Toward a constitutive model for cure-dependent modulus of a high temperature epoxy during the cure

A constitutive model, based on Kohlrausch–Williams–Watts (KWW) equations, was developed to simulate the evolution of the dynamic relaxation modulus during the cure of a ‘high temperature’ epoxy. The basic assumption of the modelling methodology proposed is the equivalence of the mechanisms underlying the evolution of the glass transition temperature and the relaxation time shift during the cure, leading to the use of a common potential function. This assumption is verified by the comparison of normalized glass transition data and principal relaxation times, which have been found to follow a single master curve. Results show satisfactory agreement between experimental data and model prediction over the range of chemical conversion considered.

During the polymerization of any synthetic thermosetting polymer the material undergoes chemical and physical transformations which lead to the hardening of the material, with a corresponding transition from a viscous liquid to an elastic solid. A constitutive model, based on Kohlrausch-Williams-Watts (KWW) equations, was developed to simulate the evolution of the dynamic relaxation modulus during the cure of a ‘high temperature’ epoxy. The considered model uses the concept of principal relaxation time for each degree of conversion with principal relaxation times normalized with respect to the value for the fully cured state in order to find a suitable correlation with structural changes. Assuming that the same mechanism of structural evolution governs both the development of the glass transition temperature and of the mechanical modulus, an identical “potential function” can be adopted.Figure optionsDownload as PowerPoint slide