Residual Stress in Epoxy-Based Insulators: Formation, Detection, and Reliability

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The article “Residual Stress in Epoxy-based Insulators: Formation, Detection, and Reliability” provides a comprehensive and well-structured overview of one of the most critical challenges affecting the performance and life of epoxy-based insulation systems. Authors successfully present a thorough analysis of residual stress formation mechanisms, detection methodologies, and reliability implications. The article clearly explains the thermo-chemical and curing processes responsible for residual stress generation. They also connect these mechanisms to practical reliability concerns in high-voltage insulation equipment. The discussion of curing kinetics, thermal gradients, chemical shrinkage, and stress evolution demonstrates a deep understanding of the underlying physics and materials behavior. It is worth underlining that the article’s emphasis is on the relationship between residual stress and the mechanical reliability of epoxy-based insulators. The authors effectively summarize existing numerical and experimental studies, highlighting how stress concentrations influence crack initiation, deformation, and service performance. This discussion provides important insights for the design optimization and manufacturing of high-voltage insulation components. Overall, this article represents a significant contribution to the field of epoxy-based insulation materials and high-voltage engineering.

 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

In this review, the authors summarize the curing mechanisms with residual stress, current residual stress detection techniques, and filler sedimentation in epoxy-based insulators with alumina fillers. Especially, they well compare the applicability and limitations of current methods for detection of residual stress. This review provides a comprehensive overview of the mechanisms underlying residual stress generation and methods for characterization. Some concerns ought to be given attention, as follows:

 

Comment 1:

In alumina-filled epoxy composites, the alumina contents significantly influence the developments of residual stress, stress concentration, and difficulty of stress detection. Therefore, adding a discussion on the effects of different alumina contents would provide a more comprehensive understanding of the topic.

 

Comment 2:

In Page 10, the sentence “NDT methods like the photoelastic and acoustoelastic methods possess advantages such as being non-contact and capable of imaging, which are useful for overall distribution evaluation. However, issues regarding sensitivity and adaptability remain when applied to complex curved structures.” Is shown as summery. Although the limitations of NDT methods for complex curved structures are mentioned in summary, these limitations are not adequately explained in the preceding sections. Providing a more detailed explanation of these limitations would improve the clarity.

 

Comment 3:

More discussion on the alumina–epoxy interface would be helpful. The interface can influence residual stress, stress concentration, and fracture behavior in alumina-filled epoxy composites.

 

 

If the revised manuscript authors have revised the paper according to the comments and answered my questions, I will support publication of the revised manuscript.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

Comments to the Editor:

The manuscript entitled “Residual Stress in Epoxy-based Insulators: Formation, Detection, and Reliability” presents a comprehensive review of the formation mechanisms, detection techniques, and reliability aspects of residual stress in epoxy-based insulators. The manuscript is generally well written, logically organized, and supported by relevant literature. The topic is timely and valuable for researchers working on high-voltage insulation systems. However, several minor issues should be addressed to further improve the quality of the review. The authors should provide a more critical comparison of the reported detection techniques, include additional recent references, and enhance the discussion on future research directions and industrial implementation. Subject to minor revisions, I believe the manuscript is suitable for publication.

Comments to Authors:

 The review is comprehensive and well organized; however, more recent references (2024–2025) should be included.

A critical comparison of residual stress detection methods would strengthen the manuscript.

Please add a summary table comparing the advantages and limitations of each detection technique.

The future perspectives section should be expanded with recommendations for industrial implementation.

Minor English editing is recommended to improve clarity and readability

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

Dear group of authors.

The  presented manuscript addresses an important and practically relevant topic: residual stress in epoxy-based insulators for GIS/GIL systems, with emphasis on stress formation during curing, available detection techniques, and implications for mechanical reliability. The topic is suitable for a review article and has clear relevance for high-voltage insulation systems, especially large epoxy/alumina components used in UHV equipment.

However, in its current form, the manuscript reads partly as a narrative summary of selected studies rather than as a sufficiently critical and comprehensive review. Substantial revision is required before the manuscript can be considered for publication.

Firstly, please define and briefly explain the all abbreviations (for example: GIS and GIL), as the manuscript is intended for an international and interdisciplinary readership. The introduction should also contain a clearly formulated research gap, explaining what is missing in the current literature and what this review specifically contributes beyond previous studies. This would make the scope, purpose, and scientific contribution of the manuscript clearer.

Next, it is not explained how the literature was selected, which databases were used, what inclusion or exclusion criteria were applied, or whether the review aims to be systematic or narrative (the authors are invited to see DOI:10.1109/ACCESS.2024.3443462 and DOI: 10.3390/polym15061532).

Could the authors clarify the limitations of the residual stress modelling approach, especially the assumptions related to linear elasticity, cure-dependent material properties, viscoelastic relaxation, gelation, vitrification, and filler-dependent shrinkage?

In my opinion, the thermo-chemical model, the notation for density, heat source, specific heat, and thermal conductivity is not always clear. Some parameters are insufficiently defined, and the physical meaning of several variables should be stated more rigorously. The mathematical formulation should be checked for consistency of symbols, units, and tensor notation.

Only if it is relevant, could authors provide a more critical comparison of the residual stress detection methods, including their limitations, measurement accuracy, suitability for curved GIS/GIL insulators, and applicability to highly filled opaque epoxy composites?

Could the authors explain more clearly how alumina filler sedimentation affects local material properties, residual stress distribution, stress concentration, and crack initiation in epoxy-based insulators?

Thank you.

 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 4 Report

Comments and Suggestions for Authors

Dears authors.

Thank you very much for your rapid correction of submíted article.

Thank you for your the complete answers (replies) to all reviewers.

I think that all of my and other reviewers' recommendations were incorporated into the final article.

Thank you