TY - JOUR A1 - Hartmann, Jürgen A1 - Werner, L. T1 - Radiation thermometry towards the triple point of water? JF - International Journal of Thermophysics Y1 - 2008 UR - http://permalink.bibkatalog.de/BV013298193 IS - 29 SP - 1052 EP - 1065 ER - TY - JOUR A1 - Hartmann, Jürgen T1 - Correct consideration of the index of refraction using blackbody radiation JF - Optics Express Y1 - 2006 UR - http://permalink.bibkatalog.de/BV013253264 VL - 14 IS - 18 SP - 8121 EP - 8126 ER - TY - JOUR A1 - Hartmann, Jürgen T1 - Advanced comparator method for measuring ultra small aperture areas JF - Meas.Sci.Techn. Y1 - 2001 IS - 12 SP - 1678 EP - 1682 ER - TY - JOUR A1 - Hartmann, Jürgen A1 - Lowe, D. A1 - Anhalt, Klaus T1 - Construction and validation of a platinum-carbon eutectic fixed-point JF - Metrologia Y1 - 2008 UR - http://permalink.bibkatalog.de/BV012573233 IS - 45 SP - 325 EP - 329 ER - TY - JOUR A1 - Höfflin, Dennis A1 - Hartmann, Jürgen A1 - Rosilius, Maximilian A1 - Seitz, Philipp A1 - Schiffler, Andreas T1 - Opto-Thermal Investigation of Additively Manufactured Steel Samples as a Function of the Hatch Distance JF - Sensors N2 - Nowadays, additive manufacturing processes are becoming more and more appealing due to their production-oriented design guidelines, especially with regard to topology optimisation and minimal downstream production depth in contrast to conventional technologies. However, a scientific path in the areas of quality assurance, material and microstructural properties, intrinsic thermal permeability and dependent stress parameters inhibits enthusiasm for the potential degrees of freedom of the direct metal laser melting process (DMLS). Especially in quality assurance, post-processing destructive measuring methods are still predominantly necessary in order to evaluate the components adequately. The overall objective of these investigations is to gain process knowledge make reliable in situ statements about component quality and material properties based on the process parameters used and emission values measured. The knowledge will then be used to develop non-destructive tools for the quality management of additively manufactured components. To assess the effectiveness of the research design in relation to the objectives for further investigations, this pre-study evaluates the dependencies between the process parameters, process emission during manufacturing and resulting thermal diffusivity and the relative density of samples fabricated by DMLS. Therefore, the approach deals with additively built metal samples made on an EOS M290 apparatus with varying hatch distances while simultaneously detecting the process emission. Afterwards, the relative density of the samples is determined optically, and thermal diffusivity is measured using the laser flash method. As a result of this pre-study, all interactions of the within factors are presented. The process variable hatch distance indicates a strong influence on the resulting material properties, as an increase in the hatch distance from 0.11 mm to 1 mm leads to a drop in relative density of 57.4%. The associated thermal diffusivity also reveals a sharp decrease from 5.3 mm2/s to 1.3 mm2/s with growing hatch distances. The variability of the material properties can also be observed in the measured process emissions. However, as various factors overlap in the thermal radiation signal, no clear assignment is possible within the scope of this work. KW - additive manufacturing processes KW - material Y1 - 2021 U6 - https://doi.org/10.3390/s22010046 SN - 1424-8220 VL - 22 IS - 1 PB - MDPI ER - TY - JOUR A1 - Wehnert, Kira-Kristin A1 - Ochs, Dennis A1 - Schmitt, Jan A1 - Hartmann, Jürgen A1 - Schiffler, Andreas T1 - Reducing Lifecycle Costs due to Profile Scanning of the Powder Bed in Metal Printing JF - Procedia CIRP 98 N2 - First time right is one major goal in powder based 3D metal printing. Reaching this goal is driven by reducing life cycle costs for quality measures, to minimize scrap rate and to increase productivity under optimal resource efficiency. Therefore, monitoring the state of the powder bed for each printed layer is state of the art in selective laser melting. In the most modern approaches the quality monitoring is done by computer vision systems working with an interference on trained neural networks with images taken after exposure and after recoating. There are two drawbacks of this monitoring method: First, the sensor signals - the image of the powder bed - give no direct height information. Second, the application of this method needs to be trained and labeled with reference images for several cases. The novel approach presented in this paper uses a laser line scanner attached to the recoating machine. With this new concept, a direct threshold measure can be applied during the recoating process to detect deviations in height level without prior knowledge. The evaluation can be done online during recoating and feedback to the controller to monitor each individual layer. Hence, in case of deviations the location in the printing plane is an inherent measurement and will be used to decide which severity of error is reported. The signal is used to control the process, either by starting the recoating process again or stopping the printing process. With this approach, the sources of error for each layer can be evaluated with deep information to evaluate the cause of the error. This allows a reduction of failure in the future, which saves material costs, reduces running time of the machine life cycle phase in serial production and results in less rework for manufactured parts. Also a shorter throughput time per print job results, which means that the employee can spent more time to other print jobs and making efficient use of the employee’s work force. In summary, this novel approach will not only reduce material costs but also operating costs and thus optimize the entire life cycle cost structure. The paper presents a first feasibility and application of the described approach for