Following the 1st report, we have performed the ring-shaped tube impact tensile test of cold drawn, seamless steel tubes, in order to study some characteristics on the impact strength of tangential direction of small-diametral and thin-walled steel tubes. As the cold drawn tubes have many fiber structures in the direction of drawing, it generally seems that the resistance to impact load in the logitudinal direction differs from that in the tangential direction of tube. But the results obtained through this test have a similar tendency to the case of notched tube impact bending test, mentioned in the 1st report. The different point from the results of impact bending test is that the impact tensile strength gets a little larger as test temperatures become lower than 100°C and has a maximum value at the temperature of -60°C or -100°C.
In this investigation we studied the effect of Ammonia Gas atmospher on the torsional creep strength of 18-8 stainless steel bars austenized, or then after twisted to 0.128π/cm at -60°-600°C, and found that the creep strength at 500°C and 600°C in Ammonia Gas was considerably smaller than the creep strength in air, and the decrease due to gas of creep limit for a mean creep rate of 4×10-4%/hr during 75 to 100hr was about 34% for 500°C and 23% for 600°C. In the creep specimens tested in Ammonia Gas a hard nitrized case of 0.16-0.25mm in thickness was formed and many fine cracks were produced in the surface of the case during creeping.
The effect of supplementary notch on the reduction of stress concentration of the initial notch (Hereafter will be called 'mother notch' in this report) is widely known, and in connection with this subject many studies are reported. Most of them, however, are concerned with multiple notches of the same configuration. From this point of view, the authors investigated on the effect of supplementary notch with a different shape from that of the mother notch. Two supplementary notches of the same shape were cut symmetrically on both sides of the mother notch, and their notch depth and root radius were varied in several steps. The effect of the root radius was small for a constant depth, but the notch depth showed a large influence, reducing the stress concentration factor of the mother notch remarkably at a little smaller depth than that of the mother notch. By finding the intersection point of two curves representing the change of stress concentration factor due to the notch depth, the optimum condition for the minimum stress concentration of the notch system was obtained at a given root radius of the supplementary notch. From the scope of the present experiment, it may be concluded that the most effective supplementary notch is that with a depth a little smaller (About 90%) and a root radius somewhat larger than those of the mother notch. In the case of the most optimum condition, the reduction of stress concentration factor showed the amount of about 11%. The case of two equal mother notches was also examined, and the relief of stress concentration was larger, because two mother notches act mutually as a supplementary notch to each other.
For the study of the effect of hydrostatic pressure on mechanical behaviour of metals and alloys, a tri-axial testing machine was designed and constructed. The machine was designed to carry out tension and compression testing under the confining pressure up to 5000kg/cmcm2 at room temperature. Tension tests on Zinc, Aluminium, Titanium, Zirconium and Mg-Al Alloy were made under confining pressure. The effects of hydrostatic pressure on ductility, for example, elongation and reduction in area were observed.
Micro-Vicker's-hardness of five typical phases obtained by different kinds of heat-treatment of Cu-Al eutectoid alloys were measured, comparing with their phase-transformations occurred in heating them from room temperature. Fundamental phase-transformation process of quenched specimen which had already been observed in micro-structual, specific heat, electric resistance and X-ray investigations, β'→β1→P→β was also verified by the results of the above high-temperature hardness testing. But both an abnormal transition observed between 200°C-300°C during tempering process of β' phase and a pearlitic decomposition at high-temperature heating of μ phase which is transformed after long time heating at lower temperature below the eutectoid temperature, are left unexplained.
Al-alloys with various concentrations of Zinc were prepared for the study of the creep phenomena at 200°C and 250°C under an initial stress of 2kg/mmmm2. The high-temperature strengh increased with the increase of Zinc concentration in the range of solid solution and the tendency was more remarkable in the dilute alloys. In the alloys containing Zinc beyond the solid solubility, the high-temperature strength reached maximum at the critical composition, and then decreased with increasing Zinc concentration in the range above the critical composition. The strength of two-phase alloys were found to be much higher than that of solid solution alloys. The high-temperature strength was affected by the structure obtained during the heat-treatment before testing. It was strongly influenced by the size, shape and distribution of precipitates.The specimens containing smaller particles were stronger and the specimens with lameller precipitates produced by a boundary reaction, as shown in the 32.26wt% Zinc alloy, were also very stong. Ductile rupture was found to occur in the solid solution alloys, but brittle rupture in the two-phase alloys. Grain boundary sliding, slip in grain and fold formation were observed on the surface of ruptured specimens. Cavities were found only at the triple point of boundaries on the brittleruptured specimens. The nucleation and development of cavities was confirmed to occur as the consequence of grain boundary sliding.