A damage-based failure model for coarsely meshed shell structures

This paper presents a fast and reliable method for failure prediction of coarsely meshed shell structures. The method is especially relevant when investigating the impact performance of offshore structures, typically stiffened panel structures where the size of the structure limits the possible detailing level during analysis. The method combines a local instability criterion with post-necking damage in order to numerically model the failure process in large shell elements. The failure model is based on power law plasticity with the stress-based Bressan-Williams-Hill (BWH) local instability criterion and a coupled damage model after incipient necking. The BWH criterion gives a robust estimation of incipient necking for coarsely meshed shell structures. After necking starts, a mesh-size dependent damage model is coupled to the element strength for material softening until failure, assuming that the strain localization occurs locally inside the element within a virtual neck. The model is incorporated in the explicit FE code LS-DYNA. The material model formulation is validated against experiments at several levels; from formability tests with varying strain states to medium and large scale impact experiments, giving a robust prediction of energy dissipation and material failure in the structure with low mesh dependency. The material model is calibrated from a single uniaxial test, and gives robust and consistent simulation results in which details of the localized necking phenomenon is included in the behavior of large shell elements. Thus, it is readily used for structural design of offshore structures in order to assess the technical safety level of the structure against collisions in all phases of the design process. (C) 2015 Elsevier Ltd. All rights reserved.