Ratcheting Analysis Of Elbow Pipe With Local Wall Thinning Under Complex Load

Ratcheting deformation was experimentally studied on elbow pipe made ofZ2CND18.12N stainless steel with local wall thinning subjected to constant internalpressure and reversed in-plane bending under load control. For sound elbow, it isfound that ratcheting strain occurs at intrados, crown and flank in hoop direction. Thelocal wall thinning is located at extrados and crown of elbow. It is shown that localwall thinning has a very pronounced effect on the ratcheting behavior of elbows, ascompared to the ratcheting behavior of sound elbow specimen. For sound elbow andthe elbow with local wall thinning at extrados, the maximum ratcheting strains occurat the intrados in hoop direction. For the elbow with local wall thinning at crown, themaximum ratcheting strains occur at crown during the first50cycles.Three-dimensional elastic-plastic analyses with ANSYS in which Chaboche andChen-Jiao-Kim (CJK) kinematic hardening model are carried out to evaluatestructural ratcheting behaviors. A reasonable agreement has been found between theexperimental and the simulated results with CJK model for the ratcheting of theelbows.Ratcheting strains were predicted with the user ANSYS for pressurized elbowwith local wall thinning at outer under reversed bending with CJK model. It is foundthat the depth of wall thinning has a very pronounced effect on the ratcheting behaviorof elbows. The hoop ratcheting strain level increases with increasing depth of wallthinning. Both of ratcheting strain rate and ratcheting strain level grow with theincrease of reversed bending load.Ratcheting strains were predicted for pressurized elbow with local wall thinningat inner under reversed bending with CJK model. For elbows with local wall thinningat crown and extrados, the maximum ratcheting strains occur at the crown in hoopdirection. For elbow with local wall thinning at intrados, the maximum ratchetingstrain occurs at the intrados in hoop direction. When the depth of wall thinningd=1mm, local wall thinning at inner has more influence to ratcheting strain at thinningarea compared with that at outer. Ratcheting strains at thinning areas of elbows withlocal wall thinning at inner are larger than those at thinning areas of elbows with localwall thinning at outer. When the depth of wall thinning d1.25mm, elbow withlocal wall thinning at outer of extrados has larger ratcheting strain than that with local wall thinning at inner of extrados.The ratcheting boundary is determined by evaluation variations in the plasticstrain increments with CJK model.