It is well known that the fatigue strength of machine part is generally reduced when plated with Chromium. But for nickel plating of steel there have yet been but scanty data for ensuring the effective fatigue strength. The author has investigated on that account the effect of nickel plating on the fatigue strength of carbon steel. The fatigue test specimens used in the present experiment were 10mm in diameter, and were made of annealed 0.15%C steel or annealed and quenched-tempered 0.45%C steel. The nickel plating of these fatigue test specimens was carried out in the Watt's type bath, having the composition NiSO4·7H2O 240g/l, NiCl2·6H2O 45g/l, H3BO3·30g/l. Then the current densities were 1.0, 0.7, 0.5A/dm2, and the bath temperature was kept at 25°C. The results obtained can be summarized as follows. 1) The higher the fatigue limit is in unplated steel the lower the limit is in nickel plate steel, no matter what the plating condition is. 2) The higher the plating current density is the larger the drop of the fatigue limit in nickel plated steel is. It is considered that this is closely connected with the presence of residual tensile stress in the plated layer. 3) Moreover, the drop of the fatigue limits in the nickel plated steel is influenced by the plate thickness. The increase of the plate thickness lowers the fatigue limit. This is probably the notch effect due to the rough plate surface and to the crack in the plated metal.
The fatigue tests of materials using objects in practical use as specimens are remarkably common in recent years. Larger amplitudes are required in the fatigue tests, therefore, both of stress and of strain. When there is large deflection of specimens in the test made by means of a hydraulic large-fatigue testing machine, it is necessary to reduce the load repetition cycle. In this kind of testing machine either electrical or mechanical, the prime mover that is in common use is capable of adjusting speed within the range about 1:4. The driving torque of these prime movers is almost constant at any speed. At low speed, therefore, both the power produced by this prime mover and the effect of the fly wheel are smaller than those at high speed. At low speed, moreover, the driving shaft of the machine receives shock due to the large reversed torque created by the reaction of the specimen. In the present paper, the author has worked out the analysis of the mean torque of the hysteresis loop of the specimen and the reversed torque caused on the driving shaft by the compressibility of oil in the hydraulic system. In order to keep uniformity against the varying torque, he installed an accelerative fly wheel capable of being switched to the driving shaft to change the gear ratio. For the purpose of increasing both the mean torque and the starting torque, he introduced an improvement on the mechanical gearing system particularly to prevent the shock of reversed torque effectively when the machine is operated at low speed. By adopting these new devices into the fatigue testing system, it is made possible now to enhance its capacity and to reduce the electric power consumption.
The large impact torsion testing machine which has recently been designed and constructed by the present authors, has the capacity of 100kg-m and the rotating speed from 100rpm to 2600rpm. This machine is fit to make intermittent loading, the detection of axial stress caused during the torsional deformation and the tests under combined stress by adding tensile deformation. The blue shortness and the reduction of twist ductility during the α-γ transformation of mild steel and 13% chromium stainless steel have been studied under various deformation rates. The brittle fracture of thin walled tubular specimens of mild steel with several grain sizes has been tested under various strain rates and low temperature, and the transition temperatures have been compared with that of impact tension and Charpy test. Finally the intermittent impact torsion has been carried out in order to evaluate the hot-working behavior of mild steel.
Experimental studies have been made for the retentivity of polycarbonate in processing the material under uniaxial compression in the temperature range from cold to warm. The“Solvent Method”polycarbonate“Iuplion”was used as test specimen. The strain recovery of the test specimen compressed at various processing temperatures was measured by free annealing at the temperatures higher than the processing temperatures. It has been revealed that the strain recovery is complete when the annealing temperature is higher than the glass transition temperature of the polymer, though the polymer has excellent cold processing ability of freezing the strain when the temperature is lower than the glass transition temperature. A new“Modified Erichsen”testing apparatus was proposed for measuring the temperature dependence of the processing ability of sheet plastics in relation to the cold and warm processing of the polymer. Sheet specimen was penetrated by a solid punch at constant rate of stroke at various temperatures and the penetration depth at fracture was measured. The processing ability of polycarbonate sheet (1mm thick) was gradually improved as the increase of the temperature up to the glass transition temperature. The strain recoverey in the Erichsen test was examined in the same way as the uniaxial compression test, and a well parallelism between the results obtained under a combined stress such as the Erichsen bulging and those under an uniaxial compression as the above was found. Test specimen worked by the“Modified Hot Erichsen”testing apparatus is being intended to be available for the environmental stress cracking test of the polymer.