Issue 47

P. Foti et alii, Frattura ed Integrità Strutturale, 47 (2019) 104-125; DOI: 10.3221/IGF-ESIS.47.09

Figure 5 : Fatigue strength of steel welded joints as a function of the averaged local strain energy density.

To evaluate the fatigue strength through the SED method, it is enough to calculate the mean-SED at the weld toe or root for a remote tensile load 1   through a static FE simulation. By means of Eqn. (25), valid only under the hypothesis of linear elastic behaviour, it is possible to evaluate the remote tensile load L   that represents the fatigue limit of the component:

1 2

 

    

W

L

    

(25)

L

i

W

i

Being L W  the critical value of the mean SED that corresponds to the fatigue limit. As regard steel welded joints, according to above, this value is 3 0.058 / Nmm mm with a probability of survival of 97.7% S P  .

F E MODELLING

n order to perform easily the wide amount of simulations that were needed, a parametric 3-D model of each detail was built. To obtain more efficient analyses and minimise the computational time, the symmetries of the details considered were exploited, using the appropriate symmetry conditions in the FE modelling; thus, only a quarter of the geometry was modelled. A simplified shape was considered for the joint. This was modelled as a sharp, zero radius, V-shaped notch with an opening angle equal to 135° and considered as an ideal linear elastic continuum. The geometries of the welded joints analysed are shown in Fig 6 while their geometrical parameters values for the reference cases (k=1) are reported in Tab. 3. To evaluate the critical point of the joint, the mean SED curve was acquired along the weld toe. The critical point represents the maximum of this curve. According to the SED approach, to evaluate the mean SED value, a control volume was built along the welding bead centred in the weld toe with a radius of 0 0.28 R mm  determined through Eqn. (24) by using data taken from the literature [49]. I

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