Two-dimensional model agglomerates were formed by successive addition of uniform discs to a core using a Monte Carlo simulation procedure. Whether the addition of a disc occurred or not was determined by comparing the pseudo-random number generated at every collision between a disc and the core with the cohesion probability P (method I). The porosity of agglomerates and the average coordination number were calculated. Another method of the formation of two-dimensional agglomerates were by placing discs of equal size at the fixed position of a rhombic lattice. The process was begun with a disc placed at the center of the lattice and the growth of the agglomerate proceeded toward the outer layers. In this treatment the packing probability Q was taken into consideration (method II). The compaction of the agglomerate, that is the reduction of porosity, was simulated by inserting discs into the vacant position of the lattice with the probability of Q'. The compaction kinetics were investigated using Kuno and Kawakita equations.
The heat of immersion of several kinds of zeolites, i.e., molecular sieves 5A, 4A, improved mordenite, natural mordenite and natural clinoptilolite, against water was determined on the basis of the“absolute method”by using a highly accurate quartz temperature sensor. In the case of zeolites the heat of immersion measurement at relative vapour pressure of about 0.2 was found suitable for the estimation of specific surface. The results were compared with the data obtained by other adsorption methods utilizing nitrogen, water vapour and CH3OH. The measurement of heat of immersion of zeolites against water requires little theoretical assumptions and is quite ingenious and considerably simple and reproducible for the estimation of specific surfaces. Although Itaya-zeolite showed less heat of immersion than molecular sieves 5A and 4A, it seems useful for heat recovery, in such fields as solar heating and cooling, or waste gas treatment.
An experimental study was carried out to obtain the solid surface increase produced in the ball mill grinding. The samples used were silica glass, quartz, feldspar, limestone, marble and talc. The pebble mill consisted of a cylinder of 12.5cm-diameter by 12.5cm-long and 35 balls of a 2.8cm diameter having the total weight of 1000g. The tests were done at the speed of 87% of critical one and with the feed size of 14∼20 mesh and feed weight of 200g. On the assumption that the shape factor is six, the specific surface was determined by the permeability method. As the result, the stepped grinding curves as shown in Figs. 1 and 4 were obtained for the relationship between the solid surface produced and grinding time. The grinding curve for closely elastic solids showed three steps as shown in Fig. 1, but it showed two steps for plastic solids (Fig. 4).
The shearing failure process of the powder bed in a direct shear tester has been represented in the Roscoe condition diagram (a three dimensional representation of the applied normal stress, shearing stress and void fraction) in conjunction with the data by tensile tests. The results show that this presentation permits to understand the effect of the void fraction on the shearing-failure process systematically and clearly. It is specially of interest that pattern of the shearing-failure process varied as a function of both the void fractions of initial and critical states corresponds well to the locus of the shearing process in the Roscoe diagram. The flow surface, the consolidation surface, the critical state line and the consolidation line for fine and coarse powders were clearly shown in the Roscoe diagram and the differences between them were interpreted qualitatively.
In order to obtain the interparticle force of powder, there exists a method of measuring a tensile strength necessary to fracture the compressed powder bed. The results obtained by this method show certain fluctuation in magnitude of the tensile strength, greatly depending on packing structure of powder. Because of lack of quantitative representation on the packing structure, the powder phase has been assumed as rather homogeneous. Accordingly the cohesion force (interparticle force) is generally estimated through the following procedures; firstly a relationship between porosity of powder and average number of contact with the nearest neighbours is established experimentally using the matters packed up irregularly from uniform sphere-particles, and then the cohesion force per one contact is assigned to individual particle dividing the macroscopic tensile strength by the total number of contact. It is, however, questionable whether or not the above assumption holds for the actual powders. In order to reconsider it, the micropore distribution of the powder samples whose porosity was artificialy controlled was measured by means of a mercury porosimeter. It was found from this experiment that a powder has a structure packing up heterogeneously of aggregations with which finer particles condensed together. A close attention was directed to a relation between tensile strength and structure of the fractured surface. For this course, two groups of powder matters were tentatively prepared which had been granulated to arbitary size from fine particles with well known size distribution, and the tensile strength of the compressed powder bed was measured both for normal powder and those granulated ones. Furthermore their fractured surface was observed by means of optical microscope. The result seemed to suggest that the fracture in the compressed powder bed caused by tensile starts from the part at which a relatively large pore resulted from the heterogeneous packing was found. Further support was given through the following experiments. As a two dimentional packing model, polystyrene pieces, which have the dimensions of 1∼5mm in size and heterogeneous shape, were floated compactly on the water and the fracture process with tensile was directly observed. It became more confident that the fracture propagates infectiously through the route where the heterogeneous packing structure is remarkable. The fact that the heterogeneity of packing within powder has a great influence on the tensile strength was also supported by the observation of the fractured surface of powders in which mica, subjected to surface treatment with hydrohobic material, was mixed in a certain ratio. From these experiments described above, it can be concluded that when Rumpf's equation is applied onto the results of tensile strength of the compressed powder bed, the interparticle force is underestimated for individual particle.
