Papers by Keyword: C/C

Abstract: Carbon fibre reinforced carbon composites (C/C) are characterised by their excellent thermal, chemical and mechanical properties. The intrinsic porosity and fibre reinforcement grant them an excellent damage tolerance. The production of complex structures is time consuming and very expensive. An innovative approach to this topic is the integration of simple geometric ceramic composite materials within complex polymer structures. The motivation of this contribution is to investigate the influence of hexamethylenetetramine as hardener (hardener content: 4, 8, 12 and 16 %) and curing parameters (tempered and non-tempered) on the microstructure and mechanical properties of the porous C/C composites. During the course of this contribution, selected carbon fibre reinforced polymer (CFRP) composites with different porosities were produced while adjusting the resin or hardening agent-ratio, as well as the processing parameters. Subsequent to the curing of the CFRP samples, porous C/C composites were produced by means of a pyrolysis process. The final part of the contribution is comprised of the microstructural analysis by light microscopy and the explanation of the flexural strengths, by utilising a “three-point-bending test”.

Abstract: The elastic modulus and fracture strength at ultrahigh temperatures over 1500°C is very important for Ultrahigh temperature ceramics (UHTCs), but no available method can be used so far because of the limitation of the testing equipments. In this work, a novel testing equipment was developed to determine the elastic modulus and fracture strength (bending, tensile and shear strength) of ceramics from 1500 °C to 2200 °C. To check the availability and reliability of this equipment, several typical UHTCs including C, C/C fiber woven composite and C/SiC ceramic composite, were used as the testing samples. The results indicate that this new designed testing equipment is a good and feasible for evaluating the ultrahigh temperature mechanical properties of ceramics over 1500 °C in vacuum or in air.

Abstract: Fibre-reinforced ceramic composite materials offer excellent thermal, mechanical and chemical properties. Due to their intrinsic fibre structure and porosity, they offer a great damage tolerance. Therefore, they provide superb attenuation characteristics, as do polymer composites. The current compound systems consisting of ceramic components feature a rather low capacity for energy absorption in relation to their weight; this is a fact in dire need of a fundamental change. In regards to the development of new hybrid ceramic/polymer material compounds basic research of the material design and binding behaviour of the different components is necessary. The advantage of this development allows for a selective implementation of positive characteristics of one component in an integrated compound-system. This opens up completely new possible are-as of application, such as wear and tear resistant and chemically inert, energy absorbing elements for the construction of reactors or areas of medical technology. During the investigation, a few selected fibre-reinforced ceramic composite materials with a specific porosity were produced, while adjusting the amount of resin/hardening agent used, as well as modifying other parameters. This was followed by tests regarding the wetting with a polyurethane component. The characterisation and analysis of the hybrid compounds on a microscopic scale is achieved by means of optical microscopic examinations. The characterisation of the mechanical attenuation characteristics on the other hand is realised by means of DM(T)A. The flexural strength is determined by utilising a “three-point-bending test”.

Abstract: In this work, a new and novel test method was developed to determine the impact bending strength of ceramic composites at ultra-high temperature from 1500-2000 °C in air. Three-point impact bending test was carried out through a SiC pressure head with a dynamic force sensor fixed on a slider and movable along a guide rail. The impact load was adjusted by different saving energy and the impact speed was lower than 0.5 m/s. The center of the sample was heated up to about 1500-2000°C by oxygen-assisted spray combustion. An impact load was put on the specimen and the impact force was recorded automatically. The impact bending strength can be calculated from the maximal load and the sample size. To check the availability and reliability for this method, several ceramics including SiC, ZrB₂/SiC and C/C fiber reinforced composite without coating, were used as the testing samples. The results indicate that this method is a good and feasible method for evaluating the mechanical properties of the ceramic composite at ultra-high temperatures.

Abstract: The mechanical and tribological behaviors of the carbon/carbon (C/C) composites were evaluated by three-point bending and sliding wear tests. The effect of carbon fiber content on their mechanical behavior was also investigated. To produce the C/C composites, the precursor was introduced to the preforms by impregnating with phenolic solution. The C/C preforms were densified by thermal gradient chemical vapor infiltration. Results indicated that, the C/C composites show excellent mechanical and tribological properties. A kind of high performance brake materials was obtained.