Prediction of stable tearing in fatigue crack growth

Stable tearing has been observed on many fracture surfaces of in-service failures of aluminium alloy aircraft components. Separate studies show that stable tearing is able to occur under constant-amplitude (CA) or variable- amplitude cyclic (VA) loads, and it has been proposed that in aluminium alloys, the first onset of tearing occurs when the maximum stress intensity factor of the cycle exceeds the fracture toughness. This paper describes a study to produce constant- and variable-amplitude tearing in 7075 aluminium alloy compact tension specimens which examines this phenomenon in greater detail. The results show that CA and VA tears are macroscopically different and initiate at different values of stress intensity factor.