TY - JOUR A1 - Stark, Wolfgang A1 - Döring, Joachim A1 - Walentowski, Heinz-Ulrich T1 - Crosslinking Instead of Glassy Transition JF - Kunststoffe : bilingual edition, German + English N2 - In processing fibre-reinforced composites, the curing reaction can be significantly retarded if the temperature and reaction time are not optimally set. In such situations, complete curing is sometimes impossible under practically relevant conditions. It is difficult for processors to recognize or detect incomplete curing. The equilibrium glass transition temperature plays an important role in complete curing in the production process. PY - 2000 SN - 0945-0084 VL - 90 IS - 4 SP - 33 EP - 35 PB - Hanser CY - München AN - OPUS4-822 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Stark, Wolfgang A1 - Döring, Joachim A1 - Walentowski, Heinz-Ulrich T1 - Vernetzen statt Verglasen JF - Kunststoffe / Deutsche Ausgabe PY - 2000 UR - http://www.kunststoffe.de/ku/default.asp SN - 0023-5563 VL - 90 IS - 4 SP - 90 EP - 92 PB - Hanser CY - München AN - OPUS4-823 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Döring, Joachim A1 - Stark, Wolfgang A1 - Mc Hugh, Jarlath A1 - Bartusch, Jürgen T1 - Ultrasound on-line cure monitoring for industrial applications JF - Advanced composites letters N2 - In recent years eure monitoring with ultrasonic methods became more important. An on-line measurement System for industrial applications is presented in this paper. It operates in through-transmission and the measured parameters are the sound velocity and the attenuation of the sound wave. An objective of this paper is to establish the ränge of possible applications for an ultrasonic eure monitoring System. KW - Ultrasonic monitoring KW - Cure process KW - Composite material KW - Process controlling PY - 2000 SN - 0963-6935 PB - Woodhead Publ. CY - Cambridge AN - OPUS4-1061 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Stark, Wolfgang A1 - Döring, Joachim A1 - Kelm, Jürgen T1 - Ultraschall on-line Prozesskontrolle bei der Vulkanisation JF - Kautschuk, Gummi, Kunststoffe (KGK) KW - Prozesskontrolle KW - Vulkanisation KW - Ultraschall KW - Sensoren KW - Schubmodul KW - Verlustmodul PY - 2000 SN - 0948-3276 SN - 0022-9520 SP - 9 Seiten PB - Hüthig CY - Heidelberg AN - OPUS4-997 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Fengler, Petra A1 - Stark, Wolfgang A1 - Döring, Joachim A1 - Mc Hugh, Jarlath T1 - Coupling of hidden ultrasound sensors to a moulding tool JF - The e-journal of nondestructive testing & ultrasonics N2 - Ultrasound on-line NDT methods have been demonstrated as a useful tool for monitoring the curing reaction of thermosets. In order to achieve this ultrasound sensors are incorporated into compression, injection and RTM (resin transfer) mould. For many commercial products imprints or any surface markings upon the moulded product are undesirable. Due to its physical properties ultrasound has a large advantage over other techniques for similar applications. The sound wave can pass through the wall of the mould and direct contact with the moulded part is not required. In this particular case one fundamental problem is a good coupling of the sensors to the mould wall. Several mediums came into question but because of the high technical (e. g. temperature and long time stability) and practical demands, it was decided that dry (non-fluid) coupling would be the most promising candidate. A handful of coupling foils suitable also at high temperatures and for long time application under industrial conditions were tested and are presented in this paper. KW - Sensors KW - Ultrasound KW - Mould wall coupling KW - Thermoset manufacturing PY - 2004 UR - http://www.ndt.net/article/v09n03/stark/stark.htm SN - 1435-4934 VL - 9 IS - 3 SP - 1 EP - 10 PB - NDT.net CY - Kirchwald AN - OPUS4-3316 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Döring, Joachim A1 - Stark, Wolfgang T1 - Ultrasonic