A Digital Twin for Friction Prediction in Dynamic Rubber Applications with Surface Textures

Round 1

Reviewer 1 Report

The article is of very high quality. He takes up the difficult subject of surface lubrication with the introduction of texturing methods. It is extremely valuable due to the complexity and number of measurement results obtained. Such studies are widely conducted by various authors. This applies in particular to internal combustion engine components. Therefore, I would recommend providing a few sample publications on the huge impact of the shape of engine components, including texturing, on energy benefits. I would recommend citing several publications in the field of texturing and the influence of the shape itself on friction losses. This is especially important in the hydrodynamic lubrication theory.

G. Ryk, Y. Kligernman, I. Etsion Experimental investigation of laser surface texturing for reciprocating automotive components Tribology Transactions, 45/4 (2002), pp. 444-449

Tomanik E. Modelling the hydrodynamic support of cylinder bore and piston rings with laser textured surfaces. Tribology International 2013;59:90–6

Wróblewski P., Iskra A.: Geometry of shape of profiles of the sliding surface of ring seals in the aspect of friction losses and oil film parameters. Combustion Engines. 2016, 167(4), 24-38. https://doi.org/10.19206/CE-2016-403

I would recommend giving the essence of the research conducted. More articulate the scientific value. Report that many works have been done, but the current one supplements this state of knowledge, introduces new methods and new research directions. Cite value for industry. An editing error with paragraphs occurred in the work. The charts are correct. Method conducting research correct. It is worth correcting conclusions and listing scientific achievements after dashes refer to the current state of knowledge.

Author Response

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Reviewer 2 Report

The manuscript describes an application well-known approach for digital representation of a physical engineering components, derived from experimental data. First and foremost, this paper is an effort in the right direction, given that real tribological systems are extremely hard to model, and doing it empirically is a promising route for doing it. Although I believe that the work has been properly executed, it is hard to go beyond my belief, due to the lack of details at multiple places. Therefore, I have listed the major and minor problems I encountered while reading the article, and I have ranked them in importance. I hope my comments will increase the article’s readability, and thus increase impact it can have on the tribological community.

Major Concerns:

1. Entire paragraphs of the paper match the publication in Ref. 19. This automatically means that it would be hard for those paragraphs to match the flow and focus of the current paper (and are probably deems them unnecessary if they are written somewhere else already).
2. Too many problems in the paper are not adequately described, but instead only point to another section, which sometimes does not contain the necessary details. The most significant one is that the resulting ROM, based on the tribology data, is never shown. I am not even sure what are the variables that it takes in are, because it is never explicitly said. There are multiple references in the results back to the introduction and Equation 1, but that’s just the general form, and it is not a result of the paper.

Once this is explained, I will be able to give the results a fair assessment.

3. I tried to find the answer to my previous question, but the raw data was not available. I am not sure if that’s just precautionary before the paper is published, but wanted to point out that it’s inaccessible, in case it was unintended.
4. The paper’s title includes a reference to the ‘digital twin’ paradigm. However, as correctly identified in line 67, digital twins are meant to be real time. I am not convinced that this is at all possible or achieved with the ROM used in the paper. Please comment on this, as I think that including ‘digital twins’ as anything more than a motivation is misleading.
5. Most of page 9 requires clarifications. Generally speaking, any reference to the data-analytics portion of the paper has to be made more tangible, by referencing real tribological objects and reasoning, instead of only using catch-all terms. As one of many examples, in line 272 the words ‘data sample’ and ‘point’ are used, but I cannot be sure at all what that means. Another one, as an extension to comment 2, is that in line 270, the mentioned limits are nowhere to be found. Being directed to section 3.3 (results), only sends me back to Equation 1 (introduction). This is the case in many other sections of the Results section, as usually only ‘Equation 1’ and ‘input data’ are mentioned, but still do not know what the actual ‘input data’ in the model was.
6. The motivation for using equation 4 is never explained.
7. Why does the y-axis label in Figure 14 include the word ‘experimental’?

