Numerical investigations of free edge effects in integrally stiffened layered composite panels

Abstract

A linear finite element analysis is conducted to examine the free edge stresses and the displacement behavior of an integrally stiffened layered composite panel loaded under uniform inplane tension. Symmetric (+Φ, −Φ, 0, −Φ, +Φ) graphite-epoxy laminates with various fiber orientations in the off-axis plies are considered. The quadratic stress criterion, the Tsai-Wu criterion and the Mises equivalent stresses are used to determine a risk parameter for onset of delamination, first ply failure and matrix cracking in the neat resin. The results of the analysis show that the interlaminar stresses at the +Φ −Φ and −Φ 0 interfaces increase rapidly in the skin-stringer transition. This behavior is observed at the free edge as well as at some distance from it. The magnitude of the interlaminar stresses in the skin-stringer transition is strongly influenced by the fiber orientations of the off-axis plies. In addition, the overall displacements depend on the magnitude of the off-axis ply angle. It is found that for Φ < 30° the deformations of the stiffener section are dominated by bending, whereas for 45° < Φ < 75° the deformations are dominated by torsion. The failure analysis shows that ply and matrix failure tend to occur prior to delamination for the considered configurations.