Fracture toughness and the corresponding toughening mechanisms of rubber-modified brittle epoxies
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The present work correlates the toughening mechanisms of grafted-rubber concentrate (GRC), dispersed acrylic rubber (DAR), and Proteus rubber-modified D.E.R. 332 epoxy resin/DDS systems with their corresponding fracture toughness values. It also determines whether or not the highly crosslinked epoxy systems can undergo shear yielding around the crack tip, when the rubber particles are incorporated. It is found that the toughening in the D.E.R. 332 epoxy resin/DDS/GRC system is mainly due to the rubber particle cavitation, which relieves the triaxial tension in front of the crack tip, followed by the formation of shear bands. The failure mechanisms of the DAR-modified D.E.R. 332 epoxy resin/DDS system are mainly crack bifurcation, crack deflection, and crack pinning. In the case of the Proteus rubber-modified D.E.R. 332 epoxy resin/DDS system, only the crack deflection and crack pinning mechanisms are observed to account for the toughening of this system.
