The effects of the cyclic frequency and the stress wave form on the fatigue strength have been investigated by many investigators, but the physical meaning of the frequency and wave form dependent fatigue behavior has not been elucidated. In the present work, an analysis of these effects was made employing a modified Johnston-Gilman's formula. The experimantal results, which were obtained from fatigue tests performed under the sinusoidal, the triangular and the rectangular stress waves and under the cyclic frequency range from 0.2 to 60c/s, were well explained by the present analysis. Particularly, the frequency effect on fatigue strength was well interpreted in terms of the dislocation motion over a wide range of cyclic frequencies.

View full abstract

The stability criterion is clarified for the finite difference equation on a two-dimensional elasto-dynamic problem. Under its criterion, the authors analyze impact stresses in a semi-infinite plate subjected to pressure impulse on a part of the boundary. On the boundary, the tangential stress is compared with the exact one obtained by the Laplace transformation. The accuracy of the finite difference solution for the ramped pressure impulse becomes extremely better than that for the step one. Illustrative numerical results are given for some points in the plate.

View full abstract

Recently, a non-linear viscoelastic theory was developed by extending the conventional linear viscoelastic theory. Especially, Ilyushin has proposed a principal quasi-linear viscoelastic theory in which multiple integral representation in the on-linear theory is rationally modified into a single integral one for convenience of evaluation. This theory is thus promising for analysis of the elastic-viscoplastic behaviour of high-polymer. In the present paper, for investigating the applicability of this theory instead of the constitutive equation hither-to use in the photo-rheologic stress analysis, a simple case of this theory was discussed comparing with results obtained from an experiment on a thin-walled tube of softened celluloid under torsion. As the result, the principal third-order viscoelasitc theory was found applicable to approximation of the experimental result with the same accuracy as with the constitutive equation hither-to used. It was also found that every stress-strain curve for combined loadings of torsion and tension could be transformed into that for the corresponding pure torsion, by modifying the stress space with consideration of invariants of stress tensor.

View full abstract

In order to investigate the factors which affect the spanwise non-uniformity of the boundary layer and its property, measurements were carried out on the mean velocity, the turbulence intensity and wall shear stress in the transverse direction in the turbulent boundary layers which developed on two types of smooth flat plates of which the shapes of leading edge are different. The tunnel used had a moderately low turbulence, that is about 0.05 % of free stream velocity. Measuring stations were 9 cross sections. Various measurements were carried out in the transverse direction at very small intervals in these sections. From the results of experiments, it was found that a steady spatial quasi-periodic variation increased slightly and its pattern remained fixed toward downstream, and an appreciable negative correlation was calculated between the mean transverse velocity distribution and the turbulence intensity distribution in the same cross section. With regard to the open area ration of a screen which may affect the spanwise variations definitely, flow patterns through a screen with open area ratios 0.41, 0.52, 0.57 and 0.68 were observed by flow visualization by means of hydrogen bubble method. From these experimental results, it was obtained an appropriate value of the open area ratio of the screen used in the wind tunnel.

View full abstract

In some cases the velocity distribution in a turbulent boundary layer shows remarkable spanwise non-uniformity even though the outer condition is is sufficiently two-dimensional from a practical point of view. In the previous paper, the authors described the characteristics of the spanwise non-uniformity in detail, from the experimental results of the spatial distributions of the streamwise velocity, turbulent intensity in the turbulent boundary layer and wall shear stress on two types of flat plates. In this report, the scale and mechanism of the streamwise vortices are investigated by the measurements of the flow direction in the turbulent boundary layer. A floating element type device is made and the local wall shear stress is measured by this apparatus. The values of wall shear stress obtained by this method are compared with the values obtained by other methods such as Clauser chart and the Preston tube method. From the result, it is inferred that the mean value of wall shear stress can be expressed by a two-dimensional equation even though the spatial variations of the mean velocity are remarkably large as in this case. The mechanism of the spatial variation of this turbulent boundary layer is clarified by using these experimental results.

View full abstract

It is well known that when a shock-boundary layer interaction is comparatively strong, the shock in a duct extends over a great distance, which is called a pseudo-shock wave. At present, however, the formation mechanism of the pseudo-shock wave is not well understood. In this paper, in order to clarify its formation mechanism, the interaction phenomena of the reflected shock wave with the contact region in a shock tube were optically observed by the schlieren method. As the results, the formation process of the pseudo-shock became clear and the factors influencing the formation of the pseudo-shock were discussed. Moreover, the methods of calculation of the velocity and the shape of the reflected shock after the interaction with the contact region were presented. The calculated values agree well with the experimental results.

