Compos.Struct. 25, 129-137, 1993


NUMERICAL INVESTIGATIONS OF FREE EDGE EFFECTS
IN INTEGRALLY STIFFENED LAYERED COMPOSITE PANELS

I.C. Skrna-Jakl and F.G. Rammerstorfer

Institute of Lightweight Structures and Aerospace Engineering,
TU Wien, Vienna, Austria


Abstract - A linear finite element analysis is conducted to examine the free edge stresses and the displacement behaviour of an integrally stiffened layered composite panel loaded under uniform inplane tension. Symmetric (+Phi,-Phi,0,-Phi,+Phi) 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 +Phi/-Phi and -Phi/0 interfaces increase rapidly in the skin-stringer transition. This behaviour 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 Phi<30° the deformations of the stiffener section are dominated by bending, whereas for 45°<Phi<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.


(hjb,960628)