Effect of Foreign Object Damage on the Fatigue Performance of Stainless Steel Blades Under Pre-Corrosion Conditions

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

It is a very interesting paper combining fatigue with object impact and corrosion. It has a real application in turbine blades of aeroengines.

Main critical points:

Page 18 (Line 490-504): I not totally agree with your results: It’s true that the average fatigue limit (50% failure) is decreasing with the corrosion. If you would look more practical on the results, you might see, that the fatigue limit (10% failure) is not changed or is increasing (statistical mistake). Therefore, in practical application (e.g. <1% failure) corrosion might be neglectable.

Page 13: Please add an important observation: The corrosion depth grows in the first 24 strong (about 1mm) and the next 24 hours … only about 0.3 mm.

 

Some further comments to the text:

Page 3 (Line 101-103): Please check which impact (edge or face-centered) has the larger fatigue limit. It can’t be the edge impact if the reduction of 55.8% is larger than that of the face-centered with 35.1%.

Page 3 (Line 128-130): The text is not clear: Here corrosion really increases the fatigue life?

Page 4 (Line 143-144): This is no complete sentence.

Page 5 (Fig. 2): Why further objects are shown if they are not used in this research.

Page 6 (Line 212): The equation is missing.

Page 7 (Line 217): ‘immersion’ or ‘accelerated’ in correlation to S_acc?

Page 8 (Fig. 4 and text): The excitation mechanism is not clear in the experiments.

Page 11 (Fig. 8): There are more than 3 results (Text on page 10, line 314) shown.

Page 12 (Fig. 10 also Fig. 14): The caption of the picture is poor visible due to grey background.

 

Some further formal comments:

Page 2: The whole page is one block. This is difficult to read.

Page 8 (Fig. 4): ‘in use’ instead of ‘in used’.

Page 9 (Tab. 2): ‘2mm’ instead of ’12 mm’; unknow symbol (not ‘,’) behind ’12 mm’.

Page 10 (Line 333): ‘the’ instead of ‘The’.

Author Response

Dear Reviewer:

Thank you very much for taking the time to review this manuscript. Please find the detailed responses below and the corresponding revisions/corrections highlighted/in track changes in the re-submitted files.

Responds to the reviewer’s comments:

Comments 1: Page 18 (Line 490-504): I not totally agree with your results: It’s true that the average fatigue limit (50% failure) is decreasing with the corrosion. If you would look more practical on the results, you might see, that the fatigue limit (10% failure) is not changed or is increasing (statistical mistake). Therefore, in practical application (e.g. <1% failure) corrosion might be neglectable. 

Response 1: Thanks for the Reviewer’s suggestion. We have improved the expression of experimental conclusions.

Comments 2: Page 13: Please add an important observation: The corrosion depth grows in the first 24 strong (about 1mm) and the next 24 hours … only about 0.3 mm.

Response 2: Thanks for the Reviewer’s suggestion. We have added this observation to the text, as shown in lines 370-372.

Comments 3: Page 3 (Line 101-103): Please check which impact (edge or face-centered) has the larger fatigue limit. It can’t be the edge impact if the reduction of 55.8% is larger than that of the face-centered with 35.1%.

Response 3: Thanks for the Reviewer’s suggestion. This is a clerical error, which we have corrected, as shown on line 103.

Comments 4: Page 3 (Line 128-130): The text is not clear: Here corrosion really increases the fatigue life?

Response 4: Thanks for the Reviewer’s suggestion. We have revised the English expression here to make the meaning clear. As shown in lines 130-132.

Comments 5: Page 4 (Line 143-144): This is no complete sentence.

Response 5: Thanks for the Reviewer’s suggestion. We have modified the English expression here to make the meaning clear and the structure complete. As shown in lines 143-146.

Comments 6: Page 5 (Fig. 2): Why further objects are shown if they are not used in this research.

Response 6: Thanks for the Reviewer’s question. We have modified the picture and added a description of the picture content, as shown in lines 177-179.

Comments 7: Page 6 (Line 212): The equation is missing.

Comments 8: Page 7 (Line 217): ‘immersion’ or ‘accelerated’ in correlation to S_acc?

Response 7、8: Thanks for the Reviewer’s suggestion. We have provided an answer to question 7,8. Based on the comments of another reviewer, we have condensed this part of the expression.

Comments 9: Page 8 (Fig. 4 and text): The excitation mechanism is not clear in the experiments.

Response 9: Thanks for the Reviewer’s suggestion. We have added the fatigue loading conditions as well as the applied stress levels in section 2.3.

Comments 10: Page 11 (Fig. 8): There are more than 3 results (Text on page 10, line 314) shown.

Response 10: Thanks for the Reviewer’s suggestion. Our statement here is not clear, and we have revised it in the original text, as shown in lines 286-287.

Comments 11: Page 12 (Fig. 10 also Fig. 14): The caption of the picture is poor visible due to grey background.

Response 11: Thanks for the Reviewer’s suggestion. We have modified it.

