The effect of contact flattening and material properties on the fracture stress calculation for the diametrical compression test used to evaluate compact strength was examined through finite element simulations. Two-dimensional simulations were carried out using linear elastic, elastoplastic, and porous elastoplastic models with commercial finite element software. A parametric study was performed by varying the elastic modulus ( E), Poisson's ratio (v), contact frictional coefficient (mu), yield stress (sigma(yield)), and compact relative density (RD). Stress contours generated from these simulations were compared to the Hertzian and Hondros analytical expressions. Linear elastic simulations show excellent agreement with the analytical solutions. Significant deviation, however, occurs for the elastoplastic and porous elastoplastic simulations at larger diametrical strain with material plasticity. A better understanding of the stress-state of diametrically loaded plastically deforming disks has been demonstrated in this computational and experimental work. Results from these finite element simulations confirm that the standard tensile strength calculation: sigma(f) = 2P/piDt, is suitable for linear elastic materials. However, the incorporation of plasticity into the material model results in a significant change in the maximum principal stress field ( magnitude and location) rendering the Hertzian estimate of tensile strength invalid. A map to check the validity of the Hertzian equation is proposed. (C) 2003 Kluwer Academic Publishers.