Fatigue-Seismic Ratcheting Interactions in Pressurized Elbows

Abstract

Three dynamic tests on pressurized elbows involving fatigue-ratcheting as the major failure mode are investigated. The fatigue analysis is carried out with two approaches: the first is global and consists of Markl’s equation; the second is local and is based on local fatigue criteria combined with a suggestion by Coffin to take ratcheting into account. The implementation of these approaches required some elementary signal processing to separate the cyclic part of the strain from ratcheting. Results on narrow-band processes were used to assess cumulative damage. Finite element computations extended the data into uninstrumented locations. The great sensitivity of the implemented criteria to their arguments is discussed and exemplified. Despite the complexities of the issue, computed results match well with the experimental data.