Laser Shock Peening: Toward the Use of Pliable Solid Polymers for Confinement
, Laurent Videau 4, Bruno Fayolle 1,*, Matthieu Gervais 1,*, Leo Morin 1, Stéphane Valadon 2, Romain Ecault 2, Domenico Furfari 5 and Laurent Berthe 1,*Round 1
Reviewer 1 Report
The authors propose an interesting development of the laser shock peening technique for the insertion of residual stresses in metallic materials, by using solid polymers as confinement. The results presented are interesting and the paper is well written, with a clear path to the final conclusions. The reviewer suggest the acceptance with few remarks and clarification requested.
The abstract and the introductory part are thorough, with a basic literature review, with a good definition of the motivation and goals of the paper .
The experimental programme is well developed and described, but some points should be checked. As first remark, it is not stated the number of tested coupons for every different confinement material. Why only pure aluminium coupons have been tested and not standard aerospace grade alloys (2xxx, 7xxx, etc.)? The motivations behind the selection of a 1mm thickness should also be introduced.
Furthermore, it is not clear if the plasma is generated by the vaporization of the aluminium first layer or there is some contribution from the inner layer of the polymer confinement? This technique can be considered as a LSP without coating?
After the laser input, the local concentrated thermal load affects the polymer performances and/or transparency? This is critical when applying more than a single spot in the same area.
The polymer must be replaced in case of multi-layer peening and how critical is the removal of those pliable tapes?
Check in line 57 the word “compagny".
About the numerical simulations, the overall model is well described.
Line 99 the sentence “as the mesh size increases the results….” is not clear. Maybe the correct statement would be “as the element dimensions decrease….”
The J.C. constitutive material model is used for the simulations. The experimental parameters in the eqn. 1 are available only for strain rates well below the 106s-1 of the LSP. How those results can be extended for the high strain rate conditions of the tests?
The discussion of the results is excellent, with clear conclusions. Check the reference in line 144.
Author Response
Dear Editor,
The authors would like to thank the Editor and the Reviewers for their constructive comments, which allowed us to significantly improve the quality of the manuscript. All the concerns have been addressed below. We hope that you will now find the manuscript acceptable for publication in Journal of Metals-Special Issue "Laser Shock Processing and Related Phenomena". The detailed changes made for the reviewers' comments are listed below point-by-point and all the changes are emphasized in blue font in the revised manuscript.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Please find the attached report.
Comments for author File: Comments.pdf
Author Response
Dear Editor,
The authors would like to thank the Editor and the Reviewers for their constructive comments, which allowed us to significantly improve the quality of the manuscript. All the concerns have been addressed below. We hope that you will now find the manuscript acceptable for publication in Journal of Metals-Special Issue "Laser Shock Processing and Related Phenomena". The detailed changes made for the reviewers' comments are listed below point-by-point and all the changes are emphasized in blue font in the revised manuscript.
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
Please find the attached report.
Comments for author File: Comments.pdf
Author Response
Dear Editor,
The authors would like to thank the Editor and Reviewers again for their constructive comments. It allowed us to improve the quality of the manuscript. All the concerns and recommendations have been taken into account and addressed below. We hope that you will now find the manuscript acceptable for publication in Journal of Metals-Special Issue "Laser Shock Processing and Related Phenomena". The detailed changes made for the reviewers’ comments are listed below.
- This revised manuscript has a significant improvement. However, some minor points need to be addressed as follows before being ready for publication.
* Some of the direct applications related to the technique applied in the current study should be presented.
* Laser shock peening applies higher residual stresses on the processed surfaces as compared to other surface treatment techniques such as shot peening. This makes LSP is one of the recommended surface treatment solutions of the parts fabricated by recent manufacturing technologies such as additive manufacturing. However, LSP is not easily accessible and expensive as well.
The authors need to add a brief critical review in the introduction section, to show the importance and the benefits of the current work compared to shot peening. In addition to considering the cost parameter value for some applications that can be processed through other techniques such as shot peening.
Some references are recommended to be included such as:
Maamoun, A.H.; Elbestawi, M.A.; Veldhuis, S.C. Influence of Shot Peening on AlSi10Mg Parts Fabricated by Additive Manufacturing. J. Manuf. Mater. Process. 2018, 2, 40.
Hackel L, Rankin JR, Rubenchik A, King WE, Matthews M. Laser peening: A tool for additive manufacturing post-processing. Additive Manufacturing. 2018 Dec 1;24:67-75.
Please revise the manuscript carefully after considering the above comments and recommendations.
Thank you for your constructive remark. The intro has been modified to incorporate a more in depth literature review of the benefits of the current work compared to shock peening. The differences are situated between lines 24 to 49 and are given below.
From there, LSP started becoming a competitor to the conventional shot peening for the improvement of the fatigue performance of treated components as laser peening is now one of the most effective surface pre-stressing treatments used to enhance the fatigue strength of metallic structures. The laser shock peening induced compressive residual stresses offer better fatigue properties [4] by retarding the crack growth and inhibiting the crack initiation [5–7]. In addition, LSP can enhance significantly the resistance to stress corrosion of the treated components [8].
Compared to the conventional shot peening, the affected depth is much larger for the laser shock peening, up to≈1.5 mm against≈300μm for shot peening [9] on Al alloys materials. In addition, the LSP induced work hardening is generally limited (about + 10% to + 30%) compared to conventional shot peening [10]. This can be explained by the fact that the loading’s duration is very short, which consequently does not allow the activation of all the sliding systems of the material and thus generate less cross dislocations. Only cyclic hardening materials such as 304L and 316L have their hardness and their level of residual stresses increase with impact’s repetition. Nevertheless, it is not possible to conclude on the amplitude of the induced compressive residual stresses, given that the contradictions exist in the literature. Therefore, conventional shot peening may be unfavorable over life-time due to controlled deformation loading (high cycle thermal loading), reducing the beneficial effects of compressive residual stresses. For laser shock, such a risk can be avoided because of the low work hardening.
Today, LSP at industrial scale is mainly applied in aeronautic for the treatment of sensitive areas on certain parts to increase their lifespan. Water is the usual confining material because it is cheap, transparent to the laser and ensures contact with surfaces. Other areas are developing quickly toward industrial applications such as the treatment of parts produced by additive manufacturing. LSP treatment on these types of materials allow more shaping and forming possibilities as well as shape correction treatment due to the highly controlled nature of the process compared to conventional shot peening [10,11]. Coupled with the deeper levels of residual stress produced it has shown to be be highly cost effective despite its higher operative cost compared to conventional shot peening.
We hope that the above response should be satisfactory to the reviewers’ question. Please let us know if any further modification is needed.
Thank you for your kindness and help.
Yours sincerely,
The Authors.
Author Response File: Author Response.pdf
