Scientists from the University of Washington, U.S.A. (Y. Liang. T. Wada, H. Kato, T. Tagawa, M. Taya and T. Mori, Mater. Sci. Eng., A, 2002, 338, (1—2), 89—96) have also developed an averaging method to calculate the uniaxial stress-strain relationship in polycrystalline Fe-Pd. Strain within a grain is caused by changes to the variants of the martensite Fe-Pd structure. Internal stress and elastic energy accumulate. Stress also acts on a grain due to the surrounding grains.