Numerical modeling and comparison study of elliptical cracks effect on the pipes straight and with thickness transition exposed to internal pressure, using XFEM in elastic behavior.

The present work deals with the effect of an external circumferential elliptical crack located at the thickness transition on a varied stepped diameter pipe. The purpose is the application of extended finite element method (XFEM) for the calculation of stress intensity factor (SIF) at the thickness transition region of the pipe considering internal pressure and comparing the effect of the crack between pipes straight and with thickness transition. To model a crack precisely, enrichment, enrichment functions are used to enrich the displacement approximation, the level set functions are calculated from the crack mesh, and the definition of the strategy of integration is performed. A comparative study is made on the SIF of the crack defect in straight pipe compared to one with thickness transition using XFEM for the variation of the crack and pipe geometrical parameters. The result shows that the XFEM is an effective and practical tool for elliptic crack modeling in a pipe with thickness transition because a crack is easily modeled through enrichment functions. The comparison of the SIF of a similar defect between pipes shows that a pressurized pipe with thickness transition is more sensitive to the used cracks.