Ductile Fracture Investigation of High-Strength Steel SM570 under Low Stress Triaxiality
Round 1
Reviewer 1 Report
The result of this paper is informative to the knowledge society for ductile fracture. The result of this paper can be understood in terms of the triaxility, and the result can be compared with other materials in terms of the term triaxility.
Please specify the terminology 'N-VG'.
Author Response
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Author Response File: 
Author Response.pdf
Reviewer 2 Report
The article deals with ductile fracture mechanism of SM570 steels under negative and low stress triaxiality using experiments and FE simulation and making a comparison with the previously studied behavior of SM490 steel. The research has been done thoroughly, and the results obtained are useful for engineering practice.
However, there are some points on which the authors should pay attention to before final acceptance:
1. The first of the two equations (7): please check the power exponent. Shouldn't it be a material characteristic?
2. The second equation: please include in the text more information about the determination of n=0.4 from the tensile test.
3. Table 1: Please use "tensile strength" instead of "ultimate stress".
4. Why do you use explicit analysis instead of implicit? Please justify in the text.
5. After using explicit analysis, what rate (mm/s) did you assign in ABAQUS?
6. Please specify the epsilon neck and sigma neck sizes in equations (7).
7. The Conclusion section largely repeats the summary. Please edit and make the conclusions more concise and clear.
Sincerely yours
Author Response
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Author Response File: Author Response.pdf
Reviewer 3 Report
Thanks for the manuscript!
The paper claims to investigate a ductile fracture behaviour of high-strength steel SM570 under low-stress triaxiality, while the samples were designed with both symmetrical and asymmetrical notches. A numerical model has been established in ABAQUS software, and the results of the simulation were compared with experimental test results.
The topic of the article fully corresponds to the journal scope. In my opinion, the state of the art, the methodology of the research, the results, as well as the discussion sections are well organized and at a good scientific level. I consider it publishable after major revisions. Please include all answers to the following comments in the manuscript:
11. It would be reasonable to describe the production/preparation of the samples (since it can influence the properties of the samples and the results), e.g.:
a. From which semi-finished product/what technology were the samples made?
b. If the samples were made from sheet metal, was the homogeneity of the structure/properties checked, ...
c. Was the semi-finished product/samples heat treated? (Probably not but please, indicate it in the manuscript).
d. If the samples were made from sheet metal, what was the orientation of the sample with respect to the direction of rolling, also ... how the notches were made and how their accuracy was checked? ...
22. How many identical samples with the same type of notch (for repeatability of experiments) were tested? Are the results reported in the article for notched samples average? Were the results statistically processed?
33. Please, add the next boundary conditions of FEA:
a. Was the FEM model set up as the elastic linear model or was the analysis nonlinear?
b. What were the Poisson number, Young´s modulus, sizes of the elements, etc? ...
c. In a selection of the mesh size and a number of nodes in FEA, the convergence of the results should be considered for appropriate selection of the element size which is absent in the meshing section). Was a sensitive analysis done?
d. Finally, in my opinion, the FE simulation results are not rich enough, so please add some simulation results pictures.
44. Provide an expert discussion on the possible root causes of the resulting errors for symmetrical notches for angles of -30° and -45° (-26.64 % and -31.06 % errors, Table 4). These are really big differences when using the N-VG model.
55. All formulas not developed/derived by the authors should be completed with a literary source.
56. Conclusions should be more specific.
Author Response
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Author Response File: Author Response.pdf
Round 2
Reviewer 3 Report
I have thoroughly studied the improved article and the authors' reactions. In my opinion, the authors responded sufficiently to the reviewers' comments, and the manuscript reached the required level so, in my opinion, the article is worthy of publication as it is.
This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.
Round 1
Reviewer 1 Report
The article aims to clarify experimentally the ductile fracture mechanisms of high-strength steel SBHS500 and SM570 under low-stress triaxiality. Symmetric shear (SYM-Shear) specimens and asymmetric shear (USYM-Shear) specimens were designed with 7 different notch angles and subjected to monotonic tensile loading.
The subject matter of the manuscript is within the scope of the journal and worthy of investigation.
The article is well written as well as readable. It provides a very nice and comprehensive study presenting interesting results, while its novelty is assured by the investigated materials and the applied approach. I evaluate the article positively, but in my opinion, some improvements should be done before the manuscript publishing.
They are:
- Provide a better theoretical basis related to failure and fracture mode, as well as crack propagation in the notches associated with the design of the notches used in the presented experimental study.
- Provide topological data and dimensions as well as pictures of the samples for testing the base materials whose curves are shown in Figure 2 (despite the fact that they were described in more detail in a previous, already published study, as not all readers have immediate access to the study).
- Provide information on how the notches were made and whether (if yes, how) their accuracy has been checked.
