Size-Independent Flexure Test Technique for the Mechanical Properties of Geocomposites Reinforced by Unidirectional Fibers

Round 1

Reviewer 1 Report

The authors have presented the outcomes of flexural tests conducted at varying span-to-thickness ratios and displacement rates on diverse geopolymer composites, each reinforced with one of three distinct types of unidirectional fibers. While the results are indeed intriguing, the central conclusion positing a linear correlation between the reciprocal effective modulus or strength and (H/L)^2 is not robustly substantiated by the provided data. Additionally, the reproducibility of the experimental procedure is not repeatable, and the microstructural characteristics of the composites remain undisclosed. Prior to endorsing acceptance, the authors should address these three critical points. The subsequent suggestions are offered to assist the authors in further enhancing the article:

Lines 78-79: It is worth noting that strain to failure and proportional limit stress are among the foremost mechanical properties of significance. To provide a comprehensive overview, the authors could incorporate these values for the depicted composites.

Lines 115-116: In the case of CMCs exhibiting a 0/90 architecture, it has been demonstrated that by tilting the specimens, the influence of shear effects can be effectively minimized, attributable to the reduction in critical tensile strength (as referenced in https://doi.org/10.1016/j.matdes.2021.109888 and https://doi.org./10.1016/S1359-835X(02)00079-9). This gimmick should be reported in the introduction.

Lines 131-133: During the flexural testing, it's noteworthy that compression stress, along with the resulting position of the neutral axis, could potentially impact the flexural modulus. A discussion regarding this phenomenon would be valuable.

Fig. 1: It is advised to verify the nomenclature of the axes within the figure.

Line 426: Please double-check the accuracy of the recorded displacement rate values.

The aspect of interlaminar shear stress holds particular relevance within the field of CMCs (see for example: https://doi.org/10.3390/nano12193406, https://doi.org/10.1016/j.matdes.2021.109888, and https://doi.org/10.1016/j.compstruct.2019.111747). Drawing a comparison with this existing literature could aid the authors in furnishing a more comprehensive discourse regarding the presented results, which currently exhibit a somewhat report-like nature.

Author Response

1. Thank you very much for this suggestion, the strain to failure and proportional limit stress are recommend together elasticity and the elasticity and strength are these high-tech construction materials' most relevant mechanical properties (line 84-85). In other publication we has discussed the values (New Generation of Geopolymer Composite for Fire-Resistance, DOI: 10.5772/17933).

2. We agree with this comment. We will use the tilting the specimens technique and compared the results to our findings in future investigation.

3. We are very appreciated this suggestion. However, in our experiments we did not record the position of the neutral axis. We consider this as the shortcoming of our research and we would like to set it in the Results and discussion.  

4. Figure 1. Ratio of the effective value E to the virtual value E*; ratios E*/G in the legend.

5. The accuracy of the recorded displacement rate values are double-checked. For the displacement rate at 2 mm/min, the experiments were taken in the Lab of Technical University of Liberec (TUL) with Instron Model 4202 and 9.2 mm/min, the experiments were taken in the Lab of VUAnCh with TMZ-3U Electronic machine.

6. Thank you very much for this suggestion,  “Microstructure and Mechanical Properties of Unidirectional, Laminated Cf/SiC Composites with α-Al2O3 Nanoparticles as Filler” by Lixia Yang, Fei Wang, Jiahao Liao, Zhaofeng Chen and Zongde Kou; “Insight into microstructure and flexural strength of ultra-high temperature ceramics enriched SICARBON™ composite” by Pietro Galizia, Diletta Sciti, Neraj Jain; and “A bi-phasic modelling approach for interlaminar and intralaminar damage in the matrix of composite laminates” by Alessandro Airoldi, Chiara Mirani, Lucia Principito have been carefully consulted to reinterpret the introduction, Results and discussion and conclusions.

