Empirical modeling of in-cure volume changes of 3501-6 Epoxy

In the interest of evaluating the cure-induced residual stresses that develop during manufacturing of a thermoset polymer composite, a course of research has been carried out to determine the nature of volume changes that occur during a cure cycle. These volume changes are known to be from two different sources: thermal expansion and cure shrinkage. A well-characterized aerospace material, Hercules 3501-6 Epoxy, has been used to develop a model for the cure shrinkage and thermal expansion during cure. The primary equipment used includes a volumetric dilatometer, which monitors total sample volume change during cure, and a differential scanning calorimeter (DSC), which is used to evaluate sample degree of cure. Cure shrinkage was isolated by monitoring isothermal cure processes, in which case there are no thermal volume changes to account for. Cure shrinkage was shown to be linear with respect to degree of cure. Thermal volmetric effects were determined by investigating cure cycles of constant heat rate. The thermal expansion coefficient was shown to be constant over a wide range of temperature and degree of cure. Based upon experimental data, a model has been developed to predict total volume changes for an arbitrary cure cycle.