TY - JOUR A1 - Jaunich, Matthias A1 - Stark, Wolfgang A1 - Wolff, Dietmar T1 - A new method to evaluate the low temperature function of rubber sealing materials N2 - A new method for the evaluation of the low temperature properties of rubber materials is presented. The method emulates the standardized compression set measurement, which is frequently used for sealing materials, but can be performed within a considerably shorter time. The results are compared with the standard test and found to be qualitatively the same. Slight differences are discussed on the basis of the differences in the measurement procedures. Further data evaluation is done by fitting functions to describe the material behaviour. KW - Sealing material KW - Elastomer KW - Compression set KW - Dynamic mechanical analysis KW - Low temperature behaviour PY - 2010 U6 - https://doi.org/10.1016/j.polymertesting.2010.07.006 SN - 0142-9418 VL - 29 IS - 7 SP - 815 EP - 823 PB - Elsevier Science CY - Amsterdam [u.a.] AN - OPUS4-21914 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Buchholz, Uwe A1 - Jaunich, Matthias A1 - Stark, Wolfgang A1 - Habel, Wolfgang A1 - Petersson, B.A.T. T1 - Acoustic data of cross linked polyethylene (XLPE) and cured liquid silicone rubber (LSR) by means of ultrasonic and low frequency DMTA N2 - Partial discharges may cause damage to electrical insulation of high voltage equipment. They initiate elastic waves in the insulating material, e.g. in the stress cone of an outdoor termination. Localisation of the origin of such elastic waves can help to predict serious damaging processes in the electrical insulation. In order to measure and evaluate the wave propagation effects in typical multilayered elastomeric structures, knowledge of the material properties is required. The propagating velocity and the attenuation of longitudinal waves are important parameters. Values for these quantities found in the literature were not appropriate. Therefore, for cross-linked polyethylene (XLPE) and cured liquid silicone rubber (LSR), the longitudinal wave velocity and the attenuation were evaluated in the temperature interval from -20°C to 50°C and in the frequency range from 200 kHz to 600 kHz using a two-sample ultrasound technique. The loss factor was determined from these measured quantities. Additionally, low frequency Dynamic Mechanical Thermal Analysis (DMTA) was applied to investigate LSR and XLPE in a temperature interval between -100 and 50°C and to check qualitatively the ultrasound data. KW - Acoustic propagation KW - Cross linked polyethylene insulation KW - Mechanical variables measurement KW - Silicone rubber PY - 2012 U6 - https://doi.org/10.1109/TDEI.2012.6180250 SN - 1070-9878 SN - 0018-9367 SN - 1558-4135 VL - 19 IS - 2 SP - 558 EP - 566 PB - Institute of Electrical and Electronics Engineers CY - New York, NY AN - OPUS4-26106 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Cappella, Brunero A1 - Stark, Wolfgang T1 - Adhesion of amorphous polymers as a function of temperature probed with AFM force-distance curves N2 - Force–displacement curves have been obtained with a commercial atomic force microscope at different temperatures and probe rates on a thick film of poly(n-butyl methacrylate) and on two films of polystyrene with different molecular weight. In a previous publication [B. Cappella, S.K. Kaliappan, H. Sturm, Macromolecules 38 (2005)1874] the analysis of force–displacement curves has been focused on the stiffness and on the Young's modulus of the samples. In the present publication we consider the temperature dependence of the work of adhesion. We have obtained master curves of the work of adhesion at fixed maximum loads and, by comparing the results of the two analysis, we show that the work of adhesion follows the Williams–Landel–Ferry equation with the same coefficients previously found for the Young's modulus. Furthermore, we show that the temperature dependence of the work of adhesion of the polymers is a consequence of the temperature dependence of the tip–sample contact area and in the end of the temperature dependence of the stiffness and of the elastic–plastic properties of the samples. KW - Atomic force microscope KW - Force-distance curves KW - Indentation KW - Elastic-plastic properties KW - Adhesion KW - Time-temperature superposition principle KW - Glass transition temperature PY - 2005 U6 - https://doi.org/10.1016/j.jcis.2005.09.043 SN - 0021-9797 SN - 1095-7103 SP - 1 EP - 8(?) PB - Elsevier CY - Orlando, Fla. AN - OPUS4-11187 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Stark, Wolfgang A1 - Jaunich, Matthias A1 - McHugh, J. T1 - Carbon-fibre epoxy prepreg (CFC) curing in an autoclave analogue process controlled by dynamic mechanical analysis (DMA) N2 - Carbon fibre prepregs have found widespread application in lightweight constructions. They are based on a carbon-fibre fabric impregnated with reactive epoxy resin. DMA measurements under temperature conditions similar to