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

Abstract 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.