The fatigue limit of a defective material provided with a notch by mechanical processing can be estimated from that of a specimen made of a non-defective material with a hole at the root of a notch given by mechanical processing. From our examination on the bending and torsional fatigue of an S35C notched specimen with a hole of 0.3 mm in diameter at the notch, root, the following results were obtained : 1) When the root radius of the notch is larger than that of the notch at the branch point, the fatigue limit is determined by the propagating conditions of the non-propagating crack at the edge of the small hole in the case of bending or torsion. 2) If the root radius of the notch is smaller than that of the notch at the branch point, the bending fatigue limit is scarcely influenced by the existence of a small hole, but the torsional fatigue limit is decreased in the range of 10-20 %. 3) The notch factor of a notched specimen with a small hole at the notch root is small in comparison with that of a notched specimen without a hole in the case of bending or torsion.

View full abstract

Corrosion fatigue test of a mild steel in salt water has been carried out at various cycle frequencies ranging from 1400 c/min to 0.28 c/min to study corrosion fatigue mechanism. The following results have been obtained from the measurement of crack growth rate and the microscopic observation on the cross section and on the fractured surface of specimens. At the cycle frequencies from 1400 c/min to 100 c/min, the decreases of the wedge action due to the hydrodynamic pressure of corrosion products are predominant for the increase of crack rate, and the crack rate increases at lower cycle frequencies from 100 c/min to several cycles par minute, the wedge effect mentioned above becomes negligibly small, and the growth of crack width due to the corrosion of crack walls increases the crack rate at lower frequencies. At the cycle frequencies lower than several cycles per minute, the dissolution of crack tips increases the crack rate. However, at extremely lower frequencies a decreases of crack rate is sometimes caused by a remarkable branching of crack tips.

View full abstract

Crack initiation and propagation in anisotropic rolled steel, the anisotropy of which was caused by a laminated structure of ferrite and pearlite bands, were studied by means of micro- and macroscopic observations of specimen surface under biaxial stress conditions. Slip bands and microcracks were initiated at an early stage of fatigue life in ferrite bands. Their direction coincided with that of the maximum shear stress, independently of the directions of the principal axes of anisotropy. However, growth of the microcracks to macrocracks and propagation of these macrocracks were much affected by anisotropy. When the direction of ferrite bands coincided with one of the two maximum shear stress directions, the micro- and macrocracks grew, coalesced and propagated fast within and in the direction of the ferrite bands. When the direction of ferrite bands intersected the maximum shear stress directions, growth of the microcracks in a ferrite band was halted at the ferrite-pearlite interface. Their growth to a macrocrack and its propagation were caused by coalescence of the halted microcracks across the pearlite bands after a certain number of stress cycles, resulting in intermittent and slower propagation of macrocracks with zig-zag paths which coincided with the directions of the maximum shear stresses.

View full abstract

Steady and non-steady two-dimensional Seebeck effects, induced by the interface temperature distribution, are investigated theoretically and experimentally. The results obtained are summarized as follows : 1. Five dimensionless parameters which affect the thermo-electric phenomena are obtained by dimensional and numerical analysis, for thermal and electric currents. 2. The limit of the above dimensionless parameters, in which the longitudinal thermo-electromotive force indicates the mean value of interface temperature distribution, are obtained. 3. It is found that the highest temperature can be estimated with use of thermoelectric eddy current voltage, induced by the interface temperature distribution.

View full abstract

In order to improve the heat transfer performance of the gas side surfaces in ordinary heat exchangers and gas cooled reactors, many types of extended surfaces are used. In these surfaces, heat transfer for transverse fins normal to the flow direction is extremely affected by the behavior of vortex flow aroused in fin spaces. However, there are no available information on the relation between the heat transfer performance and the behavior of the vortex flow in fin spaces. In this paper, to increase the heat transfer rate from transverse finned surfaces, rear corners of fin surfaces are chamfered. The heat transfer rate is measured, and the behavior of the vortex flow is analysed by a hot-wire anemometer in a wind tunnel and a visualization technique using polystyrene particles in a water tunnel. The exchange rate of fluid between the main flow and the vortex flow in fin spaces is measured. It is made clear that the surfaces with chamfered fins increase the heat transfer rate owing to the increases of speeds, turbulence intensities and the exchange rate of the fluid in fin spaces.

