Chapter 14 - Plastic Buckling and Collapse Under Axial Compression

Abstract

This chapter investigates and analyzes the fundamental problem of plastic buckling of tubes under axial compression. Stainless steel tubes with D/ts in the range of approximately 20–50 are compressed to collapse monitoring the evolution of deformation in the test section. The first instability is axisymmetric wrinkling with the critical strain and wavelength governed by the tube D/t and the plastic properties of the material, including plastic anisotropy. Under continued compression, the wrinkles grow stably, gradually reducing the axial rigidity, eventually leading to a limit load instability. For the tubes tested, the initially axisymmetric mode switches to non-axisymmetric ones with 2–5 circumferential waves, which reduces the average strain at the limit load that represents the onset of collapse. For both axisymmetric and non-axisymmetric collapse, the onset of wrinkling and the limit state are separated by significant levels of strain. The problem is analyzed using shell formulations that can predict the onset of axisymmetric wrinkling, its evolution and localization, as well as the bifurcation into non-axisymmetric modes and the subsequent limit state. The analyses serve to conduct studies assessing the effect of the tube D/t, geometric imperfections, and material parameters on the onset of instability, on the response, and on collapse. The results should be of interest to the practice and research engineer working on plastic buckling of tubular structures.