Numerical and experimental failure analysis of thin-walled composite columns with a top-hat cross section under axial compression

The paper describes a numerical and experimental study investigating the load carrying capacity of thin-walled composite columns with a top-hat cross section under axial compression. The tested columns were made of carbon-epoxy laminate with symmetrical lay-up and ply orientation [0/90/0/90]s. The experiments were performed on a universal testing machine, Zwick Z100, under full load conditions until total failure of the structure. In the experiments, post-critical equilibrium paths of the structure were determined, defining the relationship between compressive force and deflection and enabling the validation of the numerical models. Based on the obtained post-critical equilibrium paths, the critical load of the structure was determined by approximation methods. Simultaneously, a numerical analysis was performed by the finite element method using the Abaqus® software. The critical state was determined via a linear eigenvalue analysis, and the critical load and a corresponding buckling mode were estimated. The next stage of the numerical analysis involved solving a nonlinear stability problem for a structure with initialized geometric imperfection reflecting the lowest buckling mode. The geometrically non-linear problem was solved by the Newton-Raphson method. The load carrying capacity of the composite structure in the post-buckling state was determined by the progressive failure criterion which estimates damage initiation in the composite material based on the Hashin criterion, while the progression of damage is described with the energy criterion describing the degradation of stiffness of finite elements. The numerical and experimental results show high agreement, which confirms the adequacy of the developed numerical models of composite structures. Results presented in the paper are part of a study conducted under the project no. UMO-2015/19/B/ST8/02800 financed by the National Science Centre Poland.