Application Cases

Experiment Name: Finite Element Simulation and Experimental Study of Lamb Wave Defect Detection in Plates

Experiment Objective:
Ultrasonic Lamb wave detection technology is an advanced non-destructive testing method for thin-plate structures. It offers significant advantages and benefits in industries such as petrochemicals, aviation, power, and nuclear energy, generating considerable social and economic value. However, the dispersive characteristics of Lamb waves limit their practical application in industrial production. To determine parameters and conduct modal analysis, this study investigates the propagation characteristics, dispersion curves, and defect detection of Lamb waves in plates.

Testing Equipment:
Preamplifier, function generator, oscilloscope, receiving sensor, computer, etc.

Experimental Procedure:

Figure: Schematic Diagram of the Experimental System

Based on the propagation characteristics of Lamb waves in plates and the laboratory equipment, a conceptual experimental system was set up. According to the connection diagram of the equipment, a 5-cycle Hanning window excitation signal was created using a computer and transmitted to an arbitrary function generator to produce the excitation signal. The excitation signal was then transmitted to a signal-generating probe on an aluminum plate. The excitation probe generated Lamb waves that propagated through the plate, and the echo signals were received by the receiving probe. The echo signals were amplified by a power amplifier and displayed on a digital oscilloscope.

1. Compare the echo signals of Lamb waves in defect-free and defective plates, and analyze the echoes of different modes after dispersion occurs during Lamb wave propagation to determine the defect location.

2. Key parameters for Lamb wave damage detection in plates:

• Excitation signal: 5-cycle Hanning window-modulated signal with a center frequency of 500 kHz

• Incidence angle: A longitudinal wave straight probe was used to excite signals perpendicular to the aluminum plate surface

• Recording length: 1 megapoint

3. Defect size: A circular through-hole with a diameter of 10 mm

4. Save and analyze the experimental results.

Experimental Results:
The experimental setup and parameters described above were used to conduct tests on defect-free and defective aluminum plates. The experimental results are shown in Figures 2 and 3 below:

Figure 2: Experimental Results for Defect-Free Aluminum Plate

Figure 3: Experimental Results for Defective Aluminum Plate

As shown in Figures 2 and 3, since a longitudinal wave straight probe was used for excitation, the A0 mode signal in the received signal showed good resolution, while the amplitude of the S0 mode was minimal. Comparing the results for defect-free and defective aluminum plates, the received signal for the defect-free plate contained two A0 mode waveforms: the first was the A0 mode of the excitation signal, and the subsequent waveform was the A0 mode echo from the plate edge. For the defective aluminum plate, the A0 mode echo from the defect was clearly observed between the excitation signal A0 mode and the edge A0 mode echo.

For the above experiments, finite element numerical simulations were performed using ABAQUS. Models were constructed based on the experimental data to simulate Lamb wave propagation in defect-free and defective aluminum plates. The simulation results are shown in Figures 4 and 5 below:

Figure 4: Numerical Simulation Results for Defect-Free Aluminum Plate

Figure 5: Numerical Simulation Results for Defective Aluminum Plate

The experimental results closely matched the numerical simulation results. The defect location time in the numerical simulation was nearly identical to that in the experimental results, validating the accuracy of the finite element simulation.

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