Powdered polystyrene was compacted into specimens having various void fractions. The dynamic mechanical properties of these specimens were measured by the vibratory test method. The mechanical loss factor Q-1 of the compaction-molded specimen was found to increase with increasing void fraction and with increasing strain amplitude of vibration at various temperatures below the glass transition temperature of polystyrene. The dynamic modulus σ0/ε0, which was defined as a ratio of a stress amplitude σ0 to a strain amplitude ε0, varied quite little with increasing strain amplitude and decreased with increasing void fraction. The Q-1 value decreased by sintering of interparticle contact points. Therefore, it was considered that the energy dissipation mechanism was attributed to the friction at a part having weak cohesive force in contact surfaces between adjacent particles. This was also supported by the fact that the Q-1 value increased with decreasing tensile strength which implied decreasing interparticle cohesive force.
In order to investigate the axial segregation profile of binary solid mixtures during the mixing and segregation processes in a horizontal rotating conical vessel, experiments were carried out by using several kinds of binary mixtures, such as alumina/silica sand mixture and different size silica sand mixtures, as materials. The axial concentration distribution of the mixtures was measured at a different mixing time under three different initial loading conditions at the rotating speed of the vessel n=10-30rpm. It was confirmed that the demixing potential φ, proposed in the Rose's Equation, was correlated with the concentration CA of the specified particles within a specified zone of the vessel, which was itself closely related to the axial arrangement of the particles in the vessel, regardless of the mixture or dimension of the vessel. With the aid of this relationship between φ and CA, it was possible to estimate the axial concentration distribution of a mixture in the vessel.
CdTe is one of the most effective semiconductors used for solar battery, and thus it is desired to prepare its powder for usage as a printable electronic material. This work reports that CdTe powder was successfully prepared by the following procedures: The molten mixture of CdCl2 and CdTe was cooled rapidly and placed in water. CdTe powder precipitated by resolution of CdCl2 into water from the mixed solid. Doping into CdTe powder was realized by addition of a dopant material in the molten mixture. Electric conductivity, photoconductivity and action spectra were measured on the pure and doped powders, which had a similar size distribution (approximate maximum size: 0.3-0.5μm). The temperature dependencies of electric current and photocurrent were expressed, respectively, by I=I0exp(-E/kT) and Ip=Ip0exp(-Ep/kT)+Ip1, and the values of parameters obtained were shown in Tables I and II. The band gap of the powders was estimated from the action spectra to be almost the same as that of crystal, and its temperature coefficient was also the same. The electric and particulate properties showed the suitability of the present powders for the purpose.
The softening effect of more than 200 bentonite samples has been studied. The softening index, cation exchange capacity (CEC), adsorption, mineral composition and amount of soluble silica were examined. It was found that, in general, the softening effect was not a function of CEC but depended on the crystallinity of montmorillonite. Furthermore, the experimental results on various samples with classified fractions indicated that bentonite is characterized by the coexistence of cristobalite and montmorillonite and the crystallinity of montmorillonite is probably related to this coexistence.
No satisfactory method has been developed so far for analysing coated plain-weave fabric which has properties of nonlinear elasticity. In this paper, a method which is promissing for use in engineering applications like the strength analysis of membrane structures was presented. The finite element method using rectangular elements consisting of plain-weave fabric and coating material was applied. Experimental verification of the method was made by using uniaxial stress-strain responses. A square piece of coated plain-weave fabric with a square hole was analyzed as an example of application of the present method.
