TY - JOUR A1 - Launhardt, M. A1 - Wörz, A. A1 - Loderer, A. A1 - Laumer, Tobias A1 - Drummer, Dietmar A1 - Hausotte, Tino A1 - Schmidt, M. T1 - Detecting surface roughness on SLS parts with various measuring techniques JF - Polymer Testing N2 - Selective Laser Sintering (SLS) is an additive manufacturing technique whereby a laser melts polymer powder layer by layer to generate three-dimensional parts. It enables the fabrication of parts with high degrees of complexity, nearly no geometrical restrictions, and without the necessity of a tool or a mold. Due to the orientation in the building space, the processing parameters, and the powder properties, the resulting parts possess an increased surface roughness. In comparison to other manufacturing techniques, e.g. injection molding, the surface roughness of SLS parts results from partially melted powder particles on the surface layer. The actual surface roughness must thus be characterized with respect to the part's eventual application. At the moment, there is no knowledge regarding which measuring technique is most suitable for detecting and quantifying SLS parts' surface roughness. The scope of this paper is to compare tactile profile measurement methods, as established in industry, to optical measurement techniques such as Focus Variation, Fringe Projection Technique (FPT), and Confocal Laser Scanning Microscope (CLSM). The advantages and disadvantages of each method are presented and, additionally, the effect of tactile measurement on a part's surface is investigated. KW - Selective Laser Sintering (SLS) KW - PA12 KW - Surface roughness KW - Measuring technique Y1 - 2016 SN - 0142-9418 U6 - https://doi.org/10.1016/j.polymertesting.2016.05.022 SN - 1873-2348 VL - 53 SP - 217 EP - 226 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Orcesi, André A1 - O'Connor, Alan A1 - Diamantidis, Dimitris A1 - Sýkora, Miroslav A1 - Wu, Teng A1 - Akiyama, Mitsuyoshi A1 - Alhamid, Abdul Kadir A1 - Schmidt, Franziska A1 - Pregnolato, Maria A1 - Li, Yue A1 - Salarieh, Babak A1 - Salman, Abdullahi M. A1 - Bastidas-Arteaga, Emilio A1 - Markogiannaki, Olga A1 - Schoefs, Franck T1 - Investigating the Effects of Climate Change on Structural Actions JF - Structural Engineering International N2 - The changing climate with resulting more extreme weather events will likely impact infrastructure assets and services. This phenomenon can present direct threats to the assets as well as significant indirect effects for those relying on the services those assets deliver. Such threats are path-dependent and place-specific, as they strongly depend on current and future climate variability, location, asset design life, function and condition. One key question is how climate change is likely to increase both the probability and magnitude of extreme weather events under different scenarios of climate change. To address this issue, this paper investigates selected effects of climate change and their consequences on structural performance, in the context of evolving loading scenarios in three different continental regions: Europe, North America, and Asia. The aim is to investigate some main place-specific changes of the exposure in terms of intensity/frequency of extreme events as well as the associated challenges, considering some recent activities of members of the IABSE TG6.1. Climate change can significantly affect built infrastructure and the society by increasing the occurrence and magnitude of extreme events and increasing potential losses. Therefore, specific relationships relating hazard levels and structural vulnerability to climate change effects should be determined. KW - climate change KW - extreme weather events KW - flooding KW - hurricanes KW - scour KW - sea-level rise KW - tsunami Y1 - 2022 U6 - https://doi.org/10.1080/10168664.2022.2098894 VL - 32 IS - 4 SP - 1 EP - 14 PB - Taylor & Francis ER - TY - JOUR A1 - Laumer, Tobias A1 - Stichel, T. A1 - Nagulin, K. A1 - Schmidt, M. T1 - Optical analysis of polymer powder materials for Selective Laser Sintering JF - Polymer Testing N2 - This study increases the basic understanding of optical material properties of polymer powders used in selective laser sintering (SLS). Therefore, different polymer powder materials were analyzed regarding their optical material properties with an integration spheres measurement setup. By the measurements a direct connection between the absorption behavior of the solid material and the overall optical material characteristics of the same material in powdery form could be shown. The results were used to develop an advanced explanation model for the optical material properties of