Manufacture of variable angle tow laminates using carbon fibre/thermoplastic pre-preg tapes

peer-reviewed ; Variable Angle Tow (VAT) composites have gained significant interest since the introduction of Automated Tape Placement (ATP) machines in the 1980s. ATP has scope to enhance design space by laying down tapes or tows in curvilinear trajectories, i.e. in variable angles. Until recently, cutting plies, thereby introducing ply-drops, into the same layer was the only means available to change layerwise ply orientation. VAT has potential to reduce stress concentrations around cut-outs and improve buckling performance, without adding weight. Many numerical studies have shown the benefits of VAT, but few researchers have manufactured and tested VAT structures. Where VAT structures were produced, all were processed using thermoset composite material systems. Thermoset composites require two processing steps, the first to lay-up the laminate stacking sequence, while the second involves consolidating (curing) the laminate. To the author’s knowledge, there is little research available on processing VAT structures using thermoplastic composites. Thermoplastics composites allow in-situ consolidation with laser-assisted ATP (LATP). In-situ consolidation eliminates the secondary processing step, saving time, energy and consumables. This work investigates processing of VAT structures from aerospace grade thermoplastic composite, specifically carbon fibre reinforced polyether ether ketone (CF/PEEK). To determine the suitability of CF/PEEK to manufacture VAT structures, an investigation of LATP processing parameters for tape steering was carried out. Defect occurrences were observed and the bond strength of steered tapes tested for varying steering radii. Measurements showed that the width and thickness of the tapes changed as a result of steering. In addition, bond strength, was found to be a function of lay-down speed. It was shown that excellent bond strength could be achieved with suitable processing parameters. Investigation of CF/PEEK VAT structures progressed to representative structural demonstrators. A ...