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- PublicationThe Bond Gap Thickness Effect on the Fracture Toughness of Nano-Toughened Structural Epoxy AdhesivesThis work employs combined experimental and numerical studies to investigate the effect of bond gap thickness on the fracture behaviour of a nano-toughened epoxy adhesive produced by Henkel. Tapered-double cantilever-beam (TDCB) joints were subjected to a constant low loading rate. The mode I fracture behaviour of the joints was investigated as a function of bond gap thickness, which was varied from 0.25 to 2.5 mm. A detailed analysis of the fracture surfaces was carried out using scanning electron microscopy (SEM) and variations of the microstructural features with the bond gap thickness, and corresponding constraint, were revealed. The Rice and Tracey void growth model is used to relate the local plastic strain calculated by measuring the size of the voids on the fracture surfaces with the constraint calculated numerically for each bond gap thickness. It was shown that the difference in constraint imposed by different bond gap thicknesses is responsible for the observed dependency of GIC.
- PublicationTransferability of Adhesive Fracture Toughness Measurements between Peel and TDCB Test Methods for a Nano-Toughened EpoxyOur previous work  on a nano rubber modified epoxy adhesive suggested that the observed bond thickness effect was due to the level of constraint (σhyd/σeq), a measure of the stress triaxiality, in the adhesive layer. In that study tapered double cantilever beam (TDCB) specimens were tested under quasi-static conditions for a range of bond gap thicknesses. The void diameters on the resulting fracture surfaces were measured from which the fracture strain was estimated in each case. The ratio of fracture strains corresponding to different constraint levels was found to agree with the predictions of the Rice and Tracey model. The current work attempts to further investigate the effects of constraint on adhesive joint fracture. Three experimental test methods are employed (i) the standardised LEFM tapered double cantilever beam (TDCB) test, in which the substrates experiences small elastic deformations, (ii) the fixed arm peel test where the substrate peel arm undergoes extensive plastic deformation and (iii) a recently developed circumferentially deep notched tensile (CDNT) test. Finite Volume simulations of the TDCB and CDNT tests were utilised to examine the role of constraint on the adhesive joint fracture.
- PublicationThe fracture behaviour of a nano-modified structural epoxy adhesive
- PublicationCharacterisation of the fracture energy and toughening mechanisms of a nano-toughened epoxy adhesiveIn this study the adhesive joint fracture behaviour of a nano-toughened epoxy adhesive was investigated. Two experimental test methods were used; (i) the standard tapered double cantilever beam (TDCB) test to measure the mode I adhesive joint fracture energy, GIC, as a function of bond gap thickness and (ii) a circumferentially deep notched tensile test to determine the cohesive strength of the adhesive for a range of constraint levels. It was found that the fracture energy of the adhesive followed the well-known bond gap thickness dependency . SEM analysis of the TDCB fracture surfaces revealed significant plastic void growth. Finally, numerical modelling of the experimental tests suggested that most of the fracture energy was dissipated via highly localised plasticity in the fracture process zone ahead of the crack tip.
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