Methods for mechanical characterization of defects induced by fibre steering: an experimental study

Automated Fiber Placement (AFP) is a state-of-the-art manufacturing process widely used in the aerospace industry especially for structural applications with high geometrical complexity and requirements on mechanical properties. In addition to its near-net shape fiber deposition capability, AFP technology is particularly suitable for these challenges due to its ability to place tows along curved paths, known as "fiber steering". Rendering load path optimized fiber architecture possible, fiber steering acts as a technology enabler to allow for complex design approaches with a highly automated and accurate manufacturing technology. Compared to following a geodesic path, curved path layup results in mechanically downgrading effects. These effects are caused mainly by in-plane undulation of fiber, resulting in microscopic angular deviations and discontinuities. Furthermore out-of-plane undulations, observable as wrinkles in the layup, may induce undulations in adjacent layers and thus increase the deteriorating effect on the mechanical performance of the structure. This study experimentally investigates this impact by means of tensile testing of steered laminates. The laminates are manufactured using an 8x1/4’’ AFP machine. In addition to test specimen with curved fiber paths, two reference laminates containing only straight fiber are produced and tested to determine the maximum possible strength as a comparison for the steering specimen.