Experiments have been carried out in which the passage of a crack through simple, well-defined pore arrays has been studied, using poly(methyl methacrylate) as a model system. These show that the crack front bows as it passes between the pores. This causes an increase in the length of the crack front, which is associated with an increase in the applied force required for continued crack growth. At high pore volume fractions this increase in line length is limited as the bowing crack intersects a pore ahead of it in the crack plane. Using these observations it is 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.

Keywords: Porosity, cracking, fracture energy