Abstract
The compatibility between the majority of thermoplastic veils (TPVs) and epoxies is typically poor, owing to the inherently low surface energies of thermoplastics. This tends to largely affect the toughening performance of TPVs as interlayer materials of carbon fibre/epoxy composites. The traditional methods for surface activation of thermoplastics, such as corona discharge, plasma treatment and acid etches, are not applicable to TPVs as they could cause significant damage to the thermoplastic fibres with nano-/micro-scale diameters. Herein, a UV-irradiation technique was proposed to active the surfaces of polyphenylene-sulfide (PPS) veils, that effectively improved their adhesion with epoxies. Consequently, the effects of an improved veil/epoxy adhesion on the mode-I and mode-II fracture behaviour and corresponding fracture mechanisms of the interleaved laminates were investigated. It was found that an improved veil/epoxy adhesion significantly enhanced the toughening performance of the PPS veils for the laminates manufactured by resin transfer moulding of non-crimp fabrics, by introducing additional carbon fibre delamination and significant PPS fibre damage during the fracture process. In contrast, the increased level of veil/epoxy adhesion inhibited PPS fibre bridging during the fracture process of the laminates produced from unidirectional prepregs, and caused considerable adverse effects on the fracture performance.
Highlights
Carbon fibre reinforced polymers (CFRPs) are widely used in multiple industries, including aerospace, automotive and marine sectors, because of their outstanding structural performance and light weight
Polyphenylene-sulfide (PPS) veils with different areal densities were Ultraviolet light (UV)-irradiated for a short time, and used to interlay two types of aerospace-grade CFRPs produced from UD prepregs and resin transfer moulding (RTM) of non-crimp carbon fibre fabrics (NCFs)
A UV-irradiation technique was proposed to active the surfaces of PPS veils, aiming to improve the veil/epoxy adhesion in CFRPs interleaved by PPS veils
Summary
Carbon fibre reinforced polymers (CFRPs) are widely used in multiple industries, including aerospace, automotive and marine sectors, because of their outstanding structural performance and light weight. The foremost challenge for improving the thermoplastic veil/epoxy adhesion is that traditional surface treatment methods for thermoplastic materials, such as corona discharge, plasma treatment, acid etches and oxidising flame treatment are not applicable to thermoplastic veils This is because of these methods could cause significant damage to the thermoplastic fibres who possessed micro-/nano-scale diameters. Polyphenylene-sulfide (PPS) veils with different areal densities were UV-irradiated for a short time, and used to interlay two types of aerospace-grade CFRPs produced from UD prepregs and resin transfer moulding (RTM) of non-crimp carbon fibre fabrics (NCFs) These two laminate systems were studied because of their non-modified laminates exhibited significantly different fracture properties and mechanisms, which subsequently affected the toughening levels and mechanisms of the non-treated thermoplastic veils [18,19]. The results were compared with those of the laminates interleaved with nontreated PPS veils in [18,19], to obtain an understanding on the effects of the thermoplastic veil/epoxy adhesion
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