Influence of prepreg aging and tack on lay-up effects/defects in thermoset automated fiber placement

Large structural parts for state-of-the-art airliners are made of carbon fiber reinforced plastics (CFRP) using automated processes. For complex lay-ups thermoset Automated Fiber Placement (TS-AFP) is commonly used. Here, preimpregnated (prepreg) fiber slit-tapes are laid up subsequently. Quality and speed of the lay-up strongly depend on the interaction between material and process. Since material properties change as the material ages, it is crucial to know how these changes affect the interaction. Several studies have investigated the material changes. However, their influence on the occurrence of lay-up defects remains unclear. To investigate the effects of material aging at room temperature on its lay-up behavior, the authors conducted experiments on steering (lay-up along a non-geodesic path) and bridging using a robot based AFP machine. In steering the material's lay-up behavior worsens significantly after fourteen days of aging. Furthermore, the defects change from in-plane fiber waviness to out-of-plane buckling to even no adherence as a function of the material's out life. However, we did not observe these results in bridging where the bridged length appeared unaffected from material aging. In future work we will focus the generalization of these results and the effects of changing process parameters.