Quantification of Engineering Limits to J Control of Ductile Crack Growth

The J-integral has been developed as a ductile fracture parameter over the past 15 years and has been applied to an ever-expanding range of applications and materials. Limits originally placed on the application of J by analytical considerations have, in most cases, proven too stringent—and in some cases the analytical limits have even seemed to be inapplicable or irrelevant. This has been particularly true of the omega (ω) criterion introduced by Hutchinson and Paris. Experimental work has seemed to show little correspondence between the limits predicted by this criterion and the experimentally measured size limitations.

Recent experimental work by Joyce et al. has shown that the J-integral is applicable to much larger crack extensions than previously proposed. Using these experiments Joyce and Hackett have proposed an experimental method to define the limit to J-integral controlled crack growth.

This paper now shows that the ω criterion is consistent with the collected data set, except that the limiting value for ω is on the order of one, not the value of 5 to 10 originally proposed. Three simple analyses are presented using the ω criterion to develop proposed limits on J and crack extension that can be used in a predictive manner for fracture analysis.