Buckling and Post Buckling of Composite Multi⁃ Wall Box Section under Bending⁃Torsion Coupled Loads

In this paper, a research on the typical multi-wall box section of composite materials is carried out. The stability, load-bearing capacity, damage initiation and propagation under the bending-torsional coupled loads were studied by experimental tests and finite element analysis. Using (Digital Image Correlation, DIC) method, the change of buckling mode of the test piece was captured. The buckling and post-buckling strengths were determined from the load-strain curves. In the numerical simulations, the buckling and post buckling behaviors were investigated using the Hashin criterion combined the VUSDFLD subroutine incorporating the stiffness reduction based on the ABAQUS/Explicit module. The results show that when the multi-wall box section buckles under the bending-torsional coupled loads, the torque will change the distribution and symmetry of the buckling mode, with the peaks and troughs appearing alternately. The multi-wall box section has a long post-buckling stage, with the buckling mode gradually developed from first-order to high-order, until the structure is completely destroyed and loses its load-bearing capacity due to excessive deformation.