EFFECT OF SAMPLE DIMENSIONS AND DEFORMATION RATE ON THE TORSIONAL FAILURE OF DUMBBELL SHAPED GELS

Torsional failure measurements were made on gels with dumbbell and capstan geometries. As a comparison, cylindrical specimens were tested in uniaxial compression. Both brittle and elastic gels, made from carrageenan and locust bean gelling agents by selecting appropriate ratios of the two polymers, were investigated. Using the dumbbell geometry, the stress at failure was found to be independent of the sample dimensions while the failure strain decreased with increase in the aspect ratio. In addition, neither the stress nor the strain at failure depended on the strain rate. The failure parameters from the two torsion geometries and the compression test were found to agree provided comparison was made using appropriate sample dimensions.