Strain Induced Surface Change in Sheet Metal Forming: Numerical Prediction, Influence on Friction and Tool Wear

Round 1

Reviewer 1 Report

This manuscript presents experimental and numerical findings on the strain-induced roughening of the sheet metal surfaces.

The topic is reasonable with convincing results. The results are well interpreted. However, there are some clarifications needed before it is accepted for publication.

The manuscript is not easy to follow. In figure 4 the authors present the distribution of the displacement. However, the details of the FE-based model (elements, material model, material properties, etc.) have not been specified. According to the Instructions for authors "Material and Methods should be described with sufficient detail to allow others to replicate and build on published results."

It is suggested to add section Material describing the properties of the materials tested.

Figure 6: Why were the simulation results validated based on Sz instead of St (Fig. 5)?

line 259. Why was the pressure value of 2.5, 5 and 7.5 MPa selected?

Fig. 3b, 4-6, 8, 10, 11-13, 15, 18, 19, 23. In numbers, commas should be replaced with dots.

Section 4.1: Similar to section 2.1, the authors did not provide sufficient data for the numerical model: element type, mesh size (mesh sensitivity), material model (isotropic, anisotropic?), strain hardening type (if applicable), friction model, coefficient of friction (constant in all surfaces or not ?) etc.

When a cited work has three or more authors, the first in-text citation should consist of the first author followed by "et al.".

I found a lot of typos in the main text and figures.

Author Response

We have read the reviewer’s comments with great interest and are grateful for the advices that contribute to the improvement of the manuscript. The explanations and corresponding notes on the changes made in the revised version are described below. The modifications in the manuscript are highlighted in yellow.

Comments and Suggestions for Authors

This manuscript presents experimental and numerical findings on the strain-induced roughening of the sheet metal surfaces.

The topic is reasonable with convincing results. The results are well interpreted. However, there are some clarifications needed before it is accepted for publication.

The manuscript is not easy to follow. In figure 4 the authors present the distribution of the displacement. However, the details of the FE-based model (elements, material model, material properties, etc.) have not been specified. According to the Instructions for authors "Material and Methods should be described with sufficient detail to allow others to replicate and build on published results."

It is suggested to add section Material describing the properties of the materials tested.

In section 2.1, Table 1 is added for offering more information about the parameters for the material model. The procedure of the subroutine is too lengthy to list in this paper, thus a reference is given for further information of the potential readers. The information of element is also specified (highlighted in yellow).

Figure 6: Why were the simulation results validated based on Sz instead of St (Fig. 5)?

Thanks for this comment. The Sz is a typing error in the diagram. The validation is based on St (the maximal peak value of the sample surface). The figure is changed in the revised version.

line 259. Why was the pressure value of 2.5, 5 and 7.5 MPa selected?

It is dependent on the strip drawing test machine. The normal force of strip drawing test is supplied by the hydraulic cylinder. For a stabilization of blank holder speed, a back pressure in the hydraulic system is needed and the minimal hydraulic force is about 7800N, which corresponds to 2.5MPa for a contact area of 78mm x 40 mm. When the contact area is over 8 MPa, a plastic deformation for material DC06 can be observed. That’s why we selected these three pressure values. An explanation is added in the revised manuscript.

Fig. 3b, 4-6, 8, 10, 11-13, 15, 18, 19, 23. In numbers, commas should be replaced with dots.

The commas in numbers have been replaced with dots in the revised manuscript.

Section 4.1: Similar to section 2.1, the authors did not provide sufficient data for the numerical model: element type, mesh size (mesh sensitivity), material model (isotropic, anisotropic?), strain hardening type (if applicable), friction model, coefficient of friction (constant in all surfaces or not ?) etc.

The element type, mesh size, material model, friction model and coefficient of friction are specified in section 4.1 in the new version of manuscript.

When a cited work has three or more authors, the first in-text citation should consist of the first author followed by "et al.".

The authors of cited works are revised in the new version.

I found a lot of typos in the main text and figures

The spelling is double checked in the revised version.

Reviewer 2 Report

The paper presents three major issues, surface roughness prediction by computational method, effect of pre-strain on the friction coefficient and wear behavior. The strength of the paper is very comprehensive study on the above mentioned topic. However, the paper can be improved by considering the following points.

• First, in the first topic, the simulation is done for the 3D microstructure but the grain configuration through the thickness has not been considered. In this study, the approach seems to be quasi-3D model. The reviewer wonders if there is not effect of interactions among grains through thickness. There have been modeling of the crystal plasticity in consideration of serial sectioning for constructing realistic microstructure for both in-plane and through thickness grains.
• Second, the paper is well-written, but the organization is somewhat complex. In fact, the three topics are not well related. Some parts of experimental analyses are independent and the results of previous topic does not quantitatively utilized.
• In general, the manuscript is too lengthy. Authors are suggested to shorten the article by removing already well-known facts.

Author Response

The paper presents three major issues, surface roughness prediction by computational method, effect of pre-strain on the friction coefficient and wear behavior. The strength of the paper is very comprehensive study on the above mentioned topic. However, the paper can be improved by considering the following points.

• First, in the first topic, the simulation is done for the 3D microstructure but the grain configuration through the thickness has not been considered. In this study, the approach seems to be quasi-3D model. The reviewer wonders if there is not effect of interactions among grains through thickness. There have been modeling of the crystal plasticity in consideration of serial sectioning for constructing realistic microstructure for both in-plane and through thickness grains.

We have cited a reference [28] of Panin, who identified that the first layer plays the more important role on the surface roughening (highlighted in yellow). As a result, only the first layer of our approach is modeled as real crystal structure. The citing and the description have already been described in first passage of Section 2.1.

• Second, the paper is well-written, but the organization is somewhat complex. In fact, the three topics are not well related. Some parts of experimental analyses are independent and the results of previous topic does not quantitatively utilized.

In general, the manuscript is too lengthy. Authors are suggested to shorten the article by removing already well-known facts.

Thank you very much for the suggestion. Overall, the material selection makes this paper lengthy and the structure complex. But from our point of view it is reasonable to combine the three topics, cause in this way friction and wear behavior after a pre-straining process is covered holistically.