The optimal structure which maximizes energy densities (energy/weight and energy/volume) is discussed for energy storage flywheels made of high specific strength fiber-reinforced plastics. The results show that the density, thickness, and total stress i.e. sum of the radial and circumferential stresses should be constant in the flywheel. Additionally, the elastic moduli should be controlled so that the stresses are proportional to the strengths in the radial and circumferential directions.

View full abstract

Corrosion fatigue crack growth rate of a high tensile strength steel HT55 has been measured in 1% NaCl solution at a small ΔK region, where environment, cycle frequency, and load amplitude are changed during fatigue test. Load-strain hysteresis loops are divided into three region of I, II, and III with the boundaries set by a perfect crack closing load and a perfect crack opening one. The load shared by corrosion products is calculated from a shift of the region I. da/dN changes by an environmental alteration from air on 1%NaCl solution or a frequency change under the influence of a corrosion products-induced wedge effect. The region II must be taken into consideration to explain uniquely the corrosion fatigue crack growth behaviors near threshold regions. In the present study the contributory ratio of the region II is known to be 0.54 - 0.35, and a contributory stress intensity factor range ΔKconte is proposed.

View full abstract

Two step-two fold, two step-three fold and two step multi-fold program fatigue tests were carried out by rotating bending loading. The material used was a plain carbon steel, JIS S35C, and the specimens were pre-cracked and stress relieved. The main results obtained were as follows. After application of a very small number of cycles n₁ at stress amplitude above fatigue limit, a non-propagating crack growth increment 21₂ by repetition of low stress level was dependent on n₁. As n₁ increased, 21₂ became longer. Crack retardation behavior under repetitions of high stress level was more prominent when 21₂ was longer and low stress level was higher. In two step multi-fold program fatigue tests, to attain the most critical condition, the number of cycles of high stress level had to be smaller and number of cycles of low stress level had not to be long enough to cause crack arresting.

View full abstract

In the design of bolted joints, it is important to examine the sealing performance and to estimate the force ratio (the ratio of an increment of bolt axial force to a load). Up to now, in order to improve the sealing performance, raised faces of the interfaces have been used. But the uses of these interfaces depend on experiments and the theoretical grounds are not made clear. In the present paper, in the case where two hollow cylinders having raised faces are fastened by a set of bolt and nut, a contact stress distribution is analyzed using three-dimensional theory of elasticity and point matching method. The force ratio of this joint is also analyzed. For verification, experiments are carried out. Analytical results are in a fairly good agreement with experimental ones. Then, discussion is made on effects of the interface configurations on the characteristics of the bolted joint.

View full abstract

In this paper, the deformation and strength of an underground pipe subjected to the soil pressure due to a vertical concentrated load applied at an arbitrary position on the soil surface, are investigated by an exact method using a differential equation of a thin cylindrical shell introduced by one of the authors, K.Mizoguchi. Considering the ground as a semi-infinite elastic solid, the soil pressures on a buried pipe are evaluated by using Boussinesq formulas and by introducing the coefficient of subgrade reaction. In the case of two or four traveling concentrated loads maintaining constant discussed. We carried out numerical computation and the results are shown for various combinations of the positions and distances of the points of application of loads.

View full abstract

Growth and collapse motion of a hemispherical cavitation bubble, produced by a giant-pulsed laser beam irradiation forcusing on a solid boundary, and pressure waveform near the bubble are examined in detail by a high-speed photography and others. They are compared with the results of a himispherical bubble on a solid boundary, produced by an electric discharge in water. The experimental results are elucidated by a numerical analysis of a cavitation bubble model. Thus, the characteristics of a hemispherical cavitation bubble, produced by a laser irradiation, that so-called microjet and impulsive pressure like a shock wave are not detected at its collapsing stage, are revealed.

View full abstract

Studied in this paper is the effect of free-stream turbulence on the turbulent structure of a separation bubble formed at the leading edge of a blunt plate with right-angled corners. The free-stream turbulence was introduced by a thin circular rod placed upstream of the plate along its stagnation streamline. This paper is sequel to the authors' previous papers (Kiya & Sasaki 1983, Kiya et al. 1984) in which time-averaged properties of the separation bubble are given in terms of the turbulence intensity at a reference point near an edge of the plate. The longitudinal and spanwise integral length scales of vortices in the separation bubble were given as functions of the free -stream turbulence intensity. The cross correlations between the surface-pressure and velocity fluctuations suggested that large-scale vortices are similar in shape independently of the free-stream turbulence intensity. Moreover, the maximum gradient of the time-mean surface-pressure profile and the longitudinal length scale of vortices in the reattaching zone.

View full abstract

This paper presents an experimental study on the interaction of twin turbulent circular jet. The velocity and the static pressure of the jets were measured by varying the distance between two nozzles. The results of the twin-jet were compared with those of a jet parallel to a plane wall on the basis of the principle of reflected image. The main results are as follows : (1) The twin-jet interacts and joints in the form of an ellipse at the downstream distance, becoming close to a circular jet at far downstream distance. (2) The position of maximum velocity of the twin-jet shifts from the axis of nozzle to the mid-point between the jets. (3) The positions of maximum velocity of the twin-jet and the jet parallel to a plane wall are expressed by similar curves for various nozzle distances. (4) The difference between the characteristics of the twin-jet and those of the jet parallel to a plate wall is due to their different boundary conditions.

