PSI - Issue 32

O.V. Bocharova et al. / Procedia Structural Integrity 32 (2021) 299–305 Bocharova O.V., Andzjikovich I.E., Sedov A.V., Kalinchuk V.V. / Structural Integrity Procedia 00 (2021) 000 – 000

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Also, the advantage of this approach is the absence of any fundamental limitations both to the material and the shape of the structure. The method is based on use of a special mathematical method of processing of the recorded signal detected on the surface of the medium, which is initiated by impact action. Usually for the processing of the recorded signal spectral methods (Tondreau and Deraemaeker 2013), statistical approaches (Cogranne and Retraint 2014), correlation processing (Salazar et al. 2010), wavelet transform signals (Tsui and Basir 2006; Janeliukstis et al. 2016), approaches based on the use of artificial neural networks are used. In the present work a method based on using of the optimal orthogonal expansions of signal in the basis, adaptively customized by the tested sample is used. This approach has a lot of advantages, the main of which is the adaptive adjustment of an orthogonal basis by the specified parameters. A multifunctional measuring system allowing conducting studies, comparing signals, and constructing spectral characteristics by using sensors of various types was created. The experimental setup allowing evaluating a variation of surface wave field in samples of various functional materials in the laboratory conditions was constructed. Scheme of the experimental setup is presented in Fig. 1. A surface wave arose on the edge of the sample under the impact action. The surface wave’s propagation has been registered by the two ICP accelerometers PC Piezotronics and was amplified by the charge amplifier ZET 440 Zetlab. Accelerometer 1 was located between the excitation point and defect detects the reflected wave; accelerometer 2 was located after the defect detects transmitted wave. The digitizer pad ADC L-Card (E14-140) digitized the obtained signals, and then the signal has been processed by the software PowerGraph. As the samples beams with length of 960 mm and cross-section 50 mm x 50 mm made of the material with low wave propagation velocity (expended polystyrene; Young's modulus 22  E MPa, density 50   kg / m 3 ) were used. Samples have been weakened by the thin slot and the following cases were realized in the experiment, see Fig. 2: 1. the sample without defects; 2. the sample with embedded steel plate (thickness of the plate ( th ) is 0.5 mm, length of the plate is 18 mm) at depth of 10 mm from upper surface of the sample; 3. the sample with two embedded steel plates. The second plate has been embedded near to the first one at the same depth; 4. both plates were ejected from the sample, and a slot with high of 0.5 mm and length of 36 mm at the depth of 10 mm from the upper surface of the beam was formed.

Fig. 2. Types of samples used in the experiment.

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