weaving structure effects on engineering constants? Direct comparison of fiber-type effects remains questionable without this clarification.

The engineering constants in the samples according to the resonalyser procedure are assumed to be uniform.  So the values of the GFRC and BFRC samples in this study were globally identified based on the measured vibration data. The specific weaving structure is not modeled in this study.

Methodological Rigor

Lack of Empirical Validation for Temperature Uniformity

Only theoretical heat transfer parameters are mentioned (p.7). Were internal temperature gradients experimentally measured (e.g., embedded thermocouples)? Non-uniform thermal fields may cause damping ratio noise (Fig. 11). Compliance with ASTM E289 (<1°C variation) must be verified.

The delay time between subsequent temperature steps was tested previously in the laboratories for different materials using embedded thermocouples. For thin composite material plates (thickness smaller than 10mm) and good homogeneous quality materials, the measured temperature evolved according to the theory. The modified epoxy matrix of the GFRC and BFRC has relatively good conductivity properties and the samples are relatively thin (2-3mm). The delay time for the measurements in this study was taken as 5 minutes for each step of 1°C. This yields a variation of less than 0.1°C in the middle of the samples as compared to the surface temperature. However, due to the weaving and laminated structure, 100% homogeneity of temperature in every point is not possible and is probable the origin of the damping ratio noise. The authors added an additional text on this subject in the improved document.

Unaddressed Frequency Dependence in Dynamic Testing

Complex modulus theory emphasizes frequency dependence (p.3, Eq.(2)), yet the IET excitation frequency range is unspecified. Was frequency insensitivity validated across the test band (e.g., 1-10 kHz)? Dispersion effects could limit conclusion generalizability.

The complex modulus of visco-elastic material (like the tested BFRC and GFRC) is frequency dependent. During testing the resonance frequency varied between 70 Hz and 160Hz. We noticed that modulus values obtained by static testing at 1mm/minute are typically 5% lower. We are planning for a subsequent paper to do DMA tests on the test material and applying Time-Temperature superposition (TTS) in order to create master curves extended to 5 decades. These tests will hopefully allow us formulating scientifically based answers on the frequency dependence. The study any dynamically loaded composite parts in a frequency range will require modulus values in the same range. We will add comments on this in the discussion of the revised document.

Theoretical Basis for Poisson Plate Aspect Ratio

Eq.(3) defines L/W=f1L2/f2L12L/W=2f1​L2​/f2​L1​​ without citing derivation sources. Is this formula applicable to damped materials? FE modal analysis comparisons should validate this assumption.

 The formula (3) is valid for any orthotropic material and is derived in ref. [19]. The physical background of this formula is an imaginary plate with zero Poisson’s ratio. The plate hence acts as a beam in both 1- and 2-direction. The aspect ratio L/W makes the resonance frequencies of both beams equal. The authors added this information in the revised document.

Data Interpretation and Statistics

Inadequate Mechanistic Explanation for Static/Dynamic Modulus Discrepancy

Fig.9 shows lower static moduli (especially for BFRP), attributed vaguely to "viscoelasticity." Was strain rate disparity quantified (static: 1 mm/min vs. dynamic: impact)? Time-temperature superposition (WLF equation) analysis is recommended.

A correct answer on this question requires a DMA analysis with TTS. As previously mentioned, the authors like to do this specialized analysis in the nearby future.

Scientific Justification for Damping Data Smoothing

Damping curves were polynomial-smoothed (p.11), but selection criteria and residual analysis are absent. Could smoothing obscure glass transition onset (e.g., tanδ(G12)tanδ(G12​) rise post-40°C)? Confidence intervals for raw data are needed.

 The glass transition onset temperature for the used MTB350 modified epoxy resin after 1 hour curing cycle was measured by SDH composite laboratory (Sleaford, U.K.) and was equal to 144°C. The maximum temperature in the current study was 60°C. The authors added this information in the revised document.

Engineering Applicability

Limitations in Simulating Real-World Conditions

Tests used free vibration (unconstrained), whereas automotive components experience preload. Do boundary conditions significantly alter engineering constants? Clamping effects should be discussed (e.g., using Reference 41 methodology).

We fully agree with this statement. Preload can change the value of the engineering constants (especially the damping behavior will have considerable influence from the boundary conditions). Material tests should always critically access with the application conditions in mind. The authors added this information in the discussion of revised document and refer to [41].

Neglect of Hygrothermal Coupling Effects

Epoxy resins are hygroscopic (e.g., MTB350 moisture absorption ≈1.5%). Was humidity controlled or its impact assessed within -20°C–60°C? Automotive environments require humidity cycling validation (SAE J2522).

The test materials BFRC and GFRC were conditioned in the climate chamber during 24 hours at 50% humidity. We agree that material test should always critically access with the application conditions in mind. The authors added this information in the discussion of revised document.

Conclusion Extrapolation Risks

Unsubstantiated High-Temperature Performance Claims

The assertion "60°C is far below TgTg​" (p.14) lacks DMA-derived TgTg​ data. Does basalt fiber’s thermal resistance advantage (Ref.6) only manifest >100°C? High-temperature pilot data must support conclusion boundaries.

The tests in this current study were limited to temperatures till 60°C. The behavior of basalt versus glass for higher temperatures will require further investigations. The glass transition temperatures of the glass and basalt fibers are far above the use temperature of the matrix, namely about 400-500 °C. The differences can thus only be measured on the pure fibers or with an inorganic matrix that can withstand such high temperatures.

Recommended Supplementary Analyses

• Interface characterization: Fiber pull-out tests (ISO 13480) or nanoindentation for interfacial modulus.
• Frequency-sweep DMA: Verify complex modulus dispersion (1–100 Hz).
• Hygrothermal aging: Post-48h water immersion testing to assess real-world applicability.

These questions address critical reliability boundaries of the conclusions. Authors should either supplement data or explicitly limit claims (e.g., "Conclusions valid only for dry, low-frequency, unconstrained conditions").

We agree that it is important to look at the limitations of this study results. We will emphasis the attention of the readers in the discussion of the revised document.

 

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Thank you for the answers provided and for contributions made to the paper.

Author Response

Thank you for the answers provided and for contributions made to the paper.

Answer: no answer needed

Reviewer 3 Report

Comments and Suggestions for Authors

Accept in present form

Author Response

Comments 1: Accept in present form

Answer 1: no answer needed