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

本报告的第一部分涵盖了第二阶段项目的扩展，并分别对拉压和循环扭转的多轴应力状态的本构模型和寿命预测方法的适用性提出了更成熟的结果。分析结果与实验数据进行了比较。第二部分的动机涉及项目的第三阶段，这是由于工程要求，这些方案将用于实际设计目的：通过对缺口根部应力应变响应的分析与实验结果的比较，验证了非弹性本构模型在有限元计算中的适用性，采用蠕变加载、快-快、慢-慢循环应变和有拉伸保持时间的快-快循环应变4种加载方式对试件进行疲劳-蠕变寿命预测。应力/应变模拟分析的结果与测量应变在缺口根部的装置“应变-派克”，一个电容式高温引伸计使用。预测的裂纹萌生寿命也证实了由直流电位降技术检测的实验寿命，和失效寿命定义为从饱和的25%的应力降的周期。

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.