When powders are compressed statically by piston compression the porosity decreases. The process of powder compression indicates various forms as shown in Fig. 1. As the author maintained in his previous reports15∼20) the relationship between the ratio of the compressed volume C=(V0-V)/V0 and the pressure P is represented in the following equation C=(V0-V)/V0=abP/(1+bP) where V0=initial volume of powder, V=volume of powder under static load P, a and b are the characteristic constants of powder. The a corresponds to the maximum ratio of compressed volume C∞, that is the initial porosity. The b corresponds to the coefficient of compression and has the meaning related to the rheological behavior of the powders. In the case of ordinary powders the a indicates the value 30 to 80%. From the above equation we get P/C=1/ab+1/a×P The plot of P/C against P from this equation will give a straight line of positive slope 1/a, with an intercept 1/ab as is shown in Fig. 3. The applicability of this equation is a very wide range of compression process. It has been proved that the above equation is applicable to a wide variety of powders and compreses the equation put forward by Athy4). Moreover this equation is better applicable than the equations given by Balshin and Nutting as is shown in Fig. 5. In the case of tapping compression, if we take the tapping number instead of P, we can find the good applicability of its process as shown in Fig. 6.
A definition of the notch factor associated with program fatigue test, is proposed in the present study and some hypothesis are presented as to how to estimate the notch factor from the conventional fatigue tests. The conclusions are as follows: The notch factor may be estimated as the highest value among the values of the notch factor that we can determine, as a function of assigned number of cycles to failure, from two S-N curves, of which one is for the smooth specimen, and the other for the notched specimen. This hypothesis is practically very useful, because we can apply it to all cases of program load without any program fatigue test, and the estimation from this hypothesis has been proved to be on the safe side from the standpoint of machine design.
The energy absorbed in the carbon steel forgings due to impact bending decreases with the fall of temperature. In this paper, the destructive behaviors of carbon steel forgings were studied in the temperature ranging from 600°C to the liquid nitrogen temperature. With the falling temperature the fracture stress rose, the time required for the break was shortened, and the absorbed energy decreased gradually. This is the reason why precise transition temperature is not determinable by measuring the absorbed energy. According to the author's finding as the result of the test on the destructive behavior, the fracture stress fell suddenly at specified temperature, considered as the cross point of the fracture stress and the yield stress in the stress-temperature relationships. This temperature is the transition temperature of the impact bending at the loaded stress rate. The relation between this transition temperature and the stress rate was in good accord with A. N. Stroh's finding.
Although there have been few subjects in the field of physical metallurgy which have attracted more interest and attention than that of aging phenomena of mild steel, but little study has been made so far on the effect of stress upon strain aging. Using a 0.05 wt% C steel, strain aging was carried out with and without tensile stress at temperatures ranging from 55°to 250°C. The specimen was plastically strained about 9% in elongation at room temperature prior to the aging. The rate of aging was much enhanced by the stress. However, the inherent mechanism of strain aging does not seem to have been changed by the stress, since the apparent activation energy for strain aging is not changed by the stress imposed on the specimens during the aging process. The activation energy of 16000cal/mole was obtained at temperatures below 100°C which is about the same as that for diffusion of nitrogen in alpha iron, while a rather low activation energy of 9600cal/mole was obtained at higher temperatures. This difference implies that strain aging is controled by two different kinds of thermally activated processes. The early stages of strain aging at low temperatures are considered to be associated with migration of solute atoms to dislocations. But in the later stages and at higher temperatures, strain aging is caused by the strain-induced precipitation of carbides or nitrides at dislocations. It requires considerably more studies to define the effect of stress on strain aging. However, it is considered that the stress effects the vibrational frequency of the atoms around the dislocations and increases the diffusion constant of the solute atoms so that the rate of strain aging is enhanced by the stress.
The PC wire in the PC structural members is always subject to dynamic load. Bridges and rail-road ties, for example, strain whenever heavy vehicles pass over them. Therefore the load on PC wire fluctuates with the prestressing load as its center. No report has ever been published on how the PC wire behaves in terms of stress-relaxation when the load changes from time to time. The authors have developed a special device to examine the relaxation behavior of PC wire when fluctuant loads are applied. In this paper the test results are presented and discussed.
This study was made to elucidate the oxidation behavior of the alloy 426 of Fe-Ni-Cr system. The oxide layers of the alloy 426 were made by using three different methods, i.e. the wet hydrogen firing, the air baking and the air baking following the wet hydrogen firing. Our microscopic observation and X-ray analysis tell us: (1) That the firing temperature, the firing time and the moisture of hydrogen are most effective to the rate of weight gain of the oxide layer during the wet hydrogen firing. (2) That the oxidation behavior of the specimens which are rolled and washed by acid follow the parabolic law, whereas the specimens which are rolled but are not given acid washing deviate from the parabolic law. (3) That the fact that the rate of oxidation have something to do with the history of the works of the alloy, may be explained by the selective oxidation of grain boundary which is assured by the microscopic observation. (4) That the weight gain of the specimens which are given the air baking following the firing by wet hydrogen do not show a parabolic oxidation. (5) That the activation energy 28.5kcal/mol is obtained from our experimental results based upon the oxidation gain during the air baking. (6) It appears from our X-ray analysis that the main reaction products are Cr2O3 in the wet hydrogen firing and are (Cr, Fe)2O3 in the air baking.
(1) On the formation of graphite-sodium lamellar compound. Artificial and natural graphites were treated with molten sodium and vaporous sodium under various conditions in order to find out the suitable conditions for the formation of graphite-sodium lamellar compound. Only the product of graphite subjected to treatment with molten sodium at 430°C for 1.5hr suggested that the formation of lamellar compound was possible, by their X-ray diffraction patterns and the dependence of electroconductivity on temperature. It was confirmed by comparing the X-ray patterns of both the materials that the above-mentioned products differ from Asher's 8th stage lamellar compound, though the structure of the product was not analysed. This is a very interesting fact. (2) On the activation of carbon. It was expected that the treatment with molten sodium would be effective for the activation of carbon. The degree of activity of the carbon treated was shown by the increase of the oxygen adsorbability. The oxygen adsorbability was estimated by the D.P.G. adsorbability and the iodine adsorbability. Its effect was more remarkable on carbon black and wood charcoal than on graphite, active carbon and coke. For example the maximum increase of activity of wood charcoal reached about 100 times in D.P.G. adsorbability. Such ungraphitizable carbon as charcoal has in the circuference of its own network layer structure various unstable bonds based on the incomplete carbonization of the raw material. It seems that these incomplete parts were attacked by sodium and the active points were formed.