Copper and silicon, which are main alloying elements of the so-called copper silumin (JIS AC4B), seem to influence, according to their respective quantities, the mechanical properties, especially the machinability, of the alloy, even within their specified standard ratio of 2.0∼4.0% of copper and 7.0∼10.0% of silicon. In this paper, the effect of adding copper and silicon on the mechanical properties of the alloy are discussed, especially, the machinability in terms of cutting force, finished surface integrity and deposit material, built-up edge, and chip formation in turning test, and also in terms of the drilling resistance, and drilling speed. The test was perfomed on the specimen group 1, which contained about 8% silicon and varying from copper 1 to 5%, and the specimen group 2, which contained about 3% copper and silicon varying from 5 to 12%. The results are summarized as follows: The tensile strength is slightly low and the elongation is considerably greater in the alloys containing less amount of copper, but the elongation decreases and the strengths (Tensile strength, shearing strength, hardness and others) increase with the increased copper content. And the strengths of alloys containing about 8% silicon are superior to those of alloys containing silicon either more or less than 8%. From the cutting tests, no difference is recognized in machinability in the viewpoints of the cutting force, finished surface, built-up edge and others, compared among the different amounts of the alloying elements. In case of 1 to 2% copper content, fused deposits are observed on the surface, and regarding chip formation chips of continuous straight type are produced. When the copper content is more than 2%, however, there seems no difference in those measures by varied copper and silicon contents.
Here under is presented, based on the elementary theory of one-dimensional stress wave propagation, a numerical method to draft the stress-strain curves for the materials under impact tensile load, by making use of a bar and a pipe of mild steel. The materials used in the present experiment are 0.01% carbon steel and 18-8 stainless steel. The main results obtained in the range of strain rate (50∼300)sec-1 are as follows. In the case of 0.01% carbon steel, the yield strength increases with the strain rate. The ratio of dynamic stress to static one corresponding to the strain 2% is (2.3∼3.4) under the strain rate (103∼260)sec-1. In the case of 18-8 stainless steel, treated in solution but little of dependence of the strain rate on the stress-strain relation has been observed. In the case of 18-8 stainless steel as it was received, however, the stress is influenced more or less by the strain rate, and the larger the strain rate, the higher the stress. The ratios of dynamic stress to the static stress corresponding to the strain 2% for the former case and for the latter are 2.0 and 1.4 respectively, so the dynamic stress is higher than the static in both the cases.
There are two basic problems about fatigue, one is how cracks are formed, and the other is how they grow. The answers to these questions have been sought by investigators for a long time, but even now the problems remain substantially unsolved. Since the dawn of the use of electron microscopy for observing microstructural changes in metals, recent works have begun to shed light on the nature of basic physical processes involved in fatigue, and, on the other hand, a study to unravel the relationship between microscopic and macroscopic behaviors of materials has been urgently required. It is considered that if plastic replicas and optical microscope were prepared in one and the same horizon it would be possible to obtain the correlation of microscopic characteristics with macroscopic aspects of fatigue deformation. In the present paper the report is given of the examination made, to clarify the basic mechanisms of fatigue fracture in b.c.c. metals, of the thin plate specimens of high-purity iron (99.996%) subjected to alternating bending stress. Particularly the microstructural changes that occurred around the fatigue cracks were examined by optical metallography and electron microscopy, using an improved replica technique. The results obtained in this study are summarized as follows: (1) The crossing points of the two slip bands are the preferred sites for fatigue crack nucleation. In these regions the aggregation of vacancies generated by the to-and-fro slip movement could form pores in the slip bands, and these in turn could grow into microcracks. (2) There was a rather pronounced grain size effect on the nucleation and propagation of fatigue cracks. In coarse grained specimens fatigue cracks were formed preferentially in the vicinity of the grain boundaries, then spread partly along the slip bands and partly along the grain boundaries. Both the nucleation and propagation of cracks in the fine grained specimens, however, were found only in the grain boundaries. (3) Observations with an electron microscopy disclosed that large numbers of microcracks were formed in the region where the first crack was nucreated. It is confirmed that the possible coalescence of random microcracks leads to fatal cracks. (4) The microcracks are formed at the tip of the growing crack by the shear strain field which precedes the crack propagation. When microcracks are numerous enough, they in turn coalesce into the cracks. (5) Observations on the surfaces have shown that substructure develops around the fatigue crack if the grain is favorably oriented, and crack propagation occurs preferentially along the subgrain boundaries. (6) In high-purity iron, extrusions and intrusions have been observed in slip bands, and deformation bands were also formed. It is suggested that the deformations in polycrystalline materials are much complicated because of the constraints of surrounding grains.
