Simplified modelling of fixtures in FE welding simulation

The goal with this master thesis work, is to find a simplified way of modelling the fixture in FE welding simulation. To take the entire fixture into the welding model, is very CPU-time consuming since the contact between the fixture and the work piece is difficult to simulate. The method used today, is based on fixed degree of freedom boundary condition. This method do not include the stiffness of the fixture, the friction and the thermal effects between the fixture and the work piece. In order to get a more accurate modell, these things can not be neglected. The method that is presented in this master thesis report, uses already existent functions in the FEM program MSC.Marc. The main idea is to use non-linear springs and non-linear elastic foundation to model friction and support. Since the contact force between the fixture and the work piece directly affects the friction force, the distribution functions that describes how a known contact force at one point distributed through the whole fixture must be used. This function is constructed in two ways, the first uses the entire model with the fixture, the second uses Buckingham’s pi theorem. The tests that where carried out shows that the distribution functions gives a good results, but there are several problems that must be solved before the methods can be used in welding simulations. The subroutine used in welding simulation do not support the needed “new style table input” which is needed in order to use edge foundation as the friction force. MSC.Marc has problem with interaction between the facefilm and the edge foundation. The problem with the facefilm and the edge foundation is most likly a bug, since this problem do not accure in the new releace of MSC.Marc r3.

Author: Wiippola, Olof

Source: Lulea University of Technology

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