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

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Abstract
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.