Porous particle composites

There are a variety of methods which can be utilized to produce porous or cellular solids in the case of monolithic metals. Existing metallic foams fabricated by introducing gas into molten metals before solidification and artificial honeycomb structures are typical examples. Indeed, there is a great need for advanced structural and functional materials which over weight reduction in terms of high specific modulus and specific strength. However, in the case of metallic foams, as presented by Gibson and Ashby [1], the Young’s modulus of the foam Ef decreases monotonically with the increase in porosity as follows: E _f =E _s = Cφ ² (ρ _f /ρ _s ) ² + C’(1-φ)(ρ _f /ρ _s ) where subscripts f and s denote foam and bulk respectively, is density, and C, C0 and are constants. This equation shows that the specific modulus also decreases with increasing porosity. A similar situation exists with regards to both the tensile and compressive strength of foams [1]. To realize low-density structural materials, high property-to-weight ratios are required in comparison with the corresponding bulk materials. This is a difficult target to reach, but in this chapter the feasibility of achieving such high specific properties by incorporating porosity into ceramic particle reinforced composites will be discussed. In such composites, rigid ceramic materials bear external loading and the incorporated pores contribute to a reduction in weight and enhancement of other additional properties. Their limited exploitation as structural materials arises from a poor understanding of the mechanical behaviour of these porous composites.