BaTiO3 ceramics were made by changing firing temperature and amount of addition of clay. The grain size of samples were classified according to ASTM designation. The ceramics with same dielectric constant (1500) and grain size ranging from 1.2μ to 14μ were picked up as the samples. Some electrical properties were measured as a function of grain size. The results obtained were summarized as follows: (1) Dielectric loss was increased with the increasing of grain size. (2) Harmonic distortion due to polarization with long relaxation time was increased with the increasing of grain size. (3) Remaining electric charge was sharply increased at the grain size of 10μ and above.
The electric charge has been measured, and its polarity observed, in each particle of powder under the condition of about 65 per cent R.H. and the pressure of saturated vapour when friction takes place as factor of the electric charge among the powder particles that are channeled through the chute net, and in the measurement is used the method requiring alternating current as shown in Fig. 1. Four kinds of powder, polyvinyl chloride, mica, potato-starch and lactose were used for the experiment. Under about 65 per cent R.H. both polyvinyl chloride and mica produce 60 to 80 per cent of negatively charged particles in number as shown in Figs. 10, 11, while both potato-starch and lactose hold the same per cent in negatively and positively charged particles and produce the reversal of polarity which turns negative from positive in the boundary of range 50 or 60 microns in diameter as shown in Figs. 12, 13. In general, the distribution of positively and negatively charged particles has the following relations to the size of particles. The amount of charge on powder particles of less than about 70 microns in diameter increases with the surface area of the particle as shown in Figs. 2∼5. For particles larger than about 70 microns, it is in proportion to the volume. But the charge of powder particles larger than about 100 microns in diameter tends to be neutral. Under the condition of saturated vapour the amount of charge which is proportional to the volume of particle disappears especially in mica and lactose as shown in Figs. 6∼9.
A new fatigue testing machine of constant load type has been designed for the purpose of investigating the dynamic fatigue which is characteristic of plastic materials, because the plastics reinforced by glass fiber (so-called FRP) is practically used for structural members inplace of metals. Fig. 1 shows the general view of this machine which has the capacity of 1000kg and several merits described as follows. (1) Regardless the change in the rigidity of the test piece during the fatigue test, the dynamic load that acts on the test piece is still kept constant. (2) Three testing speeds can be selected. (3) Variation of the dynamic load and the testing speed is negligibly small. As the result of many fundamental tests it is confirmed that the machine operates as has previously been expected.
Either with the aim of studying the effect of the pre-strain on the fatigue strength of materials, or for the purpose of increasing fatigue strength, there have been investigators so many who have tested many materials with various amounts of pre-strain under repeated stresses, such as push-pull, rotary or reversed bending, and reversed torsion with some of those having mean stress, and the results from these tests indicate that fatigue limit is generally increased by pre-strain. On the other hand, there have been reports that the fatigue limit of specimens that have been subjected to a small amount of pre-strain (just above yield point) drops below that of the original material. The above-mentioned facts are ascertained in this paper by the experiments with 7:3 brass specimens with electro-polished and pre-strained surface. The amounts of pre-strain are 1.3, 5.3 and 8.7%. With 1.3% pre-strain, the fatigue limit decreases 8.3%. This phenomenon is explained by the fact that slips occurred in relatively weak grains on the surface of the specimen. The damage is retained and there is no artificial strengthening of the material. On the other hand, in the largely pre-strained state, the improvement by artifice is greater than the damaging effect due to the slip, and the fatigue limit is increased. By this consideration, the same phenomenon about notched prestrained specimens can also be explained.
Leaded brass, i. e. brass with small quantities of lead added to it, is used in many fields for mechanical purposes because of its anti-corrosive properties and machinability without diminishing its mechanical properties, such as tensile strength and hardness. The effect of adding lead to brass on its machinability has been studied in many fields, and it is intended in this paper to find out the characteristics of leaded brass regarding its rupture under combined stress by subjecting it to compression-torsion test. For specimens leaded brass rods based on α-brass (7/3 brass) containing 0∼3% lead, melted and extruded, were used, as the (α+β) brass is complex in structure and therefore inadequate for the purpose, and the trial compression-torsion testing apparatus was used. It has been found as the result that when lead is added to brass simultaneously under the compression stress and the shearing stress the brass is detreriorated in rupture strain, and it is found also that it is one of the reasons why the discontinuous chip is obtained when leaded brass is cut.
