Abstract
This article investigates the static stability and mode-shapes of composite laminated beams under varying axial in-plane loads. The kinematic displacement field is described by unified higher-order shear deformation theory. Six functions are assumed to describe the distribution of axial in-plane load, which are one-constant function, two-linear functions, and three-parabolic functions. The Hamilton's principle is proposed to get the equilibrium equations of unified composite laminated beams. An efficient numerical differential quadrature method (DQM) is proposed to solve the govern equations. The obtained equations are solved as an eigenvalue problem to find critical buckling loads and their corresponding mode-shapes. The validation studies are compared with published works. Numerical results illustrate effects of in-plane load type, beam thickness, orthotopy ratio, fiber orientations, and boundary conditions on the critical buckling loads. The effect of axial load functions on the buckling mode-shapes is presented for the first time. These effects play very important role on the static stability and mode-shapes of composite beam structures. The proposed model may be important in design of aircraft, civil and ship-building when non-uniform in-plane compressive load is important.