IIW White Paper

4 Needs and challenges in welding and joining technologies

4.5 Role and potential of modelling Advances in the development of welding processes and techniques are only possible with a profound understanding of the mechanisms that underlie the particular processes. In this context, modelling and simulation are indispensable tools with continuously increasing relevance. Modelling and simulation help verify the theoretical perception of a process by checking experimental results qualitatively and quantitatively against corresponding numerical models. With growing computational power, the numerical approaches become increasingly complex and accurate. Currently, numerical simulation is used on a routine basis in many fields of welding research, such as modelling weld pool and arc phenomena, microstructure development during PWHT, simulating residual stresses and hot cracking susceptibility or predicting hydrogen embrittlement. Recent developments in modelling approaches and computer programmes have opened the way to new and improved welding procedures. Recent approaches to modelling weld pool and arc phenomena as well as metallurgical processes during welding have advanced simultaneously with progress in computer power. The complexity has continuously increased and it is possible now to quantitatively describe the flow of liquid metal in the weld bead, the gas flow and energy input from the arc to the weld bead as well as the microstructural and metallurgical processes during solidification and in the heat affected zone with good accuracy. Figure 4.9 shows two very successful examples of these modelling activities for the flow pattern of the liquid metal in the weld bead and the solid-state material flow in friction stir welding. Considerable progress is evident in the fields of computational weld mechanics. The development of powerful computer codes based on Finite Elements or Finite Differences to solve the partial differential equations describing the thermal, mechanical and/or velocity fields in the welding process has opened the way to a quantitative prediction of component residual stresses. Recent developments also focus on the development of entire process models starting with the weld input parameters and finishing with a quantitative prediction of the weld bead shape and the mechanical properties of the final weld.

Figure 4.9 Modelling weld pool dynamics in arc welding (left) and material flow in friction stir welding (right) (Reproduced courtesy: Institute for Materials Science, Graz University of Technology, T. DebRoy)

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Through Optimum Use and Innovation of Welding and Joining Technologies

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