Effect of the Hole Diameter in Mechanical Properties of Wood: Experimental and Numerical Approaches

Round 1

Reviewer 1 Report

This research discusses the effect of hole diameter on the mechanical properties of wood through an experimental approach. This study is well written, interesting and very relevant to the forest journal linkup space and can add information to the development of wood science, especially wood mechanics. To improve this writing, the author must consider the following suggestions.

1.     Why are you still using the outdated ASTM D 143 (14) instead of the current ASTM D143 (2022)? the author needs to explain the use of D143 (14) compared to D 1439 (22)

2.     According to the ASTM D143 the primary method specimen utilizes a sample size of 50 x 50 x 100 mm and a loading speed of 0.003 mm/mm of nominal specimen length/min. For a length of 100 mm, the loading speed should be 0.6 mm/min. The author's use of a speed of 0.8 mm/min is questioned. Please explain this.

Author Response

This research discusses the effect of hole diameter on the mechanical properties of wood through an experimental approach. This study is well written, interesting and very relevant to the forest journal linkup space and can add information to the development of wood science, especially wood mechanics. To improve this writing, the author must consider the following suggestions.

Response: Thank you for your feedback and assessment of our paper.  

1. Why are you still using the outdated ASTM D 143 (14) instead of the current ASTM D143 (2022)? the author needs to explain the use of D143 (14) compared to D 1439 (22)

Response: Thank you for your suggestion. We checked these two version of ASTM D143 standard and we can confirm that the newest version can be cited since we followed all its requirements.

2. According to the ASTM D143 the primary method specimen utilizes a sample size of 50 x 50 x 100 mm and a loading speed of 0.003 mm/mm of nominal specimen length/min. For a length of 100 mm, the loading speed should be 0.6 mm/min. The author's use of a speed of 0.8 mm/min is questioned. Please explain this.

Response: You are completely right. We mentioned in the text that this different velocity is an adaptation from the original property suggested by the standard.

Reviewer 2 Report

1.       The background is too simple. The author should read more research to summarize what has been done and why you put forward what you do.

2.       Was the hole drilled in the different location in the sample? Please draw a figure to show the hole location. The hole location is very important to the mechanical properties of sample. If not, why?

3.       The Result and Discussion part should be further discussed and compare the result to other research. The result should be explained.

4.       Line 192-194, This difference can be explained by the different dimensions of the samples studied by Acosta et al. [14]. Furthermore, the variability of these results may be related to the wood [15]. It needs to be explained directly and cannot just mention the reference.

Moderate editing of English language required

Author Response

1. The background is too simple. The author should read more research to summarize what has been done and why you put forward what you do.

Response: Although the literature shows too few studies on this theme, we included some other new studies in the introduction to provide a more comprehensive overview of the state-of-the-art and discussion of results. We believe that these additions enhance the context of the study and the interpretation of the presented results.

2. Was the hole drilled in the different location in the sample? Please draw a figure to show the hole location. The hole location is very important to the mechanical properties of sample. If not, why?

Response: Thank you for your feedback. We have modified the figures in our paper (Figures 1, 2, and 3) that depict the precise location of the holes in the samples. These figures have been improved to enhance the clarity and aid in the visualization of the hole locations. We believe these additions helped to address your concern regarding the importance of hole location in relation to the mechanical properties of the samples.

3. The Result and Discussion part should be further discussed and compare the result to other research. The result should be explained.

Response: In response to the reviewer's feedback, we have expanded the Results and Discussion section to include a more thorough comparison with other relevant research. New studies have been incorporated to provide a comprehensive analysis and comparison with our results.

4. Line 192-194, This difference can be explained by the different dimensions of the samples studied by Acosta et al. [14]. Furthermore, the variability of these results may be related to the wood [15]. It needs to be explained directly and cannot just mention the reference.

Response: We inserted some other explanations, which can be attributed to ourselves.  

Reviewer 3 Report

1. why wood is simulated as an elastic material in the FE model? It is clear from the results of your experiments that wood behaves non-linearly. That's why you can't give all the numerical curves in Figure 6(a) up to the ultimate condition. And also, all stress/strain figures presented in this paper are based on the elastic condition of wood only.

2. no failure mechanism applied in the FE simulation.

3. It is very clear that the actual (experimental) condition of your beam is not symmetrical, then why in your FE work you simulate the beam with only half the model? This is very strange and definitely doesn't make sense.

