A multi-scale model for predicting the thermal shock resistance of porous ceramics with temperature-dependent material properties

This paper develops a novel multi-scale thermal/mechanical analysis model which not only can efficiently measure the thermal shock response but also highly reflects the effects of diversiform micro-structures of porous ceramics. Knowledge of the temperature distribution and time-varied thermal stress intensity factors (SIF) is derived by finite element/finite difference method and the weight function method in the macro continuum model. The finite element analysis employs a micro-mechanical model in conjunction with the macro model for the purpose of relating the SIF to the thermal stress in the struts of the porous ceramics. The micro model around the crack tip was established by using Voronoi lattices to accurately explore the micro-architectural features of porous ceramics. Hot shock induced center crack and cold shock induced edge crack are both considered. Effects of relative density and pore size on the thermal shock resistance are investigated and the results are well coincident with the experimental tests. The influence of cell regularity and cross section shape of the cell struts is discussed and the corresponding explanations are provided. The importance of incorporating temperature-dependent material properties on the thermal shock resistance prediction is quantitatively represented. These multi-faceted models and results provide a significant guide to the design and selection of porous ceramics against the thermal shock fracture failure for the future thermal protection system of space shuttle.