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.
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