A brief review of the mechanical characterization of viscoelastic materials under uniaxial, biaxial and multiaxial stress condition is carried out in this paper. Parametric analytical studies have been done in a simulated tubular specimen with different internal pressure loadings at various material properties. We observed that the relaxation modulus values obtained from the thick-walled hollow cylinder analyses are higher that the traditional uniaxial and biaxial test data under the same strain level. We noticed that during the initial period, the relaxation-modulus values are almost identical and later the relaxation modulus obtained from the thick-walled hollow cylinder analysis is found significantly higher than the uniaxial and the strip biaxial test data. We conjectured that in the initial stage the stress–strain ratios are almost independent of the geometry of the test specimen and subsequently the stress conditions vary according to the shape of the specimen because the relaxation modulus is found geometry dependent when loading time advances. Note that the main objective of this characterization is not to determine the magnitude of the stress actually present in the test specimen, but to help the designer to decide the best geometry in a realistic way according to the industrial applications from the viscoelastic stress relaxation point of view.

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