Experimental and numerical investigation of ratcheting behavior in seamless carbon steel 90° elbow pipe with small dimensions under constant internal pressure and in-plane cyclic bending

Abstract

The purpose of this study is to identify the effects of mean fatigue load, amplitude fatigue load, internal pressure and loading history on ratcheting behavior of seamless A234 WPB steel elbow pipe. So, in this paper the ratcheting behavior of seamless 90° elbow pipe of A234 WPB steel under constant internal pressure and in-plane cyclic bending is investigated experimentally and numerically. At first, in order to the confirm of elbow pipe material, a series of experimental tests were performed on elbow specimen, including: chemical composition analysis, metallography testing, hardness testing and uniaxial tensile testing. In the next step, the fatigue tests were performed on elbow pipe specimens at ambient temperature (25 °C) under asymmetric cyclic loading with load-control conditions. According to the experimental fatigue data, concluded that the increasing of mean load, amplitude load and internal pressure, increases the accumulation of ratcheting strain in axial direction at intrados and extrados locations, and also in hoop direction at crown location. So that the increasing of mean load or amplitude load has the greatest effect on the ratcheting strain at intrados and extrados locations. Also, it was found that the loading history affected to ratcheting behavior and premature failure of pressurized elbow pipes. Finally, the finite element simulation was carried out by ANSYS software based on the nonlinear kinematic/isotropic hardening model, and the FE simulation results were compared with experimental fatigue data and it was found that the numerical results are in good agreement with experimental fatigue data.