View full abstract

An experimental research has been carried on to study the danger of a high-speed jet discharged from a hole in hydraulic equipment of very high pressure to the people working around the equipment. In this paper, the results of the research both on the time taken for a tested jet to inflict a piercing wound on the raw skin of an ox, when it was discharged from a hole of 5mm in length and hit the skin perpendicularly, and on the process of growth of a damage to a resin board of 1cm in thickness caused by the jet, such as when the hole have a relatively small diameter and the pressure is relatively low the place where the tested jet pierces through the skin most quickly is distant a little form the hole, are reported.

View full abstract

This paper presents experimental studies on methods for reducing air flow noise which is generated in expansion cavity type mufflers. A great deal of air flow noise is generated when a jet stream from the inlet pipe directly impacts the tail pipe, so it is necessary for the flow noise reduction to reduce the impact energy. In this paper, the effects of various methods for the reduction of impact energy and air flow noise are systematically studied.

View full abstract

The instantaneous monochromatic infrared radiation from the combustion flames of a four stroke, direct injection, no-swirl diesel engine was investigated. The radiant emission was found t be well described essentially by the continuous spectral emission from the soot-particle cloud, on which the gaseous emission bands of 1.9, 2.9, and 4.2 μm were superimposed. Also it was found that the flame around the periphery of the combustion chamber cavity emitted much stronger radiation than the one in the middle. Such instantaneous characteristics of the luminous flames as the spectra land total intensities, temperature, apparent optical thickness and emissivity were obtained at four typical measuring points for various fuel air ratios. High speed photographs of the movements of the flames were taken to promote the physical understanding of the radiant emission in diesel engine.

View full abstract

In an attempt to find out the thermal load conditions of the combustion chamber wall, by the use of precise thin film thermocouples which the authors have developed recently, surface temperature variation and instantaneous heat flux of the piston and the cylinder of a 4-stroke gasoline engine, for each stroke, are obtained. As a result, thermal load conditions of parts of the piston and the cylinder are made clear, and along with this, the ratio of heat loss is determined. Thermal load aspects under abnormal combustion conditions i.e. knocking are also crarified.

View full abstract

Under some conditions a short pipe with a tapered square hole, which is called an oscillator. can rise along a vertically erected vibrating square rod. Behaviours of oscillators are investigated theoretically and experimentally. Geometrical amount of rise of an oscillator per a cycle depends on its taper angle and hole width. Amount of fall of the oscillator depends on the clearance and the friction factor between the oscillator and the rod. radius of gyration of the oscillator and the magnitude an the frequency of the vibration of the rod. Real rise of the oscillator is equal to the difference between the two amounts.

View full abstract

This paper presents a research on a simple oil damper that has an annular clearance between its cylinder and piston as a flow channel of oil. In the preceding reports, we have analyzed this type of oil damper on the assumption that the cylinder is at rest. However a large number of oil dampers are attached to moving supports, so the cylinder and piston are both vibrating . Thus we analyze the oil damper under the condition that the cylinder is vibrating in simple harmonic motion. As a result of this analysis, it is found that the drag force acting on the cylinder is a little larger than that on the piston, because the inertia force of fluid in the channel acts only on the cylinder. Moreover, it is confirmed that the mass of oil has a favorable effect on the vibration isolation ; whereas the spring mass worsens the isolation.

View full abstract

In a self-exciting system with the restoring force expressed as the product of a non-linear function of deflection and a periodic function of time, it is ascertained that parametric resonances and subharmonic resonances and moreover a subsuperharmonic resonance of order 2/3 occur. An approximate solution of subsuperharmonic resonance of order 2/3 and its stability are determined by a transformation into the rotating coordinates systems and the averaging method. In the neighborhood of the resonance, a vibration with beat character occurs and its amplitudes are approximately determined by obtaining a limit cycle. It is ascertained from numerical calculations that these approximate solutions qualitatively have high accuracy.

View full abstract

Discussions are made on super-summed-and-differential harmonic oscillations in a symmetrical rotating shaft system (i.e. a system consisting of an elastic shaft with circular cross section and a disc) with nonlinear spring characteristics. The probability of occurrence and the shapes of resonance curves are investigated, with special attention to nonlinear components represented by polar coordinates. Also experiments are made with symmetrical systems whose nonlinearity is due to single-row deep groove ball bearings, and the occurrence of super-summed and-differential harmonic oscillations which are theoretically predicted to appear are confirmed.