View full abstract

The propagation of shock waves induced by gas infection through two orifices into supersonic conical flow has been experimentally investigated. To reproduce the three-dimensional propagation of the induced shock waves, a series of evolved shadowgraphs was taken by the rotatable conical lens method. The results show that the propagation of the shock waves induced by twin injections and a single off-radial injection are identically greater than those of the single radial injections, regardless of the quantity of injection. It is also shown from the oil flow visualization that a separated region to generate strong recompression waves in the down stream of the twin injectors does not exist in the case of the single injector.

View full abstract

The effect of dual damping screens on the velocity distribution of pipe flow is analysed theoretically. The flow is assumed to be incompressible and inviscid. In this paper the case of an axi-symmetric flow is treated applying a small perturbation method. The mechanism of uniformalizing a velocity distribution of pipe flow is made clear. In case of a single screen, the damping process in pipe flow is similar to that in a two-dimensional flow treated by Taylor & Batchelor. The use of dual damping screens with each pressure loss coefficient greater than 2.0, which are set tandem with the non-dimensional axial distance L'/D of 0.51.0, gives a very uniform velocity distribution downstream of the screens, and here is a possibility of giving a very stable damping screen for contamination.

View full abstract

A supersonic plasma flow through the diverging lines of magnetic force is investigated experimentally. The Hall parameter of electrons is greater than unity, but that of ions is much smaller than unity. Measurements are made of the floating potential, electron temperature, ion density and ion velocity. The expansion of the plasma flow is suppressed by the external magnetic field. When the stream lines and the lines of magnetic force intersect, the electron temperature is higher at the downstream; when they are parallel to each other, a large potential difference occurs along the streamline, and equi-potential lines are crossed by the streamline. An extraordinary speed of ions is caused by the electrothermal acceleration. The strong electric field intensity along the streamlines agrees with the values estimated by the generalized Ohm's law.

View full abstract

Experimental investigations were conducted on the melting of a horizontal layer of ice which was directly heated by thermal radiation. Effects of the evaporation of water from the surface and the natural convection based on the density-inversion at 4°C in the liquid layer caused by the continuous melting of ice on the interfacial velocities and the transient temperatures have been studied. The onset of natural convection in the case of this experimental condition was found to be at a Rayleigh number about 500.

View full abstract

As the first step to elucidate the mechanism of combustion and stabilization of an opposed gaseous jet flame in a uniform airstream, this paper describes theoretical and experimental results of the development of the jet issued into the same fluid flow without combustion. The part of the jet can be divided into three regions termed the initial region, the fully developed mixing region and the U-turn region. The theoretical analysis shows that the results for the spread of the jets with different excess-velocity ratio can be collapsed into a single universal curve by introducing the excess-momentum radius. In the fully developed mixing region good agreement between such a theory and experimental results is obtained provided a virtual origin of jet is placed at an appropriate distance upstream of the nozzle exit. Thus the excess-momentum radius is confirmed to be a characteristic length of the opposed jet.

View full abstract

The turbulent mixing in an isothermal opposed jet, which seems to be basically similar to that of an opposed gaseous jet flame, is studied theoretically and experimentally on the same point of view as in the previous report. It has been found that the development of the turbulent mixing depends on the velocity profiles at the nozzle exit section and the excess momentum of jets, and that the character of the jet changes gradually from a self-preserving pure jet at the virtual origin of the jet into a wake type of flow depending upon the local excess-velocity ratio on the axis. The application of the idea of the excess-momentum radius to the flow with combustion gives the same type of expression and a result similar to the isothermal opposed jet, which is verified experimentally. It has been found that the concept of excess-momentum radius is of use also for the opposed gaseous jet flame.

View full abstract

To elucidate the extinction mechanism of the flame, further detailed considerations are necessary about the mutual relations among the flame shapes, the hydrodynamic features such as velocity distributions and the temperature characteristics within the flames close to both the upper and lower stability limits, in addition to the results indicated in the preceding reports. From such a view point, the velocity distributions and the axial and radial temperature profiles are minutely measured for three typical flames and two serieses of flames respectively. According to the comparison of the experimental results obtained with each visual flame shape, some special features are found, which seems to be relative to both extinctions at the stability limit and the transition of flame shape. From these results the validity of the excess-momentum radius as a characteristic length of the flame is confirmed, and a step to solve the extinction mechanism is obtained.

View full abstract

In the Computer Aided Design for a machine tool structure being developed, there are two important problems to be solved to compute the overall stiffness of a machine tool. One is the limitation of the core size of computer, which affects largely the computing accuracy. Another is how a machine tool structure is replaced by a suitable model available to the computation with good propriety. To make some countermeasures for these problems, one trial of CAD was carried out here with the cylindrical column having collared ribs and core-holes. From the results, it can be concluded that the cylindrical column in closed cross-section is well replaced by an one-dimensional beam-like element notwithstanding the existence of collared ribs and core-holes. This means that there may be some possibility of a new CAD technique to solve the present problems. In addition to this investigation, the effects of collared ribs and the influences of core-holes on the static stiffness of cylindrical column have been also described here.

View full abstract