Simulation of industrial elbow response under strong cyclic loading

Abstract

Elbow components are widely used in industrial facilities as parts of piping/tubing systems. Their performance under severe loading conditions may be critical for the structural integrity of an industrial facility In the case of an earthquake event in addition to other ser-vice loads, such as internal pressure, they are subjected to strong repeated cyclic structural loading. When these elements are subjected to strong repeated loading, they present failure modes associated with cyclic plasticity phenomena (material degradation or cyclic creep). Furthermore, due to their flexibility, significant non-linearities occur and the elbow cross-section shape distorts as cyclic loading takes place resulting at an oval or flatten shape at the end of the loading sequence. Accumulation of plastic strains (cyclic creep or ratcheting) also takes place at the most stressed parts of the element, associated with extensive bulging of the cross-section which is more pronounced in the presence of internal pressure. The present study is numerical, based on a finite element simulation of the elbow, and investigates the el-bow component behavior subjected to strong cyclic bending of various amplitudes in the presence of different levels of internal pressure. The material constitutive model has a domi-nant effect on the elbow response, and this is shown trough the use of 3 different plasticity models. The capabilities and drawbacks of each plasticity model regarding the simulation of cyclic plasticity phenomena are discussed in detail.