Attention is focussed on the determination of the crack growth resistance curve of a ductile material from load, load-point displacement and crack extension measurements using a single laboratory test specimen. A commonly used procedure is based on the separation of J_D into an elastic component J_E and a plastic component J_(DP), coupled with the ability to express J_(DP) for a non-growing crack in terms of the plastic energy and complementary plastic energy integrals via eta factors that are independent of the applied loadings. Against this background, the author reviews his two extremes procedure, whereby the appropriate eta factors are obtained by ensuring that J_(DP) assumes the correct form at the two extreme levels of deformation: small-scale yielding and extensive deformation at limit load conditions.
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