Analytical formulas for the effective width caused by bulging and flattening of curved aircraft panels

Abstract

The skin of a curved aircraft panel flattens, if it is subjected to circumferential tension, and bulges, if it is subjected to compression. These deformations distort the hoop stress distribution, which further leads to a reduced load-carrying width of the skin in circumferential direction. The book Roark's Formulas for Stress and Strain (W. C. Young and R. G. Budynas, 2002) presents a method to calculate the effective width of wide flanges of curved beams under tension. Although often used, it is shown in the current article that this method is not applicable to assess the effects of flattening and bulging of aircraft panels. As a reason, the support provided by the longitudinal stringers is identified. The current article consists of two parts. The first part presents the derivation of an analytical method to calculate the effective width caused by bulging and flattening of curved aircraft panels. The underlying model uses standard theories for straight and curved beams and is thus consistent with the assumptions made for Roark's formula. For improving the accuracy of this analytical result, the second part presents a simple procedure to fit this analytical approach to results from parametric Finite Element studies.