PSI - Issue 83

Niccolò Vilotta et al. / Procedia Structural Integrity 83 (2026) 246–255

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3.4. Fracture surfaces properties The non-welded specimen in Figure 10(a) displays a classic ductile fracture characterized by a grey, fibrous, and "torn" macroscopic appearance, typical of the high plasticity of AISI 316L [5,7]. In contrast, the welded specimen Figure 10 (b) exhibits a much flatter and cleaner fracture, suggesting a more brittle failure mode with significantly less plastic deformation [9–11]. While the first sample failed due to the coalescence of micro-voids (dimples) likely initiated by AM-induced porosity, the second sample shows a distinct vertical crack and a sharp separation plane. This suggests that the partial penetration acted as a severe stress riser or a "pre-crack," causing the fracture to trigger prematurely at the weld root. Consequently, the weldment bypassed the material’s natural ductility, leading to a localized brittle-like cleavage or intergranular separation [9–11]. This confirms that the welding process, rather than the AM material properties, became the primary cause of structural failure in the second case.

(a) (b) Figure 10: Macroscopic fracture surfaces of the DMLS-manufactured AISI 316L specimens: (a) non-welded specimen, characterized by a typical ductile fracture appearance; (b) welded specimen, showing a flatter fracture surface and a more localized failure morphology.

Conclusions The present study assessed the mechanical response of DMLS-manufactured AISI 316L in both non-welded and welded conditions by combining global tensile testing with local hardness-based analysis, thermographic monitoring, and post fracture observations. The results demonstrate that welding markedly alters the mechanical behaviour of the material, reducing the overall tensile performance and introducing clear spatial gradients across the joint. In particular, hardness and strength were found to decrease progressively from the base material to the heat-affected zone and weld metal, indicating that the welded region represents the mechanically weakest part of the system. For the non-welded material, the constitutive reconstruction based on hardness data provided a satisfactory approximation of the tensile behaviour, confirming the effectiveness of this approach for a comparatively homogeneous DMLS microstructure. By contrast, the weaker agreement observed for the welded configuration highlights the intrinsic limitations of local hardness-based estimations when they are used to represent the global response of a mechanically heterogeneous joint. Thermographic measurements and fracture observations further support this interpretation, showing localized dissipation and failure in the welded specimens, as opposed to the more uniformly ductile response of the non-welded material. Overall, the findings confirm that the mechanical integrity of welded DMLS AISI 316L is governed by the interaction between the additively manufactured base material and the local modifications introduced by welding. In addition, the developed procedure, from non-disruptive local hardness measurements, can effectively predict the mechanical strength of AM specimens. References [1] DebRoy, T., Wei, H.L., Zuback, J.S., Mukherjee, T., Elmer, J.W., Milewski, J.O., Beese, A.M., Wilson-Heid, A., De, A., Zhang, W. Additive manufacturing of metallic components – Process, structure and properties. Progress in Materials Science 92 (2018) 112–224. https://doi.org/10.1016/j.pmatsci.2017.10.001. [2] Herzog, D., Seyda, V., Wycisk, E., Emmelmann, C. Additive manufacturing of metals. Acta Materialia 117 (2016) 371–392. https://doi.org/10.1016/j.actamat.2016.07.019.