Low-cycle fatigue of stainless steel plates under large plastic strain demands

The low-cycle characteristics of structural subassemblies under large cyclic strains play an important role in contemporary seismic design. Obtaining these characteristics can lead to an understanding of a structure's degradation and nonlinear response behaviour, and can serve as a basis for developing efficient numerical models to predict seismic collapse mechanisms. The austenitic stainless tubular grade of steel has shown promise in terms of strain hardening character, structural overstrength and ductility, but existing test data is limited or constrained to small plastic strains, which is hardly useful in earthquake engineering applications. This article presents an experimental study designed to characterize the hysteresis of stainless steel plates under large inelastic cyclic strains and to assess their potential use in buckling-restrained brace components for seismic applications. Axial coupons machined from austenitic Grade 304L stainless steel and from regular carbon steel Grade 350WT were tested under uniaxial tensile loading, as well as constant and variable strain amplitude cyclic loadings. Results of the uniaxial tests confirmed higher ductility and strain hardening capacity for the stainless steel plates compared to those of carbon steels. These results were subsequently used to validate a novel technique based on image analysis to derive the true stress-strain characteristics. The stainless steel Grade 304L plates showed higher cyclic hardening but shorter low-cycle fatigue life compared to the carbon steel. Parameters for representing the low-cycle fatigue behavior of these materials, useful for developing a cyclic plasticity hardening numerical model, were derived from the test data.