Cyclic inelastic constitutive equations and their impact on the fatigue life predictions

Cyclic plasticity and viscoplasticity constitutive equations are revisited in the context of fatigue life analysis of components submitted to small strain amplitudes but high strain ratio. The model used is based on a series of back stresses, each of them containing a threshold in the dynamic recovery term. Capability to correctly reproduce the cyclic softening and the limited mean stress relaxation is particularly examined, with the help of analytical solutions for uniaxial conditions. Comparisons are made with available experimental data on a Titanium alloy and a Nickel base superalloy, both in terms of the stabilized mean stresses and for the corresponding fatigue life prediction.