Modeling of the transformation-induced plasticity in SMAs and porous SMAs
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Shape Memory Alloys (SMAs) have emerged as a class of materials with unique thermal and mechanical properties that have found numerous applications in various engineering areas. Recently a new class of SMA-based materials - porous SMAs - was developed. It is envisioned that this new material will find applications in the field of medicine as well as in various energy absorption devices and mechanisms. In this research effort the modeling of porous SMAs using incremental averaging techniques will be investigated. Based on the experimental observations, several modeling issues are identified and addressed. The occurrence of irrecoverable plastic strain during cyclic loading of SMAs at temperatures above the austenitic finish temperature has been reported by many authors. Similar effects have been observed during compressive loading of porous SMAs. Thus the focus of the first part of the current work is on establishing a three-dimensional constitutive model for dense SMAs, which is able to account for the simultaneous development of transformation and plastic strains during cyclic loading. In addition, the evolution of the material parameters during cyclic loading is also addressed. As a second task, the developed model is used in a micromechanical averaging scheme to model the behavior of porous SMAs. The current approach extends the micromechanics averaging method to establish macroscopic constitutive model for the porous SMA material using the properties of the dense SMA and the information about the pore shapes and porosity. The model utilizes the standard micromechanics averaging techniques where the scale transition is performed by introducing stress and strain concentration factors. The Mori-Tanaka method is used in this work to calculate the concentration factors. The properties of the porous SMA material are obtained by using the constitutive model for dense SMAs to model the matrix and treating the inhomogeneities as clastic phase with stiffness equal to zero. Results for different porous SMAs are presented and discussed. EDP Sciences.
