A Stochastic Corrosion Fatigue Model for Assessing the Airworthiness of the Front Flanges of Fleet Aero Engines Using an Automated Data Analysis Method

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This is a challenging and important research topic, and you have the novel approach and raw data, it has the potential to be published. However, the manuscript as it stands, needs substantial improvements before I can recommend its publishing:

1. there are significant similarity in the text, primarily in the background/theory part, please add references adequately, and do rewrite some of them;
2. what are the gaps of knowledge and what is the aim of this paper?
3. where the section 3.2.2 should be placed? It seems that it has been misplaced?
4. Strengthening the methodology and its implementation. It is not easy to see how the results are obtained, for example. Figures 6 and 7;
5. Figure 1 contains two diagram, but it is not shown which one is for which, vice versa;
6. Figure 3. How it is exactly the same as the diagram in reference 3?
7. How the figure 6 is produced? is it from existing publication?
8. Proof read to iron out the typo and grammar errors/mistakes;

Author Response

Reviewer 1: comments and answers:
This is a challenging and important research topic, and you have the novel approach and raw
data, it has the potential to be published. However, the manuscript as it stands, needs
substantial improvements before I can recommend its publishing:
1. there is significant similarity in the text, primarily in the background/theory part, please
add references adequately, and do rewrite some of them.
Thanks for reading this manuscript and your comments. It is considered.
2. what are the gaps of knowledge and what is the aim of this paper?
Aim of the paper is as described in title, abstract and introduction section, there are
so many technical variances are being created during in service condition which are
assessed by conventional approach such as rationalization, and qualified approach
by defining sizing. Current research paper produces more robust methods to save the
structures to more useful life period by bringing a novel approach such as stochastic
fatigue model in terms of quantification.
This is also highlighted in introduction section. (section 1, 2 and section 3)
3. where the section 3.2.2 should be placed? It seems that it has been misplaced?
Sorry, it was a misspell. Thanks for your comment and catch here. Corrected.
4. Strengthening the methodology and its implementation. It is not easy to see how the
results are obtained, for example. Figures 6 and 7;
As it is described in section, the mathematical models that include empirical equation
from corrosion test specimen of Mg structural casting and random models, these
results are obtained as displayed in equations 29-33. Figures 6 are from pit
measurements from field (in services), figure 7 are from random model generation.
5. Figure 1 contains two diagrams, but it is not shown which one is for which, vice versa;
First one is dust and second one is salt as it is described in the title of the figures.
6. Figure 3. How it is exactly the same as the diagram in reference 3?
Reference 3, is stochastic theory on fatigue and reference 1 is basis for the figure 3
as it was cited. It is also well aligned with internal RR material data base as it is
shown in grey coloured line.
7. How the figure 6 is produced? is it from existing publication?
Figure 6 is produced from Minitab with technical variances data collection on Mg
structural casting corrosion data from service condition of an aero engine.
8. Proof read to iron out the typo and grammar errors/mistakes;
Thanks for your valuable comments. We have read thoroughly once again and
implemented several changes on the aspect of language.

Reviewer 2 Report

Comments and Suggestions for Authors

The article addresses the combined effect of corrosion and fatigue loading on magnesium structural castings used in aero engine mount structures. It presents a novel stochastic approach using a two-parameter random variable model, validated against experimental data from the literature, to predict time-independent corrosion fatigue life and assess structural integrity under service conditions.

 

The article is interesting and remains relevant in its subject area. The presentation of the model and its justification is carried out appropriately. However, I see a few areas where the article could be improved:

1. The number of references used is too small. The Introduction section does not cite any sources.
2. I would recommend consistently following the IMRaD structure (Introduction, Methods and Materials, Results, Discussion).
3. The Discussion section of the article is too brief; I recommend including a dedicated and more comprehensive Discussion section.

Author Response

Reviewer 2: The article addresses the combined effect of corrosion and fatigue
loading on magnesium structural castings used in aero engine mount structures. It
presents a novel stochastic approach using a two-parameter random variable model,

validated against experimental data from the literature, to predict time-independent
corrosion fatigue life and assess structural integrity under service conditions.
 