Comments 12: Page 2: The whole page is one block. This is difficult to read.

Response 12: Thanks for the Reviewer’s suggestion. We have broken down this paragraph. The work of domestic and foreign researchers is introduced respectively.

Comments 13: Page 8 (Fig. 4): ‘in use’ instead of ‘in used’.

Response 13: Thanks for the Reviewer’s suggestion. We have modified it.

Comments 14: Page 9 (Tab. 2): ‘2mm’ instead of ’12 mm’; unknow symbol (not ‘,’) behind ’12 mm’.

Response 14: Thanks for the reviewer's question. ‘12mm’ was an error, we have fixed it in the table and added content to make the table clearer.

Comments 15: Page 10 (Line 333): ‘the’ instead of ‘The’.

Response 15: Thanks for the Reviewer’s suggestion. We have modified it.

Reviewer 2 Report

Comments and Suggestions for Authors

This paper deals with an interesting topic related to aerospace industry, focusing on a specific material and its resistance to fatigue under corrosive conditions. The paper should be accepted following some minor revisions. Below are the comments about all the issues that need to be addressed. 

1. Abstract (lines 16,17) - Damage depending on the velocity and size is obvious and should not be mentioned as part of the results. This sentence should be moved before the previous. Real result contributions are reflected in the remaining sentences, about corrosion etc.
2. Introduction (line 26) - Not all stainless steels are necessarily of high hardness, but the one analusedin this paper is, so I suggest to add “13Cr” into the first sentence, to make it more specific.
3. Introduction (line 71) - Probably a typo, strain rate is given in incorrect units (seconds).
4. Introduction - considering the overall length of this section, as well as a very detailed literature review, I suggest that this chapter is divided into two, the second one being “Literature review”.
5. Materials and methods (lines 152,153) - It would be more evident if you provided metallography images, or at least a reference about this. Also, please provide the mechanical properties and cheimcal composition of 13Cr steel
6. Materials and methods (line 249) - number of cycles is displayes as 1x107 instead of 10⁷. If the original draft of the paper does not contain this error, please ignore the comment.
7. Results (line 423) - This sentence was already written in slightly different form in line 420. Is it necessary to mention this result twice in quick succession?
8. Conclusions - while the conclusion section does nicely summarize the obtained results, it should be expanded with the potential practical benefits of the presented findings. In addition, the authors could mention the future direction in which this research could go, if they intend to continue with the analyses of this particular topic.

Comments on the Quality of English Language

Some minor corrections should be made in terms of English, e.g. the authors occasionally repeat themselves in certain sentences. While there are no noticeable typos or grammar errors, some sentences could be written in a more clear manner.

Author Response

Dear Reviewer:

Thank you very much for taking the time to review this manuscript. Please find the detailed responses below and the corresponding revisions/corrections highlighted/in track changes in the re-submitted files.

Responds to the reviewer’s comments:

Comments 1: Abstract (lines 16,17) - Damage depending on the velocity and size is obvious and should not be mentioned as part of the results. This sentence should be moved before the previous. Real result contributions are reflected in the remaining sentences, about corrosion etc.

Response 1: Thanks for the Reviewer’s suggestion. We have modified it.

Comments 2: Introduction (line 26) - Not all stainless steels are necessarily of high hardness, but the one analusedin this paper is, so I suggest to add “13Cr” into the first sentence, to make it more specific.

Response 2: Thanks for the Reviewer’s suggestion. We have added it.

Comments 3: Introduction (line 71) - Probably a typo, strain rate is given in incorrect units (seconds).

Response 3: Thanks for the reviewer's question. There is a clerical error. We have corrected this in the text, as shown in line 71.

Comments 4: Introduction - considering the overall length of this section, as well as a very detailed literature review, I suggest that this chapter is divided into two, the second one being “Literature review”. 

Response 4: Thanks for the Reviewer’s suggestion. We have modified it.

Comments 5: Materials and methods (lines 152,153) - It would be more evident if you provided metallography images of materials, or at least a reference about this. Also, please provide the mechanical properties and cheimcal composition of 13Cr steel

Response 5: Thanks for the Reviewer’s suggestion. The Metallography images of materials we added is shown in Figure 2. The mechanical properties data of the material are added to Table 1, and Table 2 is added to show the chemical composition of the material.

Comments 6: Results (line 423) - This sentence was already written in slightly different form in line 420. Is it necessary to mention this result twice in quick succession?

Response 6: Thanks for the Reviewer’s suggestion. We have streamlined the content and removed redundant narratives.

Comments 7: Conclusions - while the conclusion section does nicely summarize the obtained results, it should be expanded with the potential practical benefits of the presented findings. In addition, the authors could mention the future direction in which this research could go, if they intend to continue with the analyses of this particular topic.

Response 7: Thanks for the Reviewer’s suggestion. We have added these in the Abstract section.

