Direct Evaluation of J-Resistance Curves from Load Displacement Records

The objective of this work was to experimentally develop a key curve for compact specimens of Hy130 steel and to use this experimental function to generate the J-resistance curve from load displacement records alone usingthe analysis of Ernst et al. Eight ½T compact tension specimens with crack lengths from a/W = 0.59 to 0.94 were used to generate a series of load displacement records, which were assembled in a computer file as the key curve for geometrically similar compact specimens of this steel. Using this file, J-resistance curves (J-R curves) for IT compact specimens were then obtained directly from the load displacement records and compared with unloading compliance J-R curves obtained for the same specimens. The critical J-values were found to be identical, but the new analysis gives much lower J-R curve slopes beyond the criticalJ for nonside grooved specimens. For side grooved specimens in which the crack does not tunnel, however, the J-R curves for the two methods were nearly identical. The J-R curves evaluated using the key curve method showed much less dependence on crack length than those obtained by the unloading compliance method. Agreement between the predicted and measured final crack length was excellent using the key curve method.