View full abstract

Regarding a latticed rib as a sound reflector, its effect on sound radiation from a housing is discussed. A module of the reflector, a box with a baffle, surrounding four rectangular reflector plates and an aperture, is taken up for proposing a new formulation in terms of mirror images. Taking multiple reflections into account, the reflecting process is replaced by diffractions from an array of mirror images toward the aperture through the diffraction windows corresponding to the reflectors. And only centripetal diffractions to the aperture are selected for the convergence in calculation. The formulation is applied to a latticed reflector by summing the sound radiation from each module of reflector, When the ratio of bending wavelength in the housing plate to the wavelength of sound in air is greater than 1, the rib has some effect of decreasing the radiation power. Under the contrary condition, the power increases remarkably due to the existence of the rib.

View full abstract

On a pair of power transmission helical gears with a comparatively narrow facewidth, the relation between contact ratio and vibration is investigated experimentally for the purpose of decreasing vibration and noise. It has been confirmed that the power transmission helical gears are classified into three categories related to the transverse contact ratio and the overlap ratio as follows. The pair whose overlap ratio is over 1.0 has good vibration characteristics. When the total contact ratio is less than 2.0, the vibration characteristics are similar to those of spur gears. Under the condition that the total contact ratio is over 2.0 and the overlap ratio is less than 1.0, the pair shows a good performance by a modification of tooth profile and trace of the driven gear.

View full abstract

The authors found that there is an interference which causes unfavourable contact at the tooth-top edge of gears with a concave tooth profile, and established the design method for eliminating the interference. Two dimensionless parameters to calculate the bending and twisting deflections of pinions with Z₁ = 3 to 5 were obtained by numerical calculations and experiments. Changes in the tooth bearings and gearing errors caused by elastic deflections were examined numerically. Load carrying capacity of Novikov gears with a small number of pinion teeth was investigated to clarify the effects of hardness upon the surface durability of the Novikov gears with Brinell hardnesses in the range of 190 to 330 HB. The best results were obtained when a low hardness steel was used for both the pinion and gear and also when a harder pinion was combined with a gear made of a low hardness steel.

View full abstract

By allowing for a small amount o gearing errors, the authors established a new design method of internal gear pumps with an appreciably larger specific-delivery than that of the internal trochoid pumps, etc. Using this method, three kinds of internal gear pumps with numbers of teeth z₁ = 8 and z₂ = 11 and also with z₁ = 7 and z₂ = 10 were designed and made in the author's laboratory. The performance of the trial-made gear pumps was as good as supposed, and almost the same as that estimated from the theory. Endurance tests were conducted using one of the trial-made gear pumps because there was a possibility of tooth surface failure due to excessive contact stress between the meshing teeth. However, no failure occurred at all when the gear pump was operated at a delivery pressure of 1.0 MPa (≒ 10 kgf/cm²) for 5×10⁶ revolutions.

View full abstract

The authors designed and made a new precision gear grinder with a cubic boron nitride (CBN) wheel and succeeded in producing ground gears with a very small roughness of R_max ≒0.1 μm although it has been believed that the CBN wheel produces rougher tooth-surface (R_max = 3-10μm). the reason why the unexpected result was obtained by the author's grinder was presented. Effects of the surface roughness of hardened gears upon the surface durability of the mating gears were roughness of hardened gears upon the surface durability of the mating gears were examined using test gears with three different surface finishes. When a hobbed gear was combined with a hardnened gear with mirror finished surface, the surface durability of the gear pair increased appreciably due to effective running-in. In contrast to this, the hobbed gear failed at the same load before 2×10⁶ revolutions due to severe wear when it was combined with a conventionally ground gear.

View full abstract

Static and dynamic stresses in helical springs are analyzed systematically by using the finite element method. In the static stress analysis, the effects of the pitch angle on stresses are investigated and it is reveald that the maximum principal stress governing the fatigue fracture of springs is larger on the outside of coils than on the inside of coils in the case of a large pitch angle and that the cracks may start from the outside of coils. In the dynamic stress analysis, stress distribution along the wire are evaluated in a similar way to the static stress analysis and it is indicated that dynamic stress are much larger than static stresses. The results obtained are corroborated with the experimental results.

View full abstract

Comparison of two kinds of cutting fluid was carried out in a test : It was recognized that a fluid in which original solution containing a large amount of additive is highly diluted with water causes less tool wear than one of which original solution with a small amount of additive is diluted with water in a low ratio for the same concentration of additive in each fluid. The reason why the wear is small is that surface active agents and mineral oil of low or middle viscosity in the fluid become an lower in the concentration and they cause an increase of the wear. However, mineral oil of high viscosity decreases the wear. And synthetic fluids of high viscosity give a good performance causing very little wear.

View full abstract

As a basic study for the automated design, an automated computer simulation method and a computer program for two-dimensional elastostatic problems are developed in this first report. This method consists of two parts, automated mesh generation and automated stress analysis. The stress analysis is based on the Boundary Element Method and Gaussian Elimination Method. As the Boundary Element Method is adopted, the mesh generation is carried out only for the boundaries of two-dimensional regions. The computer program developed in this report can determine the elastostatic stresses of two-dimensional bodies so that the relative error of each computed stress to the exact value does not surpass the allowable error.

View full abstract