An experimental study on the mechanical behavior of thermoplastic single lap joint bonded using a thermoset-based epoxy film adhesive

This study aims to experimentally characterise the mechanical behaviour of a single lap joint thermoplastic (TP) adherend bonded with a thermoset (TS) adhesive. Understanding the interface behavior of these joints is crucial, given the lower surface energies of thermoplastics compared to thermosets, making adhesion a challenging task over the TP surfaces. Therefore, prior surface modification of TP adherends is essential for effective adhesive bonding. Plasma treatment (PT), a method being explored here, alters the surface roughness, improves the contact angle, and increases the surface free energy. Surface roughness induced by PT is quantified using an atomic force microscope (AFM). The correlation between NDT assessment, surface roughness parameters, and single lap shear strength (SLSS) is being investigated. Fractography analysis and other findings contribute to a comprehensive understanding of the factors influencing the joint strength and integrity of such bonded systems, thereby establishing an appropriate bonding scheme for greater structural integrity towards aircraft applications.