Modelling infinite length panels using the finite element method

This paper compares three finite element models for determining the buckling and post-buckling performance of infinite length thin walled composite and metal stiffened panels — such as for modeling theoretical aircraft upper wing skin panels — namely single bay, double half-bay and quad half-bay models. The quad half-bay model is shown to be the ideal model as all wavelengths of buckling are permitted. This model gives an accurate estimate of postbuckling behavior that can include advanced behavior such as mode jumping or collapse while the single bay and double half-bay models are more restrictive and do not allow for accurate mode jumping to take place. Sample panels are analyzed for buckling performance using the computer program VICONOPT, which assumes an infinite length structure based on exact strip theory. This analysis is then compared to results from the quad half-bay FEM model, using the Abaqus solver, where the two models are in good agreement for the initial buckling performance for both the metal and composite panels. Buckling prediction for the quad half-bay model is within 0.5% 0.5% for the critical buckling mode, and within 3% 3% of all compared modes; and postbuckling performance compares well with the results of previous investigation of the same sample panel geometry