Crack closure in 2219-T851 aluminum alloy

Abstract

The effects of specimen thickness, stress ratio ( R) and maximum stress intensity factor ( K max ) on crack closure (or opening) were studied using a 2219-T851 aluminum alloy. The crack length and the occurrence of crack closure were measured by an electrical potential method. The experimental work was carried out within the framework of linear-elastic fracture mechanics. The experimental results show that the onset of crack closure (or opening) dependes on R, K max ), and specimen thickness. In terms of the “effective stress intensity range ratio” ( U), as defined by Elber, the results show that U tends to increase for increasing R, decrease for increasing K max , and decrease with increasing specimen thickness. From these trends, it is shown that the “effective stress intensity range” ( ΔK eff ) does not always increase with increasing stress intensity range ( ΔK). The experimental results show that crack closure cannot fully account for the effects of stress ratio, specimen thickness and K max on fatigue crack growth. The use of ΔK eff as a parameter for characterizing the mechanical driving force for fatigue crack growth is questioned.