Papers by Author: Gang Chen

Abstract: With the considerable use of high-grade pipeline steel in onshore and offshore project, welded joints are recognized as the weak link in pipeline because of the non-uniform microstructural regions induced by welding heat input. At first, the microstructural of different regions in API X80 pipeline welded joints was characterized and quantified by SEM, which indicate that the pipeline steel is a typical acicular ferrite steel. In this paper we investigated the J-integral resistance curve (J-R curve) in different locations of API X80 pipeline welded joints through low constraint SENT specimens with side grooves at room temperature. The effect of notch orientation (longitudinal-radial (L-R) and transverse-radial (T-R)) on resistance curve were investigated in base metal, which reveal the orientation almost have no effect on resistance curve. As the welded joints adopted in this study is two-pass steel arc welds, so the J-R curves of the inner surface, the outer surface and through-thickness surface notches specimens in the weld metal were investigated. The inner surface sample have the highest toughness through three samples because of the effect of second pass welding process. The effect of constraint on resistance curve was conduct between low constraint SENT specimen and high constraint SENB specimen, which found that the lower constraint corresponding to the higher resistance curve. After finishing the test, crack advancing plan of different positions were etched and observed by OM to demonstrate that the crack path always in the region which we would like to test.

Abstract: In this study, a series of multiaxial ratcheting tests under combined cyclic axial and inner pressure were conducted on M5 zirconium alloys tubes used as nuclear fuel cladding in Pressurized Water Reactors (PWRs) for the purpose to investigate the multiaxial ratcheting behavior of M5 and the factors of loading history may influence it. The experiment was stress-controlled and designed in a special loading path that all tubes in actually were under axial symmetrical cyclic load and constant inner pressure. A set of new patent multiaxial clamp was designed and applied to make sure the tubes can withstand inner pressure and axial load at the same time. A dynamic closed-loop multiaxial testing controller was used to manipulate two actuators simutaneously. Biaxial strain gauges were adopted to detect the signals of axial and hoop strain during the tests. The experimental results show that axial ratcheting strain decreases obviously within the original cycles reaching to a stop in certain cycles, the axial ratcheting increases with the cycles going. Loading history has obvious influence on the ratcheting behavior in axial direction. Higher stress amplitude level after loading history with lower stress amplitude level leads to an abnormal ratcheting behavior. The axial ratcheting shows a high sensitive to the complex loading history, especially when the stress amplitude is high. The hoop ratcheting strain accumulates continuously with the cycles going. Loading history has no obvious influence on hoop ratcheting strain and its ratcheting when the stress amplitude is low. The ratcheting strain and its rate shows more sensitive to the loading history when the stress amplitude increases to a certain value.

Abstract: A Voice Coil Motor (VCM) for precise positioning with high output force was designed. The stability and heat dissipation of VCM were analyzed. The performance of VCM was also compared with that of the same type VCM produced by SMAC. Uniaxial ratcheting behavior of solder wire (Sn63/Pb37) was studied by uniaxial cyclic stress controlled tension deformation tests,to verify the VCM systematically.

Abstract: The ratcheting strains of the straight and elbow piping under two kinds of loads—pressurized piping under symmetric cyclic bending and pulsating cyclic pressure were analyzed based on Chaboche constitutive model. The locations of the maximum ratcheting strain were determined. The ratcheting boundaries of the two piping structures under two kinds of loads were compared and calculated by the C-TDF method. For the pressurized piping under symmetric cyclic bending, the allowable bending load increases from E90S to E90L under the same pressure. In the higher cyclic pressure range, the allowable pressure have little difference under the same bending load which indicates that the bend moment have a bit effects on the ratcheting boundary in the higher cyclic pressure range.

Abstract: In order to understand the influence of Heat-Affected Zone (HAZ) on fatigue properties of 16Mn steel, a series of cyclic torsional tests were conducted on 16Mn weld metal, the base metal, and the HAZ metal. The specimens of 2mm diameter were uniformly-spaced taken from a bulk 16Mn plate, which included a V-style welded joint in the center, and the space for each specimen was 4mm. From cyclic fatigue tests performed on specimens at different positions, one can observe that the fatigue damage evolution in the HAZ is faster than those in the weld and the base metal, i.e., HAZ has a significant effect on fatigue life of 16Mn. In addition, the peak stress decline curves of HAZ specimens in different rows are considerably diversified, but the damage evolution and fatigue properties of HAZ metal are similar in spite of their locations.