Issue 45

L.M. Viespoli et alii, Frattura ed Integrità Strutturale, 45 (2018) 121-134; DOI: 10.3221/IGF-ESIS.45.10 133 Figure 7 : Capture at the optical microscope of the crack initiation area. C ONCLUSIONS he aim of the present work was to provide a comparison among different procedures to assess the fatigue life of a welded joint. Of relevance are the Nominal Stress Method and the Hot Spot Stress Method, which nowadays are the widely used in design offices. It has been shown how these two methods can provide a fast estimate of the strength of a joint to withstand a fatigue load spectrum. The Hot Spot Stress Method is especially suitable in “heavy” carpentry, where complex structures are usually modelled through plane SHELL elements. The drawback of the above mentioned methods is that, due to their simplicity, they do not provide detailed information on the stress field in the critic regions of the material, being such aspect demanded to the experimental procedure on which the corresponding endurable SN curves have been evaluated. The Strain Energy Density approach constitutes, instead, a more general tool, depending only on the material properties and may be adopted in a wide variety of cases for a more accurate fatigue life evaluation. Subsequently a series of numerical analyses to compare the results provided by Nominal Stress, Hot Spot Stress and SED approaches has been performed and validated via experimental tests on a sample welded geometry. The specimens, realized with MIG welding, have been fatigue tested as welded and the failures have occurred accordingly to what stated in the literature. On the other hand, an observation of the results permits to point out that: • the SED approach provides more precise results and a more reliable estimate of the fatigue life, compared to the other methods adopted; • this advantage in design comes at the cost of a more detailed FEM modelling with respect to the Nominal and the Structural Hot Spot stress methods while, if compared to a more detailed fracture mechanics based analysis, the mesh insensitivity of the mean SED guarantees a much easier modelling. T