Effect of surface pre-treatment on the behaviour of adhesively-bonded CFRP T-joints

This work aims to better comprehend the mechanical behaviour, including failure sequence and failure modes, of differently surface-treated CFRP T-joints when subjected to out-of-plane loadings. Specimens consisted in two CFRP adherends - skin and stiffener - adhesively bonded with a structural film adhesive. The adherends' untreated and treated (by peel ply or abrasion) surfaces were firstly characterized using scanning electron microscopy (SEM), profilometry and wett-ability measurements. Stiffener pull-off tests (SPOT) were then experimentally conducted under quasi-static loading. The fractured surfaces were analysed by fractography to identify the failure mechanisms. The peel ply treatment has led to the worst results in terms of maximum load, while the abrasion-treated specimens performed the best of the three series. Surface characterization and fractography analysis were properly correlated with the SPOT results. Fracture damage typically initiates as mode I within the tip of the stiffener's flange, but as the fracture extends along the stiffener's foot, it does it under predominant mode II.