An extension was made of the applicability of the concept of the elastic analogue in the creep stress analysis proposed initially by Hoff. It was found that the elastic analogue is valid, with some restrictions imposed on the creep stress-strain-time relation, for all the boundary-value problems and independently of the assumption of either the time-hardening theory or the strainhardening theory, when the boundary conditions are independent of time. Under non-steady conditions of boundary values, the elastic analogue is applicable to the materials which follow the time-hardening theory, irrespective of the manner of change in boundary values with time. For materials which obey the strain-hardening theory, the elastic analogue is valid only when the boundary values are expressed as a product of a time-function and a position-function, which means a kind of the proportional loading.

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In this paper the results of experiments on the creep and creep rupture of internally pressurized cylinders of a low carbon steel and a 2 1/4 Cr-1Mo steel are reported. Theoretical analysis of the stress distribution of thick-walled cylinders during creep was derived on the basis of a nonsteadystate multiaxial stress creep theory as well as a finite strain theory. These results were checked by comparing with the experimentally determined stress distributions which were derived from the measurement of residual stress in the cylinders which have crept by means of the Sachs and X-ray method of stress analysis, and a fairly good agreement was obtained between the two. In addition, a discussion was made on the stress criterion for creep rupture of pressurized tubes in consideration of the effects of stress increase due to creep deformation, hydrostatic component of stress, wall thickness, maximum principal stress and anisotropy of the material. It was concluded that the so-called mean diameter formula is valid for the design formula of boiler and pressure vessels irrespective of materials and testing conditions.

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In this report, the problem of elastic torsion of circumferentially grooved shafts is numerically solved by the same method as presented in the first report. The solutions are obtained for the cases where contours of grooves are circalar arcs. The stress concentration factor, the stress gradient at the bottom of the groove and the angle of twist are calculated. The numerical results about the stress concentration factors coincide fairly well with Neuber's solutions, but it is proved that generally his solutions give somewhat unsafe values. A method for evaluating the angle of twist on arbitrary length over the groove is presented, and its reliability is checked experimentally.

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In this report, the problem of elasto-plastic torsion of circumferentially grooved shafts is solved by the same numerical method as presented in the 1st report. The solutions based on both flow and deformation type theories are obtained for the Ramberg-Osgood material. The numerical calculations are carried out for several characteristic parameters of material, then the stress and strain concentration factors, stress distributions, the angle of twist, etc. are presented. The results calculated by the flow theory are experimentally verified, and comparing them with the deformation theory, it is proved that both results coincide fairly well with each other about the angle of twist, but about other quantities, for example, the stress and strain concentration factors, the difference between both results becomes larger as torque increases.

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The strain concentration at the tip of fatigue crack in coating film such as electroplating, painting, lining, etc., is restrained by the base metal when both the materials are completely bonded. And the strain in the base metal increases due to the strain concentration in the coating film. As the binding effect decreases in the direction of thickness from the interface, the strain at the surface of coating film decreases with the thickness of the coating film. The strain also depends on the elastic moduli of coating film and base metal. In the present paper, the binding effect is calculated elastically with a simple model. The stress distribution near the circular hole of epoxy resin plate is measured by the reflective polariscope, before and after the plate has been bonded to another non-notched resin plate. The experimental results are found to agree well with the results of calculation on the simple model. These results are also applicable to the effect of lining thickness on the propagation rate of fatigue crack in bearing alloys lining on steel plates reported in the previous paper.

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The fatigue damage most closely related to the practical fatigue life of the material should be the accumulation of a power function of the plastic strain. On the basis of this concept, the authors proposed a fracture criterion based on strain under varying strain amplitude instead of the linear damage law, (Σn/N)_f=1, based on stress. The fracture criterion under varying strain amplitude is expressed as below : In the present report, this criterion was extended and applied to the results of the plastic fatigue tests on steels under rotary bending which were carried out over several years in their laboratory. The experimental results were summarized by the above criterion and compared with those calculated by the linear damage law. As a result, this criterion based on strain is found applicable to the estimation of the fatigue life as precisely as under the linear damage law. Although the linear damage law is well established for the low-cycle fatigue, it is expected that the criterion based on strain will be more effective for the ordinary fatigue of comparatively lower stress levels than for the low-cycle fatigue.

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In the vibratory systems of multiple degrees-of-freedom with natural frequencies p_i, p_j, etc. and under parametric excitation of frequency ω, unstable oscillations of summed and differential types of higher order with frequencies ω_i (≒p_i), ω_j (≒p_j) take place when sω (s=2, 3, ……) becomes nearly equal to a sum of or a difference in two natural frequencies p_i and p_j, i.e., sω≒p_i±p_j=p_ij. Any possibility of occurrence of the oscillations of summed and differential types with sth order does not exist until the small quantities of sth order, i.e., the terms of order ε^s are taken into account ; it follows there from that these oscillations do not appear until the sth approximation. Further, it is concluded that there is no unstable oscillation of differential type of higher order as well as the first order, and that the effects of damping on these oscillations are similar to those of the first order, that is, the existence of damping does not always reduce the width of unstable region.

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The research presented in this paper concerns the experimental studies of two-phase air-water flow phenomena in the disturbed flow region that exists downstream from an air-water mixer. Experiments were carried out using a horizontal acrylic resin tube of 26.0 mm I.D. and 7.0 m long. The results obtained are summarized as follows : 1. Within the disturbed flow region, there occur drastic changes in the flow configuration and the pressure gradient along the tube. A transition point exists at which the flow pattern at the downstream section is quite different from that at the upstream. 2. The change of pressure gradient mainly results from the momentum change of two-phase mixtures, and so it is closely related to the change of flow configuration. 3. To establish a fully developed flow, a distance equal to 40 to 200 times the diameter from the mixing point may be required. This distance is nearly proportional to the superficial velocity of two-phase mixtures.

