Investigating the mechanical behavior of carbon fiber single lap joints utilizing structural adhesive: experimental and numerical analyses

The automotive field has always been one of the driving fields for mechanical research and development for many years. This brought many new complex and expensive solutions to be investigated and developed mainly in racing or high-end applications and then commercialized on road or commercial vehicles later on. Composite materials are a great example of this and in particular in the last decades a lot of research went into adhesive bonding, a technique used to join similar or dissimilar materials of any kind. Adhesive bonding applied to composites allowed to reduce drastically the weight of assemblies usually made of many components, which traditionally were made out of metals and joined by welding or bolted connections which increased a lot the weight of the structures. This outcome allowed for an increase of performance in the racing field, a decrease in fuel consumption and consequently a decrease in emissions in road vehicles, which is a crucial factor in these years. The aim of the following thesis work was to characterize a structural adhesive and correlate numerical simulations with experimental tests. The adhesive used for this research is a toughened and high impact-resistant bi-component adhesive with an epoxy and amine base for the two components respectively. The adhesive has been tested with different loading conditions through Double Cantilever Beam test (DCB) on metal substrates, Single Lap Joint test (SLJ) on carbon fiber substrates and Dogbone test on pure adhesives specimens, all of them were following restrict requirements given by regulations. Different adhesive thicknesses were tested in order to understand properties trends by varying this parameter, knowing in advance that too high thickness can bring to a high degradation of the mechanical properties of the joint. The paramaters needed to validate a numerical Finite Element Method (FEM) model were determined for a further study of the adhesive joint configurations. The final goal was to have a clear understanding of the adhesive behavior, to be able to simulate any kind of structure in any loading condition, achieving accurate results.