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Multiaxial elastic, yield and failure behaviour of bonded joints using a hot-curing epoxy film adhesive: analytical and experimental investigation

ABSTRACT Film adhesives provide an excellent method for joint manufacturing with minimum waste and highly accurate thickness. Here, the multiaxial behaviour in terms of elasticity, yielding and failure of a hot curing epoxy film adhesive was analytically and experimentally investigated. Butt, scarf and thick adherend shear test joints were tested under static conditions. The variation between normal and shear stress among the different joint types allowed the variation of the multiaxiality using the same experimental set-up with a uniaxial testing machine. A consistent set of elastic constants was obtained by carefully calibrated displacement sensors, proper consideration of adherend elasticity and of lateral strain restrictions. The presentation of the von Mises equivalent stress and the hydrostatic pressure at the point of yield and failure indicated that hydrostatic stresses have a large influence on the static strength of the film adhesive. Failure and yield conditions were formulated based on linear or exponential forms of Drucker-Prager type models. A strain-based failure hypothesis was formulated using the second invariant of the strain deviator, and the first invariant of the strain tensor. Results showed that high values of volumetric strain are detrimental to the strength of the adhesive joints.