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A reference value of the thermal properties for a fluid at a supercritical pressure is proposed as, F=1/(tω-t∞)∫tωt∞F (t) dt where F : reference thermal property F (t) : thermal property as a function of temperature tω : wall temperature t∞ : bulk temperature. The heat transfer coefficient of a supercritical fluid can be determined by applying the reference value to an ordinary heat transfer formula for constant thermal properties. Experiments of heat transfer for carbon-dioxide at a supercritical pressure were made for three types of heat transfer, viz. (1) natural convection from a horizontal pipe, (2) natural convection from a vertical plate, and (3) forced convection from a circular pipe. The experimental result agrees with the proposed calculation.

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To investigate the influence of the electric potential on the heat transfer from a plasma to a solid wall, the heat input rates to the water-cooled Cu-pipe in an atmospheric pressure argon plasma jet were measured applying the potential difference ranging from -20 V to 5 V between the plasma and the pipe. The electric currents to the Cu-pipe were measured at the same time. It was found that in the lower potential difference the heat input rates are proportional to the currents and the proportional coefficient coincides with the work function of copper, but in the higher potential difference the heat input rates increase more due to the joule heating in the low temperature region about the pipe. It was also shown that the minimum point of the heat input rates is recognized at a slightly negative potential with respect to the floating potential.

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In adopting the DC arc plasma torch as a heat source of plasma tunnel, it is, first of all, important to know the nature of non-uniformity of the plasma flame in interpreting the data obtained in the test section. In this experiment, the authors pointed out that the non-uniformity occurred even in the domain equivalent to static arc, and that it seemed, therefore, doubtful to use the anode nozzle as a supersonic nozzle. Next, it is observed that, in the domain in which cyclic voltage fluctuation is present, the nature of the fluctuation is analogous to the vibration of string with both end being fixed, and from the energy equilibrium consideration, the desirable operating condition of torch is proposed. Some comments are made on the electrode failure.

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Results are reported of the experiments with a shock tube on inert-gas MHD power generators utilizing nonequilibrium ionization. By preheating the whole low-pressure chamber of the shock tube, it was possible to seed sufficient amount of potassium to the working gas and to realize the conditions required for MHD power generation. The first type of generator made use of the induced electric field, resulting from the interaction of gas flow and magnetic field, to obtain nonequilibrium ionization. Whereas the steady-flow experiments reported so far have not yielded high electrical conductivities predicted by nonequilibrium theory, the results of detailed measurements in the present device were fairly close to those predictions. The reason is considered to be the absence of appreciable boundary effects and flow instability in experiments of such short durations. The unfavorable effect of small amount of impurities on the generator performance was also demonstrated. The second type of nonequilibrium MHD generator utilizing metastable nitrogen was similarly tested, and was found to be a promising alternative.

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This paper is concerned with a survey on the effect of air-bleed systems on the fuel-air ratio of the mixture which is made by a carburettor having a main system only. Calculations and experiments were made to investigate the influences of the location of the air-bleed hole relative to the fuel level in the float chamber, and diameters of air jet and nozzle upon the mixture strength. The results calculated using the equations have been found in good qualitative agreement with these obtained from the experiments. The following are noteworthy results : (1) The location of the air-bleed hole affects the mixture strength in a range of the smaller air flow through the venturi. (2) The diameter of the air jet affects the mixture strength in a range of the larger air flow through the venturi. (3) The increase of the nozzle diameter weakens these effects.

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Magnetic bearings with control circuits are very attractive for their frictionless property, but the analytical researches made before in this field are unsatisfactory. The authors studied this problem theoretically and experimentally. First, a mathematical model was constructed by means of linearizing procedures ; next, the root-loci were calculated on a highspeed electronic computer, and the results were compared with experimental ones which were obtained on a real model. Here the authors summarize that : (1) Among the many factors which affect the stability of the control system, the electromagnetic solenoid has the greatest importance. (2) It is seen that the optimum condition of the compensating circuit depends largely upon the distance between the electromagnet and the rotor. Thus, thes analyses will be useful for the deeper understanding of the control systems and for the better design of magnetic bearings.

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Whirl instability of an externally pressurized gas journal bearing which has a peripheral row of feeding holes is theoretically investigated and the analytical results about the natural frequency of the shaft-bearings systems, whirl onset speed and whirl frequency are compared with the experimental ones presented in a previous paper by the authors in relation to the bearing factors such as radial clearance, supply pressure and number of feeding holes. Based on the assumptions that the pressurized gas flows adiabatically into a bearing clearance space through an annular feeding slot and that the fluid motion in the bearing is completely viscous and isothermal, the reacting force of gas film for a small vibration of the shaft is obtained by making use of the perturbation method with respect to eccentricity ratio. The analytical natural frequency of non-rotating shaft is slightly larger than the experimental one. The analytical whirl frequency shows good agreement with the experimental one for the clearance larger than about 0.03 mm, but becomes considerably larger than that when the radial clearance is as small as 0.02 mm. On the whirl onset speed, the analytical results are found in good agreement with the experimental ones for the clearance of about 0.05 mm. The calculated onset speed becomes smaller than the experimental one for the clearance larger than about 0.05mm, whereas the former becomes larger than the latter inversely for the clearance smaller than about 0.05 mm

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