In-Process Porositätserkennung für den PBF-LB/M-Prozess

Das Fertigungsverfahren des selektiven Laserschmelzens mit Metallen (PBF-LB/M) wird zunehmend auch für die Herstellung von hochbelastbaren Bauteilen in einer Serienfertigung eingesetzt. Die fehlende Reproduzierbarkeit von Prozessergebnissen und das stochastische Auftreten des Defektes Porosität stellen dabei eine besondere Herausforderung dar, da dieser Defekt einen wesentlichen Einfluss auf die mechanischen Kennwerte eines Bauteils hat. Dies kann in der Folge ein Versagen des Bau-teils unter Last zur Folge haben. Aus diesem Grund ist für solche hochbelasteten Bauteile die Qualitätssicherung unerlässlich. Die zerstörungsfreie Prüfung auf Porosität erfolgt im industriellen Kontext oftmals durch die Röntgen-Computertomografie (CT). Aufgrund langer Messzeiten entstehen hohe Kosten durch die Qualitätssicherung, welche die Wirtschaftlichkeit des PBF-LB/M-Fertigungsverfahrens einschränken. Je nach verwendetem Material und Bauteilgröße ist eine Porositätsanalyse mittels CT auch technisch nicht möglich. Aus diesen Gründen können alternative in-process Prozessüberwachungen für die industrielle Nutzung des PBF-LB/M-Fertigungsverfahrens einen Vorteil bringen. Bestehende Forschungsansätze zur in-process Porositätserkennung weisen vor allem Defizite im Bereich der industriellen Anwendbarkeit und in der quantitativen Defektcharakterisierung auf. Im Rahmen der vorliegenden Arbeit wird mithilfe von Methoden der datengetriebenen Modellbildung eine Prozessüberwachung auf Basis optischer Sensoren und akustischer Körperschallmesstechnik entwickelt, welche die Porositätsverteilung innerhalb eines Bauteils während des Fertigungsprozesses vorher-sagen kann. Dazu werden 104 Probekörper additiv gefertigt und die Sensordaten auf-gezeichnet. Die Probekörper werden nachfolgend mittels Computertomographie auf Porosität untersucht. Diese Informationen werden im Rahmen der datengetriebenen Modellbildung mittels künstlicher neuronaler Netze als Label für das Training genutzt. Die trainierten Modelle sind in der Lage, Bauteile räumlich aufgelöst hinsichtlich ihrer Porosität zu klassifizieren. Dabei können variable Schwellwerte als Klassengrenze genutzt werden. Die quantitative Vorhersage der numerischen Porosität durch Regression sowie die Einzeldefekterkennung bedarf weiterführender Forschungsarbeit. Die Datenfusion von optischer und akustischer Sensorik wurde im Rahmen der Arbeit betrachtet, konnte aber keine besseren Ergebnisse als die separate Betrachtung der Sensoren erzielen. Die Rohdaten der Arbeit werden im Rahmen des Promotionsverfahrens ebenfalls veröffentlicht, um weiterführende Forschungsarbeiten zu ermöglichen

Opaque voxel-based tree models for virtual laser scanning in forestry applications

Virtual laser scanning (VLS), the simulation of laser scanning in a computer environment, is a useful tool for field campaign planning, acquisition optimisation, and development and sensitivity analyses of algorithms in various disciplines including forestry research. One key to meaningful VLS is a suitable 3D representation of the objects of interest. For VLS of forests, the way trees are constructed influences both the performance and the realism of the simulations. In this contribution, we analyse how well VLS can reproduce scans of individual trees in a forest. Specifically, we examine how different voxel sizes used to create a virtual forest affect point cloud metrics (e.g., height percentiles) and tree metrics (e.g., tree height and crown base height) derived from simulated point clouds. The level of detail in the voxelisation is dependent on the voxel size, which influences the number of voxel cells of the model. A smaller voxel size (i.e., more voxels) increases the computational cost of laser scanning simulations but allows for more detail in the object representation. We present a method that decouples voxel grid resolution from final voxel cube size by scaling voxels to smaller cubes, whose surface area is proportional to estimated normalised local plant area density. Voxel models are created from terrestrial laser scanning point clouds and then virtually scanned in one airborne and one UAV-borne simulation scenario. Using a comprehensive dataset of spatially overlapping terrestrial, UAV-borne and airborne laser scanning field data, we compare metrics derived from simulated point clouds and from real reference point clouds. Compared to voxel cubes of fixed size with the same base grid size, using scaled voxels greatly improves the agreement of simulated and real point cloud metrics and tree metrics. This can be largely attributed to reduced artificial occlusion effects. The scaled voxels better represent gaps in the canopy, allowing for higher and more realistic crown penetration. Similarly high accuracy in the derived metrics can be achieved using regular fixed-sized voxel models with notably finer resolution, e.g., 0.02 m. But this can pose a computational limitation for running simulations over large forest plots due to the ca. 50 times higher number of filled voxels. We conclude that opaque scaled voxel models enable realistic laser scanning simulations in forests and avoid the high computational cost of small fixed-sized voxels

