On the risk of cracking in clay drying

Based on the assumptions related to porous media, the governing equations of mass transfer and static equilibrium are presented. The mechanical stresses generated by the drying strains are expressed according to the linear-elastic model. The von Mises cracking criterion is introduced in order to locate the area where risk for cracking occurs. The model is applied to the drying of Kaolin clay. Moisture and solid displacements results as well as evolutions of the criterion are exposed. The danger of cracking is the highest at the beginning of the drying, since the yield stress is low. The criterion reaches its peak value during the first hour and at a particular point, located on the surface, exactly in-between two corners. Moisture evolution has been measured by means of nuclear magnetic resonance (NMR) imaging, during the drying of a piece of Kaolin clay. The diffusion coefficient is evaluated from these experimental results. Finally, the model is used to reproduce them.