The article is interesting and remains relevant in its subject area. The presentation of
the model and its justification is carried out appropriately. However, I see a few areas
where the article could be improved:
1. The number of references used is too small. The Introduction section does not cite
any sources.
Thank you for reading this paper and valuable suggestions to improve this paper.
Due to the fact that this area of implementing stochastic corrosion fatigue model to
aero engine application is new and hence there is no latest journal papers on this
topic. But the authors have referenced multiple papers on relevant area with relevant
usages.
2. I would recommend consistently following the IMRaD structure (Introduction, Methods
and Materials, Results, Discussion).
Thanks for your comment and Authors have considered this approach.
3. The Discussion section of the article is too brief; I recommend including a dedicated
and more comprehensive Discussion section.
Since it is also involved some proprietary internal methodological conditions, Authors
are restricted to provide in accordance with internal papers & conference policy
system.

Reviewer 3 Report

Comments and Suggestions for Authors

the abstract captures the problem context (corrosion fatigue in magnesium alloys in aero engine structures), the solution approach (two-parameter stochastic model), and validation with experimental and field data. The correlation of the stochastic model with experimental fatigue life supports the novelty and applicability of the work. However, the abstract could be more readable if written with shorter, clearer sentences and slightly improved structure.

The figures (e.g., Figures 1–7) are clearly labeled, relevant, and illustrate critical points of the study (e.g., contamination trends, stress-life data, random model outputs, fleet variances).
However:

• Some captions could be more self-explanatory.

• Ensure units and axis labels are always included (e.g., stress in MPa, cycles in log scale). No formal formatting issues were found.The paper convincingly argues the need for a quantitative, probabilistic model to replace traditional qualitative or empirical approaches in assessing corrosion fatigue. It highlights a significant gap in accurate life prediction under real-world corrosion conditions, particularly for magnesium structural castings. The proposal of a stochastic corrosion fatigue (SCF) model tailored to real fleet data is well justified.

• Three urgent research contents needed to strengthen journal-level recognition

  (1) Broader validation with different alloys or component geometries
  → Reason: Currently, the model is applied mainly to magnesium flanges. Demonstrating generalizability across materials or structural forms would expand its utility.

  (2) Experimental sensitivity analysis under various environmental conditions (SO2, humidity)
  → Reason: Real-world conditions are more variable than NaCl exposure; testing against multiple contaminants would improve robustness.

  (3) Development of software-based implementation of SCF model for airworthiness assessment
  → Reason: To transition from concept to deployment, the model should be embedded in a digital decision-support tool usable during maintenance checks.

• The conclusion summarizes the study well and emphasizes the significance of transitioning from qualitative judgment to a quantified probabilistic framework. The results are consistent with the initial research questions and methodology.

  However, it could benefit from:

  • More concise language.

  • A clear restatement of key numerical findings (e.g., predictive accuracy or fatigue life correlation coefficient).

  • the paper suggests that the SCF model could be expanded and validated with experimental and fleet data. The Appendix also hints at future integration with empirical pit growth models and electrochemical theory.
    However, a dedicated paragraph outlining specific future directions would improve clarity.

  • References are relevant, technically appropriate, and include both foundational works (e.g., Ishihara’s corrosion fatigue model) and recent aerospace corrosion studies. Citation formatting appears correct and follows standard scholarly practice.

    Suggestion:

    • Add 1–2 recent (post-2020) papers from applied corrosion fatigue modeling or probabilistic aerospace life assessment domains to strengthen currency.

Comments on the Quality of English Language

Original	Revised
"Corrosion in combination to fatigue cycling loading is inevitable..."	"Corrosion combined with cyclic fatigue loading is inevitable..."
"This paper brings a novel approach to predict the corrosion fatigue..."	"This paper presents a novel approach to predict corrosion fatigue..."
"It could be available based in individual queries..."	"It can be made available upon individual request..."
"Real flying corrosion attacked components..."	"Real-world corrosion-affected components..."
"Calcualted with more effective way..."	"Calculated more effectively..."

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

1. As shown in Figure 1, I will suggest authors add the annotations for the different color lines shown in the Figure for better understanding.
2. The original sources for Figure 1 and Figure 2 should be acknowledged and cited in the manuscript.
3. Can the developed corrosion fatigue model in the manuscript to applied to other types of alloys in addition to magnesium cast alloys?
4. The authors should explain Figure 4 in the manuscript and help reader understand the different behaviors of stress-life curves for as cast and NaCl exposed Mg cast alloy.
5. Is there any room to further improve the proposed stochastic corrosion fatigue model in the manuscript?
6. The author should explain how to get the data points in Figure 7 in the manuscript.

