Fracture toughness of brittle honeycombs

Existing models for the fracture toughness of brittle cellular materials are based on the assumptions that the crack is large relative to the cell size and that the modulus of rupture of the cell wall material is constant: both may, in practice, be invalid. Here, we account for the effect of short cracks by using a finite element analysis and for that of the variability in the cell wall modulus of rupture by describing it by a Weibull distribution. The results of the analysis indicate that if the crack half length/cell size is less than 7 the fracture toughness is reduced and that the way in which the fracture toughness varies with cell size depends on the Weibull modulus of the cell wall material.