Plasticity based material modelling of ice and its application to ship-iceberg impacts

The present paper considers numerical modelling of ship-iceberg collisions with emphasis on material modelling. A material model is proposed for ice. The model is pressure-dependent and strain rate-independent. The so called Tsai-Wu yield surface envelop is adopted, and plastic flow theory is used to derive the constitutive relationships. The ice is assumed to be isotropic, the temperature profile of icebergs is considered in the present model, and the influence of strain rate is discussed. A user-defined failure criterion is proposed; the criterion is based on effective plastic strain and hydrostatic pressure and enables crack initiation and damage evolution. The material model has been simulated using the commercial code LS-DYNA. Both local and global contact pressures have been investigated. Numerical examples show that the present model produces reasonably good results. It is applied to integrated analysis of iceberg impacts for the Accidental Limit State. Results from simulations of a head-on collision between a ship bow and icebergs are presented and discussed with respect to validity.