1. Modified Hyper-Viscoelastic Constitutive Model for Elastomeric Materials

Elastomers constitute an essential group of materials that are widely used in the automotive, aerospace industry, biomedical, microfluidic and signal processing applications. Elastomeric materials undergo large deformations without fracture and exhibit time dependency under a prescribed displacement or load. Characterization of elastomeric materials can be challenging, hence the use of a proper constitutive model that captures the behavior of elastomeric materials is essential. Experimental data obtained from simple uniaxial tension tests and creep tests performed at various constant stress levels using dog bone samples were used to approximate hyperelasticity and the time-dependent responses of the material respectively. The experimental results suggested that the instantaneous strains were largely responsible for the nonlinear behavior of the material. Thus, a rheological hyper-viscoelastic constitutive model consisting of a nonlinear spring, which would capture the nonlinear instantaneous strains, and a two parameter Kelvin-Voight model, which would model the linear time-dependent strain responses, was developed. The Mooney-Rivlin model, a classic phenomenological hyperelastic model, was used to represent the nonlinear spring. The resulting hyper-visco constitutive model, which obeys the Boltzmann’s superposition principle, was used for numerical predictions of time-dependent behavior of this material in a commercial finite element software (Abaqus). The creep deformations predicted using this approach demonstrated good consistency with experimental results over the applied range of stresses and the duration of time measurements.