Toughening method and mechanisms for thermosets

A new toughening method that can be used to improve toughness for thermosets was developed. The method involved heat treatment to produce compressive residual stresses around hollow microspheres in solidified matrix. An epoxy resin system with expandable hollow microspheres for modification was adopted for demonstration. Toughening based on the method was shown to be more than twice as effective than the usual hollow microsphere toughening and its major toughening mechanism was deduced to be due to compressive residual stresses rather than cavitation. A necessary condition for cavitation in the presence of compressive residual stress was proposed and comparatively discussed for the toughening mechanisms involved. (c) 2005 Wiley Periodicals, Inc.