Auswahl von Materialgesetzen und Parameteridentifikation für nichtlinear-elastische Werkstoffe

Selection of Material Laws and Identification of Material Parameters for Nonlinear Elastic Materials Elastomer components are used for a wide range of applications (e.g. seals, load introduction and damping elements, coatings). Their importance for the proper function of complete subassemblies has continuously increased over the last years. Despite the comparatively low cost of elastomer parts the design and testing of these components requires a high standard of expertise and thorough understanding. Modern analysis and appropriate software tools (e.g. finite-element codes) are utilized by manufacturers and customers (OEMs) to simulate the behavior of elastomer components under operational conditions. Realistic geometries and boundary conditions can be investigated at acceptable expenses. The quality of the results obtained depends substantially on an accurate model for the complicated material behavior. This article provides an insight into development and application of material laws which describe the hyperelastic and viscoelastic behavior of elastomer materials. Suitable experimental and numerical procedures are presented to identify the material parameters. The verified material models are input to structural analyses, dimensioning and assessment of strength and long-term behavior for elastomer components.     

Werkstoffe und Oberflächenmodifikationen – Schlüssel für eine ökonomische Spritzgießfertigung

Materials and surface modifications – Keys to an economical injection moulding An economical injection moulding includes a cost‐effective tool production, a free‐moving tool, a production which consumes low amounts of resources and runs with short cycle times and last but not least a low need of tool repair all over the life‐time of the tool. It can be shown, that no material can satisfy all the mentioned demands. So it is advisable that these properties which are determined by the properties of the tool surface can be performed by a coating. Those properties which are characteristics of the tool volume can be performed by a suitable base material. Following this concept it is possible to configure a light weight tool which is running without maintenance for a long time and makes short cycle times possible. It will be shown that a tool body produced by applying an aluminium alloy finally coated with an electroless applied nickel‐plating is one possibility to achieve the aim.     

Reibmodelle für elastomere und thermoplastische Werkstoffe und ihre Implementierung in Finite-Elemente-Codes

Polymer Friction Models And Their Implementation Into Finite-Element-Codes In order to support the development of seals and other frictioninvolved parts by numerical simulation methods an exact modeling of the frictional behavior is of essential importance. In case of polymeric materials the friction coefficient significantly depends on real contact area, contact stresses, relative sliding velocity and temperature. This cannot be described with the classical Coulomb-Friction-Model and advanced friction models are not commonly available in commercial FE-Codes. Therefore such advanced friction models have to be formulated and implemented by the users. In this article results of calculations with an implemented friction model are shown. Calculations of contact generation dependent on normal load are compared with the analytical results of the Hertzian Theory. Comparing the results of different FE-models the influence of discretisation is discussed. For verification purposes experimentally determined friction coefficients are listed.     

Laser CVD – Status und industrielles Potential für Faserbeschichtungen

Laser activated CVD can be applied in different ways: (i) wide area coating having the potential of continuously coating temperature sensitive substrates (parallel beam), (ii) coating on shaped parts, e. g. fibres, (iii) micro structuring/ patterning, e. g. for rapid prototyping or repair of wafers, (iv) build‐up of 3‐dimensional microstructures on substrates under for designing/making microsystems, (v) forming nano‐powders with narrow size distribution, e. g. for advanced ceramics. Evaluation of the industrial potential of the most prospective developments is underway. One of these areas being covered more in detail comprises high speed coating of fibers. The fibres are used for manufacturing damage‐tolerant fiber reinforced ceramic composites. Based on a industrial 6 kW cw‐CO2 laser, an atmospheric pressure laser CVD process has been established which performs continuous coating of fiber bundles. The laser CVD method is characterized by several significant advantages, among them deposition rates of typically > 1 μm/s, small volume cold‐wall reactors, and short residence time of the fibers in the deposition chamber, which avoids fiber degradation. As another feature favoring industrial application, the process can be performed at atmospheric pressure in an open reactor with a continuous air‐to‐air coiling of the fiber bundles. The prototype laser CVD reactor established at Fraunhofer Institute is equipped with in‐situ FTIR sensorics for process monitoring and chemistry control. Cost distribution analysis is used for making preliminary efficiency assessment of the innovative coating process.     

Konvergente Elektronenbeugung in der analytischen Elektronenmikroskopie keramischer Werkstoffe – eine Anleitung für die Praxis

Convergent beam electron diffraction (CBED) is introduced as a complementary method to analytical electron microscopy. Unlike selected area diffraction (SAD) spatial resolution of CBED is not aperture limited, but a function of probe size only. The three-dimensional reconstruction of crystal lattices is possible because of excitation of higher order laue zones (HOLZ) with the HOLZ line symmetry providing a fundamental criterion for the determination of point and space groups respectively. Some typical applications for CBED from carbide and nitride materials are discussed. Practical advice is given how to run the scope for CBED and get the most out of it.     

Glasartiger Kohlenstoff Sigradur® – ein Werkstoff für Chemie und Technik

Glassy Carbon Sigradur® – a Material for Chemistry and Technology Glassy carbon is a carbon modification characterized by its glasslike fracture behaviour. Raw material, manufacturing, microstructure, and studies on fracture mechanics are discussed and examples for the widespread application of glassy carbon are given.     

