Empirical modeling of in-cure volume changes and elasticity development of thermoset polymers

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 developed methods are also applied to RS-3 and EX-1515 resins. The primary equipment used includes a volumetric dilatometer, which monitors total sample volume change dung cure, a differential scanning calorimeter (DSC), which is used to evaluate sample degree of cure, and a cure induced stress test (CIST) which monitors the cure induced stresses that are developed in embedded fibers. 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 volumetric 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. As a follow-on study, the volume change data has been combined with analysis of the polymer stress state to develop an investigation of m-cure development of elastic modulus. The development of elasticity was shown to mimic the progression of degree of cure.