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Autor

  • Bruno, Giovanni (165)
  • Mishurova, Tatiana (38)
  • Müller, Bernd R. (33)
  • Kupsch, Andreas (27)
  • Cabeza, Sandra (17)
  • Lange, Axel (17)
  • Evsevleev, Sergei (13)
  • Hentschel, Manfred P. (13)
  • Léonard, Fabien (13)
  • Requena, G. (13)
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Erscheinungsjahr

  • 2021 (1)
  • 2020 (31)
  • 2019 (22)
  • 2018 (31)
  • 2017 (26)
  • 2016 (20)
  • 2015 (10)
  • 2014 (17)
  • 2013 (7)

Dokumenttyp

  • Zeitschriftenartikel (84)
  • Vortrag (48)
  • Beitrag zu einem Tagungsband (25)
  • Posterpräsentation (8)

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  • Englisch (137)
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Referierte Publikation

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  • ja (78)

Schlagworte

  • Additive manufacturing (25)
  • X-ray refraction (24)
  • Residual stress (22)
  • Computed tomography (20)
  • Neutron diffraction (16)
  • Additive Manufacturing (12)
  • Neutron Diffraction (9)
  • Porosity (9)
  • Selective laser melting (9)
  • Composites (8)
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Organisationseinheit der BAM

