Bending instability of composite tubes

In this paper, a set of simple formulations is derived to predict the instability critical loads of orthotropic composite tubes under pure bending. The formulations are based on the assumption that the instability of an orthotropic composite tube under pure bending is due to the ovalization of its cross section. For the static instability case, the ovalization increases steadily as the curvature increases, which results in a reduction in the bending rigidity of the tube. The interaction of longitudinal bending and cross-section ovalization causes the tube to have a limit load instability. For the dynamic instability case, the instability of the tube is due to the interaction of two vibrations, one is the longitudinal bending of the tube as a beam, the other is the circumferential bending of the tube as a thin-walled shell.