Review Reports - Influence of Lubricant Properties on Elastohydrodynamic Oil Film Thickness in Angular Contact Ball Bearings: A Numerical Investigation

Round 1

Reviewer 1 Report

This study presents a numerical investigation using a five-degree-of-freedom (5-DoF) shaft–bearing model to predict oil film thickness in ball bearing contacts under elastohydrodynamic lubrication (EHL) conditions. As a reviewer, the following strengths and weaknesses can be highlighted:

Predicting oil film thickness under EHL conditions is a critical problem, particularly in terms of lubrication safety in bearing systems, and it has direct engineering applications. The use of a 5-DoF model improves the mechanical accuracy and the capability to capture interactions in the system. The effects of key parameters such as viscosity, shaft speed, and pressure–viscosity coefficient on film thickness are clearly analyzed and supported with quantitative results (e.g., a twofold increase in speed results in a 57% increase in film thickness).
The impact of film thickness variations on bearing design and lubricant selection is emphasized, which facilitates the transition of results from theory to practical applications.
The limitations of the model are not sufficiently discussed. The isothermal assumption (neglecting thermal effects) can have a potentially significant impact on EHL behavior. The influence of this assumption on the results, and the validity range of the model, should be clearly addressed. Additionally, some of the findings need to be supported by appropriate references from the literature.
A quasi-static solution approach has been adopted in the study. However, in bearing systems, especially during speed variations, the absence of transient effects can reduce the adequacy of the model for some practical cases.
The analysis focuses only on a limited number of parameters such as viscosity and speed, while the effects of other important factors such as load, contact geometry (e.g., radius difference, curvature ratio), or temperature seem to be neglected. These effects could be addressed in future work.
The solution algorithm (e.g., iterative methods), convergence criteria, solution accuracy, and mesh configuration should be clearly explained. This would allow a more objective evaluation of the reliability of the results.
Some figures (e.g., Figures 4–5) could be made clearer or more informative to enhance the reader's understanding.

Overall Evaluation

This study provides valuable insights for researchers working in the fields of tribology and bearing systems. The modeling approach is detailed, the analyses are comprehensive, and the results are meaningful from both mechanical and design perspectives. With minor revisions, this work can be significantly improved in quality.

Predicting oil film thickness under EHL conditions is a critical problem, particularly in terms of lubrication safety in bearing systems, and it has direct engineering applications. The use of a 5-DoF model improves the mechanical accuracy and the capability to capture interactions in the system. The effects of key parameters such as viscosity, shaft speed, and pressure–viscosity coefficient on film thickness are clearly analyzed and supported with quantitative results (e.g., a twofold increase in speed results in a 57% increase in film thickness).
The impact of film thickness variations on bearing design and lubricant selection is emphasized, which facilitates the transition of results from theory to practical applications.
The limitations of the model are not sufficiently discussed. The isothermal assumption (neglecting thermal effects) can have a potentially significant impact on EHL behavior. The influence of this assumption on the results, and the validity range of the model, should be clearly addressed. Additionally, some of the findings need to be supported by appropriate references from the literature.
A quasi-static solution approach has been adopted in the study. However, in bearing systems, especially during speed variations, the absence of transient effects can reduce the adequacy of the model for some practical cases.
The analysis focuses only on a limited number of parameters such as viscosity and speed, while the effects of other important factors such as load, contact geometry (e.g., radius difference, curvature ratio), or temperature seem to be neglected. These effects could be addressed in future work.
The solution algorithm (e.g., iterative methods), convergence criteria, solution accuracy, and mesh configuration should be clearly explained. This would allow a more objective evaluation of the reliability of the results.
Some figures (e.g., Figures 4–5) could be made clearer or more informative to enhance the reader's understanding.

Overall Evaluation

Comments for author File: Comments.pdf

Author Response

Dear Reviwer,

Thank you for your valuable comments and contribution to the my paper. All of your comments has exemined carefully and all of them addresed. Response to comments can be seen in the attached file. According to comments all updates/modifications/revisions has completed. During the manuscript revision, all changes has traced. Therefore, changes in the paper can be seen easily.

Thank you very much for your consideration.

Yours Sincerely,

Dr. Hikmet BAL

OSTIM Technical University of Turkiye

Tel.: +90-532-260-4826

E-mail: hikmet.bal@ostimteknik.edu.tr

Author Response File: Author Response.pdf

Reviewer 2 Report

Thank you for involving me for the reviewing of the manuscript entitled "Influence of Lubricant Properties on Elastohydrodynamic Oil Film Thickness in Angular Contact Ball Bearings: A Numerical Investigation". Generally, the theme of the entire paper is clear, the writing is also very standardized, and the results are presented very clearly.

1) General: The theme of the entire paper is clear, the writing is also very standardized, and the results are presented very clearly.
2) Keywords: Keywords suggest to be sorted from big to small, from core issues to conditions.
3) Section2:
—Fig.1: The image is a bit blurry, it is recommended to increase the size and raise the DPI.
—Fig.1: It's a Shaft, not a Raft. In addition, what's the meaning of CG?
—Fig.1: The author should provide the parameters in the diagram, such as a0, a1, b0, and b1. Are they useful in the calculation process?
—Page5 Line152: Should there be a unit for "film thickness range 10-7 ≤ h ≤ 10-6"?
—TableA1 should be placed in this section, there is no need to include it as an appendix.

4) Section3: Figure B.1.should be placed in this section.
5) References:
—"ISBN: 0301-679X Publisher: Elsevier" should be removed.
—The title of the journal should be abbreviated.

Author Response

Dear Reviwer,

Thank you very much for your consideration.

Yours Sincerely,

Dr. Hikmet BAL

OSTIM Technical University of Turkiye

Tel.: +90-532-260-4826

E-mail: hikmet.bal@ostimteknik.edu.tr

Author Response File: Author Response.pdf

Reviewer 3 Report

Dear Author,

you present only numerical calculations, so the manuscript can't be accepted for publication in the Journal of Applied Mechanics.

Most of the references are outdated.

"By reducing the surface roughness of bearing components through surface finishing techniques" - how do you want to obtain it? What would be the cost of surface improvement of components which have a very good surface finish.

Best

Reviewer

No detailed comments, because the manuscript is not suitable for publication.

Author Response

Dear Reviwer,

Thank you very much for your consideration.

Yours Sincerely,

Dr. Hikmet BAL

OSTIM Technical University of Turkiye

Tel.: +90-532-260-4826

E-mail: hikmet.bal@ostimteknik.edu.tr

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

All corrections have been made carefully and meticulously. It can be published.

Reviewer 2 Report

Thank you very much for revising the manuscript adequately. The quality of the revised version has notably improved.