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 deflections, 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 lamination length. For more accurate predictions, however, a three-dimensional analysis is required.Krueger, Ronald and Minguet, Pierre J. and Bushnell, Dennis M. (Technical Monitor)Langley Research CenterFINITE ELEMENT METHOD; TWO DIMENSIONAL MODELS; TENSILE STRESS; COMPOSITE MATERIALS; DEBONDING (MATERIALS); BENDING; SKIN (STRUCTURAL MEMBER); NONLINEARITY; PLANE STRAIN; LOADS (FORCES); STRESS-STRAIN RELATIONSHIPS; DEFLECTION; FLANGES; COMPUTERIZED SIMULATION...