  • 8 Zerstörungsfreie Prüfung (140)
  • 8.5 Mikro-ZfP (138)
  • 5 Werkstofftechnik (20)
  • 9 Komponentensicherheit (20)
  • 9.4 Integrität von Schweißverbindungen (17)
  • 5.0 Abteilungsleitung und andere (9)
  • 5.1 Materialographie, Fraktographie und Alterung technischer Werkstoffe (6)
  • 5.2 Experimentelle und modellbasierte Werkstoffmechanik (5)
  • 7 Bauwerkssicherheit (5)
  • 9.3 Schweißtechnische Fertigungsverfahren (5)
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The correlation between porosity characteristics and the crystallographic texture in extruded stabilized aluminium titanate for diesel particulate filter applications (2020)
Chen, Cong ; Müller, Bernd R. ; Prinz, Carsten ; Stroh, Julia ; Feldmann, Ines ; Bruno, Giovanni
Porous ceramic diesel particulate filters (DPFs) are extruded products that possess macroscopic anisotropic mechanical and thermal properties. This anisotropy is caused by both morphological features (mostly the orientation of porosity) and crystallographic texture. We systematically studied those two aspects in two aluminum titanate ceramic materials of different porosity using mercury porosimetry, gas adsorption, electron microscopy, X-ray diffraction, and X-ray refraction radiography. We found that a lower porosity content implies a larger isotropy of both the crystal texture and the porosity orientation. We also found that, analogous to cordierite, crystallites do align with their axis of negative thermal expansion along the extrusion direction. However, unlike what found for cordierite, the aluminium titanate crystallite form is such that a more pronounced (0 0 2) texture along the extrusion direction implies porosity aligned perpendicular to it.
Analysis of the Combined Strengthening Effect of Solute Atoms and Precipitates on Creep of Aluminum Alloys (2020)
Fernández, R. ; Bokuchava, G. ; Toda-Caraballo, I. ; Bruno, Giovanni ; Turchenko, V. ; Gorshkova, Y. ; González-Doncel, G.
The creep strengthening mechanisms in (age-hardenable) aluminum alloys are analyzed on the basis of a new microstructural study of powder samples, an analysis of a comprehensive revision of creep data from the literature, and a new modeling approach. A strategy based on the strength difference (SD) method to separate the contributions of solid solution atoms and precipitates to creep strengthening is proposed. The new methodology considers the combination of the two contributions avoiding the need of a threshold stress term in the creep equation. The contribution of both precipitates and solid solution is taken into account by means of the analysis of the lattice parameter variation with aging time. For this study, powders of two commercial AA2xxx alloys have been analyzed using diffraction methods. The experimental results are modeled using Lubarda's approach combined with the SD method.
Fully experiment-based evaluation of few digital volume correlation techniques (2019)
Powierza, Bartosz ; Gollwitzer, C. ; Wolgast, D. ; Staude, A. ; Bruno, Giovanni
Digital Volume Correlation (DVC) is a powerful set of techniques used to compute the local shifts of 3D images obtained, for instance, in tomographic experiments. It is utilized to analyze the geometric changes of the investigated object as well as to correct the corresponding image misalignments for further analysis. It can therefore be used to evaluate the local density changes of the same regions of the inspected specimens, which might be shifted between measurements. In recent years, various approaches and corresponding pieces of software were introduced. Accuracies for the computed shift vectors of up to about 1‰of a single voxel size have been reported. These results, however, were based either on synthetic datasets or on an unrealistic setup. In this work, we propose two simple methods to evaluate the accuracy of DVC-techniques using more realistic input data and apply them to several DVC programs. We test these methods on three materials (tuff, sandstone, and concrete) that show different contrast and structural features.
Advanced Deep Learning-Based 3D Microstructural Characterization of Multiphase Metal Matrix Composites (2020)
Evsevleev, Sergei ; Paciornik, S. ; Bruno, Giovanni
The quantitative analysis of microstructural features is a key to understanding the micromechanical behavior of metal matrix composites (MMCs), which is a premise for their use in practice. Herein, a 3D microstructural characterization of a five-phase MMC is performed by synchrotron X-ray computed tomography (SXCT). A workflow for advanced deep learning-based segmentation of all individual phases in SXCT data is shown using a fully convolutional neural network with U-net architecture. High segmentation accuracy is achieved with a small amount of training data. This enables extracting unprecedently precise microstructural parameters (e.g., volume fractions and particle shapes) to be input, e.g., in micromechanical models.
Determination of macroscopic stress from diffraction experiments: A critical discussion (2020)
Mishurova, Tatiana ; Bruno, Giovanni ; Evsevleev, Sergei ; Sevostianov, I.
The paper is motivated by some inconsistencies and contradictions present in the literature on the calculation of the so-called diffraction elastic constants. In an attempt at unifying the views that the two communities of Materials Science and Mechanics of Materials have on the subject, we revisit and define the terminology used in the field. We also clarify the limitations of the commonly used approaches and Show that a unified methodology is also applicable to textured materials with a nearly arbitrary grain shape. We finally compare the predictions based on this methodology with experimental data obtained by in situ synchrotron radiation diffraction on additively manufactured Ti-6Al4V alloy. We show that (a) the transverse isotropy of the material yields good agreement between the best-fit isotropy approximation (equivalent to the classic Kröner’s model) and the experimental data and (b) the use of a general framework allows the calculation of all components of the tensor of diffraction elastic constants, which are not easily measurable by diffraction methods. This allows us to extend the current state-of-the-art with a predictive tool.
Using SXRR to Probe the Nature of Discontinuities in SLM Additive Manufactured Inconel 718 Specimens (2020)
