[in Japanese]

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[in Japanese]

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[in Japanese]

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Hardness can be related to brittleness in steels through yield stress and reduction in area by the usual tensile test. Here the effects of low temperature, neutron irradiation and tensile work-hardening on brittleness in steels were investigated by Vickers hardness. The temperature dependence of Vickers hardness on several steels was studied over a range from -196°C to 100°C. It was found that the logarithmic hardness versus the reciprocal of absolute temperature can be described by several linear stages. If the intersection of the two lowest temperature stages is defined as a hardness ductile-brittle transition temperature, it will turn out that the increase in the transition temperature during the neutron irradiation is approximately consistent with the data obtained by the Charpy impact tests and reviewed by Pellini, et al.
The intersections of the two lowest temperature stages in the hardness-temperature curves of the tensile work-hardened steel shift to the higher temperature side as in the case of neutron irradiation, and it is considered that their increases are approximately in accord with the results obtained by the Charpy impact test.
Therefore it may be suggested that the influence of neutron irradiation on notch sensitivity may be neglected, and that low temperature, neutron irradiation and prestraining embrittlement in steels can be detected in terms of the temperature dependence of Vickers hardness.

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Concerning the strength and rigidity of foamed materials there have been various views proposed hitherto all based on what is considered to be the physical properties of foamed materials obtained by analysis of the models that have only been assumed as such.
There have so far been two types of proposed models, one will be called the film-shaped model, and the other the voided-solid model. The former matches to the foam of elastic materials having low density. The latter matches to the foamed glass and A.L.C. of brittle materials of high density.
The author points out the differences and similarities involved in these two types, and proposes his own views on the subject. He calculates the values by their theoretical analysis, and comparing those with the observed values, discusses the reasons for the differences between these two.
The present paper will form a sequel to his work under the title“A Study on the Construction of Foamed Materials, ”published in January 1963.

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The fatigue strength of unsaturated polyester has been studied with respect to the effect of temperature, humidity, water absorption and its exposure to ultraviolet ray, and the following facts have been made clear.
(1) The fatigue strength of unsaturated polyester has been much affected by temperature, but hardly affected by humidity.
(2) When the relation between the work of internal friction per cycle ΔW and the number of cycles to failure N is presumed as (ΔW)^a·N=K, the fatigue Strength σ_a is presented by
σ_aN^α=k(E/δ)^1/2,
where δ and E denote respectively the logarithmic decrement and the modulus of elasticity.
The relation shows good coincidences with the experimental results. It is explained by the decrease of E/δ that the fatigue strength is lower under higher temperature, While ΔW is independent of temperature.
(3) The fatigue strength of unsaturated polyester is reduced by exposure to the ultraviolet ray. The reduction of fatigue strength may be mainly attributed to the roughening of the surface.

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An apparatus was constructed for determining the viscosities of small flat pieces of glass from the rate of penetration of a cylindrical indenter. A diagrammatic sketch of the apparatus is given in Fig. 1. The essential parts of the apparatus are; (1) A cylindrical indenter, (2) A device to supply the load to the indenter, (3) An optical system to magnify the penetration distance of the indenter into the glass, (4) An electric furnace to provide a suitable constant temperature enclosure. Using the NBS 710 glass the relation between the rate of penetration and viscosity of glass was determined with this viscometer. This relation is given by a formula of the type Wt/η=AP²+BP in which P: penetration depth, η: viscosity of glass, W: supplied load, t: time and A, B: constants.
This method is adapted to the measurement of the viscosity η in the range of 10⁴∼10¹² poises with experimental accuracy of about Δlogη=±0.1. And then the viscosity of some chalcogenide glasses was measured in the range of 10⁶∼10¹¹ poises.

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