Reviewer 3 Report

Comments and Suggestions for Authors

Dear Authors,

Major remarks:

1. The paper is related to fatigue problems, however, fatigue loading conditions are completely not specified. The research design must be described in detail with an explanation of the loading conditions and stresses applied during the tests. The level of the applied stresses should be also compared with the fatigue properties of the investigated material.
2. Section 2.3. This part must be significantly revised and improved:
3. The fatigue loading is not specified at all.
4. Due to missing loading conditions and material properties, I am not able to assess the correctness of eq. (12).
5. Figure 5 – variables must be given in the descriptions of the axes.
6. How stress and displacement was measured?
7. How it was confirmed that the structure is in the elastic condition at the notch (eq 13)?
8. „Through formulas (12) and (13), the different times can be calculated, allowing for the determination of the actual stress value at the notch”- How different times and what Times can be calculated by these equations?
9. Subsection 2.1 – The chemical composition and material properties must be added (i.e.: tensile strength, the Yield limit, fatigue limits, etc.).
10. Section 2.4 and Table 2 – based on the information given in the paper it can be concluded that the information in the table is wrong (i.e. FOD = 12 mm). Check carefully all data and revise. The number of groups should be also given in Table 2. It is not clear what is the first category. This part must be revised.
11. Subsection 2.2.2 is too large and should be revised. In my opinion, it is not necessary to provide all these 11 equations. This part can be significantly shortened and improved.
12. Line 71 „When the strain rate is 3864 s” – check and revise.
13. Figure 9b - missing scale, the left hand-side is unreadable.
14. Line 354 „Fe3O4, Fe2O3” – check and revise.
15. Figure 10 – The description of the vertical axis should be improved (i.e. „content of elements in the surface layer”). Could you explain the increase of Fe content for corrosion time 24 and 48h?
16. Figures 11, 13 are blurred. Images should be provided with high quality.
17. Figures 12 and 18 „corrosion time” should be added in the horizontal axis description.
18. Lines 418-420 „The damage depth of FOD after 24 and 48 hours of corrosion was slightly greater than that observed without corrosion” Where are results for non-corroded samples shown?

 

Minor remarks:

13. The designation of the investigated steel should be unified in the whole paper.
14. Line 144 „Through modal analysis and dynamic stress testing, the blade's dangerous position is determined.” – the position should be shown in Figure 1 or the phrase should be given later in the text.
15. Table 1 – Units must be corrected.
16. Line 180 „through the experiment” – performed experiment or from literature?
17. Lines 106-107 „Therefore, scholars and researchers in the field of science and engineering at home and abroad have studied the problem of corrosion fatigue for a long time.” – phrase should be revised (home and abroad).
18. Figure 1 and text. Why did you use the name „simulated”?
19. Line 153 „13Cr15Ni4Mo3N stainless steel offers good corrosion resistance” – repeated information, see Line 151. It should be deleted.
20. Lines 211-212 „then the mass loss per unit area of the accelerated environmental spectrum test is:” – something is missing. Check and revise.
21. Line 249 „1×107 cycles,” typo.
22. Table 2 - check and revise commas.
23. Line 315 „the typical damage inflicted on steel balls” – It looks like a mistake. Rather „by steel balls”. Check and revise.
24. Section 3.2.2 – I recommend improving the text style.

Kind Regards,

Comments on the Quality of English Language

Grammar and style remarks:

1. Lines 106-107 „Therefore, scholars and researchers in the field of science and engineering at home and abroad have studied the problem of corrosion fatigue for a long time.” – phrase should be revised (home and abroad).
2. Figure 1 and text. Why did you use the name „simulated”?
3. Line 153 „13Cr15Ni4Mo3N stainless steel offers good corrosion resistance” – repeated information, see Line 151. It should be deleted.
4. Lines 211-212 „then the mass loss per unit area of the accelerated environmental spectrum test is:” – something is missing. Check and revise.
5. Line 249 „1×107 cycles,” typo.
6. Table 2 - check and revise commas.
7. Line 315 „the typical damage inflicted on steel balls” – It looks like a mistake. Rather „by steel balls”. Check and revise.
8. Section 3.2.2 – I recommend improving the text style.

Author Response

Dear Reviewer:

Thank you very much for taking the time to review this manuscript. Please find the detailed responses below and the corresponding revisions/corrections highlighted/in track changes in the re-submitted files.

Responds to the reviewer’s comments:

Comments 1: The paper is related to fatigue problems, however, fatigue loading conditions are completely not specified. The research design must be described in detail with an explanation of the loading conditions and stresses applied during the tests. The level of the applied stresses should be also compared with the fatigue properties of the investigated material.

Comments 2: Section 2.3. This part must be significantly revised and improved:

Comments 3: The fatigue loading is not specified at all.

Comments 4: Due to missing loading conditions and material properties, I am not able to assess the correctness of eq. (12).

Response 1-4: Thanks for the Reviewer’s suggestion. We have provided an answer to question 1,2,3,4. We have added the fatigue loading conditions as well as the applied stress levels in section 2.3.

