PROBLEM TO BE SOLVED: To provide a measuring method of transformation strain of a shape memory alloy in the case where stress and temperature are specified.SOLUTION: A measuring method of transformation strain of a shape memory alloy comprises the steps of: describing accommodation behavior by representing a shape memory alloy as a parallel connection of crystals having different crystal orientations from one another and further dividing each crystal grain into partial elements; calculating elastic strain and stress of the each crystal grain from average transformation strain, to which the transformation strain of the each crystal grain becomes equal, of the partial elements; and calculating resolved shear stress of the each crystal grain in each transformation plane and defining that transformation occurs in order of value of the resolved shear stress. An expression of the stress is induced when strain and temperature are given by representing the above described step as an expression 1. An expression 5 for obtaining the strain is induced when the stress and the temperature are given by transforming the expression 1. By using the expression 5, the strain is calculated. However, since the transformation strain contained in the expression 5 is represented as a function of the strain, calculated values of the transformation strain are different from each other before and after calculation thereof if it is left as it is. In order to solve the above described problem the transformation strain is caused to converge by performing repeated calculations thereof.
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