ELASTIC-PLASTIC FINITE ELEMENT SIMULATION AND FATIGUE DAMAGE ANALYSIS OF WRINKLEBENDS

The elastic-plastic finite element analysis (FEA) is performed in this paper to simulate the complicated plastic deformation of wrinklbends during bending and operation. The effects of element types, mesh sensitivity, and material input data of a stress-strain curve on the FEA results are discussed in details. To characterize the work hardening and Bauschinger effect on cyclic plastic deformation, three plastic hardening models: isotropic, kinematic and combined isotropic/kinematic hardening models are used and compared in the FEA simulation. Based on these investigations, a reliable nonlinear FEA model is developed, and then detailed FEA calculations are conducted for a wide range of wrinkle sizes under the cyclic pressure of 72% to 10% of SMYS (specified minimum yield stress) of X42 pipeline steel. Using the numerical results and an energy-based fatigue damage parameter, fatigue damage is quantified and a criterion is formulated as an H/L-N curve for wrinklebends. In the criterion, the wrinkle aspect ratio H/L is a key parameter that is directly related to the fatigue life. The results show that the proposed criterion and the H/L-N curve are simple and can be effectively used to evaluate integrity and estimate service life for wrinklebends.