Model for simulation of the mechanical behavior of a porous shape memory alloy with a non-ordered structure

Abstract

A model for simulation of the mechanical properties of porous NiTi shape memory alloy samples (SMA) with high through porosity has been proposed. Such samples are obtained from nickel and titanium powders by self-propagating hightemperature synthesis under specially selected technological conditions. The structure of the samples corresponds to a set of ligaments without a clearly defined orientation of the pore channels. In this work, a study of microphotographs of porous NiTi samples with a porosity of 60 % has been carried out. Basing on this study such a porous material has been approximated by a beam structure consisting of horizontal beams supported by vertical curved beams. A specially developed technique of finding the geometric parameters of this beam structure was used for its characterization. The object for modeling determined in this way provides the opportunity to take into account the basic structural features of the sample. The strain of the porous sample is then calculated with the use of the methods of the strength of materials by calculating the displacements of all structural elements. The constitutive relations of the SMA microstructural model have been used to describe the SMA deformation. This model proved to be an efficient tool for simulation of the functional and mechanical behavior of a solid SMA under various thermal and mechanical loadings. The deformation curves of porous NiTi under compression at different temperatures corresponding to the martensitic and to the austenitic state of the SMA have been calculated. The results of the simulation have shown good agreement with the experimental data.