Study on mechanical properties and constitutive model for polycrystalline ice samples

In this paper, the triaxial compression tests with different confining pressures and strain rates are carried out on polycrystalline ice samples at - 6 degrees C, and under these conditions all the samples behave strain softening, with volumetric contraction followed by dilatancy at the lower confining pressure, and dilatancy at the higher confining pressure. Based on the framework of breakage mechanics and the above test data, a binary medium constitutive model is established to describe the mechanical properties of polycrystalline ice samples. In this model, polycrystalline ice is composed of two parts: the bonded elements and frictional elements. The bonded elements behave the mechanical properties of elastic-brittle, and the frictional elements have the mechanical properties of elastoplasticity. Under the external loads, the bonded elements gradually break up and transform into frictional elements, and both bear the load together. With the homogenization theory, the definitions of breakage ratio and strain concentration factor are given, which describe the evolution of the polycrystalline ice structure and the uneven distribution of strain on the mesoscopic level. Some parameters of the constitutive model are determined from the triaxial compression test results and the others are determined by trial and error. Meanwhile, the evolution law of the parameters varying with confining pressure is given. Finally, the test curves are compared with the predicted curves to verify the rationality of the model.