Testing and Analysis of Uniaxial Mechanical Fatigue, Charpy Impact Fracture Energy and Microhardness of Two Low-Carbon Steels

Round 1

Reviewer 1 Report

Dear authors

The research work is well prepared and presented. Matric research is always useful for science and industry. I have no comments on the paper and the form of presentation. Editorial comments, e.g. notations in tables and bold designations, are left to the Editor.

Best wishes

Reviewer

Author Response

The authors would like to thank the reviewer for the comments that contributed to the improvement of the quality of the article, and responded to those comments as best as possible.

 

Author Response File: Author Response.pdf

Reviewer 2 Report

Dear author.

The presented article is rather chaotically written, it seems to me as if the individual parts were taken out of a textbook on the mechanical properties of low-carbon steels and not a scientific article.

The introduction does not provide sufficient information about the topic you subsequently address in the article. There are also typos in the text. It seems unnecessary to use italics to such an extent to highlight the text. In that sense, it feels like a textbook rather than a scientific article.

In the section "Basic data on experimental research“, there is an exact text - directly marked in the article. The formatting of the table is confusing and the Fe content is missing.

For example, the entire chapter 3.2 would rather belong in the Introduction and not in the "Experimental results and discussion" section. There are few real results. And to refer to a figure that is published in other literature, let's say that it can be, but it is confusing for the reader, specifically, ......the obtained diagram representing the impact fracture energy CVN versus temperature may have one of the shapes shown in Fig. 14 in Ref. [19].). Section 3.2.1 discusses the CE carbon equivalent, in what sense is this important to the article? If the article deals with the fatigue properties of weldable steels and welds, then yes, it makes sense, but there is no mention of weldable steels in the Introduction or the title of the article, except that they are low carbon steels.....

Chapter 3.3.1 – General consideration – should be a brief introduction to the fatigue of structural materials. In that case, I would probably choose a different concept of dividing material fatigue into the so-called Manson-Coffin approach and the Wöhler approach. There is not even a mention of the individual stages of the fatigue process.... In this sense, the chapter is irrelevant to the reader, and for those who deal with the fatigue of materials, the information is known and insufficient.

In the same sense Ch. 3.3.1 is also written in chapter 3.3.2. This is all information that I would rather expect in the Introduction and not in the chapter about the experimental results..... Tables 2-6, I appreciate the number of experimental results, but the processing and form of their presentation are unsatisfactory and unclear. I am not even talking about formatting. It is common practice that parameters such as mean stress, load amplitude and cycle asymmetry parameter R are important for the fatigue process. Description in the style given in Tab. 2-3 is, let's say, non-standard and strange ...

Chap. 3.4 Hardness testing – inappropriately chosen heading, because in the text you describe microhardness according to Vickers with a load of 0.025g. Again, there are typos here, once the microhardness is HV0.025 and then HV0.052? Where did the second value come from? Fig. 4 is beyond description.....

In the "Fracture surfaces" section, I would also like pictures of the fatigue crack initiation sites. What was the mechanism of initiation? From the surface, or subsurface particles? Fatigue crack initiation is an important parameter from the point of view of the total fatigue life since up to 60% of the total fatigue life is the number of cycles required for fatigue crack initiation. Crack propagation is already a question of plastic deformations at the front of the fatigue crack.....

For the EDS analysis part, I don't know what you mean by there are oxides in the steels. That is perhaps obvious. Why did you focus on the EDS analysis of these tiny particles? Did they have any significant effect on your experiment? If yes, please specify, if not, this section is useless in that regard.

Where is the discussion of the results?? Chap. 3 is called Experimental results and discussion, but I somehow miss the discussion of the obtained results.

