The effect of temperature on compaction behavior has been examined on several fine powders by using the compressive apparatus composed of parallel plates in the temperature range from room temperature to 500°C. A straight line relation was found to exist between the logarithm of compressive stress and void fraction, and at a constant compressive stress, the void fraction became larger with increasing temperature. The compaction behavior of thermostable powders at high temperatures can be easily estimated from the test result at room temperature, because the lines showing the relation between the logarithm of compressive stress and the void fraction at different temperatures are parallel to each other. But, in the case of the particles cohering each other during compression at high temperatures or those showing remarkable elastic deformation, the relation between logarithm of compressive stress and void fraction showed a unique characteristic, deviating from a straight line.
The internal friction factor, cohesion factor, tensile strength and flowability of the packed beds made of several kinds of fine coals and fly ash have been measured by using a direct shear tester and a tensile tester. An attempt was also made to correlate these factors with the fuel ratio. It was found that brown coal and anthracite coal were more flowable while hemebituminous coal had the lowest flowability. The bed made of fine coal with higher flowability showed better transmission of applied normal stress and more uniform stress distribution. The internal friction factor and the tensile strength of fly ash were less than those of fine coals and the flowability of fly ash was better than those of fine coals.
To get large and uniform size granules by a closed circuit granuration process, experiments were carried out by simultaneous operation of granulation and separation in a single horizontal rotating conical vessel which has a pair of outlets at both ends. In the above closed circuit granulation, the fine materials (CaCO3 powder) fed into the conical vessel with water droplets were granulated and separated in the vessel, simultaneously. The small granules discharged from the narrow end of the vessel were returned to the feeding point and refed with new materials. The large granules were obtained from the wide end of the vessel as the final product. The effect of the closed circuit granulation on the quality of the final product was examined by dividing the products into three size-ranges. (1) In the small size-range of the products (4_??_x<7mm), the closed circuit granulation was more effective than the open circuit granulation to get uniform size granules. (2) In the middle size-range (7_??_x<10mm), the closed circuit granulation has no marked effect on size and its distribution of the products. (3) In the large size-range (x_??_10mm), larger size granules can be obtained in the closed circuit granulation than in the open circuit granulation under the same feed ratio of binder to solid materials.
A new device for measuring the size distribution of fine powders has been developed based on the principle of the balancing machine reported previously by one of the authors. The new balancing machine has two cells which are set symmetrically to the rotor axis. One of them is filled with powder suspension, while the other contains only the suspension medium having the same weight as that of the suspension in another cell. The balancing machine detects the movement of the center of mass caused by the centrifugal sedimentation of the particles. The particle size distribution is determined from this movement of the center of mass by using the computer analysis. The size distributions of various powders were measured with this new device and the results were compared with those measured by other methods. It should be noted that the size distribution of the powders having a wide range of the particle size can be measured with this device by changing the speed of rotation during one measuring procedure.
The experimental K-value evaluation method proposed in the previous paper was applied to a pressurized cylinder with an internal surface crack. A partially-embedded circular crack was introduced in the longitudinal or circumferential direction inside the tubular specimen using a grinding disk 0.47mm in thick for dental cure use. The measured K-values were compared with those numerically analyzed by Newman and Raju. The results obtained are summarized as follows: (1) The fracture toughness of the material tested (Acrylite®) was found isotropic in the longitudinal and the circumferential directions. (2) The experimentally determined relationship between the non-dimensional stress intensity factor Me and the crack depth ratio a/t indicated the same trend as that numerically calculated for both longitudinal and circumferential surface cracks under a constant crack aspect ratio a/c. The measured values of Me, all of which were larger than the calculated values, agreed with the numerical values within 10% accuracy. (3) The initial slit introduction technique employed gave a valid K-value for a surface crack with the crack depth ratio larger than 0.5. In the case of a shallow crack, i. e., a/t<0.5, it was judged that the initial slit should rather be regarded as a notch. (4) In the case of a longitudinal crack, Me was independent of the curvature of the specimen. (5) The circumferential crack rapidly changed its propagation path into the longitudinal direction from the early stage of crack growth at fracture. This phenomenon was explained sufficiently by the simulation analysis of crack growth path.
The present work is the initial part of a basic investigation on the assessment of embedded defects, where attention is focussed on the development of a practical and convenient assessing method combined with non-destructive inspection. Specimens with embedded cracks were produced by using the diffusion welding method. The mechanical properties and microstructure of the bond region in the embedded crack specimen were almost equivalent to those of the base metal. The KIc-value obtained by using the embedded circular crack specimen was equal to that of the base metal specimen with a circumferential crack. It is clear from these results that the present method using the diffusion welding is effective in producing specimens with shape- and size-controlled embedded cracks. From the result of fracture toughness tests on the specimens with embedded elliptical cracks, it was found that the K-value of an embedded elliptical crack could be estimated by using a reduced circular crack with an area equivalent to that of an elliptical crack. This fact suggests that a convenient method of assessment of embedded defects can be developed when incorporated with ultrasonic inspection which gives the area of crack easily. The effect of the eccentricity of an embedded circular crack on K-estimation was also investigated and a convenient method for evaluating the K-value, combined with ultrasonic inspection, was developed.
