| Advanced ceramic materials are finding increasing use in different adverse mechanical and chemical situations due to their good mechanical properties, corrosion resistance and thermal stability. Their wider use is however impeded by their brittleness, especially in applications involving dynamic loads, in which dynamic fracture and fragmentation events are often observed.; Most of the research aimed at the understanding of dynamic crack initiation and propagation mechanisms in this class of materials do not take into account the inherent granular microstructure of ceramics. In this project, we develop a grain-based finite element scheme that allows for the mesoscale study of a range of dynamic failure events in granular media, including propagation and branching of inter-granular cracks and fragmentation. The scheme relies on Voronoi tessellation to generate the granular microstructure and on a 2-D explicit cohesive/volumetric finite element (CVFE) scheme to simulate the constitutive and failure response of the material under dynamic loads. A non-linear kinematics description is used in our analysis to account for the possible large deformations and/or rotations of the grains during the fracture event. A viscoplastic update algorithm is also introduced to model problems (such as dynamic indentation and grinding) for which localized plasticity plays a key role. The numerical scheme finally relies on robust contact search and enforcement algorithms to capture the complex contact events between fracture surfaces, between individual grains and between the impactor/tool and the ceramic specimen.; To demonstrate the capabilities and versatility of the grain-based CVFE code, we investigate four dynamic fracture problems. The first one is concerned with the propagation of dynamic intergranular cracks under mode I loading, with special emphasis on the effect of the microstructure on the branching instability of the crack motion. The second problem is that of dynamic fracture under mode II loading and the capture of the associated elastic bridging of the crack by partially or completely dislodged grains. The third application is that of dynamic fragmentation of ceramic materials primarily under tensile conditions. The emphasis here is to understand the effect of the microstructure and cohesive strength of the material on the onset of the failure event and on the fragment size distribution. Finally, we present the results of a preliminary study of a dynamic single grit scratch test used to simulate the damage created by a single grinding particle on the machined ceramic component. |
