Modelling of propagating instabilities in pseudoelastic NiTi tubes under combined tension-torsion: helical bands and apparent yield locus

INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES

卷:221

Article

Rezaee-Hajidehi, Mohsen¹  Stupkiewicz, Stanislaw¹ 

[1] Polish Acad Sci, Inst Fundamental Technol Res IPPT, Pawinskiego 5B, PL-02106 Warsaw, Poland

关键词: Shape memory alloys;    Phase transformation;    Strain localization;    Finite-element method;   

DOI  :  10.1016/j.ijsolstr.2020.09.011

来源: Elsevier

【 摘 要 】

This paper is concerned with modelling of propagating instabilities and transformation patterns in NiTi tubes subjected to combined tension-torsion loading. A recently developed gradient-enhanced finite-strain model of pseudoelasticity is employed for this purpose, and respective finite-element computations are carried out. It is shown that the model is capable of representing a number of experimentally observed effects. The major effect, which has not been successfully modelled to date, is that the transformation is inhomogeneous under tension-dominated loading and alters towards a homogeneous transformation as the level of torsion is increased. To capture this effect, the model must deliver a non-monotonic (up-down-up) stress-strain response in tension and a monotonic one in torsion, and this can be achieved if the model includes three features: tension-compression asymmetry, transverse isotropy of the transformation strain, and deformation-dependent hardening/softening response. A detailed study is also carried out regarding the transformation yield locus. The results reveal an ambiguity in determination of the yield locus for tension-dominated loading and hence an ambiguity in determination of the tension-compression asymmetry. This aspect seems to have been overlooked in the literature despite its impact on correct interpretation of experimental results. (C) 2020 Elsevier Ltd. All rights reserved.

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