The present test was carried out on the 0.37% carbon steel specimens that were plastically twisted at a room temperature and aged under stress at 350°C., in order to investigate the changes of the proportional limit, the yield strength and the hardness due to pulsating or completely reversed torsional stress cycles. Particularly, the proportional limit and the yield strength were measured not only in the same direction as pre-torsion but also in the reverse direction. Subsequently, the same experiment was carried out to study whether the similar changes are caused when these specimens are heated at comparatively low temperatures.
The results obtained may be summarized as follows:
(1) When the specimens were subjected to reversed torsional stress, the proportional limit and the yield strength decreased in the same direction as pre-torsion, while they increased in the reverse direction, and it was confirmed that the Bauschinger effect diminished appreciably.
(2) The above changes of mechanical properties due to repeated stress were more remarkable in the early stage of stress cycles and became nearly constant after some number of cycles. It seems that the relation between the direction of pre-torsion and that of development of the fatigue deformation may be explained by such changes in mechanical properties.
(3) The Bauschinger effect could be diminished by heating cold-worked specimens at comparatively low temperatures.
(4) Aging treatment under pulsating stress cycles was more effective in promoting agehardening as compared with the case of strain aging or of aging under static stress. But, in our test, plastically pre-twisted specimens had been softened slightly by completely reversed stress cycles at a room temperature.

抄録全体を表示

One of the present authors previously carried out the rotating bending fatigue tests at elevated temperatures, using some carbon steels, and clarified the effect of test speed on the high temperature fatigue strength.
However, it is necessary to investigate the behaviour of material during the fatigue by some method, in order to make clear the mechanism of the fatigue failure. Considering this point, as described in this paper, we made some rotating bending fatigue tests at room temperatures, 300°C, and 500°C, using the low carbon steel, and simultaneously measured the deflection of test specimens during the fatigue with a specially devised apparatus, and then calculated the strain of surface layer of test specimens.
Main results obtained are as follows:
1) At a room temperature, strain increases considerably at an early stage of fatigue when the stress is comparatively high, and after that, the strain is practically constant during the most period of the total life.
At 300°C, the alteration of strain is small as compared with the tests at room temperature and 500°C.
At 500°C, strain decreases first, then gradually increases with number of stress cycles, and before the failure a considerable increase of strain can be observed.
2) From these results, the relation between bending stress σ and strain ε, and that between the stress and residual strain ε_p during the fatigue are plotted on a stress-strain diagram, and comparing this diagram with σ-1/N diagram obtained from the fatigue test data at respective temperature, where N is number of stress cycles to failure, we may conclude that the relation ε_pN^α=K is formed as the condition of fatigue failure, in which α and K are constant. Logarithmic plot of both residual strain ε_p and number of stress cycles to failure N indicates that α takes the value of about 0.5, and K remains near the maximum elongation in static test at room temperatures, and little influenced by the test temperature.
In order to generalize the above relation, much more systematic studies will be required for various fatigue conditions, but we may say that this result is of some help towards clarification of the mechanism of fatigue failure of materials.

抄録全体を表示

Previously, some of the present authors conducted experiments on the fatigue creep of various kinds of steel and brass under bending, torsional and axial stress at room temperature, and clarified various features of the fatigue creep of these materials.
This report is on our study concerning the fatigue creep of 0.21%C carbon steel at a temperature of 300°C and 500°C, for which a newly devised axial fatigue testing machine for high temperature tests was used.
Results obtained were as follows: At 300°C, a fatigue creep strain occurred to the specimen increases considerably at the early stages of fatigue, when it is subjected to a combined mean and alternating stress, and, in subsequent repetitions of stress cycles, a slight increase of strain can be observed. But the general feature of fatigue creep strain is similar to that of this material at a room temperature. Namely, the fatigue creep strain is larger than the static creep strain at the same temperature, if the comparison is made under the same maximum stress both in fatigue and static creep tests, and the fatigue creep limit takes substantially the same value of yield point in the static test at this temperature.
At 500°C, the general feature of fatigue creep strain essentially differs from that at 300°C and a room temperature. The fatigue creep strain at this temperature increases gradually with repetitions of stress cycles, and we can observe a remarkable increase of strain in the final stage of fatigue, except when the mean stress is very low. Besides, the fatigue creep strain is smaller than the static creep strain at the same temperature and under the same maximum stress, contrary to the above tendency noticed at 300°C and a room temperature. These phenomena seemed to be resulted from so-called time effect which is recognized at high temperature tests.

