Role of particle cavitation in rubber-toughened epoxies: II. Inter-particle distance

Two types of conventional rubber modifiers and a series of hollow plastic m icro-spheres were employed as toughening agents in a diglycidyl ether of bi sphenol A (DGEBA) epoxy in Part I (Bagheri R, Pearson RA. Polymer 1996;37:4 529) of this study. It was found that the rubber modifiers with different c avitation resistance and hollow plastic micro-spheres which act as pre-exis ting microvoids toughen epoxies in the same manner. The current study is co mposed to further examine the previous results in terms of the role inter-p article distance in rubber/microvoid toughened epoxies. It is shown that th e fracture toughness in toughened blends goes through a ductile-to-brittle transition with inter-particle distance. The source of this transition is f ound to be a stress state change provided by voided particles. The Ligament between neighboring particles, thus, experiences a transition from plane s train to plane stress state by decreasing the inter-particle distance. Inte restingly, it is shown that the transition in toughened blends does not occ ur at a specific inter-particle distance as frequently proposed in literatu re, but varies with the size of the modifier. Therefore, there is an influe nce of particle size on yielding of the toughened epoxies that is responsib le for the shift in transition. (C) 1999 Elsevier Science Ltd. All rights r eserved.