Investigation of Fatigue Crack Acceleration under Variable Amplitude Loading for a Structural Steel and Aluminium Alloy

There are currently serious doubts about the accuracy of Miners rule for designing welded structures subjected to variable amplitude loading, particularly under spectra cycling down from a constant maximum stress. The deficiency has been attributed primarily to stress interaction effects that cause crack growth acceleration. In this paper the crack growth response of a structural steel and an aluminium alloy to a loading spectrum designed to promote fatigue crack acceleration is studied and the potential mechanisms responsible are evaluated.

Specimen Geometry Effects on Dynamic Crack Propagation

Dynamic crack propagation in PMMA was studied using the method of caustics in combination with a Cranz-Schardin type high-speed camera. Three different types of specimen geometries were employed to achieve the crack acceleration, deceleration and re-acceleration process in one fracture event. Dynamic stress intensity factor KID and the crack velocity were evaluated in the course of crack propagation to obtain the relationship between KID and the velocity The effect of crack acceleration and deceleration on the KID -velocity relations was examined.