On Fatigue Crack Growth and Stable Tearing

Abstract

An experimental and analytical investigation has been performed to examine the effect of concurrent fatigue cycling and stable tearing on the crack growth fracture resistance of EN3A steel at 360°C. The steel was tested in the as-received and hardened conditions, hardening being achieved by pre-cracking at a load comparable to the elastic limit of the test specimens. For each condition of the steel, resistance curves are obtained both with and without concurrent fatigue cycling.A significant increase in the crack growth rates occurred as a result of concurrent fatigue cycling. The rates are in reasonably close agreement with the values predicted from the sum of the fatigue crack growth and stable tearing components. The J-estimation formula of Ainsworth is used to demonstrate that there is no interaction between stable tearing and fatigue in the tests for the steel in the as-received condition. NOMENCLATURE a, a, = crack length, effective crack length C, 9 = constants in the Paris equation B, Be, B, = specimen thickness, effective thickness, net section thickness of a side grooved specimen da -= crack growth rate dn dJRda = slope of the J-Aa curve _ --increment of J per cycle dJ dn E = Young's modulus F ( a / W ) = stress intensity function J = fracture resistance K = stress intensity factor m (a/ W) = limit load function P = load Po = limit load W = specimen width cxf = reference strain p = constant v = Poisson's ratio uo = yield stress Q,~ = reference stress

On numerical analysis of damage evolution in cyclic elastic‐plastic crack growth problems

“…This increase may be attributed to static fracture modes, for example, from ductile tearing. Previous studies show that for some materials the interaction between the fatigue mode and static modes is negligible, [21][22][23] and the increased crack growth due to ductile tearing may be simulated by an amplification factor obtained from a monotonic J R curve:…”