The present paper describes results of a comprehensive numerical investigation of Ice-structure interaction phenomena using the finite element method. The formulation includes the effects of both material nonlinearities and large deformations. The numerical solution is obtained in a stepwise manner by applying the external loading in finite increments and restoring equilibrium by iterations. The approach described in the present paper is based on a viscoplastic constitutive model for ice. In this model the elastic, creep and plastic components of strain are additively combined. As a result, ice forces on structures can be predicted for a broad range of strain rates. The constitutive model which has been developed for general orthotropic (i.e., orthogonal anisotropic) materials, encompasses a variety of creep laws and failure criteria. To check the capabilities of the present formulation, the case of simple ice indentation under plane stress conditions was selected. Results from numerical simulations were obtained for different aspect ratios and for varying indenter velocities.
The prediction of Ice forces on structures relies heavily on a thorough understanding of how ice deforms under stress. The constitutive behaviour of ice is, however, highly complex and more intricate than that of ordinary engineering materials. First of all, ice is a very inhomogeneous and variable material whose mechanical behaviour may range from highly ductile to extremely brittle, depending on the state variables. More detailed descriptions of the constitutive behavior of ice can be found in the textbooks by Michel and Sanderson. The constitutive properties of ice are directly tied to the microstructure of the material. Like other crystalline materials, the crystal structure, i.e., size and orientation of the crystals, plays an Important role in determining the mechanical properties of ice Columnar grained ice, therefore, exhibits anisotropic mechanical properties. Other factors which influence the constitutive properties are temperature, porosity, salinity or brine volume and presence of organic or inorganic inclusions.
