Nonlinear constitutive model of uncured epoxy resin

The Bingham model characterizes the yield stress of a viscous fluid but does not take into account the shear-thinning effect; on the other hand the power-law fluid model characterizes the shear-thinning effect but does not incorporate a yield stress. Based on rheologic test results, a new epoxy resin constitutive equation is proposed with mathematical justification. It is different from the existing models because every term and every coefficient in it have physical meaning, which clarifies the essence of viscoelasticity of resin materials. The proposed model indicates that the yield stress is one of the main reasons for the shear-thinning effect, and it reveals why some materials have double Newtonian regions with the shear viscosity value in the first region higher than that in the second region.