Investigation of the Thickness Differential on the Formability of Aluminum Tailor Welded Blanks

Round 1

Reviewer 1 Report

Dear Authors. You've done tons of experiments to organize your knowledge of tailor welded blanks. This is a valuable aspect of this publication. However, it was necessary to look a bit more at the available sources of knowledge. The research on the deformability of TWBs has been carried out for over 20 years, which is not mentioned in your article here. Testing the effect of thickness variation on the effects in the spherical punch bulge test is essential. I am not surprised by your choice of a model study. However, I have the impression that the purpose of the presented research was to demonstrate the usefulness of the latest version of the Forge NxT software for modeling TWBs deformability and the Aramis vision system for the measurement of deformation after stamping tests.

To make your work more perfect, I propose to improve it a little more in range of:

- supplementing the data from the literature on the use of the LDH test for testing TWBs deformability,

- explain why did you test LDH @ 18%, 22.5% and 34% fracture strain?

-what is the difference between fracture strain and effective strain looking on table 3 and table 4 and fig. 5 page 6-7?

- which of the tested TRs will be the LTR?

-what values ​​are the normalized effective strain and normalized LDH value that are proposed (and please explain to me the idea of ​​Figure 7 page 8 than).

It's a bit hard to compare the images from Aramis and the simulation results from cross-sections, is it impossible to standardize it somehow? Either a graph or a distribution?

From the experience known to me, the deformability of TWB is determined by the properties of a thinner or structurally weaker sheet. Are you not observing the same phenomena by accident? Maybe You can match the LTR to this.

Supplementing the paper in the indicated scope will increase its readability and its value. I believe that after the improvement, this work can be published.

Author Response

Point 1: - supplementing the data from the literature on the use of the LDH test for testing TWBs deformability,

Response 1:

References [10]-[12] are added to the introduction to reflect the current state of the art. Limiting Dome height test is the formability characterization method of tailor welded blanks in these references.

 

Point 2:- explain why did you test LDH @ 18%, 22.5% and 34% fracture strain?

Response 2: Fracture criterion is not defined in the simulations, so we set 18%, 22.5% and 34% as criteria for evaluation the LDH value. It is not possible to hit whole numbers each time in the experiment, but we were close.

Point 3:-what is the difference between fracture strain and effective strain looking on table 3 and table 4 and fig. 5 page 6-7?

Response 3: Effective strain (in the revised version is changed into equivalent plastic strain) is the output variable in our simulation. Fracture strain is the fracture criterion defined to obtain the LDH value. When the effective strain exceeded the fracture strain, the critical displacement of the punch is defined as the LDH value.

Point 4:- which of the tested TRs will be the LTR?

Response 4: What we concern is the thickness differential on the formability of tailor welded blanks. Two thickness ratios are discussed in this paper.

 

Point 5:-what values are the normalized effective strain and normalized LDH value that are proposed (and please explain to me the idea of Figure 7 page 8 than).

Response 5: Normalized effective strain = effective strain/thickness differential

Normalized LDH = LDH/thickness differential

For example: When thickness ratio is 1.5:1, the effective strain is 0.217, thickness differential is 0.5. So the normalized effective strain is 0.434.

It means the rate of change of the effective strain and LDH with the thickness differential.

Point 6: It's a bit hard to compare the images from Aramis and the simulation results from cross-sections, is it impossible to standardize it somehow? Either a graph or a distribution?

Response 6: The strain obtained by Aramis is surface strain, so it is impossible to standardize the cross-section. What we called cross section is the surface strain cross a path from one side to the other side which can be seen in Fig. 3

 

Point 7: From the experience known to me, the deformability of TWB is determined by the properties of a thinner or structurally weaker sheet. Are you not observing the same phenomena by accident? Maybe You can match the LTR to this.

Response 7: You are exactly right that the formability of TWB is determined by the properties of a thinner or structurally weaker sheet. The LDH value obtained is a function of the thin side and also a function of the softening next to the weld.

Reviewer 2 Report

1. In introduction literature of FSW is not well discussed, so recent references to be discussed. In fact, limited numbers of references are used. So, I suggest to Refer: Experimental and numerical investigations of bonding interface behavior in stationary shoulder friction stir lap welding; Recent development in friction stir processing as a solid-state grain refinement technique: microstructural evolution and property enhancement; Formability of an AA5083 aluminum alloy T-joint using SSFSW on both corners.
2. There are good papers on friction stir welding published in Metals recently, so I suggest to refer and use in Introduction to make literature as state of art. Refer: https://www.mdpi.com/2075-4701/8/4/202, https://www.mdpi.com/2075-4701/9/3/270, https://www.mdpi.com/2075-4701/8/12/987.
3. Results must be discussed in more comprehensive manner

4. Provide firm conclusion of this study.

Author Response

Point 1: In introduction literature of FSW is not well discussed, so recent references to be discussed. In fact, limited numbers of references are used. So, I suggest to Refer: Experimental and numerical investigations of bonding interface behavior in stationary shoulder friction stir lap welding; Recent development in friction stir processing as a solid-state grain refinement technique: microstructural evolution and property enhancement; Formability of an AA5083 aluminum alloy T-joint using SSFSW on both corners.

Response 1: The following description “friction stir welding not only be a welding technique for lap welding、T-joint and butt welding, but also can be a grain refinement technique for different materials such as aluminum, magnesium, copper and steels” is added in introduction part of the paper. Three new references are implemented to address this concern [5-7].

 

Point 2: There are good papers on friction stir welding published in Metals recently, so I suggest to refer and use in Introduction to make literature as state of art. Refer: https://www.mdpi.com/2075-4701/8/4/202, https://www.mdpi.com/2075-4701/9/3/270, https://www.mdpi.com/2075-4701/8/12/987.

Response 2: The following description“As a solid state welding process, friction stir welding is considered as promising joining technique providing one of the best alternatives to fusion welding (such as laser welding) in order to produce a good combination of microstructure、mechanical properties and formability” is added in introduction part of the paper. Three references are added to respond to this suggestion [2-4].

 

Point 3: Results must be discussed in more comprehensive manner

Response 3: we have added some discussion on the section 3: Results and Discussion in which is written in red by Track Changes

 

Point 4: Provide firm conclusion of this study.

Response 4:  We nearly rewrote the conclusion section you can see in Section

Round 2

Reviewer 1 Report

Thanks to the Authors for improving the work in accordance with my suggestions and submitted responses for review. As a result, it has become more readable. Thus, the valuable results have become more appealing to the reader. The work also benefited from the expansion of information on previous results, which became the beginning of the presented research and analysis. Similarly, the addition of references to the publications of other Authors enriched the scientific value of the study.

My concern is also the description of formula (1), where we still have an "effective strain", and this is "von Mises equivalent stain rate". Please take a look at the explanations for this formula. Correct use of quantity descriptions from plasticity theory is very important in modeling.
Thanks to the extension of conclusions from the work, it has become more complete and scientifically valuable. Now, I can calmly accept this version of the work. I am asking only for minor editing corrections in the lines: 35- add "," 37, 41- add spce, 49 - reduce "ce.", 51- add "]", 75 - add ".", 86 - I think that results "are presented"; all "FORGE" should be converted to "Forge NxT" on lines: 100, 192, 198, 243.
 In table 2, "," is missing between "Elong" and "%".
After these cosmetic corrections, I can accept the work for publication in MDPI.

Reviewer 2 Report

Accept