Ratcheting study of pressurized lateral nozzle of cylinder

Lateral nozzle of cylinder or lateral tee piping is widely used in nuclear,electric, petroleum and chemical industries. The cylinder or the piping maysuffer plastic accumulation, namely ratcheting, due to fluid pressuretogether with seismic load and thermal expansion. Extensive and quantitativeratcheting investigation is necessary to detemine the ratcheting boundaryfor the safety of the structure. As the phenomenological cyclic plasticconstitutive models have made a great progress in the last two decades, someinvestigators have taken advantage of the advanced model to evaluate theratcheting of simple structure of pressure vessels and piping. However, fewliterature studied ratcheting and ratcheting boundary of complicatedstrctures such as lateral nozzle of cylinder or lateral tee piping.In this paper, ratcheting of pressurized lateral nozzle of cylinder made of20^\# carbon steel was experimentally studied with a multiaxial fatiguetesting system and a self-designed in-plane bending apparatus for lateralnozzle structure. The specimen, pressurized by a pumping station withadjustable pressure, was simply supported on a stiff beam, and pulled in apulsatile way by the servo-hydraulic testing machine to simulate thein-plane cyclic bending. Ratcheting strains were acquired by multi-channelstrain processors with strain gauges. The cyclic loading and the strainacquirement were controlled and processed simutaneously by a computer.Ratcheting strains were detected around the acute angle region of thestructure. It was found that ratcheting mainly occured in the direction ofthe first principle strain, which is directed to the intersecting weld. Themaximum ratcheting strain occured at the nozzle side of the acute angleregion in the symmetrical plane for the structue. Ratcheting boundaries ofgauged points were experimentally determined by step pressure loading.Numerical ratcheting analysis of structure was accomplished by secondarydevelopment of ANSYS with four typical kinematic hardening models, in whichOhno-Wang model and its modified models improved the prediction ofratcheting strain. Ratcheting boundaries of gauged points were numericallydetermined by the equivalent plastic strain increment control method withMJS model(Modifed Jiang-Sehitoglu model) and validated to be in goodagreement with that experimental results. Finally, the ratcheting boundaryof the structure was determined according to the values of maximumratcheting strain point, which may be used to evaluate the shakedown of thestructure.