New materials and coatings have been introduced in car manufactures to reduce vehicle weight and improve corrosion resistance. In body shop, multimaterial design is joined using structural adhesives. The former epoxy crash adhesive gave adhesive failure on new steel coatings. This kind of failure is not accepted by carmakers. One way to obtain cohesive failure, is by adding glass beads in adhesive formulations. The aim of this work was to analyze how the addition of glass beads to the adhesive layer affects the failure mechanism. Single lap bonded specimens with mild steels were tested in quasi-static conditions and with different amount of glass microspheres. The results showed that the glass microspheres act as reinforcement particles which introduce stress concentration around the particles and their vicinities. This new phenomenon led the cracks to propagate in the middle of the adhesive layer rather than interfacial. This promote the cohesive failure. This novel effect solved the adhesion issue on difficult surfaces.
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