High cycle fatigue analysis in the presence of autofrettage compressive residual stress

An experimental and numerical investigation of the effect of residual compressive stress on the high cycle fatigue life of notched low carbon steel test specimens is presented. Experimentally determined cyclic stress strain curves for S355 low carbon steel are utilized in a finite element analysis plasticity modelling framework incorporating a new cyclic plasticity material model representative of cyclic hardening and softening, cyclic mean stress relaxation, and ratcheting behaviors. Fatigue test results are presented for standard tensile fatigue test specimens and novel double notch specimens. Double notch specimens are tested with and without compressive residual stress prior-induced through tensile overload. It is shown that cyclic plasticity phenomena have a significant influence on the induced residual stress distribution and also on material behavior when fatigue tested in the high cycle regime. It is observed that higher initial compressive residual stresses magnitude does not necessarily lead to a longer fatigue life. Finite element analysis using the new cyclic plasticity material model shows this behavior is due to combined residual stress redistribution under fatigue test cyclic loading and cyclic hardening effects. A fatigue life methodology based on the stress-life approach augmented by a critical distance method is proposed and shown to give good agreement with experimental results for test specimens with no induced residual stress. The results obtained for specimens with induced residual stress are more conservative, but the degree of conservatism is significantly lower than that in the conventional stress life approach. The proposed methodology is therefore suitable for analysis and design assessment of components with pre-service induced compressive residual stress, such as autofrettaged pressure components.