Comments 5: Figure 5 – variables must be given in the descriptions of the axes.

Response 5: Thanks for the Reviewer’s suggestion. We have supplemented the explanation of the meaning of coordinate axes in lines 225-226 of the text.

Comments 6: How stress and displacement was measured?

Response 6: Thanks for the reviewer's question. The measurement methods of stress and displacement are explained in lines 210-213 and 218-219.

Comments 7: How it was confirmed that the structure is in the elastic condition at the notch (eq 13)?

Response 7: Thanks for the reviewer's question. In fact, in the high-cycle fatigue test of the blade, the fatigue limit of the notched blade is defined as the nominal stress at the notched position, that is, the stress value without considering the notched stress concentration. Therefore, the stress value determined by formula 13 is the stress value without considering the notched position, and the position is always in an elastic state.

Comments 8: „Through formulas (12) and (13), the different times can be calculated, allowing for the determination of the actual stress value at the notch”- How different times and what Times can be calculated by these equations?

Response 8: Thanks for the reviewer's question, we are not clear here, and we have explained it in detail in lines 232-239 of the paper.

Comments 9: Subsection 2.1 – The chemical composition and material properties must be added (i.e.: tensile strength, the Yield limit, fatigue limits, etc.).

Response 9: Thanks for the Reviewer’s suggestion. We have added relevant content to the article.

Comments 10: Section 2.4 and Table 2 – based on the information given in the paper it can be concluded that the information in the table is wrong (i.e. FOD = 12 mm). Check carefully all data and revise. The number of groups should be also given in Table 2. It is not clear what is the first category. This part must be revised.

Response 10: Thanks for the reviewer's question. ‘12mm’ was an error, we have fixed it in the table and added content to make the table clearer.

Comments 11: Subsection 2.2.2 is too large and should be revised. In my opinion, it is not necessary to provide all these 11 equations. This part can be significantly shortened and improved.

Response 11: Thanks for the Reviewer’s suggestion. We have streamlined section 2.2.2 to remove the redundant content.

Comments 12: Line 71 „When the strain rate is 3864 s” – check and revise.

Response 12: Thanks for the reviewer's question. There is a clerical error. We have corrected this in the text, as shown in line 71.

Comments 13: Figure 9b - missing scale, the left hand-side is unreadable.

Response 13: Thanks for the Reviewer’s suggestion. We have added a scale to the drawing.

Comments 14: Line 354 „Fe3O4, Fe2O3” – check and revise.

Response 14: Thanks for the Reviewer’s suggestion. We have corrected it, as shown in line 322.

Comments 15: Figure 10 – The description of the vertical axis should be improved (i.e. „content of elements in the surface layer”). Could you explain the increase of Fe content for corrosion time 24 and 48h?

Response 15: Thanks for the Reviewer’s suggestion. We have modified the vertical axis of Figure 10 and added the analysis of Figure 10, as shown in line3 329-334.

Comments 16: Figures 11, 13 are blurred. Images should be provided with high quality.

Response 16: Thanks for the Reviewer’s suggestion. But the sharpness of the image is limited by our three-dimensional stereo microscope.

Comments 17: Figures 12 and 18 „corrosion time” should be added in the horizontal axis description.

Response 17: Thanks for the Reviewer’s suggestion. We have added it.

Comments 18: Lines 418-420 „The damage depth of FOD after 24 and 48 hours of corrosion was slightly greater than that observed without corrosion.” Where are results for non-corroded samples shown?

Response 18: Thanks for the reviewer's question. We have added the data of non-corroded samples in the Figure 14.

Minor remarks:

Comments 19: The designation of the investigated steel should be unified in the whole paper.

Response 19: Thanks for the Reviewer’s suggestion. We have modified it.

Comments 20: Line 144 „Through modal analysis and dynamic stress testing, the blade's dangerous position is determined.” – the position should be shown in Figure 1 or the phrase should be given later in the text.

Response 20: Thanks for the Reviewer’s suggestion. The specimen shown in Figure 1 is a simulated blade designed by us according to the geometric and stress characteristics of the dangerous parts of the real blade.

Comments 21: Table 1 – Units must be corrected.

Response 21: Thanks for the Reviewer’s suggestion. We have modified it.

Comments 22: Line 180 „through the experiment” – performed experiment or from literature?

Response 22: Thanks for the Reviewer’s suggestion. It is the conclusion of other people's experiments, and I have added the references in the paper, as shown in line 186.

Comments 23: Lines 106-107 „Therefore, scholars and researchers in the field of science and engineering at home and abroad have studied the problem of corrosion fatigue for a long time.” – phrase should be revised (home and abroad).

Response 23: Thanks for the Reviewer’s suggestion. We have modified it, as shown in lines 106-108.

Comments 24: Figure 1 and text. Why did you use the name „simulated”?

