Superior fatigue life of Fe-15Mn-10Cr-8Ni-4Si seismic damping alloy under asymmetric cyclic loading with tensile mean strain

Abstract

An Fe–15Mn–10Cr–8Ni–4Si (in wt%) alloy was recently developed for hysteretic seismic dampers that protect constructions against earthquakes. The alloy was found to exhibit a stable hysteresis response and an extraordinarily long low-cycle fatigue (LCF) life, Nf, under symmetric cyclic loading (tension/compression strain ratio Rε = −1), owing to reversible cyclic deformation associated with ε-martensitic transformation. The LCF life and failure microstructure of the alloy were studied at Rε values ranging from − 1–0.5, so that the strain domain of the cyclic deformation changed from symmetric tension–compression to asymmetric loading with tensile mean strain. The shift of the strain to the tensile domain, which is known to frequently have a negative effect on fatigue resistance because it induces tensile mean stress, brought about only a moderate fluctuation in Nf (Nf = 9200, 9500, 7500, and 8400 cycles at Rε = −1, −0.2, 0.2, and 0.5, respectively). The stress–strain hysteretic response remained stable, and the mean stress observed in early cycles was relaxed to zero during cyclic deformation. This stress relaxation is associated with strengthening of austenite texture with (111)// loading direction and suppression of the martensite fraction, which the reversible cyclic deformation mechanism seems to sustain.