Lightening structures is one of the main challenges of the aviation industry today. Friction stir welding is an alternative to replace conventional assembly processes and reduce the mass of the structure.The mechanical behavior of this assembly must be determined to understand the failure mechanisms.The concept of fracture mechanics is often used to characterize the fracture of thin sheets. In this document, a global energy approach proposed to characterize the phenomenon of rupture and to determine experimentally the essential work of fracture in Aluminum Alloy welded by Friction Stir Welding process. The tests were carried out on DENT specimens welded by the process of friction stir welded and not welded specimens. The results obtained show that the not welded sheets show that the strength of the specimens welded by FSW has a low tear resistance compared to the welded specimens.