Abstract
Up to the present, the studies on the torsional fatigue of steel wires with small diameters have not been made so much.
Therefore, in order to study this problem we designed and manufactured the torsional fatigue testing machine for these wires. Generally, there are many types in the torsional fatigue testing machines, but we adopted the rotating-specimen-type because of the simplicity in the mechanism and the suitability to steel wires with small diameters (1.5-2mm).
In our machine the specimen is gripped by the chucks on the rotating head, and the repeated torsional stress is applied by hanging the dead weight on the lever in the center of machine.
But this type machine has a weak point that this lever vibrates in operation. This vibration is due to the inclination of lever and this inclination rises from the torsional deformation of specimen caused by hanging the dead weight.
Then, in order to reduce this vibration, we made our machine giving particular considerations to the next three points.
(1) To shorten the chuck interval of test specimen and to reduce the inclination of lever rising from the torsional deformation of specimen.
In our machine, the chuck interval of specimen is 5mm.
(2) To shorten the length of lever (Arm of twisting moment working on the specimen) and to reduce the fall of the hanging point of dead weight.
In our machine, the length of lever is 35mm.
(3) To operate the machine at a speed far below the critical speed which is to cause this vibration.
In our machine, the speed is 650rpm
Some experimental results of cold drawn steel wires with 1.7mm dia. showed that our machine was very suitable to the torsional fatigue testing for steel wires with small diameters.
