Failure assessment diagram of tilted cracks

In existing failure assessment codes of flawed structures, a tilted crack in pressure vessels is dealt with by projecting the crack onto principal planes and then analyzing the projections on the planes as I mode cracks. However, the "projecting" approach, in fact, is derived from mixed mode fracture criteria of LEFM, so the application in pressure vessels is beyond the limitation of brittle fracture that seldom takes place in pressure vessels. In the present paper, a theoretical explanation of failure assessment diagram of flawed structures was generalized from EPRI's explanation that was given to explain the two-criteria approach for materials hardening in accordance with Ramberg-Osgood's law. Assimilating the features and advantages of CEGB report R6-Res3, a failure assessment diagram of structures containing tilted cracks was proposed based on the recent advances in research of I-II mixed mode fracture in China using meso-mechanics of ductile metals.