PSI - Issue 79

Santi Marchetta et al. / Procedia Structural Integrity 79 (2026) 224–232

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NSIF Notch Stress Intensity Factor R Load ratio R 0,I Mode I SED control radius S 0 SED circular sector SED Strain Energy Density t Horizontal plate thickness V S0 Control volume extension W Local Strain Energy Density ̅ W C Critical Strain Energy Density 2α Weld toe opening angle Δ 1 MODE I NSIF fatigue strength Δ σ hs

Cyclic average Strain Energy Density

Hotspot stress value associated to a cyclic load

Williams' eigenvalue for MODE I

λ I

σ hs Hotspot stress value σ hs,maxload Hotspot stress value associated to the maximum load σ hs,minload Hotspot stress value associated to the minimum load

2. Materials and Methods This section provides a brief overview of the investigated approaches and describes the methodology adopted for their validation. Furthermore, the testing configuration and the experimental data drawn from the literature for the steel and titanium T-joints are presented. 2.1. Hotspot stress approach This approach involves extracting the surface stress values at reference points, located at specific distances from the weld toe, and then obtaining the critical stress σ hs at the “hot spot” (i.e. the weld toe) by applying either a linear or a quadratic regression to the extrapolated data and determining the intersection with the “y - axis” of the obtained “Stress vs Distance from the weld toe” curve. The number and the exact location of the reference points depend on the type of stress – Type A (weld toe on plate surface) or Type B (weld toe at plate edge) (Hobbacher, (2016)) – and, in the case of finite element analysis, on the mesh sizing and quality. For this specific study, crack propagation occurs at the weld toe on plate surface, as confirmed by experimental evidence. Therefore, given the fine mesh adopted, the calculation scheme is the one presented in Fig. 1.

Fig. 1. Type a hotspot stress calculation scheme (fine mesh).