In previous papers, the effect of a mean stress on a fatigue crack initiation and its propagation from a circular hole was estimated. It is well known that a crack initiated at a bottom of a dull notch have a large propagating rate. Therefore, a degree of the effect of the mean stress on the fatigue crack initiation and its propagating rate may be affected by sharpness of the notch.A fatigue test was additionally made with specimens containing two kinds of shapes of the notch and it is discussed how the degree of the effect of the mean stress on them is affected by sharpness of the notch and the following onclusions are obtained : (1) The mean stress does not affect the crack initiation at every shape of the notch. A life to the crack initiation at the circular hole or two slits is determined only by an alternating stress at the point inner ε₀ from the bottom of the each notch without regard to the shape of notch. ε₀ corresponds to a mean size of a ferrite patch of S35C steel used in this experiment.(2) The degree of the mean stress on the fatigue crack propagating rate decreases with sharpening of the notch and this can be explained by the behaviour of the crack propagation previously reported by the authors.

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The purpose of this investigation if to clarify the effects of alloying elements and heat treatments on fatigue strengths of steels quantitatively with correlation equations among the fatigue limit, static strength and metallurgical factors.On the analogy with the case of static strengths, a regression equation is assumed between the fatigue limit and the amount of alloying elements, and effects of carbon and heat treatments are described in this report.There exists a more general relationship between σ_w and σ_s than between σ_w and σ_B. It can be written as foloows; σ_w(α, T)=K(e₁, α, T)σ_s(T)+H(e, α, T). H is a function of alloying elements e, stress concentration factor α and heat treatment T. If carbon is taken as e₁, one of the alloying elements, K is nearly constant within a broad range of heat treatments.

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Previously, the authors reported on the severe erosion where the pit was made by a single blow of cavitation pressure. The present paper deals with the erosion of mild steel under cavitation of comparatively low intensity. Under the test conditions, the incubation period is found in early stage of damage progress, where slips and plastic deformations occur in ferritic crystals but not in pearlitic crystals. From these, the blow intensity of the cavitation is known to be tens of thousands of atm. Cracks are made by the accumulation of plastic deformations and they propagate to a falling off of large particles. Neither residual stresses nor cold worked layers are found in the damaged portions under this progressing stage. This may be one of the characters of erosion under low cavitation intensities.

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An experimental study on the plastic wave propagation in a cylindrical lead bar was made using a Hopkinson bar system under the conditions of several constant end velocities and a constant duration time. The stress history as well as the strain history at several locations along the length of the bar were measured. The unloading wave and the secondary wave generated in the bar were observed clearly. On the other hand, compression tests in a wide range of strain-rates were carried out to determine the strain-rate dependency of the material.It was found that a plateau, the region of constant stress and strain, exists but the results predicted from the rate-independent theory based on the static stress-strain relation do not agree well with the experimental results.

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In this report, "ultrasonic vibro-Brinell hardness H_ur" is defined in order to estimate the resistance to the plastic deformation of materials under the ultrasonic pulsating loads. The ultrasonic vibro-indentation hardness testing (20 kHz, 500 W, the ratio of the load amplitude and the mean indentation load : P_a/P_m=0.5) of annealed carbon steels (0.15% and 0.55% carbon included respectively) with a spherical indenter, made of hardened steel, was performed. Experimental results show that this testing method is useful as a simulative test of the plastic working under the ultrasonic pulsating compressive load, and that for the same material the differences of the estimating methods of the vibro-indentation load give different results, as "vibro-softening" of "vibro-hardening".

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A new method of variation of parameters starting with a linear damped vibration slution as its generating solution is advocated to analyse transient responses of various control systems and shock absorbing systems, which have usually large damping and strong nonlinearity.As a numerical example shows, this method yields a good accuracy with simple program and coarse steps when applied with a digital computer.

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The paper describes a method of calculating the natural frequency of a complicated piping system which is connected to a reciprocating compressor. Principle of calculation method is the application of Holzer's method generally used in the torsional natural frequency analysis.By multiplying matrix of each element in order, total transfer matrix of the system is obtained, and by applying the end condition, the natural frequency of the system will be gained in such a way that the residue value becomes zero. Calculation program for using a digital computer is completed. Difference of convergence of solution depending on the difference of the choice of lines is also discussed. By this calculation method the natural frequency of any complicated piping system can easily be obtained and great advantages will be found in the design of a piping system which can avoid the damage of piping and equipment due to resonance.

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The paper deals with the experiment conducted for examining the calculation method of natural frequency of a complicated piping system connected to a reciprocating compressor, which is described in the preceding paper. Experiment is conducted on 5 cases such as (1) Helmholz's resonance chamber, (2) piping with different sections, (3) piping with 2 inflow lines, (4) piping with bypass line and (5) general complicated piping, which are chosen as the combination of typical examples of elements. Experimental models used are made of vinyl chloride and resonant frequency and vibration mode then are measured by exciting the piping from one end by the loud-speaker. The results of experiments very well coincide with those of calculation and ascertain the applicability of the calculation method of the natural frequency in the preceding paper.

