Compression and buckling of composite panels with curvilinear fibers

Abstract

The plane in-plane compression response for a symmetrically laminated composite panel with a spatially varying fiber orientation has been analyzed for four different boundary conditions. Variation of the fiber angle along the length of a composite laminate results in stiffness properties that change as a function of location. The laminates are therefore termed variable stiffness panels. This work presents an analysis of the stiffness variation and its effect on the in-plane and buckling response of the panel. The fiber orientation is assumed to vary only in one spatial direction, although the analysis can be extended to fibers that vary in two spatial directions. A system of coupled elliptic partial differential equations that govern the in-plane behavior of these panels has been derived. Solving these equations yields the displacement fields, from which the strains, stresses, and stress resultants can be subsequently calculated. A numerical solution has been obtained using an iterative collocation technique. Corresponding closed form solutions are presented for the in-plane problem for four different sets of boundary conditions. Three of the cases presented have exact solutions, and therefore serve to validate the numerical model. The Ritz Method has been used to find the buckling loads and buckling modes for the variable stiffness panels. Improvements in the buckling load of up to 80% over straight fiber configurations were found. Results for three different panel aspect ratios are presented.