The nonferrous material that is fit for standard block of hardness for industrial purpose is at present 7-3 brass. But it is inefficient at lower hardness because its variation range gets extensively scattered then. The present research was conducted to control the hardness of brass and its variation range by replacing some of its zinc contents with such metals as beryllium, manganese, aluminium, and silicon, under various draft of cold rolling and heat treatment. Stable hardness could be attained around HRB 30 with controlling zinc content of lower hardness materials to 3∼5%. The added elements are in the range of 0.3∼1.0%. These ternary alloys are constructed with α-phase only, of which the standard composition is shown in Table I. The working process of homogenizing, initial rolling, intermediate annealing, final rolling, final annealing, etc. is respectively shown in Table II. The research has proved that beryllium is the most effective as additive element, and aluminium and manganese come after it with their variation range of hardness at around HRB 30∼40.
In order to study the effects of age and of heat-treatment etc., after rolling, on the repeated impact tensile strength of rolled screw bolts, we have conducted repeated impact tensile test of 3"/8 rolled screw bolts, made of SS41-, S55C-and SCM3-steels. The results obtained are outlined as follows. (1) The repeated impact tensile strength of rolled screw bolts is larger than that of cut screw bolts. (2) The age increases the repeated impact tensile strength of rolled screw bolts made of SS41-steel, after rolling. (3) The heat-treatment (quenched and tempered) decreases the repeated impact tensile strength of rolled screw bolts remarkably after rolling. (4) The screw rolling increases the repeated impact tensile strength of heat-treated screw bolt made of SCM3-steel, after heat-treatment. (5) The hot dip zinc plating decreases the repeated impact tensile strength of heat-treated screw bolts slightly after heat-treatment.
Many studies have hitherto been published on multiple repeated stress tests, most of which are based on the final fatigue fracture consideration. The research on the fatigue has mainly been made in consideration of the effect of repeated cycle stress based on the number of cycles and stress amplitude at final fracture. In this report the auther tries to take into account not only the failure point but also, and still more, the crack initiating point and the crack propagation process. This report is intended then to show the progress of fatigue in two separate steps, first up to the crack initiation period and then during the crack propagation period. The test has been made by means of a rotary bending fatigue testing machine, using as specimen a low carbon steel (0.17%C) bar with a V shaped notch. The results obtained are as follows in brief. (1) In the test of constant stress amplitude, the rate of crack propagation dλ/dN is low when the crack is initiated, then it shows a sudden increase after a certain depth of the crack is attained. This may be attributed to the stress concentration on the crack which begins to show crack-tip. (2) The effect of the repeated cycle stress prior to initiation of the crack on the width of the crack and the number of the crack initiating cycle seems to follow the linear damage law.
This paper describes the sintering process of ferrites under hot pressing and their magnetic properties. Bulk density ρ and grain growth aspect were investigated as a function of the maximum firing temperature Tm and the hot pressing pressure at Tm (Ph) in the case of Ni0.3 Zn0.7 Fe2O4 and Cu0.4 Zn0.6 Fe2O4 and compared hot pressed specimen with the specimen obtained by conventioned firing method. From ρ-Tm curves of CuZn and NiZn ferrite, we can see that the specimen prepared by the conventional method shows anomalous expansion in the sintering process. However, in the case of hot pressing, no expansion phenomenon was observed and the densification was considerably promoted. As the result, we could obtain the specimen with same density as the conventionally sintered one under hot pressing at lower temperature by 200°C than the ordinary firing. The effect of hot pressing on grain growth was examined by means of an electron microscope. The result shows that hot pressing greatly obstructs grain growth. The magnetic properties of the hot pressed ferrite differed from that of the ordinary fired ferrite. Especially, in the NiZn ferrite, the decrease of initial permeability μ and altered temperature characteristic of μ were the result of hot pressing. And, in the hot pressing case, lower maximum flux density Bs and higher coercive force Hc were also obtained as compared with that prepared by the conventional method. Measurement on the ferromagnetic resonance was carried out on NiZn specimen at 6790Mc. From this result we can see that the static magnetic field required for resonance Hc decreases and the magnitude of line width ΔH increases considerablly by hot pressing.
In order to study the effects of irradiation on the surface layer of polyethylene samples, %-crosslinking and gel-fraction of test pieces shaved down to the various thickness after irradiation were measured by means of a vibrating reed method and a Soxhlet extractor respectively. And then, the values of %-crosslinking and gel-fraction on each layer were calculated. Although, at the internal layer, the linear relation between (1-g)+√1-g and 1/R has held as predicted by the theory of solubility, but approaching the surface, this linearity has not held for samples irradiated in air. Moreover Young's moduli on the surface have behaved non-lineally for the dose. These results, however, could be comprehended if the proportion of the main chain unit fractured were not proportional to the irradiation dose on the surface. The value of r/2c, the ratio of the unit fractured to one crosslinked reached 1.5 on the surface, about 3 times the value in the internal layer. Even on the layer near the surface where r/2c is larger than unity, a considerable degree of gel-formation took place. By using the data of Young's modulus and gel-fraction measurements, the initial number average molecular weight may be estimated.