Complete elastic characterization of viscoelastic materials by dynamic measurements of the complex bulk and Youngʹs moduli as a function of temperature and hydrostatic pressure

Two independent systems to measure the dynamic complex Youngʹs and bulk moduli of viscoelastic materials as a function of temperature and hydrostatic pressure are described. In the Youngʹs modulus system, a bar-shaped sample is adhered to a piezoelectric shaker and mounted vertically inside an air-filled pressure vessel. Data are obtained using both the traditional resonant approach and a wave-speed technique. In the bulk modulus system, the compressibility of a sample of arbitrary shape immersed in Castor oil and placed inside a pressure chamber is measured. Data can be obtained at frequencies typically ranging from 50 Hz to 5 kHz, at temperatures comprised between −2 and 50 °C and under hydrostatic pressures ranging from 0 to 2 MPa (Youngʹs), or 6.5 MPa (bulk). Typical data obtained with both systems are presented, and it is shown how these data can be combined to completely characterize the elasticity of the material under investigation. In particular, they can be used to obtain experimental values of the complex Poissonʹs ratio, whose accurate measurement is otherwise quite challenging to perform directly. As an example, the magnitude and loss tangent of Poissonʹs ratio are presented for a nearly incompressible rubber.