TY - JOUR A1 - Yildirim, Arda A1 - Krause, Christina A1 - Zorn, R. A1 - Lohstroh, W. A1 - Schneider, G. J. A1 - Zamponi, M. A1 - Holerer, O. A1 - Frick, B. A1 - Schönhals, Andreas T1 - Complex molecular dynamics of a symmetric model discotic liquid crystal revealed by broadband dielectric, thermal and neutron spectroscopy N2 - The molecular dynamics of the triphenylene-based discotic liquid crystal HAT6 is investigated by broadband dielectric spectroscopy, advanced dynamical calorimetry and neutron scattering. Differential scanning calorimetry in combination with X-ray scattering reveals that HAT6 has a plastic crystalline phase at low temperatures, a hexagonally ordered liquid crystalline phase at higher temperatures and undergoes a clearing transition at even higher temperatures. The dielectric spectra show several relaxation processes: a localized gamma-relaxation a lower temperature and a so called alpha-2-relaxation at higher temperatures. The relaxation rates of the alpha-2-relaxation have a complex temperature dependence and bear similarities to a dynamic glass transition. The relaxation rates estimated by hyper DSC, Fast Scanning calorimetry and AC Chip calorimetry have a different temperature dependence than the dielectric alpha-2-relaxation and follows the VFT-behavior characteristic for glassy dynamics. Therefore, this process is called alpha-1-relaxation. Its relaxation rates show a similarity with that of polyethylene. For this reason, the alpha-1-relaxation is assigned to the dynamic glass transition of the alkyl chains in the intercolumnar space. Moreover, this process is not observed by dielectric spectroscopy which supports its assignment. The alpha-2-relaxation was assigned to small scale translatorial and/or small angle fluctuations of the cores. The neutron scattering data reveal two relaxation processes. The process observed at shorter relaxation times is assigned to the methyl group rotation. The second relaxation process at longer time scales agree in the temperature dependence of its relaxation rates with that of the dielectric gamma-relaxation. KW - Discotic Liquid Crystals PY - 2020 DO - https://doi.org/10.1039/c9sm02487e VL - 16 IS - 8 SP - 2005 EP - 2016 PB - Royal Chemical Society AN - OPUS4-50466 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Hutt, S. A1 - Eisele, G. A1 - Krause, Martin T1 - Ultraschalltransmissionsanalyse am Cottaer Sandstein - Erste messtechnische Tastversuche N2 - Besonders beim Bauen im Bestand und der Bauwerkserhaltung werden zur Bestimmung des Tragvermögens von historischen, oft unter Denkmalschutz stehenden, natursteinernen Bauteilen Materialkennwerte benötigt. Die üblichen Verfahren mittels Probeentnahme am Objekt und Bestimmung der Kennwerte im Labor bedeuten bei Denkmälern einen massiven Eingriff und sollten vermieden werden. Vermehrt wird daher der Einsatz von zerstörungsfreien Untersuchungsmethoden erforscht und angewendet. Eine dieser Methoden stellt die Ultraschallprüfung dar. KW - Ultraschalltransmission KW - Naturstein KW - Uniaxialer Druck PY - 2015 SN - 0933-4017 VL - 2 SP - 22 EP - 29 PB - Callwey CY - München AN - OPUS4-32980 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Krause, G. A1 - Wehrstedt, Klaus-Dieter A1 - Malow, Marcus A1 - Budde, K. A1 - Mosler, J. T1 - Safe transport of acrylic acid in railroad tank cars. Part 1: Determination of the self-accelerating decomposition temperature N2 - Experiments according to a test specified in the UN Recommendations on the Transport of Dangerous Goods, Manual of Tests and Criteria, and numerical simulations by means of a finite element method are employed to determine the self-accelerating decomposition temperature of acrylic acid in a railroad tank car. The results demonstrate that the transport of acrylic acid in big tank cars is safe as long as some basic conditions are taken into account. KW - Acrylic acid KW - Dangerous goods KW - Finite element method KW - Railway transport KW - Self-accelerating decomposition temperature PY - 2014 DO - https://doi.org/10.1002/ceat.201300778 SN - 0930-7516 SN - 1521-4125 VL - 37 IS - 9 SP - 1460 EP - 1467 PB - Wiley-VCH Verl. CY - Weinheim AN - OPUS4-31298 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Wiggenhauser, Herbert A1 - Samokrutov, A A1 - Mayer, K A1 - Krause, Martin A1 - Alekhin, S. G. A1 - Elkin, V T1 - Large aperture ultrasonic system for testing thick concrete structures N2 - A Large Aperture UltraSonic system (LAUS) has been designed and built for testing thick concrete structures. The scalable system consists of twelve ultrasonic units, each hosting 32 individual shear wave transducers with mechanical dry point contact (DPC) to the concrete surface. The twelve units are attached to the concrete surface using a vacuum case which holds them in place during operation. Each LAUS unit can be placed individually on the surface to achieve optimal ultrasonic condition, e.g. to avoid rebars. For the generation of vacuum, air pressure is supplied to each unit through an air hose. The twelve units define an aperture which is necessary for fast reconstruction of the subsurface structure. The well-known SAFT (Synthetic Aperture Focusing Technique) algorithm has been adopted to this situation, where the individual LAUS units form a linear aperture with not