This report, first, explains the measuring method of the shearing residual stress of fine wires. Then it shows the experimental data of the residual stress, measured by this method, of 1mm∅ nickel-silver wires which were straightened by die blades, and the relation between the residual stress and their mechanical properties.
Wire straightening by a single or combined rotary die blades produces in it the shearing residual stress which is nearly symmetrical to axis. In the outer layer of specimen the stress is 2-3kg/mm² in any case, while in the inner part the opposite stress to the outer increases as the degree of straightening increases. Such residual stress is considered to have much effect on the following work of the wire. The distribution of the shearing residual stress correlates well with that of hardness of wires in section.

View full abstract

In order to make clear the feasibility of forming of hardened steel during tempering, 4-pointssupport bending tests, acute-angle bending tests and tests on accuracy of forming were performed. Materials tested were S30C, S45C, SUP3 and quasi-SUP6.
The results of tests were as follows:
(1) For the sake of high-deformability of hardened steel during tempering, the steel could be bent in an acute angle without fracture during its heating from room temperature to tempering temperature when there were no defect on its surface.
(2) The load necessary for such working during heating upto the temperature that was used to obtain hardness suitable for springs (c.a. Rc 42), was about 15-times as much as that was required in the usual hot-working at the temperature above Ac₁.
(3) The higher the carbon content of hardened steel, the better the accuracy of such forming works.

View full abstract

Network-like hair-cracks were found on the surface of hardened high-carbon steel (SUP3) which was water-quenched from high quenching temperature (higher than 1050°C). As the causes of such cracks, embrittlement due to grain boundary oxidation and residual tensile stress in the decarburized surface-layer were considered.
These cracks grew by low tensile stress (over 4kg/mm²) during tempering and transformed into cracks like heat-checks.

View full abstract

The present experiment was carried out for the effect of speed of cyclic stressing upon the fatigue strength of 18-8 stainless steel wire. The followings are the results obtained:
The fatigue strength which is governed by the reduction factor is larger in the case of higher speed (12000rpm) than in that of lower speed (1000rpm).
(1) That of austenite structure may be varied in the range of 1000-12000rpm but that of 12000rpm is higher by 16% than that of 1000rpm.
(2) That of 41% reduction factor may be varied in the range of 1000-12000rpm.
(3) Specimens of over 80% reduction factor with martensite structure which were worked very hard may be sensitively governed by the speed of cyclic stressing. That is, that of 12000 rpm is higher by about 20-25% than that of 1000rpm.
(4) Irrespective of the value of reduction factor, the temperature rise of the specimen due to the repeated stress falls below 70°C in the neighbourhood of endurance limit.
(5) The temperature rise of the specimen just after fatigue fracture is governed by the value of speed of cyclic stressing and repeated stress. It is about 700°C in specimens with austenite structure, which were tested under the speed of cyclic stressing of 4000rpm and the repeated stress with over yield point value, and also it is about 200-400°C in the specimens with martensite structure which were worked hard.

View full abstract

Tensile creep tests of unplasticized polyvinyl chloride were carried out under constant load. Test pieces used in these tests were cut from the sheet of 1mm thickness.
We see that the following expression may be applicable in primary period of creep obtained from these tests,
ε=mtⁿ
where ε is creep strain, t is time duration for loading, and m, n are constants. Both these constants vary their values subjecting to applied stresses and testing temperatures.
Next, creep in secondary period may be shown nearly as a straight line with tendency slightly concave upwards in the strain-time diagram as it may be regarded to be in the steady state.
Relation between minimum creep rate ε_min, which is considered to be characteristics in secondary period, and conventional tensile stress σ at a constant temperatures is expressed by
ε_min=c exp.(aσ),
where c and a are constants.
Minimum creep rates under constant stress at various absolute temperatures T are expressed by
ε_min=A exp.(-B/RT),
where A and B are constants and R is gas constant.
The specimens kept at 60°C for 5 days show themselves to have smaller values of minimum creep rates than the normal, and become more brittle and considerably anisotropic.

View full abstract

Some fractures or cracks of the refractory clay bodies generated in the low firing temperature range were observed, and the relation between the thermal cracks and the packing of the material powders were investigated. The following results were obtained:
(1) The original packing characteristics were changed remarkably by the thermal expansion produced in the bodies during heating procedure, but the effects in the cooling period were not remarkable.
(2) The fractures of the bodies produced in the heating period were also affected by the blending of the component powders. Cracks were generated by poor blending.
(3) However, poor blending produced good packing of the material powders in the heating procedure. Coarse constituents produced also good packing of the powder in the heating period.
(4) When Roseki powder were used as the coarse constituent and clay powder as the fine one, the resultant composition was quite proof against producing the none-similar changes of the void spaces.

View full abstract