PSI - Issue 5

Rui F. Martins et al. / Procedia Structural Integrity 5 (2017) 633–639 Diogo F. Almeida et al. / StructuralIntegrity Procedia 00 (2017) 000 – 000

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4. Presentation of results and its discussion

Through a macrograph of the welded sample (Fig. 6), it was possible to compare the size of the weld pool with the results obtained through the numerical simulations. It was noticed that the depth of the weld puddle obtained numerically was very close to the real weld sample, only presenting an error of 2.7 % for the 1 st weld pass and 2.6% for the 2 nd weld pass.

Fig. 6. Numerical vs. experimental results - 1st weld pass (linear dimensions are in millimetres, with temperature ‘ scale in ºK).

In addition, in Figure 7a, it is shown the evolution of heat source position with time (50, 100, 200, 350 seconds), while in figure 7b is presented the values of the maximum and minimum principal stresses computed. As can be seen, the tensile stresses were calculated in the weld bead area, in a region where the plate was not constrained, with values varying between 0 MPa and 336 MPa. Additionally, the very low compressive stresses determined in the numerical simu lations (Fig. 7b) were calculated at the outer fixed nodes of the plates that simulated the “weld spots” introduced before welding, in order to minimise distortion (Fig. 1). In fact, it is frequent to clamp or to restrain components to be welded in order to prevent distortion; however, this restraint results in higher residual stresses due to numerical singularities, which, in the case herein studied, were localised near the seven fixed boundary nodes defined and far away the region where maximum residual stresses were measured. As previously stated, the experimental residual stress results obtained through the hole-drilling method, showed a maximum principal stress of 418 MPa (Table 1). Comparing this result with the maximum principal residual stress calculated (336 MPa), which occurred almost at the same location where the experimental residual stresses were measured, there is a deviation of 19.6 % for the maximum principal stress. In addition, numerical results showed a minimum principal stress of -185 MPa at the location where experimental residual stresses were measured. Comparing this value with those obtained by the hole-drilling method (approximately -205 MPa, Table 1), the numerical values exhibited a deviation of 9.8 %.

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Fig. 7. (a) Heat source position with time, at 50, 100, 200 and 350 seconds; (b) Maximum principal residual stress distribution after 2 nd weld pass was carried out (units are in Pascal).

5. Conclusions