The fracture behaviour of a nano-modified structural epoxy adhesive

Structural epoxy adhesives typically contain second phase particles to improve their resistance to crack growth. The presence of these particles can dramatically raise the toughness of the system to several times that of the neat epoxy. One of the most common tougheners are core shell rubber (CSR) particles which consist of a glassy shell surrounding a rubbery core. The bulk fracture properties of these systems have been studied by many authors. It is generally accepted that the improvement in toughness is derived from the plastic growth of voids that nucleate from the failure of CSR particles and the development of shear bands between these voids [1]. The development of these mechanisms within the joint are affected by the level of stress triaxiality which depends on many factors including the thickness of the adhesive layer, ha [2]. The aim of this work is to identify the primary toughening mechanisms that develop during fracture of metal joints that are bonded with these adhesives. This is completed with tapered double cantilever beam (TDCB) fracture tests combined with fracture surface analysis, numerical modelling of the adhesive joints and analytical modelling of the adhesive microstructure. Additionally, a novel test method, the bonded circumferentially deep notched tensile test (CDNT) is used to measure the traction separation behaviour of the adhesive as a function of constraint. The findings of this work also support another study which involves the development of a numerical micromechanical model of the adhesive microstructure. Ultimately, this will evolve into a design tool for the development of improved materials.