Abstract
The mechanism of fatigue crack propagation in pure aluminum was investigated. Two types of fatigue crack propagation tests were carried out. One of them was a cyclic torsion test with static tension using a pre-cracked specimen. In this test, the effect of static tension on shear mode crack propagation by cyclic torsion was examined. The other was a push-pull fatigue test of plate type specimens in which a slit was cut in the center section of the test section. The slit direction cut in specimen was perpendicular or a 45 degree inclined direction to the specimen axis. In the former, it was found that the application of some static tension was necessary to continue the shear mode crack growth by cyclic torsion. In the latter, crack propagated by mode I or by a mixed mode, which combined mode I and shear mode, depended on the testing conditions. In these cases, the crack propagation rate da/dN was evaluated with a modified effective stress intensity factor range, which was independent of the crack propagation mode. In the pure aluminum case, the shear stress strongly affected crack propagation rate. This was thought to be related to the crystal structure.