Conclusions section: Charpy test - is it a well-known fact that steels with a BCC lattice have transit behaviour, what is your measurement new? It is known for BCC that the value of the fracture (toughness) energy changes and decreases with decreasing temperature. The interpretation of the results of the fatigue tests is confusing, it is not clear at what temperature the tests were carried out. It would probably be easier to describe the influence of the cycle asymmetry parameter R on the change in fatigue life ..... The hardness of the materials was not measured, but the microhardness, it is questionable whether the results of the microhardness measurement can be considered as the overall hardness of the material, since it is not clear, the microhardness of which phases (ferrite, pearlite) was measured.

Generally, the article is written without any significant concept. It is a mixture of brief information about low-carbon steels, but I miss a deeper analysis of the results and their practical significance. The authors write that these are widely used materials in engineering practice, so I would welcome more comprehensive and not fragmented information like this. The formatting is strange and the presentation of the results degrades their importance and meaning. The text is full of typos - marked in the text. 

For the above reasons: Reconsider after major revision

Comments for author File: Comments.pdf

Author Response

The authors would like to thank the reviewer for the comments that contributed to the improvement of the quality of the article, and responded to those comments as best as possible.

Author Response File: Author Response.pdf

Reviewer 3 Report

 

The manuscript “Testing and analysis of uniaxial mechanical fatigue, Charpy impact fracture energy and hardness of two low carbon steels” describes the results of basic experimental tests of common structural steels realized according to selected standards. Considering the range of studies and standard implementation, it should be assumed that novelty/originality is low, especially as selected experimental results have been published in Ref. [6, 7].

General comments:

1. The manuscript provides statements relating to basic engineering knowledge (e.g., Sections 3.1, 3.2, 3.3.1, 3.4).

2. The phrase "fatigue limit," although used, is imprecise. In the range of very high fatigue cycles, the failure below the knee point ("fatigue limit") has been confirmed. Please see the paper:

Sonsino CM. Course of SN-curves especially in the high-cycle fatigue regime with regard to component design and safety. International Journal of Fatigue 2007;29(12):2246–2258. https://doi.org/10.1016/j.ijfatigue.2006.11.015

3. The experimental data are approximated by deterministic models (linear regression) for the selected failure probability. The approach is recommended for engineering calculations. The model does not provide data scatter analysis, including the prediction of fatigue life/strength for variable failure probability.

Detailed comments:

4. Page 2, line 48: Add an explanation for each auto-cited reference [4, 5].

5. Page 3, lines 125-138: Repeated text.

6. Page 5, Fig. 1: No marking in figures a), b).

7. Page 6, Fig. 2: The figure requires detailed comments - the discussion of the results, the data approximation used.

8. Page 8, lines 300, 302: Mark Eq. (3).

9. Page 10, Fig. 3: Specify the frequency of the loading change.

10. Page 10 line 421: Clarify the statement „… due to differences in cross-sectional dimensions…”.

11. Page 11, 16, lines 438-447, 533-540: The references [41-45, 48-50] are not directly related to the manuscript subject.

12. Page 12-13, Tables 5, 6: Describe the algorithm for determining the “fatigue limit” concerning the included data in Tables 5, 6.

13. Page 12: Table 5, Eq (3) – Check the marking Eq. (3) – lines 300, 302.

14. Page 13, Fig. 4: No figure caption.

15. Page 14, lines 482-483: Point out the results of your studies or references. If your studies have been completed, provide the statistical measures to support the statement.

16. Page 14, lines 499-504: The repetition of information is pointless.

17. Page 16-17, Fig. 7, 8: It would be useful to add a photo of the entire cross-section with the zoom areas from Figs. 7, 8 marked.

18. Page 18, lines 577-578: Specify the measure determining the BCC crystal structure.

19. Page 18, lines 580-584, 591-592: The statements can be classified as Summaries, not Conclusions.

 

Author Response

The authors would like to thank the reviewer for the comments that contributed to the improvement of the quality of the article, and responded to those comments as best as possible.

