Use of Material Tailoring to Improve Buckling Capacity of Elliptical Composite Cylinders

Discussed is the importance of improvement of the axial buckling capacity of elliptical fiber-reinforced composite cylinders throughmaterial property tailoring by appropriately varying fiber orientation as a continuous function of circumferential position. The study is numerical in nature and relative to a baseline quasi-isotropic elliptical cylinder with the same geometry and the same number of composite layers, and therefore the same weight, increases in buckling capacity of 30 % are predicted for what are considered small cylinders. Increases of 35 % are predicted for larger cylinders. Several fiber angle variations with circumferential position are investigated, and each one results in improved buckling capacity. The scheme to determine the fiber angles as a function of circumferential position is based on an approximate buckling analysis of circular cylinders. Intralaminar material failure and postbuckling collapse of the cylinders are also investigated to determine if thematerial tailoring scheme has a detrimental effect on those responses. It is found that before collapse no material failure is predicted. Upon collapse, generally speaking, failures because of high stresses perpendicular to the fibers are more prevalent in the tailored designs than for the baseline quasi-isotropic case. However, with some tailored designs, no failures in the fiber direction are predicted, unlike the baseline case. Convergence of the numerical predictions is discussed, as is the effect of cylinder boundary conditions on the predicted improvement in buckling capacity. I