The wave propagation and the buckling phenomena are studied theoretically for the elastic composite materials reinforced with inextensible rigid fibers. Three kinds of inextensible elastic materials are taken into consideration, that is, the materials with one, two and three directions of inextensible fibers. The constitutive equations are obtained, where the indefinite normal stresses occur along the directions of the inextensible fibers. The acceleration waves of singular surface and the small sinusoidal waves are adopted. Depending upon the propagation direction, the wave characters change. When propagation direction is not perpendicular to a fiber for the material with one inextensible direction, a quasi-longitudinal wave and two transverse waves may propagate, where the amplitude vectors are perpendicular to the fiber. If the material is compressed along the fiber the waves propagate with lower velocities. There are two critical stress values. If the stress is less than the lower critical value, the wave can not exist. If the stress is between two critical values, the quasi-longitudinal wave can exist but the transverse wave can not. If the stress is equal to one of the critical values, some statical deformations may occur, and the buckling phenomena appear. The waves and buckling phenomena are also investigated for the materials with two and three inextensible directions.
The combined creep-fatigue tests, in which the creep loading and fatigue loading are repeated alternately, were carried out on SUS 304 stainless steel up to 3000hr at 700°C. The data obtained were analyzed using different linear damage rules, and the relationship between the results evaluated by them and the appearance of fracture was discussed. When the creep damage was assumed to be defined as Σtc/tr (where Σtc is the time spent under creep stress, σc, in the combined creep-fatigue test, and tr is the time to rupture under σc in the creep test), the sum of creep and fatigue damage depended on σc and the degree of work hardening due to the cyclic deformation under fatigue loading. When the creep damage was assumed to be defined as Σεc/εf (where Σεc is the sum of creep strain accumulated in the combined creep-fatigue test, and εf is the true strain at fracture in the creep test), a better correlation between creep and fatigue damage was obtained with no dependence on the test variables of the combined creep-fatigue test. For higher creep damages the sum of creep and fatigue damage was less than 1 because the fracture resulted from the linkage of grain boundary cracks. The important factors of creep-fatigue interaction under the combined creep-fatigue loadings were found to be the work hardening due to the cyclic deformation under fatigue loading and the linkage of grain boundary cracks.
In uniaxial compression tests of rocks, the quasi-static strength has a tendency to increase with increasing strain rate. In order to study this effect of strain rate on strength, a computer model of failure process of rocks was developed with Finite Element Method (F. E. M.) from the view point of stochastic process. In this computer model, inhomogeneity of rock specimens can be easily taken into account by changing elastic constants for each element. The failure of each element in this model was taken to be the elementary process of macroscopic failure, and the failure process of each element was assumed to be a 3-stage i.e. 2-step Poisson process. By noting that the rate constant of failure for each element is a function of the stress level, the extended concept of stress severity was introduced to express the relation between the stress level and the rate constant of failure. Although this computer model is based on the most simple assumption, the calculated results represented well the strain rate dependence of rock behavior in uniaxial compression, such as the effect of strain rate on strength and the stress-strain curve. This conclusion was well confirmed experimentally.
A study on arc resistance of insulating materials at low temperatures is considered important in the insulation design of various electric apparatus, especially at terminal parts of electric apparatus, where cryogenic temperature liquid is used as the electric insulating material. In this paper, the arc resistance tests of synthetic resins at low temperatures were carried out in air and in liquid nitrogen and the effect of low temperature on arc resistance was investigated. The low temperature effect on the process of arc deteriorations were also discussed. As the test method, ASTM D495 standard test method was followed closely. Since the firing potential becomes high in air at low temperatures, the applied voltage was fixed at 28kV. In liquid nitrogen, it was fixed at 45kV, because the firing potential is still higher. It was found that the arc resistance generally increased in air at low temperatures compared with that at room temperature. In liquid nitrogen, however, there were two cases; the one with increasing arc resistance and the other with decreasing arc resistance. When the temperature was changed from low temperatures to room temperature in the air, the change of arc resistance showed different patterns, such as a slowly decreasing curve with temperature or an abruptly decreasing curve, depending upon the species of resins. The carbonization did not take place in liquid nitrogen in Epoxy-unfilled, phenolic paper-filled, PVC resin, etc. but the erosion took place in those resins, indicating the change in form of arc deterioration. When the electrodes were placed not on the same plane of sample but on the upper and side surface of polyester-glass laminate, Melamine-glass laminate and Silicone-glass laminate in liquid nitrogen, the arc resistance decreased occasionally by the dielectric breakdown of the specimen which took place at the tip and the other part of upper electrode.