Buckling of unsymmetric composite laminates

Abstract

An initial experimental and analytical investigation was conducted to examine the effects of the inherent mechanical couplings exhibited in fully anisotropic (i.e. unsymmetric) graphite/epoxy laminates on the buckling loads and mode shapes. Experimental techniques were devised to test 254 mm square plates of AS1/3501-6 graphite/epoxy under uniaxial compressive load with free, simply-supported and clamped edges. The results indicate that the mechanical couplings, especially those which relate stretching and bending behavior, cause out-of-plane deflections prior to buckling and reduce the buckling load significantly, i.e. the load at which out-of-plane deflections become large. The analytical results also show that the buckled mode shapes exhibit twisting due to the mechanical couplings. Suggestions are offered for improvements in the experimental and analytical techniques to better understand these phenomena.