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.     

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).     

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.     

Präparation und Charakterisierung von nanokristallinem ZrO2

Preparation and characterization of nanocrystalline ZrO₂ Synthesis routes for the preparation of nanocrystalline ZrO₂ as a component of heterogeneous catalysts are briefly discussed. Especially the relation between the phasecomposition and the synthesis parameters is investigated. The use of RAMAN spectroscopy for the phase determination of highly amorphous samples with high surface areas is illustrated.     

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.     

Charakterisierung von Randentkohlungsvorgängen bei der Austenitisierung des Wälzlagerstahls 100Cr6. Teil 1: Korrelation zwischen Randschichteigenschaften und Kohlenstoff‐Tiefenverlauf

Characterization of Decarburisation Processes During Austenitising of the Rolling Bearing Steel 100Cr6. Part 1: Correlation between Rim Zone Properties and Carbon Concentration Profile The influence of a decarburisation process during austenitising of the through‐hardenable rolling bearing steel 100Cr6 (SAE 52100) on the rim zone properties of the martensitic through‐hardened material was investigated by means of material analysis and diffusion calculations. For this purpose, two specimens were prepared under defined heat treatment conditions, and the near‐surface carbon distribution was determined micro‐chemically by using secondary ion mass spectrometry (SIMS). In part 1 of the present work, these concentration profiles are compared with the depth variation of the micro‐hardness and with the distance curves of the residual stresses and the line broadening ({211} α'‐Fe diffraction line) both measured by X‐ray diffraction (XRD). In addition, microstructure investigations were performed. In part 2, a refined kinetics model of a diffusion‐controlled reaction based on the finite element method (FEM) will be applied to the decarburisation process in order to describe the carbon distributions obtained.     

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.