Approximate bifurcation load of short thin-walled laminate plate structures with imperfection

Abstract

The bifurcation buckling load can be determine solving a linear eigenproblem of buckling. If the structure is not perfect, the effect of bifurcation doesn’t occur. So, how to estimate a value of the lowest buckling load of the real structure? A methodology for determination of the lowest buckling load of a real structure with initial imperfection using a post-buckling path is presented. The investigation is performed for a Z-column made of carbon-epoxy laminate. The amplitude of initial imperfection is small less than half of the walls thickness. The column is simply supported on both ends. All calculations are performed by the finite element method and Koiter’s method. A plate model of the thin-walled structure has been applied. First, an eigenvalue buckling problem is solved to determine bifurcation loads. Next, post-buckling equilibrium paths for the plate structures are determined to calculate the lowest approximate bifurcation loads by the P-w and P-w2 methods, the inflection point method and the Koiter’s method. The presented methodology is correct, when the uncoupled buckling is considered. The numerical results were verified in experimental tests. A Aramis system was applied. A static compression test was performed on a universal testing machine. Specimens were obtained with an autoclave technique. Tests were performed at a constant velocity of the cross-bar equal to 2 mm/min. The compressive load was less than 150% of the bifurcation load.