Determination of viscoelastic Poisson’s ratio on a novel combined torsional-axial MultiDrive device

The lateral contraction of a material when stressing the material in axial direction is described by the Poisson’s ratio. In case of viscoelastic materials, like polymers, this parameter is a function of temperature and excitation frequency, when measured in oscillatory mode, and important for e.g. structural mechanics simulations. Methods to determine the viscoelastic Poisson’s ratio are manifold and can be classified in direct methods, which directly measure the change of the specimen dimension, and indirect methods from which the measurement of two moduli like shear modulus and Young’s modulus seems to be the most effective. A new measuring device concept is introduced which allows one to do combined torsional and axial measurements on one single device. In this contribution measurements on both cylindrical and rectangular specimens are presented in order to determine the viscoelastic Poisson’s ratio of different solid polymers. Using a linear and a rotational measuring drive in one instrument enables the determination of complex shear modulus |G*| as well as the complex Young’s modulus |E*| on a single sample in a continuous measurement run. Consecutive frequency sweeps at room temperature in both torsion and tension deformation modes were performed to obtain the viscoelastic Poisson’s ratio. A suite of polymers ranging from amorphous (PMMA, PC), thermoplastic polyurethane (TPU) to thermosets were studied.