An idea for predicting crack growth time to fracture under creep–fatigue conditions

The crack growth behavior of an iron based superalloy GH2132 (equivalent to A286) under creep–fatigue conditions has been studied and the three stages I, II and III of crack growth rate curve da/dt−σn have been analyzed in the present paper. It is proved that the I-to-II transition point B and II-to-III point C separately depend on the initial test stresses, σ0, and the high-temperature mechanical properties (the yield strength, σ0.2, and the reduction of area, ϕ%), and that the ratios of the time through stage I (TAB ) and I+II (TAC) to the total lifetime (T) are related to cyclic frequency, f, and initial test stress, σ0 . An equation has been proposed to predict crack growth time to fracture (T) under creep–fatigue conditions:T=G ∫aBaC da/Aσmnwhere, a is a variable meaning crack length, aB and aC are the values of crack lengths separately corresponding to the transition point B and C, and G, A and m are constants of the alloy at the test temperature for a given cyclic frequency.