The Brazilian test: a tool for measuring the toughness of a material and its brittle to ductile transition

Due to their brittleness, assembling of ceramics pieces is generally achieved through brazing but thermal stresses during cooling frequently induce cracking of the material used for brazing. In order to check if such damage is avoidable, it is necessary to characterize the brittle to ductile transition (BDT) of the material. Simple compression is not suited for crack studies, because of mixed loading (mode 11 + compressive mode I cracking). Another type of test, the cylinder splitting test, known as the Brazilian test, can be carried out by applying compressive forces on two opposite generatrix of a cylinder: this causes a uniform tensile stress on the plane containing the axis of the cylinder and the generatrix, leading to mode I cracking. The advantage of this test is to avoid expensive and random machining of brittle samples. This study shows that the Brazilian test is well adapted for the measurement of toughness and the characterization of the BDT of materials whose room temperature behaviour is brittle (silicides, intermetallics etc.).