Diffusionssperrschichten für Polymere – Messtechnische Herausforderung

Barriere Coatings on Polymers – A Challenge for the Measuring Technique The sustainment of the potency and thus the shelf life of many pharmaceutical compounds for medical purposes such as antibiotics, infusions, enzymes, and vitamins as well as cosmetics, different (convenient) foods and beverages is limited and depends on the barrier properties of their packaging. This limitation is mainly related to the long‐term storage of certain agents and flavorings and accordingly their natural sensitivity on oxygen and water vapor, which are part of our atmosphere. On one hand there are latent risks seriously compromising the reliability of products, while on the other hand technical improvements to avoid these risks are available. Furthermore, the permeation measuring technique has made progress, whereby health risks through deterioration of such products are correspondingly reduced. In the context of product quality and health, problems related to “hidden cause – disastrous effect” should be avoidable in future.     

EVICD – eine Lebensdauermethode für komplexe mehrachsige Betriebsbelastungen für die Praxis

EVICD – an advanced crack intiation life prediction method for engineering application In the present paper an overview of the latest stand in the development of EVICD, a crack initiation life prediction method for arbitrary multiaxial loading, is given. The incremental prediction method which was originally proposed by W. Ott and which was later extended by the introduction of a secondary damage parameter either based on the normal stress on the planes with maximum shear stresses (EVICD‐N) or the normal stress on the octahedral planes (EVICD‐J1) has been further developed: A special Input Section was created, which is open to all important types and formats of engineering input data for fatigue calculations. The results of strain measurements can also be taken. Further on, the multiaxial Neuber‐Method has been worked in for a fast determination of the elastic plastic stresses and strains at fatigue critical locations of components. At the end of the Input Section the elastic plastic stress or strain path at the fatigue critical location is transferred to the damage evaluation modul of EVICD for an evaluation of the crack initiation life. The Mróz‐Garud plasticity model has been worked in the damage evaluation model. The fatigue damage evaluation does occur after a transparent flow diagram and has been realized as a FORTRAN Code. This is important for a general use of EVICD in practice. Meanwhile EVICD has been verified on a broader basis. A representation of the prediction results after EVICD vs. the corresponding experimental results after a proposal of E. Haibach shows, that the prediction capability of EVICD has become better than that of conventional fatigue prediction methods.     

Sicherheitnorm DIN EN 1012 – 2 für Vakuumpumpen und VBG 16

The European Standard EN 1012 – 2 Compressors and vacuum pumps – safety requirements is established in March 1996. The English text will be published in 1997. This standard is deduced from the ?Mashinery directive”? which has the state of a law in all EC member states and superseeds all so far existing national standards on this subject. In Germany for vacuum pumps it is the ?Unfallverhütungsvorschrift für Verdichter”? (compressors and vacuum pumps) VBG 16, which now is partially replaced by the new standard EN 1012. In the following the contents and the mode of employment of the new standard is discussed.     

Organische Polymere als funktionelle Werkstoffe für chemische Sensoren

Organic polymers as functional materials for chemical sensors The function of many chemical sensors for measurements in liquids and in gases with ambient temperature is based on the combination of a transducer with organic membranes. These membrans determine essential sensor properties as selectivity, sensitivity and response characteristics. In addition they protect the detection system against external influences. Therefore the selection and synthesis of polymer membranes are an essential constituent of the sensor investigation and sensor development. Electrical, optical and biological properties of the polymers are important in this case. A survey of the materials used in the remote sensing is given. Of special interest to the sensor investigation are in last time intrinsic conducting polymers (ILP) whose properties opened new possibilities of the sensor development. With the help of an electrochemical pH glass electrode with inner solid contact it is shown that polypyrrole can be used as a material for a long‐lived inner solid contact and as substitute for inner secondary reference electrode. Practice tests confirm the suitability of this polymer material. Aspects of the transport mechanism of electrical charges through the boundary surface conducting polymer | glass are discussed.     

Oberflächen‐ und Dünnschichtanalytik – unverzichtbares Werkzeug für Schichtentwicklung und ‐produktion

Surface and thin film analysis – indispensable tool for coating development and ‐production Development and production of thin films for functional coating on special materials is unalterable combined with a permanent quality control and therefore use of sophisticated analysis and measurement techniques. The field of interest is belonging to all steps of the production chain, starting with the characterization of the substrate surface (e. g. glass, plastics), followed by polishing and cleaning processes up to depth profiling of complex multilayers. The typical analyses are focused onto topographical and chemical features and their influence onto the product functionality. The use of surface and thin film analytics for problem oriented characterization is demonstrated by a few examples, which deal with surface roughness, contamination, impurities and dopand profiles as well as composition variations in the surface near region.     

Festwalzen – eine Technologie für effizienten Leichtbau

Deep Rolling – a technology for efficient lightweight design Deep rolling is a proven method for increasing the fatigue strength of dynamically loaded parts. Although this application has been used for many years, procedures that induce work hardening and residual stresses are not well known. This article concerns both deep rolling and the potential for considering the resultant residual stresses in the design phase of components to achieve efficient lightweight design. In addition, the article includes new research results regarding the numerical modelling of deep rolling.