Research On Fracture Mechanics Analysis Of Crack Propagation For Thin-walled Pipe Based On Finite Element Method

In recent years,mechanical bulging processing,as a new processing method,has been widely used in mass production of mechanical products due to its advantages of high production efficiency,low cost,material saving,high quality and so on.However,in the forming process,the processing method will cause excessive local stress and crack,and then appear serious deformation,excessive wear,fatigue fracture and other phenomena,reduce the production quality and efficiency,increase the production cost,seriously make the forming "failure",resulting in the failure of production.But it is difficult to avoid the crack in the process of thin-walled parts,and it has an important effect on the quality of the workpiece.By analyzing the machining process of components with numerical analysis method,the mechanism of crack generation and development during machining process can be understood,and the mechanism of crack occurrence can be assisted to analyze,so as to solve various problems occurring in the forming process and minimize the probability of crack occurrence.In this paper,thin-walled pipe fitting is selected for research.Based on fracture mechanics theory and finite element model,Ansys software is used to simulate and analyze the eccentrically compressed member of thin-walled pipe fitting containing oblique crack,and the mechanical analysis and propagation of crack are studied.The main research contents of this paper are as follows:(1)Research status of fracture mechanics and the application of finite element method in the analysis of crack generation process.(2)The main types of cracks,the stress-intensity factor solution method and the dynamic crack growth law were analyzed.(3)The finite element model of thin-wall pipe eccentric compression member under tensile load was established.The position extrapolation method was used to obtain the value of stress intensity factor,and the variation law of stress intensity factor with crack length and crack tilt Angle was studied respectively.(4)The relationship between stress intensity factors of the two types and the variation rule of crack length and crack inclination Angle under the action of tensile bending load was studied.The differences between the calculated values of stress intensity factors under tensile and flexural effects are obtained,and the causes are analyzed.The influence of bending moment on stress intensity factor is analyzed.(5)In this paper,the test method of increasing the number of singular elements at the crack tip is adopted to calculate the crack initiation Angle of thin-walled pipe with oblique crack under tensile and tensile bending combination,and compare it with the crack initiation Angle predicted by the maximum cyclic tensile stress theory,so as to analyze the factors affecting the crack initiation Angle.