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In the friction stir welding (FSW) technique, the friction stir tool is submitted to a system of forces that influences the main phenomena of the process. However, experimental studies for all the forces in FSW have received little attention. For a better process understanding, an analysis of the individual contribution of each part of the tool on the forces is required. In this paper, the influence of the pin and shoulder on the axial force is separately considered as a function of the rotational, plunging and welding speeds. Three experimental designs were carried out for the tool pin, the tool shoulder and the complete tool. Additionally, the welding and transverse forces are measured during FSW experiments for different combinations of the main process parameters. The results showed an important contribution of the pin to avoid excessive loads during the plunging phase and an interaction between the effects of the tool geometry, and rotational and plunging speeds factors on the maximum axial force.

We compare a family of mixed interpolations on triangles with straight edges as applied to limit analysis. The aim of this paper is to prove theoretically that the approximate collapse factors obtained with these finite elements always comply with certain inequalities that exist among them. Two of these interpolations are used in limit analysis for the first time in this article. The inequalities in the proposition are also demonstrated via numerical applications. To this end, the most frequently used benchmark problems in limit analysis are revisited and discussed with respect to the results computed with these finite elements.