Interpretation of experimental data for Poisson's ratio of highly nonlinear materials

The Poisson's ratio of a material is strictly defined only for small strain linear elastic behavior. In practice, engineering strains are often used t o calculate Poisson's ratio in place of the mathematically correct true str ains with only very small differences resulting in the case of many enginee ring materials. The engineering strain definition is often used even in the inelastic region, for example, in metals during plastic yielding. However, for highly nonlinear elastic materials, such as many biomaterials, smart m aterials and microstructured materials, this convenient extension may be mi sleading, and it becomes advantageous to define a strain-varying Poisson's function. This is analogous to the use of a tangent modulus for stiffness. An important recent application of such a Poisson's function is that of aux etic materials that demonstrate a negative Poisson's ratio and are often hi ghly strain dependent. In this paper, the importance of the use of a Poisso n's function in appropriate circumstances is demonstrated. Interpretation m ethods for coping with error-sensitive data or small strains are also descr ibed.