Nonlinear Response and Failure of Pressurized Composite Curved Panels

Abstract

Results of an experimental and analytical study of the nonlinear response and failure characteristics of internally pressurized 4- to 16-ply-thick graphite-epoxy cylindrical panels are presented. Specimens were clamped in a test fixture to simulate the skin between two frames and two stringers of a typical transport fuselage and tested to failure. Aluminum specimens were also tested to failure and the results of these tests are compared with the graphite-epoxy test results. The graphite-epoxy specimens failed at their edges where the magnitudes of severe local bending gradients and interlaminar stresses are maximum. A shell analysis using the STAGS computer code showed that the response is independent of the axial coordinate outside of the bending boundary layers at the curved ends. A nonlinear, one-dimensional analysis in the circumferential coordinate is developed that includes transverse shearing deformations and computes interlaminar stresses. Accurate panel radius measurements and measurements of edge circumferential displacements associated with specimen slipping were required in the one-dimensional analysis to obtain good correlation between analytical and experimental results. Results indicate that all panels tested, including the thin four-ply panels, can support supplied internal pressures that are well above the proof pressure loading expected for transport fuselage structures.