Obrabotka Metallov 2019 Vol. 21 No. 2

OBRABOTKAMETALLOV Vol. 21 No. 2 2019 37 TECHNOLOGY Studies on the Reliability of Crack Diagnosis by the Forced Oscillations Portraits Distortions Vladimir Berns 1, 2, a,* , Egor Zhukov 1, b , Pavel Lakiza 1, c , Evgenii Lysenko 3, d 1 Siberian Aeronautical Research Institute named after S. A. Chaplygin, 21 Polzunov str., Novosibirsk, 630051, Russian Federation 2 Novosibirsk State Technical University, 20 Prospekt K. Marksa, Novosibirsk, 630073, Russian Federation 3 Academician M.F. Reshetnev Information Satellite Systems, 52 Lenin str., Zheleznogorsk, 662972, Russian Federation a http://orcid.org/0000-0002-2231-7581, v.berns@yandex.ru , b http://orcid.org/0000-0001-6378-6352, zh-ep@yandex.ru, c http://orcid.org/0000-0002-3863-2762, qinterfly@gmail.com , d https://orcid.org/0000-0001-5561-2934, mla340@iss-reshetnev.ru Obrabotka metallov (tekhnologiya, oborudovanie, instrumenty) = Metal Working and Material Science. 2019 vol. 21 no. 2 pp. 26–39 ISSN: 1994-6309 (print) / 2541-819X (online) DOI: 10.17212/1994-6309-2019-21.2-26-39 Obrabotka metallov - Metal Working and Material Science Journal homepage: http://journals.nstu.ru/obrabotka_metallov ARTICLE INFO Article history : Received: 15 March 2019 Revised: 25 April 2019 Accepted: 04 May 2019 Available online: 15 June 2019 Keywords : Airframe elements Fatigue crack Vibration diagnostics of cracks Nonlinear distortions of the oscillations portrait Normalization of the oscillation portraits distortions Influence of the oscillations amplitude Electrical interference Tracking the state of the test object ABSTRACT Introduction. One of the methods for the vibration diagnosis of fatigue cracks in the airframe metal elements is based on the analysis of the monitor objects forced oscillations portraits. The assessment of the reliability of this method in relation to real structures is an urgent task. Objective of the work: to assure the reliability of cracks detecting in metal structures by nonlinear distortions of oscillations portraits. Research technique. With the help of harmonic sources, forced oscillations of the diagnosed structure are created and recorded by acceleration sensors. Initially, the acceleration sensors are placed with condensation in the most loaded areas, which are determined by the calculations results or in vibration tests. Then, the sensors positions can be shifted to the defect locations. The signal of each sensor is represented as an oscillations portrait, the vertical scanning of which is proportional to this signal, and the horizontal one – to the first harmonic of the signal, phase shifted by π/2. Such an oscillation portrait is a circle for a linear dynamic system. The fatigue crack initiation is accompanied by nonlinear distortions of the oscillation portraits because of the collision of its edges and dry friction at the tips. For the numerical evaluation of distortions, the first harmonic is subtracted from the Fourier series for the oscillations portrait; the absolute maximum for the oscillation period is determined in the series remainder, the maximum value related to the first harmonic amplitude and is taken as the distortion parameter. Distributions of the oscillation portraits distortion parameter are built over the surface of the test object. Locations of cracks are determined from the locations of the distortions local maximums. At the same time, the amplitudes of the oscillations of the airframe and the methods of normalizing the distortion parameter changed, electrical interference in the test equipment systems are evaluated. Results and discussions. The reliability of the fatigue cracks detecting by distortions of the oscillations portraits are estimated by the example of the aircraft fuselage metal panel diagnosing. The influence of the panel vibrations amplitude, the method of normalization of the oscillation portraits distortions and the level of electrical interference in the excitation system on the effectiveness of crack diagnosis is established. Amethod for mathematical processing of distributions of the oscillations portraits distortion parameter, allowing to exclude the initial state of the test object from analysis, to track the dynamics of changes in its state and record the development of each defect separately, to eliminate the influence of the fastening system that can introduce nonlinearities in the test object oscillations is proposed to improve the reliability of defects diagnosis. The result of cracks detection in the aircraft wing ribs in the process of strength tests is presented. For citation: Berns V.A., Zhukov E.P., Lakiza P.A., Lysenko E.A. Studies on the reliability of crack diagnosis by the forced oscillations portraits distortions. Obrabotka metallov (tekhnologiya, oborudovanie, instrumenty) = Metal Working and Material Science , 2019, vol. 21, no. 2, pp. 26–39. DOI: 10.17212/1994-6309-2019-21.2-26-39. (In Russian). ______ * Corresponding author Berns Vladimir A. , D.Sc. (Engineering), Associate Professor Novosibirsk State Technical University, 20 Prospekt K. Marksa, 630073, Novosibirsk, Russian Federation Tel.: 8 (383) 346-31-21 , e-mail: v.berns@yandex.ru