ABSTRACT Comparison of 2D Finite Element Modeling Assumptions with Results From 3D Analysis.pdf

1Comparison of 2D Finite Element Modeling Assumptions with Results From 3D Analysis for Composite Skin-Stiffener Debonding Ronald Krueger , Isabelle L. Paris , and T. Kevin OBrien NASA Langley Research Center, Hampton, Virginia Pierre J. Minguet? The Boeing Company, Philadelphia, Pennsylvania ABSTRACT The influence of two-dimensional finite element modeling assumptions on the debonding prediction for skin-stiffener specimens was investigated. Geometrically nonlinear finite element analyses using two-dimensional plane-stress and plane-strain elements as well as three different generalized plane strain type approaches were performed. The computed skin and flange strains, transverse tensile stresses and energy release rates were compared to results obtained from three-dimensional simulations. The study showed that for strains and energy release rate computations the generalized plane strain assumptions yielded results closest to the full three-dimensional analysis. For computed transverse tensile stresses the plane stress assumption gave the best agreement. Based on this study it is recommended that results from plane stress and plane strain models be used as upper and lower bounds. The results from generalized plane strain models fall between the results obtained from plane stress and plane strain models. Two- dimensional models may also be used to qualitatively evaluate the stress distribution in a ply and the variation of energy release rates and mixed mode ratios with delamination length. For more accurate predictions, however, a three-dimensional analysis is required. BACKGROUND Many composite components in aerospace structures are made of flat or curved panels with co- cured or adhesively bonded frames and stiffeners. Previous investigations of the failure of secondary bonded structures focused on loading conditions typically experienced by aircraft crown fuselage panels. Tests were conducted with specimens cut from a full-size panel to verify the integrity of th