 

 

 

Reviewer 2 Report

The authors have presented the results of tests done with traditional mechanical procedures according to some existing standards. Right from the title, this work hit the wrong note with the use of the word "Novel". The narrative fails to describe the novelty. Apart, the misuse of engineering terminologies are very confusing. For example, the word "elasticity" is used to describe the engineering property of Young's Modulus or the modulus of Elasticity. What is meant by "geopolymer resin" is unclear, and this statement appears too many times, making one question what exactly the authors are trying to communicate. The key outcome of this paper applies to be mostly on fitting data to Tarnopolsky's equations. It concluded that loading displacement is relevant in the outcome; however, only one displacement rate of 2mm/min is ever used (or reported). 

I believe there are too many confusing terminologies, the introduction is excessively long, and I don't see the validity of the concluding statements.

 

Abstract

This abstract starts with procedure and I would have expected to see a summarised rationale at the start of an abstract.

Consider the statement.

"Simple evaluation of tests for flexural properties of geopolymer composites reinforced  with unidirectional fibers, as performed in accordance with relevant American and European standards,…"

 

Line 15 "… provides effective values of flexural strength m* and, respectively, elasticity modulus E*."

This statement is disorganised and can not be comprehended.

Line 24 -25 "Also, the influence of loading displacement rate is relevant and should be considered under each particular condition."

There is a problem with this statement since only one displacement rate of 2mm/min is reported! The displacement rate is not a reported variable in the work and in the experimental procedure.

 

Introduction

 The introduction is too long and needs to be shotertened. There are too many repetitive information that sometimes reads like dot points.

Line 42 -45: "These innovative materials … autoclave process.

Confusing statement hard to understand. Can be cured at room temperature or thermosetting" appears to be two different routes! Is it? Thermosetting simply means once consolidated, it can not be reversed by heating!.

 

Consider Lines 58 -99

It is confusing what "geopolymer resin is. Line 62.

 

The generic reference to fibres in this narrative does not give any useful information. There are well-known engineering fibres, C, glass, Basalt, etc. The reference to fibres in this section gives the impression that only the volume proportion of fibres matters. The significant contribution of the primary properties of fibres was grossly underreported.

 

Line 118             "… that the influence of shear was never insignificant."

This statement appears to be oxymoronic. Is it significant or not? The statement can be simplified to make it clear.

 

2.1 Elasticity

I foud the subtile of “Elaticity” to be improper. Is this section about Young's Modulus or Elesatic Modulus? Elasticity is not a property, it is a non-quantitative description of deformative behaviour under loading. The characterising property is the "Modulus of elasticity" or "Young's Modulus."

 

Overall, I do not see the relevance of Lines 121 – 305. This could be reduced to a few lines and appropriately referenced. There is no need to reproduce information as published elsewhere in this manner. It does not add to the quality of the paper.

 

3 Experimental

This section is poorly written. A few line diagrams would improve the quality of the procedures employed in the testing.

Lines 328 – 330: Composites are typically described by the volume fraction of fibres. The reference to weight fraction is irrelevant.

 

Results

These are not orderly presented. It is hard to follow the narrative. If the component "Novel" must stay, this is the section to expatiate on the novelty. What IO  see is a disorderly presentation of graphs with little explanation other than they satisfy the theory!

 

4. Conclusions

I do not see how these conclusions were reached. No inductive or deductive reasoning was expressed that led to these vague conclusions.

 

Line 502 "The slow displacement rate (2 mm/min) at the tests…"

A displacement rate of 2mm/min is not slow! It is actually fast in test terminology. Again, this is an indication that the displacement rate was not varied in the experiments, contrary to what was indicated in the abstract.

 

 

The manuscript could be imrpoved by passing through a language editor. For readability, the introduction part need to be reduced to maximum of two paragrahs. 

Author Response

Dear Reviewer 2,

First of all, we would like to express our deep gratitude for your comments. Based on the comments and suggestions, the authors have carefully discussed and established the response section in the attached file, and we have also revised the manuscript.
Although we have tried our best, we certainly cannot answer and fully satisfy your request. I hope you will consider and help us.
Thank you very much.

Hung Tran Doan

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors have improved the manuscript, and it can be published, although they have not completely fulfilled all the points

Reviewer 2 Report

The authors have sufficiently responded to the feedback, and the manuscript is now recommended for publication. 

Well structured enough for an average person to follow the narrative.