Issue 78

G. Palomba et alii, Fracture and Structural Integrity, 78 (2026) 233-247; DOI: 10.3221/IGF-ESIS.78.14

higher stiffness and limited local deformation compared to adjacent zones. The peaks in strain intensity on both sides of the welded region are symptomatic of the interface with the heat-affected zone (HAZ), which exhibits elevated strain levels, consistent with their transitional hardness and lower yield strength. The stiffer response and earlier strain localization observed experimentally are reflected in the numerical results with a high degree of correspondence, indicating that the employed hardness-to-property conversion methodology captures the essential mechanical gradients. The agreement between DIC and numerical results was quantified using RMSE, which results equal to 0.34%, and the mean absolute error which equals 0.28%.

[mm/mm] Figure 12: Strain contour plot.

Figure 13: Comparison between strain: experimental (DIC) and numerical results. The plot in the figure focuses on the comparison of ε yy trend in the welded region. Below the profile, a color contour map extracted from the DIC output visually confirms the strain concentration behavior. The weld centre appears in a cooler color range (blue/green), corresponding to lower strain values, while the BM areas show warmer tones, indicating higher extensibility. An arrow highlights the region of interest, linking the strain profile to its spatial location in the specimen. The depth and width of the strain path obtained experimentally and with numerical model correspond well with the weld bead geometry and hardness gradient, reinforcing the interpretation that strain concentrates near the WM–HAZ interface due to the abrupt change in mechanical properties. The zones identified in the plot mark the interface between the harder WM and more ductile BM and and may therefore be more susceptible to strain localization. The pronounced strain gradients observed at these interfaces suggest that local mechanical mismatches may influence the distribution of deformation. While the implications for damage evolution and failure initiation require further investigation, the present results indicate that these interfaces warrant particular attention in the assessment of local mechanical behavior. Overall, this figure validates the numerical assumption of heterogeneity in material behavior and reinforces the need for local property assignment in finite element modelling of welded joints. The presence of these transition zones may provide

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