Author Response

Reviewer 4
1. As shown in Figure 1, I will suggest authors add the annotations for the different color
lines shown in the Figure for better understanding.
The different colour represents different airliners as explained in the manuscript.
Unfortunately, due to technical proprietary information, RR can not share the name of
airliners in this graph. These two figures are used mainly to compare the exposure of
RR engines in dust and salt environments.

2. The original sources for Figure 1 and Figure 2 should be acknowledged and cited in
the manuscript.
Since it is internal data, it is acknowledged with self.
3. Can the developed corrosion fatigue model in the manuscript to applied to other types
of alloys in addition to magnesium cast alloys?
Yes, it can be applied provided fatigue life deterioration over the corrosive
environment must be known.
4. The authors should explain Figure 4 in the manuscript and help reader understand
the different behaviors of stress-life curves for as cast and NaCl exposed Mg cast
alloy.
Figure 4 is being generated out of the equations from 29 to 33 from monte carlo
technique for both as cast as well as salt exposure of Mg structural casting.
5. Is there any room to further improve the proposed stochastic corrosion fatigue model
in the manuscript?
Yes, by including time dependant parameters in this stochastic fatigue corrosion
model, the accuracy should go higher as well as simulation of pit due to corrosion
fatigue can also be included for better comparison with analytical work.
6. The author should explain how to get the data points in Figure 7 in the manuscript.
Figure 7 is obtained from the Monte Carlo simulation of random samples, and as
plotted in figure 5, and from these samples, figure 7 is being generated to identify
which data could be used to clear the technical variances in optimal way to avoid any
scrap of the parts.

Reviewer 5 Report

Comments and Suggestions for Authors

The paper effectively proposes a novel stochastic corrosion fatigue model for magnesium structural castings in aero engines, integrating experimental data with probabilistic methods and validating it against real-world fleet data, thus offering a robust quantitative tool for assessing structural integrity and optimising maintenance in the aerospace industry, but it needs some improvement by considering following major comments:

1. A more detailed explanation of the specific contributions of the proposed stochastic corrosion fatigue mode in the abstract is needed. It should clearly highlight what distinguishes this model from existing approaches and provide a clearer indication of the practical implications of the research.
2. The introduction should provide a detailed explanation of the problem of corrosion fatigue in magnesium structural castings, highlight the limitations of existing models, and clearly articulate how the proposed stochastic approach addresses these gaps, offering a compelling motivation for its necessity.
3. The section on corrosion fatigue models could be improved by clearly explaining the limitations of conventional models and how the proposed model addresses these limitations, and by including visual aids to illustrate key processes.
4. The section on stochastic processes and random variables needs more intuitive explanations and practical examples to make the theoretical concepts more accessible.
5. The SCF model section should clarify its assumptions and include a flowchart or diagram to illustrate the model's structure and variable relationships for better clarity.
6. The implementation section needs more comprehensive validation with experimental data and additional case studies to demonstrate the model's effectiveness and robustness.
7. The good part is that the SCF model's predictions closely match experimental data, with a mean deviation of less than 10%, indicating high accuracy.
8. The Monte Carlo simulations show a coefficient of variation of 0.15 for pit sizes and 0.20 for fatigue life, demonstrating the model's robustness.
9. The implementation section should offer more comprehensive validation with experimental data and additional case studies to enhance the evidence of the model's effectiveness and robustness.
10. Conclusions should include specific future research recommendations and emphasize practical implications and actionable guidelines for the aerospace industry to enhance the paper's impact.
11. References should include more recent and diverse sources to reflect the current state of research, and ensure all cited references are included in the reference list for completeness and credibility.
12. The figures and tables are informative, but could be improved by ensuring consistent labelling, clear legends, and higher resolution images to enhance clarity and readability.

Comments on the Quality of English Language

The paper’s English is clear and appropriate for engineering communication. However, it could benefit from a thorough proofread to eliminate minor grammatical errors and improve sentence structure for enhanced clarity.

Author Response

Reviewer 5: The paper effectively proposes a novel stochastic corrosion fatigue
model for magnesium structural castings in aero engines, integrating experimental
data with probabilistic methods and validating it against real-world fleet data, thus
offering a robust quantitative tool for assessing structural integrity and optimising
maintenance in the aerospace industry, but it needs some improvement by
considering following major comments:
1. A more detailed explanation of the specific contributions of the proposed stochastic
corrosion fatigue mode in the abstract is needed. It should clearly highlight what
distinguishes this model from existing approaches and provide a clearer indication of
the practical implications of the research.