Minor concerns:

1. References could include more than just a link to a website/Data.zip/PDF.
2. The sentence in line 99 has to be modified and specify that all the models, except one, that are considered concern elastomers and textured surfaces.
3. All figure descriptions list the annotation (e.g. (a) or (b)) after the relevant sentence. That makes it hard to find the relevant caption.
4. Figure 2 (b), could use a few labels, for example, with the location of the texture.
5. Figure 3 (b) needs to be enlarged, and the components from the technical drawing could be annotated.
6. Using F_R for friction force could be confusing to an international audience, as R does not stand for friction.
7. The paragraph at row 164 is very unclear and the exact experimental procedure is hard to reconstruct. For example: is the normal force varied or not? Was it varied while the rotational speed was varied? ‘n’ should be italicized probably too.
8. The FEA model used for contact area calculations is not mentioned, only the material behavior model.
9. It is unclear what the purpose of Figure 5 is, since any variation is impossible to be inferred from the resolution of the axes.
10. The use of ‘respectively’ in line 201 is unnecessary and confusing.
11. Were there any tilt/surface corrections to the 3D surface scans?
12. It could be acknowledged in the Results section that no uncertainty range, based on metrologically traceable calibration, is provided for the tribological data. Although, a pervasive practice in tribology, in this case lateral error bars in your prediction data points could further help your case that the predictions are very good.
13. There are multiple smaller language and stylistic mistakes, which I am sure you will catch as you rework the paper.
14. Multiple paragraphs are not indented.

 

I wish luck to the authors and I am keenly looking forward to the revised manuscript!

Author Response

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Reviewer 3 Report

This work uses a very interesting concept to optimize surface texturing in rubber seals. The idea is excellent. However, I don´t think it should be accepted because it is not written as a journal article. It is very long, difficult to follow and does not give a clear message to readers. Below I describe the problems in some detail.  

1. Introduction: It is a little unclear to start the Introduction talking about situations when friction needs to be increased when the main focus of the work is friction reduction
2. The Introduction was written more like a literature review instead of concisely presenting the problem, the state of the art, the gaps of knowledge still existing in the literature and then finally define the objectives of the work. The authors should consider having an Introduction and then a separate section such as “Background”. Anyway, even if they to need, it needs to be shortened and presented more like an academic paper rather than a PhD report.
3. Describe the texturing procedure and conditions
4. “The reason is the greater number of effective dimples in the direction of the fluid film flow for f=45o” – This is not obvious to me
5. The description of the test rig is too lengthy.
6. It is absurd in a tribology journal to use an equation to define friction coefficient, this is too obvious. Moroever, it should be Amonton´s law and not Coulomb´s law.
7. As a whole, the manuscript is too long and reads more like an academic report than a paper. The authors should use an intelligent way of summarizing their results in fewer and more meaningful figures, this should strongly facilitate the analysis
8. The conclusions are very vague.
9. Editorial problems:

• The language is often unclear and should be revised
• Adjectives should be singular, not plural, e.g.: “outliers population” – outlier population (correct same problem in other instances).

Author Response

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Reviewer 4 Report

The authors of the article investigate the method of reducing the friction of surfaces with a gasket by texturing. To form a texture on the surface, the authors suggests laser treatment of the molds into which the polymer material will be poured.
In conclusion, the authors achieved a reduction of friction by 79%. The article corresponds to its title and subject. An in-depth analysis of the obtained data was performed. I recommend the paper for publication as is.

Author Response

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Round 2

Reviewer 2 Report

After this revision, all my concerns have been addressed to a good-enough level.

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Reviewer 3 Report

The manuscript has been substantially improved. I only ask for two minor corrections:

1. The objectives of the work need to be clearly stated at the end of the Introduction
2. Do not cite specific Figures or sections in the Conclusions.

Author Response

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