An engineering interpretation of pop-in arrest and tearing arrest in terms of static crack arrest, KIa

Abstract

When fracture toughness specimens are tested under displacement controlled conditions, they are often observed to exhibit unstable cleavage fracture followed by arrest of the cleavage mode wherein a significant load remains on the specimen (pop-in arrest). This behavior carries over into the ductile tearing regime wherein tearing may occur rapidly identified by load reduction and then proceeds at a discernible less rate (tearing arrest). Both these behaviors represent an initiation condition followed by an arrest condition. In this paper it is demonstrated that from either of the arrest conditions an arrest value may be determined which, for available experimental data, is shown to be an engineering estimate for the static crack arrest toughness, K Ia . A general lower bound property for the arrest value is postulated based on referenced information. A data analysis procedure is outlined and K Ic and K Ia estimates from sixty-eight 1/2, 1 and 2 in. thick compact specimens from two steels (A533 Grade B Class 1 and AISI 1018) tested between -40°F and 200°F are summarized. The crack arrest estimates are seen to compare favorably with K Ia results obtained by other investigators using 2 in. thick specimens. Also it is demonstrated that when failure is by fully ductile tearing, the crack arrest toughness is at least equal to the estimate for K Ia for the specimen. It is judged that an engineering procedure has been demonstrated for obtaining reasonable estimates of K Ia throughout the transition region and onto the upper shelf. Based on referenced work, shelf values are most likely specimen size dependent.