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End date: 2022 × End date: 2022 × Start date: 2022 × DDC: 600 × Subject: Additive manufacturing ×

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Now showing 1 - 4 of 4
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    In situ detection of cracks during laser powder bed fusion using acoustic emission monitoring
    (Amsterdam : Elsevier, 2022) Seleznev, Mikhail; Gustmann, Tobias; Friebel, Judith Miriam; Peuker, Urs Alexander; Kühn, Uta; Hufenbach, Julia Kristin; Biermann, Horst; Weidner, Anja
    Despite rapid development of laser powder bed fusion (L-PBF) and its monitoring techniques, there is still a lack of in situ crack detection methods, among which acoustic emission (AE) is one of the most sensitive. To elaborate on this topic, in situ AE monitoring was applied to L-PBF manufacturing of a high-strength Al92Mn6Ce2 (at. %) alloy and combined with subsequent X-ray computed tomography. By using a structure borne high-frequency sensor, even a simple threshold-based monitoring was able to detect AE activity associated with cracking, which occurred not only during L-PBF itself, but also after the build job was completed, i.e. in the cooling phase. AE data analysis revealed that crack-related signals can easily be separated from the background noise (e.g. inert gas circulation pump) through their specific shape of a waveform, as well as their energy, skewness and kurtosis. Thus, AE was verified to be a promising method for L-PBF monitoring, enabling to detect formation of cracks regardless of their spatial and temporal occurrence.
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    Temperature-dependent dynamic compressive properties and failure mechanisms of the additively manufactured CoCrFeMnNi high entropy alloy
    (Oxford : Elsevier Science, 2022) Chen, Hongyu; Liu, Yang; Wang, Yonggang; Li, Zhiguo; Wang, Di; Kosiba, Konrad
    CoCrFeMnNi high entropy alloy (HEA) parts were fabricated by laser powder bed fusion (LPBF), and their dynamic compressive properties at different temperatures as well as the resulting microstructures were analyzed. The HEAs showed an unprecedented strength-ductility combination, especially at a cryogenic temperature of 77 K and a high strain rate of 3000 s−1. Under this testing condition, the yield strength (YS) of the HEAs amounted to 665 MPa. Regardless of the testing temperature, the deformation mechanism of all investigated HEAs was dominated by a synergistic effect consisting of deformation twinning and dislocation pile-up around twins. The fraction of twin boundaries and dislocation density within the deformed microstructure of the HEA correlated with the test temperature. At 77 K, the formation of nanotwins together with dislocation slip prevailed and contributed to pronounced twin-twin and twin-dislocation interactions which effectively restricted the dislocation movement and, hence, contributed to a higher YS as well as strain hardening rate in comparison to that of the HEAs at room temperature of 298 K. The LPBF-fabricated HEAs showed unpronounced thermal softening even at a high testing temperature of 1073 K. Continuous dynamic recrystallization was restricted in the HEA because of its inherent sluggish dislocation kinetics and low stacking fault energy.
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    Additively manufactured AlSi10Mg lattices – Potential and limits of modelling as-designed structures
    (Amsterdam [u.a.] : Elsevier Science, 2022) Gebhardt, Ulrike; Gustmann, Tobias; Giebeler, Lars; Hirsch, Franz; Hufenbach, Julia Kristin; Kästner, Markus
    Additive manufacturing overcomes the restrictions of classical manufacturing methods and enables the production of near-net-shaped, complex geometries. In that context, lattice structures are of high interest due to their superior weight reduction potential. AlSi10Mg is a well-known alloy for additive manufacturing and well suited for such applications due to its high strength to material density ratio. It has been selected in this study for producing bulk material and complex geometries of a strut-based lattice type (rhombic dodecahedron). A detailed characterisation of as-built and heat-treated specimens has been conducted including microstructural analyses, identification of imperfections and rigorous mechanical testing under different load conditions. An isotropic elastic–plastic material model is deduced on the basis of tension test results of bulk material test specimens. Performed experiments under compression, shear, torsion and tension load are compared to their virtual equivalents. With the help of numerical modelling, the overall structural behaviour was simulated using the detailed lattice geometry and was successfully predicted by the presented numerical models. The discussion of the limits of this approach aims to evaluate the potential of the numerical assessment in the modelling of the properties for novel lightweight structures.
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    Structure-property relationships of imperfect additively manufactured lattices based on triply periodic minimal surfaces
    (Amsterdam [u.a.] : Elsevier Science, 2022) Günther, Fabian; Hirsch, Franz; Pilz, Stefan; Wagner, Markus; Gebert, Annett; Kästner, Markus; Zimmermann, Martina
    Lattices based on triply periodic minimal surfaces (TPMS) have recently attracted increasing interest, but their additive manufacturing (AM) is fraught with imperfections that compromise their structural integrity. Initial research has addressed the influence of process-induced imperfections in lattices, but so far numerical work for TPMS lattices is insufficient. Therefore, in the present study, the structure–property relationships of TPMS lattices, including their imperfections, are investigated experimentally and numerically. The main focus is on a biomimetic Schoen I-WP network lattice made of laser powder bed fusion (LPBF) processed Ti-42Nb designed for bone tissue engineering (BTE). The lattice is scanned by computed tomography (CT) and its as-built morphology is examined before a modeling procedure for artificial reconstruction is developed. The structure–property relationships are analyzed by experimental and numerical compression tests. An anisotropic elastoplastic material model is parameterized for finite element analyses (FEA). The numerical results indicates that the reconstruction of the as-built morphology decisively improves the prediction accuracy compared to the ideal design. This work highlights the central importance of process-related imperfections for the structure–property relationships of TPMS lattices and proposes a modeling procedure to capture their implications.