Numericial Study Of Three Dimensional Surface Crack Growth Characteristics Under Corrosive Environmential

Mobile pressure vessels,like high pressure gas cylinders for transporting compressed natural gas have an internal pressure of 20MPa in full load.Since the joint action of hydrogen sulfide?H₂S?in natural gas and water forming the wet H₂S environment,The stress corrosion is formed under the high working stress.Furthermore,with the gas cylinder charging and discharging everyday and bumped on the road,the corrosion fatigue condition is formed.In this case,the three-dimensional surface cracks on the equipment are easy to expand into plane through cracks,causing leakage and causing major accidents.Many experimental methods have been studied on the problem of crack propagation of corrosion fatigue,but the research on the law of corrosion fatigue crack propagation through numerical simulation method is relatively less.In this text,numerical study of three-dimensional surface crack growth characteristics under corrosive environment is carried out.By means of the boundary element software FRANC3D,the life problem of the penetrating crack model and the surface crack model under the same stress ratio is studied by numerical calculation method.Because the analytical solution of the surface crack model life is very complex,the factors affecting the life of the surface crack model are discussed in this paper.In order to study the problem of crack propagation on the surface of corrosion fatigue,the method of Matlab spline function derivation is first proposed to work out the propagation rate of surface crack Based on this method,the effect of the crack propagation rate and morphology of the surface crack model under different stress ratio?R=0.1?0.3?0.5?is investigated by numerical simulation method.Finally,for evaluating the effect of the crack growth rate of the surface crack model on hydrogen induced stress,a numerical loading method for additional internal stress exerting the same stress ratio with external loads is proposed.Through that,The effect of the propagation rate of surface crack in the corrosive environment under different stress ratio?R=0.1?0.3?0.5?is studied,which is compared with the rate of crack propagation in the air.The main work and results of this article are as follows:?1?The crack propagation life model of the initial surface crack under different stress ratio is obtained.The relationship among the three-dimensional surface crack model life,the stress ratio R and the long semi axis c of the initial surface crack is nonlinear.?2?The a-N.c-N curve,the crack propagation rate da/dN-?K.dc/dN-?K and the morphology of the surface crack propagation under different stress ratio?R=0.1?0.3?0.5?are obtained,and a numerical method for the propagation of corrosion fatigue surface crack is proposed.?3?By using the numerical method of corrosion fatigue,it is found that the different stress ratio?R=0.1?0.3?0.5?has no significant effect on the rate of surface crack growth in corrosion environment,and corrosion increases the rate of surface crack growth.