Production Control JF - Kunststoffe : bilingual edition, German + English N2 - Ultrasound waves penetrate solid objects without damaging them. Their fields of application range from the imaging of internal organs in medicine, to interior testing of mechanical and chemical engineering components. However, ultrasonic systems can also be used to visualise the way the mechanical properties of reactive resins change during processing in the mould. PY - 2001 SN - 0945-0084 VL - 91 IS - 1 SP - 35 EP - 36 PB - Hanser CY - München AN - OPUS4-2135 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Döring, Joachim A1 - Stark, Wolfgang A1 - Bartusch, Jürgen A1 - Mc Hugh, Jarlath T1 - Contribution to ultrasound cure control for composite manufacturing JF - The e-journal of nondestructive testing & ultrasonics N2 - The curing conditions play an important role in the quality assurance of composite products. Especially as composite materials are widely used in high tech areas so that they are required to fulfil high quality Standards. Some problems which occur during curing, for instance undercuring, can hardly be detected using Standard NDT investigations, mainly because they are manifested only at high temperatures, particularly close to glass-rubber-transition. On-line eure monitoring has the outstanding advantage that it can monitor the material parameters even at the highest temperatures possible. In recent years eure monitoring with ultrasonic methods has become more populär. In comparison to dielectric methods mechanical parameters are measured directly. The quantities to be measured are the velocity and the attenuation of the sound wave. On this basis the storage and loss modulus can be calculated. Depending on the form of excitation with longitudinal or transversal waves these moduli are referred to as long wave or shear modulus. Well developed Computer based technology and sensor materials are available in the non-destructive testing (NDT) market. The measuring equipment employed a commercial NDT System, which worked computer-aided. With a special Software the demands of automatic Operation under industrial conditions was accomplished. This measurement equipment was tested on composites. Its structure, performance and some practical results will be presented in the following paper. T2 - 15th World Conference on Non-Destructive Testing (WCNDT) CY - Roma, Italy DA - 15.10.2000 PY - 2000 UR - http://www.ndt.net/article/wcndt00/papers/idn482/idn482.htm SN - 1435-4934 VL - 5 IS - 11 PB - NDT.net CY - Kirchwald AN - OPUS4-2136 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Döring, Joachim A1 - Stark, Wolfgang T1 - Produktionskontrolle mit Ultraschall JF - Kunststoffe / Deutsche Ausgabe N2 - Ultraschallwellen durchdringen Festkörper, ohne sie zu schädigen. Der Einsatzbereich von Ultraschall reicht von der Darstellung der inneren Organe in der Medizin bis zur Prüfung des Inneren von Bauteilen im Maschinen- und Anlagenbau. Ultraschall-Systeme können jedoch auch genutzt werden, um sichtbar zu machen, wie sich mechanische Eigenschaften von Reaktionsharzen während ihrer Verarbeitung im Werkzeug verändern. PY - 2001 UR - http://www.kunststoffe.de/directlink.asp?KU101838 SN - 0023-5563 VL - 91 IS - 1 SP - 83 EP - 85 PB - Hanser CY - München AN - OPUS4-2137 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bovtun, Viktor Petrovic A1 - Döring, Joachim A1 - Bartusch, Jürgen A1 - Gaal, Mate A1 - Erhard, Anton A1 - Kreutzbruck, Marc A1 - Yakymenko, Y. T1 - Enhanced electromechanical response of ferroelectret ultrasonic transducers under high voltage excitation JF - Advances in applied ceramics N2 - Polypropylene based ferroelectret films exhibit a strong electromechanical activity and provide a promising solution for the air coupled ultrasonic (ACUS) transducers. Ultrasonic transmission between two air coupled ferroelectret transducers in dependence on the amplitude and polarity of the