Crack Stress Intensity Factor And Crack Propagation Of Spherical Pressure Vessel

In the production of pressure vessels,due to various reasons such as production technology and conditions,the pressure vessel will have certain defects.The central oblique crack is usually located inside the component rather than on the surface of the component,which is often the most difficult to find.After the working load,the micro cracks will gradually begin to expand until the component fails.There will be production accidents and cause huge losses to workers’personal safety and social economy.This paper analyzes the crack stress intensity factor and crack growth of spherical pressure vessels.The change trend of the crack stress intensity factor under different crack deflection angles,as well as the propagation path of the crack in the weld zone under different loading angles,and the expansion of the surface cracks of the container under different stress and stress ratios are analyzed.The main research contents and results are as follows:（1）Research on the cracks of a single-material spherical pressure vessel found that under the same initial crack angleβ,the stress intensity factors K_Ⅰand K_Ⅱat the crack tip increase with the increase of the crack size ratio 2a/h;at different initial crack angles underβconditions,the trend of K_Ⅰand K_Ⅱis the same with the crack size ratio of 2a/h.Whenβincreases,the J integral and equivalent stress intensity factor K_eincrease,and the type I stress intensity factor K_Ⅰgradually becomes dominant in K_e;when the eccentricity e decreases,the left crack angle of the crack gradually Increase;under the condition of constant eccentricity e,the left initiation angle of the crack increases when the tensile stress increases.（2）Through the study of the crack stress intensity factor of the bi-material pressure vessel,it is found that the typeⅠstress intensity increases due to the increase of the deflection angleβ.When the deflection angleβis about 45°,the typeⅠstress intensity is achieved by K_ⅠI Maximum value.The stress intensity factor of the crack tip near the interface of the high-strength material is always greater than the stress intensity factor of the crack tip near the low-strength interface,and the crack is more likely to expand first to the end of the Q345 material interface.The larger the deflection angleβ,the I-type stress intensity factor K_Ⅰplays a dominant position in the equivalent stress intensity factor K_e.（3）Numerical simulation of the crack propagation path in the weld zone was carried out under compound loads.After changing different loading angles,it was found that the crack propagation path under compound loading conditions would change,and the propagation path and load direction were basically vertical,in line with the maximum circumferential force criterion.With the increase of the loading angleαof the load,the propagation path of the crack in the weld zone will gradually deflect from the expansion along the interface and continue to expand through the material interface.（4）Numerical simulation of crack growth of bi-material pressure vessel cracks under different stress to stress ratios.By changing different stress levels and stress ratios,it is found that the stress intensity factor of pressure vessel cracks has a linear relationship with the internal pressure received.The greater the pressure,the greater the stress intensity factor.The larger the stress ratio R,the smaller the crack growth rate,and the number of load cycles the pressure vessel will bear will increase.