Querschnittseinfluss beim Zugversuch von siliziertem kohlenstoffkurzfaserverstärktem Kohlenstoff (C/C‐SiC)

On the influence of cross section in tensile tests of siliconized short carbon fibre reinforced carbon (C/C‐SiC) This study deals with the mechanical testing of a carbon short fibre reinforced ceramic. For this material group, which has already been successfully used in several applications, no valid testing specifications are existing at present. This is one of the reasons why manufacturers and research institutes often make use of test standards for monolithic or composite materials. In these tests, sample cross sections and testing volumes are choosen freely or on the basis of a standard and are accordingly adapted by an appropriate factor. This approach can lead to misinterpretations. Because of the broad variety in the different kinds of fibre reinforced ceramics, this study examines the influence of cross sections in tensile tests in an examplary study on a siliconized short carbon fibre reinforced carbon of the Schunk Kohlenstofftechnik GmbH labeled FU2952/1P77. In order to verify the test results, the fracture surfaces will be examined by means of incident light photography and scanning electron microscopy (SEM).     

Ermittlung mechanischer Kenndaten von Kohlenstoffaserverstärktem Kohlenstoff (CFC) mit dem Biege- und Zugversuch

Research on Mechanical Data of Carbon Reinforced Carbon (CC) in Bending and Tensile Mode CC is a ultra high temperature material used until 2200°C in inert atmospheres. The testing geometries of reinforced carbon (CC) are not standardized in West Germany today. Therefore the SIGRI GmbH has defined material specific geoand tensile mode. It is shown, that the tensile strength has a higher level than the bending strength when the laminate orientation is (0/90°). When the laminate has a (0/± 45/90°)-orientation, the relation is inverted. If the laminate orientation is known, the fracture mode can be predicted.     

Veränderung des elektrochemischen Korrosionsverhaltens und der mechanischen Eigenschaften von C/Al-Verbunden durch Faserbeschichtungen aus SiC und pyrolytischem Kohlenstoff

Changes of the electrochemical corrosion behavior and the mechanical properties of C/Al-composites due to SiC and pyrolytic carbon fiber coatings The following contribution describes the modification of the electrochemical and mechanical behavior of carbon fiber reinforced pure aluminum (C/Al-composite) due to two different fiber coatings. Tests include potentiodynamic corrosion tests, Transmission electron microscopy, bending tests and single fiber-“push in”-tests. The potentiodynamic corrosion tests were carried out in 3,5 wt.% NaCl solution. The results give evidence of a considerable decrease of the corrosion resistance of the C/Al-composites due to the application of the pyrolytic fiber coating. The SiC coating improves the corrosion resistance of the composite. However, the mechanical properties of the composites were harmed by the SiC coating. The pyrolytic carbon coating leads to a remarkable energy dissipation due to “stick-slip” effects on the interface under load. Consequently, the application of suitable multilayers of pyrolytic carbon and SiC fiber coatings could result in improved electrochemical and optimized mechanical properties of the C/Al-composite.     

Ermittlung des Festigkeits‐ und Schädigungsverhaltens von Airbaggewebe bei verschiedenen Belastungszuständen und Dehnraten

Determination of strength‐ and failure behaviour of airbag fabric subjected to different types of loading This paper presents experimental investi‐gations of the material behaviour of a typical airbag fabric (Polyamid 6.6) at different loading types and strain rates. Fundamental results are a linear decrease of failure stress and a linear increase of failure strain with increasing temperature. Another important material parameter of airbag fabric, the burst pressure where the fabric bursts, was measured as 4‐5 bar. The determined material data are important for the fabrication of airbags.     

Das Grenzflächenverhalten von SiC und seine Anwendung in faserverstärktem Aluminium

The interface Behavior of Sic and its Application to Fiber Reinforced Aluminium SiC barrier layers on carbon fibers can be deposited by thermal decomposition of methyl trichlorosilane. The influence of the CVD parameters on their structure and composition is presented by the results of surface-analytical and electronmicroscopical investigations. During the preparation of fiber reinforced Al chemical reactions and segregation effects result in the formation of undesirabled phases at the interface between matrix and fiber. The stability of the barrier layer is negativly influenced by it.     

