AN EXPERIMENTAL PARAMETER J(MAX) IN ELASTIC-PLASTIC FATIGUE-CRACK GROWTH

Imitating Garwood's 3-parameter technique, an experimental parameter J (max) was introduced to predict fatigue crack growth rate (da/dN) over a wide range including small scale yielding and large scale yielding. It was found that for a Delta K-increasing fatigue test condition, J( max) is a valid parameter. A significant crack growth acceleration, ca used by a transition of fracture mechanism, occurs when J(max) = J(IC) . The fracture mechanism involving striation formation when J(max) < J (IC) becomes ductile tearing when J(max) > J(IC). Equations to predict the effect of stress-ratio on J(max) as well as on da/dN are given.