Figure 7 Row of elements (in green) simulating the left side plate A;
suppression of the elements of row activation of the symmetric
constraints along x direction B.
Also the mechanical properties46,47 have been
considered temperature dependent (Figure 6C). Moreover, since the
structural analysis involves plastic deformation of the material, in
this work, the hardening material model with von Mises yield criterion
and the isotropic strain hardening rule have been assumed. The stress
vs. strain curves, as a function of the temperature, are shown in Figure
6D.
Moreover, in steels, martensite is formed from austenite containing
carbon atoms and, in view of the diffusionless nature of its formation,
it ideally inherits the carbon atoms of the parent austenite. Therefore,
while for some steel welded parts the solid-state austenite–martensite
transformation during cooling has a significant influence on the
residual stresses and distortion17,33,34,48,49,50,51,
especially when the equivalent carbon content is high, for others (low
equivalent carbon content), it may be neglected as well demonstrated by
Cho et al52 and Deng.53 According to
Cho et al52 and Deng53, the
modelling of the transformation phase does not change the level of
accuracy of the FE model, in terms of residual stresses and distortions
prediction, when the welding process involves low carbon steels with low
equivalent carbon content (about Ceq = 0.23%), as the
steel used in this work. As a result, the solid-state transformation
phase has not been considered in the modelling.
In order to evaluate the influence of the interaction between the
plates, a second mechanical analysis has been carried out without
considering the row of finite elements placed along the left side of the
longitudinal symmetry plane (Figure 7) and by applying only the
translational constraints along the x direction to simulate the
symmetry constraints.
3. Results and discussion
In this section, numerical results of the welding simulation are
presented and compared with experimental ones, in order to assess the
reliability of the used FE models.
3.1 Thermal analysis
The temperatures measured at six points by means of six thermocouples
have been compared with the respective predicted ones.
Figure 8 shows the temperature distributions at the middle section of
the plate along the transverse direction during the two passes, with the
welding arc located at the middle of the welding path. It is possible to
appreciate a good agreement between numerical and experimental results,
with the numerical curves that well estimate the experimental
measurements during both welding passes.