Untersuchungen an stahlfaserverstärktem Aluminium unter Torsions- und Druckbeanspruchungen

Investigation of Steel Fiber Reinforced Aluminium under Torsional and Compressive Loading A fiber-shaped composite material which, due to its fabrication process and internal structure may be called a double fiber composite, and whose strength behaviour is significantly influenced by boundary layers and porosity has been tested by means of two test methods:

• 1 The possibility is demonstrated to determine by a non-destructive elastic torsional test the useful cross section for the utilization of the material, taking the quality-reducing factors into consideration.
• 2 Pressure tests have shown good agreement with Timoshenko and Gere's wave theory extended in this particular case.

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Charakterisierung des Delaminationsverhaltens von Schichtverbunden unter Mode I- und Mode II-Belastungen

Characterization of the delamination behaviour of composites under mode I- and mode II-loading In order to determine fracture toughness properties of fibre-reinforced polymers the „Double Cantilever Beam”︁-test (DCB) has been used for mode I loading and the „End Notched Flexure”︁-test (ENF) for mode II loading. By these methods the energy release rate G and the corresponding R-curve (crack resistance curve) have been measured which characterise the crack resistance of the material against delamination. Especially the influence of fibre coatings, different structures of the laminate, and matrix modifiers on fracture toughness have been examined for epoxy as well as for thermoplastic composites (polyamide and polypropylene/glass fibres).     

Ellipsometrische Charakterisierung von C‐Schutzschichten für die Speichertechnologie

Spectroscopic Ellipsometry is a fast, non‐destructive and reliable method for characterizing thin films, based on interaction between incident light and a multilayer system. For our investigations, light in the visible spectral range has been used to characterize protective carbon coatings with thicknesses of 2‐7nm on magnetic hard disks. The specific disk layer stack has been described with an adequate one‐layer model. With regard to an accurate analysis of the covering carbon coating a reproducible procedure for determining the underlying metallic material has been developed. The measured ellipsometric parameters (ψ, Δ) display a linear dependence on carbon film thickness which shows an appropriate application of the used model down to a thickness of 2 nm. By means of simulation calculations, criteria for the selection of optimized wavelengths with respect to film characterization has been established. Furthermore, an increasing extinction coefficient κ with rising nitrogen content in the carbon coating could be stated. Apparent time instabilities in the determination of layer thickness d and extinction coefficient κ of the carbon film could be explained as due to adsorption processes on the surface.     

C/C‐SiC Composites for Advanced Friction Systems

Ceramic Matrix Composites (CMC), based on reinforcements of carbon fibres and matrices of silicon carbide, show superior tribological properties in comparison to grey cast iron or carbon/carbon. In combination with their low density, high thermal shock resistance and good abrasive resistance, these Si‐infiltrated carbon/carbon materials, called C/SiC or C/C‐SiC composites, are promising candidates for advanced friction systems. Generally, the carbon fibres lead to an improved damage tolerance in comparison to monolithic SiC, whereas the silicon carbide matrix improves the wear resistance compared to carbon/carbon. In combination with new design approaches cost‐efficient manufacturing processes have been developed and have lead to successfully tested prototypes of brake pads and disks, especially for passenger cars and emergency brake systems.     

Experimentelle und analytische Untersuchung des out‐of‐plane‐Verhaltens von unbewehrten Mauerwerkswänden unter Erdbebenbelastung

Experimental and analytical investigation of the seismic out‐of‐plane behavior of unreinforced masonry walls In addition to the vertical and horizontal load‐bearing in‐plane, masonry must also withstand out‐of‐plane loads that occur in earthquake scenarios. The out‐of‐plane behavior of unreinforced masonry walls depends on a variety of parameters and is very complex due to the strong non‐linearity. Current design methods in German codes and various international codes have not been explicitly developed for out‐of‐plane behavior and contain considerable conservatism. In the present work, shaking‐table experiments with heat‐insulating masonry walls have been conducted to investigate the out‐of‐plane behavior of vertical spanning unreinforced masonry walls. As shown in previous numerical investigations, important parameters are neglected in existing design and analysis models and the out‐of‐plane capacity is underestimated significantly. In the conducted experiments the results of these numerical investigations are verified. Furthermore, the development of an analytical design model to determine the force‐displacement relationship and the out‐of‐plane load‐bearing capacity considering all significant parameters is presented.     

