Experimental and Numerical Investigation of Mechanical and Thermal Effects in TiNi SMA during Transformation-Induced Creep Phenomena.

Vladimir Dunić,Elżbieta Pieczyska,Zbigniew Kowalewski,Ryosuke Matsui,Radovan Slavković

doi:10.3390/ma12060883

Abstract

(1) The paper presents experimental and numerical results of the TiNi shape memory alloy (SMA) subjected to a modified program of force-controlled tensile loading. The time-dependent development of transformation strain under the constant-force conditions was investigated to describe transformation-induced creep phenomena. (2) Mechanical characteristics of the TiNi SMA were derived using a testing machine, whereas the SMA temperature changes accompanying its deformation were obtained in a contactless manner with an infrared camera. A 3D coupled thermo-mechanical numerical analysis, realized in a partitioned approach, was applied to describe the SMA mechanical and thermal responses. (3) The stress and related temperature changes demonstrated how the transformation-induced creep process started and evolved at various stages of the SMA loading. The proposed model reproduced the stress, strain and temperature changes obtained during the experiment well; the latent heat production is in correlation with the amount of the martensitic volume fraction. (4) It was demonstrated how the transformation-induced creep process occurring in the SMA under such conditions was involved in thermo-mechanical couplings and the related temperature changes.

Highlights

It is of great importance to understand and to predict the behavior of materials and structures in cases which are usually encountered in contemporary applications
The proposed model reproduced the stress, strain and temperature changes obtained during the experiment well; the latent heat production is in correlation with the amount of the martensitic volume fraction
(4) It was demonstrated how the transformation-induced creep process occurring in the shape memory alloy (SMA) under such conditions was involved in thermo-mechanical couplings and the related temperature changes

Summary

Introduction

It is of great importance to understand and to predict the behavior of materials and structures in cases which are usually encountered in contemporary applications. An interruption of the loading, due to the accidents or a shortage of energy supply, is a situation that needs to be studied to anticipate the behavior of devices made of SMA such as sensors or actuators. Recent research on this topic, e.g. Matsui et al [1], Pieczyska et al [2,3], considered that the strain-controlled loading interruption, when the strain was kept constant, leads to the stress relaxation in the loading branch of the stress-strain curve, and the stress increase in the unloading one. They conducted a 12-h experiment and recorded that stress arrest leads to strain accumulation, mainly in the first 10 minutes

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