Response 24: Thanks for the reviewer's question. Because the experimental object in this paper is designed according to the real blade and is not in service on the aeroengine itself, we call it the simulated blade.

Comments 25: Line 153 „13Cr15Ni4Mo3N stainless steel offers good corrosion resistance” – repeated information, see Line 151. It should be deleted.

Response 25: Thanks for the Reviewer’s suggestion. We have modified it, as shown in line 152.

Comments 26: Lines 211-212 „then the mass loss per unit area of the accelerated environmental spectrum test is:” – something is missing. Check and revise.

Response 26: Thanks for the Reviewer’s suggestion. We have made significant changes to this section, specifically in question 11.

Comments 27: Line 249 „1×107 cycles,” typo.

Response 27: Thanks for the Reviewer’s suggestion. We have modified it, as shown in line 205.

Comments 28: Table 2 - check and revise commas.

Response 28: Thanks for the Reviewer’s suggestion. We have modified it.

Comments 29: Line 315 „the typical damage inflicted on steel balls” – It looks like a mistake. Rather „by steel balls”. Check and revise.

Response 29: Thanks for the Reviewer’s suggestion. We have modified it, as shown in lines 282-284.

Comments 30: Section 3.2.2 – I recommend improving the text style.

Response 30: Thanks for the Reviewer’s suggestion. The text style in section 3.2.2 has been carefully reviewed and modified.

Reviewer 4 Report

Comments and Suggestions for Authors

This study investigated the fatigue performance of 13Cr stainless steel (engine blade material) subjected to pre-corrosion and FOD. There are many interesting results, but some problem areas are also found. I think the paper should be improved based on the following comments.

(1) Introduction, line 135:　

This study investigated the fatigue behavior of stainless steel materials that had been subjected to pre-corrosion and FOD. Stainless steel materials are not subjected to FOD in a corrosive environment. Therefore, if we write "the coupled effect of corrosion and FOD," readers will probably understand this to mean "subjected to FOD in a corrosive environment." Also, although it says "the damage law," the results of this study are limited to experimental observations and qualitative considerations, so the expression "the damage law" seems inappropriate.

(2) It would be easier for readers to understand if the term "foreign object damage" was used only at the time of the first appearance, and thereafter the term "FOD" was used consistently. Also, I think it would be better to standardize "corrosion" as "pre-corrosion" to prevent misunderstandings by readers.

(3) Is Figure 1(d) a right side view of 1(c)? Also, where is Figure 1(e) a cross-sectional view? An explanation is needed.

(4) Lines 151 and 153: The same content is written.

(5) Section 3.1.3 states that this material shows ductile damage due to FOD. In light of this, please add the yield stress and elongation values ​​of this material to Table 1.

(6) In Figure 2, what is the cylindrical test piece on the right? A specific explanation is needed for the figure. Other figures also lack specific explanations.

(7) The image on the left in Figure 4 has no scale.

(8) The "definition of corrosion depth" shown in Figure 6 (b) can be applied to general corrosion, but I think it would be difficult to apply to pitting corrosion. What do you think?

(9) The horizontal axis in Figure 10 is corrosion time (h).

(10) If Figure 11 included an explanation of corrosion pits, general corrosion, etc., it would be easier for readers to understand.

(11) Figure 12: It would be interesting to go beyond the discussion of data reproducibility and consider the relationship between corrosion pit depth and time t. For example, is the corrosion pit depth proportional to t, or does it follow a power law of t? It would be interesting to discuss this.

(12) Figure 13: What are the FOD test conditions?

(13) Figure 14: After 96 hours (or even 48 hours) of corrosion, the data for both width and depth of corrosion show large variations. I think it would be good to consider the reason for this.

(14) In Figure 15(a), can the reason why there is difference in deformation on the left and right of the dashed line be considered mechanically, for example, using Hertz's contact theory?

(15) Figure 18: The staircase method and other methods are used to determine the fatigue limit, but how was the fatigue limit determined in this study? Also, to show the fatigue resistance, how about showing the relationship between stress and fatigue life (S-N curve) since this would be easier to understand?

(16) In Figure 20: An enlarged view of Zone 1-Zone 3, it is thought that it would be easier for readers to understand if the direction of crack growth was indicated.

(17) Line 534: The phrase "under corrosive conditions" may lead readers to misunderstand that the blade is subject to FOD under a corrosive environment. It would be easier for readers to understand if you change the phrase to "a blade that has been pre-corroded."

Author Response

Dear Reviewer:

Thank you very much for taking the time to review this manuscript. Please find the detailed responses below and the corresponding revisions/corrections highlighted/in track changes in the re-submitted files.

Responds to the reviewer’s comments:

Comments 1: Introduction, line 135:

This study investigated the fatigue behavior of stainless steel materials that had been subjected to pre-corrosion and FOD. Stainless steel materials are not subjected to FOD in a corrosive environment. Therefore, if we write "the coupled effect of corrosion and FOD," readers will probably understand this to mean "subjected to FOD in a corrosive environment." Also, although it says "the damage law," the results of this study are limited to experimental observations and qualitative considerations, so the expression "the damage law" seems inappropriate.

