Modification of the Johnson–Cook Material Model for Improved Simulation of Hard Milling High-Performance Steel Components

Round 1

Reviewer 1 Report

The reviewed article offers a systematic and comprehensible investigation on the modification of a widely used model  to be applicable for multi-cutting operations.
The language is clear and precise, the figures decent. On the whole this is a valuable article for the Applied Mechanics journal with interesting  model for prediction of deformation behavior during the milling process. Following are the comments about the paper that should be addressed by the authors before acceptance:

1)Detailed description on the importance of including kinematic hardening into the material model needs to be included in the introduction. Suitable references citing the prevalence and importance of the phenomenon in such milling operations needs to be added. The motivation for the work needs to be elaborated.

2) What are the strain rates experienced during the operation? Why is Johnson-Cook model appropriate for this milling process? This needs to be elaborated in the manuscript.

3) In figure 9, why is the experimental plot devoid of any error bars?

Author Response

Dear Ladies and Gentlemen
Thank you very much for the numerous comments and useful information. We have taken all suggestions into account in the revised version of the paper. As a PDF file you will find the answers to your questions and comments.

Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript entitled “Modification of the Johnson-Cook material model for improved simulation of hard milling high performance steel components 42CrMo4“authored by Andrey Vovk et al. attempted to modified Johnson-Cook material model using finite element Abaqus software. The topic is relevant. The authors’ effort in performing analytical and experimental work is commendable. I do not think this manuscript can be published in its current status and some remarks and comments are given.

1. The introduction is very concise and references are very minimal, authors are advised to summarize and add recent references;
2. Finite element model, more information should be added about the mesh size sensitivity and number of elements. Authors have spoken about effect on lower mesh size but have not spoken about mesh sensitivity? Meaning at what point there is no more difference in simulation result;
3. The authors would add, in the revised manuscript, sentences describing the kinematic hardening behavior;
4. Authors wrote: “It should be noted that the mesh size of the model has a direct influence on the accuracy of the results, as shown in Figures 5 and 6” , reviewer believes that both curves are following almost the same trend, there is no significant influence;
5. The quality of Figure 1 should be improved;
6. In the manuscript, authors wrote Figure, Fig, and figure, it would be suitable to be consistent;
7. Beside the quality of the image which should be improved, the scale is missing in Figure 8;
8. It would be better if authors label the specimen in Fig 3;
9. Authors wrote: “test specimens are: width: 10 mm, height: 5 mm, length: 100 mm.” , authors must add ‘and’ after 5mm;

In my opinion, after the proposed major comments were made, the manuscript can be accepted for publication in the journal of Applied Mechanics.

Author Response

Dear Ladies and Gentlemen
Thank you very much for the numerous comments and useful information. We have taken all suggestions into account in the revised version of the paper. As a PDF file you will find the answers to your questions and comments.

Author Response File: Author Response.pdf

Reviewer 3 Report

In this article, the authors present a modification of the Johnson-Cook material model for studying milled 42CrMo4 steel. The study reported appears to be sound, although not well-motivated by the authors. The article itself is relatively poor and needs a significant amount of revision before it could be seriously considered for publication in Applied Mechanics. If presented as a letter or technical brief, the paper could be acceptable after revision - however, if presented as a research article, it needs significant expansion and revision. I think that this work could be revised into an acceptable article, but I think it will take longer than normally provided for a major revision. Therefore, I recommend that the paper be declined on the first round with the authors encouraged to resubmit it once the revision is done. 

Specific major comments: 

1. The topic of the paper is a modification of the Johnson-Cook model for a hard steel. After reading the paper, three major concerns about this study are obvious: (1) why is the Johnson-Cook model appropriate for a hard steel? It is usually used for more ductile materials; (2) the authors do not explain or really present what the Johnson-Cook model is or how it can be modified validly (from a mathematical/physical perspective); (3) a simple bending experiment is not nearly enough evidence to prove a new material model - generally these kinds of models are validated using tensile experiments first, with bending experiments used to support. Most material models also require some study of the fracture behavior - this is especially true for the Johnson-Cook model, as many of the approaches for studying ductile fracture use the Johnson-Cook model in some capacity. The authors mainly study the model using Abaqus, but this requires rigorous support from the mathematics behind the model. Therefore, this paper seems more like a class project to explore material models and Abaqus but not nearly scholarly enough to be a research article. 

2. The order the study is presented in is strange. Almost none of the details behind the Johnson-Cook model or the proposed modifications are presented at the beginning of the paper. The materials and methods section present experiments before modeling. 

3. There is no real literature review, discussion of the models, motivation, or discussion of the material used. This is not acceptable for a research article. While the presented study is clearly novel (even if the usefulness is unclear due to the very short and incomplete presentation), there is not a clear and convincing motivation for a new model or method. I could argue from a practical perspective that the Johnson-Cook model is not meant to be used with hard steel or other brittle-leaning materials, so it is a trivial conclusion that there will be errors in experiments. It is a good thing that the authors found a modification to extend its usefulness (claimed), but the actual need for this modification or a new model for this material is not clear. The authors need to discuss all these points and present the conclusions from the literature to support their claims. 

4. The experimental section does not give enough detail to allow an outside party to replicate the experiments. However, I do see that there is supplemental material with the paper that was not provided to the reviewers which may address this. Please at least check and make sure that across the paper and the experimental data that the experiments can be fully replicated. 

5. The discussion section is less than 150 words. This needs to be several pages based on the amount of data collected and the claims made in the paper. The discussion needs to support the presentation of the model(s) and follow up on the motivation for the new study. 

6. The conclusion section is weak, as it is essentially just four bullet points with no support or transition between them. Based on the previous comments, I think the authors would agree that all of these conclusions need to be revisited and reconsidered after providing a more rigorous treatment of the problem in the previous sections. 

More minor points: 

7. On the bending figures (Figures 5, 6, 10), please add the strain rate, temperature, and the resolution to each of the figures or figure captions.

8. Technical works in English should always be written in third person voice (i.e., do not use "we" or "our" or "us")

9. Five authors seems very excessive for a study this short and limited. Double check that all the authors meet the criteria to be authors. Remember, general project admin, funding acquisition, reviewing, and being the lab head do not in themselves qualify an author. Review the journal guide for authors and make sure all the authors actually should be named. 

Please note that all my comments are meant to help the authors and ensure the rigor of the literature. They are in no way meant to reflect personally on the authors nor meant to question their research abilities or field knowledge. I hope the authors are able to make a successful revision after addressing these comments. Good luck!

Author Response

Dear Ladies and Gentlemen
Thank you very much for the numerous comments and useful information. We have taken all suggestions into account in the revised version of the paper. As a PDF file you will find the answers to your questions and comments.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors have addressed the concerns satisfactorily and thus it is my recommendation to accept the manuscript in present form.

Reviewer 2 Report

This paper can be published after address all reviewers' comments.  

Reviewer 3 Report

The authors have made a much stronger case for their approach with the revised article. While I still do not necessarily agree personally that some of the presented ideas, approaches, and conclusions are the best ones, I do acknowledge that this is a rapidly growing field of research and I am open to exploring new ideas. With the stronger arguments and better presentation in the revised version, I think the article deserves to be published as it is. Congratulations to the authors - I will be following future work from their group and I am interested to see how these ideas develop over time.