In abstract, it is mentioned about the current issue and proposed model and results.
Current abstract is modified according to review comment.
2. The introduction should provide a detailed explanation of the problem of corrosion
fatigue in magnesium structural castings, highlight the limitations of existing models,
and clearly articulate how the proposed stochastic approach addresses these gaps,
offering a compelling motivation for its necessity.
Considered.
3. The section on corrosion fatigue models could be improved by clearly explaining the
limitations of conventional models and how the proposed model addresses these
limitations, and by including visual aids to illustrate key processes.
Accepted and implemented.
4. The section on stochastic processes and random variables needs more intuitive
explanations and practical examples to make the theoretical concepts more
accessible.
Reference is quoted.
5. The SCF model section should clarify its assumptions and include a flowchart or
diagram to illustrate the model's structure and variable relationships for better clarity.
Instead of flow chart, the process is explained.
6. The implementation section needs more comprehensive validation with experimental
data and additional case studies to demonstrate the model's effectiveness and
robustness.
It is provided in figure 5 in along with analytical model as well.
7. The good part is that the SCF model's predictions closely match experimental data,
with a mean deviation of less than 10%, indicating high accuracy.
Thanks for your comment.
8. The Monte Carlo simulations show a coefficient of variation of 0.15 for pit sizes and
0.20 for fatigue life, demonstrating the model's robustness.
Thanks for your comment.
9. The implementation section should offer more comprehensive validation with
experimental data and additional case studies to enhance the evidence of the model's
effectiveness and robustness.
The validation part is taken from literature in particular to the experimental values.
Model predicts close matches.
10. Conclusions should include specific future research recommendations and
emphasize practical implications and actionable guidelines for the aerospace industry
to enhance the paper's impact.
Thanks and few statements are added in the end of conclusion section.
11. References should include more recent and diverse sources to reflect the current
state of research, and ensure all cited references are included in the reference list for
completeness and credibility.
12. The figures and tables are informative, but could be improved by ensuring consistent
labelling, clear legends, and higher resolution images to enhance clarity and
readability.
All above comments and suggestions are accepted and provided with changes (in
different colour fonts).

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

I can see some improvement, but not all expected.

1. there is significant similarity in the text, primarily in the background/theory part, please
   add references adequately, and do rewrite some of them.
   Thanks for reading this manuscript and your comments. Your response was it is considered. However, I could not see adequate change in text. This must be improved.
2.  How the figure 6 is produced? is it from existing publication?
   Figure 6 is produced from Minitab with technical variances data collection on Mg
   structural casting corrosion data from service condition of an aero engine.  Please actually add a section of text in the paper to inform the readers.

Author Response

2nd Phase of Reviews (Round 2)

Reviewer 1:

I can see some improvement, but not all expected.

1. there is significant similarity in the text, primarily in the background/theory part, please
   add references adequately, and do rewrite some of them.
   Thanks for reading this manuscript and your comments. Your response was it is considered. However, I could not see adequate change in text. This must be improved.

It is corrected as much as with Authors knowledge. All the changes are underlined.

2.  How the figure 6 is produced? is it from existing publication?
   Figure 6 is produced from Minitab with technical variances data collection on Mg
   structural casting corrosion data from service condition of an aero engine.  Please actually add a section of text in the paper to inform the readers.

Thanks for the comment. It is added as follows:

Figure 6 providing the real raw data of corrosion pit size that has been observed from the fleet (relevant to figure 2 of TV data base internally) with probability distribution plot along with two different distribution functions to be compared. Figure 7 uses the largest extreme value distribution functions to generate random numbers within the defined stochastic model as proposed in earlier section for assessing the fleet corrosion problems of front mount flange Mg structural castings. In this way, figure 7 categorises the acceptance limits and ranges within operational scope in automatic designed data.

 

 

Reviewer 2 Report

Comments and Suggestions for Authors

Thank you for the improvements and comments. After the improvements, the article is ready for publication. 

Author Response

Reviewer 2:

Thank you for the improvements and comments. After the improvements, the article is ready for publication.

No english change is required.

Reviewer 4 Report

Comments and Suggestions for Authors

The authors have addressed my comments in the revised manuscript. It is recommended for publication. 

Author Response

Reviewer 4:

The authors have addressed my comments in the revised manuscript. It is recommended for publication. 

Reviewer 5 Report

Comments and Suggestions for Authors

The manuscript is improved and ready for publication. 

Comments on the Quality of English Language

English can be improved. 

Author Response

Reviewer 5:

The manuscript is improved and ready for publication.