Fracture mechanics analysis of delamination buckling of a porous ceramic foam coating from elastic substrates

Ceramic foams are ideal materials for thermal protection systems such as those used as a thermal shield on the space shuttle. The working temperature difference between the outer and inner surfaces of the ceramic foam is extremely high. Under this adverse condition, the ceramic foam coating could buckle from its underneath structures. Therefore, the general problem of damage due to buckling delamination of a ceramic coating on an elastic substrate is investigated in this paper. The delamination buckling amplitude and the stress intensity factor at the tip of buckling region are derived in closed form in terms of the porosity of the ceramic foam. Based on the maximum amplitude and the critical stress intensity factor criteria, critical temperatures of coating buckling from the substrate are established. A fitting formula of maximum buckling amplitude as a function of outer surface temperature is given. It is found that higher porosity and length-to-thickness ratio of the coating will result in a smaller stress intensity factor. However, it seems that the buckling amplitude is independent of the porosity of ceramic foams.