Increasing the efficiency of computational welding mechanics by combining solid and shell elements

This paper emphasizes the benefits encountered when solid and shell elements are combined in a single 3-D finite element analysis (FEA) thermomechanical model - simulating a typical problem of computational welding mechanics. In order to clearly obtain the aforementioned benefits, FEA models containing only solid elements are compared with FEA models containing a combination of solids and shells. More specifically, in the current paper the post-weld heat treatment of a typical marine structure is simulated by using four different 3-D finite element analysis models. In the first model (model I), thermoplastic solid elements were used, whereas in the second model (model II), a mix of thermoplastic and thermoelastic solids was employed. In order to investigate whether the combination of solids with shells can substantially increase the computational efficiency, and therefore reduce the duration of the analyses and the model sizes, two more models were set up by combining thermoplastic and thermoelastic solid elements with thermoelastic shells: constant (model III) and varying aspect ratio (model IV). As expected, these four models presented equivalent results as far as the calculation of the thermally induced temperatures, displacements and stresses was concerned however, severe differences in computational efficiency were observed. The aim of this paper is to quantitatively present the benefits encountered from the combination of solids with shells in thermal and thermal stress analyses and to discuss the computational efficiency increase that was observed as a result of this element scheme. Important numerical issues like position of the solid to shell transition area, coupling of solids and shells, and aspect ratio of the elements, which affected the overall efficiency, are also discussed. As a result, increase in computational efficiency was observed when solid elements were combined with shells of varying aspect ratio, the latter modeling the far field area of the weld. This combination proved to be very beneficial in computational welding mechanics and is expected to facilitate the simulation of thermal and thermal stress analyses of large scale welded structures using the finite element method.