FRACTURE MECHANISMS AND LIFE ASSESSMENT UNDER HIGH-STRAIN BIAXIAL CYCLIC LOADING OF TYPE 304 STAINLESS STEEL

Abstract— In order to investigate the elevated-temperature low-cycle fatigue characteristics of Type 304 stainless steel under biaxial loading, strain-controlled push-pull and torsional fatigue tests were conducted at 550°C under proportional and nonproportional loading conditions with phase differences of 0, α/6, α/4, α/3 and α/2 between the applied sinusoidal axial and torsional strains. Based on the experimental results, this study presents a discussion on fracture mechanisms and failure criteria. In the case of proportional loading, the fracture mode was found, from fractographic observations, to be classified into either Mode I or Mode II, while the fractures were of mixed mode under nonproportional loading. However, failure lives under both the loading conditions could be correlated well in this study with the equivalent shear strain range, Δy, defined by extending the β -plane theory of Brown and Miller. The failure life under nonproportional loading could also be predicted by applying a strain-energy-based approach.