An experimental and analytical study was conducted to determine the buckling and postbuckling behavior of stiffened laminated composite panels under compression loading. The panels with two I-, hat-, andblade-shaped stiffeners and the honeycomb sandwich panel with I-shaped stiffeners were investigated.
In the analysis, the nonlinear finite element method combined with an improved arc-length method was used and the updated Lagrangian scheme based on the second Piola-Kirchhoff stress tensor and the Green strain tensor was utilized. For the finite modeling of stiffened panels, the eight-node degenerated shell element was used. For the progressive failure analysis, the maximum stress criterion and complete unloading failure model were adopted. The effects the stiffener spacings and shapes, the cap thickness, and the fiber angles on buckling and postbuckling behavior were investigated.
In the experiment, the web and the lower part of cap of stiffener were fabricated by the continuous plies of the skin for cocuring the stiffened panels. Therefore, the separation between stiffener and skin was not found in the junction part even after postbuckling ultimate load, and the stiffened panels had excellent postbuckling load carrying capacity. A shadow moire technique was used to monitor the out-of-plane deformations of the panels during tests. The piezoelectric films were attached to the panels to determine the failure characteristics of the panels.
The analytical results on the buckling load, postbuckling ultimate load, postbuckling deformed shapes and failure pattern showed good agreement with the experimental results for I- and blade-stiffened panels.