Pulsating tension fatigue tests were made of some full scale machine parts, such as PC wire strand 1×4, 1×7 and 1×19, wire rope 6×19, steel wire, tie rod, etc.……. As a result of these tests, it has been found that the stress amplitude of fatigue strength sometimes drops as low as less than 5kg/mm2, which is rather small values as laboratory fatigue test results. It is often experienced that real fatigue strength of machine parts is much lower than what is expected from the fatigue test results of standard smooth specimens. The authors expect that the laboratory fatigue test result reported in the present paper will be of help in estimating the fatigue strengths of full-scale machine parts under service conditions.
The moiré method is a means of strain measurement which utilizes the change of interfringe spacing due to the applied stress. The errors introduced in the measurement of interfringe spacing have thus direct influence on the calculated values of strain. In the present study, the equation for calculating the strain from the measured interfringe spacing was derived from arbitrary amounts of mismatch and misalignment, and the relation between the exact strain and the errors in measurement was obtained from this equation. Further, the procedure is described for determining the lowest limit of strain which can be measured within the prescribed allowable errors. The results of this study may be summarized as follows. (1) The rate of change in the interfringe spacing due to the applied load is smaller for larger amounts of mismatch and misalignment. (2) From the relation between the errors of measurement and the rate of change in the interfringe spacing, there exists a certain domain of unmeasurable strain. (3) The lowest limit of the measurable strain under predetermined amounts of mismatch and misalignment can be determined from the curves of relative errors versus the exact amount of strain. Besides, this lowest limit of strain becomes larger with the increase of mismatch and misalignment as well as the errors in the measurement of interfringe spacing.
The melt flow characteristics of blends of PVC and a copolymer of vinyl chloride and cetyl vinyl either were measured by means of a flow tester, and compared with those of PVC homopolymer, lightly plasticized PVC and other rigid PVC compositions. The apparent melt viscosity ηa of the blends was less dependent on temperature, in contrast to other polymers. In the blends containing 25 to 75% of copolymer, there was no change in flow activation energy. The results of microscopic observation and dynamic loss measurement of the fabricated products showed that the blends had rather two-phase structure than perfectly compatible phase. From these results, it was considered that the copolymer in the blends covered the surface of flow unit of compatible mix of PVC and the copolymer in the course of processing.
It is reported in a recent paper that manufacture of concrete by utilizing cinder ashes of pulverized coal burnt at thermal powerhouses has been developed. The cementing materials that are by-products of fine cinder ashes, furnace slag, quick lime and some mixtures, are called CS cement, and they have as high as 600kg/cm2 of compressive strength when they are mixed at high rotating speed and steam curing is applied to them. In the present paper is presented a brief report of experimental study made on the use of CS cement. (1) The efficiency of the retarder used to control the heat generation of the quick lime is remarkably affected by the temperature of the mixture. When the temperature of the mixture is at 50°C the retarder is of no use. (2) The physical properties of CS cement is affected by the CaO content. The CaO ratio at 25% is favorable for the setting and strength of the cement, but for its soundness and drying shrinkage the favorable CaO ratio is at 15%. The drying shrinkage of CS cement is smaller than that of normal portland cement. (3) A special mixer with a rotating cone has been developed so designed as to retain coarse aggregate in the concrete. The result of the test shows that the concrete has 450kg/cm2 of compressive strength with 500kg/m3 of cement content. Ordinary portland cement is suitable for water curing concrete, but CS cement is more suitable for steam curing. Cinder ashes are excellent cementing material for manufacture not only of ordinary mortar and concrete, but of light-weight concrete and artificial aggregate.