Abstract
When the forms of the stress wave change or the order of the stress-amplitudes and stress-frequencies change, the fatigue strength becomes very complicated in comparison with that at the time of the normal sine wave.
In order to clarify these problems, we devised for trial a random type fatigue testing machine. This machine is composed of two parts, that is, the ordinary Schenck-type machine (used the double excentric mechanism and drived by induction-motor) and a newly designed random loading apparatus.
This random loading apparatus is composed of the following five parts:
(i) Program oscillator is composed of ink-writing oscillogram to be entered in in special ink (it can lead the electric-current) and the tracing apparatus of oscillogram (on-off type).
(ii) Thervo-amplifier
(iii) Oil-pressure source
(iv) Oil-pressure mechanism (Servo-valve and ram-cylinder)
(v) Load-checker and load-indicator.
We can carry on the fatigue test only by the Schenck-type machine, or only by the random-type loading apparatus, and also we can practise the same test superposing the two apparatus on one another.
We tested some fatigue tests as follows:
(1) Torsional fatigue test of C=0.34% steel (d=15mm plain specimen)
(i) Ordinary fatigue test of 1450rpm by Schenk-type only.
(ii) Ordinary fatigue test of 30cpm by the random-type only.
(iii) Secondary sine wave by motor (1450rpm) superposed on the first sine wave of 12cpm by the random-type.
(iv) Secondary sine wave by motor (1450rpm) superposed on the first rectangular wave by the random-type.
(v) Secondary sine wave by motor (1450rpm) superposed on the first random wave by the random-type.
(2) Plane-bending fatigue test of the induction-hardened V-notched specimen (low carbon steel)
(i) Ordinary fatigue test of 1450rpm by Schenk-type only.
(ii) Ordinary fatigue test of 60cpm by the random-type only.
(iii) At first fatigue test of 1450rpm and secondly fatigue test of 60cpm.
(iv) At first fatigue test of 60cpm and secondly fatigue test of 1450rpm.
