TY - JOUR A1 - Stark, Wolfgang A1 - Döring, Joachim A1 - Walentowski, Heinz-Ulrich T1 - Crosslinking Instead of Glassy Transition 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 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 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 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 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 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 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 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 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 U6 - 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 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 -