FATIGUE CRACK PROPAGATION BEHAVIOUR OF SHORT CRACKS; THE EFFECT OF MICROSTRUCTURE

TLDR

Fatigue cracks shorter than a critical length propagate anomalously quickly. This paper examines the concept of a ‘critical length’, identifying three regimes of behaviour for different crack lengths. The authors review published work across a wide range of materials to investigate the critical length concept and its three behavioural regimes. An approximate correlation between the critical length for short‑crack behaviour and the microstructure scale is found, LEFM cannot be applied to cracks shorter than this critical length, and a fatigue design philosophy incorporating short‑crack behaviour is suggested.

Abstract

Abstract— –Fatigue cracks shorter than some critical length tend to propagate anomalously quickly. This paper examines the concept of a ‘critical length’, identifying three regimes of behaviour for different crack lengths. Some published work is examined, covering a wide range of different materials. It is concluded that there is an approximate correlation between the critical length for short crack behaviour and the scale of the microstructure. LEFM is difficult, if not impossible, to apply to cracks shorter than this critical length because the material surrounding a crack cannot be assumed to approximate to a homogeneous continuum. Suggestions are made for a fatigue design philosophy which incorporates short crack behaviour.