Limited Life of Shells of Revolution Subjected to Severe Local Bending

Abstract

Tests were performed on axially loaded expansion bellows in order to obtain the relationship between maximum strain, load and deflection in the plastic region. A numerical method, previously proposed by the authors, was also used to investigate the behaviour of the bellows. The experimental and calculated results were found to be in reasonable agreement. The strains measured at collapse did not exceed three and a half times the strain at first yield while the strains after collapse were of a higher order of magnitude. The bellows were finally tested to failure in the low-cycle regime. The results agreed with fatigue tests on the parent material. A simple model based on the behaviour of the bending of a beam is proposed for predicting the strains in a shell of revolution with severe local bending. This model is used to classify the types of loading which lead to different modes of failure in the plastic region. The proposed design procedures are then used in case studies of the limited-life design of bellows and pipe bends, and comparison made with the observed fatigue lives.