Takeshi Uchida

An Analysis of Deformation of Steel Coated With Ceramics in Rolling-Sliding Contact

The stresses, strains, and deformations produced by repeated, two-dimensional rolling-sliding contacts are analyzed both in the coated layer of ceramics SiC and in the substrate of two types of steels using a finite element method. Rolling and sliding are simulated by translating an appropriate set of normal and tangential surface tractions across the surface of an elastic-plastic model. A peak-pressure to shear-strength ratio of p0 /k = 5 and normal to tangential force ratios of T/P = 0.2 are examined. The effect of thickness of the coated layer on the mechanical behavior of the substrate is discussed.

Effects of Crystal Orientation on Fracture Toughness and Macrofractography of Single-Crystal Ice.

The effects of crystal orientation on fracture toughness and macrofractography of single-crystal ice specimens were examined by three-point bending test at -10°C. The loading rate KI was about 200kPa√m/s. Four types of single-crystal ice specimens, whose longitudinal directions were normal to the notch planes making respective angles of θ=0°, 45° (I), 45° (II) and 90° from the crystal orientation, were used. These specimens have a sharp edge notch made by pressing the edge of a razor blade on the bottom of the saw-cut slot. A macro replica was made on one side of the fracture surfaces using a dental impression material. The crystal orientation was measured using an etch-pitting method.The specimes of θ=0° and θ=90° exhibited similar fracture toughness values which offered a median value of Kc]50%=110.5kPa√m, and those of θ=45° (I) and θ=45° (II) also yielded similar values which gave Kc]50%=99.2kPa√m. The fracture toughness of columnar grained ice specimens estimated from that of single-crystal ice specimens was higher than the experimental values. Macro replicas clearly showed that the morphology of fracture surface was affected by those crystal orientations and it contained many traces of crack extension along the basal plane {0001} or the prismatic plane {1010}.

Effects of various factors on rime icing. Part II: Effects of stick diameter and water vapor content.

筆者らは屋内で人工的な霧氷を生成し,年間を通して霧氷の観察を可能にすること,ならびに自然環境下では種々の条件にかなりのばらつきがあることを勘案して,低温室内で超音波加湿器により発生させた噴霧の雲粒を用い,雲粒半径および温度のばらつきを最小限に抑えた実験的研究を行っている.第一報では,着氷形状や着氷速度と実験条件(特に温度・風速)との関係について報告した.本報では,雲水量を先報での値より一桁ほど小さく設定し,被着氷物の直径を5種類さらに材質を2種類変化させ,着氷成長の連続観察を行い,着氷の外観形状および雲粒の捕捉率などを調べた.その結果,着氷長さへの被着氷物直径の影響はあまり認められなかった.また,被着氷物直径が4mm以上では着氷幅はその直径程度までしか成長せず,雲粒の捕捉率は時間の依存をほとんど受けない.一方,4mm以下では着氷は風上に向かって末広がりに成長し,雲粒の捕捉率は大きくなった.被着氷物の材質の差は,着氷の初期を除くと着氷長さおよび雲粒の捕捉率への影響はあまり認められない.さらに,雲水量も気温や風速に併せて着氷の成長に対する大きな影響因子の一つであることなどがわかった.

Effects of loading rate on fracture toughness of ice. III. Statistical study on fracture toughness of ice.

A method to express the distribution of the experimental results of fracture toughness of ice was investigated by postulating the Weibull distribution with three parameters. The data were taken from the previous experiments conducted to study the effect of loading rate on the fracture toughness9), 10). Weibull parameters were estimated by several estimation methods11), 12) and the parameters obtained were compared with each other. The effect of loading rate together with that of specimen size on the parameters were discusssd at three loading rate ranges. It was confirmed that the parameters estimated were closely related to the experimental value of fracture toughness.