Issue 46

I. Shardakov et alii, Frattura ed Integrità Strutturale, 46 (2018) 383-390; DOI: 10.3221/IGF-ESIS.46.35 388 stages. The cracks were located in the cross sections of the cross beams. The depth of the crack was 150 mm, the thickness of the undestroyed part of the crossbar was 100 mm. The location of the prospective sensor for recording the dynamic deformation response is indicated by a red dot on the vertical column above the crack formation zone (point S in Fig. 6). It is evident that the cracks always locate in the region between the impact point and the sensor. Figure 6 : Location of cracks at the bottom of the column. The results of the numerical simulation in the form of vibrograms and their Fourier images for point S are shown by red lines in the graphs in Fig. 7. A blue line shown in the same graphs for the sake of comparison corresponds to the experimental data obtained for the defect-free structure (Fig. 5, vibrogram b). These results demonstrate that a significant distortion of the vibration patterns and their Fourier images occurs at each stage after nucleation of a new crack. Stage Vibrogram Fourier image 1 2 3 4 Figure 7 : Changes in vibrograms at crack formation. The most intense free vibrations of the structure are realized at frequencies around 3400 Hz. A comparison of the amplitude value k a of the Fourier image at this frequency with the value 0 a obtained at the same frequency in the defect- free structure carries important information. The ratio of these values  * 0 / k K a a can be considered as an informative parameter that responds to the process of crack growth. Fig. 7 shows a variation in the criterion * K taken at the