STUDY OF THE FATIGUE STRENGTH OF FERROMAGNETIC MATERIALS BY RAPID NON-DESTRUCTIVE METHOD

The results of fatigue tests of steel 30 – 35 CHG carried out on a laboratory unit of original design are presented. The unit consists of a fatigue machine, eddy current sensor and electronic measurement module. The structural scheme of the force mechanism of specimen bending upon testing is presented. To avoid runout of the sample we use cycling in conditions of steady stress. The developed eddy current transducer (sensor) consists of cylindrical coil made of a nonmagnetic material with two windings (design and equivalent circuit of the sensor windings are also presented). It is shown that electronic block of the measuring complex consists of a low-frequency generator of sinusoidal current, electronic engine revolution counter capable of automatically stopping of the sample cycling at a given number of cycles, and harmonic analyzer. The operation procedure is considered. The experimental data thus obtained proved that the method provides up to 30 – 40-fold shortening of the test time which is rather convenient for determination of the actual strengthening effect attributed to different types of steel processing, since the endurance limit can be determined both before and after strengthening. The eddy current method provides studying of rather thin surface layers, where fatigue cracks used to originate, thus being convenient for studying chemical heat treatment of steel surface and thin coatings without their destruction upon testing.

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