On the transferability of fracture mechanics parameters from specimens to structures using fem

Abstract

Reasons for different crack resistance behaviour in dependence on specimen size and geometry as well as conditions for the transferability of test results from specimens to structures are discussed on the basis of elastic-plastic FEM calculations for specimens and a cylindrical shell with a semi-elliptical inner surface crack. Up to general yield of the ligament no size effect on crack resistance should be expected in CT specimens as the stress strain field near the crack tip can be characterized by the J- integral or the crack tip opening displacement (CTOD). The conservation of a similar high multiaxiality of stress state in center cracked panels as observed in CT specimens is not possible due to ligament necking in the course of plasitification. The highest multiaxiality of stress state along the crack front region of a semi-elliptical surface crack in a tube or pressure vessel is very similar to that in the midplane of a CT specimen. Therefore, the strength assessment of such components can only be successfully performed on basis of tests on large or side-grooved CT specimens.