Author Response File: Author Response.pdf

Reviewer 4 Report

Dear respected author

The present work includes esults of experimental tests performed on two non-alloy low-carbon steels (1.1141 and 1.0122) in cases of their exposure to impact fracture energy and uniaxial high cyclic mechanical stress controlled fatigue. This is an exciting topic and may improve the knowledge in this regard. However, several points to be considered by the author may improve the level of the manuscript significantly. Such points are addressed as follows:

1.       When discussing the present work, use the (active or passive) present perfect or simple past tenses. Please, check the manuscript thoroughly.

2.       The introduction section should be improved.After mentioning the objectives of the study in "Introduction" section, please provide significance of this study in engineering sector.

3.       What is original, and what is significant about this work? Deep discussion are needed.

4.       There are many grammar mistakes. It should be revised.

5.       Fig5-Fig10 must be detailed.

6.       Provide a view of the real tests used in the considered experiment data.

7.       Provided discussions on the results is not enough.

8.       Please re-upload all figures at least 300 dpi.

9.       Include a table summarizing all test results and damages.

10.   The conclusion section needs to be re-written by incorporating general conclusions from the findings of this research. Please point out the novelty of this research article in this section. % are needed.

 

11.   What is the lesson learned? Please clarify before acceptance. 

Author Response

The authors would like to thank the reviewer for the comments that contributed to the improvement of the quality of the article, and responded to those comments as best as possible.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Dear authors.

Your article shows improvement but still has formatting errors.

Again, Tables 2-6 have a different format. Once they are centred on the left, then on the centre, both columns and rows have a special shape. It is necessary to unify these tables and put them in a uniform format.

Figure 4, its position, or embedded in the text should be handled differently so that the text does not wrap around the image. Also the description of the picture... "Figure 4. Mrohardness test: C15E+C and S235JRC+C steel alloys" should be Microhardness test.....

Chapter 3.5 - sometimes you use a dot to separate the number of cycles, other times the values are without a separator, please unify the style. "C15E+C material was failed at 1,527,527 cycles, while S235JRC+C material was failed at 352,348 cycles" (rows 674-675)....... "Number of cycles to failure (fracture) was: 352348 cycles (S235JRC+C); 1527527 cycles (C15E+C)" (rows 695-696 in Fracture surfaces section).

In the "Conclusions" section, please remove the error, two dots at the end of the sentence (row 787) ..... "high-cycle mechanical fatigue tests.. The details that character". What is the meaning of the added sentence at the conclusions ....." In this case, if the unit cell edge length is "a" and the atomic radius "R", then the measure "a = 4R/√3." ??? even with different font sizes, is this sentence important in context when, for example, I don't know the atomic radius of Fe? Furthermore, this relationship only applies to a BCC lattice (as you correctly point out) and can easily be derived from the volume of a cube …. I don't think this sentence is important to the article….

Concerning the adjustments made, but the remaining shortcomings, my recommendation is:

Accept after minor revision (corrections to minor methodological errors and text editing)

Author Response

The authors would like to thank the reviewer for the given remarks that affect the improvement of the quality of the article. In this sense, the authors hope that with their answers and the changes made, they have achieved improvements that can satisfy the ideas of the reviewer.

Author Response File: Author Response.pdf

Reviewer 3 Report

The authors do not provide manuscript revision, detailed for comments 1, 2, 3, 7. Please point out (lines) the corrections to each comment.

Author Response

The authors would like to thank the reviewer for the given remarks that affect the improvement of the quality of the article. In this sense, the authors hope that with their answers and the changes made, they have achieved improvements that can satisfy the ideas of the reviewer.

Author Response File: Author Response.pdf

Reviewer 4 Report

 Accept in present form

Author Response

The authors would like to thank the reviewer for the given remarks that affect the improvement of the quality of the article. In this sense, the authors hope that with their answers and the changes made, they have achieved improvements that can satisfy the ideas of the reviewer.

Author Response File: Author Response.pdf

Round 3

Reviewer 3 Report

No more comments.