Modified creep constitutive equation for an epoxy-based adhesive with nonlinear viscoelastic behavior

This article presents the procedure to obtain constitutive equations to express the creep behavior of Araldite 2015 epoxy adhesive using the results of the uniaxial creep tests. The experimental data show that the examined adhesive has a nonlinear viscoelastic behavior. Three types of constitutive equations have been used: (a) Bailey-Norton equation, (b) generalized time-hardening model and (c) rheological model which is a series combination of springs and dampers known as Maxwell and Zener combination. The first two models have vast application in commercial finite element-based software. It is shown that the generalized time-hardening model can simulate the creep behavior of the adhesive better than the Bailey-Norton model. However, this model is less accurate at the elevated temperatures. Therefore, an empirical equation based on Maxwell and Zener's was proposed which demonstrates a very good consistency with the results of the experimental data over the assumed range of stress and temperatures.