Abstract
Based on rheological test results, a new viscoelastic constitutive equation for unvulcanized rubber has been set up, with mathematical justification to describe its mechanical properties in relation to the yield stress and shear-thinning effect. In this model, every term or coefficient has an explicit physical meaning.
The proposed model indicates that the yield stress is one of the main causes for the shear-thinning effect and reveals why some materials possess double-Newtonian regions with the shear viscosity in the first region higher than that in the second region. The yield stress makes the flow index of the power law fluid model vary widely, so that it needs to be eliminated from the power law fluid model. The model can also distinguish the true shear viscosity from the apparent shear viscosity effectively.
The parameters of the equation are determined by the step fitting method, which is the precondition for quantitative analysis.
However, the equation is a one-dimensional model, so further research is needed.