Acoustical determination of the shear relaxation functions for polymethyl methacrylate and Epon 828-Z

A differential-path ultrasonic technique is used to obtain the acoustic propagation characteristics of shear waves in polymethyl methacrylate (PMMA) and Epon 828-Z. The acoustic velocity and attenuation are measured at 0.5, 1, and 2 MHz over a temperature range of −60 to 70 °C. Time-temperature superposition is used to transform these data into their ’’master curve’’ form. Using this representation, the shear-stress relaxation modulus is then deduced and combined with the previously determined longitudinal data to form a complete characterization of the short-time linear response of these two homogeneous and isotropic viscoelastic polymers.