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Design of a Composite Panel with Continuous Tow Steering Around an Elliptical Cut-Out



Cut-outs are inevitable in many structural components such as in aircrafts to accommodate windows or openings for access purposes or fasteners. Engineers usually view cut-outs, especially in primary structures, with disfavour as they result in stress/strain concentration and consequently reduced load carrying capability. Local reinforcements usually increase cost and weight to the overall design which is not favourable in aerospace applications. In case of composite panels, emerging advanced manufacturing methods such as 3D printing of automated fiber placement made it possible to continuously steer fibers/tows around a cut-out to potentially alleviate stress/strain concentration problem. Another advantage of tow steering in this case is maintaining the continuity of fiber/tow paths without any fiber cut which precludes ply-level, 3D stress/strain concentration which could otherwise lead to delaminationinduced damage. In this study, potential capability of tow steering around an elliptical cut-out (manhole) in reducing stress/strain concentration in a composite wingbox is investigated Buckling response under compression loading together with stress and strain concentrations under both tensile and compression loads are examined. Under tensile loading, the maximum stress and strain concentration factors around the cut-out in the straight fiber design are shown to be approximately 29% and 32% larger than its counterpart with steered tows around the cut-out. For the compression loading condition, the direct strain of the panel with straight fiber orientations was found to be three times that of steered fiber trajectories in the vicinity of the cut-out.


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