Variable complexity modeling of postbuckled stiffeners for delamination initiation
Barlas, Fatma Aylin
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Delamination at the free edge is analyzed as a mode of failure for uniaxial compression of postbuckled structural components. Analyses are performed for I-section stiffeners and for a dropped-ply laminate, all of which failed due to free edge delamination in earlier experimental studies. These specimens were made of AS4/3502 graphite-epoxy unidirectional tape. The nonlinear response of the specimens is modeled by a geometrically nonlinear finite element analysis. A variable-complexity modeling scheme is developed to economize computer resources for the nonlinear analysis. The three-dimensional stress field near the free edge is investigated by employing 20-node solid elements in that region. A dimensionless delamination index is calculated to investigate the severity of the interlaminar stress state. Numerical results correlated reasonably well with the experiments on load-end shortening plots. The nodallines and/or inflection points of the out-of-plane deflection along the free edge in the postbuckled configuration are found to be delamination critical sites. Both interlaminar shear stress tangent to the free edge and tensile interlaminar normal stress are significant at these critical locations and are likely to initiate delamination.
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