Deformation and Damage Behavior of a 1Cr-Cast Steel Under Multiaxial Loading at Elevated Temperatures

Abstract

Rising demands on material performance at high temperature in components under complex loading such as steam- and gas turbine housings require an increase in versatility and precision of component life modeling approaches. However, the database to calibrate those models is commonly derived from uni-axial testing. The impact of multi-axial loading, both proportional and nonproportional, is usually addressed theoretically by the use of equivalent stress/strain formulations or reduction ratios derived from few specific validation tests. Therefore, a research program which systematically investigates the fatigue life of a 1Cr-cast steel both experimentally and theoretically has been initiated recently. For the experimental part, cruciform specimens are tested in a servohydraulic biaxial test rig equipped with an induction heating device. Each experiment is accompanied with finite element simulations before and after the test to parametrize the loading condition and derive equivalent loading parameters at hot-spot locations. When assessing cycles until crack initiation in the experiments using the von Mises equivalent strain range, a reoccurring sequence in the impact of the axis ratio can be observed. Beside the fatigue life in terms of cycles to crack initiation, the multi-axial loading conditions may also affect the deformation behavior, in detail cyclic softening. Such effects are discussed by comparing the produced experimental evidence with results gained from a unified constitutive material model. Furthermore, different lifetime parameters are applied in order to judge their accuracy and suitability for design applications.