Drying-induced strain and stress: A review

This paper is to review the works on strains and stresses in materials during drying. The strains and stresses are caused when temperature and moisture gradients are generated in materials whose volume changes with heating and moisture removal. In such materials, failure and irregular deformation may be generated which affect considerably the quality of the products after drying. In the first part, modeling procedure is introduced for the analysis of the strain-stress behavior in elastic, viscous and viscoelastic materials combined with heat and moisture transfer. An overview of the works on strains and stresses and drying characteristics are presented for materials such as porous media, clay, sol-gels, agricultural products and foods in the second part. There are some materials that show both elasticity of the solid phase and viscosity of the fluid phase (water or solvents) or viscoelasticity. The stresses are often correlated with a suction pressure of fluids in pores and the flow rate is based on Darcy's equation for the elastic and viscous media and a kind of viscoelastic media. The general constitutive equations for strains and stresses are often analyzed with the strain behavior given by a function of moisture for some media as well. The emphasis is on the introduction of comprehensive criteria for understanding the problems of strain and stress development in materials subjected to drying.