Phenomenological model of thermal shock propagation in ceramic monolith

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Abstract

A discrete model is used to study the behavior of shock propagation, crack formation, and crack propagation of a thin ceramic plate. This plate represents a wall of a channel in a monolithic structure. The model involves a spring-node formulation on a rectangular geometry, which approaches the continuum model correctly when the Poisson ratio is taken as 0.25. Viscous damping is also included. Shock waves originate from perturbations due to local ignition (hot spots), sudden quenching or other changes in operating and driving conditions. The shock wave propagates from the perturbed region. Internodal displacements are used to calculate strains, and the values are compared to a maximum strain associated with failure. Spring constants are set to zero when the maximum strain is exceeded. Reflection of compressional waves from free boundaries as tensional waves leads to enhanced crack formation near the free boundary. Shock waves attenuate much faster when the plate is precracked. Propagation velocities are lower for precracked plates, due to a decrease in (effective) Young's modulus. Velocities of pure compressional and shear waves compare quite well with theoretical values.

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