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The characteristics of cyclic fatigue crack growth in a silicon nitride which hardly shows rising R-curve behavior were investigated by using specimens having an indentation-induced flaw. V-shaped behavior was observed in the relation between the maximum stress intensity factor K[sub max] and crack growth rate. When a crack growth rate is plotted as a function of the effective maximum stress intensity factor K[sub eff,max] which takes account of the residual crack opening stress component K[sub r] in addition to K[sub max], crack growth behavior is expressed by a power law relationship for the region above a crack length of about 0.37 mm in this experiment. However, it deviates from this relation below the critical length. Such crack growth behavior is explicable by introducing the term of the effective stress ratio R[sub eff] defined as (K[sub min] + K[sub r])/(K[sub max] + K[sub r]). Crack growth behavior in the terms of K[sub eff,max] and R[sub eff] is expressed by a unique growth law, irrespective of crack length, i.e. da/dN = C(K[sub eff,max])[sup 30]([Delta]K[sub eff])[sup 5], where [Delta]K[sub eff] = (1 [minus] R[sub eff])K[sub eff,max]. Such behavior is consistent with that in the specimen containing a through-thickness crack. This equation indicates thatmore » fatigue crack growth rate in the present material is particularly sensitive to K[sub eff,max], and less sensitive to [Delta]K[sub eff].« less |
