Stochastic fracture of ceramics under dynamic tensile loading

Three-dimensional numerical simulations are performed to investigate the dynamic tensile properties of ceramics, using explicit dynamic FEM and cohesive element techniques. A micro-cracking model considering the stochastic distribution of internal defects is developed. The model consists of a Weibull distribution of the local strengths, and a facet area modification that accounts for the equivalent geometry of the elements. Preliminary calculations are performed to verify the capability of this model in addressing mesh-dependency. The calculations show that the brittleness of the material tends to deteriorate the mesh-dependency problem. However, by using the equivalent geometry modification with adequate parameters, the unwanted mesh-dependency can be satisfactorily corrected. Parametric studies are performed to investigate the influences of the fracture energy and Weibull modulus. It is seen that for a fixed loading speed, the strength of the specimen increases with the fracture energy, but decreases when the material becomes more heterogeneous. The scatter of specimen strengths decreases when the material becomes more ductile. The observed phenomena are explained by the micro-cracking mechanism of ceramics failure. The effect of loading speed is also investigated, significant rate-hardening effect is observed. It is shown that the micro-cracking mechanism, which is different in the dynamic loading case and static loading case, can explain the observed rate-dependency of the ceramic tensile strength. (C) 2004 Published by Elsevier Ltd.