__Multi-axial Strength Data for Al _{2}O_{3}- and MgO-ZrO_{2}-Ceramics :__

Multi-axial strength tests have been carried out using tubular specimen made from Aluminiumoxide (Al_{2}O_{3}) and partially stabilised Zirconiumoxide (MgO-ZrO_{2}). The specimen were loaded with tension, compression and internal pressure to create a large variety of biaxial stress states in the specimen.

It is shown that for biaxial tensile stresses the effect of the multi-axial stress state can be neglected because of the large scattering of the material strength. Therefore for practical applications the computation of ceramic components can be simplified by using the maximum principle stress. A multi-axial stress hypothesis is not required. Under tension-compression the tension strength decreases with increasing compression load, when the compression is higher than one third of the uniaxial compression strength. Obviously in this case a multi-axial strength effect exits and has to be taken into account when computing ceramic components.

For computation a new multi-axial stress hypothesis was developed, that bases on a l ink between Weibull statistic and Mohr's circle. The total risk of rupture is understood as the sum of the risk of rupture created by shear and normal load.