Technical requirements of complex systems the nuclear industry is obliged to develop new types of materials and methods mechanical tests to determine their mechanical properties. The development of known and development of new methods of mechanical testing is an important task for nuclear power. It is proposed to use the test of bending small thin disk specimens simply supported along the contour, to determine the resistance of material to tensile strain. The results of computer analysis of stress-strain state and test a thin disk specimens made of brittle materials are cast iron and graphite as a possible model, and directly samples made by electro-impuls methods are presented. It is shown the effect of size of specimens on the resistance to their destruction and different character of deformation and destruction of samples of cast iron and graphite. The possibility of application of thin disc samples for the determination the resistance to tensile strain of the composite ceramics based on SiAlON with various additives Y2O3, SiC, TiN, and boron carbide B4C is confirmed.