test workpieces in comparison to conventional monitoring systems on an EOS M290 machine. Y1 - 2021 UR - 10.1016/j.procir.2021.01.175 VL - 98 SP - 684 EP - 689 PB - Elsevir ER - TY - JOUR A1 - Hay, Bruno A1 - Beaumont, Oliver A1 - Lambeng, Nora A1 - Cataldi, Michel A1 - Lorrette, Christophe A1 - Knopp, Kevin A1 - Hartmann, Jürgen A1 - Beckstein, Fabia A1 - Stobitzer, Dorothea A1 - Milošević, Nenad A1 - Stepanic, Nenad A1 - Wu, Jiyu A1 - Mildeova, Petra T1 - Inter‑laboratory Comparison on Thermal Diffusivity Measurements by the Laser Flash Method at Ultra‑high Temperature JF - International Journal of Thermophysics N2 - thermal diffusivity measurements by the laser flash method in the temperature range from 23 °C to 3000 °C. The main objective was to assess the variability and coherency of thermal diffusivity measurements performed at ultra-high temperatures at the European level. Three refractory materials (molybdenum, tungsten and isotropic graphite IG210) were selected for this inter-laboratory comparison, due to their high melting point. The disk-shaped specimens needed were machined from the same blocks of materials in order to reduce any potential scattering of results between participants due to inhomogeneity effects. The homogeneity of the sets of specimens was studied by the pilot laboratory (LNE) before launching the comparison process. Thermal diffusivity measurements were then carried out by the seven participants on the three materials during two successive thermal cycles up to the maximum temperatures that can be reached by the devices used. The analysis of results showed a good agreement between the participants for temperatures above 400 °C, with relative deviations within the uncertainties of measurement and lower than ± 4 % for molybdenum, ± 5 % for isotropic graphite and ± 9 % for tungsten. Y1 - 2023 UR - https://doi.org/10.1007/s10765-023-03159-5 VL - 2023 SP - 44 EP - 48 ER - TY - JOUR A1 - Manara, Jochen A1 - Hartmann, Jürgen A1 - Kerwagen, Fabian A1 - Maak, Christoph A1 - Muscio, Albert A1 - Paeth, Heiko A1 - Ebert, Hans-Peter T1 - Passive Radiative Cooling Materials with Special Focus on the Reduction of Urban Heat Island Effect: A Current Summarized Classification of Need, Approaches and Characterization Methods JF - International Journal of Thermophysics N2 - Rapidly rising global temperatures and the intensification of the urban heat island (UHI) effect necessitate new, energy-efficient solutions to mitigate heat stress in cities. Passive radiative cooling (PRC) offers a highly promising, low-energy pathway to achieve sub-ambient temperatures by reflecting incoming solar radiation while emitting long-wave infrared radiation through the atmospheric infrared window. This review summarizes key aspects of PRC and its role in reducing UHI impacts. Furthermore the fundamental physics of heat transfer and radiative heat exchange, including the materials properties such as solar reflectance and thermal emissivity which are correlated with the figures of merit, temperature drop below ambient temperature and cooling power. A comprehensive classification of current PRC materials is presented based on both structural architectures and physical effects. Additionally an overview on measurement techniques are employed to determine the performance of PRC materials, focusing on the key performance indicators. For this purpose in-field as wells as laboratory measurement techniques are introduced and opportunities in standardizing testing protocols are highlighted. Finally, future research directions are outlined, focusing on novel material development, theoretical advancements, scalable fabrication processes, and integration strategies within urban infrastructures. These innovations are important for enhancing building energy efficiency, reducing urban heat stress, and promoting sustainable urban development in the face of climate change. Y1 - 2025 U6 - https://doi.org/10.1007/s10765-025-03529-1 VL - 46 IS - 58 ER - TY - CHAP A1 - Blotevogel, Thomas A1 - Goldlücke, Jürgen A1 - Egermann, Jan A1 - Leipertz, Alfred A1 - Hartmann, Matthias A1 - Schenk, Martin A1 - Berckmüller, Martin ED - Dingel, Oliver T1 - Gemischbildungsuntersuchung in Gasmotoren mittels optischer Messverfahren, speziell in Wasserstoffmotoren T2 - Gasfahrzeuge N2 - Planar laser-induced fluorescence (PLIF) has been successfully used for the investigation of the mixture formation process in hydrogen engines for passenger cars. Detailed information has been obtained about process development (qualitative measurement) and on fuel/air-ratio (quantitative measurement) inside the combustion chamber. These results can be used for further optimization of mixture formation and combustion process concerning emissions and fuel consumption. The measurement technique used is not only limited to hydrogen or to passenger car engines, but can also be applied to other fuel gases like natural gas or to other engine sizes like bus engines. The main topic of this paper is the experimental verification of the procedure which was executed by simultaneous PLIF and Raman scattering measurements. By Raman scattering the fuel/air-ratio can directly be determined from direct concentration measurements of the different gas species. The fuel/air-ratios determined by PLIF and Raman measurements are in good agreement indicating that a quantitative fuel/air-ratio measurement during the mixture formation process of gas and hydrogen engines is possible by PLIF. This fact is also confirmed by other measurements, e.g., global fuel/air-ratio calculated from measured intake air and fuel gas flow. KW - Wasserstoff Gasmotor Laser Optische Messtechnik Y1 - 2004 SN - 3816924395 SP - 205 EP - 229 PB - expert verlag CY - Renningen ER - TY - JOUR A1 - Strasser, Claire A1 - Moukhina, Elena A1 - Hartmann, Jürgen T1 - Time–Temperature-Transformation (TTT) Cure Diagram of an Epoxy–Amine System JF - Macromolecular Theory and Simulations Y1 - 2024 UR - https://doi.org/10.1002/mats.202400039 VL - 33 IS - 6 SP - 2400039 ER -