Experimental investigation and numerical modeling of elastic properties and strength of porous ceramics

Advanced ceramics are widely used in responsible structures that work at conditions of high temperature changes, strong electrical fields and impact loads. Sintered ceramics are usually porous which affects their strength and elastic properties. In the first part of this work the results of experimental and numerical strength investigations of hot-pressed alumina ceramic are presented. The disk-shaped specimens with different porosity (4-23 %) were subjected to Piston-on-Ring bending test up to failure. Ultimate tensile strength is varied in the range of 180…490 MPa. Finite element method was used for stress state analysis of ceramic disk during bending test. Elastic properties of porous ceramic for numerical simulations were determined by using the known approximation of dependences “property - porosity” and some experimental data. In the second part of this work three-dimensional numerical micro-model was created in ANSYS. This model is a cube with set pores up to 160 of spherical forms. The diameter of sphere is given by Weibull distribution with mean value m = 0,139 μm and standard deviation s = 0,075 μm (defined by SEM analysis of fracture surfaces). Scale parameter λ = 0,156 μm and shape parameter k = 1,919 of the Weibull distribution was determined by the least squares method. The authors generated three to six models with a random distribution of pores for each average porosity; and analyzed stress state under axial tension for each case. The maximum normal stress, stress concentration factor, elastic modulus and Poisson's ratio are dependent on the average porosity. The values of the tensile strength were defined for different porosity according to the Rankine criterion (maximum normal stress criterion). These values are in a good agreement with the experimental results.