The paper deals with analytical determination of the stress concentrator location on a sample serving for diagnosing multiaxial fatigue lifespan of aluminium alloys, which are applied for reducing weight of road and rail vehicle constructions for acquiring decrease of fuel consumption. This article put emphasis on significance of appropriate sample specification and notch location according to the material type and mounting in the testing device. It operates also with suitable welding technology selection and thus ensures input parameters for numerical simulations of selected welding technology. The aim of numerical simulations is obtaining important information that will serve for detailed fatigue lifespan prediction in comparison of basic and weld material.