A new method to reduce cure-induced stresses in thermoset polymer composites, part I: Test method

The inhomogeneous structure of polymeric composites causes internal stresses to develop due to matrix volume changes during processing. The volume changes occur during cure and during cooldown after the curl is completed. Most of the previous studies on residual stresses concentrated on stress development during cooldown. In this study, a new test method was used to monitor fiber stresses that develop during cure in single fiber model composites. The method was used to study the effect of changing the cure cycle on curing induced fiber stresses. It was seen that changing the cure cycle changes the resulting stress significantly. Also, it was shown that the cure-induced stresses and their contribution to final residual stresses vary for different resins. A cure cycle with almost zero cure-induced stresses is demonstrated. The new cycle was found to satisfy the cure requirements such as glass transition temperature and cure cycle duration.