Control of gaps in technical structures during ground vibration testing

OBRABOTKAMETALLOV Vol. 20 No. 3 2018 MATERIAL SCIENCE EQUIPMENT. INSTRUMENTS 3 2 21 as a rule, discontinuously. Measuring the А 0 value is complicated because of its small magnitude. It is pos- sible to artificially increase it by changing the balance of the deflectable surface or introducing the static component to the driving force. Moreover, there are filters in the measurement system to eliminate noise. It needs to be highlighted that usage of the filters makes the signals smoother as well as changing the oscillation amplitude. When using a low-pass filter, nonlinear effects due to the presence of the gap may disappear. So, Figure 4 illustrates the results of applying the second-order low pass Butterworth filer with cutoff frequencies of 50 and 100 Hz to the portrait of oscillations of a system. The first natural frequency did not exceed 10 Hz. Fig. 4 . The portraits of oscillations for the different cutoff frequencies of a filter Even if there are several gaps in the control wiring, its overall value is evaluated by means of the second equation. The sizes of the gaps located at each damaged structural part are calculated according to the ξ parameter. Results and Discussions The method for detecting gaps based on the distortions of the portraits of oscillations was utilized to monitor the layout of the control wiring and the aeronautical vehicles in the course of the GVT. The study [28] contains the results of detecting backlashes in the layout of the control wiring (Fig. 5). The example of identifying the backlash in the node 6 by means of the distortion parameter of the Lissajous figures is summarized in Table 1. Table 2 summarizes the numerical evaluations of the backlashes calculated by using the equation (2). Fig. 5 . A layout of a control wiring and its scheme: а – a deflectable surface; b – a cable; c – a rocker