The Numerical Simulation Analysis On The Mechanical Characteristics Of Some Typical Cracks In Pressure Pipes

Pressure vessel or pressure pipe to store and transport high pressure gas and liquid substances can sometimes cause serious accidents of vessel or pipeline. According to some studies, in these accidents, the stress of the structural materials in the event of a failure is often far lower than the limit of the material carrying capacities. After more in-depth studies, people found that the reason of the low-stress brittle fracture or damage is because there are many small cracks in the original structure which bring to the low-stress brittle fracture or damage of the structures. Especially for some tiny cracks which can only be seen by the microscopes. And because these cracks are so tiny that they are often ignored by people in most cases. But in many areas, it is these mini-cracks that induce the low-stress brittle fracture or damage of the structures.To the three main forms of the complex cracks (oblique cracks, offset parallel cracks and fork-shaped cracks) in the practical engineering, we can use the large general-purpose finite element analysis software ANSYS to make model calculation analysis on them. At last, we could extract the stress intensity factors of the three crack models.To the oblique cracks in the pressure pipes, after analysis we can find that the Ⅰ-stress intensity factor will increase as the oblique angle increases, and the increasing trend will decrease; However, the II-stress intensity factor will first increase and then decrease in this process, and it will reach a maximum value when the oblique angle is45degree.To the offset parallel cracks, we have studied the intensity factors of the internal and external ends of the crack in the different staggered rate. Finally, we have got the staggered location of the two cracks when the intensity factors value is maximum or minimum. And to the fork-shaped cracks, we have also studied the intensity factors under the influence of the crack angle and the length ratio of the major and minor cracks. The result is, the intensity factors of the crack tips will increase as the length of the minor crack increases when the crack angle is certain; And if the lengths of the major and minor cracks are certain. we can also get the value of the crack angle when the intensity factor reaches maximum value.In the end, we can compare the results of the pressure pipe with that of the plane problem in the Stress Intensity Factor Handbook, and summarize the differences and relations in the two different cases.