Some physical, mechanical, and transport properties of crackers related tothe checking phenomenon

Several key properties relevant to the checking phenomenon of crackers were experimentally determined. Linear expansion coefficients were determined f rom direct measurement of the changes in the distances on the cracker surfa ce. Aw of crackers was measured and the isotherm data were fitted with the GAB equation. Effective moisture diffusivities were determined from drying data using the slope method. The moisture diffusivities ranged from 1.4 x 1 0(-4) - 1.8 x 10(-9) m(2)/s over a temperature and moisture range of 40-90 degrees C and 3-14%, respectively. The diffusivities change little at high moistures but decrease sharply as moisture content drops below 6%. Fracture strength, strain, energy, and bending modulus were measured using a 3-poin t beam bending technique. They were all dependent on temperature but showed little dependence on moisture between 1.5% and 4%. Results from the stress relaxation tests demonstrated the cracker can be treated as a thermo- and hydrorheologically simple material. A master curve was constructed for the uniaxial relaxation modulus and represented by a generalized Maxwell model. (C) 1999 Elsevier Science Ltd. All rights reserved.