Crack Growth Modelling in the Silicon Nitride Ceramics by Application of the Cohesive Zone Approach

Abstract

Specific silicon nitride based materials are considered according to certain practical requirements of process, the influence of the grain size and orientation on the bridging mechanisms was found. Crack-bridging mechanisms can provide substantial increases in toughness coupled with the strength in ceramics. The prediction of the crack propagation through interface elements based on the fracture mechanics approach and cohesive zone model is investigated and from the amount of damage models the cohesive models seem to be especially attractive for the practical applications. Using cohesive models the behaviour of materials is realized by two types of elements. The former is the element for classical continuum and the latter is the connecting cohesive element. Within the standard finite element package Abaqus a new finite element has been developed; it is written via the UEL (users element) procedure. Its shape can be very easily modified according to the experimental data for the set of ceramics and composites. The new element seems to be very stable from the numerical point a view. The shape of the traction separation law for three experimental materials is estimated from the macroscopic tests, JR curve is predicted and stability of the bridging law is tested.

Cohesive Zone Modelling and the Fracture Process of Cement-Based Composites

“…The input parameters for the material based on the glass matrix were determined from the experiments to determine the fracture toughness and compared with the procedures and predictions in [12]. Thus, the fracture energy was assigned to the region under the traction separation law.…”

“…The development of an adequate CZM in this case is a rather delicate task: namely [9] refers to various both potential and non-potential formulations, whereas [10] works with nonlocal damage evaluations. The classical finite element technique is not optimal for such numerical analysis, which stimulated its upgrades working with special enhancement basis functions on variable interfaces, as the extended finite element method (XFEM) by [11], applied to special ceramics by [12]. Nevertheless, the physically transparent and computationally robust coupling of diffuse damage with sharp cohesive cracks, as suggested by [13], is still a significant research challenge, even in mathematical existence and convergence theory, applying the method of discretization in time (relying on the properties of some special types of Rothe sequences), as sketched by [14].…”