A Study on the Application of Inelastic Constitutive Relations under Plasticity-Creep Interaction and the Evaluation of Life Prediction Methods

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The first Part of this report covers the extension of the second phase project, and presents more developed results on the applicability of the constitutive models and life prediction methods, respectively, to the multiaxial stress state of combined tension-compression and cyclic torsion. The results of analysis were compared with the experimental data.The motivation of the second part concern the third phase of the project which arises from engineering requirement that the schemes are to be used for practical design purposes : Applicability of the inelastic constitutive models to finite element calculation is examined by comparing the analytical stress/strain response near notch root of the bar with experimental results, and fatigue-creep lives of the specimen are evaluated by applying the life prediction methods.Four loading patterns such as creep loading, fast-fast and slow-slow cyclic straining and fast-fast cyclic straining with a tension hold-time were applied to the specimen. The results of analysis of stress/strain simulation were compared with measured strain at notch root by means of "Strain-Pecker", a capacitance type extensometer for high temperature use. The predicted crack initiation Life was also confirmed by the experimental lives which were detected by a direct current potential drop technique, and failure life was defined as the cycles of 25% stress drop from saturation.