Continuous tow steering around an elliptical cut-out in a composite panel

Cut-outs are widely used to accommodate windows, openings for access purposes or fasteners in primary structural parts of airplanes. The presence of cut-outs in composite panels results in stress or strain concentrations and potentially reduced load carrying capacity. A promising solution to alleviate the stress concentration is to tailor the panel membrane stiffness by steering tow paths around the cut-out which is provided by emerging technologies such as 3-D printing or automated fiber placement (AFP). As such, it is possible to reduce stress concentrations around the cut-out and still have improved buckling load capacity. Continuous tow steering around cut-outs also eliminates fiber cutting which, by itself, acts as a weak spot due to the interruption it makes in the continuity of load transfer leading to delamination-induced damage. This work shows the potential of continuous tow steering around an elliptical cut-out in a laminated composite panel. The panel is designed to be a sub-component of a wingbox. The buckling behavior of a single panel is analyzed by finite element analysis and shows that tow steering around the manhole results in improved buckling response. The buckling performance of this panel is compared against a control panel using constant fiber orientations around the cut-out. Then, the structural behavior of the panel is investigated when it is used as a sub-component of a wingbox, which is subject to two different loading conditions. Finally, for both loading conditions, the benefits of the proposed technology are discussed through numerical testing.