Experimental and numerical thermo-mechanical analysis of shape memory alloy subjected to tension with various stress and strain rates

Abstract

TiNi shape memory alloy (SMA) is experimentally and numerically investigated in tension tests under different loading rates. The thermomechanical behaviour of the SMA, related to the stress-induced martensitic transformation (SIMT) noticed during the experimental tests, is analysed and the observations are considered for numerical analysis. Initiation, development and saturation of the SIMT are monitored by a fast and sensitive infrared camera. The estimated temperature changes of the SMA sample, related to the exothermic martensitic forward and endothermic reverse transformation, have been analysed with the focus on the rate-dependent response and on the influence of the heat transfer on the mechanical behaviour. The effectively modified constitutive model, proposed by Lagoudas, is implemented in structural PAK finite element method (FEM) software and is thermomechanically coupled with the heat transfer FEM software in a partitioned approach. The experimental results are quantitatively and qualitatively reproduced by the numerical FEM model, which verifies the efficiency and accuracy of the proposed investigation method.

A thermo-mechanically coupled finite strain model considering inelastic heat generation

“…The force is obtained as constrained forces along the Y-direction for all the nodes at the top face. As it can be noticed, the thermo-mechanical coupling has influence on the force-displacement diagram what has been recently observed for the uniaxial tension tests in [4].…”

“…The integration is done with respect to the current configuration for the left Cauchy-Green deformation tensor and the elasto-plastic Von Mises material model with isotropic and kinematic (mixed) hardening [1,[9][10][11]21] and SMA material model [2,4,13,24]. Modified relative deformation gradient F t+Δt t :…”

“…Once the solution is computed, the material state is updated. For more details, please see [4,9,13].…”

“…Material parameters (Table 4) used for the thermo-mechanical simulation of the stent unit cell behavior are given according to [25] and constitutive model demands. More details can be found in [4,13]. The prescribed boundary conditions for the stent unit cell are as follows: The nodes on the bottom face are describing a Y-symmetry; on the left face is described X-symmetry, while on the top face, a displacement profile is prescribed along direction-Y for all the nodes.…”

“…Many advanced material models [e.g., plastic materials, materials with phase transformation, shape memory alloys (SMA)] require the thermo-mechanical interaction for the accurate simulation of the material behavior [4]. However, in practice the heat transfer and the mechanical behavior of the structure are very often simulated independently with the help of the corresponding FEM routines.…”