Design, manufacturing and testing of an in-situ consolidated variable stiffness thermoplastic composite wingbox for bending and torsion

Automated fiber/tow placement (AFP/ATP) techniques can provide cost-effective, reduced waste, and repeatable high rate production of laminated composite structures with some unprecedented capabilities such as in-situ consolidation and fiber/tow steering. In fiber steering, the fiber orientation angles are continuously changed in-plane to make composites with optimum path between the loading points and supports in a structure. Thermoplastic composites (TPC) have gained increasing interest from the aerospace sector for their increased formability, weldability, recyclability and their superior toughness and fatigue performance in comparison with their thermoset counterparts. Their potential for out-of-autoclave manufacture (OOA) also makes them an excellent candidate for low cost production of large structures for aerospace applications. To investigate the potential for aerospace structures, an OOA variable stiffness, unitized, integrated-stiffener thermoplastic wingbox demonstrator was recently built at the University of Limerick. A number of different techniques were targeted: fiber steering to achieve the variable stiffness skin, in-situ consolidation to weld the stiffeners to the wingbox skin, and as manufacturing methodology a laser-assisted tape placement (LATP) in combination with winding was used. In the design process, the wingbox loads were determined by assuming its location to be at 85% of the wing semi-span of a B737/A320 size aircraft. Previously we reported on a full-scale structural test using a bespoke testing frame with representative bending moment and shear load. Indeed, the wingbox buckled elastically at a load close to that predicted numerically. Our results highlight the potential advances that become possible in primary aerospace structures by combining fiber steering and in-situ consolidation of carbon fiber thermoplastic composites together with new blended, unitized structural concepts. Herein, we report on the results of a new test that include torsion as well as bending moment and shear. An overview of the design against buckling, manufacture and structural testing for load carrying capability is given.