Influence of Fiber Undulations on Buckling of Thin Filament-Wound Cylinders in Axial Compression

The filament-winding process introduces inherent geometric defects into thin-shell cylinders in the form of fiber-bundle, or tow, crossovers. This research identified the micromechanical geometry in the fiber crossover regions of filament-wound cylinders. A stiffness model was developed for the crossover regions based on a modified classical lamination theory. The local stiffness-coupling values predicted by this model were incorporated into a global finite-element model of thin-shell, filament-wound cylinders. Eigenvalue buckling analyses performed using this enhanced finite-element model are compared to eigenvalue analyses performed without incorporating the influence of the stiffness couplings at the fiber crossover regions. Experiments were carried out in which 16 filament-wound cylinders with four different surface patterns were fabricated and tested. The results showed that the accuracy of a finite-element analysis improved significantly when the stiffness coupling effects due to fiber undulations were properly accounted for in the analytical model.