Fractography of Fatigue Cracks Obtained under Simplified Flight-Simulation Load211 Histories

摘要

A fractographic investigation was made of fatigue cracks in two specimens tested211u001eunder simplified flight load histories. SEM observation showed striations in good 211u001eagreement with the crack growth records. Incompatibility of the crack front 211u001eorientation for the OL's when the crack was macroscopically still in the tensile 211u001emode led to a microscopically rough fracture surface. Another incompatibility 211u001eoccurred for larger cracks when the fracture surface was macroscopically already 211u001ein the shear mode. A zigzag fracture surface topography with alternating dark and 211u001elight bands was then obtained. These macro bands (one per flight) also agreed 211u001ewith the crack growth records.