Improved Adhesive Bonding Strength of Bonded Repair of Thermoplastic Composites Using Laser Surface Patterning

Composite structures are gaining more and more importance in a variety of industrial applications, thereby novel maintenance and repair techniques are required to ensure their proper operation. Surface pre-treatment is one of the key processes in the bonded repair of fiber-reinforced polymer composites. Laser surface treatment can be easily monitored and adjusted for fast, precise, scalable, and reproducible surface patterning of composites that is capable of automation. This paper, for the first time, investigates the feasibility of laser surface patterning as a surface activation method for the repair of Thermoplastic Glass Fibre/Elium® Composites. The composite adherents are structured in parallel lined-like textures using a 1064 nm pulsed nanosecond laser. The influence of laser parameters such as fluence on the produced surface microstructures and resulting bonding performance are discussed. The surface morphology and microstructure were characterized by scanning electron microscopy (SEM) and fourier transform infrared spectroscopy (FTIR) analyses were carried out to study the effect of laser texturing on the functional groups of composites’ surfaces. Bonded specimens were mechanically tested using a single lap shear test. It was found that the optimum laser fluence is 12.8 J/cm² leading to the bonding improvement of up to 30% compared to the untreated specimens and the highest shear strength of 15.2 MPa thus reducing repair area and costs significantly. Furthermore, it is demonstrated that this improvement in adhesive strength is achieved only by selective removal of resin at controlled laser parameters without exposing or damaging fibers on the composite surface resolving the main concern about damaging the underlying plies.