The effect of surface treatments on the behaviour of adhesively bonded, thermoplastic composite lap joints

Adhesive bonding of composite materials reduces the requirement for penetrating fixtures that add weight and influence the geometry of the structure. Thermoplastic resin composites are currently of great interest, as they possess greater fracture toughness, are potentially recyclable and form imperishable prepregs, in comparison to their more commonly used thermosetting resin counterparts. However, thermoplastic resin composites present challenges when they are adhesively bonded. They have relatively low surface energies and do not adhere to adhesives as readily as their thermosets [1]. It is therefore desirable to improve the adhesive properties of thermoplastic composites to improve the adhesive bonded strength. Improvement of the adhesive properties through enhancement of surface energies has been previously demonstrated to increase the peel strength of adhesively bonded thermoplastics, demonstrating the efficacy of surface modification in affecting the behaviour of the adhesive substrate bonds strength for this load case [2]. This work will determine the effect of surface modification methods on lap shear strength. The following study describes the behaviour of adhesively bonded single lap joints, with and without surface treatments. The effect of UV/Ozone (UV/O3) and atmospheric plasma discharge surface treatments, on the static behaviour and strength of thermoplastic composite single lap joints (SLJs), is characterised. All SLJs in this study were sandblasted and degreased (using a non-linting solvent wipe) prior to adhesive bonding. An improvement in joint lap shear strength (LSS) occurred after surface treatments, using both UV/O3 and atmospheric plasma. When compared with SLJs that had been sandblasted only, the UV/ O3 LSS improved by 18.2% and the atmospheric plasma discharge LSS improved by 22.2%. © 2017 International Committee on Composite Materials. All rights reserved.