Application Cases

Experiment Name: Experimental Study on Wave Monitoring Using the Prefabricated Block Embedment Method

Research Direction: Ultrasonic Testing

Test Objective:
Piezoelectric smart aggregates are commonly used sensors for structural health monitoring in concrete structures, enabling ultrasonic monitoring of dynamic stress and material properties. When embedding smart aggregates into structures, they often need to be fixed to supporting structures such as steel bars by bonding or tying. These supporting structures interfere with the stress field in the monitoring area, and the sensor position stability is poor, thereby affecting monitoring accuracy. This paper proposes a new method for embedding piezoelectric smart aggregates—the prefabricated block embedment method. Through numerical and experimental studies, it was found that compared with traditional embedding methods, the new method significantly reduces the impact on the stress field in the embedded area, the sensor position is more stable, and monitoring randomness is lower.

Testing Equipment: ATA-2041 voltage amplifier, arbitrary waveform generator, acquisition card, charge amplifier, computer.

Experimental Procedure:
Three reinforced concrete columns were prepared as test specimens. The 12 normal stress piezoelectric smart aggregates in each reinforced concrete column were divided into 6 paths. Each path consisted of two vertically aligned normal stress piezoelectric smart aggregates, with the one near the ground serving as the excitation end and the other as the transceiver end. Smart aggregates in the same layer were positioned as centrally as possible within the column, ensuring appropriate spacing between them.

Figure: Flowchart of the Wave Monitoring Test System

First, the signal was modulated by an arbitrary waveform generator and transmitted to the ATA-2041 power amplifier to amplify the signal amplitude. The signal was emitted through vibration of the normal stress piezoelectric smart aggregate acting as the excitation end. The vibration signal was received by the normal stress piezoelectric smart aggregate acting as the receiving end and converted into an electrical signal. This electrical signal was converted into a voltage signal by a high-frequency charge amplifier, received by the acquisition card, and finally transmitted to a laptop equipped with LABVIEW 2014 software for recording. The data acquisition program for this test was programmed using commercial software LABVIEW 2014, the data processing program was written using commercial software MATLAB, and final graphing was uniformly performed using ORIGIN 9 and CAD 2014.

Figure: On-Site Photo of the Wave Monitoring Test

This experiment selected 9 types of modulated six-cycle sinusoidal signals (each cycle duration denoted as T) with center frequencies of 30 kHz, 50 kHz, 70 kHz, 90 kHz, 100 kHz, 110 kHz, 140 kHz, 170 kHz, and 190 kHz.

Figure: Schematic Diagram of First Wave Signal Waveforms from 30 kHz to 250 kHz

Experimental Results:

Figure: Comparison of Wave Parameters for Different Embedding Methods: (a) Wave Velocity, (b) Center Frequency, and (c) Amplitude

The experiment found that even when using the prefabricated block embedment method for installing smart aggregates in wave monitoring, the coefficient of variation for wave amplitude across the six paths reached 46%. A simulation of the wave monitoring test was conducted using Field II (a program callable by MATLAB). Five paths were set up, and without considering embedding interference, only the distribution of coarse and fine aggregates was varied among the five paths. The coefficient of variation for the frequency-domain wave amplitude of the received signals across the five paths was approximately 45%. In this experiment, using the prefabricated block embedment method for smart aggregate installation in wave monitoring, the coefficient of variation for wave amplitude across five paths reached 46%. This indicates that the variability in frequency-domain wave amplitude is primarily caused by the random distribution of concrete aggregates. Even when using amplitude as an indicator, the response randomness of normal stress piezoelectric smart aggregates installed with the prefabricated block embedment method was the smallest. The prefabricated block embedment method (CBC) significantly reduced the randomness in wave monitoring caused by embedding. Its amplitude coefficient of variation was 92.5% and 94% of that for the cross-node tying method (CJB) and the opposite-side bonding method (DSB), respectively. The coefficient of variation for wave velocity with the prefabricated block embedment method was 28% and 25% of that for the two traditional embedding methods, respectively. The coefficient of variation for center frequency was 96% and 62.5% of that for the two traditional methods, respectively. Overall, when using the prefabricated block embedment method for installing normal stress piezoelectric smart aggregates in wave monitoring, the embedding impact on the normal stress piezoelectric smart aggregates is minimal.

Figure: ATA-2041 High-Voltage Amplifier Specifications and Parameters