An analysis tool for design and certification of postbuckling composite aerospace structures

Abstract

An experimental and numerical investigation was performed into the damage mechanisms and failure loads in skinstiffener sections. In the experimental investigation, thin strips consisting of a skin and single stiffener were cut from a range of various fuselage-representative panels. There were seven panel designs, which involved changes in geometry, lay-up, material, stiffener shape and the use of co-curing or secondary bonding to join the skin and stiffener. A total of 203 thin strip sections were cut from these panels and tested to failure. The sections were loaded in two test rigs that aimed to simulate the various symmetric and antisymmetric loads on skin-stiffener interfaces in a postbuckling panel. Five failure modes were observed, corresponding to the first damage event occurring at different locations: stiffener bend, stiffener blade, core region under the stiffener, flange edge, and skin. In general, there was good repeatability of the experimental results, particularly when classified according to failure mode, though there was a significant degree of variability in some results. For the numerical analysis, two-dimensional finite element models were analysed, and strength criteria applied in order to predict the initiation of interlaminar damage. In general, the numerical predictions gave good comparison with the experiment in terms of the critical damage locations and initiation loads, which were within the experimental scatter. Discussion is given on the sensitivity of the specimen designs, and how the twodimensional analysis approach has been applied to large fuselage-representative structures.