an autoclave programme were carried out using commercially available prepreg material with a high glass transition temperature. The characteristic of the temperature programme was a dynamic heating segment at 1.5 K/min followed by a longer isothermal segment at 180 °C. The courses of the storage modulus E', loss modulus E'' and tanδ were recorded. The measuring frequency was varied between 1 Hz and 33.3 Hz. Gelation and vitrification are assigned. The influence of the measuring frequency on the time to vitrification and the correlation with DSC are discussed. The reaction does not end even after 10 h curing at 180 °C, which is interpreted as the slow cessation of the reaction caused by vitrification. KW - Prepreg KW - CFC KW - Curing KW - DMA KW - DSC KW - Autoclave KW - Gelation KW - Vitrification KW - Glass transition PY - 2013 U6 - https://doi.org/10.1016/j.polymertesting.2013.09.014 SN - 0142-9418 VL - 32 IS - 8 SP - 1487 EP - 1494 PB - Elsevier Science CY - Amsterdam [u.a.] AN - OPUS4-29479 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bovtun, Viktor Petrovic A1 - Stark, Wolfgang A1 - Kelm, Jürgen A1 - Pashkov, V.M. A1 - Yakimenko, Y. T1 - Characterization of carbon black filled rubber compounds by the Microwave Coaxial Method KW - Dielectric parameters KW - Microwave methods KW - Filled rubber compounds KW - Vulcanisation PY - 2005 SN - 0025-5300 VL - 47 IS - 3 SP - 118 EP - 122 PB - Carl Hanser Verlag CY - München AN - OPUS4-7273 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Jaunich, Matthias A1 - Stark, Wolfgang A1 - Wolff, Dietmar T1 - Comparison of low temperature properties of different elastomer materials investigated by a new method for compression set measurement N2 - The method for the determination of compression set values with a Dynamic Mechanical Analysis (DMA) setup at low temperatures, which was presented previously, allows a much faster and readily automated procedure than the standardized compression set test according to ISO 815-2. This method is applied to a series of different elastomeric materials that are commonly used for sealing applications. The results of the compression set test are compared with results from thermal analysis to allow an in depth comparison of the material behaviour at low temperatures. Furthermore, a comparison between two EPDM materials is presented. These materials show very similar properties determined by thermo analytical methods such as Differential Scanning Calorimetry (DSC) and Dynamic Mechanical Analysis (DMA) but differ clearly in their compression set behaviour. This comparison shows the importance and value of information of the compression set test in addition to thermal analysis to judge the behaviour of sealing materials and confirms the relevance of the new compression set test method for the investigation of low temperature properties of elastomers. KW - Sealing material KW - Elastomer KW - Compression set KW - Dynamic mechanical analysis KW - Low temperature behaviour PY - 2012 U6 - https://doi.org/10.1016/j.polymertesting.2012.07.016 SN - 0142-9418 VL - 31 IS - 8 SP - 987 EP - 992 PB - Elsevier Science CY - Amsterdam [u.a.] AN - OPUS4-26538 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 - 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 - 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 - Braun, Ulrike A1 - Brademann-Jock, Kerstin A1 - Stark, Wolfgang T1 - Cure monitoring of epoxy films by heatable in situ FTIR analysis: Correlation to composite parts N2 - The curing mechanism of an epoxy film containing dicyandiamide (DICY) and an epoxy formulation based on diglycidyl ether of Bisphenol A (DGEBA) polymer was studied as a function of various temperature programs. The investigation was performed in situ, using a thin film of the epoxy mixture on a silicon wafer substrate in a heatable transmission tool of a FTIR spectrometer. Based on these model-curing experiments, a major curing mechanism was proposed, taking into account the appearance, the decrease, and the development of characteristic bands at various temperatures. The conclusions of the model curing were correlated to FTIR measurements on a real, 50-mm-thick glass fiber reinforced component composite part from a technical process. It could be shown that characteristic bands that develop at curing temperatures above 150°C appear especially in the center of the thick sample. From the chemical or molecular point of view, this demonstrates the established technician's understanding that temperature control inside a large-scale fiber composite of, for example, aircraft, wind-turbine, automotive applications component is of major importance. KW - Crosslinking KW - Resins KW - Spectroscopy KW - Thermosets KW - Thermal properties PY - 2014 U6 - https://doi.org/10.1002/APP.39832 SN - 0021-8995 SN - 1097-4628 VL - 131 IS - 3 SP - 39832, 1 EP - 10 PB - Wiley InterScience CY - Hoboken, NJ AN - OPUS4-30716 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -