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 (Rε) 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 Rε = −1). In the negative range of strain ratios (Rε<−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 (Rε<−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. 

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

Ratcheting characterization and its effect on low cycle fatigue behavior of DP600 steel sheet under cyclic shear path

Study of Strain Ratio effects on Low Cycle Fatigue (LCF) Behavior of Dual Phase (DP) Steel

Fatigue Properties of Rolled Steel Sheets for Automotive Structure

The fatigue behaviors of dual-phase steels (DP600) under cyclic shear path are studied and the effects of strain ratio are analyzed. Based on twin bridge shear specimens, complete reverse strain-controlled fatigue tests are carried out on DP600 sheet (1.2 mm) under different strain ratios (R = −1, −0.5, 0, and 0.5) with strain amplitudes in the range 0.8–3.0%. DP600 exhibits cyclic softening with a relatively constant softening rate related to amplitude and strain ratio. Smaller loading amplitude and higher strain ratio are beneficial to improve the softening ability of the material. The γ-fiber-type ( //ND) texture components are well developed at higher strain ratios, which improve the fluidity of the dual-phase steel, thus making the microstructure deformation more uniform and reducing the risk of damage caused by deformation compatibility. The uniform deformation of the material improves the absorption of plastic strain energy. Therefore, higher strain ratios are beneficial to improve the fatigue life of dual-phase steel.

C.W. Xu

Papers

Strain ratio effects on microstructure discovery and low-cycle fatigue behavior of DP600 steel under cyclic shear path