Accounting for initial plastic deformation for fatigue crack growth predictions under TMF loading condition

Crack propagation rates from isothermal and in-phase high temperature thermomechanical fatigue crack propagation tests for Inconel 792 resulted in a rather large scatter band when plotted against the linear-elastic stress intensity function Delta K. Previous observations indicated that the residual strains generated during the first few cycles in the uncracked specimen can explain, to a large extent, the differences between the tests. An effective Delta K-eff was calculated for each test based on non-linear FE simulations. When the crack propagation rates for each test were plotted against the calculated Delta K-eff, the curves collapsed to a smaller scatter band.