Buckling and Crack Propagation of Cracked Box Beams

Abstract

The stress-intensity factors of cracked box beams under torsion, geometrically linear and nonlinear twist buckling, and crack propagation under combined loading are discussed. This study is motivated by a previous work which derived a closed-form expression of Mode II stress-intensity factor for thin-walled beams with a centered longitudinal crack and subjected to torsion. Naturally, the way in which Mode I stress-intensity factors are influenced by torsion is of interest. The influence of parameters like crack length, crack angle, width and depth of beam, wall thickness, stiffener size on Mode I and Mode II stress intensity factors have been studied using the finite element method and represented the data in a surrogate model using two approaches: a) a Fourier-series based correction factor, and b) an artificial neural network. The torsional-buckling problem and crack propagation are also of interest. Specifically, the former is studied based on both geometrically linear and nonlinear theory for the critical loading and the load-twist angle relation; the crack propagation study focuses on both the limit loadings and the angle in which the initial crack growth occures. The results, which are based on finite element analysis of a box beam in the presence of a crack, indicate, that even for a tiny crack, the crack grows prior to buckling.