抄録全体を表示

In the previous studies made by the present authors, it was found that the creep curve of low carbon steel and ferritic as well as austenitic stainless steel in the test with temperature variation under a fixed applied stress can be predicted from the results of constant temperature tests of the respective materials. In those tests temperature cycle was comparatively slow. However, for practical purposes, studies of creep behaviours under rapid temperature cycling are important. In this report, by using an apparatus for rapid cyclic heating and cooling, the creep behaviours under rapid temperature cycling are investigated by experiments, and we are trying to make predictions as to creep curve from the data of constant temperature creep tests. The followings are the conclusions from our studies:
(1) The apparatus for rapid cyclic heating and cooling gave a good pattern of temperature cycling for the creep test under rapid temperature cycling.
(2) The uneven distribution of temperature along the gauge length of specimen was inevitable and so the mean temperature T^* was defined as the temperature at which the gauge length of uneven temperature distribution elongates in the same amount with the case of uniform temperature distribution.
(3) The creep curve for rapid cyclic heating and cooling could be predicted from the data of creep test in primary stage made at constant mean temperature, by introducing “Equivalent steady mean temperature” T_e^*. The predicted curves were fairly close to the experimental ones as to low carbon steels and austenitic stainless steels.
(4) With regard to the creep damage of the materials caused by being exposed to rapid cyclic heating and cooling, the crept specimens were subjected to tension test at room temperatures and also microscopic observations was made on the structure, in which no noticeable change was found.

抄録全体を表示

The gears, which are used in the nose-suspended motor of a motor car, necessarily come to mesh at the end of face width on account of the mechanism of motor suspension. This mechanism is usually the cause of gear tooth failures. In order to prevent the gear tooth failures, the traction gears of motor cars of the Japanese National Railway are crowned. From the results of investigations to introduce the method of deciding the form of crowning of gear, the author found that the total length of the face width of the nose suspension type traction gears used at present does not share the load effectively. Thereupon, the author tentatively designed the gear, which has the face width reduced to 2/3 and is crowned.
Further, the author designed the tentative gear which is divided into two pieces, gear rim and gear boss, which are connected by the compression type rubber unit buffer. In this gear the gear rim can displace itself in relation to gear boss and the uniform tooth bearing all over the face width can be expected.
These two kinds of gears which were manufactured to prevent the gear tooth failures were set on the axles of motor car, and the running experiment to test the functions of the gears were carried out. By measuring the fillet stresses with the wire resistance strain guages, the author confirmed that the trial gears had the expected functions. The results are as follows:
1. In the crowned gear with reduced face width, the load is shared over all the length of the face width effectively, and the maximum fillet stress of the gear tooth appeared at the middle of the face width and was of sufficiently safe magnitude.
2. The gear having the compression type rubber unit buffer has the uniform tooth bearing all over the face width, and the function to prevent the uneven contact was confirmed.
These gears fabricated for trial are being tested for practical use at present.

抄録全体を表示

The flexural fatigue testing on a polyester/glass-mat laminate was carried out at temperatures +30--30 deg C, and it was found that the fatigue strength of the material apparently increases at subnormal temperatures, and that the following empirical formula is applicable to the relation between the fatigue strength and environmental temperature,
S_f=kT^-q
where S_f: fatigue strength at a certain number of cycles to failure in kg/mm², T: environmental temperature in deg K (Absolute), k and q: constants.

抄録全体を表示

For the purpose of comparative studies on the notch strength and the notch brittleness of unplasticized PVC, low and high pressure polyethylene and high impact polystyrene at a low temperature, the present reporters carried out tension tests on specimens which had been provided with sharp razor notches. The results of tests were compared with those of unnotched specimens.
Unplasticized PVC, low pressure polyethylene and high impact polystyrene (Specimens cut perpendicular to the extruded direction) show a remarkable decrease of strength at a low temperature, but high pressure polyethylene and high impact polystyrene (Specimens cut parallel to the extruded direction) give no such decrease in spite of the existence of very sharp notch. The latter materials are considered to be suitable materials for the use at low temperatures.

抄録全体を表示