Next Article in Journal
Characterization of Base Oil and Additive Oxidation Products from Formulated Lubricant by Ultra-High Resolution Mass Spectrometry
Next Article in Special Issue
A General Approximate Solution for the Slightly Non-Axisymmetric Normal Contact Problem of Layered and Graded Elastic Materials
Previous Article in Journal
Dynamic Temperature Prediction on High-Speed Angular Contact Ball Bearings of Machine Tool Spindles Based on CNN and Informer
Previous Article in Special Issue
Efficient Sub-Modeling for Adhesive Wear in Elastic–Plastic Spherical Contacts
 
 
Article
Peer-Review Record

A Multi-Scale Investigation to Predict the Dynamic Instabilities Induced by Frictional Contact

Lubricants 2023, 11(8), 344; https://doi.org/10.3390/lubricants11080344
by Farouk Maaboudallah * and Noureddine Atalla *
Reviewer 1:
Reviewer 2: Anonymous
Lubricants 2023, 11(8), 344; https://doi.org/10.3390/lubricants11080344
Submission received: 13 June 2023 / Revised: 3 August 2023 / Accepted: 8 August 2023 / Published: 11 August 2023
(This article belongs to the Special Issue Advances in Contact Mechanics)

Round 1

Reviewer 1 Report

Comments to the Author

Title: A multi-scale investigation to predict the dynamic instabilities induced by the frictional contact

Comments: It is important to review and to overcome the assumption of perfectly flat surfaces by taking into account the statistical characteristics of rough surfaces. In this paper, propose a new variational formulation to model and predict the dynamic instabilities of frictional systems. Most of the discussions are meaningful, but there are some problems in the article. The article should be major revised according to the following comments:

1. In the introduction, the authors should describe in detail the basic definition of dynamic instabilities or the basic theory involved, which is one of the core discussion points of this article.

2. Fig. 5a is the computed 2D-PSDF of the topography shown in Fig. 4? The results may not match, please check it.

3. The positions of icons a and b in Fig. 4 are inaccurate and can easily cause ambiguity.

4. The number of pixels used in the whole text is not uniform, and whether the difference in pixels will have a certain impact on the results.

5. The meaning of ‘the latter’ in line 325 is unclear.

6. The very latest references about friction (e.g., Friction 10(11): 19131926 (2022); Composites Part B 263 (2023) 110833) may be of interest to the authors for citations.

7. In addition to the results shown in Fig. 9, please provide more data comparison and explanation for the result that the multi-scale approach is more accurate than the classical approach using a perfect contact law.

Moderate editing of English language required

Author Response

Reviewer #1:

 

Comments: It is important to review and to overcome the assumption of perfectly flat surfaces by taking into account the statistical characteristics of rough surfaces. In this paper, propose a new variational formulation to model and predict the dynamic instabilities of frictional systems. Most of the discussions are meaningful, but there are some problems in the article. The article should be major revised according to the following comments:

  1. In the introduction, the authors should describe in detail the basic definition of dynamic instabilities or the basic theory involved, which is one of the core discussion points of this article.

[Farouk, M.]:

Thank you for your comment. I have explained this point in the last paragraph of the introduction.  

  1. Fig. 5a is the computed 2D-PSDF of the topography shown in Fig. 4? The results may not match, please check it.

[Farouk, M.]:

Indeed, the Y and X dimensions are not the same in Figure 4. I highlighted this point in the beginning of section 3.1.

 

However, the calculation of the 2D-PSD is based on a square measurement (which is not the case in Fig. 4), where the scan length along the Y axis is the same along the X axis. I've explained that the calculation of the 2D PSD is done on a square surface of 15x15 mm2 with a resolution of 512x512. Please see the caption of Fig. 5.

  1. The positions of icons a and b in Fig. 4 are inaccurate and can easily cause ambiguity.
  2. The number of pixels used in the whole text is not uniform, and whether the difference in pixels will have a certain impact on the results.

[Farouk, M.]:

I’m sorry to hear that. In fact, I have struggled a lot with the MDPI latex template. I am planning to work closely with the editorial office (if the paper is accepted) to reorganize Figures as well as the text size.

 

 

  1. The meaning of ‘the latter’ in line 325 is unclear.

[Farouk, M.]:

The highlighted line “It depicts the evolution of the normalized contact pressure, $\frac{P}{E^*}$ (where $E^*$ is the composite modulus) versus the separation. The latter is defined as a distance between the imposed displacement of the rigid surface …”

Here the latter refers to the separation. To avoid the repetition, I used “The latter”. So, we should read it as follows:

The separation is defined as a distance between …

 

  1. The very latest references about friction (e.g., Friction 10(11): 1913–1926 (2022); Composites Part B 263 (2023) 110833) may be of interest to the authors for citations.

