A STRESS WAVE STUDY OF THE DILATATIONAL RESPONSE OF SOME VISCOELASTIC SOLIDS.
Technical rept. no. 8,
BROWN UNIV PROVIDENCE R I DIV OF APPLIED MATHEMATICS
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Measurements of the change of shape of spherically diverging stress pulses in polyethylene, polymethylmethacrylate, and polystyrene were made. The stress pulses were produced by the detonation of small explosive charges on blocks of these materials and the pulses were detected by the use of condenser microphones. The stress amplitudes were sufficiently small for the theory of linear viscoelasticity to apply and the attenuation and dispersion of the pulses enabled values to be obtained for the real and imaginary parts of the bulk modulus. Such measurements would be extremely difficult to carry out in this frequency range by any other means. It was found that for both polyethylene and polymethylmethacrylate the bulk loss was about one fifth of the mechanical loss in shear, whilst for polystyrene the bulk losses were so small that the assumption of elastic behavior was as close as any other assumption and in this material the shear losses are also very small. Author