No. 108, 2001, 33-45

Residual stresses and shape memory effect


It is possible to estimate the 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 results of the residuai stress field changes in actuator manufactured using shape memory alloy (SNIA) 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 alioy. To induce the reversible martensite transformations in the material the external loading is applied with subsequent data recording using the X-ray method. The results of experimental measulements of the RMS microst rain and coherent block size in austenite are presented. Basing on the experimental data a modified (by Brechko [4-5]) mathematical model of Likhachev and Malinin [3] is proposed, which is used in the computer simulations including the martensite transformations, twining, elastic and irreversible deformations. The experimental and computer modeling results of stress and strain field generated by the defects in polycrystailine materiais are discussed. 


shape memory alloy