- Provide conclusions for real practice with regard to the investigated types of steels and discussed fractures/failures.
Author Response
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Author Response File: Author Response.pdf
Reviewer 2 Report
This study purely resort to experiment to investigate fracture of high-strength steels under low stress triaxiality. I don't know how much the findings of the authors contribute to the contemporary knowledge society,
where the fracture behavior is understood in terms of the stress state (e.g., triaxiality and Loade parameter) characterized via the simulation of the fractured structures used in the 'experiment' like the specimens of the current study. Because no stress state is characterized (quantified via simulation) in this paper, the contribution to the knowledge society is believed to be marginal. The current reviewer recommend to resubmit after analyzing the experimental result in terms of stress state quantified via appropriate simulation.
The authors may further consider following points for future revision.
-In Introduction, please explicitly address the reason why investigating the fracture behavior especially at low triaxialities is important.
-Please define the angles in the diagrams of Figures 3 and 4. Please eliminate Non-English notations there.
-Please obtain accurate stress-strain curves for two types of the materials, and use the curves as the input for simulating the invested structures (specimens) herein.
Author Response
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Author Response File: Author Response.pdf
Reviewer 3 Report
The authors carried out a series of experiments to clarify the ductile fracture mechanism of high-strength steel SBHS500 and SM570 under low-stress triaxiality. The paper potentially contributes to the literature as it presents novel results of interest for both research and practice purposes. However, the paper required corrections and additions.
General report and comments:
- Line 31. The dot should be replaced by ‘:”.
- Line 33. The ‘von-Mises’ should be replaced by ‘Huber-Mises-Hencky (HMH)’.
- Line 39, 48. ‘…steel SM490.’, ‘SBHS500’ Please add a reference to the standard (JIS G3106 [?]) according to the steel denotation used.
- Line 66-67. Please add information about national standards and procedures applied during the tests. Please describe the equipment (laboratory test stand).
- Table 1. Please add mechanical properties given by the national standard and made a comparison with the laboratory test result.
- Table 1. It is not clear what is elongation (engineering elongation)? Please add an additional explanation. Is it an elongation (add units) in rupture?
- Table 1. Please specify the mean value and +/-SEM.
- Line 73. Please explain the denotation ‘ey’.
- Figure 2. Please unite figures 2a and 2b with load-displacement curves and add a new figure with the presentation of the stress-strain curves.
- Table 1 and Fig. 2a. Why for the SBHS500 steel only two results were given. Please refers to the national standard and give a guideline for the minimum number of test specimens.
- Line 78-91. Lack of information about the thickness of the prepared shear specimens. Please explain how technology/method was used to prepare/cut the shear specimens. Please also specify whether the chosen method could have an influence on the mechanical properties of the steel in the places of the cuts.
- Line 120. Please supplement information about the rate of grip displacement.
- Line 124. Red dash. Please correct the colour of the dash.
- Figure 7. Please increase the size of the graphs in the range of the presented curves.
- 7, 8 and 9. Please supplement curves on figures for each test. It should be two curves for all specimens types.
- Line 184-185. It should be added numerical table results for the maximum load and fracture failure.
- Figure 10. The results for the SM490 steel should be referred to by citations.
- Line 251. The discussion on obtained results should be extended.
- The ‘Result and discussion’ section is more like a project report, not a scientific paper, but I still appreciate that the valuable data are provided. I hope the authors can try to get more scientific conclusions from the performed experiments.
- A greater effort should be done in the conclusion chapter. Additionally, there should be closing remarks after the points of conclusion, keeping in mind all the outcomes obtained.
Author Response
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Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
Purely experimental mechanical test study is admissible when the test result is correlated with micorstructure. It is also admissible when the test result is modeled using analytical model. No studies in the references of the current manuscript carried out mechanical test (especially fracture) studies without simulation except for the above two cases. Among the references, only the authors' previous study in the current journal (Reference [18]: Metals, 2022, 12(4): 672) reported a phenomenological report of the mechanical test result without simulation. The current manuscript also follows the same methodology.
The findings herein and Reference [18] are dependent on the triaxiality, Lode angle, and anisotropy of the material (microstructure). The reviewer does not feel interest in this phenomenological report of the mechanical test result in terms of the angles in Fig. 4 and 5 of the current manuscript, unless the angles are correlated with the triaxility and Lode parameter values near the fracture strain, which can be obtained via simulation.
The authors carried out simulations in the past (References [13] and [14]). Simulation-supported part can be added to each type of the materials, and prepare two manuscripts for each material type, both of which may receive immediate interest.
Reviewer 3 Report
I recommend the paper "Experimental study on ductile fracture of high-strength steels under low stress triaxiality” for publication.
