A measure of a material's resistance to the propagation of an existing crack. Useful for evaluating the material's ability to resist the effects of fabrication defects and operational damage on mechanical service.
Materials with a higher fraction toughness can sustain larger defects before failing under the same load. Uses units of stress (force per unit area) times square root of distance.
ASTM testing standards include B645 and B646 for aluminum alloys, B771 for cemented carbides, C1421 for advanced ceramics, D5045 for plastics, D5528 and D6671 for fiber reinforced polymeric composites, E399 and E1304 for metals in general, E1221 for ferritic steels, E1820 for no material in particular, and E2818 for welds.
ISO standards include 12135 and 12737 for metals, 15024 for fiber reinforced composites, 15653 for welds, 15732 and 18756 for fine ceramics, and 13586 and 17281 for plastics.