PSI - Issue 25

Romanin Luca et al. / Procedia Structural Integrity 25 (2020) 149–158 Author name / Structural Integrity Procedia 00 (2019) 000–000

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Fig. 1. Main steps of the simplified method

2. Virtual Weld Bead method The main principle is to decouple every joint side and mode of deformation considered: angular deformation, and transverse shrinkage. Angular deformation is obtained by applying a thermal gradient over the thickness while the transverse shrinkage by means of a pre-strain. A virtual region that represents the weld is created, as it can be seen in Fig. 2. In the spirit of simplifying and automatizing the geometry preparation phase, this region has a constant width. A second advantage is that the method is more robust in terms of design changes such as thickness or weld size; the virtual regions width is in fact independent from these variables. While common FE models are made of linear elastic isotropic shell elements, the virtual weld bead region employs an orthotropic behaviour. An orthotropic element allows to control the curvature in both directions in order to have the maximum flexibility on the angular joint deformations. The mechanical properties are isotropic while the thermal expansion coefficient is defined as x =0 and y =10 -6 1/°C (Fig. 3). The element local coordinates are oriented with the X axis longitudinal to the weld and the Y axis in the transversal direction. It is noted that only common type elements have been employed; the method can be thus implemented on a general purpose FE code. The limit is that a reference deformation of each type of welded joint has to be available either from a CWM analysis or from an experimental measurement; anyway, this is a limit common to all simplified methods.

Fig. 2. Virtual Weld Bead regions for a T joint

The equivalent loads are applied on the Virtual Weld Bead regions elements, moreover the method is mesh insensitive. On each side of the joint each ‘load couple’, pre-strain and thermal gradient, is applied on the same region as in Fig. 3. In the case of a T joint 6 parameters have to be calculated, while in the case of a butt joint 4 parameters are needed.