Fatigue analysis of shape memory alloys: energy approach

Abstract

The purpose of this paper is to define a low cycle fatigue criterion for NiTi shape memory alloys (SMAs) in order to perform numerical calculations necessary for designing structures made of SMA and subjected to cyclic loading. For this purpose, fatigue tests are performed in a temperature and deformation regime in which the alloy exhibits pseudoelasticity. A behavior similar to plastic shakedown is observed; during the first cycles a hysteresis loop with a varying size which eventually stabilizes is obtained. Therefore, by analogy with plastic fatigue (low cycle fatigue), it is shown that the dissipated energy of the stabilized cycle is a relevant parameter for the estimation of lifetime.

Fatigue crack initiation and propagation of a TiNi shape memory alloy

“…As many authors [6,11,13,14] this stabilization effect occurs around the 100 th cycle. Contrary to Moumni et al [4] or Paradis et al [13], no residual strain is noticed after the first unloading. Residual strain starts to appear at the end of the second unloading, increases during cycling and tends to saturate with a value of 0.4%.…”

“…Although the test is stopped, the cyclic behavior looks like the one described by Moumni et al [4] or by Miyazaki et al [11] on not stopped tests. Namely the strain-stress response is characterized by hysteresis loops which evolve during cycling.…”

“…Contrary to usual metallic alloys, they exhibit very specific thermo-mechanical behaviors : including shape memory effect [1,2], two-way shape memory effect [2], superelasticity [3][4][5] and damping [6]. Many engineering applications have been developed using these properties in various fields (medical, aeronautic, automobile, domestic or civil engineering).…”

Cyclic behavior and energy approach to the fatigue of shape memory alloys

“…The figure shows a quasilinear dependence of log ᐃ d on log N f for several values of the mean stress. Hence it is interesting to approximate the experimental results using the following curve from [Moumni et al 2005]:…”

“…Using the analogy with plastic fatigue (low-cycle fatigue) [Halford 1966;Charkaluk et al 2002], a relation was established in [Moumni et al 2005] between the amount of dissipated energy associated with the stabilized hysteresis cycle and the number of cycles to failure. In this paper, we provide an application of the cyclic model, developed previously by the authors within the framework of generalized standards materials with internal constraints [Moumni et al 2008], in order to simulate the dissipated energy at the stabilized cycle.…”