Comparison of 2D and 3D carbon/carbon composites with respect to damage and fracture resistance

The static mechanical responses of two- and three-dimensionally reinforced carbon/carbon composites (2D- and 3D-C/Cs) were compared. The mechanical properties examined included tensile and shear stress-strain (S-S) relations, and fracture behavior using compact tension and double edge notch configurations. Compared with 2D-C/Cs, 3D-C/Cs were shown to possess a similar tensile S-S relation, lower shear strength, higher ultimate deformation in shear, and much higher fracture resistance. The differences in shear and fracture resistance were shown to be derived from a weaker fiber/matrix interface and weaker bonding between fiber bundles in the 3D-C/Cs. These weak interface characteristics of 3D-C/Cs are due to the high value of residual stresses caused by the three-dimensional fiber constraint of 3D-C/Cs.     

Comparative study on tensile fracture behavior of monofilament and bundle C/C composites

Strength controlling factors in C/C composites were experimentally examined using monofilament fiber reinforced C/C composites and those reinforced by one carbon fiber bundle. Tensile strength of the monofilament C/C composites was almost the same level with that of the carbon fiber. This result indicated that carbon fibers in the C/C composites were intact even after the processing. On the other hand, remarkable reduction was observed in the bundle C/C composites. It was indicated that the fracture of the C/C composite is dominated by the brittle fracture of the sub-bundles, in which the fiber/matrix interface is bonded well.     

Si-rich surface layer of photochemically deposited silicon nitride

The etching reaction of a photochemically deposited silicon nitride film with F₂ has been observed in situ using polarization-modulation infrared spectroscopy and quadruple mass spectrometry. The infrared spectrum of the silicon nitride film before etching exhibited two bands at 1030 and 975 cm^–1, arising from Si-N vibration. Exposure of the film at 423 K to F₂ led to an intensity decrease of the lower-frequency band, while the higher-frequency band increased. Simultaneous mass analysis revealed that the etching products evolved into the gas phase were SiF₄ and H₂. However, a further admission of F₂ resulted in a slight decrease in intensity of the 975 cm^–1 band as well as a slight evolution of SiF₄. These results strongly suggest the presence of a metastable Si-rich layer on the surface of the silicon nitride film prior to reaction with F₂. Infrared measurements have also been made in the Si-H stretching region, the results of which are described and discussed.     

Thermal Conductivity Measurement of Thermally-Oxidized SiO<Subscript>2</Subscript> Films on a Silicon Wafer Using a Thermo-Reflectance Technique

This paper describes the development of an advanced method to measure the normal-to-plane thermal conductivity of very-thin insulating films. In this method the metal film layer, which is deposited on thin insulating films, is Joule heated periodically and the ac-temperature response at the center of the metal film surface is measured by a thermo-reflectance technique. The one-dimensional thermal conduction equation of the three-layered system was solved analytically, and a quite simple and accurate approximate equation was derived. In this method, calibration factors of the thermo-reflectance coefficient were determined using the known thermal effusivity of the substrate. The present method was examined for thermally-oxidized SiO₂ films (1000--20 nm thick) on a silicon wafer. The present results of the thermal conductivity agree with those of VAMAS TWA23 within ±10%.Paper presented at the Fifteenth Symposium on Thermophysical Properties, June 22--27, 2003, Boulder, Colorado, U.S.A.     

Identification of a Hydra homologue of the beta-catenin/plakoglobin/armadillo gene family

The effect of a single neonatal convulsion on subsequent behaviour was investigated in the male rat. Convulsions were induced by heat or pentylenetetrazol on days 1, 10 or 21. As adults, locomotor activity, spatial ability and convulsion susceptibility were measured. Significant differences were seen in some measures and some groups but a single neonatal convulsion did not induce a consistent and significant pattern of behavioural change, despite the persistent change in hippocampal physiology shown in a previous study.     

Tensile properties of fine-grained 7475 aluminium alloy at various temperatures and strain rates

For a superplastic 7475 alloy, tensile properties are tested under various conditions in order to investigate the effects of the tensile conditions on the mechanical properties as well as on the microstructure after working. The results obtained here suggest a possibility of high-speed forming of this alloy. Under conditions of 400°C and 8.3×10⁻²s⁻¹ strain rate, a comparatively large elongation of about 200% can be attained. This may be due to the fact that the fine subgrains arise during the deformation. Also, mechanical properties at room temperature of the specimen prestrained under this condition are found to be fairly satisfactory.     

Metallographic observations of stainless steel sheets produced by twin-roll type strip caster

Microstructures and textures of austenitic stainless steel sheets produced by a twin-roll type strip caster are investigated at various stages of casting, cold-rolling and annealing processes. Strip casting is a rapid solidification process and, therefore, the cast strip sheets have fine columnar dendrites and very sharp (100) textures. After cold-rolling and annealing the strip sheets have equiaxial and somewhat finer grains than those produced by the conventional process, and the texture is composed mainly of the (110)[1?2] orientation.     

Predictable modelling for cooling process of a hot steel plate by a laminar water bar

A numerical model is proposed to predict the cooling process of a hot steel plate by a laminar water bar. This model gives a close agreement with the experimental cooling history for arbitrary water flow rate and water temperature.     

Fundamental property of electric field in rapeseed ester oil based on Kerr electro-optic measurement

In the future, environmentally friendly insulating oil such as rapeseed ester oil is expected to be utilized as a substitute for mineral oil for power transformers. In addition, electrical insulation design for transformers becomes more important regarding size reduction and enhancement of electric field stress. The fundamental property of the electric field distribution in the rapeseed ester oil and in the oil/solid dielectrics composite insulation system should be clarified. In this paper, we have directly measured the electric field in the rapeseed ester oil with parallel-plane electrode and the rapeseed ester oil/pressboard (PB) composite insulation systems under DC voltage application using the Kerr electro-optic technique. From the results, we compared measurements of electric field and charge behavior for the rapeseed ester oil and the mineral oil and confirmed the applicability of the rapeseed ester oil for use in transformers.     

Application of three-dimensionally reinforced carbon–carbon composites to dovetail joint structures

In development of an air-turbo-ramjet engine with an expander cycle (ATREX) for a space plane, application of carbon–carbon (C/C) composites plays an important role to achieve high performance. Above all, dovetail joints are one of the key structures to realize the turbine system made of C/C composites. In this study, the feasibility of dovetail joints made of three-dimensionally reinforced C/C composites was investigated. Tensile tests were carried out on simplified dovetail joint models. The shoulder angles of the dovetail joint and fiber volume fractions of the C/C composites were taken as parameters to optimize the shape of the dovetail joint. Finite element analyses were also carried out for various cases. Comparison between the experimental and the calculated results suggests that fracturing of the dovetail joint was controlled by the average shear stress, which implies that the shear stress concentration on the shoulder was relaxed during the fracture process. It was also shown that the dovetail joint made of C/C composites is feasible for use in the ATREX engine.