Evaluation of Inelastic Constitutive Equations under Plasticity-creep Interaction Condition subjected to Multiaxial Stresses

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Some of the results of the bench mark project on the evaluation of constitutive equations and life prediction methods conducted by the project members are reported. As an extention of the work done for material behavior under uniaxial stress, inelastic deformation under plasticity-creep interaction condition and life estimation in fatigue-creep regime are both examined in combined stress state of tension (compression) and torsion. By specifying normalized and tempered 2 Cr-1Mo steel at 600゜C, ten kinds of problems of five categories (they are simple and cyclic tension or torsion, tensile creep followed by combined plasticity and vice versa, response under cruciform or circular path, mechanical ratcheting under combined stresses, and in-phase and out-of-phase cyclic straining) were established for the first part of the project, and in-phase and out-of-phase fatigue-creep tests were performed in the second part.Predictions of inelastic response by ten constitutive models by fourteen way sare compared with the corresponding experimental results to evaluate the accuracy in simulating the actual behavior of the material, and the estimated lives by seven methods are also plotted in comparison with the observed lives. Here, the emphasis is focused on the life estimation procedure by three methods employing caluclated stress-strain response by the constitutive models.