high voltage exciting pulse revealed a strongly non-linear electromechanical response of the ferroelectret transmitter which provides an increase in the transmitter efficiency. The authors present a simple model describing both promotion and competition of the piezoelectric and electrostriction contributions, as well as increase in the transducer constant under high voltage excitation. Enlargement of the inverse transducer constant of the polypropylene ferroelectret film by a factor of 4 was demonstrated. The non-linear properties of the polypropylene ferroelectrets result in a strong increase in their ACUS figure of merit under the high voltage excitation, which exceeds the results of their technological optimisation. Consequently, enhancement of the ACUS system transmission by 12 dB and signal to noise ratio by 32 dB was achieved. KW - Air coupled ultrasonics KW - Non-contact transducers KW - Ferroelectrets KW - Piezoelectric effect KW - Electrostriction KW - Cellular polypropylene KW - Ultrasonic transducer PY - 2013 DO - https://doi.org/10.1179/1743676112Y.0000000021 SN - 1743-6753 SN - 1743-6761 VL - 112 IS - 2 SP - 97 EP - 102 PB - Maney CY - London AN - OPUS4-27880 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Döring, Joachim A1 - Bartusch, Jürgen A1 - Gaal, Mate A1 - Kreutzbruck, Marc A1 - Erhard, Anton A1 - Bovtun, Viktor Petrovic T1 - Ferroelektret-Prüfköpfe für die zerstörungsfreie Prüfung mit Luftultraschall JF - Materials testing N2 - Für die luftgekoppelte Ultraschall-Prüfung wird der Prototyp eines neuartigen Prüfkopfes vorgestellt. Statt eines piezokeramischen Ultraschall-Wandlers mit einer λ/4-Anpassschicht wird eine Ferroelektret-Folie aus schaumförmigem Polypropylen eingesetzt. Durch die außerordentlich geringe akustische Impedanz der Folie reduzieren sich die Reflexionsverluste an den Grenzschichten zur Luft so stark, dass bei diesem Prüfkopf auf eine λ/4-Anpassschicht verzichtet werden kann. Außerdem ist die Folie hochspannungsfest. Sie konnte mit Spannungen von mehr als 3500 V angesteuert werden und erlaubte eine Vorspannung am Ultraschall-Wandler des Empfangsprüfkopfes von 2000 V. Mithilfe der hohen Anregungsspannung stieg die Amplitude des akustischen Prüfimpulses auf das 11,2-Fache. Die Empfindlichkeit des Empfängers erhöhte sich durch die Vorspannung weiter um den Faktor 4,3. Insgesamt steigt die Amplitude am Empfänger also auf das 48-Fache, bei gleichbleibendem Rauschpegel. Ein abschließender Vergleich mit kommerziellen Luftultraschall-Prüfköpfen belegt die Überlegenheit der Folien-Prüfköpfe. Damit rückt der Einsatz einer vollwertigen Impuls-Echo-Technik auch bei der luftgekoppelten Ultraschallprüfung deutlich näher. KW - Prüfkopf KW - Ferroelektret KW - Luftultraschall KW - Zerstörungsfreie Prüfung PY - 2013 SN - 0025-5300 VL - 55 IS - 2 SP - 96 EP - 102 PB - Hanser CY - München AN - OPUS4-27778 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Döring, Joachim A1 - Stark, Wolfgang A1 - Bartusch, Jürgen A1 - Mc Hugh, Jarlath A1 - Simon, W. T1 - Ultraschall-Prozesskontrolle mechanischer Parameter von aushärtenden Polymeren - Inline-Sensorik für die Herstellung von Kunststoffkomponenten JF - MP materials testing KW - Aushärtung KW - Ultraschall KW - Sensoren KW - Materialparameter PY - 2007 SN - 0025-5300 VL - 49 IS - 5 SP - 238 EP - 242 PB - Hanser CY - München AN - OPUS4-14976 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bovtun, V. A1 - Döring, Joachim A1 - Bartusch, Jürgen A1 - Beck, Uwe A1 - Erhard, Anton A1 - Yakymenko, Y. T1 - Air-coupled ultrasonic transducers based on cellular polypropylene ferroelectret films JF - Ferroelectrics N2 - Analysis of the dielectric and electromechanical properties of the cellular polypropylene ferroelectret films (EMFIT) evidences their high potential for the application in the air-coupled ultrasonic transducers. Simple prototype transducers, based on the EMFIT films, were developed and their