A Fast Identification Method of Yield Strength of Materials Based on Bending Experimental Data

Round 1

Reviewer 1 Report

The manuscript presents a procedure to identify the yield stress of metals through bending tests. The manuscriopt is well written and the method sound. The discussion is also adequate.

However, in my opinion the topic is quite outdated. It is well known that the yield stress and indeed even the material stress-strain curve may be identified from bending tests. Hence I wonder if the paper has much value for researchers, although it may be interesting for practicioners and as a discussion of the alternative method.

Author Response

Point 1: However, in my opinion the topic is quite outdated. It is well known that the yield stress and indeed even the material stress-strain curve may be identified from bending tests. Hence I wonder if the paper has much value for researchers, although it may be interesting for practicioners and as a discussion of the alternative method.

Response 1：

   The real stress of material can be calculated by dividing the value of tensile load with the real cross-sectional area. The experimental results show that there is a correlation between the bending yield load and the yield strength of material, which is not same with that the result obtained from uni-axial tensile test. Therefore, it is necessary to determine the scientific mechanism of the corresponding relationship through experiments and simulations, which is one of the scientific values of this paper.

   During the bending process, the nonlinear transition can be observed from the measured load-displacement curve when the material shows yield behaviour. The characteristics of the curve in this stage are related to the geometric dimensions of the punch fillet and other geometry of the bending device. In this paper, the influence of these factors on the characteristics of the transition curve has been studied, and a suitable mold geometry have been determined to get the nonlineatr transition curve which can reflect the yield characteristics obviously.

   The yield strength of materials has an effect on many properties of materials, such as the fatigue design of stamping parts, the springback calculation of forming process, the determination of subsequent yield of materials, etc. How to evaluate the yield strength of material objectively is of great significance. Judging yield by uniaxial tensile data will change with the subjectivity of the tester. To solve this problem, this paper presents two innovative evaluation algorithms, which can effectively avoid the influence of subjectivity of testers on the determination of yield strength, which is very helpful for scholars to objectively evaluate the yield strength of materials.

   The shape of the test piece on bending deforming is simple, and it can be easily tested online. If these algorithms are available, online sensors can be made to test the yield properties at any time. For example, after the austenization of boron steel and quenching on the die, the material properties will have a certain dispersion. The bending test method in this paper can be used to form a closed-loop feedback control model, so the die temperature, heating time and holding time can be adjusted online to realize the process parameter self-learning, which also provides a new idea of process control for hot stamping researchers.

Author Response File: Author Response.pdf

Reviewer 2 Report

Line 109: “Many scholars use the Ramberg-Osgood model…” – please provide some references

There are some deviations from the journal template (figures caption, references – names of the journals are not abbreviated).

The authors should elaborate upon the deviation results of experimental materials. Assumptions as “… are all below 4%, which can meet many technical and industrial requirements” should be backed up by some examples.

Author Response

Point 1: Line 109: “Many scholars use the Ramberg-Osgood model…” – please provide some references

Response 1: For Ramberg-Osgood model, the reference about this model has been added.

Point 2: There are some deviations from the journal template (figures caption, references – names of the journals are not abbreviated).

Response 2: Referring to the journal template given by the website, the caption of figure and the journal name in the reference have been modified respectively, and the modified part has been updated to the latest revision.

Point 3: The authors should elaborate upon the deviation results of experimental materials. Assumptions as “… are all below 4%, which can meet many technical and industrial requirements” should be backed up by some examples.

Response 3: 

For example, the determination of yield parameters of materials is important for the control of bending rebound, but the performance of plates will fluctuate with different batches and turns. The yield fluctuation of some high-strength steel plate is greater. If the yield parameters of plates are measured in advance by feed-forward method, the rebound can be compensated. The rebound is positively related to the stress. If the actual performance fluctuation is 10%, the application of this method can reduce the fluctuation of at least 6%, and the rebound is also reduced by 6%, which can significantly improve the product consistency.

In the hot stamping process, after the austenization of boron steel and quenching on the die, the material properties will have a certain dispersion, which will cause the performance change of more than 4% in the part. The bending test method in this paper can be used to form a closed-loop feedback control model, and the die temperature, heating time and holding time can be adjusted online to realize self-learning of process parameters to control the consistency of parts.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

I had concern about the suitability of the paper for the journal, becuase there is little novelty in the paper from a scientific standpoint. However, it is a well written paper with a discussion of interest for practicioners. Then, if the Editor finds the paper suitable for the journal, it can be accepted as is.