高耐力耐熱合金の疲労・クリープ相互作用下におけるき裂進展に基づく寿命評価法の検討

概要

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A new life prediction method is proposed for a cast Ni base superalloy, Rene80, 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 (N_f) and crack initiation life (N_c) of a high strength superalloy under FCI conditions. The tensile strain energy parameter was obtained from the total tensile strain energy (ΔW_<TT>) and the loading time (τ_<TT>) 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'(ΔW_<TT>τ^n_<TT>)^l・a where B', l, n are material constants. A new life prediction method taking account of surface crack propagation behavior and initiation life can be defined ; N_<2a>=A(ΔW_<TT>τ^n_<TT>)^m+B(ΔW_<TT>τ^n_<TT>)^<-l>(log(2a)-log(2a_0)) If the grain size (2a_0) and the number of cycles [N_<c2a_0>=A(ΔW_<TT>τ^n_<TT>)^m] needed for the surface crack length to grow to 2a_0 are known, the number of cycles (N_<2a>) in a certain crack length (2a) can be determined from the above equation.
1990-04-15