FRACTURE-BEHAVIOR OF SINTERED SILICON-NITRIDE UNDER MULTIAXIAL STRESS STATES

Combined tension/torsion and compression/torsion tests were carried out at room temperature. Tension, torsion and 4-point bending tests have been also carried out in order to estimate Weibull's two parameters for predicting the fracture stress under multiaxial loading. The maximum tensile stresses at fracture for the combined tests increased with increasing ratio τ(torsion)/σ(tension). The fracture stresses predicted from the data of uniaxial tests by Weibull statistical theory of uniaxial fracture and the statistical theory of multiaxial fracture for shear-insensitive cracks are in agreement with the experimental data. However, the fracture stresses predicted by the statistical theory of multiaxial fracture based on various fracture criteria for shear-sensitive cracks were lower than the experimental data. These results indicate that the actual flaws in the ceramic components are not shear-sensitive cracks.