On the Growth of Small Fatigue Cracks in Two Squeeze-Cast Aluminum Alloys

Abstract

It is now recognized that the fatigue lifetime of many structural components is determined by the rate of growth of small fatigue cracks. However it is not a straightforward matter to analyze the growth of these small cracks through the use of a traditional linear-elastic fracture mechanics approach for the following reasons: (1) on going from the micro-crack growth range to the macro-crack growth range, fatigue crack growth behavior undergoes a transition from stress control to stress intensity factor control; (2) because of the large plastic zone size to crack length ratio in the small crack growth regime, crack growth is elastic-plastic in nature rather than linear-elastic, and (3) the crack closure level increases from zero up to the level associated with a macroscopic fatigue crack as the fatigue crack increases in length in the small crack regime. The present paper presents an analysis of short crack growth data in two squeeze-cast aluminum alloys, and also discusses the Nisitani-Goto elastic-plastic relationship for fatigue crack growth.