The effects of variable stress amplitude on cyclic plasticity and microcrack initiation in austenitic steel 304L

In this paper, recent results of the numerical simulation and experimental investigation of variable stress amplitude effects on cyclic plasticity and microcrack initiation in 304L steel are presented. A volume of the material corresponding to a realistic microstructure, containing about 150 grains, has been modeled on the basis of crystal plasticity theory. This model takes account of dislocation densities on the 12 slip systems, isotropic and kinematic hardening, grain sizes, crystal orientations and elastic anisotropy. er to investigate the effects of variable stress amplitude on cyclic plasticity, the fatigue tests were conducted under stress amplitude of 220–320 (overload) −220 MPa. Four loading paths were considered, which only differ in signs of the beginning and end of the overload block but not in level of amplitude. The fields of local stress and strain, maximum shear strain amplitude of 12 slip systems and the normal stress on the critical plane of maximum shear strain amplitude were simulated before, during and after overload. The numerical studies performed on a realistic polycrystalline aggregate of 304L have demonstrated that overload effects on cyclic plasticity and microcrack initiation are significant in all these four loading paths. By comparison with experimental results, local stress and maximum shear strain amplitude may be the good indicators for prediction of crack initiation under variable stress amplitude.