The scale effects, which are characteristic for quasi-static and dynamic fracture of ice cover are determined. It is shown that in similar conditions of stable crack growth, vertical and horizontal components of external force acting upon the ice are proportional to different strengths of ice thickness: 13/8 and 2 respectively. Hence it is necessary to change its angle of inclination during the process of modelling. Other factors are also analysed which are necessary to take into account, particularly, the alteration of fracture pattern, which occurs "earlier" in model conditions when the ice thickness is smaller than in natural ones.
The development of fracture, i.e. the crack growth, diminishes the rigidity of a body, which brings about energy release. According to Griffith's criterion, if there is enough of this energy to form a new surface, and, to be more accurate, if the energy released is no less than the surface energy, then the crack grows. Their localization - the formation of the main crack - may take place after a long period of damage accumulation or immediately after the critical stress value is achieved, almost simultaneous with the initiation of volume distributed microcracks. However, independent of the type and level of volume distributed microcracks, the released energy is directly proportional to stresses, and so the corresponding criterion consists in evalution of stresses (development of volume distributed microcracks is analysed . Accounting for the influence of surface energy and volume distributed damages (or, which is essentially the same, Griffith's criterion and the classical criterion simultaneously) makes it possible to describe not only the scale effect connected with the crack advance but also the alteration of fracture mechanism and its dependence upon the size of the body [5J, particularly upon the thickness of ice.