high sensitivity was proved in the air-coupled ultrasonic experiment. Amplitude and delay time scanned images of the polyethylene step wedge with holes, obtained in both pulse-echo and transmission modes, demonstrate that non-contact ultrasonic imaging with EMFIT transducers is possible. KW - Air-coupled ultrasonics KW - Non-contact transducers KW - Ferroelectrets KW - Electromechanical properties PY - 2007 SN - 0015-0193 SN - 1563-5112 VL - 353 IS - 1 SP - 186 EP - 192 PB - Taylor & Francis CY - New York, NY AN - OPUS4-14977 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Straet, T. A1 - Bayerl, H. A1 - Stark, Wolfgang A1 - Döring, Joachim A1 - Kürten, Ch. T1 - Ultrasonic Measurements on Thermoset Moulding Compounds JF - Kunststoffe : bilingual edition, German + English KW - Ultraschall KW - Fertigungskontrolle KW - Schallgeschwindigkeit KW - Vernetzungsreaktion KW - Qualitätssicherung PY - 2005 SN - 0945-0084 VL - 95 IS - 7 SP - 1 EP - 5 PB - Hanser CY - München AN - OPUS4-10304 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bovtun, Viktor Petrovic A1 - Döring, Joachim A1 - Bartusch, Jürgen A1 - Beck, Uwe A1 - Erhard, Anton A1 - Yakymenko, Y. T1 - Ferroelectret non-contact ultrasonic transducers JF - Applied physics A N2 - Dielectric and electromechanical properties of the cellular polypropylene ferroelectret films (EMFIT), combining strong piezoelectric response with a low density and softness, evidence their high potential for the air-coupled ultrasonic applications. The disadvantage of the low coupling factor is compensated by the extremely low acoustic impedance, which provides excellent matching to air and promises efficient sound transmission through the air–transducer interface. The influence of the electrodes on the electromechanical properties was investigated. Electron beam evaporation technology was adapted to the EMFIT films, and films with both-sided Au and Al electrodes were prepared without reducing or suppressing of the electromechanical properties. Finally, prototype transducers based on the EMFIT films were developed. In spite of the simple construction and absence of matching layers, high sensitivity of the EMFIT transducers was proved in the air-coupled ultrasonic experiment. Amplitude and delay time scanned images of the polyethylene step wedge with holes, obtained in both pulse-echo and transmission modes, demonstrate that non-contact ultrasonic imaging and testing with EMFIT transducers is possible. KW - Piezoelectric film KW - Air borne transducer KW - Non-destructive testing PY - 2007 SN - 0947-8396 VL - 88 IS - 4 SP - 737 EP - 743 PB - Springer CY - Berlin AN - OPUS4-15074 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Stark, Wolfgang A1 - Döring, Joachim A1 - Kürten, C. T1 - Vernetzung reaktiver Kunststoffe mit Ultraschall überwachen JF - Werkstoffe in der Fertigung KW - Elastomer KW - Epoxidharz KW - Phenolharz KW - Vernetzung KW - Vulkanisation KW - Schallgeschwindgkeit KW - Prozesskontrolle PY - 2008 SN - 0939-2629 SN - 0176-6058 IS - 2 SP - 31 EP - 33 PB - Holzverl. CY - Kissing AN - OPUS4-17587 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Stark, Wolfgang A1 - Bartusch, Jürgen A1 - Döring, Joachim A1 - Mc Hugh, Jarlath T1 - Making cure visible: monitoring the crosslinking process using integrated ultrasound sensors JF - JEC Composites Magazine N2 - A special ultrasonic measuring system was developed to monitor the cross-linking process, enabling interaction with the manufacturing process in order to optimise part quality and reduce cycle times. KW - Thermoset KW - Ultrasound sensors KW - Mould KW - Rtm KW - Gelation KW - Vitrification PY - 2008 SN - 1639-965X IS - 38 SP - 64 EP - 66 PB - JEC CY - Paris AN - OPUS4-18610 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Döring, Joachim A1 - Bovtun, Viktor Petrovic A1 - Bartusch, Jürgen A1 - Erhard, Anton A1 - Kreutzbruck, Marc A1 - Yakymenko, Y. T1 - Nonlinear