Abstract
In this paper the effect of pores on cracking is studied to establish how porosity influences the thermal shock resistance. Experiments have been carried out in which the growth of cracks through simple, well-defined pore arrays has been studied, using poly (methyl methacrylate) as a model system. It is shown that the crack front bows as it passes between the pores causing an increase in the length of the crack front, which is associated with an increase in the applied force required for continued crack growth. Comparison of predictions with experiments shown that the estimated change in the length of the crack front with porosity is very similar to the experimentally observed variation in the fracture energy in different ceramic systems. Using these ideas it is found that the temperature change required to initiate cracking can be increased by adding a pore volume fraction of approximately 0.1, but diminishes at higher pore volume fractions. However to obtain these improvements it is essential to ensure that there is no concomitant increase in the flaw size. The extent of cracking is only marginally affected by porosity.
