A Fracture Surface Rotation Mechanism for Fatigue Tested 2219-T87 Aluminum Sheet

Fatigue crack propagation tests were conducted on 2219-T87 aluminum sheet to identify the factors that control the rate of fracture surface rotation. Center-cracked, axial loaded specimens were tested in air at room temperature using tension-tension loading. The log (da/dn) versus (ΔK) curve contained an inflection point that was associated with the flat to slant fracture transition. The size and shape of the plastic zone at the crack tip were determined as a function of the half-crack length by using optical interferometry. It was found that the rate of fracture surface rotation was controlled by the changing size of the crack tip plastic zone. It is proposed that fracture surface rotation in this material occurs by a process of crack movement within active slip zones. A discussion is given on the deformation mechanisms associated with fatigue fracture surface rotation.