Flow of viscoplastic fluids through expansions and contractions are found in several industrial processes. In this work, a numerical simulation of a viscoplastic fluid flow through a sudden axysimetric expansion followed by a contraction is performed. Experimental results show that under certain conditions, for this kind of flow a stagnant flow region may appear in certain conditions, causing a material fracture between this region and the flow region. One of the goals of this work is to verify if the constitutive model used in the numerical simulation can predict this kind of behavior. The effects of rheological and geometrical parameters on flow patterns are also investigated. The numerical solution of conservation equations of mass and momentum is obtained via finite volume method. In order to model the non-Newtonian behavior of the fluid, it is used the Generalized Newtonian Fluid constitutive equation. Two different equations for the viscosity function are used: the Carreau-Yasuda model and the Herschel-Bulkley model. The numerical solution gives the velocity, viscosity and pressure fields. It is observed that there is a flow pattern transition as the length of the central duct (which is the one with larger diameter) is increased. For low values of the ratio between the length and diameter of the central duct, the viscoplastic material seems to fracture near the core region of the flow. For larger values of the same ratio, the viscoplastic materials flow pattern has the same qualitative behavior of that one that occurs for Newtonian fluids, and no fracture is observed.