Effect of meso to micro transition in morphology dependent fracture of silicon carbide ceramics.

摘要

The fracture behavior of brittle material such as Silicon Carbide (SiC) is affected by multiple factors during the fracture process. However, the increase use of SiC ceramics in numerous fields of industries is because of its superb thermal resistance, therefore, crack propagation analyses is of great importance. SiC usually is found in a polycrystalline form with grain boundary thickness ranging from a few nanometers to a few hundred nanometers and grains with multiple orientations with size of the order of few micrometers. This study focuses on analyzing how the interplay between different orientations of SiC and grain boundary thicknesses can be exploited for targeted improvement in the fracture resistance properties of SiC. Owing to the multiple length scales involved, a multiscale modeling strategy is employed. Images of experimentally processed nanoscale SiC morphologies were used to simulate crack propagation using the cohesive finite element method (CFEM). Dependence on specimen scale was considered by simulating microstructures of 2 different length scale windows: 300mum x 60mum (scale 1) and 75mum x 15mum (scale 2). In this study, the microstructural window at scale 1 did not explicitly consider the presence of grain boundaries. Due to stronger focus at scale 2, grain boundaries were explicitly modeled in the microstructural window. Loading rates of 0.1m/s and 1m/s were applied and element size was chosen to be 3000 nm and 450nm for scale 1 and scale 2, respectively, after the proper convergence study. The grain orientation and grain boundaries are big factors influencing the length scale dependent fracture behavior. Grain orientation layout is able to change not only the path of the cracks, but also the starting time of pre-crack propagation. By conducting such a computational study, unanswered experimental results of various brittle materials' fracture can be reconsidered. For different scales' simulations, cohesive energy as a function of crack length is not much different while the percentage of primary crack in terms of area is significantly larger than microcracks in scale 1. By adopting a preestablished equation based on the work of JR Rice to the simulation results, the role of microcraking versus the role of primary crack propagation on the overall fracture behavior was analyzed.