Laquai, René ; Müller, Bernd R. ; Schneider, J. ; Kupsch, Andreas ; Bruno, Giovanni
The utilization of additive manufacturing (AM) to fabricate robust structural components relies on understanding the nature of internal anomalies or discontinuities, which can compromise the structural integrity. While some discontinuities in AM microstructures stem from similar mechanisms as observed in more traditional processes such as casting, others are unique to the AM process. Discontinuities in AM are challenging to detect, due to their submicron size and orientation dependency. Toward the goal of improving structural integrity, minimizing discontinuities in an AM build requires an understanding of the mechanisms of formation to mitigate their occurrence. This study utilizes various techniques to evaluate the shape, size, nature and distribution of discontinuities in AM Inconel 718, in a non-hot isostatic pressed (HIPed) as-built, non-HIPed and direct age, and HIPed with two step age samples. Non-destructive synchrotron radiation refraction and transmission radiography (SXRR) provides additional information beyond that obtained with destructive optical microscopy. SXRR was able to distinguish between voids, cracks and lack of melt in, due to its sensitivity to the orientation of the discontinuity.
Connecting Diffraction-Based Strain with Macroscopic Stresses in Laser Powder Bed Fused Ti-6Al-4V (2020)
Mishurova, Tatiana ; Artzt, K. ; Haubrich, J. ; Evsevleev, Sergei ; Evans, Alexander ; Meixner, M. ; Serrano Munoz, Itziar ; Sevostianov, I. ; Requena, G. ; Bruno, Giovanni
The laser powder bed fusion (LPBF) production process often results in large residual stress (RS) in the parts. Nondestructive techniques to determine RS are badly needed. However, a reliable quantification of macro-RS (i.e., stress at the component level) by means of diffraction-based techniques is still a great challenge, because the link between diffraction-based strain and macro-RS is not trivial. In this study, we experimentally determine (by means of in-situ synchrotron radiation diffraction) this link for LPBF Ti-6Al-4V. We compare our results with commonly used models to determine the so-called diffraction elastic constants (DECs). We show that LPBF materials possess different DECs than wrought alloys, simply because their microstructural and mechanical properties are different. We also show that the existing models can be used to calculate DECs only if high accuracy of the RS values is not required. If the peculiarities of the microstructure have to be taken into account (as is the case of additively manufactured materials), a radically new approach is desirable.
Explaining Deviatoric Residual Stresses in Aluminum Matrix Composites with Complex Microstructure (2020)
Evsevleev, Sergei ; Sevostianov, I. ; Mishurova, Tatiana ; Hofmann, M. ; Garcés, G. ; Bruno, Giovanni
The residual stresses in multiphase metal Matrix composites with both random planar-oriented short fibers and particles were studied by neutron diffraction and by a model based on the reformulation of classic Maxwell’s homogenization method. Contrary to common understanding and state-of-the-art models, we experimentally observed that randomly oriented phases possess non-hydrostatic residual stress. The recently developed modeling Approach allows calculating the residual stress in all phases of the composites. It rationalizes the presence of deviatoric stresses Accounting for the interaction of random oriented phases with fibers having preferential orientation.
Talbot- Lau interferometry with a non- binary phase grating for non-destructive testing (2016)
Shashev, Yury ; Kupsch, Andreas ; Lange, Axel ; Britzke, Ralf ; Bruno, Giovanni ; Müller, Bernd R. ; Hentschel, M. P.
Grating interferometric set-ups have been established in the last decade. They are promising candidates to obtain enhanced image contrast from weakly absorbing micro and nano structures. They are based on X-ray refraction and near-field diffraction using the Talbot effect. At the expense of taking multiple images, Talbot-Lau grating interferometry allows separating the absorption, refraction, and scattering contributions by analysing the disturbances of a phase grating interference pattern. Contrary to other refraction enhanced methods, this technique can be applied using conventional X-ray tubes (divergent, polychromatic source). This makes it attractive to solve typical non-destructive testing problems. We investigated the efficiency of phase gratings, i.e. the visibility (the amplitude of oscillations) upon variation of propagation distance and phase grating rotation around an axis parallel to the grid lines. This grating rotation changes the grating shape (i.e. the distributions of phase shifts). This can yield higher visibilities than derived from rectangular shapes. Our study includes experimental results obtained from synchrotron radiation, as well as simulations for monochromatic radiation. The advantages of Talbot-Lau interferometry are demonstrated at the example of glass capillaries.
Residual stress in selective laser melted Inconel 718: Influence of the removal from base plate and deposition hatch length (2018)
Thiede, Tobias ; Cabeza, S. ; Mishurova, Tatiana ; Nadammal, N. ; Kromm, Arne ; Bode, Johannes ; Haberland, C. ; Bruno, Giovanni
The residual stress distribution in IN718 elongated prisms produced by Selective Laser Melting was studied by means of neutron (bulk) and laboratory X-ray (surface) diffraction. Two deposition hatch lengths were considered. A horizontal plane near the top surface (perpendicular to the building direction) and a vertical plane near the lateral surface (parallel to the building direction) were investigated. Samples both in as-built (AB) condition and removed (RE) from the base plate were characterized. While surface stress fields seem constant for AB condition, X-ray diffraction shows stress gradients along the hatch direction in the RE condition. The stress profiles correlate with the distortion maps obtained by tactile probe measurements. Neutron diffraction shows bulk stress gradients for all principal components along the main sample directions. We correlate the observed stress patterns with the hatch length, i.e. with its effect on temperature gradients and heat flow. The bulk stress gradients partially disappear after removal from the baseplate.
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