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Two graphite/epoxy anisotropic laminates used in the wing skins of recent aircraft designs were selected for a study of the interaction they can induce between wing bending and twist. The two laminates were used as covers for two subscale box beams. Each beam was supported as a cantilever and tested for two load conditions: tip shear and tip torque. Beam response, in the form of bending and twist slopes, was measured using a reflected light technique. Test results, expressed as beam displacement and induced twist, and twist and induced displacement, were compared with linear finite-element model predictions. Prior to beam tests, the stiffness characteristics of these two laminates were determined by tension tests and compared to analysis. The analyses were made using a piece-wise linear approach and material properties determined by simple tension tests.
The results have indicated that the in-plane stiffness properties of anisotropic laminates can be predicted if the layer properties of the composite materials are accurately known. Consequently, the coupled bending/twist response of wing type structures made from these laminates can be determined satisfactorily provided the limits of the laminate linear behavior are not significantly exceeded.
composite materials, graphite composites, epoxy laminates, anisotropic laminates, aeroelastic tailoring, stiffness properties
Senior engineer, Grumman Aerospace Corporation, Bethpage, N.Y.