Mesoscale modeling of fragmentation of ceramics under dynamic compressive loading

We present the results of a numerical analysis of ceramics under dynamic compressive loading conditions. The analysis is performed at the mesoscale level using a grain-based finite element scheme that accounts for the granular microstructure of the material. An explicit cohesive/volumetric finite element scheme is used to simulate the constitutive and failure response of the ceramic specimen subjected to uniform or impact-induced compressive loading. In this analysis, failure is assumed to be of intergranular nature, i.e., the cohesive elements are placed along the grain boundaries. A rate-independent, damage-dependent cohesive failure model is used to characterize the progressive failure of the cohesive surfaces. Coupling between normal and shear failure is achieved by expressing the normal and tangential components of the cohesive traction vector in terms of the L₂ norm of the non-dimensionalized displacement jump vector. Contact between the fracture surfaces and between the fragments is captured through a combination of a cohesive-based and minimization-based contact enforcement schemes. The damage evolution during the fragmentation process is characterized in terms of two different and complementary damage parameters: the first one denotes the appearance and propagation of the distributed damage (or micro-cracks) as cohesive surfaces progressively fail under the effect of the dynamic loading conditions; the second one characterizes the coalescence of the micro-cracks and the creation of fragments. Special emphasis is placed in this paper on the analysis of the frictional contact effect on the initiation, propagation and final extent of the fragmentation process. A detailed parametric analysis is performed to study how the value of the friction coefficient affects the energy absorption process associated with the fragmentation event under various strain rate levels and for different grain sizes.