Experimental and numerical analysis of ratcheting behavior of A234 WPB steel elbow joints including corrosion defects

Abstract

In this paper, ratcheting behavior of intact and corroded 90o elbow pipe specimens of A234 WPB steel is investigated at intrados, crown, and extrados positions. A special fixture was designed and constructed to carry out the fatigue experiments. Then, the effects of fatigue loading parameters (mean and amplitude) and defect depth were examined on ratcheting responses of intact and corroded specimens at intrados, crown, and extrados positions. To simulate the ratcheting behavior of specimens, a finite element analysis was performed based on the combined nonlinear isotropic/kinematic hardening model. As a reasonable agreement was found between the finite element (FE) simulation results and experimental data, the influence of constant internal pressure during the cyclic loading was examined on ratcheting responses through FE simulation. Results indicated that decreasing the load amplitude was more effective on decreasing the ratcheting strain than that of the mean fatigue load. Moreover, the most critical ratcheting response was associated with the intrados location of the pipe. For defective specimens, decreasing fatigue loading parameters resulted in a shakedown behavior for a defect placed at extrados, while, for the defects at intrados and crown, an increasing behavior was observed for the ratcheting strain. It was revealed that, at extrados position, the ratcheting behavior was arrested up to 1 mm defect depth. The ratcheting strains were increased at intrados and crown by increasing the internal pressure, while they were decreased at extrados.