Elastic plastic fracture mechanics investigation of toughness of wet colloidal particulate materials: Influence of saturation.

Hypothesis: Previous use of linear elastic fracture mechanics to estimate toughness of wet particulate materials underestimates the toughness because it does not account for plastic deformation as a dissipation mechanism. Plastic deformation is responsible for the majority of energy dissipated during the fracture of wet colloidal particulate materials. Plastic deformation around the crack tip increases with saturation of the particulate body. The toughness of the body increases with increasing saturation.

Experiments: Elastic plastic fracture mechanics using the J-integral approach was used for the first time to measure the fracture toughness (J) of wet micron sized alumina powder bodies as a function of saturation. The samples were prepared by slip casting. The saturation was controlled by treatment in a humidity chamber. The elastic modulus (E) and the energy dissipated by plastic flow (A) were measured in uniaxial compression. The critical stress intensity factor (K) was measured using a diametral compression sample with a flaw of known size. The fracture toughness (J) was calculated from these measured quantities and the geometry of the specimen.

Findings: Elastic plastic fracture mechanics was used for the first time to quantitively account for plastic deformation of wet particulate materials. The linear elastic fracture mechanics approach previously used accounted for less than 1% of the total energy dissipated in fracture. Toughness (J) was found to increase with increasing saturation due to plastic deformation that increased with saturation level. The improved understanding of toughness as a function of saturation will aid in providing quantitative analysis of cracking in drying colloidal films and bodies.