Application Cases

Experiment Name: Simulation Study on Debonding Defect Imaging Using Power Amplifier Based on Lamb Wave Time Reversal Method

Experiment Purpose:
In the practical structure of large solid rocket motors, composite material casings have a small curvature, and glass fibers are laid in a specific pattern. Debonding is the primary defect form at the interface between the composite casing and the insulation layer. A laminated plate specimen with debonding defects was designed and fabricated. Combined with the theoretical foundation of the time reversal method and the constructed dry-coupled Lamb wave detection platform, simulation and experimental research on debonding defect imaging were conducted.

Experimental Equipment:
Dry-coupled probe, arbitrary signal generator, ATA-4051 high-voltage power amplifier, multi-channel oscilloscope, computer, etc.

Experimental Procedure:

Hardware Setup:
The hardware system for dry-coupled Lamb wave detection mainly consists of dry-coupled probes, an arbitrary signal generator, a power amplifier, a multi-channel oscilloscope, a computer, and corresponding detection software.

Figure: Schematic Diagram of the Dry-Coupled Ultrasonic Imaging Detection System

The working principle of the dry-coupled ultrasonic detection system is illustrated in the figure. First, the computer software ArbExpress compiles the waveform in two ways: (1) using a function editor to input the waveform's function expression, or (2) importing discrete data sequences. Both methods are used during the time reversal process. The original excitation waveform is compiled based on specific function expressions to ensure proper triggering of the transmitting probe, while the time-reversed signal requires importing discrete data sequences for secondary loading. The compiled waveform is then sent to the signal generator, where parameters such as frequency and amplitude of the original excitation waveform are set. The power amplifier amplifies the original waveform to meet the required gain. The amplified signal is loaded onto the dry-coupled transmitting probe to excite Lamb waves in the plate specimen. The receiving probe captures the response signal and transmits it to the multi-channel oscilloscope. Finally, the detection data from each channel are read in the LabVIEW environment, and the results are post-processed.

Experimental Results:

Figure: Six-Probe Defect Experimental Imaging

(1) As shown in Figure 5.13, the positions of the detection probes are clearly visible, and the contrast between damaged and undamaged areas is evident. The fabricated specimen has a defect center at (400, 400), with a horizontal range of 390–430 mm and a vertical range of 380–420 mm. The thresholded image obtained using the baseline-free damage imaging method reveals two defects.
(2) The shape of the prefabricated defect in the specimen is triangular, but the edges in the damage imaging appear blurred, making it difficult to discern the exact shape of the defect.
(3) The damage imaging contains several virtual images with slightly lower brightness than the defect area, forming transition zones that indicate two defects. Possible reasons include:

1. The limited number of detection probes results in multiple intersections of elliptic curves.

2. The anisotropy of the glass fiber material causes nonlinearity in signals propagating in directions not aligned with the fiber layering.

3. Uneven adhesive application during specimen bonding affects the detection signals.

4. Variations in the experimental environment influence the results.

   
   

Figure: ATA-4051C High-Voltage Power Amplifier Specifications and Parameters