Figure 14 Comparison of the experimental distortions with those predicted by the FE models considering and not the plates interaction: A, along the path at y = 248 mm and z = 0 mm and B, along the path at x = 125 mm and z = 0 mm.
As aforementioned, in order to appreciate the effects provided by the modelling of the plates interaction during the welding process, the predicted residual stresses and distortions have been compared with those provided by the simulation performed by deactivating the plates interaction (Figures 13 and 14).
According to Figure 13A, as expected, it can be noticed that the longitudinal residual stresses distribution seems to be unaffected by the plates interaction. As matter of the fact, plates have not been constrained along the longitudinal direction. Contrary, the plates interaction affects the transversal residual stresses distributions, because of the plates rotation during the welding process. Residual stresses appear to be slightly higher (Figure 13B) for the model that does not consider the plates interaction and they are expected to increase for longer plates, because of their rotation.
If the effects of the plates interaction on residual stresses distribution may be considered negligible for the selected test case, a similar consideration cannot be done in terms of distortions distribution. According to Figure 14, the predicted distortions distribution appears to be sensibly higher and far from the experimental data for the FE model that does not consider the plates interaction. As a result, the plates interaction plays a key-role in the modelling of the welding process induced distortion.
5. conclusions
This paper presents a novel numerical model, based on the Finite Element method, for the simulation of a welding process aimed to make a two-passes V-groove butt weld joint. In order to evaluate the residual stresses, a 3D non-linear thermo-mechanical analysis has been carried out. The thermo-mechanical response of the joint has been simulated by using an uncoupled approach. Specifically, the “element birth and death” technique has been used to simulate the welding filler during the welding process. The originality of the proposed technique has to be found in the simulation of the interaction occurring between the two plates during the welding process, never considered in literature when the problem is faced through a symmetrical approach. As a result, it was possible to predict more accurately the residual stresses affecting the joint, caused by the thermal distortions which lead the plates to rotate. The proposed modelling technique appears to be fundamental for long plates, since the plates interaction becomes not negligible as the plate length increases. Specifically, in order to save the computational costs, only a plate and half seam have been modelled. As a result, in order to simulate the plates interaction, a row of finite elements has been placed along the left side of the longitudinal symmetry plane. This approach allows predicting the residual stresses also for long joined plates, which require a higher number of nodes and elements and, consequently, a higher time analysis. A surface to surface contact algorithm has been considered between the half seam and the finite elements row.
Moreover, differently from the literature, the heat amount is supplied to the finite elements as a volumetric generation of the internal energy, allowing overcoming the time-consuming calibration phase required by the Goldak’s model, commonly adopted in literature.
The reliability of the FE model has been shown by assessing the predicted results, in terms of temperatures distribution and joint distortion, against the results provided by an experimental test. Temperatures distribution has been measured during the welding process by using six thermocouples placed at different locations nearby the weld bead; welding distortions were measured by means of a Coordinate Measuring Machine. A good agreement has been found between numerical and experimental results, showing the effectiveness of the proposed FE modelling technique.
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