This paper presents results from a recent combined experimental-analytical study of the inelastic response and the sequence of events that lead to collapse of pipes bent under internal pressure. Experimental results from stainless steel 321 seamless tubes with D/t of 52 are reported. The tubes were loaded by pure bending at fixed values of pressure ranging from zero to a value that corresponds to 0.75 times the yield pressure. The moment-curvature response is governed by the inelastic characteristics of the material. Bending induces some ovalization to the tube cross section while, simultaneously, the internal pressure causes the circumference to grow. Following some inelastic deformation, small amplitude axial wrinkles appear on the compressed side of the tube, and their amplitude grows stably as bending progresses. Eventually, wrinkling localizes, causing catastrophic failure in the form of an outward bulge. Pressure increases the wavelength of the wrinkles as well as the curvature at collapse. The onset of wrinkling is established by a custom bifurcation buckling formulation. The evolution of wrinkling and its eventual localization are simulated using a FE shell model. The material is represented as an anisotropic elastic-plastic solid using the flow theory, while the models are assigned initial geometric imperfections that correspond to the wrinkling bifurcation mode. It will be shown that all aspects of the observed behavior including the failure by localized bulging can be successful reproduced by the models developed.

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