Mechanical properties of unplasticized polyvinylchloride under tension and compression were reported in this paper. The following results were obtained:
(1) This material shows a distinct yield point and the strain corresponding to this point becomes larger as the testing temperature becomes low, and reaches the maximum value at about 0°-10°C.
(2) The stress-strain curve up to the yield point is affected remarkably by the testing temperature and strain velocity which also greatly affect the total elongation at the breaking point.
(3) Regarding the process of cross-necking, a peculiar type of deformation is observed as shown in Fig. 12.
(4) A secondary test was made at a different temperature on a specimen stretched primarily at a certain temperature and the mechanical properties were examined.
a) Properties of the specimen streched previously at a high temperature up to the yield point are in the second low temperature test not affected by the previous treatment.
b) When the primary elongation at high temperature is greater than the breaking elongation at low temperature, the specimen shows no new necking deformation in the second test (low temperature test) and is fractured in a brittle manner.
c) On the contrary, the specimen stretched previously at low temperature over the yield point, shows in the second stretching at high temperature no yield point and deforms according to its original stress-plastic deformation curve.

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The investigation was carried out to improve the mechanical properties of medium carbon steel by the low-temperature quenching (LTQ) and the spheroidizing treatments.
The fatigue and the impact strengths are remarkably increased by the LTQ and further more increased by spheroidizing treatments. The endurance limit and the notch impact value are improved by the LTQ about 33% and 83% respectively, and about 26% and 430% respectively by spheroidizing the carbide.
The static strengh and hardness are also increased by these treatments, while the ductility is not decreased.
An interpretation on the present results is offered on the metallurgical and the mechanical basis. The LTQ strengthens the ferrite itself by super-saturating the carbon in it and the spheroidizing treatment relieves the internal notch effects.

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Creep phenomenon is effected greatly by stress and temperature. The effect of temperature on creep characteristics is an important aspect of the study on creep.
In the present study, the influence of temperature on the primary creep of steel is investigated. A device is introduced to predict the creep characteristics (creep strain ε_c or creep rate ε) at any temperature T differing by ΔT from a reference temperature T₀, by using the creep data (creep strain ε_c0 or creep rate ε₀) of the material at the reference temperature. This relation under a given applied stress is represented as follows;
ε_c/ε_c0|_t=ε/ε₀|_t=exp[K/(T₀+T₀²/ΔT)],
where t is elapsed time, K factor of temperature-dependence and T absolute temperature.
Experiments were made on mild steel. It is found that the empirical formulae satisfactorily explain the experimental results when the stress and temperature are within a certain range.

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The magnitude of the threshold stress to propagate fatigue crack was calculated by using the fatigue limit of notched specimens at the branch point.
As soon as a fatigue crack develops at the root of the notch of a specimen the mode of stressing at the end of the developed crack changes from an alternating stress to a repeating stress, ranging from 0 to σ_s', where as the load on the specimen is still an alternating one. This, and the fact that the fatigue limit of the specimen at the branch point is equal to the yield point of the material, enable us to calculate the threshold magnitude to spread fatigue crack of the stress σ_s'.
It was found that, in the case of annealed carbon steels, the threshold stress σ_s' is nearly equal to twice the rotary bending fatigue limit of the material.
The load carrying capacity of specimens with fatigue crack was discussed and it was concluded that the compressive stress existing at the root of the crack increases the crack spreading resistance of the material considerably.

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In general, practical machine parts and structures are subjected to repeated stresses of various magnitudes. Therefore it is very important to know the effects of repeated stress with varying amplitude on the fatigue strength. Fatigue tests under the multiple repeated stress in two stress levels seem to be the most fundamental case. Then we made a research on the effect of the “primary stress”on the fatigue life of the“secondary stress.”
In this research, three kinds of cabon steels-mild, medium and hard-have been tested by the Ono's rotating bending fatigue testing machine.
The results obtained are as follows.
1. In general, the theory that fatigue fracture occurs at ∑n/N=1 does not coincide with the experimental results.
2. It is convenient to represent the results of tests under multiple repeated stress by taking the equivalent number of cycles as the abscissa on S-N diagrams.
3. The S-N curves for the secondary stress bend at the place of the primary stress for the case of mild steel, but do not bend for the case of hard steel. For the case of medium steel, they bend when the primary stress is small, and do not bend when the primary stress is large.
4. When the primary stress is relatively small and the secondary stress is larger than the primary stress, the value of ∑n/N is larger than 1 in most cases.
5. When the primary stress is relatively small and the secondary stress is smaller than the primary stress, the value of ∑n/N is larger than 1 or nearly equal to 1.
6. When the primary stress is relatively large and the secondary stress is larger than the primary stress, the value of ∑n/N is nearly equal to 1 in most cases.
7. When the primary stress is relatively large and the secondary stress is smaller than the primary stress, the value of ∑n/N is smaller than 1 in general, excluding the case when the secondary stress is a little smaller than the primary stress for mild and medium steels.

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In order to know the fatigue strength of gear which is important in gear design, it is desirable to test the gear itself, especially for the hardened gear. For this purpose the authors devised a new fatigue testing machine of simple construction for gears, using a fuel injection pump of the Diesel engine as load source and a maximum pressure indicator as regulator of maximum load acting on gear tooth.
In this paper, some characteristics of the machine and some results obtained by the machine are reported.

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