JIc tests were performed on HT80, A533B, SM50A and SUS 304 steels, as per the JSME Standard Method of Test for Elastic-Plastic Fracture Toughness JIc. The fracture processes of toughness specimens were also observed in detail. Microcracks nucleated in the blunting region at almost the same time as the initiation of a stable ductile crack and were elongated with increasing deformation. It was found that the critical stretched zone width SZWc was influenced by the elongated microcracks. The JIc values determined by the JSME SZW method tended to be higher than those by the JSME R-curve method. The modified SZW method, using SZW0 which is given by subtracting the microcrack region width from SZWc, gave almost the same JIc values determined by the JSME R-curve method.
A classification method of acoustic emissions (AE) accompanied by the crack initiation in fracture toughness testing was proposed. The AE signals during fracture testing of compact specimens of hot rolled steel, HT-60 steel and 7075-T6 aluminum alloy were measured and the frequency spectra of the initial part of the observed signals were obtained. The source rise time and the characteristic AE energy were calculated from each power spectrum. It was found that the high energy AE events were closely related to the crack initiation determined by the electric potential method. Fracture initiation in hot rolled steel and 7075-T6 aluminum alloy was precisely determined by using the energy above method, but not easily determinable from the conventional AE parameters, RMS, event count and rate, AE energy by Vp2 or the observed waveform. High energy events corresponding to the stable crack initiation were not observed in ductile HT-60 steel. From the source rise time analysis, it was revealed that the sampling time was too short to evaluate the energy.
The fatigue crack growth behavior at Stage 2 was investigated on two kinds of Cr-Mo steel from the viewpoints of the crack closure and the fracture mechanism. It was confirmed that the crack growth rate at Stage 2a and Stage 2b was correlated with the effective stress intensity factor range, ΔKeff, regardless of the strength level and the stress ratio. The crack growth rate at Stage 2c, on the other hand, was controlled by the maximum stress intensity factor, Kmax, regardless of the stress ratio, as the area percentage of the pseudo-monotonic fracture became more than 70%. Then, it was experimentally clarified that the oxide deposits produced by the fretting of fracture surfaces participated in the crack closure at the very low (near-threshold) stress intensity factor range.
Fatigue crack propagation tests were carried out under two kinds of programmed random loadings to investigate the effects of variations of mean load and compressive peak load on fatigue crack propagation rate and crack closure. Crack length and crack closure were measured by using the unloading elastic compliance method with the aid of a mini-computer. The crack opening point was affected by the variation of mean load and took a different value from that of stationary random loading without variation of mean load. This value was found to depend not only on the maximum range-pair of the stress intensity factor and its stress ratio but also on the block size of random loadings. It was also found that the periodic compressive peak load lowered the closure level and caused the acceleration of crack propagation. The validity of the linear accumulation law of crack propagation in terms of the effective stress intensity range-pair was confirmed for the estimation of fatigue crack propagation rate under the programmed random loading conditions investigated in this study.
Impact fatigue strength and behavior of plastic deformation due to cyclic creep in the fatigue process were experimentally studied for the annealed oxygen-free copper. The impact fatigue properties were analyzed in consideration of the duration time as well as the magnitude of impact stress. The impact fatigue strength was well represented by a linear relation between stress σ and cumulative duration time NfT. The behavior of cyclic creep plastic deformation was clearly divided into three regions of i) primary creep, ii) minimum creep rate and iii) accelerative creep, and it was expressible by a formula with the terms of plastic strain εp and, normalized number of cycles N/Nf but without σ and T. The minimum creep rate region occupys about 90% of the total impact fatigue life and governs the life to failure Nf due to impact fatigue damage. The property parameters (m0, D0) of impact fatigue strength and the material constants (a1, a2) in the cyclic creep plastic deformation's formula are related to the static tensile property values i.e. tensile strength σB, reduction of area ψ, elongation δ, including the cases of various other copper materials as well as the annealed oxygen-free copper. The impact fatigue strength and the cyclic creep plastic deformation in the fatigue process can be well estimated from the static tensile property by use of these relations.