4. You perform compression, bending, and tensile tests in your experiments. but in the title of your paper you only wrote "..compression and bending properties..". Why ?

5. This paper is lacking in state-of-the art and the discussion of results is less comprehensive.

Author Response

1. why wood is simulated as an elastic material in the FE model? It is clear from the results of your experiments that wood behaves non-linearly. That's why you can't give all the numerical curves in Figure 6(a) up to the ultimate condition. And also, all stress/strain figures presented in this paper are based on the elastic condition of wood only.

Response: Thank you for your insightful observation to improving this work. The main focus of our research was to investigate the influence of anisotropic effects on stress concentrations around holes in pine wood samples. We chose to model wood as an elastic material in our finite element model (FEM) due to its computational simplicity and the exploratory nature of the study. We acknowledge that wood exhibits nonlinear behavior, as evidenced by the experimental results showing an increase in stress concentrations around holes as the hole diameter increases.

It is important to note that our intention was not to capture the full nonlinear behavior of wood, but rather to investigate the variation in stress concentrations caused by holes of different diameters. By limiting our analysis to the elastic behavior of wood, we were able to isolate and specifically study the anisotropic effect on stresses around the holes. We recognize that including a nonlinear material model could provide a more accurate representation of wood behavior, especially at more advanced loading stages.

Thank you for your attention and feedback, which will be valuable for further refining our research and addressing the complexities of wood behavior more comprehensively in future studies.

Some sentences have been modified in items 2.3 and 3.1 to improve the explanation of the model's limitations.

We also explained in the last paragraph of the Introduction that, rather than examining the entire mechanical behavior of wood, this study offers valuable insights into the specific aspect of stress concentration induced by anisotropic effects in wood due to the presence of holes.

2. no failure mechanism applied in the FE simulation.

Response: We appreciate the reviewer's comment regarding the absence of a failure mechanism in the finite element (FE) simulation. It is important to note that our study was focused on investigating the influence of anisotropic effects on stress concentrations around holes in wood samples, rather than on the specific failure mechanisms. Therefore, the inclusion of a failure mechanism was beyond the scope of our work. While the incorporation of failure criteria could provide additional insights into the structural behavior of wood, our study aimed to lay the groundwork for future research in this area. We believe that our findings regarding stress concentrations and anisotropic effects are valuable contributions to the field and can serve as a basis for more comprehensive studies that include failure mechanisms in FE simulations.

Some sentences have been modified in item 3.1 to improve the explanation of the model's limitations.

As we explained before, instead of delving into the entirety of wood's mechanical behaviour or some failure mechanisms, this study provides valuable insights into the specific aspect of stress concentration induced by anisotropic effects in wood due to the presence of holes.

3. It is very clear that the actual (experimental) condition of your beam is not symmetrical, then why in your FE work you simulate the beam with only half the model? This is very strange and definitely doesn't make sense.

Response: We appreciate the reviewer's observation regarding the symmetry of the beam in our FE model. While it is true that the actual experimental condition of the beam is not symmetrical, we chose to simulate only half of the beam in our FE work to reduce computational complexity. This approach is commonly used in FE analysis to simplify the model without significantly affecting the results. By utilizing symmetry, we were able to efficiently analyze the behavior of the beam and focus on the specific aspects relevant to our study. We acknowledge that this approach may seem unconventional, but it was a deliberate decision made to balance computational efficiency with the accuracy of our analysis.

Some works has been used the symmetry conditions for bending test: https://doi.org/10.1080/17480272.2019.1587506

https://doi.org/10.1016/j.matdes.2009.05.024

4. You perform compression, bending, and tensile tests in your experiments. but in the title of your paper you only wrote "..compression and bending properties..". Why ?

Response: We now addressed this suggestion. Thank you for that.

5. This paper is lacking in state-of-the art and the discussion of results is less comprehensive.

Response: New studies have been included in the introduction to provide a more comprehensive overview of the state-of-the-art and discussion of results. We believe that these additions enhance the context of the study and the interpretation of the presented results.

Reviewer 4 Report

The paper is correctly written and conforms to the requirements of the research methodology. The purpose and objectives of the research are mentioned, and the conclusions are in accordance with the results of the tests.

