High strength steel tubular frames are a cost effective solution for urban electric vehicles. On one hand the high mechanical characteristics of HSS together with advanced design methodologies makes possible to create an almost non-deformable cabin to guarantee passengers’ and battery’s safety, on the other hand, their predictable behavior and high elongation allow to improve the energy absorption of the collapsible zones.

But one of the challenges of the high strength structures when they are highly demanded is the welding process. In this case the welding process has been optimized to nearly obtain the same mechanical properties of the base material, mainly DP800 and DP1000. But the development has gone one step forward, because Cidaut has developed a methodology to determine the effect of the welding process in the fatigue life of the joints in the vehicle structure.

The methodology is based in the use of finite elements simulations and takes into account not only the longitudinal geometry of the beams, but also the section of the beam and the influence of the welding process. The methodology has been validated through the testing of specimens at laboratory scale, and nowadays is been validated in a full vehicle structure test.

The fatigue loads have been determined thanks to the use of a multiboby analysis, where the everyday manoeuvers have been modelled (curves, braking, small potholes, braking in turn, acceleration,…) and the forces in the four corners of the vehicle have been determined to be used in both the finite element simulation and the validation test.

This development has been made in the frame of the European Project Avangard, a three years European Project that has recently reached his midterm. The research leading to this result has received funding from the European Union Horizon 2020 Programme under Grant Agreement nº 869986.