Influence of cork microparticles on the fracture type in single lap joints

Abstract

Over the years, the use of structural adhesive bonding has significantly grown in numerous technological sectors, including the aeronautical, aerospace, medical and automotive industries. The growing need to design lighter and better performing structures has pushed designers to improve their construction techniques, and consequently adhesive joints have appeared as an optimal joining solution, providing the necessary high strength and stiffness, low cost and excellent capabilities to join multi-material structures. In many of these applications, perhaps most importantly in the automotive industry, it is fundamental to ensure that when the joint is loaded to destruction, such as in a vehicle collision, failure is always cohesive and adhesive failure is avoided. This work proposes a novel technique to ensure that the failure mode is not adhesive, forcing a failure mode that does not propagate through or near the interface. To accomplish that, an epoxy adhesive typically used in the automotive industry was studied and reinforced with microparticles of cork. This study was validated experimentally with joint configurations typical of industrial applications, such as single lap joints, supported by numerical simulations performed to better understand the failure mechanism. The influence of the amount and size of these particles on the fracture type was evaluated. Overall, both the experimental and numerical results showed that by increasing both the size and the amount of the particles in the adhesive, the failure mode tends to be more cohesive (in the middle of the bondline) with a small reduction in joint strength, demonstrating that this can be a viable technique if cohesive failures in the adhesive layers are necessary.