Abstract
The fracture toughnesses of some precipitation-hardened aluminum alloys have been evaluated, mainly by the use of precracked three-point bend specimens in instrumented impact testing. A recently developed interpretation of the specific surface energy method has been applied to calculate the initiation values of KIc and these values have been compared with those calculated using stress analysis equations. The value of unity thereby deduced for the geometrical constraint factor in these non-rate-sensitive materials may be appropriate to the type of fracture mode occurring in these alloys, that is, semiductile. The distinction in principle between fracture initiation toughness, expressed as GIc = w/ηA, and the average propagation toughness w/A has been noted and the latter used in studying crack tunnelling during semiductile crack propagation in thick sections of the alloys in the form of large, double-cantilever beam specimens.