Response 1: Thanks for the Reviewer’s suggestion. We have modified it, as shown in lines 134-136.

Comments 2: It would be easier for readers to understand if the term "foreign object damage" was used only at the time of the first appearance, and thereafter the term "FOD" was used consistently. Also, I think it would be better to standardize "corrosion" as "pre-corrosion" to prevent misunderstandings by readers.

Response 2: Thanks for the Reviewer’s suggestion. We have modified it.

Comments 3: Is Figure 1(d) a right side view of 1(c)? Also, where is Figure 1(e) a cross-sectional view? An explanation is needed.

Response 3: Thanks for the Reviewer’s suggestion. We have modified it.

Comments 4: Lines 151 and 153: The same content is written.

Response 4: Thanks for the Reviewer’s suggestion. We have modified it.

Comments 5: Section 3.1.3 states that this material shows ductile damage due to FOD. In light of this, please add the yield stress and elongation values of this material to Table 1.

Response 5: Thanks for the Reviewer’s suggestion. We have added it.

Comments 6: In Figure 2, what is the cylindrical test piece on the right? A specific explanation is needed for the figure. Other figures also lack specific explanations.

Response 6: Thanks for the Reviewer’s question. We have modified the picture and added a description of the picture content, as shown in lines 177-179.

Comments 7: The image on the left in Figure 4 has no scale.

Response 7: Thanks for the Reviewer’s suggestion. We have added it.

Comments 8: The "definition of corrosion depth" shown in Figure 6 (b) can be applied to general corrosion, but I think it would be difficult to apply to pitting corrosion. What do you think?

Response 8: Thanks for the Reviewer’s suggestion. According to the experimental results, corrosion damage of specimens in corrosion test is relatively uniform, which is general corrosion. Therefore, after the test, I chose to use corrosion depth to describe the severity of corrosion damage to the specimen.

Comments 9: The horizontal axis in Figure 10 is corrosion time (h).

Response 9: Thanks for the Reviewer’s suggestion. We have modified it, as shown in lines316-318.

Comments 10: If Figure 11 included an explanation of corrosion pits, general corrosion, etc., it would be easier for readers to understand.

Response 10: Thanks for the Reviewer’s suggestion. The corrosion damage results of all specimens were general corrosion, and no corrosion pits were found.

Comments 11: Figure 12: It would be interesting to go beyond the discussion of data reproducibility and consider the relationship between corrosion pit depth and time t. For example, is the corrosion pit depth proportional to t, or does it follow a power law of t? It would be interesting to discuss this.

Response 11: Thanks for the reviewer's suggestions. This paper focuses on the influence of foreign matter damage on fatigue properties of blades under pre-corrosion conditions, so the corrosion damage mechanism is not deeply considered.

Comments 12: Figure 13: What are the FOD test conditions?

Response 12: Thanks for the Reviewer’s question. the FOD test conditions are 3mm、200m/s.

Comments 13: Figure 14: After 96 hours (or even 48 hours) of corrosion, the data for both width and depth of corrosion show large variations. I think it would be good to consider the reason for this.

Response 13: Thanks for the Reviewer’s question. The damage width nearly matches that of the entire corroded area. The damage depth of FOD after 24 and 48 hours of pre-corrosion was slightly greater than that observed without pre-corrosion. We believe that this is due to the thinning of the leading edge of the blade caused by corrosion, and the thinner leading edge produces greater material loss under the impact of the steel ball, which is manifested as a larger damage width on the macro level.

omCments 14: In Figure 15(a), can the reason why there is difference in deformation on the left and right of the dashed line be considered mechanically, for example, using Hertz's contact theory?

Response 14: Thanks for the reviewer's suggestions. The difference in deformation and material loss on the left and right side of the dotted line is because it is difficult to ensure that the impact position is completely located in the center of the leading edge of the blade, and the impact Angle is difficult to ensure that the zero Angle is 100%, so different loss conditions on the left and right sides are generated.

Comments 15: Figure 18: The staircase method and other methods are used to determine the fatigue limit, but how was the fatigue limit determined in this study? Also, to show the fatigue resistance, how about showing the relationship between stress and fatigue life (S-N curve) since this would be easier to understand?

Response 15: Thanks for the Reviewer’s suggestion. We have provided an answer to question 1,2,3,4. We have added the fatigue loading conditions as well as the applied stress levels in section 2.3. And the fatigue test in this study is to explore the fatigue limit of the blade under the specified life (10⁷), so the S-N curve cannot be drawn.

Comments 16: In Figure 20: An enlarged view of Zone 1-Zone 3, it is thought that it would be easier for readers to understand if the direction of crack growth was indicated.

Response 16: Thanks for the Reviewer’s suggestion. We have added the direction of crack growth to the diagram.

