Experimental study and computer simulation of changes in the residual stresses of structure defects in the shape memory alloys

It is possible to estimate reliability of the materials during their use by recording the changes in defect density of polycrystalline structure, which can be estimated on residual stresses at a crystal micro-level. In this paper the experimental measurement results of the residual stress field changes in actuator manufactured using shape memory alloy (SMA) are presented. The experimental data are based on the investigation of the changes in the root-mean-square (RMS) micro-strains and size of coherent block in the SMA caused by thermal and mechanical loading. The study is performed on the samples of approximately equiatomic TiNi alloy. To induce the reversible martensite transformations in the material the external loading is used with subsequent data recording using the X-ray method. The results of experimental measurements of the RMS microstrain and coherent block size in austenite are presented. Based on the experimental data a novel mathematical model is proposed, which is used in the computer simulations that include the martensite transformations, twining, elastic and irreversible deformations. The experimental and computer modeling results of stress and strain field generated by the defects in polycrystalline materials are discussed.