Ratcheting assessment of pressurized elbow pipes using the visco-plastic Chen-Jiao-Kim hardening rule frameworks

In this study, the ratcheting responses of pressurized long and short radius 90 degrees elbow pipes made of 304L austenitic stainless steel under displacement-controlled cyclic loading is evaluated mainly using the Chen-Jiao-Kim (CJK) kinematic hardening rule at room temperature. Visco-plastic flow rule and isotropic hardening are introduced into the CJK model to better reflect the time-dependent behavior and cyclic hardening characteristics of the 304L stainless steel material. The model is implemented employing the user material subroutine (UMAT) in the ABAQUS finite element software. The predictions show that the maximum ratcheting strain occurs at the flank of the long and short radius 90. elbow pipes. The influence of internal pressure, cyclic loading, and bending radius on the ratcheting responses of the elbow pipes is respectively investigated. It is found that the predictions of the CJK model are very nearly the same as the test data. In addition, the ratcheting responses of two long radius elbow pipe specimens under force-controlled cyclic bending are evaluated. Further, the C-TDF (The Committee of Three Dimensional Finite Element Stress Evaluation) combined with CJK model and Linear Matching Method (LMM) is respectively used to determine the shakedown and ratcheting boundaries of the pressurized long and short radius 90. elbow pipes under displacement-controlled and force-controlled bending. The comparison with the test data in this study shows that the shakedown and ratcheting boundaries determined by LMM, divides the shakedown and ratcheting zone well.