1988 Volume 96 Issue 1113 Pages 539-545
Combined tension/torsion and compression/torsion tests for sintered silicon nitride specimens were carried out at room temperature to investigate the fracture behavior of ceramics under multiaxial stress states. 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 principal stresses at fracture for combined tension/torsion and compression/torsion 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 were 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. The statistical theory of multiaxial fracture which has a little contribution of shear stress to fracture can be used for designing components made of sintered silicon nitride.
