Ductile Fracture Prediction for Marine Structures

Reliable modelling of fracture on a structural scale restricts the type of the finite elements used in the analyses to shell elements with in-plane dimension larger than the thickness. Thus, we consider a comprehensive constitutive formulation embedded in the shell mechanics framework. We propose a three-invariant plasticity model that accounts for dependence of the strain at fracture on both stress triaxiality and the third invariant of the deviatoric stress, which has a significant influence for shear-dominated stress states. This is achieved through a phenomenological damage evolution equation that includes both the dilatational term and plastic deviatoric energy term. The latter is dependent on the omega parameter, which can be considered a normalization of the Lode angle. A consistent calibration procedure is also developed based on a small number of carefully selected coupon-level experimental tests.