Indentation of rubber sheets with spherical indenters

The problem of indentation hardness for elastomer blocks has been examined at two levels. Initially an examination of the geometric non-linearity was undertaken. It was observed that the empirical equations adopted by the various standards organisations to predict the stiffness relationships were not always applicable. It appears that the classical Hertz solution to the problem gives a better representation of the general behaviour. A finite element approach was also adopted here to tackle the large displacement problem and the limitations of this approach have been discussed. This geometric problem is further complicated in practice by the effect of the finite thickness of the elastomer sheet. This problem has also been analysed and a suitable general relationship proposed to account for the finite thickness effects. The second problem examined was how the effects of the non-linear elasticity of the material could be tackled. It is shown that the form of the elastic stored energy function at small strains influences the indentation behaviour.