Bending Strength of Smooth and Notched Specimens of Porous Silicon Carbide.

Abstract

Smooth specimens of porous silicon carbide with porosity 37% showed nonlinear relations between load and strains under four-point bending. The relation between the true stress and the strain determined from non-linear relations was nonlinear for the tension side, while linear for the compression side. The bending strength of smooth specimens followed a two-parameter Weibull distribution. Single-edge notched specimens with the notch depth ranging from 0.1 to 2.8 mm were fractured under four-point bending. The fracture of specimens with a notch depth of 0.1 mm did not start from the notch ; the fracture strength of the notched specimen was equal to the smooth specimen. The notch depth of 0.1 mm is roughly equal to the size of silicon carbide particles in porous ceramics. The load versus strain record showed nonlinearity before the maximum load, suggesting the R-curve behavior of porous ceramics. The R-curve was constructed from the compliance change of the specimen, and was used for determining the maximum load point in bending tests. The intrinsic crack model was proposed to predict the effect of the notch size on the fracture toughness of porous ceramics. Fractographic observations showed the fracture path along the binder phase between silicon particles.