Slow crack growth study of plaster using the double torsion method

Double torsion tests were performed to study slow crack growth (SCG) behavior of dry plaster. Preliminary, the fracture toughness KIc was measured, and higher value than that obtained with notched beams in bending test was found. This can be attributed to interactions between the surfaces of the initial crack in the DT samples. For SCG investigation, both load relaxation and constant loading tests were conducted. It is found that the relaxation method is not suitable for quantitative determination of the SCG law. Indeed, the load relaxation is very limited for dry samples and cannot be correlated to the crack propagation observed on the tensile surface. The constant loading results show that subcritical crack propagation occurs at KI values lower than 30% KIc. This can be explained by the linkage of the main propagating crack with secondary cracks, the nucleation of which occurs at very low applied stresses.