[Farouk, M.]:

Interesting. I have added them to the introduction.

  1. In addition to the results shown in Fig. 9, please provide more data comparison and explanation for the result that the multi-scale approach is more accurate than the classical approach using a perfect contact law.

[Farouk, M.]:

Unfortunately, this is the only result that the industrial partner has allowed us to publish, where we can see that the proposed approach outperforms the conventional one at low frequencies.

 

 

In the end, I would like to thank you for your constructive comments.

 

Sincerely,

 

Mr. Farouk Maaboudallah

Reviewer 2 Report

Dear Author(s), the manuscript ‘A multi-scale investigation to predict the dynamic instabilities induced by the frictional contact’, Manuscript ID: lubricants-2411827, have some weakness that must be improved suitably.

Below you can find some of the most crucial comments:

1.      In the ‘Abstract’ section some introduction words reflecting the area of study could be placed. The Author(s) should provide some words before initiating what was proposed. This should be the second part of this section.

2.      The ‘Introduction’ section is interesting. However, some sentences are difficult to follow, e.g. ‘With the development of computational facilities, accurate numerical models, free of assumptions unlike the previous analytical models, have emerged.’, lines 73-74. Please try to re-write them.

3.      The motivation, written in lines 110-131, is partially hidden. Especially since it does not derive from the critical review but some Author(s) proposals. The novelty should be received from the lack of the current state of knowledge, which was not specified in this section.

4.      The second section, ‘Governing equation’, including three subsections, is not clear and, unfortunately, a little messy:

4.1.What is already known and which equations are newly proposed? The Author(s) should refer to the primary sources of each of the techniques presented, e.g. Dirichlet, Neumann, Cauchy, Hook, Hertz-Signorini-Moreau etc.

4.2.The equations proposed by the Author(s) must be strongly separated from those common, already known. What is the novelty of the formulas?

4.3.Some of the decision looks selected arbitrarily like, in the sentence ‘In this paper, the potential energy of the contact interaction will be formulated as follows,’, page 7. Authors should justify each of the selections proposed.

4.4.The idea presented in lines 212-244 should be introduced with some flow chart or separated into a further subsection. Currently, it is messy with previous proposals.

5.      Considering the measurement of the surface roughness, there is no detailed information on the process used. The CLSM (confocal laser scanning microscopy) is well-known method, however, classified into contactless techniques, is fraught with many errors influencing the accuracy of the results obtained. Please look for some examples of the mentioned issues and try to present it more in detail:

(1)   https://doi.org/10.1088/2051-672X/3/3/035004

(2)   https://doi.org/10.3390/coatings12060726

(3)   https://doi.org/10.1016/j.cirp.2014.03.086

6.      From Figure 3a, how Area1 is selected? Randomly? This selection can strongly influence the final results. Different brake pad areas have much different roughness. It is not clearly presented and described.

7.      It is not obvious if the PSDF (power spectral density function) is newly proposed by the Authors or not. Please emphasize it on page no. 10. From my perspective it is the PSD, generally known and often applied. It looks like the Author(s) are trying to present it as their novelty. I suggest using the PSD abbreviation. It is obvious and defined many years before that the PSD is a function and there is nothing new so, respectively, shouldn’t be presented as PSDF.

8.      In Figure 5 and some of the descriptions in the text, Authors used the 2D-PSDF sentence. As far as it is presented, there was only an areal PSDF analysis presented. From that matter, if profiles are not separately studied, this is not required to emphasize an areal analysis. To simplify, I would suggest to use only PSDF (PSD) description without any further additions.

9.      In the whole 3rd section it is difficult to find any critical discussion. Moreover, the advantages and disadvantages of the method presented are not obvious. The Author(s) must emphasize it strongly.

10.  There are many variables, parameters, abbreviations and shortcuts that the Nomenclature section should be provided. Currently, the Reader can feel lost.

11.  The ‘Conclusion’ section is long but not providing short crucial information. Firstly, this should be divided into separated and numbered gaps. Secondly, the main purpose must be emphasized that currently, it is difficult to judge what is the most important.

From the above, the reviewed manuscript must be improved significantly before any further processing of the Lubricants journal, if allowed by the Editor.

Author Response

Please pdf document below.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Thanks for a positive response. All the questions have been satisfactorily addressed, so an acceptance of this promising work is recommended.

Reviewer 2 Report

The manuscript was improved suitably that can be further processed by the Lubricants Editorial Office.

Back to TopTop