The present study has been made to inquire experimentally into the effect of testing conditions, such as the gripping pressure on the specimen, the size of the specimen and the weight of the ball, upon the impact resistance of some plastics in the experiment worked by the falling ball method.
The results obtained are as follows;
(1) The gripping pressure has the greatest influence on the impact resistance, and the greater the pressure is, the less the impact resistance is.
(2) The impact resistance increases with the increment of its supporting distance and the thickness of the specimen, but generally it does not increase with the increment of the breadth of the specimen.
(3) The required falling height H to break the specimen is lowered by the increment of the weight W or the size of the falling ball, but the energy WH to break the specimen is little affected by that.

View full abstract

Vehicles in general such as airplanes, automobiles and railroad cars, and structures in general, such as bridges, are subject to random repeated loads. To design machine elements included in those vehicles and structures, ordinary statistical summarization of stress spectra is performed and the“linear damage criterion”, (Σn/N)_f=1, is applied to the resulting cumulative cycle ratio. The value of cumulative cycle ratio to fracture obtained from experiments does not always coincide with the value calculated from the linear damage criterion. As the authors consider that the cause of this fact comes from the variation of strain amplitude due to stress interaction, several series of low-cycle fatigue tests of steel are conducted under the condition of rotating bending with the multiple repeated loads and the relation between the deformation (deflection) measured during the tests and the resulting fatigue life is discussed.

View full abstract

The tests were carried out of specimens of specially prepared medium carbon steels which were designated as A1, A2 and B2. A1 and A2 steels contained respectively Mn-silicate and Al-silicate inclusions. B2 steel was the top part of ingot, and had a number of large flaws. The fatigue limits due to rotary bending for these materials were obtained after the specimens were preworked by statical tensile deformations beyond the yield point.
As the supplementary test, the torsional fatigue machine was stopped at intervals after additional cycling in order to investigate the initiation and propagation of fatigue cracks for annealed specimens, and photomicrographs were taken in the same area on the surface of the specimen
The results obtained are as follows.
(1) Comparing with the results for annealed states, the fatigue limits in A1 and A2 materials decrease few percent for small strains, and increase for large strains of preworking. This tendency is similar to that obtained previously for 0.15% C steels, and the effect of the presence of inclusions can not be found.
(2) In B2 steel, however, the above-mentioned tendency is not found, and also the scatter of fatigue test results for S-N curves is obtained. It should be pointed out that the influence of the large flaws on the fatigue strength is much more than that of the structural variation of metal by tensile preworking.
(3) The specimens made of B2 steel contained a number of large flaws as longitudinal directed inclusion lines parallel to the specimens axis, but these flaws had no harmful influence on the fatigue life of specimens.
(4) The surface of specimens not broken at 10⁷ torsional stress cycles was found a large number of small cracks, but the number of small cracks in B2 specimens was much less than that in A1 and A2 specimens.

View full abstract

This investigation has been conducted to make clear the effect of strain rate at pre-stretching on the fatigue strength. The 18%Cr-8%Ni stainless steel has been used for specimens in this study.
The specimens pre-stretched 30% rapidly have presented high fatigue limit than the specimens pre-stretched 30% statically.
It is recognized that this fact is due to higher amount of promoting martensite transformation in the case by rapid pre-stretching than in the case by static pre-stretching.

View full abstract

Corrosion fatigue tests of mild steel have been carried out in 0.3N HCl, and electrochemical discussions are made on corrosion fatigue with the polarization characteristics measured by the rapid method. The anodic Tafel line is much affected by cyclic stresses, while the cathodic Tafel line is hardly varied. The increase of the corrosion current with the progress of cycles shows the similarity with the crack propagation. Therefore, the damage of corrosion fatigue is estimated by the corrosion current. The activation energy has the value of 14.0kcal/mol at the beginning of tests and tends to increase with the progress of cycles. On the other hand, the activities of metals much increase with the stress cycles, and in consequence the corrosion current is found to increase. The effects of cycle frequency are no more observed under frequency lower than 1100rpm. A linear relation is found between corrosion potential and logarithmic value of corrosion current. Therefore, the damage caused by corrosion fatigue can be also proved by the trends of corrosion potential.

View full abstract

The electrical resistance of a single crystal of cadmium sulfide was measured at pressures up to 40kbar and at temperatures up to 700°C in a cubic compact anvil high pressure apparatus.
The electrical conductivity of CdS of either the atmospheric wurtzite phase or the high-pressure rock salt phase is semiconductive. In the high-resistivity samples used in the present experiment the electrical resistance increased with pressure in either phases, the wurtzite or the rock salt. From the measurements of electrical resistance as a function of temperature, it is found that a band gap of CdS of the wurtzite phase is about 2.5eV. For the CdS of the rock salt phase a band gap of about 0.8eV is obtained.

View full abstract

In the present paper is presented the report of the study of the fatigue properties of the satin woven glass fabric reinforced polyester. The experiment was made of fatigue test of the above mentioned materials by bending, rotating bending, torsion, tension and compression under varied test temperatures and mean applied stresses. (See Table II)
Further experiment was made also of their static test of tension, bending and torsion in order to find the ratios of their fatigue value to their corresponding static value respectively.
The summary of the results of this study is as follows.
(1) It has been made clear that there is relation between the tension and compression fatigue strength values of the materials and the test temperature and mean applied stress.
This relation is expressed in the following equation.
σ_f=A_T{tanh k σ_m-tanh k(σ_m-B_T)}+σ_m
where σ_f is the fatigue limit of this FRP materials,
σ_m is the mean applied stress,
k is the constant and A_T and B_T are the values related to the test temperature.
(2) It has been made clear that the so-called Gerber's law for metals is valid also in our tension and compression fatigue test at room temperature.

View full abstract

In the previous papers report was presented of simultaneous measurement that was made of the films of low and high density polyethylene and polypropylene with respect to their change in infrared dichroism and the stress and strain during stress relaxation at constant length and stretching at constant rate of strain. This new rheo-optical method was found very effective in interpreting the stress-strain curves of these materials. Because this technique enables us to determine the molecular orientation of each component in a blend subjected to deformation from the dichroic ratio of some absorption bands characteristic to each component, it can be powerful means to study the true deformation mechanism of polymer blends which have been hitherto discussed only hypothetically. In the present paper report is made of measurement that has been made by this technique of the contribution of each component in polyethylene-polypropylene blends to the total deformation and its deformation mechanisms have been discussed. At the same time, the temperature dependences of the tensile storage modules E' and loss modulus E" have been measured for the same samples.
The sample blends of high density polyethylene (PE) and isotactic polypropylene (PP) having different compositions were obtained by mixing the components in the molten state. The variation of the dichroism of 998, 730, and 720cm^-1 bands with elongation has been observed during the stretching at a constant rate of strain, and the change in orientation functions for crystallographic c axis of each component has been determined. The result shows that when Φ_p>0.7 (Φ_p is the weight fraction of PP in the blend), PP becomes the continuous phase or matrix and PE becomes the dispersed phase, while when Φ_p<0.3, PE becomes the continuous phase and PP becomes the dispersed one. It has also been observed that the dispersed phase can not be elongated so much as the continuous phase. This is much more remarkable when the phase separation occurs. With the aid of such information, the results of temperature dependences of E' and E" for the blends have been interpreted consistently.

View full abstract