Comparison of SIF solutions obtained by XFEM and conventional FEM for cracks in complex geometries like valve body

摘要

Globe valve is a type of industrial valve used to obstruct or regulate flow of the fluid in pipelines via linear motion of the plug. The main component of the valve, the valve body, is the carrier of the internal and often variable pressure. The body itself is usually made by sand casting which may result in impurities and metallurgic or shrinkage defects. The above-mentioned, coupled with the relatively geometrically complex shape of the valve bodies, makes the accurate determination of the crack formation and growth often challenging. Additionally, formation of the cracks in a pressure vessel such as globe valves usually leads to one of the two outcomes. If the crack reaches its critical size under specified loading conditions, a catastrophic failure may occur. On the other hand, the preferred option of stable crack growth can lead to the effect known as leak-before-break. Therefore, it is necessary to accurately determine stress intensity factors (SIF) for cracks in such geometry. This determination is usually made by classical finite element method, and it is very hard to do on complex shape. In addition, it is possible to determine SIF using extended Finite Element Method (X-FEM) which is proved on simple geometry. In this paper, the verification of the X-FEM has been conducted by comparison of results obtained by this method and by the classical method on valve body. Presented computational model suggest the possibility of accurately determining fracture mechanics parameters for cracks in geometrically complex components such as those of valve bodies.