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Eingeladener Vortrag
- nein (3)
The investigation of low temperature properties of elastomeric sealing materials by means of thermo-analytical methods is a sound way to get information about the glass transition process.
The breakdown temperature of the sealing function of O-ring seals was measured in a component test setup depending on material and degree of compression.
An in depth explanation of the observed component tests behaviour is currently in preparation. It requires the results of thermo-analytical methods and measurements as the compression set (not shown here). With that, a model was developed to describe the correlation between physical material parameters and observed component behaviour.
Rubbers are often used for seal applications due to their special material properties and easy use. In many applications the material is exposed to low temperatures during Operation. Therefore it is important to know the material behavior at low temperatures to determine the temperature ränge that allows a Safe Operation of the seal, e.g. in storage and transport Containers for radioactive materials.
The seal function of an elastomer is limited in temperature by the rubber-glass transition during which the material properties change from rubber-like to stiff and glass-like. For a given application this correlation is not trivial and therefore needs an in-depth investigation under consideration of the physical properties and the
application conditions.
In this work different analytical methods are used to characterize the material behavior at low temperature in the ränge of the glass-rubber-transition and are compared with the quality of Operation of a component which is here defined by the detected leakage rate.
The prospects of modern thermoanalytical methods for characterisation
of flow, curing and final mechanical behaviour of
moulding compounds were demonstrated. Using urea resin
moulding compounds from different manufacturers the possibilities
of the various techniques could be shown. With comparatively
low effort, fundamental information can be gained
before production process had been started. On this basis it is
possible to make appropriate material selection at an early
point in the process chain. On the basis of thermoanalytical
data an incoming goods inspection can be established. Also it
is easy to control the compliance with the conditions of delivery.
In some cases it could also be helpful to have stored analysis
data especially when problems appear in manufacturing
process or unexpected part damages occur
With the ultrasound measuring system it is possible to transfer
the findings from the analytical methods directly to the processes
in the mould. The application of ultrasound provides
Dynamic Mechanical Analysis in the mould. Beside quality
assurance ultrasound can also be used for process optimisation,
especially for reduction of cycle time. In an advanced form
ultrasound information can be used as a basis for improved
machine control based on material state. The ultrasound measuring
system developed by ISK Iserlohn and BAM can be
obtained from the ISK.
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 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.
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.
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