Comments 17: Line 534: The phrase "under corrosive conditions" may lead readers to misunderstand that the blade is subject to FOD under a corrosive environment. It would be easier for readers to understand if you change the phrase to "a blade that has been pre-corroded."

Response 17: Thanks for the Reviewer’s suggestion. We have modified it.

Reviewer 5 Report

Comments and Suggestions for Authors

Dear Authors,

 

Your article shows an interesting experimental investigation on the effect of the impact of foreign objects on the fatigue performance of a 13Cr 533 stainless steel compressor blade under corrosive conditions. However, there are several aspects to improve such as:

• Line 32 - Why did you mention only Gobi (I know it is an example) and then after coma write desert? This part is confusing.
• In general, there are many abbreviations, which should be explained in a list at the beginning.
• Section 2 is entirely to improve, it is not clear and it is missing many information about methods. The first paragraph is vague, anti-damage performance, how if your paper concerns damage performance, obviously later on you can relate to this and propose the design method, at this stage it is not the object of your paper. You should write more about modal analysis and dynamic stress tests.
• Poor quality of the figures, especially 2 and 11.
• You should improve Fig. 1, it is chaotic and some parts are irrelevant such as part b).
• In paragraph (line 150), the qualities of the material are highlighted twice.
• Table 1, are you referring to your experimental data or are they cited from the literature?
• You say nothing about the numerical model, but show it in Fig. 3.
• How did you choose immersion time, is there any standard to follow?
• Please provide more information about fatigue test? What was the frequency?
• In my opinion, the number of specimens is too small to talk about the fatigue limit. We can see that in Fig. 18, the discrepancies are very large.

In general the paper is interesting; however, the way is written is chaotic and at many points unclear. It needs to be improved, especially in the aspect of readability.

Comments on the Quality of English Language

• English through the manuscript should be improved and corrected in many places. There are also some missing parts, such as: after the colon in line 212.
• We do not use abbreviations as in line 516.

Author Response

Dear Reviewer:

Thank you very much for taking the time to review this manuscript. Please find the detailed responses below and the corresponding revisions/corrections highlighted/in track changes in the re-submitted files.

Responds to the reviewer’s comments:

Comments 1: Line 32 - Why did you mention only Gobi (I know it is an example) and then after coma write desert? This part is confusing.

Response 1: Thanks for the Reviewer’s question. Because the engine serving in the Gobi and desert environment is more likely to inhale foreign objects, of which the Gobi environment is more serious, we will give priority to studying the engine blade damage in the Gobi environment.

Comments 2: In general, there are many abbreviations, which should be explained in a list at the beginning.

Response 2: Thanks for the Reviewer’s suggestion. There are two abbreviations involved in this paper, foreign object damage (FOD) and high cycle fatigue (HCF). In reference to your suggestion and the format requirements of the journal, we have detailed where the abbreviation first appears in the paper.

Comments 3: Section 2 is entirely to improve, it is not clear and it is missing many information about methods. The first paragraph is vague, anti-damage performance, how if your paper concerns damage performance, obviously later on you can relate to this and propose the design method, at this stage it is not the object of your paper. You should write more about modal analysis and dynamic stress tests.

Response 3: Thanks for the Reviewer’s suggestion. We have revised our statement to remove content that is less relevant to the study in this article.

Comments 4: Poor quality of the figures, especially 2 and 11.

Response 4: Thanks for the Reviewer’s suggestion. We have updated Figure 2, but the quality of specimen photos such as Figure 11 is limited by 3D stereoscopic microscopy.

Comments 5: You should improve Fig. 1, it is chaotic and some parts are irrelevant such as part b).

Response 5: Thanks for the Reviewer’s suggestion. We have corrected the contents of Figure 1 to remove part (b).

Comments 6: In paragraph (line 150), the qualities of the material are highlighted twice.

Response 6: Thanks for the Reviewer’s suggestion. We have modified it, as shown in line 152.

Comments 7: Table 1, are you referring to your experimental data or are they cited from the literature?

Response 7: Thanks for the Reviewer’s question. The data in Table 1 are the actual test data.

Comments 8: You say nothing about the numerical model, but show it in Fig. 3.

Response 8: Thanks for the Reviewer’s question. We have modified it.

Comments 9: How did you choose immersion time, is there any standard to follow?

Response 9: Thanks for the Reviewer’s question. According to the maintenance standards of modern fighter jets, most modern fighter jets generally adopt the standard of overhaul every ‌1200-2000 flight hours ‌, which is about 1.7-2.7 months. The initial design calendar life of a modern fighter aircraft is 20 years or 3,000 hours, whichever comes first. Based on a 3,000-hour calendar life, the engine's flight time is approximately 4.2 months. If a fighter jet flies 300 hours per year, a 20-year calendar life corresponds to 6,000 hours of flight time, or about 8.3 months. According to this, we determine the pre-corrosion time.

Comments 10: Please provide more information about fatigue test? What was the frequency?

