A novel experimental configuration – a confined compression loading scheme – was used for the characterization of viscoelastic constitutive behavior of polymers. In this paper we present a brief description of the configuration, discuss its applicability to the determination of viscoelastic constitutive response, and examine the precautions needed for specimen preparation. The configuration is then utilized in the simultaneous determination of the bulk and shear relaxation response of polymethylmethrylate and polycarbonate. Time-temperature superposition is utilized to obtain master curves of the bulk and shear moduli. Issues related to the interconversion between these moduli and the uniaxial relaxation modulus are also discussed. It is found that the effect of the confinement is to retard the rate of relaxation of the polymers; this is discussed in the framework of a free-volume model of viscoelastic material behavior.
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