Recent Developments in JIc Testing

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Abstract
The J-integral, as proposed by Rice, has been shown to characterize the crack-tip stress and strain field under both elastic and plastic stress-strain conditions. The parameter offers a logical extension of linear elastic fracture mechanics concepts to include cases of large-scale plastic behavior. Begley and Landes proposed the J-integral (labeled JIc) as a measure of material fracture toughness under plane-strain conditions ranging from linear elasticity to large-scale plasticity. Data originally presented by Begley and Landes on two steels showed that JIc characterized fracture toughness under fully plastic conditions and was compatible with KIc in the linear elastic range. Subsequent work has shown that this approach is successful in a variety of metal alloy systems. In this paper the basis for the JIc approach to fracture toughness characterization is discussed. The recent developments in the method for determining JIc experimentally are explained as well as the future trends in the development of the test method. The present test method relies on the development of a fracture resistance curve where J is plotted as a function of stable crack extension. The present method employs multiple specimens where each specimen supplies one point on the fracture resistance curve. New test methods have been developed which allow this curve to be developed from a single specimen. Sample data are presented to illustrate the method. The relationship between KIc and JIc is illustrated in regions where both test methods apply. The present work directed at establishing the limitations of the JIc test method is presented, A brief description of the extension of the J-integral approach to other areas of cracking behavior is also included.