Projekt Science4Exit: Professionalisierung von angehenden Lehrkräften durch Videovignetten im Lehr-Lern-Labor

In diesem Artikel wird die Integration von Videografie in die Lehramtsausbildung im Rahmen eines Seminars zur Professionalisierung von angehenden Lehrkräften aus dem Fachbereich Chemie vorgestellt. Die Bedeutung dieses Themas liegt im Bestreben, angehende Lehrkräfte bestmöglich auf den Schulalltag vorzubereiten, indem ihre Fähigkei-ten und Kompetenzen, die für einen guten Chemieunterricht benötigt werden, reflektiert werden. Die Fragestellung dahinter ist, ob die Videografie diesen Prozess gewinnbringend beeinflussen kann. Um dieser Fragestellung nachzuge-hen, wurde im Rahmen des Projekts Science4Exit ein Seminarkonzept entwickelt, welches im Master-Studiengang des Lehramts der Sekundarstufe verortet ist. Die ersten Ergebnisse der Pilotierung liefern Hinweise, dass diese Methodik von den Studierenden als hilfreich und wertvoll wahrgenommen wird. Durch den Einsatz der Videografie wird den Studierenden die Möglichkeit eröffnet, ihr eigenes Lehrverhalten zu analysieren und zu reflektieren

Individual tree point clouds and tree measurements from multi-platform laser scanning in German forests

Laser scanning from different acquisition platforms enables the collection of 3D point clouds from different perspectives and with varying resolutions. These point clouds allow us to retrieve detailed information on the individual tree and forest structure. We conducted airborne laser scanning (ALS), uncrewed aerial vehicle (UAV)-borne laser scanning (ULS) and terrestrial laser scanning (TLS) in two German mixed forests with species typical of central Europe. We provide the spatially overlapping, georeferenced point clouds for 12 forest plots. As a result of individual tree extraction, we furthermore present a comprehensive database of tree point clouds and corresponding tree metrics. Tree metrics were derived from the point clouds and, for half of the plots, also measured in the field. Our dataset may be used for the creation of 3D tree models for radiative transfer modeling or lidar simulation studies or to fit allometric equations between point cloud metrics and forest inventory variables. It can further serve as a benchmark dataset for different algorithms and machine learning tasks, in particular automated individual tree segmentation, tree species classification or forest inventory metric prediction. The dataset and supplementary metadata are available for download, hosted by the PANGAEA data publisher at https://doi.org/10.1594/PANGAEA.942856 (Weiser et al., 2022a)

Biomechanical Effects of a Cross Connector in Sacral Fractures – A Finite Element Analysis

Background: Spinopelvic fractures and approaches of operative stabilization have been a source of controversial discussion. Biomechanical data support the benefit of a spinopelvic stabilization and minimally invasive procedures help to reduce the dissatisfying complication rate. The role of a cross connector within spinopelvic devices remains inconclusive. We aimed to analyze the effect of a cross connector in a finite element model (FE model). Study Design: A FE model of the L1-L5 spine segment with pelvis and a spinopelvic stabilization was reconstructed from patient-specific CT images. The biomechanical relevance of a cross connector in a Denis zone I (AO: 61-B2) sacrum fracture was assessed in the FE model by applying bending and twisting forces with and without a cross connector. Biomechanical outcomes from the numerical model were investigated also considering uncertainties in material properties and levels of osseointegration. Results: The designed FE model showed comparable values in range-of-motion (ROM) and stresses with reference to the literature. The superiority of the spinopelvic stabilization (L5/Os ilium) ± cross connector compared to a non-operative procedure was confirmed in all analyzed loading conditions by reduced ROM and principal stresses in the disk L5/S1, vertebral body L5 and the fracture area. By considering the combination of all loading cases, the presence of a cross connector reduced the maximum stresses in the fracture area of around 10%. This difference has been statistically validated (p < 0.0001). Conclusion: The implementation of a spinopelvic stabilization (L5/Os ilium) in sacrum fractures sustained the fracture and led to enhanced biomechanical properties compared to a non-reductive procedure. While the additional cross connector did not alter the resulting ROM in L4/L5 or L5/sacrum, the reduction of the maximum stresses in the fracture area was significant. © Copyright © 2021 Gierig, Liu, Weiser, Lehmann, Wriggers, Marino and Saul

