Issue 9

T. Marin et alii, Frattura ed Integrità Strutturale, 9 (2009) 76 - 84; DOI: 10.3221/IGF-ESIS.09.08 83 the transverse section). These stresses are to be intended as located on the upper surface of the plate and at the intersection of the weld elements and plate elements. The graph shows that there is an obvious symmetry due to the geometry, and, above all, that the fine mesh and coarse mesh plots are consistently overlapped with differences substantially negligible almost everywhere. There are some sensible discrepancies only close to the points P as discussed before. It is evident from the graph that the membrane content is dominant as could have been expected since the specimen is loaded in tension. The macro-geometric notch effect caused by the attachment is responsible for the bending component. Peak values are reached at the tip of the “T” (point Y in Fig. 8) and in the middle point of the top leg of the “T” (point Q in Fig. 8) . These are actually the locations of the fatigue failures, the choice between Y and Q being dictated by the local weld quality. Along the sides of the “T”, which are parallel to the load direction, the structural stress is close to zero because only the stress component normal to the weld fillet is considered. Figure 9 : Finite element model using 3D elements and real specimen with the solid block. Analogous plots are obtained for type “H” specimens and for sake of brevity are not reported. The presence of the massive block in type “B” specimens prevents the use of shells so for that case solid 3D elements are employed, Fig. 9. It is important to note that the failure location is always in correspondence with the highest value of the structural stress so these tests confirm the ability of the method to take into account the main features of fatigue failure in a simplified but correct way. The fatigue data for the all the specimen types are inserted into the 2007 ASME Div. 2 Master curve as shown in Fig. 10. All the data, independently of the specimen geometry, fall within the ±2   S-N curves, therefore demonstrating that the predictions using the presented calculation approach are quite accurate. Figure 10 : 2007 ASME Div.2 master S-N curve and experimental results.