Response of Damaged and Undamaged Tailored Extension-Shear-Coupled Composite Panels

Abstract

The results of an analytical and experimental investigation of the response of composite I-stiffener panels with extension-shear coupling are presented. This tailored concept, when used in the panel cover skins of a tiltrotor aircraft wing has the potential for increasing the aeroelastic stability margins and improving the aircraft productivity. The extensionshear coupling is achieved by using unbalanced ± 45° plies in the skin. Experimental and STAGS analysis results are compared for eight I-stiffener panel specimens. The results indicate that the tailored concept would be feasible to use in the wing skin of a tiltrotor aircraft. Evaluation of specimens impacted at an energy level of 500 in.-lbs indicate a minimal loss in stiffness and less than 30 percent loss in strength. Evaluation of specimens with severed center stiffener and adjacent skin indicated a strength loss in excess of 60 percent.

On Extension–Shearing coupled laminates

“…Extensional anisotropy, or more appropriately, Extension-Shearing coupling, is discussed at length in much of the preamble of articles on anisotropic composite laminate materials, but no specific details of stacking sequences for such laminates are given, particularly in the context of laminates with standard ply orientations for use in air vehicle construction. Indeed recently published work [3], describing in detail an application for laminates with shear-extension coupling reveals, only through additional calculation of the laminate stiffness terms, that significant Bending-Twisting coupling also exists in the stacking sequences adopted.…”

On tapered warp-free laminates with single-ply terminations

“…bend-twist coupled wing box structures [16], but can now be seen to extend to geodesic fuselage designs, involving angled or helical stiffener arrangements [17], in order to counteract the tendency for bendingtwisting coupling behaviour due to angled stiffeners at +φ on the inner surface of the fuselage skin and -φ on the outer surface.…”

On Extension-Shearing Bending-Twisting coupled laminates

“…Section 4 provides information on the extent of the feasible design space for Extension-Shearing Bending-Twisting coupled laminates, including the dominant forms of sub-sequence symmetries. Extension-Shearing Bending-Twisting coupled laminates arises from un-balanced and symmetric designs [6], but symmetry is shown here to be a sufficient rather than a necessary constraint. Expressions for ply orientation dependent lamination parameters are also given, together with graphical representations, which allow the available design space to be visually interrogated.…”

“…A complete list of Extension-Shearing Bending-Twisting coupled laminate is therefore developed, beyond the less well-known un-balanced and symmetric design rule [6].…”