Characterization of Graphite/Epoxy Laminates for Aeroelastic Tailoring

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.