Issue 9

T. Marin et alii, Frattura ed Integrità Strutturale, 9 (2009) 76 - 84; DOI: 10.3221/IGF-ESIS.09.08 79 mesh but regularly spaced and with a low aspect ratio in the rows of elements corresponding to the two weld toes. The second case considered, Fig. 3b, has weld toes characterized by distorted elements having a wide spectrum of shape metrics. Fig. 3c shows the third mesh with a regular and fine discretization. Any experienced finite element analyst would prefer the last one for a local stress investigation but such level of refinement may not be necessary for a fatigue analysis based on the present procedure. The proof comes from Figure 4 where the structural stress (  s ), the membrane (  m ) and bending (  b ) components are plotted along the weld toe lines 1 and 2 indicated in Fig. 3a . The results from the three meshes are drawn with different line styles (refined mesh: continuous lines, distorted mesh: dashed lines, coarse mesh: dash-dot lines) but they are barely distinguishable since they are closely overlapped. The distorted mesh plots have few little jerks in correspondence of some elements but the trends are completely captured and so are the peak values and positions. Even the coarse mesh does not fail in revealing the maximum values. These graphs give also useful information about the relative magnitude of the structural stress components, membrane and bending, so the analyst has a clear picture of the loading mode in each point along the weld toes. In the example discussed here there is a strong predominance of bending stress in most parts of the toe lines. Figure 3 : Curved profile welded to a flat plate: a) shell model using a coarse regular mesh at the toes; b)-c) close views of the fillet for the irregular mesh and the refined regular mesh. Figure 4 : a) Comparison of the structural stress and its membrane and bending components along the weld toes of Fig. 3. FM: fine mesh mesh, CM: coarse mesh, DM: distorted mesh. (a) (b) (c)