Fatigue Damage in Coarse Al Crystals

Abstract

Many studies reported so far on fatigue fracture mechanisms suggest that slip deformation in crystals plays the most fundamental role in fatigue damage formation. In this study, fatigue damages in each crystal grain, such as development of slip bands, formation of extrusion and intrusion or persistent slip bands and crack initiation, have been observed in conjunction with Schmid factors which are useful to explain quantitatively the easiness of slip deformation in each crystal grain. A mechanism of fatigue damage formation is discussed here on the basis of the relationship between these results and the misorientation measured by back-reflection Laue method.
The results obtained are as follows;
(1) A fatigue crack appears in the crystal which has two equally large Schmid factors on Critical-slip-plane and Primary-slip-plane. The formation of such critical damage as a crack is independent of the other two Schmid factors on Conjugate-slip-plane and Cross-slip-plane.
(2) A fatigue crack is always observed in the persistent-slip band on Primary-slip-plane.
(3) Before the crack initiation, only the slip bands on Primary-slip-plane can be observed, but after the initiation, slip traces of Critical-slip-plane also appear around the crack, forming the structure of the double slip bands.
(4) The formation of fatigue damage is considered to be promoted by the activity of the second slip system on Critical-slip-plane.