Concurrent design and manufacture of a thermoplastic composite stiffener

Fibre reinforced composite materials are finding increasing application in aerospace structures due to their superior specific properties. Aerospace structures make widespread use of stiffening elements, such as stringers, for example in wingboxes and fuselage structures. Sizing of stiffeners to fulfil strength, stiffness and manufacturing considerations is a significant challenge. Herein, a novel manufacturing approach using winding in combination with laser-assisted tape placement is used to manufacture an omega-shaped stiffener made from carbon fibre thermoplastic material. This paper discusses the integrated approach taken by considering material choice, manufacturing constraints and structural design on the performance of a closed-section omega stiffener. The sizing is based on the buckling response of the wingbox, with manufacturing constraints taken into consideration. In the collapsible mould, a low-melt aluminium alloy is used as a spacer, which can be removed post-process by exposing the mould to the alloy melt temperature, which is below the glass transition temperature of the thermoplastic composite material. Manufacturing tests show that repeatable stiffeners of the appropriate dimensions are manufactured. Characterisation tests show that both the bond strength, measured using an interlaminar shear strength test, and the corner strength, assessed using a four-point bend test, are satisfactory.