BIFURCATION AND LOCALIZATION INSTABILITIES IN CYLINDRICAL-SHELLS UNDER BENDING .1. EXPERIMENTS

This two-part series of papers is concerned with the response and various instabilities which govern the behavior of circular cylindrical shells under pure bending. Part I describes the experimental part of the study and Part II presents the numerical simulation of the various phenomena observed experimentally. Experiments were conducted on long aluminum 6061-T6 shells with 11 different diameter-to-thickness ratios ranging from 60.5 to 19.5. For such geometries, the structural response and inherent instabilities are strongly influenced by the plastic characteristics of the material. Thinner shells were found to develop short wavelength periodic ripples on the compressed side of the shell. The shells buckled locally and collapsed soon after the appearance of the ripples. Thicker shells were found to exhibit a limit load instability as a direct consequence of the ovalization of the shell cross-section caused by bending. Following the limit load, the ovalization was found to localize, leading to the eventual collapse of the shells. For shells with intermediate D/t values, short wavelength ripples developed at the same time as localization of ovalization was recorded. The shells buckled locally and catastrophically following the development of a limit load.