Thermoplastic composite stiffener design with manufacturing considerations

Fiber 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 the wingbox or the fuselage. Sizing of stiffeners to fulfill strength, stiffness and manufacturing considerations is a significant challenge for aircraft designers. This paper proposes a novel manufacturing approach using winding and laser-assisted tape placement (LATP) to manufacture an omega-shaped stiffener. The stiffener design is used as the stiffening elements in a wingbox; the sizing of the stringer is based on the optimized buckling response of the wingbox, with manufacturing constraints also taken into consideration. The stringer is manufactured by LATP winding over a novel collapsible tool. The tool utilizes a low-melt alloy as a spacer, which can be removed post-process by exposing the mold to the alloy melt temperature, which is below the glass transition temperature of the thermoplastic composite material. Manufacturing tests have shown that using the new mold design leads to repeatable stiffeners of the correct dimensions. Characterisation tests have shown that the strength of the corners has to be checked in future work. The bond strength of the stiffners is satisfactory.