Prediction of Stable Crack Growth and Instability Using the VR-Curve Method

Abstract

This paper presents a methodology for predicting stable crack growth and instability of cracked structural components from results of laboratory tests on metallic materials under plane-stress conditions. The methodology is based on the displacement (VR) at the tip of a stably tearing crack. Basically, the VR-curve method is a resistance curve approach, such as KR and JR, except that the “crack drive” is written in terms of crack-tip displacement instead of K or J. The relationship between crack-tip-opening displacement, crack length, specimen type, and tensile properties is derived from the Dugdale model for the cracked structure of interest. This report describes the laboratory test procedure and calculations used to obtain the VR resistance curve from fracture tests of compact or of middle-crack tension (formally center-crack) specimens. The analysis procedure used to predict stable crack growth and instability of any through-the-thickness crack configuration made of the same material and thickness, and tested under the same environmental conditions, is presented. The various limitations of the present VR-curve method are given. Four example calculations and predictions are shown.