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The purpose of this study is as follows : two groups of carbon steels were studied on effects of the melting processes, the metallographic structures, the seasons of summer and winter in Japan and the annealing in vacuum on the behavior of sliding wear at ambient temperature to 600°C, at which the oxidation tendencies of steels were taken into consideration. One group had benn produced in air by a high frequency furnace, and the other had been remelted in a high frequency vacuum furnace after the porduction in air.The relations between the results of wear test and the oxidation tendencies that were measured from increases in weight of the specimens heated at 700°C for 1 hour to oxidation were studied in the first place. Then, the effects of both seasons of summer and winter and the annealing in vaccum before the wear test on the behavior of sliding wear were studied at ambient temperature.The results showed that the macroscopic oxidation tendency and the microscopic one must be considered in the study of the sliding wear, when the oxidation tendency obtained by heating at 700°C for 1 hour is called the macroscopic one and the oxidation tendencies of the broken surface at the welding contact points on the sliding area is called the microscopic one.

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An experimental study was made on the interference between the flow around the rotating blades of an impeller and the flow issuing from the circular nozzle in mixed and inward-flow radial turbines.The pressure distribution along stationary blades of the circular nozzle and the rotating blades of the impeller was measured for various radial clearances between the circular nozzle and the impeller. The flow pattern in the radial clearance was also measured by means of a small Pitot tube.When the radial clearance was very small, the effect of the interference was found mainly in the pressure distribution along the rotating blade, i. e. in the lift-force of the impeller and, there existed a several-percent reduction in the effective efficiency of the turbine due to the interference.

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The mechanism of a reduction of turbulent friction drag of a dusty gas is studied. The viscous sublayer of the dusty gas is increased with an increase of turbulence energy dissipation due to the presence of dust particles without producing additional turbulence energy, and is dependent on the kinematic viscosity of the gas, the friction velocity, the relaxation time of dust particle and the mass concentration of dust. Assumptions used in this analysis determine the minimum friction velocity, the maximum mass concentration, the maximum density ratio and the maximum particle size of dust at which the drag reduction occurs. For an air of normal temperature the minimum friction velocity is 0.053m/sec and the maximum particle diameter is 142μ. The reduction rate is relatively small and is decreased with an increase of friction velocity for given dust particles.

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For an exact design of quenching, the knowledge of boiling heat transfer has to be put to more practical use. In order to get some fundamental concepts on the design, some experimental and theoretical studies were made, and these include the boiling curves in a moderately unsteady state, the calculation of cooling curves for mass effect and the control of the quenching liquids.The results are as follows : The relations of the heat flux in quenching to surface temperature are almost the same as in a steady state; To calculate many cooling curves with accuracy, heat transfer coefficients as a function of temperature must be applied; And practically, it is necessary to get a quenching liquid with proper boiling curve, and it is shown that favorable liquids for each purpose can be obtained by applying some boiling data in a steady state.

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There are several kinds of optical methods for the measurements of temperature distribution in transparent fluids, such as the Mach-Zehnder interferometer, the Schlieren photo method, the shadow graph method etc.But the Mach-Zender interferometer needs doubled optical paths for reference, and the Schlieren method and the shadow graph have difficulty in getting exact temperature distributions although they can somehow give the maximum value of temperature gradients on the walls.The new method reported herein, which is called the "oblique shadow graph", is a very simple optical technique. It is only to take pictures of an object with a grid of parallel oblique-lines in its behind.The detail of thermal structure of boundary layers, the temperature distributions, and the maximum heat flux at the walls, can be known from the deviations of grid line in the picture taken by this method.In further application, this method can measure mass transfer, measure a temperature distribution of a boundary layer even when pressure changes, and measure boiling heat transfer.

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In the case in which a specimen was pressed against a rigid smooth surface, assuming its surface irregularities had a form of similar truncated cone in the same manner as the 1st report and the deformation of the truncated cone was elasto-plastic, the analytical values of equivalent gap for the fluid leakage between them were derived considering the permanent reduction of the central height of surface roughness. The results obtained can be summarized as follows : (1) The analytical values of equivalent gap obtained by assuming the surface irregularities as elasto-plastic were in agreement with the experimental values with a deviation of about 7%, excepting the condition of which the applied load was low, i.e. less than about 5kg/cm², where abnormally high surface irregularities existed on the surface roughness. The values obtained by assuming the surface irregularities as ideally plastic, furthermore, were derived in the same results as above.(2) The analytical expression of balance conditions between applied load and supplied gas pressure between contact surfaces was derived and the analytical values were in good agreement with the experimental results.

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