Abstract
Large composite structures manufactured out-of-autoclave require the assembly and bonding of multiple parts. A one-shot cure manufacturing method is demonstrated using powder epoxy. Lap shear plates were manufactured from powder epoxy and glass fiber-reinforced plastic with four different bonding cases were assessed: secondary bonding using standard adhesive film, secondary bonding using powder epoxy, co-curing, and co-curing plus a novel Z-pinning method. This work investigates the lap shear strength of the four cases in accordance with ISO 4587:2003. Damage mechanisms and fracture behavior were explored using digital image correlation (DIC) and scanning electron microscopy (SEM), respectively. VTFA400 adhesive had a load at break 24.8% lower than secondary bonding using powder epoxy. Co-curing increased the load at break by 7.8% compared to powder epoxy secondary bonding, with the co-cured and pinned joint resulting in a 45.4% increase. In the co-cured and co-cured plus pinned cases, DIC indicated premature failure due to resin spew. SEM indicated shear failure of resin areas and a large amount of fiber pullout in both these cases, with pinning delaying fracture phenomena resulting in increased lap joint strength. This highlights the potential of powder epoxy for the co-curing of large composite structures out-of-autoclave.
Highlights
The autoclave process remains a benchmark for creating high-quality composites parts; it involves significant acquisition, operating, and tooling costs, especially for large parts [1]
Glass fiber-reinforced powder epoxy plates were manufactured using a process developed in a previous study [19] and subsequently used to produce lap shear plates
The tensile lap-shear strength of the glass fiber reinforced powder epoxy lap shear plates was investigated, with results showing an increased load at break for co-curing methods compared to secondary bonding
Summary
The autoclave process remains a benchmark for creating high-quality composites parts; it involves significant acquisition, operating, and tooling costs, especially for large parts [1]. OOA-manufactured large composite structures currently require the assembly of a number of parts using an additional adhesion step due to oven size restrictions [3]. The joining of these parts generally uses one of three techniques: co-bonding, secondary bonding, and co-curing. The benefits from reduced assembly costs must be balanced against this additional cost In this context, one-shot (or single) cure manufacturing processing methods (RTM, Prepreg) have recently been gaining popularity in industry due to their lower cost and higher processing speed [13]. A novel pinning technique, developed at Ulster University, has been combined with the co-curing bonding method
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