Issue 9

T. Marin et alii, Frattura ed Integrità Strutturale, 9 (2009) 76 - 84; DOI: 10.3221/IGF-ESIS.09.08

The specimens consisted of plates (thickness t =8 or 10mm, width w =50mm, length L ranging from 250 to 300mm) with attachments on the top surface. The attachments were H-shaped, T-shaped and a solid cubic block (“H”, “T”, “B” types in the following). The specimen types “H” and “T” had 5 mm thick attachments that were centered and aligned with the longitudinal direction, while the solid block (37x37x30mm) was not symmetrically positioned on the top of the plate. The material was a typical structural steel Fe510. The failure criterion adopted was the complete propagation of the fatigue cracks through the plate thickness, so the tests were continued until final fracture had occurred and the total number of cycles could be determined. A detailed presentation of the computed structural stress is provided for type “T” specimen. Fig. 7 shows two finite element models constructed using shell elements. Because of the particular geometry, the T-shaped attachment is completely wrapped by the inclined elements forming the fillet. The simplified toe line in Fig. 7b is continuous and smooth except in two points where there is an abrupt change in direction and a 90° angle. At these points (marked with a P in the figure) some disturbance in the structural stress distribution has to be expected.

Figure 7 : a) Specimen with the T-shaped attachment; b)-c) shell models with different mesh size. The V.Mises stress is normalized by the nominal tensile stress.

Figure 8 : Structural stress and its components along the fillet weld of type “T” specimen. CM: coarse mesh, FM: fine mesh.

The results of the post-processed simulations are illustrated in Fig.8 for two mesh sizes. The graph has in the x-axis the position of the nodes on the toe line with respect to a curvilinear abscissa with origin on the tip of the “T” and running along the whole fillet. The continuous lines refer to the coarse mesh while the dashed lines correspond to the fine mesh. The structural stress values are normalized by the nominal stress in the section (  nom = F/A , F : applied force, A : area of

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