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891.
Solidification after extrusion of coaxial cables has been experimentally simulated. Solidification tests were performed with two HDPE grades and under several pressures; the extrusion velocity was varied in a suitable range so as to detect the critical velocity for void formation. A qualitative analysis of the void formation mechanism is carried out, and the predicted trends favorably compare with the critical velocity data.  相似文献   
892.
Partially stabilized zirconia (PSZ) /β-alumina composites exhibit extensive non-elastic deformation during fracture. Repeated loading/stable fracture/unloading experiments were performed on chevron-notched four-point-bend specimens of the composite and pure PSZ. The energy consumption during the propagation of long cracks in the composite (∼500 J/m2) is 1 order of magnitude larger than for PSZ (∼50 J/m2). Breaking strengths of 127 MPa were obtained with a Weibull modulus of 43.  相似文献   
893.
Previous solid state analyses of sintering in Ti4+-doped-commercial alumina are shown to be in error because a liquid phase exists in the appropriate region of the Al2O3−TiO3−Na2Ophase diagram at least by 1350°C, a temperature lower than that at which "solid state" studies were conducted. It is suggested that liquid-phase sintering is a much more common occurrence than was realized formerly.  相似文献   
894.
The results presented in the literature, which attempt to elucidate the mechanisms by which triglyceride oils are bleached by earths, are reviewed. The impact of this work and how the mechanistic proposals affect changes in oil properties are considered, with particular emphasis on the needs of the palm oil processor. Important properties include color, metals and phosphorus content and oxidative stability of the oil. Investigations made in our own laboratories have been aimed at elucidating the effect of varying physical and chemical properties of the bleaching earth on the quality of bleached and deodorized oils. Techniques used in this work are pore-size distribution, surface area, scanning and transmission electron microscopy and a variety of chemical and X-ray analysis methods. The ability to vary such parameters in montmorillonite clays by alteration of process conditions to give materials with specific performance characteristics is demonstrated. Comparisons are made between acid-activated montmorillonites and other clay types.  相似文献   
895.
Glasses with two composition in the CaO---Al2O3---SiO2 system were prepared with different cooling conditions. Glass A has a eutectic composition of wollastonite-gehlenite-rankinite and glass B has that of wollastonite-gehlenite-anorthite. The effects of the thermal history on the structure and hydraulic properties were discussed. Effects of cooling rate on the physical and chemical properties of glasses are found to be different with chemical composition of glass. Cooling rate affects the hydraulic reactivity and crystallization temperature, especially in glass A, but scarcely affects the physical properties such as chemical shift of AlK and surface basicity of the glass.  相似文献   
896.
Two versions of the pressure swing adsorption process are analysed as a means for purification of the light component of a binary feed of arbitrary composition. Local equilibrium with linear, uncoupled isotherms is assumed. The results of the analysis show that a critical pressure ratio must be exceeded before complete purification is possible and that this pressure ratio increases as the light-component content of the feed decreases. When clean up of the light component is complete, pressurization with product leads to higher light-component recoveries than pressurization with feed. This difference becomes large for small separation factors, small fractions of the light component in the feed, and large pressure ratios.  相似文献   
897.
Perturbation testing is an approach to software testing which focuses on faults within arithmetic expressions appearing throughout a program. This approach is expanded to permit analysis of individual test points rather than entire paths, and to concentrate on domain errors. Faults are modeled as perturbing functions drawn from a vector space of potential faults and added to the correct form of an arithmetic expression. Sensitivity measures are derived which limit the possible size of those faults that would go undetected after the execution of a given test set. These measures open up an interesting view of testing, in which attempts are made to reduce the volume of possible faults which, were they present in the program being tested, would have escaped detection on all tests performed so far. The combination of these measures with standard optimization techniques yields a novel test-data-generation method called arithmetic fault detection  相似文献   
898.
A very effective non-reflecting boundary condition is proposed for the three-dimensional finite element analysis of hydrodynamic loads on offshore structures under motion due to earthquake, waves or machinery forces. The effect of surface waves is considered and the analysis is conducted in the frequency domain. The structure is assumed to be sufficiently large such that the non-linear effect of drag force is negligible. The unbounded extent of water surrounding the structure is assumed to be incompressible. The boundary condition, which is derived for the general analysis of structure-water interaction, is found to depend on the frequency of excitation, the location of the truncation boundary and the depth of water in the far field. Through some simplified numerical examples, it is shown that the proposed technique is very efficient for a wide range of the frequency of excitation. Incorporation of the boundary condition into a finite element program requires practically no extra effort.  相似文献   
899.
900.
Conversion of acrylonitrile-based precursors to carbon fibres   总被引:1,自引:0,他引:1  
The progress of stabilization of two compositions of acrylic fibres with various orientations has been followed by a variety of techniques. The thermooxidative treatments for stabilization have been carried out in a continuous process and also in a batch process under free shrinkage, constant length and constant tension conditions. The morphological model of acrylic fibres consists of an alternating sequence of laterally ordered and laterally disordered regions along the fibre direction. This structure is consistent with the observations based on small-angle X-ray scattering of copper- impregnated precursor fibres and thermomechanical response, thermal stress development, calorimetry, wide- and small-angle X-ray scattering and sonic modu-lus measured at different extents of stabilization. Lateral as well as orientational order in these fibres can be increased markedly through a high-temperature deformation process prior to stabilization. An increase in perfection and extent of order is observed in the early stages of stabilization. There is also a simultaneous decrease in the orientation of the disordered phase at this stage and the extent of this decrease depends on the axial constraints imposed on the fibre. Little difference in the rate of stabilization is observed as measured by density or oxygen uptake for fibres with different extents of orientation, lateral order or restraint. Fibres containing itaconic add, a stabilization catalyst did show an increased rate of stabilization. Inferences have been drawn regarding additional research pertaining to achieving high order in precursor fibres, minimizing orientational relaxation during oxidative stabilization, and the techniques for monitoring the extents of the stabilization treatment and the changes in relevant morphological parameters.  相似文献   
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