Search for squarks and gluinos with the ATLAS detector in final states with jets and missing transverse momentum using √s=8 TeV proton-proton collision data

A search for squarks and gluinos in final states containing high-p T jets, missing transverse momentum and no electrons or muons is presented. The data were recorded in 2012 by the ATLAS experiment in s√=8 TeV proton-proton collisions at the Large Hadron Collider, with a total integrated luminosity of 20.3 fb−1. Results are interpreted in a variety of simplified and specific supersymmetry-breaking models assuming that R-parity is conserved and that the lightest neutralino is the lightest supersymmetric particle. An exclusion limit at the 95% confidence level on the mass of the gluino is set at 1330 GeV for a simplified model incorporating only a gluino and the lightest neutralino. For a simplified model involving the strong production of first- and second-generation squarks, squark masses below 850 GeV (440 GeV) are excluded for a massless lightest neutralino, assuming mass degenerate (single light-flavour) squarks. In mSUGRA/CMSSM models with tan β = 30, A 0 = −2m 0 and μ > 0, squarks and gluinos of equal mass are excluded for masses below 1700 GeV. Additional limits are set for non-universal Higgs mass models with gaugino mediation and for simplified models involving the pair production of gluinos, each decaying to a top squark and a top quark, with the top squark decaying to a charm quark and a neutralino. These limits extend the region of supersymmetric parameter space excluded by previous searches with the ATLAS detector

Search for direct production of charginos and neutralinos in events with three leptons and missing transverse momentum in √s = 7 TeV pp collisions with the ATLAS detector

A search for the direct production of charginos and neutralinos in final states with three electrons or muons and missing transverse momentum is presented. The analysis is based on 4.7 fb−1 of proton–proton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with Standard Model expectations in three signal regions that are either depleted or enriched in Z-boson decays. Upper limits at 95% confidence level are set in R-parity conserving phenomenological minimal supersymmetric models and in simplified models, significantly extending previous results

Measurement of the production of a W boson in association with a charm quark in pp collisions at √s = 7 TeV with the ATLAS detector

The production of a W boson in association with a single charm quark is studied using 4.6 fb−1 of pp collision data at s√ = 7 TeV collected with the ATLAS detector at the Large Hadron Collider. In events in which a W boson decays to an electron or muon, the charm quark is tagged either by its semileptonic decay to a muon or by the presence of a charmed meson. The integrated and differential cross sections as a function of the pseudorapidity of the lepton from the W-boson decay are measured. Results are compared to the predictions of next-to-leading-order QCD calculations obtained from various parton distribution function parameterisations. The ratio of the strange-to-down sea-quark distributions is determined to be 0.96+0.26−0.30 at Q 2 = 1.9 GeV2, which supports the hypothesis of an SU(3)-symmetric composition of the light-quark sea. Additionally, the cross-section ratio σ(W + +c¯¯)/σ(W − + c) is compared to the predictions obtained using parton distribution function parameterisations with different assumptions about the s−s¯¯¯ quark asymmetry

Search for direct pair production of the top squark in all-hadronic final states in proton-proton collisions at s√=8 TeV with the ATLAS detector

The results of a search for direct pair production of the scalar partner to the top quark using an integrated luminosity of 20.1fb−1 of proton–proton collision data at √s = 8 TeV recorded with the ATLAS detector at the LHC are reported. The top squark is assumed to decay via t˜→tχ˜01 or t˜→ bχ˜±1 →bW(∗)χ˜01 , where χ˜01 (χ˜±1 ) denotes the lightest neutralino (chargino) in supersymmetric models. The search targets a fully-hadronic final state in events with four or more jets and large missing transverse momentum. No significant excess over the Standard Model background prediction is observed, and exclusion limits are reported in terms of the top squark and neutralino masses and as a function of the branching fraction of t˜ → tχ˜01 . For a branching fraction of 100%, top squark masses in the range 270–645 GeV are excluded for χ˜01 masses below 30 GeV. For a branching fraction of 50% to either t˜ → tχ˜01 or t˜ → bχ˜±1 , and assuming the χ˜±1 mass to be twice the χ˜01 mass, top squark masses in the range 250–550 GeV are excluded for χ˜01 masses below 60 GeV