PSI - Issue 66

Vladimír Chmelko et al. / Procedia Structural Integrity 66 (2024) 426–432 Vladimír Chmelko at al ./ Structural Integrity Procedia 00 (2025) 000–000

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From the experimental results, it is possible to identify specificities in the cyclic properties of additively manufactured metals in agreement with the results of other authors. 3.1. Anisotropy of cyclic properties Additive manufacturing technology largely eliminates an important property of metallic materials, which is the anisotropy of their mechanical properties. While in the strength properties obtained by tensile testing, the anisotropy due to additive manufacturing is in most cases of little significance [7, 8], on the contrary, the cyclic properties are mostly significantly affected by additive manufacturing [9-11]. The difference of the S-N curves for horizontal and vertical deposition of the layers is documented by the plots in Fig. 2. AlSi10Mg MS1

Fig. 2. Significant (AlSi10Mg) and less significant (MS1) influence of the direction of layer addition on the S-N curve in alternating tension.

In the current state of development of additive technologies, it is not possible to predict the direction of material addition in the most stressed cross-section in variable stress amplitude operation. Thus, the curve with the lowest values of allowable amplitudes is determining for fatigue strength assessment. These values are significantly lower compared to conventionally manufactured components. 3.2. Internal defects Internal defects are present in the microstructure of conventionally manufactured materials mostly in the form of inclusions and impurities. Bubbles and pores are also present in welded joints. Additive technology causes defects of missing grains (lack of fusion) or sintered grains. In terms of fatigue properties, these are defects from which fatigue cracks can propagate. Their shape is important (Fig. 3), which determines the stress-strain relations in the region of the defect in correlation with the direction of the external load. Sharp defects oriented in the planes of maximum shear stresses are potential fatigue crack initiation locations.