Elastomers in oscillatory extension

Abstract eng:
We subject elastomers to a fixed pre-stretch in uniaxial extension upon which a large-amplitude oscillatory uniaxial extensional (LAOE) deformation is superposed. Our new continuum model, the Voigt element with strain—hardening spring, for this behavior combines a new nonlinear spring in parallel with a Newtonian dashpot. We consider this three-parameter model to be the simplest relevant one for the observed convex banana-shaped stress-strain (In —8) loops. We fit the three parameters (Young’s modulus, viscosity and strain-hardening coefficient) to our LAOE measurements. We develop analytical expressions for the Fourier components to the parts of the stress response, both in-phase and out-of-phase with the strain, for the zeroth, first, second and third harmonics. We find that the part of the second harmonic that is out-of-phase with the strain must be negative, for proper banana convexity.

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