Crack model for toughness of green parts with moisture or a fluid binder

A model is presented to predict the toughness, K _IC, of green ceramics based on the binding forces of meniscuses formed between particles near the tip of the critical flaw. The model considers capillary pressure, surface tension, and the viscous flow of binders. Calculated toughness values were determined for moisture only, but the model can also be applied to binder meniscuses. Capillary pressure is highest at low moisture content. By using well-established force-distance relationships for the meniscus between single particles, toughness was determined as a function of moisture content. For nonagglomerated particles, K _IC increases with moisture content and decreases with contact angle. The particle-size dependence, predicted at a constant humidity is approximately the same as the Kendall model and experimental results found in the literature. If particles are agglomerated and the meniscus is between agglomerates, the toughness peaks at low moisture content. This model assumes that the capillary pressure is transmitted through the agglomerate. The calculated values of K _IC are approximately in agreement with the magnitude of the measured toughness values of binderless green parts having two different specific surface areas.