Cork in composite structures: from low to high energy dynamics

Due to their cellular structure, open and closed-cell foams, porous materials and some natural cellular materials are generically and fundamentally good energy absorbers. Mechanisms such as cell wall buckling and collapse, plastic deformation and fracture explain this particular behaviour. However, the capability of such materials to absorb energy strongly depends on their microstructure (i.e. cell or pore structure, size, dispersion and arrangement), base material properties and loading induced strain-rates. Cork is a natural foam composed of closed cells of suberin, an impermeable and visco-elastic material. Cork composites can have a wide range of densities (0.2-1.5 g/cm3) with strengths ranging from 1 to 30 MPa. The constitutive behaviour of most cellular materials, including cork and most of its composites, and their strain-rate dependency are the main factors deWining their applicability as efWicient energy absorbers. A detailed description of the microstructure and behaviour of cork and its composites will be given, focusing on its strain-rate dependency and energy accumulation and absorbing capabilities. Examples will be given, through numerical analysis and quasi-static and high strain-rate experimental testing, of how to assess the potential of the use of cork in structural and energy absorption applications. The importance and relevance of using such materials in critical situations and extreme conditions, such as in the aerospace, defence and nuclear industries, will be explored in detail, with a large number of examples and results/observations being provided. Focus will be on defence applications (e.g. blast wave mitigation and protection against ballistic impact), low energy impact (e.g. crashworthiness), personal protection and structural integrity (e.g. earthquake mitigation).