Displacement or a load is applied to an elastic-plastic material to deform the elastic-plastic material plastically to acquire experimental values of a stress-strain relation. With a kinematic-hardening incremental vector d± ij of a yield surface in an elastic-plastic constitutive model as a predetermined first equation, the elastic-plastic constitutive model being defined as a function of stress and back stress, a computer identifies material constants contained in the elastic-plastic constitutive model with the acquired experimental values. The computer identifies material constants contained in a predetermined second equation on the basis of the acquired experimental values and the predetermined first equation into which the identified material constants are substituted. The computer simulates the stress-strain relation of the elastic-plastic material with the predetermined first equation, the predetermined second equation, and the elastic-plastic constitutive model into which the identified material constants are substituted.
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