A new life prediction method is proposed for a cast Ni base superalloy, René80, under fatigue -creep interaction (FCI) conditions based on its surface crack propagation behavior. In the previous ...paper, we proposed that the frequency modified total strain energy parameter was useful for evaluating the failure life (Nf) and crack initiation life (Nc) of a high strength superalloy under FCI conditions. The tensile strain energy parameter was obtained from the total tensile strain energy (ΔWTT) and the loading time (τTT) under tensile stress. In this paper, not only the failure and crack initiation lives but also surface crack propagation behavior are found to be evaluated by this parameter under FCI conditions. The surface crack propagation rate (da/dN) is a function of the parameter and surface crack half length (a); da/dN=B'(ΔWTTτnTT)l·awhere B', l, n are material constants. A new life prediction method taking account of surface crack propagation behavior and initiation life can be defined; N2a=A(ΔWTTτnTT)m+B(ΔWTTτnTT)-l(log(2a)-log(2a0))If the grain size (2a0) and the number of cycles Nc2a0=A(ΔWTTτnTT)m needed for the surface crack length to grow to 2a0 are known, the number of cycles (N2a) in a certain crack length (2a) can be determined from the above equation.
Proposed inelastic constitutive equations relevant to describing the effect of plasticity-creep interactions is classified and reviewed. Emphasis is focused on the unified constitutive models which ...are expected to provide the applicability to high temperature material behavior. Two series of simulations of material response by use of the models for the uniaxial and multiaxial stress states are presented for evaluation ; one is the results of a cooperative benchmark project carried out by the Subcommittee on Inelastic Analysis and Life Prediction of High Temperature Materials, JSMS, and the other is by the author.
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