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

Abstract

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.

Analysis of residual stress relaxation of aluminum alloys EN AW 6061/‐82 T6 under cyclic loading

“…to Sellen et al 6 for 6082 and Repplinger et al 7 for 6061). No sign of mean stress relaxation was observed, but cyclic loading may result in a shift of the residual stress field 24 . The FE material model should fully include the cyclic material characteristics.…”

“…Common residual stress measurement techniques for metals are based upon non‐destructive X‐ray diffraction or on the destructive incremental hole‐drilling method combined with strain determination 23 . Okorokov et al 24 used a prestressed, notched tensile test specimen of the material S355 to analyze stress relaxation during axial cyclic loading, thus clarifying the complexity depending on the geometry, material response, nature, and magnitude of loading. Fatigue tests showed that the fatigue life of a component not only depends on the magnitude of induced compressive residual stress but also on cyclical hardening and plastic strain accumulation during high cycle fatigue loading.…”

“…Furthermore, these authors clarified also that equivalent von Mises stress identifies locations of plastic yielding and hence locations where residual stress relaxation can occur. Okorokov et al 24 analyzed the cyclic fatigue behavior in the presence of autofrettage regarding compressive residual stress for low carbon steel (S355), where no stress relaxation could be identified.…”

“…The equivalent stress σ v is also of interest as it can lead to stress relaxation if the maximum equivalent stress is higher than the cyclic yield strength as described in the work of Okorokov et al 24 The cyclic yield strength is given by the mean stress and the maximum allowable stress amplitude for the relevant Wöhler curve 40 or Haigh diagram 20 . The corresponding Haigh diagram for cyclic bending loading is presented in Figure 11.…”

Optimum Autofrettage Pressure of Hydrogen Valve Using Finite Element and Fatigue Analysis

“…An inspiring fatigue prediction method of parts subjected to an autofrettage process described the work [11].…”