Research on the Shock Response Characteristics of a Threaded Connection Using the Thin-Layer Element Method
Round 1
Reviewer 1 Report
Main Comment
Nonlinear factors such as the contact stiffness and friction damping at the threaded inter- face of a projectile-fuse system significantly affect the dynamic response characteristics. To obtain the dynamic response of the fuze body accurately during penetration, it is necessary to characterise these nonlinear factors reasonably. Because the existing structural dynamic software cannot effectively deal with nonlinear factors, the thin-layer element method was used to represent the nonlinear factors in this study. By combining the thread elastic model with thin-layer element principles, an effective method for determining the material parameters of the thin-layer element was established theoretically, which provided a different method of determining material parameters, not just relying on experiments. The accuracy of the material parameters was verified based on modal experiments with threaded tubes having different specifications. The errors were within 5 %, indicating the reliability of the theoretical determination method for the material parameters. In addition, projectile penetration into a semi-infinite concrete target was tested to verify the accuracy of the thin-layer element modelling. Compared with the ‘TIED’ constraint method, the resonant frequency obtained with the thin-layer element method was in better agreement with that of the experimental data. The maximum error decreased from 15.7 % to 7.8 %, indicating that the thin-layer element method could accurately represent the nonlinear factors. Thus, this study serves as a reference for accurately evaluating the dynamic response of the fuze body of a penetrator.
The paper is well structured and informative, with updated references, but authors are encouraged to go to another phase of manuscript review to address the following issues.
The manuscript should be revised to address errors in several places. Several examples from the text follow (p - page):
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(p.18) In conclusion, in addition to the above, I would expect an expression of opinion and perspective of the authors on the issue of the paper. Finally, the authors of the article should pay more attention to the overall writing and clarity of their article, which should support the demonstration of their findings.
Comments for author File: 
Comments.pdf
Author Response
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Author Response File: Author Response.pdf
Reviewer 2 Report
In this paper, the nonlinear dynamic behaviour of a projectile-fuse system is studied. In particular, the influence of contact stiffness and friction damping, which represent relevant nonlinear factors, at the threaded interface of the system is investigated on the basis of Thin-Layer Element method.
The present paper is scientifically interesting, well written and arranged, reporting several relevant observations and results. It presents many strengths and some little weaknesses.
Strengths
1) The accuracy of the theoretical model proposed is properly verified by means of comparisons with experiments to understand actual effect of nonlinear factors on the vibration response of the system.
2) The theoretical procedure adopted to determine TLE material parameters, i.e. Young’s modulus, Poisson’s ratio and shear modulus, is correct.
3) FE modelling of the projectile-fuse system and FRF curves of TLE vs. TIED method are right.
Weaknesses
1) Several small English Language mistakes are present throughout the text, which must be corrected​ in the reviewed version of the paper.
2) Quality of Figure 1 should be increased.
3) Term “fuse” instead of “fuze” should be adopted within the text.
4) How are “free boundary conditions” simulated in the theoretical model?
5) In this work, TLE method is adopted to analyse friction damping at the interface of the system. Vibration reduction of mechanical components represents a relevant issue. Actually, this can be obtained by increasing the damping behaviour at the interfaces of multi-layer functionally graded composites. The Authors are invited to consider and also discuss this topic in the Introduction, by reporting related references available in literature, as for example:
a) Catania, G.; Strozzi, M. Damping oriented design of thin-walled mechanical components by means of multi-layer coating technology. Coatings 2018, 8, 73.
b) Yu, L.; Ma, Y.; Zhou, C.; Xu, H. Damping efficiency of the coating structure. International Journal of Solids and Structures 2005, 42, 3045-3058.
c) Rongong, J.A.; Goruppa, A.A.; Buravalla, V.R.; Tomlinson, G.R.; Jones, F.R. Plasma deposition of constrained layer damping coatings. Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 2004, 218, 669-680.
Therefore, in the opinion of the Reviewer, by considering the previous notes, the paper should be accepted for publication after minor revision.
Author Response
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Author Response File: Author Response.pdf
