PSI - Issue 75

Alberto Campagnolo et al. / Procedia Structural Integrity 75 (2025) 564–571 Alberto Campagnolo, Giovanni Meneghetti/ Structural Integrity Procedia (2025)

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where E is the Young’s modulus and ν denotes the Poisson’s ratio . It is worth mentioning that the available experimental fatigue data on HFMI treated joints from the technical literature indicate that the advantages of HFMI treatment are primarily attributed to the introduction of compressive residual stresses and localized material hardening, rather than a significant increase in the weld toe radius. Based on this, a direct implementation of the Peak Stress Method (PSM) has been recommended in (Campagnolo et al. 2022): the FE model should reflect the original as-welded configuration, characterized by a sharp V-notch with a zero radius (ρ = 0) at the weld toe, instead of modeling the HFMI- treated geometry with a finite radius (ρ > 0). The equivalent peak stress is derived directly from the opening peak stress calculated at the weld toe, the reader being referred to (Meneghetti and Campagnolo 2020) for more details about the required mesh patterns and the equations to be used. Then, the design curves specifically developed for HFMI-treated joints must be applied for the fatigue assessment. This procedure notably reduces the complexity and computational effort of the FE analysis by taking full advantage of the simplicity of the PSM applied to sharp V-notches. 3. Experimental data taken from the literature: geometry of the welded joints and FE stress analysis Experimental fatigue data used in the present study were taken from the literature and were generated by testing full-penetration longitudinal stiffeners (see Fig. 2 and Table 1), made of high-strength steel and subjected to uniaxial loading, as reported in (Yonezawa et al. 2020).

FE type: Tetra-10 (SOLID 187)

y

1/8 joint geometry

t = 12 mm

u x = 0 (y-z plane)

x

z

t = 12 mm

Fatigue crack initiation at the weld toe of the main plate

100

u z = 0 (x-y plane)

d global = 2 mm

700

u y = 0 (x-z plane)

y

110

y

x

z

Δσ

80

z

x

R 0 /2 = 0.14 mm

d = 0.05 mm

2α

ρ HFMI

α

∆W̅ FEM

z

depth

R 0 = 0.28 mm

Fig. 2: Geometry and FE analysis for fatigue assessment of longitudinal stiffeners according to the PSM for HFMI treated joints (Eq. (2)).

In that work (Yonezawa et al. 2020), Yonezawa et al. investigated welded joints made of three high-strength steels commonly employed in bridge construction — namely SBHS400, SBHS500, and SBHS700. For brevity, only the experimental dataset corresponding to SBHS500 steel has been selected for analysis herein. The HFMI treatment in (Yonezawa et al. 2020) was applied using the Applied Ultrasonics Esonix® 27 UIS device, operating at a frequency of 27 kHz. The treatment employed indenters with a tip radius of 3 mm and was performed until a groove depth of approximately 0.3 mm was reached at the weld toe. The nominal load ratio R applied during the axial