The threshold stress (nominal) of which the repetitions develope a fine crack at root of a notch in notched specimens is different from the threshold one (nominal) to spread the developed crack. The values of these stresses depend on the severity of the notch action; they become equal to each other in specimens in which the maximum stress, at the root of notch, under a load of fatigue limit is equal to the yield point of the material. The point at which these two threshold stresses become equal to each other is called the branch point.
When the form-factor of a notch is larger than that of the branch point, a small plastic zone develops at the root of the notch under action of load equal to the fatigue limit of the specimen and as a consequence the specimen becomes more resistant to crack-spreading than to crack-forming action of the external load.

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This investigation was performed to clarify the diagram of endurance limit of notched specimens under repeated torsion. The materials used were of two kinds of carbon steels, and specimens had V-grooves of two or three kinds of sharpness.
Results obtained are as follows:
(1) In this experiments the authors defined the fatigue limit as a maximum reversed stress at which cracks do not yield at the root of notch. Such a determination of fatigue limit is more appropriate theoretically than such case that a maximum reversed stress, at which the specimen does not break down, is defined as the fatigue limit. By such determination, the diagrams of endurance limit under reversed torsion were procured for a few notched specimens.
(2) The effect of mean stress in the diagram of endurance limit was much considerable in this experiments than in early experiments basing upon whether the specimen break down or not. Further it was cleared from this results that the diagram of endurance limit of notched specimens under reversed torsion becomes a line drawn from the completely reversed fatigue limit, on the ordinate, to a point on the abscissa, obtained from dividing the torsional strength of unnotched specimen into the stress concentration factor α.
(3) Above tendency was understood from consideration of the distribution of mean stress in the specimen during the fatigue tests.

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When containing small holes of faults which are the source of fatigue fracture, or when their inner fatigue limits are lower than outer ones, materials are often cracked from inner parts.
In this report, by an illustration of large size rotational bending fatigue test, the author relates the mechanism of fatigue fracture started from inner parts.

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In this investigation we made experiments to obtain the effect of surface rolling on the abrasion resistance of steels by the Amsler abrasion testing machine under the conditions of dry and lubricated states.
A surface rolling apparatus was specially designed for this investigation. The materials applied to tests was 0.34% carbon steel. Surface rolling pressure was 258, 326, 411 and 517kg/mm² by Hertz's formula, and experiments were also made on steels without surface rolling for comparisons.
In the abrasion tests the materials paired with the specimens were gray cast iron and were fixed, while the specimens were rotated at the peripheral velocity of 0.5m/s. Experiments were made till the rubbing distance of about 5.74km under dry state and 57.4km under oil lubrication. Amount of wear, moment of friction and temperature were measured. As the results, it was cleared that the abrasion resistance of the steels surface rolled is generally superior to that of the steels not surface rolled.

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In this paper, a new relationship between compressibility of suspension and those of its components were led considering the effect of the interfacial actions at the surface of suspended particle.
The approximations, showing us the possibility that the compressibility of suspended particles could be determined graphically, were obtained by using some assumptions and were verified experimentally by measurements of sound velocity in suspension and its density.
The value for the compressibility of the particle in question derived from these approximations with the suitable quantity of the constant “p” was in good agreement with the values obtained by another investigators.

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The author defined the suitable range of the color tone of portland cement by the Munsell color card test and G. E. recording spectyrophotometer, and examined that the chemical conditions and the cooling conditions of clinker influence to the color tone of cement.
Moreover, he explained the color harmony for portland cement by using the theory of P. Moon -D. E. Spencer.

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