Destruction of materials by drying

Abstract

In this Chapter we shall analyze two approaches to the problem of fracture during drying: a microscopic approach that explains fracture as a result of the interaction of body particles and growth of individual cracks; and a macroscopic approach that attributes fracture to stresses generated during drying. Experimental observations and numerical simulations show that nucleation, growth and coalescence of microvoids and microcracks play the most important role in the process of ductile and brittle failure. These physical mechanisms of fracture (ductile, brittle and mixed, brittle-ductile) are sensitive to the history of acting stresses. In the case of dried materials the history of stresses is rather not involved. Fracture is involved in the actual state of stress and is influenced by the microstructure, the level of moisture content and temperature. Any suitable fracture theory for dried materials should account for the common observation that fracture is more likely if the dried body is thick or the drying rate is high. Both these items are conductive to generation of the internal shrinkage stresses.