Herstellung und komplexe Charakterisierung von Metall‐Keramik‐Verbundschichten

Formation and characterization of metal‐ceramic coatings The influence of the formation process and used materials of metal‐ceramic coatings on the structural properties of the deposited layers were investigated and optimized to increase the mechanical properties. There the deposition of the metal‐ceramic‐layers occurred by a combination of electrophoretic and galvanic deposition with siloxane as bonding compound. Layers with a high ceramic content were successfully created. As ceramic components commercial silicon carbide and silicon nitride were used. Nickel and Copper respectively were applied as metal component to fill the porous ceramic structure with the aim to increase the strength of the layers, where nevertheless a pre nickel‐plating or pre cupper plating of the steel substrate X6Cr17 before ceramic component deposition had to be done to increase the adhesion of the layers. The layer characterization was made by optical microscopy and scanning and transmission electron microscopy, where especially the bonding of the single particles by the siloxane was in evidence.     

Charakterisierung von Glas und Glasbeschichtung mittels oberflächensensibler Sondenverfahren

The presented results of investigations by surface and microanalytical methods confirm the suitability of electron beam and scanning probe techniques for process monitoring, support of process development and defect analyses in the glass industry. More and more glass and coating specialists use the high tech service provided by an external laboratory with its wide range of experience and knowledge.     

Das zyklische Spannungs-Dehnungs-Verhalten metallischer Faserverbundwerkstoffe am Beispiel von stahlfaserverstärktem Silber und Kupfer

The Cyclic Stress-Strain Behaviour of Metallic Fibre Reinforced Composites – a Study of Steel Fibre Reinforced Silver and Copper Under fatigue loading conditions unidirectionally reinforced fibrous composites often show a cyclic stress-strain behaviour which can not be simply explained by the properties of the components but only by their cooperation in the composite (so-called synergetic effects). The observed behaviour may either result from the composite production process or subsequent heat treatments and is usually attributed to residual stresses between the matrix and the fibres and the distribution of the fatigue load on the components. Some experimental observations in steel fibre reinforced copper and silver are discussed. Deviations from the initially expected stress-strain response may lead to premature damage of the composite. On the other hand, the effects may also be used for the improvement of fatigue loaded fibre reinforced composites.     

Abscheidung,Charakterisierung und Anwendung von Plasma‐Polymerschichten auf HMDSO‐Basis

Deposition, Characterisation and Application of HMDSO‐based Plasma Polymer Films High quality organosilicone coatings can be produced via plasma enhanced chemical vapor deposition of hexamethyldisiloxane (HMDSO). In this article aspects of deposition, analysis and application of HMDSO/O₂ processes are presented. The coatings’ organic/inorganic character can be adjusted by an appropriate combination of plasma power and gas mixture which is shown by XPS. Particularly multi layer and gradient layer systems can be deposited within the same process. Quantitative chemical depth profiling of such layer systems can be performed by secondary neutral mass spectrometry (SNMS). AFM investigations exhibit that the surface roughness of the coatings is determined by the appearance of hemispherical agglomerates, which is more pronounced, the more glass‐like the coatings are. As an example of use it is shown, that an appropriate HMDSO plasma treatment can distinctly improve the tribological behavior of elastomer devices. The presented work is done within a project of the German Federal Ministry of Education and Research (BMBF) entitled: “nano functionalization of interfaces for data‐, textile‐, building‐, medicine‐, bio‐, and aerospace‐ technology”.     

Grenzflächenpressung von Eisenwerkstoffen und Leichtmetallen unter kontinuierlicher Beanspruchung

Limiting surface pressure under continued pressure of ferrous and lightweight metals In this article the results of tests examining the limiting surface pressure of ferrous and light weight metals are presented. The tests were carried out under consistent conditions using a standardised test procedure.     

Charakterisierung des tribologischen Verhaltens von keramischen Gleitpaarungen mit moderner Oberflächenanalytik

Characterization of the Tribological Behaviour of Ceramic Sliding Couples with Modern Surface Analysis Methods Dry friction and wear tests were performed in ambient atmosphere with various self-mated couples of SiC, Al₂O₃, Si₃N₄ and ZrO₂. The temperature was varied between 22 °C and 1000 °C and the sliding velocity between 0.03 m/s and 5 m/s. Normal force, temperature and sliding velocity are kept constant during the tests. The materials and wear mechanisms were characterized by various surface analytic methods – optical microscopy, scanning electron microscopy, transmission electron microscopy, electron microprobe analysis, IR-spectroscopy, X-ray diffraction, auger electron spectroscopy and X-ray photoelectron spectroscopy. High wear/low wear transitions could be explained. On the basis of these results new ceramic materials with lower friction and/or wear were selected or successful developed.