Powder Metallurgy Progress, Vol.1 (2001), No 1 5 OPTIMIZATION OF MECHANICAL PROPERTIES OF POROUS MATERIALS S. Firstov, Yu. Podrezov ABSTRACT Possible ways to improve mechanical property of porous materials, depending on volume fraction of pores, are discussed. The first possibility is an enhancement of fracture toughness of porous material by increasing the volume fraction of pores. The second is the growth of relative stiffness of high-porous systems. The third case is to increase the absorbing capacity of strain energy at a high porosity. The sensitivity of these effects to the morphology of porous space, and structure of solid phase, is analysed. The methods of structure optimisation in order to obtain maximum effects are proposed. Solid state structure and porous space morphology were taken into account. There is a good agreement between theoretical calculation and experimental data. Requirements of designers will always be met if the morphology of porous structure and mechanical property of basis metal is optimal. Keywords: porous materials, fracture toughness, relative stiffness, structural effect, work hardening, damper stress INTRODUCTION Pores are one of the structural elements of a material. Porosity can be a result of material technology as well as being regulated consciously, for example, when producing filtered or low-weight materials. In the first case, one usually tends to get rid of porosity by improving material technology or realising special treatments, for example, isostatic hot- pressing. In the second case, special technologies are worked out for obtaining regulated porosity. With this aim, both a simple combination of powder pressing condition or sintering modes and a special heat treatment are used in powder metallurgy. Therefore, both investigations of porous material structure and the influence on physical-mechanical properties of the materials are of considerable interest. A number of physical properties (for example, thermal expansion coefficient) do not depend on porosity, other properties (for example, density) depend on porosity linearly. The mechanical properties of sintered materials are drastically reduced when the porosity increases. In particular, the following formulas have been derived in a number of publications [1-6] y ) ( θ σ = , m y ) 1 ( 0 θ σ − (1) θ σ θ σ b f f e − = 0 ) ( , (2) θ θ σ θ σ 3 4 ) 1 ( ) ( 2 0 − − = y y , (3) Sergey Firstov, Yuriy Podrezov, Institute for Problems in Materials Science of the Academy of Sciences of Ukraine, Department of Physics Strength and Plasticity, Kiev, Ukraine