DOI: 10.14489/td.2017.08.pp.052-058

Konovalov A. M., Kugushev V. I., Yakovlev A. Yu.
TWO PROMISING TRENDS FOR FLAW DETECTION OF CRACKS USING SELF-OSCILLATIONS OF THE OBJECT UNDER TEST
(pp. 52-58)

Abstract. A simple and rapid method of flaw detection of cracks is presented using self-oscillations of the object under test. A generality of the proposed method is demonstrated through experimental investigation of two different objects. The first object is an injector head. The state of its inner jacket which is operated under high temperatures and which is not accessible from outside due to a cooling system requires monitoring. Disassembling of the injector head when in idle condition in the process of operation is excluded. The following physical process forms the basis of the proposed method. During excitation of the injector head self-oscillations presence of cracks on the inner jacket in the process of deformation will contribute to conversion of mechanical energy of oscillations to thermal energy, i.e. to inner energy increase. The conversion results from the action of two factors, when the crack edges are shifted, its walls would rub against each other in the course of oscillations, also yielding of metal in the angles of the crack would happen. Any body tends to have minimum of internal energy. Therefore, if cracks are available the modes of self-oscillations of the injector head, which contribute to increase of internal energy in the process of deformation, will be damped by cracks. The energy received by the body in the result of external excitation of self-oscillations will be redistributed onto other modes of oscillations whose deformation impacts the cracks the least. Implementation of this method consists in plotting of a restricted spectrum of self-oscillations for a normal injector head which would consist of a number of specially selected modes of self-oscillations and frequency ranges within which they should be measured. Self-oscillations were excited by slight taps with a hammer to certain points, self-oscillations were measured by frequency meter. The indicator of cracks is the situation when any selected mode of self-oscillations replaces other selected modes and can be persistently measured in their ranges. The second object is the railway wheels. Use of this method provides their quick and simple express-control while the railroad trains are in idle condition at the train stations, which is not possible by using any other methods of non-destructive testing.

Keywords: self-oscillations, frequency, cracks, tap, ranges, express-control.

 

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