Tensile tests were carried out on the precracked specimens of mild steel in liquid zinc in order to investigate the crack propagation resistance of mild steel against liquid zinc embrittlement. The maximum load, Pmax, decreased at the existence of liquid zinc, i.e. Pmax can be used as a measure of liquid zinc embrittlement in the precracked specimens. Pmax decreased with decreasing tensile speed, x2, and with increasing testing temperature, T, but it was independent of annealing temperature or ferrite grain size. The relation among x2(m/s), Pmax(N) and T(K) was represented by the following equation. x2=3.11×10-42Pmax15.9exp(-92000/RT) where R is gas constant.
The micro-Vickers hardness measurements showed that the thin surface layer of ABS resin was readily hardened to the extent of the hardness of AS resin by irradiation with ultraviolet light. The Charpy impact strength of ABS resin with such hardened surface layer was remarkably reduced due to the disappearance of plastic deformation. The critical crack length at the ductile-brittle transition of ABS resin was found to be only about 10μm from the observation of the hardened surface layer of the resin. To protect ABS resin from ultraviolet light in outdoor use, a coating on ABS resin is useful, but the ABS resin coated with a conventional thermosetting paint showed a brittle manner in the same way as the ABS resin irradiated with ultraviolet light, due to the early crack initiation in the brittle coat. The ABS resin with a rubber layer as an undercoat and with a thermosetting paint as a topcoat maintained the same ductility as the original ABS resin in a long time outdoor exposure. This behavior of such coated resins can be well explained from the elastic stress distribution analysis by the use of finite element method.
The tensile strength of polystyrene decreases with decreasing molecular weight and with increasing temperature, showing S mark curves with the change of molecular weight and temperature. As amorphous polymers such as polystyrene maintain their strength with the entangled bonds of molecular chains, the following theoretical equations representing the relation between the molecular weight M and the tensile strength Ts have been introduced from by the three dimensional network structure model based on the entangled bonds of molecular chains of linear polymers. Ts=K(1-2meM-4mem0/meM-m02-2mem0), M≤m0 Ts=K(1-2m0me/M2+m0me), M≥m0 K is a constant related not only to the rate of effective molecular chains determined by the directional distribution, chain length distribution and non-uniformity of the density of molecular chains, but also to the strength and breaking mechanism of molecular chains, m0 is the molecular weight at the condition that the three dimensional perfect network structure is formed, and me is the molecular weight of unit molecular chain between two connecting positions. The experimental data of polystyrene indicate a sufficient agreement with the theoretical curve.
The experimental and numerical values of dynamic effective elastic modulus E* for thin plates with penetrated holes arranged in a square or rectangular pattern have been critically examined. Two parameters, ψ and η, which are associated with the hole size and the arrangement condition of perforated holes respectively, were established. The results obtained were as follows. (1) An appropriate exprimental equation was suggested to evaluate the dynamic effective elastic modulus of the perforated plate. (2) The finite element method was developed to calculate E* of a perforated plate with a general hole pattern. A satisfactory agreement between the simulated and experimental results was found.
Ceramic fibers are widely used in refractory furnaces as a low thermal conducting, heat-insulating material and in FRM as a high Young's modulus material. Most of ceramic fibers for such applications have alumina-silica compositions with various alumina/silica ratios. In the present work, alumina-silica fibers were synthesized by a new processs using sodium alginate. Sodium alginate forms viscous solutions and gels at the present of Ca2+ or other divalent and trivalent metal ions, which facilitates the preparation of fibrous gels of metal alginate. The heattreatment of the product at high temperatures gives ceramic fibers of metal oxide. This “sodium alginate method” is a promising one for the industrial purpose, since the spinning of metal alginate is simple and the spinning condition is not so restrictive. This process can be extended to other ceramic fibers, for example, spinel, magnesia and zinc oxide fibers. This method would be also applied to the formation of ceramic thin films. The present paper describes the details of the synthesis of alumina-silica fibers. The thermal transformation of the produced metal alginate and its chemical structure were examined by using X-ray diffraction, DTA, TG, IR measurement etc. The role of chromium oxide added in suppressing the crystal growth of mullite in the alumina-silica fiber was also examined in order to avoid the deterioration in strength.
Birefringent and mechanical properties of epoxide resins are markedly influenced by both curing agents and cure rate, although phthalic acid anhydride is generally recommended to bisphenol type epoxide resins used as photoelastic materials. A systematic study has been undertaken, therefore, to clarify the influence of acid anhydride agents with various molecular structures on the properties of the resins prepared at a constant network chain density. As the results, the following facts have been obtained. In the rubbery region, some agents displayed higher figure of merit than that of phthalic acid anhydride hitherto employed. The Poisson's ratio of the resins was accurately determined by using an electro-optical device. In the glassy region, the modules of elasticity of the resins decreased unexpectedly while their photoelastic sensitivity increased gradually under the curing process. Besides, the coefficient of thermal expansion, Charpy impact value and other physical properties of the cured resins were presented as the basic data for photoelastic experiments.