The present writers have investigated the fatigue strength of hard drawn steel wire for combined stresses of rotary bending and static torsion and also the effect of torsional and tensile working on the fatigue strength for combined stresses.
The specimen was a 0.6% carbon steel wire having a diameter of 1.05mm. Hunter type rotary bending fatigue testing machine equipped with an apparatus applying the twisting moment to the specimen was employed.
The principal results of this investigation can be summarized as follows:
(1) For the range of low static torsional stress, the fatigue limit for combined stresses of asdrawn wire increases slightly compared with the fatigue limit under rotary bending, but as the static torsional stress increases beyond 22kg/mm², it decreases, though its decrement is comparatively small.
(2) Through the torsional working with plastically twisted angles 0.03π/cm and 0.2π/cm, the fatigue limit for combined stresses can be made larger than that of as-drawn wire, and this increasing is remarkable for the range of higher static torsional stress.
(3) Also, through the tensile working, the fatigue limit for combined stresses becomes larger than that of as-drawn wire.

View full abstract

The lengths of cracks which were propagated under the repeated impact bending energy of 20kg-cm and 50kg-cm at -40°C, -18°C, and 0°C were measured. The results obtained are as follows:
(1) The lengths of cracks are exponential functions of repeated number, and their cyclic speeds are almost similar at respective temperature.
(2) In case of impact energy of 20kg-cm at 0°C and 30°C, the “hesitation period” appears at the initial stage of propagation by the effect of residual compressive stress, but disappears at lower temperature.
(3) The cracks under repeated impact at low temperature propagate with a similar tendency to those of fatigue at room temperature which have been observed by numerous investigators.
(4) In case of impact energy of 50kg-cm at -18°C and -40°C, the cleavage fracture occurs in a few repeated number. The growth of weak cracks are observed prior to the cleavage fracture.
(5) The plastic energy, which is consumed by the growth of the crack prior to the cleavage fracture, is proportional to the length itself.

View full abstract

Concerning Cr-Mo steels used actually for motor shafts, etc. by Japanese National Railways, we examined their mechanical properties with the same test material, especially tensile strengths, strains, contractions and rotational bending fatigue strengths.
As a result of our experiments, in which we compared the effects of the difference of forging ratio and heat treatment conditions, or those of standard specimens and sectional parts of large size materials given on statical tension and fatigue strengths, we found various differences in data.
About the standard specimens, we could not find any difference in influences of heat treatment conditions on statical tension data. But the fatigue strengths of materials oil-or water-tempered were larger than those of materials air-tempered.
Also, the effects of the difference in forging ratio did not appear in the statical tension experiments, but appeared a little in the rotational bending fatigue tests.
On the other hand, about the sectional parts of large size specimens (840°C HWQ-680°C OT or AT), we found fairly large differences, namely in yielding p't σ_s, tensile strength σ_B, and fatigue strength σ_wb; data of outer layer parts were larger than those of inner parts.
The tensile strength was in a range of 78-92kg/mm², and the fatigue strength was about 37-41kg/mm².

View full abstract

In order to find out the prevention of wear in case of being used for the high manganese point of railway, the author carried out an experiment using an Amsler-type light load abrasion testing machine, at various slip speed, of 0-30cm/sec, and under contact pressures of 20-40kg/mm².
The test piece of tyre is of about 0.7%C steel of standard structure, and the other material of high manganese steel is from 1050°C water-toughening.
The results are summarized as follows:
(1) Hardness of high manganese steel rises up to a certain extent at the beginning of the test. However, anti-wearing character can not be expected to increase owing to the growing of its hardness.
(2) Wear resistance effect of high manganese steel is more notable under low pressure contact (σ<40kg/mm²) than under high pressure contact (σ>40kg/mm²).
(3) Under the low pressure contact, high manganese steel is effective for sliding wear.

View full abstract

In order to research on the behaviors of destruction of carbon steel forgings by impact bending, we designed an impact testing machine of drop hammer type. The total height of this testing machine is about 5m. The weights of the used drop hammers are 12.5, 25 and 50kg respectively. The maximum distance from the position of test piece to the drop hammer is 3.200m. Consequently, the maximum energy of impact bending of this testing machine is 160kgm.
The induced resistance forces of test pieces at impact bending were measured by the strain quantities of the strain gages which had been pasted on the canti lever beams used as supports for test piece.
The drop hammer fell naturally, with an initial velocity=zero. The absorbed energy of the test piece at impact bending, could be calculated from the measured area of the induced resistance forces versus the destruction time curve.

View full abstract