powders. At present, existing explanation models only consider the occurring of multiple reflections in the gaps between the particles to explain the overall optical material properties of powder materials. Thus, by also considering the absorption behavior of the single particles, the basic understanding of the beam-matter interaction and their effect on the optical material properties of powder materials can be expanded. KW - Additive manufacturing KW - Selective Laser Sintering KW - Optical material characteristics KW - Integration spheres KW - Material qualification KW - New materials Y1 - 2016 U6 - https://doi.org/10.1016/j.polymertesting.2016.10.010 SN - 1873-2348 SN - 0142-9418 VL - 56 SP - 207 EP - 213 PB - Elsevier Science CY - Amsterdam [u.a.] ER - TY - CHAP A1 - Laumer, Tobias A1 - Stichel, T. A1 - Sachs, M. A1 - Amend, Philipp A1 - Schmidt, Michael ED - Bártolo, Paulo T1 - Qualification and modification of new polymer powders for laser beam melting using Ulbricht spheres T2 - High value manufacturing : Advanced research in virtual and rapid prototyping ; Proceedings of the 6th International Conference on Advanced Research and Rapid Prototyping, Leiraia, Portugal, 1-5 October, 2013 N2 - The restricted amount of available materials for Laser Beam Melting (LBM) of polymers is one of the main limitations for expanding the technology. Current qualification methods deal with problems like inadequate powder flowability or high part porosities among others but do not offer a detailed analysis of the important beam-matter-interaction between powder particles and electro-magnetic laser radiation. In this paper, polyethylene powder is qualified for the LBM process and specifically analyzed regarding the optical material properties of the powder for a wavelength of 10.6 μm. By admixing graphite as absorption intensifier the change of the optical material properties and the thereby connected processing parameters are analyzed. Furthermore an explanation approach is given to explain the relation between different transmittances of different powder particles and the optical material properties of the polymer powders. Y1 - 2014 UR - https://www.researchgate.net/publication/286311000_Qualification_and_modification_of_new_polymer_powders_for_laser_beam_melting_using_Ulbricht_spheres SN - 978-1-138-00137-4 SN - 1138001376 SP - 255 EP - 260 PB - CRC Press CY - Boca Raton ER - TY - JOUR A1 - Hupfeld, T. A1 - Laumer, Tobias A1 - Stichel, T. A1 - Schuffenhauer, T. A1 - Heberle, J. A1 - Schmidt, M. A1 - Barcikowski, S. A1 - Gökce, B. T1 - A new approach to coat PA12 powders with laser-generated nanoparticles for selective laser sintering JF - Procedia CIRP N2 - The modification of selective laser sintering (SLS) powder materials by nanoadditives offers the possibility to adapt the powder properties to the laser sintering process or the resulting part properties. To avoid agglomeration of the nanofiller, a new approach in which surfactant-free laser-generated colloidal nanoparticles are adsorbed onto the polymer surface directly in an aqueous solution is demonstrated. Based on this novel approach, polyamide 12 (PA12) powders are decorated with metal and oxide nanoparticles and processed via SLS. Electron microscopy and confocal laser scanning imaging are utilized to analyze the dispersion of the filler. KW - laser additive manufacturing KW - nanoparticles KW - polymer powders KW - pulsed laser ablation in liquids KW - selective laser sintering Y1 - 2018 U6 - https://doi.org/10.1016/j.procir.2018.08.103 VL - 74 SP - 244 EP - 248 PB - Elsevier ER - TY - JOUR A1 - Klein, C. A1 - Nabbefeld, T. A1 - Hattab, H. A1 - Meyer, D. A1 - Jnawali, G. A1 - Kammler, Martin A1 - Meyer zu Heringdorf, Frank-Joachim A1 - Golla-Franz, A. A1 - Müller, B. H. A1 - Schmidt, Th A1 - Henzler, M. A1 - Horn-von Hoegen, Michael T1 - Lost in reciprocal space? Determination of the scattering condition in spot profile analysis low-energy electron diffraction JF - Review of scientific instruments N2 - The precise knowledge of the diffraction condition, i.e., the angle of incidence and electron energy, is crucial for the study of surface morphology through spot profile analysis low-energy electron diffraction (LEED). We demonstrate four different procedures to determine the diffraction condition: employing the distortion of the LEED pattern under large angles of incidence, the layer-by-layer growth oscillations during homoepitaxial growth, a G(S) analysis of a rough surface, and the intersection of facet rods with 3D Bragg conditions. Y1 - 2011 U6 - https://doi.org/10.1063/1.3554305 VL - 82 IS - 3 PB - American Institute of Physics ER -