1.1 This test method covers the determination of the resistance to fracture of metallic materials under Mode I loading at static rates using any of the following notched and precracked specimens: the middle-cracked tension M(T) specimen, the compact tension C(T) specimen, or the crack-line-wedge-loaded C(W) specimen. A K-R curve is a continuous record of toughness development (resistance to crack extension) in terms of KR plotted against crack extension in the specimen as a crack