Welding and Joining

Welding is the most used assembling process for industrial structures. The weld is a heterogeneous zone considered as a « hot spot ». Indeed, the heat transferred to the assembly during welding induces phase change, introduces residual stresses and strains and changes the local geometry.

Although welding produces high resistance assembly, stress concentration, defects, heterogeneous microstructure and residual stresses can lead to fatigue cracks.

Our research activities focus on the numerical and experimental study of the physics of welding. We develop finite element models of the arc plasma, the weld pool and the workpiece to understand the influence of the welding parameters on the weld properties. For example, we have studied the effect of pulsed current or alternate gas distribution of helium and argon on the weld shape and heat transfers. We have also studied the effect of gravity on the weld dissymmetry. The development of thermomechanical and metallurgical constitutive models and their numerical integration, the development of efficient steady and transient algorithms, allowed us to predict the residual stresses in welding.

Our works are applied to several welding process and materials such as:

  • Gas Tungsten Arc Welding with constant and pulsed current with or without the addition of filler metals for steels and stainless steels;
  • Gas Metal Arc Welding for steels and in the near future the GMA Welding of aluminium alloys;
  • Friction Stir Welding of aluminium alloys.

Our numerical approach is associated with experimental analysis. We use welding equipments to reproduce the operating parameters of our industrial partners, to make parametric studies, to observe the fusion zone with infrared or high speed CCD cameras. We have a Panasonic 6 axles welding robot with the possibility to weld in GTAW or GMAW mode, a GTAW Castolin welding generator, an infrared camera -40/2000°C and a high speed camera 1000 pictures/s with filters.

Mechanical testing equipments, a nanoindentation machine and microscopes help us to characterize the weld microstructure and the mechanical properties of the assembly.