Apparatus for Measuring the Time-Dependent Poisson’s Ratio in Uniaxial Tension

Abstract

Polymers and composite materials are widely used in applications requiring lightweight and high damping capacity. Since these materials show viscoelastic behavior under static and dynamic loading, the stress analysis involving such materials has recently become an important subject. The time-dependent Poisson’s ratio as well as the tensile relaxation modulus are the primary input properties for finite element methods (FEM), and are also required in the constitutive modeling of a material’s mechanical behavior (Emri et al., 1997). Previous attempts at measuring the time-dependent Poisson’s ratio have shown convincingly that it is indeed difficult to obtain experimentally. Because the total range of response is compressed effectively between 0.3333 and 0.5 the measurements require high accuracy. This is made more complicated because they are strongly influenced by number of parameters such as e. g. temperature, pressure, humidity, etc., and the reproducibility of the material properties of the specimen. We report here on the development of an apparatus designed to enable us to determine the time-dependent. Poisson’s ratio, v(t), with the required accuracy while simultaneously determining the tensile relaxation modulus, E(t). Using the E-T algorithm (Emri and Tschoegl, 1992–1997) we hope to be able to obtain the fundamental moduli, the shear relaxation modulus, G(t), and the difficult-to-determine bulk relaxation modulus, K(t), by computer calculation.