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Eingeladener Vortrag
- nein (29)
Two different approaches to investigate the local complex conductivity and the surface charge with Scanning Force Microscopy (SFM) techniques are presented. It is shown that the measurement of local electrical properties with SFM leads to interesting information about the composition of electrically heterogeneous surfaces
With an extended contact and non-contact mode scanning force microscope samples with different heterogeneous electrical properties can be characterized. The contact mode method allows the determination of local electric conductivities of heterogeneous systems at the sample surfaces. An interpretation of this behaviour can be obtained in combination with other SFM modes such as topography, friction and compliance used simultaneously. The non-contact mode SFM allows to get more information about the local surface charge of heterogeneous samples. In this paper two new SFM approaches will be discussed on examples of carbon-fibre reinforced, organic and ceramic materials
Das Fließ-Härtungs-Verhalten von Duroplastformmassen wird gegenwärtig nur
unvollständig durch empirische Größen beschrieben. Diese ungenauen und
unsicheren Angaben können zu Schwierigkeiten bei der optimalen Einstellung
der Fertigungsmaschinen des Verarbeiters führen. Insbesondere Veränderungen
der Formmasseeigenschaften während des Transportes und der Lagerung stören
die Produktion. Das vorgestellte Messverfahren mit Ultraschall-sensoren ermöglicht
die schnelle und vollständige Erfassung des Fließ-Härtungs-Verhaltens, auch
während des technologischen Prozesses. Experimentelle Ergebnisse zu
Alterungs-erscheinungen dieser Formmassen illustrieren den Nutzen des
Verfahrens für Formmasse-produzenten und -verarbeiter.
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.
Vernetzen statt Verglasen
(2000)
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.
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.
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.
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.
Zusammenfassung
In diesem Beitrag wird zunächst die für die on-line Prozesskontrolle an duroplastischen Formmassen entwickelte Ultraschallmesstechnik vorgestellt. Die Methode basiert auf der Durchschallung des vernetzenden Materials mit Hilfe von in das Werkzeug integrierten druck- und temperaturfesten 4 MHz-Ultraschallsensoren. Die Auswertung von Schalllaufzeit und Signalamplitude erfolgt vollautomatisch und dient der Berechnung von Schallgeschwindigkeit und -dämpfung. Beide Größen repräsentieren die änderung der mechanischen Eigenschaften infolge der Vernetzungsreaktion. Durch Anwendung auf vulkanisierende Materialien sollte die Anwendbarkeit der bewährten Methode erweitert werden. Im Ergebnis wird gezeigt, dass die Größe des Messeffekts von der Menge an Vernetzer (Schwefelkonzentration) abhängt. Bei ausreichend hohem Vernetzungsgrad zeigt die Ultraschallgeschwindigkeit signifikante, gut auswertbare Resultate, die den Ablauf der Vulkanisation on-line zu verfolgen gestatten. Ein Vergleich mit Vulkameterkurven zeigt große ähnlichkeiten und berechtigt zu der Hoffnung, dass die Methode industriellen Einsatz finden kann.
The application of microwave measurements to the characterisation of rubber compounds vulcanisation is considered. The behaviour of mechanical and microwave (20 GHz) dielectric parameters during vulcanisation was investigated for rubber compounds with different concentrations of active and non-active carbon black. An increase of concentration or activity of carbon black results in the increase of both dielectric permittivity ε?(T) and loss ε?(T) and in the increase of torsion modulus as well. The start of the vulcanisation reaction is indicated by an increase of dielectric permittivity and torsion modulus in all investigated unvulcanised compounds with carbon black. While for compounds with non-active carbon black the vulcanisation can be better indicated by the ε?(T) anomaly, for compounds with active carbon black it is more clearly seen by the change of ε?(T) behaviour.