Papers by Keyword: Carbon Composites

Abstract: An experimental researches was performed for carbon black-reinforced cement-matrix composites. The carbon black used was in the form of particles with a nano-size. Results show that when content of the carbon black is between 0.25% and 0.75% by weight of cement, both flexural and compressive strengths of the composite can be enhanced. Flexural strength increases up to 9.69%, and compressive strength increases up to 6.92%, respectively. Moreover, the carbon black-reinforced composite is of high strain-sensing ability. The fractional change in resistance () increases monotonically upon compressive loading, and decreases monotonically upon unloading. These properties indicate that the carbon black-reinforced composite can be used for structural function, while at the same time act as a strain sensor itself. Compared with carbon fiber-reinforced composites, the carbon black-reinforced composite has a low price and is easy for mixing.

Abstract: The fatigue limit and crack growth behavior of slit specimens of carbon fiber reinforced epoxy composites were investigated. The fatigue limit was defined by the maximum stress amplitude that the specimen endured 10⁶ times repeated stress when S-N curve was used. The highest fatigue limit was obtained when all the fiber directions were parallel to the load axis. The fatigue limits were evaluated in the cases of composites using alternately parallel and perpendicular to the load axis and compared with the result of the specimen having all the carbon fiber orientations were parallel to the load axis. When the measured value of the fatigue limit was lower, shear damage to the epoxy resin and peeling of fiber from epoxy resin occurred clearly. According to those results, it was expected that the fatigue limit of smooth specimens of carbon composites with long fibers can be evaluated from the results of the slit specimens.

Abstract: Thermoplastic polymer matrix composites with continuous carbon fibre reinforcements are of crucial relevance in automotive industry. The mix of high performance and cost effective manufacturing makes them attractive for high volume production. However, it could be shown that production integrated end of line quality control is of strong importance to ensure continuous and traceable part quality. Besides, typical non destructive testing method specifications, higher production volumes additionally require short testing times. Herein, the application of active thermography as end of line quality control in composite production is evaluated and compared with results obtained by X-ray radiometry. It could be revealed that transient pulse phase thermography is a powerful tool to analyse part quality of continuous thermoplastic polymer matrix composites in short testing times.

Abstract: This contribution firstly presents results gathered during the development of a lightweight multifunctional trailer made of composite material. Focusing on various cross country activities, such as mountain biking, hiking or trail running, significant technical improvements compared to existent products were obtained. This includes technical features like an integrated design to reduce accelerated mass, increase flexibility and provide shock suspension for the child carried during sports activities. As a key feature of the trailer, an agile steering system was engineered to both fit the specific requirements during the trailer’s use as a stroller and as a baby jogger. Due to the integrated design the weight of the single child prototype trailer was reduced by up to 50 % compared to conventional models and the driving comfort was considerably increased. To evaluate both the safety of the carried child during sports activities and the comfort for the adult as well as - last but not least - the resulting fun of those both users during sports activities a series of test rides was conducted. Selected results of the developed measuring setup and test track design are presented in this paper. Finally gathered measurement data are discussed and further design improvements are derived.

Abstract: Special-effect finishes are used in many applications to create new color impressions, pronouncing the design of a product and at the same time making the product appear alive. Total appearance conducting color and geometrical factors such as gloss, shape, etc. Gloss is an attribute of visual appearance that originates from the geometrical distribution of the light reflected by the surface. This paper presents new technologies that were developed to objectively describe total impression of appearance special effect finishes, coated composites and automotive paints after real live tests.

Abstract: The fracture behavior and fatigue limit in notched specimens of C/C composites were investigated. Also, the effect of specimen thickness on fatigue limit was discussed. Two plates of different thicknesses of plates of C/C composites using fine-woven carbon fiber laminates with α=0°/90° direction were used for testing. α is the angle between the carbon fiber direction and specimen axis. The crack growth behavior and failure mechanism of specimens are derived from the shear damage in the fiber bundle and matrix. Slits of several sizes were cut on both sides of a test section and different geometries of the specimens were prepared. Specimens with slits and blunt-notches were used to compare the fatigue strength. The fatigue limit is related to the method of making the plate of carbon composites. Large sizes of voids are observed in the case of specimens of thinner thickness. The fatigue limit was related to the void fraction, and thinner specimens showed a lower fatigue limit.

Abstract: Carbon composites have good mechanical properties and preserve the inherent excellent biocompatibility of carbon, which make them great potential as orthopedic implants in human body. The present work reviews the biocompatible behavior and research situation of such materials for medical application. The mechanical properties, interface and surface modification problem of carbon composites are discussed in detail. Finally, the medical prospects and some problems needed to be solved of carbon composites are put forward.

Abstract: The use of carbon fibre reinforced carbon composites in oxidizing atmospheres is limited to temperatures below 400 °C. To benefit from their excellent mechanical strength that is still preserved at high temperatures, suitable oxidation protection coating systems have to be developed. Composites which are capillary infiltrated with Si and coated with SiC via chemical vapour deposition show significantly enhanced oxidation resistance. For the increase of service temperature above 1300 °C, high temperature stable materials with low oxygen diffusivities such as yttrium silicates have to complement the SiC coating. The electrophoretic deposition performed under constant current conditions leads to relatively high green densities and therefore good sinterability of the applied coatings. In this work we present the preparation of suspensions, their characterization regarding particle size and electrophoretic mobility for yttrium silicate powder prepared by the solid state method. Depending on particle charge and conductivity of the investigated suspensions iodine is employed to increase particle charge. The use of current densities between 0.5-5mA/cm² leads to smooth and homogeneous layers. Layers sintered as low as 1400 °C for 2h already show promising protection of the C/C-Si-SiC substrate during thermogravimetric analysis.

Abstract: An adherent apatite coating was deposited on titanium substrate through the three steps. First, titanium substrate was modified in 10M NaOH solution at 60°C, and then immersed in acidic solution of calcium phosphate resulting in the deposition of monetite (CaHPO4) coating using induction heating technique. Finally the monetite crystals were transformed to HA by a hydrothermal process at 160°C for 2 hours. Composition、morphology and structure of the initial and final coatings were identified using X-ray diffraction (XRD), Scanning Electron Microscopy, and Energy Dispersive Spectroscopy (EDS). The final coating consisted of compact HA crystals and these HA apatite crystals stacked tightly and kept the initial morphology of the monetite crystals. The coating adhesion measured using scratch test was 25.25N. In conclusion, hydrothermal treatment and induction heating techniques are effective surface coating methods that improve bonding to titanium substrate.

Abstract: The effect of low-level oxidation (weight loss less than 6wt.%) on mechanical property of two-dimension (2D) carbon/carbon (C/C) composites was investigated in present work. C/C samples were oxidized in a mixture gas, composed of 10vol%O2 and 90vol%N2, at temperatures of 850°C and 1300°C, respectively. The strength of C/C composites before and after oxidation was measured by three point flexural tests. At different temperature, similar influences of low-level oxidation on mechanical property of C/C samples were observed. As a result, failure of the as-received composites was accompanied by brittle, catastrophic reduction in force. As oxidation progressed, the fracture model of oxidized samples changed from brittle model to pseudoplastic failure model. Especially, the changes of flexural strength with the weight loss increasing could be divided into two stages: (i) at low weight loss, the strength increased with weight loss and is slightly higher than that of the unoxidized composites; (ii) at high weight loss, the strength decreased gradually with the weight loss.