PSI - Issue 58

Mirjana Opačić et al. / Procedia Structural Integrity 58 (2024) 87 – 94 M. Opa č i ć et al. / Structural Integrity Procedia 00 (2019) 000–000

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crack whatsoever. Furthermore, it is impossible to tell which part of the welded joint contained the crack, based on the image shown in Fig. 7. One possible explanation was that the crack itself was too constrained, due to being located in the immediate vicinity of one of the boundary conditions. Hence, it was later decided to create another simulation, wherein this boundary condition will be removed (since this would represent a more realistic case).

Fig. 7. Stress distribution along the location of the crack in the welded metal.

For the new model, the geometry, crack location and dimensions, as well as the internal pressure load were all adopted in the same way as in the case of the initial models. In addition to removing the bottom fixed boundary condition, the finite element mesh was further refined in the area around the welded joint, to improve the accuracy of the model, since in this case it was expected that the resulting stresses will be greater compared to the original models, thus the deformation will also increase, which can require smaller elements to avoid excessive distortion. In addition, smaller elements provide better stress distribution at the crack tip(s), which was an issue that was not present in the original FE mesh. New finite element mesh is shown in Fig. 8.

Fig. 8. New finite element mesh in the vicinity of the internal crack.

Stress distribution in the new model can be seen in Fig. 9. This time, there was a noticeable difference in stress values around the crack and the rest of the welded joint, which was also expected in the first case. Maximum stresses were observed in the crack tips, with a magnitude of 526.7 MPa, which is almost twice as high as the values from the initial simulations. Another important observation can be made about the crack itself - in this case it actually deformed, in the transversal direction (which can be seen in the figure). It should be noted that, however, there was no crack growth in the longitudinal direction.