Experimental Method to Determine the Draping Behavior of Auxiliary Materials for the Vacuum Bagging of CFRP Parts on Doubled-Curved Surfaces

The production costs of aircraft primary structures made of carbon fibre reinforced polymer (CFRP) are significantly higher than for comparable metal-based structures. Today substantial effort is made to achieve a sufficient reproducibility and parts’ quality in manufacturing processes of CFRP structures. Especially the sub process vacuum bagging for infusion processes is still expensive. One of the reasons is the complex positioning of the flexible auxiliary materials which have to be stacked on the preform. During the positioning on doubled-curved surfaces these materials tend to form wrinkles, which can lead to defects of the composite part. Yet, a defined description of the wrinkling behavior of the auxiliary materials on doubled-curved surfaces does not exist. In this work a characterization of the wrinkling behavior on doubled-curved surfaces is investigated for the auxiliary materials of the Vacuum Assisted infusion Process (VAP^®): release film, perforated peel ply, flow media, membrane and vacuum foil. Therefore, an experimental test method is derived similar to established hemisphere deformation test methods. The wrinkling behavior for the specific VAP auxiliary materials is empirically determined on differently curved surface geometries. It is shown that the draping behavior can be characterized by partial wrinkle-free surfaces between the wrinkles. A material specific threshold is derived to determine the appearance of wrinkles. The work shows that a characterization of the draping behavior of auxiliary materials on doubled-curved surfaces is possible. With the gained knowledge the potential for an increase of the vacuum bagging reproducibility is given.