Estimation techniques for the calculation of J have enabled the development of simpler data reduction methods for multiple specimen J-integral tests and also prompted the development of single-specimen tests. This report describes an experimental program conducted to evaluate the accuracy of these estimation techniques. Comparisons between the values of J as calculated by the energy rate definition and those calculated by the estimation techniques for compact toughness, three-point bend, and center-cracked tension specimens are made.

A JIc test procedure using a single deeply cracked specimen is proposed. The crack extension is measured by partially unloading the specimen to determine the elastic compliance. JIc tests were made using ASTM A469 steel. Compact specimens from 1/2T to 5T were tested. No size effect was found. Results from two independent laboratories are presented and are in agreement. The errors due to simple formulation of JI calculation, periodic partial unloading, and simplified analysis for the extension of deep cracks in compact specimens are explored. The measurement point of crack extension for establishing JIc is discussed. The results indicate that a practical and effective single specimen test procedure has been developed.

Since the development of the unloading compliance method, numerous improvements to this JIc and J-R curve testing procedure have occurred over the past five years. This paper presents a description of many of these test technique improvements along with the results of the improvements. Improvements in both mechanical and electrical systems are shown to greatly improve the reproducibility of the unloading compliance data. Computerization of the data reduction has led to a better understanding of the requirements necessary for an accurate J-versus-Δa R-curve.

Methods for determining the J integral from an experimental load versus load point displacement curve for the compact specimen are discussed. The original analysis by Merkle and Corten, which accounted for the tension component in the compact specimen, is presented along with a simplified version (of the analysis) that is shown to be essentially equivalent to the original formulation. Based on experimental results from Landes, Walker, and Clarke, a further simplified expression is recommended as the best expression to use for determining J for the compact specimen.

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