necessarily equidistant spacing between the units. The exact geometrical position of the units, which are individually marked with retroreflective labels, is determined using photographs and image processing. All transducers are synchronized and work either as transmitter or receiver. A full scan consists of 12 * 11 recordings, where each unit acts as transmitter once and all others as receivers. An electronic sub-unit on the back of the ultrasonic device holds the battery and handles data acquisition, synchronization and data communication. A computer is used as base unit which communicates with each LAUS unit for control and data acquisition, the synchronization is performed by a radio modem that uses a special algorithm similar to a digital PLL (phase locked loop). No wire connections are necessary between the units and the base system. The LAUS system is designed to investigate concrete structures with thicknesses in excess of 2 m, depending on the acoustic condition of the object under investigation. Highly reinforced concrete may have less penetration depth. The LAUS provides quasi real time imaging, once the transducers are put in place and the data has been acquired. First measurements on a foundation slab confirm, that the system can register ultrasonic echoes from the back wall at 4 m distance. KW - Ultrasound "Large Aperture" NDT Concrete PY - 2017 DO - https://doi.org/10.1061/(ASCE)IS.1943-555X.0000314 SN - 1076-0342 SN - 1943-555X VL - 23 IS - 1 SP - B4016004-1 EP - B4016004-9 PB - American Society of Civil Engineers (ASCE) CY - Reston, VA 20191-4400 USA AN - OPUS4-39372 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Wiggenhauser, Herbert A1 - Samokrutov, A.A. A1 - Mayer, K. A1 - Krause, Martin A1 - Alekhin, S. G. A1 - Elkin, V. T1 - LAUS - Large aperture ultrasonic system - for testing thick concrete structures N2 - A Large Aperture UltraSonic (LAUS) system has been designed and built for testing thick concrete structures. The scalable system consists of twelve ultrasonic units, each hosting 32 individual shear wave transducers with mechanical dry point contact (DPC) to the concrete surface. The twelve units are attached to the concrete surface using a vacuum case which holds them in place during operation. Each LAUS unit can be placed individually depending on the surface condition and optimal ultrasonic condition, e.g. rebar position. Air pressure is supplied to each unit through an air hose. The following extended abstract is a short version of an article to be published in the special edition of ASCE JIS that will describe the outline of the system, the principle of functioning, the data processing and adapted reconstruction calculation based on SAFT as well as the system performance during first applications. T2 - NDT-CE 2015 - International symposium non-destructive testing in civil engineering CY - Berlin, Germany DA - 15.09.2015 KW - Ultrasonic imaging KW - Linear array KW - Reconstruction calculation (SAFT) PY - 2015 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-345383 UR - http://www.ndt.net/?id=18313 SN - 1435-4934 VL - 20 IS - 11 SP - 1 EP - 4 PB - NDT.net CY - Kirchwald AN - OPUS4-34538 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Auer, C. A1 - Kalinka, Gerhard A1 - Krause, T. A1 - Hinrichsen, G. T1 - Crystallization Kinetics of Pure and Fiber-Reinforced Poly(phenylene Sulfide) KW - Verbundwerkstoffe KW - Thermoplaste KW - Kristallisation KW - Kristallisationskinetik KW - Erstarrung KW - Avrami KW - Modellrechnung KW - Simulation PY - 1994 SN - 0021-8995 SN - 1097-4628 VL - 51 SP - 407 EP - 413 PB - Wiley InterScience CY - Hoboken, NJ AN - OPUS4-11991 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Krause, T. A1 - Kalinka, Gerhard A1 - Auer, C. A1 - Hinrichsen, G. T1 - Computer Simulation of Crystallization Kinetics in FIber-Reinforced Composites KW - Verbundwerkstoffe KW - Thermoplaste KW - Kristallisation KW - Kristallisationskinetik KW - Erstarrung KW - Avrami KW - Modellrechnung KW - Simulation PY - 1994 SN - 0021-8995 SN - 1097-4628 VL - 51 SP - 399 EP - 406 PB - Wiley InterScience CY - Hoboken, NJ AN - OPUS4-11992 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Krause, Martin A1 - Mayer, K. A1 - Friese, Martin A1 - Milmann, Boris A1 - Mielentz, Frank A1 - Ballier, G. T1 - Progress in ultrasonic tendon duct imaging N2 - Ultrasonic imaging of tendon ducts enables the precise localisation of grouting faults in many cases. Additionally to well known criteria for detecting grouting faults in tendon ducts recently new possibilities were developed. Two main effects influence the complex behaviour of wave propagation and reflection: a) different arrangement and number of strands or internal rebars; b) superposition of reflecting signals and different wave modes propagating into the interface region around the tendon duct. In order to understand the experimental results, EFIT modelling is performed (EFIT: Elastodynamic Finite Integration Technique). KW - Ultrasonic imaging KW - Prestressed concrete structures KW - Reconstruction calculation KW - SAFT KW - EFIT modelling PY - 2011 DO - https://doi.org/10.3166/ejece.15.461-485 SN - 1964-8189 VL - 15 IS - 4 SP - 461 EP - 485 PB - Lavoisier CY - Paris AN - OPUS4-23853 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -