New perspective on slip band decohesion as unifying fracture event during fatigue crack growth in both small and long cracks

摘要

Fractographic observations obtained from the aluminium alloy 2024- T351 form the basis for a qualitative model of fatigue crack growth which seeks to provide a unified understanding of crack initiation, small crack growth, and long crack growthfrom threshold to well advanced stage II growth. During this range of crack growth, it is deduced that plastic deformation at the crack tip can be localized by a three-dimensional array of in tense slip bands. Decohesion at these slip hand interfaces isviewed as being the underlying fracture event that leads to crack growth. This concept explains the observed crack path, is consistent with several basic features of fatigue crack growth, and links crack growth with an accepted model for crack initiation. It identifies a unit increment of crack growth and provides a source of damage for the process zone ahead of the crack tip. The concept is not material dependent, but does depend upon the concentration of slip into persistent slip bands. An effect ofenvironment on crack growth is expected to follow from its effect on slip hand decohesion.