Modeling of interfacial crack velocities in snow

Weak layers sandwiched between strong layers are found within a snowpack. The interface between the layers may have regions that are weakly bonded which act as stress raisers from where propagation of crack can take place, in mode II, along the interface. Damage ahead of the crack tip is modeled using a cohesive zone model. The crack propagation along the interface under a shear and compressive load (due to the weight of skier and snow) is studied using a finite element model with cohesive zone elements to describe the interface between the weak and strong layers. Four properties of the interface namely fracture energy in normal separation, fracture energy in shear separation, tensile and shear strengths are needed to characterize the cohesive elements. Tension and shear experiments on sieved snow with an ‘ice lens’ and shear experiments on natural snow with a weak interface are performed to get an estimate of the cohesive zone properties. The cohesive model, incorporated in a finite element mesh, is used to determine the speed of crack growth along the interface. The average cracks speed depends on modulus of the layers on either side of interface and for the modulus values studied here, is between 50 m/s and 300 m/s. The nature of crack propagation changes with thickness of the snowpack.