Study of Ratcheting Behavior of 304L Stainless Steel Branch Pipes by Using Chaboche and Combined Hardening Models

In this paper, finite element analysis with combined (nonlinear isotropic/AF kinematic hardening model) and chaboche hardening models are employed to investigate ratcheting behavior in stainless steel branch pipes under dynamic moments and internal pressure. Obtained results show that the maximum value of ratcheting strain takes place in the junction of branch pipes in the hoop stress direction. In this case, the rate of progressive strains increases with the increase of the bending moment levels in constant internal pressure. Furthermore, this study reveals that the geometry and dimensions of branch pipes have a significant impact on the rate of progressive strains. The bending moment levels to initiate strain accumulation phenomena will be increased with the increase of the dimensions of branch pipes. In the BSS1 sample, comparison between results obtained using progressive strains with combined and chaboche hardening models are much better than those of Armstrong-Fredrick hardening model and are near to the experimental data. Of course, in BSS2 sample, the behavior of ratcheting with combined hardening model is near the experimental results. For the BSS3 sample, the prediction of ratcheting with the chaboche hardening model is better than using the other strain hardening models and are near to the experimental data. Like the carbon steel samples studied in the recent paper, compared to the Armstrong-Frederick hardening model, the chaboche and combined hardening models exhibit an appropriate prediction and similar to experimental results in stainless steel samples.