Low-cycle fatigue behavior of Silafont®-36 automotive aluminum alloy: Effect of negative strain ratio.

The aim of this study was to determine cyclic deformation behavior of a high-pressure die-cast Silafont®-36 automotive alloy with heterogeneous microstructures, focusing on the effect of strain ratio (R ε) ranging from negative infinity (-∞) to +0.5 at a constant strain amplitude of 0.4%. Pronounced cyclic hardening behavior was observed from the stress-strain hysteresis loops at different strain ratios. The degree of cyclic hardening, evaluated via both the traditional method and a newly-proposed slope method, increased with decreasing strain ratio. Fatigue life of the alloy was slightly lower at positive strain ratios, with its peak emerging at zero mean strain (or R ε = −1). In the negative range of strain ratios (R ε <−1), the fatigue life increased slightly with increasing strain ratio, which was mainly related to the plastic strain amplitude. A new power-law based equation was proposed to describe the change of mean stress relaxation at negative strain ratios (R ε <−1), along with a polynomial equation for depicting the situation at zero and positive strain ratios. Strain-energy density analyses corroborated that the intrinsic fatigue toughness was a material constant since it was not affected by strain ratio. [ABSTRACT FROM AUTHOR]