electromechanical response of the ferroelectret ultrasonic transducers JF - Applied physics A N2 - The ultrasonic transmission between two air-coupled polypropylene (PP) ferroelectret (FE) transducers in dependence on the amplitude of the high-voltage exciting pulse revealed a strongly nonlinear electromechanical response of the FE transmitter. This phenomenon is described by a linear increase of the inverse electromechanical transducer constant t33(1) of the PP FE film with an increase of the exciting electrical pulse amplitude. Enlargement of t33(1) by a factor of 4 was achieved by application of 3500 V exciting pulses. The electrostriction contribution to t33(1) can be attributed to the electrostatic force between electrodes and the Maxwell stress effect. The nonlinear electromechanical properties of the PP FE result in a strong increase of its air-coupled ultrasonic (ACUS) figure of merit (FOM) under the high-voltage excitation, which exceeds results of the PP FE technological optimization. The FOM increase can be related to the increase of PP FE coupling factor and/or to the decrease of its acoustic impedance. A significant enhancement of the ACUS system transmission (12 dB) and signal-to-noise ratio (32 dB) was demonstrated by the increase of excitation voltage up to 3500 V. The nonlinear electromechanical properties of the PP FEs seem to be very important for their future applications. KW - Airborne ultrasonics KW - Electret film KW - Transducer KW - Nonlinearity PY - 2010 DO - https://doi.org/10.1007/s00339-010-5752-7 SN - 0947-8396 VL - 100 IS - 2 SP - 479 EP - 485 PB - Springer CY - Berlin AN - OPUS4-21809 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bovtun, Viktor Petrovic A1 - Döring, Joachim A1 - Wegener, M. A1 - Bartusch, Jürgen A1 - Beck, Uwe A1 - Erhard, Anton A1 - Borisov, V. T1 - Air-coupled ultrasonic applications of ferroelectrets JF - Ferroelectrics KW - Air-coupled ultrasonics KW - Non-contact transducers KW - Ferroelectrets KW - Electromechanical properties PY - 2008 DO - https://doi.org/10.1080/00150190802380243 SN - 0015-0193 SN - 1563-5112 VL - 370 IS - 1 SP - 11 EP - 17 PB - Taylor & Francis CY - New York, NY AN - OPUS4-20924 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Döring, Joachim A1 - Bovtun, V. A1 - Gaal, Mate A1 - Bartusch, Jürgen A1 - Erhard, Anton A1 - Kreutzbruck, Marc A1 - Yakymenko, Y. T1 - Piezoelectric and electrostrictive effects in ferroelectret ultrasonic transducers JF - Journal of applied physics N2 - Electromechanical response of polypropylene ferroelectret transducers under application of high-voltage pulses was measured by laser Doppler vibrometry and compared with results of ultrasonic through-air transmission between two ferroelectret transducers. The electromechanical response was completely explained by piezoelectric and electrostrictive effects. The electrostrictive effect dominates at high voltages and provides significant enlargement of the transducer constant, up to factor of 2.5. The induced strain of 1.7% was achieved at – 2000 V. The nonlinear ultrasonic transmission was shown to be well described by the piezoelectric and electrostrictive response of transmitter, except in the range of high negative exciting voltages where some limitation of the transmitted signal was observed. This limitation seems not to be a fundamental one and does not abolish the advantages of high-voltage excitation of polypropylene ferroelectret transducers. KW - Electromechanical effects KW - Ferroelectric devices KW - Piezoelectric transducers KW - Piezoelectricity KW - Ultrasonic transducers KW - Ultrasonic transmission KW - Cellular polypropylene KW - Ferroelectret KW - Electrostriction PY - 2012 DO - https://doi.org/10.1063/1.4759052 SN - 0021-8979 SN - 1089-7550 VL - 112 IS - 8 SP - 084505-1 - 084505-6 PB - American Institute of Physics CY - Melville, NY AN - OPUS4-26806 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -