Fracture of Thin Walled Translucent Polycrystalline Alumina (PCA) Tubes

Room temperature fracture behavior of short thin walled translucent coarse-grained polycrystalline alumina (PCA) tubes was investigated under compression loading in radial direction using conventional mechanical tests combined with the finite element modelling (FEM). FEM indicated strongly inhomogeneous stress distribution with the maximum tangential tensile stresses in the centre of the inner surface of a tube and opposite to the line of loading. Another zone of tangential tensile stresses form on the outer surface of the tube and oriented perpendicularly to the loading direction. However, these tensile stresses are lower compared to those under contact lines. Radial stresses were negligible compared to tangential stresses which were concluded to control tube fracture. Fracture occurs in two steps: firstly along the loading lines under the lines of contacts and secondly in the direction perpendicular to loading. It results in four regular pieces along the lines with the highest tangential tensile stresses. The results were analysed using Weibull statistics and standard fractography methods. The characteristic strength of the PCA tubes was 186 MPa and the Weibull parameter m'(corr) = 16.9 +/- 0.5. High m values and the absence of the obvious fracture origins were attributed to homogeneous microstructure and well developed PCA technology.