Modeling of the martensite transformation and reorientation in SMA under thermomechanical loading. Design of Finite Element adaptative micro-components

摘要

A macroscopic three dimensional constitutive law for Shape Memory Alloys is presented. It is based on a thermodynamical description of the martensitic phase transformation and a simplfied micromechanical approach. It takes into account mechanical aspects such as superelasticity or martensite reorientation and thermal ones as the shape memory effect. The material behavior is described by three internal variables: the martensite volume fraction, the mean tensorial transformation strain of the martensite and the mean tensorial strain due to martensite variants detwinning. The thermodynamical potential adopted is the Gibbs free energy, which can be differentiated into three processes: martensitic phase transformation, martensite orientation and martensite variants twinning. The interaction energies between grains of a Representative Volume Element (inter-granular), between variants inside grains (intra-granular) and between twins inside martensite variants (inter-twins) are taken into account in an averaged way. Three material parameters represent these interactions. They are identied from experimental thermomechanical tests. The model is implemented into the finite element code ABAQUS with the subroutine UMAT (User Material) in order to analyse the response of structures in Shape Memory Alloys. Thermomechanical tangent operators are computed. An application of the analysis for a structure using the shape memory effect is detailed. Further investigations will be made to take into account the size and surface effects. The aim is to provide a numerical tool for the design of microfluidic applications using thin SMA films (micropump, microvalve,...).