Control of gaps in technical structures during ground vibration testing

OBRABOTKAMETALLOV Vol. 23 No. 2 2021 51 EQUIPMENT. INSTRUMENTS Control of gaps in technical structures during ground vibration testing Nikolay Testoyedov 1, а , Vladimir Berns 2, 3, b,* , Egor Zhukov 2, с , Evgenii Lysenko 1, d , Pavel Lakiza 2, е 1 Academician M.F. Reshetnev Information Satellite Systems, 52 Lenin str., Zheleznogorsk, 662972, Russian Federation 2 Siberian Aeronautical Research Institute named after S. A. Chaplygin, 21 Polzunov str., Novosibirsk, 630051, Russian Federation 3 Novosibirsk State Technical University, 20 Prospekt K. Marksa, Novosibirsk, 630073, Russian Federation a https://orcid.org/0000-0002-1280-5303, testoedov@iss-reshetnev.ru , b https://orcid.org/0000-0002-2231-7581, v.berns@yandex.ru , c https://orcid.org/0000-0001-6378-6352, zh-ep@yandex.ru , d https://orcid.org/0000-0001-5561-2934, mla340@iss-reshetnev.ru, e https://orcid.org/0000-0002-3863-2762, qinter fl y@gmail.com Obrabotka metallov (tekhnologiya, oborudovanie, instrumenty) = Metal Working and Material Science. 2021 vol. 23 no. 2 pp. 40–53 ISSN: 1994-6309 (print) / 2541-819X (online) DOI: 10.17212/1994-6309-2021-23.2-40-53 Obrabotka metallov - Metal Working and Material Science Journal homepage: http://journals.nstu.ru/obrabotka_metallov ARTICLE INFO Article history : Received: 11 March 2021 Revised: 19 March 2021 Accepted: 29 March 2021 Available online: 15 June 2021 Keywords : Technical structures Gaps in moving structural connections Backlashes in force-displacement application systems Backlashes and gaps as structural defects Aeronautical vehicles Ground vibration testing Portrait of oscillations Nonlinear distortions of a portrait of oscillations Gap control ABSTRACT Introduction. A fair number of technical structures have gaps (backlashes) which can be contingently divided into two types. One of them is the gaps in connections between substructures which are introduced so that the connections may operate correctly. Sizes of such gaps are usually normalized. Another type is the backlashes which occur during operation. Due to the normalized gaps usually expand while operating, both of the types may lead to increased loading and wear of mechanical parts, an alteration in dynamical characteristics and a deterioration in a technical state of mechanical structures. It explains the necessity to control the gaps. When the ground vibration testing of the structures is performed, it seems appropriate to use these tests to detect such gaps. Research Objective: developing the method to control the gaps in the technical structures during the ground vibration testing based on distortions of portraits of forced oscillations. Research Technique. The steady-state forced oscillations of the technical structures, which were measured by acceleration sensors, are excited by means of shakers. The sensor signals are represented as the portraits: the vertical scanning is proportional to the signal and the horizontal scanning – to its fi rst harmonic with the phase shift of π /2. In case of a linear system, the portraits are circles. The presence of the gaps distorts the portraits of oscillations speci fi cally. To estimate the distortions numerically, the fi rst harmonic is subtracted from the Fourier series of the portrait of oscillations, the absolute maximum of the residue is calculated over the oscillation period and used subsequently as the distortion parameter Ψ . The value of the parameter Ψ is normalized and denoted as ξ . The ξ distributions are plotted on controlled objects. The locations of the gaps are determined through the positions of the local maxima of the distortions. While calculating the parameter ξ , the two types of normalization, which were conditionally named the global and local ones, are being used. In case of the global normalization, the value of Ψ is related to the amplitude of the fi rst harmonic at the control point of the structure. The local normalization means that the magnitude of Ψ is related to the amplitude of the fi rst harmonic of the sensor where that parameter was previously calculated. The global normalization is required to analyze the distortion distribution of the portraits of oscillations of the entire technical structure. The local normalization of the distortions of the portraits of oscillations is utilized to establish the locations of the gaps in the mechanical parts and structural connections. The ground vibration tests were carried out via Test.Lab softw are. The subprogram is integrated into the software interface in order to analyze the portraits of oscillations. It enabled one to calculate the distortions of the portraits of oscillations, plot the distortion distributions of the structure and save it for further use. It allowed one to control the gaps during vibration strength tests, as well as while the structures being used, by means of comparing the distortion distributions of the parameter ξ related to different states of the structure. Additionally, the plotting of the distortion distributions of the portraits of oscillations for each structural component is added to the subprogram so as to control the defects subsequently. Not only the locations of the gaps are determined in the force-displacement application systems but also the equation is given to calculate its magnitudes. The practical recommendations on using that equation are presented. Results and Discussion. The possibility of detecting the gaps by the distortions of the portraits of oscillations is illustrated with the example of the diagnostics of the layout of the control wiring and the airplanes during the ground vibration testing as well as the open-type spacecraft structures. It is shown that the developed method enables one to detect all the gaps in the testing object which distort the portraits of oscillations. For citation: Testoyedov N.A., Berns V.A., Zhukov EP., Lysenko E.A., Lakiza P.A. Control of gaps in technical structures during ground vibration testing. Obrabotka metallov (tekhnologiya, oborudovanie, instrumenty) = Metal Working and Material Science , 2021, vol. 23, no. 2, pp. 40–53. DOI: 10.17212/1994-6309-2021-23.2-40–53. (In Russian). ______ * Corresponding author Berns Vladimir A. , D.Sc. (Engineering), Associate Professor Siberian Aeronautical Research Institute named after S.A. Chaplygin 21 Polzunov str., 630051, Novosibirsk, Russian Federation Tel.: 8 (383) 278-70-42, e-mail: v.berns@yandex.ru