When effective preservation tests are performed using wood specimens to which Coriolellus palustris, one of the oxalic acid producing fungi, is cultured, it has often been found that decay is limited to a particular portion where tissue is completely destroyed to make a hole, in the case of the specimen treated with preservatives containing copper salt. Under the microscopic observation of the decayed wood tissue light green colored, minutely crystalized substance is observed. Copper concentration is apt to be high around the hole. Accordingly, oxalic acid which is metabolized by the fungi is assumed to react on copper salts to form copper oxalate, and it is pressumed that there is a certain relation between the partially serious decay phenomenon and copper oxalate accumulation by fungi. In order to test these hypotheses a fundamental experiment was carried out by culturing the fungi in solution, agar and filter paper each of which contained copper salt with various concentration. Light green colored precipitate was obtained from the former two, and the surface of the filter paper was colored light blue. The substance precipitated by the fungi was identified to be copper oxalate by means of infrared absorption and X-ray diffraction methods. The surface of the filter paper colored light green was found to be remarkably rich in copper concentration by fluorescent X-ray analysis. It was found also that whereas the fungi cultured in water without any copper salt ingredient grew dispersed in the whole expanse of water, those in a solution containing copper salt grew concentrated like a concentric circle. The higher the concentration, the more distinct the denser, the smaller was the colony. It is noticed that untreated timber decays altogether shrunk. It is assumed that this is similar to the growth of fungi in water without copper salt ingredient. Timber treated with copper salt dacays partially but seriously. It appears that this is similar to the growth of fungi in copper salt solution. So it is only assumed, and so it only appears. It requires further studies to account for the decay of timber treated with copper salts.
In the previous paper very efficient use was made of simultaneous measurement of stress, strain and infrared dichroism in interpreting the stress-strain curve of low density polyethylene. The stretcher employed in the previous studies has been improved so that the upper and lower crossheads can move up and down at the same rate, attaining the total stroke of 30cm. A drawtube has also been furnished in the way of an oven to control measuring temperature by circulating air at a controlled temperature. For high density polyethylene, the dichroic ratio D(⊥/||)for 730 and 720cm-1 bands has been measured as a function of strain at a constant rate of elongation of 30%/min, and the orientation functions of a-, b- and c-axes, Fα, Fβ and Fε, have been evaluated. These orientation functions plotted against strain give similar curves to those for low density polyethylene reported previously, indicating that quite the same explanation can be given to the stress-strain curve of the high density polyethylene sample as in the case of low density polyethylene. For polypropylene, on the other hand, the orientation function Fε for c-axis evaluated from the dichroic ratio D(||/⊥) for 998 and 840cm-1 bands takes negative values at first and then positive values as the strain increases, indicating that molecular chains in crystalline regions orient at first perpendicularly and then in parallel in the direction of elongation. This negative dichroic ratio is consistent with negative birefringence observed at small strains for the same material. The strain at which Fε takes its minimum coincides with the strain at the yield point. From these observations, the following deformation processes can be considered to occur during the stress-strain measurement: Below the yield point, spherulites or superstructures consisting of lamellae show elastic deformation, in which the lamellae rotate their axes in the direction of elongation. Beyond the yield point, the spherulites or superstructures show irrecoverable deformation due to the unfolding of folded chains which can orient in the direction of stretching as the strain increases. In this case, the strain at which the necking of the sample film can be observed coincides with the strain at which the unfolding takes place.
The X-ray diffraction patterns of materials which are used in the construction of industrial structures and machines generally have so widely diffused profiles that their K-alpha doublets can not be distinguished and these peaks are superposed. The calculation of residual stresses with the use of X-ray are carried out by measuring the peak positions of back reflection lines, but these broad lines contain some errors in the measurement of the peak shift. The shift of the peak positions are the movement of the whole profile and it would be calculated from Fourier's coefficients when the profiles are analysed by Fourier's method. This method of calculation is described in this paper.