Less is touched the aspect regarding the importance of these researches. It would have been interesting if, for the compression and bending stress, the placement of the hole had been in different positions on the height of the cross section, above and below the neutral axis. It is known that in the neutral axis the values of the normal stress from the bending load is almost zero, therefore the conclusions for this set of laboratory research did not show important influences on the behavior of the specimen. But finite element modeling is an aspect that ensures a higher level of research.

It is recommended to the authors to continue the research with the modification of the position and diameter of the hole on the height of the cross section. Thus, the conclusions regarding the behavior of the specimen related to the position of the hole and its diameter would certainly be of great interest. Maybe the authors will do these analyzes only on the finite element model, once it (the specimen and load model) has been validated at this stage of the research.

Author Response

The paper is correctly written and conforms to the requirements of the research methodology. The purpose and objectives of the research are mentioned, and the conclusions are in accordance with the results of the tests.

Response: Thank you for your feedback and assessment of our paper.

Less is touched the aspect regarding the importance of these researches. It would have been interesting if, for the compression and bending stress, the placement of the hole had been in different positions on the height of the cross section, above and below the neutral axis. It is known that in the neutral axis the values of the normal stress from the bending load is almost zero, therefore the conclusions for this set of laboratory research did not show important influences on the behavior of the specimen. But finite element modeling is an aspect that ensures a higher level of research.

Response: Thank you for your feedback and assessment of our paper.

It is recommended to the authors to continue the research with the modification of the position and diameter of the hole on the height of the cross section. Thus, the conclusions regarding the behavior of the specimen related to the position of the hole and its diameter would certainly be of great interest. Maybe the authors will do these analyzes only on the finite element model, once it (the specimen and load model) has been validated at this stage of the research.

Response: Thank you for your feedback and assessment of our paper.

Round 2

Reviewer 2 Report

The manuscript can be accepted after the language is improved.

The manuscript can be accepted after the language is improved.

Author Response

Thank you for your feedback. We appreciate your suggestion regarding the language improvements. We have carefully revised the manuscript to enhance its clarity, coherence, and overall readability. We believe that these revisions have addressed the concerns raised and improved the quality of the manuscript. We hope that the revised version meets the standards expected for publication.

Improvements Made:

On the Abstract:

• Clarified sentence structures for better readability.
• Corrected spelling and grammatical errors.
• Improved coherence and flow of the abstract.

On the Introduction:

• Clarified sentence structures for better readability and coherence.
• Corrected spelling and grammatical errors.
• Enhanced flow and organization of ideas within the introduction.
• Improved clarity in summarizing previous studies and their contributions to the field.
• Streamlined explanations of complex concepts and methodologies for better understanding.

On the Materials and Methods (M&M) Section:

• Clarified and corrected sentence structures for better readability and coherence.
• Standardized terminology and units for consistency throughout the section.
• Streamlined descriptions of experimental procedures and equipment used.
• Enhanced clarity in explaining the statistical analysis process and rationale.
• Improved organization and flow of the section for easier understanding.

On the Results and Discussion (R&D) Section:

• Refined the text structure for better clarity and flow.
• Enhanced terminology and description of concepts for greater accuracy.
• Corrected grammatical and typographical errors.
• Adjusted formatting and organization of sections and subsections for clearer and more professional presentation.
• Added details and additional explanations where needed to enrich the content and clarify discussed points.
• Standardized the presentation of figures and tables to facilitate understanding and referencing throughout the text.

On the Conclusion:

• Clarified and corrected the L/h ratio used in bending tests based on Brazilian standard ABNT NBR 7190, addressing its inconsistency with ASTM D143.
• Introduced finite element (FE) analysis to explore stress concentrations around holes in wood samples, enhancing the depth and understanding of the study.
• Included comparative insights with existing literature, strengthening the validity and credibility of the study's findings.
• Recognized and acknowledged study limitations, particularly the absence of a failure mechanism in the FE simulation and the observed variability in tensile tests perpendicular to the grain.

Reviewer 3 Report

The paper must be prepared in a proper scientific manner.

Author Response

In response to this reviewer's feedback, the necessary corrections have been made to enhance the scientific rigor and presentation of the manuscript. Specifically, the methodology and results sections were revised for improved clarity, consistency, and adherence to standard scientific protocols. The paper now better aligns with the journal's requirements for a rigorous scientific presentation.