View full abstract

The numerical method on the transient heat conduction with temperature-dependent thermal properties by the authors is extended to the solution of heat conduction with freezing or melting. In this method, multiphase problems are reduced to single phase ones by using a temperature-dependent function for heat capacity in which the latent heat is taken into account. The main advantages of this method are that problems on freezing or melting can be handled with substances having a fixed melting point and/or unfixed melting point but melting ranges, and that it can easily be applied to two dimensional problems. The freezing of water is mainly examined in this paper. The numerical results are compared with experimental results and Neumann's exact solution, and the results are indicated to be satisfactorily accurate for the solution of heat conduction with freezing or melting.

View full abstract

Vaporization and combustion processes of liquid fuel droplets in a fluctuating turbulent gas environment without any time-mean flow velocity are investigated. Such environment simulates adequately the flow field where average flow velocity is nearly equal to the droplet particle velocity. This paper also deals with the methods and instruments used in measuring turbulence quantities such as intensity and scale in this turbulent environment. Steady state empirical equations of heat and mass transfer for liquid sphere are applicable accurately to the evaporation of droplets under the condition of quasi-steady state in this turbulent environment. On the other hand, combustion in the turbulent environment is not like that under the forced convection and the flame shape is not tailed but almost spherico-symmetrical with wrinkled edges. The burning rate increases proportionately with eddy diffusivity and the ratio of this value to that in a stagnant atmosphere is represented by the ratio of eddy diffusivity to thermal diffusivity.

View full abstract

This study constitutes a part of the attempt to clarify the process of ignition of general higher hydrocarbon fuels following a suddn homogeneous heating. A special shock-tube device was constructed in which two plane shock waves of equal strengths collide with each other in the observation plane to form a stagnant region of controlled temperature and pressure free the cooling effects in the test gas. The oxidation reaction of butane-oxygen mixtures and the decomposition reaction (in the absence of oxygen) of butane were observed. Especially, the heat absorption rate in the latter reaction at various temperatures was determined in situ from pressure and (interferometric) density recordings, and the corresponding decomposition rate constant was deduced. The ignition delays of butane-oxygen mixtures were measured with much better time resolution than in the previous incident-shock study (with an overall agreement with the previous data) but a randomness in the appearance of ignition spots was observed which constituted a source of the scatter in the data. The half life of butane subject to thermal decomposition was demonstrated to be shorter than the ignition delay below about 1100°K, but to become longer than the latter above this temperature. these findings are considered to help in the modelling of the ignition mechanism of hydrocarbon fuels.

View full abstract

Scratch friction has been investigated in which the metallic transfer could be neglected. The scratch tests on some metal surfaces were carried out using conical and spherical sliders of hard materials. the geometric shapes of the scratched groove were examined in detail and a comparison of the friction force with these was made. Experiments showed obviously that there is a good correlation between the friction force and the groove shape. The coefficient of friction on the slider face was found to decrease with a decreasing groove depth under an influence of the surface films on the softer metal. An analysis to determine the friction force quantitatively has been developed. This theory specially includes an effect of the height of front ridge formed in front of the slider during scratching on the friction force. The results of the scratch tests show that the theory is very useful for the derivation of the friction force.

View full abstract

Before this paper, it is pointed out that the barrel shaped hob for generating the internal gears is difficult to make with theoretical exactness, and the conception of using a cylindrical forming hob instead of the generating one is reported. This forming hob has a tooth helix wound once and is made very easily. From the cutting test with the above hob made on trial, a new excellent hob is developed. Present paper describes the designing and manufacturing method of the new hob, the results of cutting test and the instructions for its practical use. This hob has the broach-like teeth wound twice along the helix, and can be made by almost the same technique as the one used in the manufacture of the ordinary hob. An accurate internal gear can be continuously cut with this hob, which will be especially suitable for large internal gear production.

View full abstract

In rolamites, the band-generated forces can be known when the profiles of bands are given, but it cannot be known what profiles generate the prescribed forces. Then, in order to apply the rolamite as a transducer between force and displacement, the profiles of bands have been investigated to generate the desired functions of forces in the case where the distances between guides, diameters of rollers and moduli of longitudinal elasticity of bands are known. The prescribed forces have been generally obtained by solving an inhomogeneous difference equation about the flexural rigidities of bands. The forces have been also obtained by the bands with partially constant rigidities though the maximum displacement of rollers are limited to certain values.

View full abstract