Effect of Shear/Axial Stress Ratio on Multiaxial Non-Proportional Loading Fatigue Damage on AISI 303 Steel

Round 1

Reviewer 1 Report

The article  aims to evaluate the cyclic response of AISI 303 stainless steel subjected to non-proportional loads with different amplitude ratios between shear stresses and normal stresses, a subject of particular interest for the evaluation of structural health monitoring of structures and mechanical components.  The relationship established between the proportional reference load and a varied range of non-proportional loads  may be used further, as direct application, for the evaluation of accumulated damage resulting from variable amplitude loading spectra.

Author Response

The authors are grateful for the reviewer's comments.

Reviewer 2 Report

1. It would be interesting to have more references, especially about accumulated damage.
2. In methodology, briefly describe the method of Anes et al.
3. In the text it is necessary:

• Be consistent with (º) and (°).
• Check (.) and (,) in numerical values.
• Take care of spaces in equations before and after (=).
• Equations numbered and not included in the text.
• Take care of tabulation of the text.

4. Take care of graphics quality and format coherence between them.
5. The format of Tables 5 to 10 is not adequate or consistent with the rest of the document.
6. Some SEM image of the specimen fractures could be included.

Author Response

The authors would like to thank the reviewer for suggestions for improvement.

1. It would be interesting to have more references, especially about accumulated damage.

The introduction section has been improved with additional references to accumulated damage.

2. In methodology, briefly describe the method of Anes et al.

This methodology has already been described in subsection 2.3.

3. In the text it is necessary: Be consistent with (º) and (°), Check (.) and (,) in numerical values. Take care of spaces in equations before and after (=). Equations numbered and not included in the text. Take care of tabulation of the text.

The manuscript was revised according to the suggestions made, however, some observations regarding these comments:

• The equations were made using MathType which do not allow spaces before and after (=)
• All equations are mentioned in the text (page 12 below Figure 7)

4. Take care of graphics quality and format coherence between them.

Figures have now 600dpi, Figure 7 was reformulated.

5. The format of Tables 5 to 10 is not adequate or consistent with the rest of the document.

Tables 5 to 10 were adjusted according to the template.

6. Some SEM image of the specimen fractures could be included.

This work deals with the relative damage between proportional and non-proportional loading paths by means of SN curves prepared according to the instructions of the ASTME466 standard. The work carried out aimed to estimate non-proportional damage based on a reference curve SN of a proportional load, in order to provide a mechanical design tool for the evaluation of cumulative damage. In this sense, the study of the microstructure and the analysis of the fracture surfaces and their correlation with the non-proportional damage was reserved for another article.

Reviewer 3 Report

The article proposed is excellent. The authors concluded that: the predominance of normal stresses in the non-proportional loading caused greater damage than the predominance of shear stresses.  It would be interesting to correlate this fact to crystalline imperfections to justify the increase/reduction of structural damage. Fractographic analyzes for some proportional and non-proportional loading conditions could be included in the work. The objective, in this case, would be to correlate fracture aspects with stress ratio and structural damage.

Author Response

The authors would like to thank the reviewer for suggestions for improvement. The suggestions made are very interesting. The correlation between fracture surfaces, the ratio of shear stresses to normal stresses, and structural damage is of particular interest for the analysis of fatigue failure of components and structures through the study of fracture surfaces and corresponding SEM analyses. These results are important in the search for the root causes that led to the failure that is often found during inspections. However, despite the very interesting topic, the correct documentation of the mentioned relationship would lead to a new article and require a new investigation strategy. In this article, the main objective was to study the relationship between the SN curves of the proposed loading paths in order to draw conclusions about their relative damage and to develop a tool for estimating the non-proportional damage using the SN curves of a proportional reference load. In practice, the results of this work are not used for failure analysis (which is more focused on the study of fractography), but for the estimation of accumulated damage due to non-proportional loads, which is an aspect more focused on mechanical design and in-service damage assessment. On the other hand, an average of 7 specimens were used for each loading path. Each specimen was polished to a mirror finish to remove all surface defects, and the test instructions given in the ASTME466 standard were followed. In this sense, the obtained SN curves meet the necessary requirements for their validation and can be used to draw conclusions about the relative damage between loading paths. However, the authors will consider the suggestions made in future work.