Response 10: Thanks for the Reviewer’s suggestion. We have provided an answer to question 1,2,3,4. We have added the fatigue loading conditions as well as the applied stress levels in section 2.3. And the frequency information of the simulated blade is also added in Section 3.2.1.

Comments 11: In my opinion, the number of specimens is too small to talk about the fatigue limit. We can see that in Fig. 18, the discrepancies are very large.

Response 11: Thanks for the Reviewer’s suggestion. According to the provisions of HB 5277-2021, when using group test method, the number of samples in each group should not be less than 3. First with economic cost and time cost, we selected 3 samples per set. In addition, the large difference of test results is also due to the uncontrollability of the damage gap of foreign objects. Under the same impact condition, the shape of the notch is different, and the residual stress at the root of the notch is different.

Comments on the Quality of English Language

Comments 12: English through the manuscript should be improved and corrected in many places. There are also some missing parts, such as: after the colon in line 212.

Response 12: Thanks for the Reviewer’s suggestion. We have streamlined section 2.2.2 to remove the redundant content. At the same time, we also have solved these English language quality problems.

Comments 13: We do not use abbreviations as in line 516.

Response 13: Thanks for the Reviewer’s suggestion. We have modified it.

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

Dear Authors,

Major remark:

1. Line 240 “The test continues until the specimen fails in less than 107 cycles.” Is the test made for the same sample that was subjected to HCF fatigue loading with lower maximal stress? If yes how were the damage level of the previous loading evaluated and fatigue strength calculated? Each stress cycle affect the structure of the object and introduce micro-damages to the material. Because of this, the new test with higher or lower loading should be made with the use of new specimen, but not this one which was tested before. Why you did not use the Dixon and Mood method? These problems must be clarified and discussed in more detail in the paper.

Minor remarks:

1. Table 1- “Fatigue limits” – there is only one fatigue limit. There are many different fatigue limits. Because of this limit must be clarified – tensile/bending, etc. and repeated/fully reversed, etc.
2. Line 192 “corrosion. [39] So it” – check and revise.
3. Line 211 „The test was performed at 1×107 cycles” – please check. Here, it also should be given information that tests are made with the use of the step loading method.
4. Line 238 “The fatigue strength of specimens under 107 lifetime was tested by step loading method.” – the reference to the step loading method should be provided.
5. Line 242 “previous work experience” - the reference should be given
6. Table 3, Line 384 – check and correct commas.
7. Line 373 “we observe” – check and revise.
8. Line 598 “22. .” – reference 22 is missing.

Kind Regards,

 

Author Response

Comments 1: Line 240 “The test continues until the specimen fails in less than 107 cycles.” Is the test made for the same sample that was subjected to HCF fatigue loading with lower maximal stress? If yes how were the damage level of the previous loading evaluated and fatigue strength calculated? Each stress cycle affect the structure of the object and introduce micro-damages to the material. Because of this, the new test with higher or lower loading should be made with the use of new specimen, but not this one which was tested before. Why you did not use the Dixon and Mood method? These problems must be clarified and discussed in more detail in the paper.

Response 1: Thanks for the reviewer's question. We explain the reason for the progressive loading test method, as shown in lines 209-218.

Comments 2: Table 1- “Fatigue limits” – there is only one fatigue limit. There are many different fatigue limits. Because of this limit must be clarified – tensile/bending, etc. and repeated/fully reversed, etc.

Response 2: Thanks for the reviewer's suggestion. The fatigue limit in Table 1 refers to the bending fatigue limit of the material. And we have completed in Table 1.

Comments 3: Line 192 “corrosion. [39] So it” – check and revise.

Response 3: Thanks for the reviewer's suggestion. We have modified it.

Comments 4: Line 211 „The test was performed at 1×107 cycles” – please check. Here, it also should be given information that tests are made with the use of the step loading method.

Response 4: Thanks for the reviewer's suggestion. We have added information that tests are made with the use of the step loading method, as shown in lines 213-214.

Comments 5: Line 238 “The fatigue strength of specimens under 107 lifetime was tested by step loading method.” – the reference to the step loading method should be provided.

Response 5: Thanks for the reviewer's suggestion. We have added it, as shown in line 214.

Comments 6: Line 242 “previous work experience” - the reference should be given

Response 6: Thanks for the reviewer's suggestion. We have added it, as shown in line 252.

Comments 7: Table 3, Line 384 – check and correct commas.

Response 7: Thanks for the reviewer's suggestion. We have modified it, as shown in line 394.

Comments 8: Line 373 “we observe” – check and revise.

Response 8: Thanks for the reviewer's suggestion. We have modified it, as shown in line 383.

Comments 9: Line 598 “22. .” – reference 22 is missing.

Response 9: Thanks for the reviewer's suggestion. There was an incorrect line break that resulted in an error in the numbering order. We have modified it.

Reviewer 5 Report

Comments and Suggestions for Authors

I accept all answers. 

Author Response

Thank you for your suggestions and comments, which have greatly helped me to improve the article.