PSI - Issue 57

6

Alberto Visentin et al. / Procedia Structural Integrity 57 (2024) 810–816 Alberto Visentin et al./ Structural Integrity Procedia 00 (2023) 000 – 000

815

3000

3000

(a)

(b)

Δσ A,50% = 214 MPa N A = 2 ∙ 10 6 cycles ScatterIndex (2.3% - 97.7%): T σ = 296/156 = 1.90 Slope k = 3.0

Δσ A,50% = 354 MPa N A = 2 ∙ 10 6 cycles ScatterIndex (2.3% - 97.7%): T σ = 488/257 = 1.90 Slope k = 5.0

PSM design scatter band for steel joints ( λ > 0)

PSM design scatter band for steel joints ( λ = 0)

1000

1000

488 354 257

Δσ eq,peak (MPa)

Δσ eq,peak (MPa)

Weld toe failures

296 214 156

T, AW, Λ = ∞, R τ = 0.1 B+T, AW, Λ = 1, R σ = 0.1, R τ = 0.1, φ = 0 ° B+T, AW, Λ = 1, R σ = 0.1, R τ = 0.1, φ = 90 ° B+T, AW, Λ = 1/√3, R σ = 0.1, R τ = 0.1, φ = 0 ° B+T, AW, Λ = 1/√3, R σ = 0.1, R τ = 0.1, φ = 90 °

Weld toe failures

B, AW, Λ = 0, R σ = 0.1

100

100

N A

1.00E+04

1.00E+05

1.00E+06

1.00E+07

1.00E+04

1.00E+05

1.00E+06

1.00E+07

N A

Number of cycles to break-through, N bt

Number of cycles to break-through, N bt

Figure 6 . Fatigue assessment of tube-to-flange welded joints with reinforcement ribs according to the PSM. (a) Comparison between the PSM based fatigue design scatter band ( λ = 0) and the experimental fatigue data evaluated in terms of the equivalent peak stress. (b) Comparison between the PSM-based fatigue design scatter band ( λ > 0) and the experimental fatigue data evaluated in terms of the equivalent peak stress. The design scatter bands were calibrated in Refs. (Meneghetti and Lazzarin 2011 ; Meneghetti 2013 ), respectively, and are not fitted on the experimental data shown in the figure. 4. Conclusions In this work, the fatigue strength of tube-to- flange S355 steel arc -welded joints with reinforcement ribs under constant amplitude multiaxial loading has been investigated. A test rig has been designed to fatigue test the specimens under pure bending, pure torsion as well as combined bending and torsion constant amplitude loadings. All tested specimens exhibited crack initiation and propagation at the weld toe between the tube and the reinforcement ribs. The developed PSM tool has been adopted to automatically assess the fatigue strength of the welded details according to the PSM. The PSM correctly identified the fatigue crack initiation point, i.e. the weld toe between the tube and the reinforcement ribs, in all considered load cases. Moreover, a good agreement has been obtained between the experimental fatigue data, evaluated in terms of the equivalent peak stress, and the proposed PSM-based fatigue design scatter bands for steel joints. Additional constant amplitude as well as variable amplitude pure bending, pure torsion and combined bending and torsion fatigue tests are currently planned. Eventually, fatigue cracks initiation and propagation in broken specimens will be the subject of more detailed future investigation. Amstutz H, Storzel K, Seeger T (2001) Fatigue crack growth of a welded tube-flange connection under bending and torsional loading. Fatigue Fract Eng Mater Struct 24:357 – 368. https://doi.org/10.1046/j.1460-2695.2001.00408.x Campagnolo A, Roveda I, Meneghetti G (2019) The Peak Stress Method combined with 3D finite element models to assess the fatigue strength of complex welded structures. Procedia Struct Integr 19:617 – 626. https://doi.org/10.1016/j.prostr.2019.12.067 Campagnolo A, Vecchiato L, Meneghetti G (2022) Multiaxial variable amplitude fatigue strength assessment of steel welded join ts using the peak stress method. Int J Fatigue 163:107089. https://doi.org/10.1016/j.ijfatigue.2022.107089 Frendo F, Bertini L (2015) Fatigue resistance of pipe-to-plate welded joint under in-phase and out-of-phase combined bending and torsion. Int J Fatigue 79:46 – 53. https://doi.org/10.1016/j.ijfatigue.2015.04.020 Lazzarin P, Livieri P, Berto F, Zappalorto M (2008) Local strain energy density and fatigue strength of welded joints under u niaxial and multiaxial loading. Eng Fract Mech 75:1875 – 1889. https://doi.org/10.1016/j.engfracmech.2006.10.019 Lazzarin P, Sonsino CM, Zambardi R (2004) A notch stress intensity approach to assess the multiaxial fatigue strength of welded tube-to-flange joints subjected to combined loadings. Fatigue Fract Eng Mater Struct 27:127 – 140. https://doi.org/10.1111/j.1460-2695.2004.00733.x Lazzarin P, Zambardi R (2001) A finite-volume-energy based approach to predict the static and fatigue behavior of components with sharp V shaped notches. Int J Fract 112:275 – 298. https://doi.org/10.1023/A:1013595930617 Livieri P, Lazzarin P (2005) Fatigue strength of steel and aluminium welded joints based on generalised stress intensity factors and local strain energy values. Int J Fract 133:247 – 276. https://doi.org/10.1007/s10704-005-4043-3 Meneghetti G (2012) The use of peak stresses for fatigue strength assessments of welded lap joints and cover plates with toe and root failures. Eng Fract Mech 89:40 – 51. https://doi.org/10.1016/j.engfracmech.2012.04.007 Meneghetti G (2013) The peak stress method for fatigue strength assessment of tube-to-flange welded joints under torsion loading. Weld World 57:265 – 275. https://doi.org/10.1007/s40194-013-0022-x References