Development of Ultrasonic Techniques for Measurement of Spatially Non-Uniform Elastic Properties of Thin Plates by Means of a Guided Sub-Sonic A0 Mode

Abstract

Air-coupled ultrasonic guided A0 mode is already used for material characterization. By measuring the phase velocity of the A0 mode the elastic properties, such as the Young’s modulus, can be determined. The objective of this work was the development of measurement methods and corresponding signal processing procedures enabling the acquisition of spatial distributions of non-uniform elastic properties of thin films and plates. Those methods are based on the excitation of a slow sub-sonic A0 Lamb wave mode in a plate, the measurement of normal displacements at different distances from the source, the formation of the B-scan, and processing the collected signals. Two different signal processing methods were proposed and investigated. In the first method the all zero-crossing instants of the ultrasonic signals at different distances are found and from them spatial distributions of the A0 mode velocity are determined. According to the second method 2D spatial-temporal spectrum of the B-scan is calculated and propagating A0 modes with different velocities are identified. Efficiency of the proposed methods was evaluated theoretically and experimentally using thin mineral MICA paper samples, which is used in the electrical and aerospace industries as an insulating material. The zones with different A0 mode phase velocities (95 ± ∆3 m/s and (106 ± ∆6 m/s) at the frequency 47 kHz were identified.

Excitation and Reception of Higher-Order Guided Lamb Wave’s A1 and S1 Modes in Plastic and Composite Materials

“…For determination of the dispersion curves for the PE-300 sample under investigation, we used the method based on the analysis of a 2D spatial-temporal spectrum of the B-scan of the normal displacements [ 45 ]. Dispersion curves using the semi-analytical finite element method (SAFE) are shown by red lines, and the 2D Fourier transform of the B-scan converted in the frequency-phased velocity domain is presented in Figure 11 .…”

“…Lamb waves propagating at different velocities are indicated in this figure. More about the 2D Fourier transform and 2D spatial-temporal spectrum of the measured B-scan methods can be found in our paper [ 45 ]. Using the 2D spatial-temporal spectrum of the measured B-scan modes in the case of the PE-300 sample, where the red dotted line is A 1 mode from the simulated SAFE method, is presented in Figure 12 .…”

Mathematical Modeling and Computer-Aided Simulation of the Acoustic Response for Cracked Steel Specimens

“…The results indicate that the micro-cracks lead to the generation of second harmonics [44]. For internal defect detection, some studies extract and combine spatial and temporal features to estimate the physical properties such as Young's modulus [45]. Previous studies also suggest that faults can be detected by estimation of absolute acoustic nonlinearity parameter, beta, defined by the displacement amplitudes of the fundamental and secondorder harmonic frequency components of the ultrasonic wave propagating through the material [46].…”

Application of Laser Vibrometry to Assess Defects in Ship Hull’s Welded Joints’ Technical Condition

“…NDT testing techniques are well researched and give results with usually sufficient reliability [ 10 , 11 , 12 , 13 , 14 ]. However, they have a fundamental disadvantage—they are carried out periodically.…”

“…Especially in case of critical events such as a strong storm or collision, it is important to know the possibility of further exploitation of the object. This information must include the degree of potential disaster risk together with the parameters of exploitation with particular emphasis on the time of safe use of the object [ 13 , 14 , 15 , 16 ]. To this end, research on new techniques known as structural health monitoring (SHM) is being developed [ 1 , 5 , 17 , 18 , 19 , 20 ].…”