Views: 5 Author: Site Editor Publish Time: 2019-09-24 Origin: Site
Piezoelectric materials piezoelectric disc transducer have excellent force-electric coupling properties and are widely used in the field of non-destructive testing. The piezoelectric vibration nondestructive testing technology has the following characteristics: 1) it id sensitive to small internal damage of large structures; 2) stable and reliable, wide linear range of operation, able to adapt to more complicated working conditions; 3) more reliable stability .The subsequent data processing is simple. This paper presents the overall design of the piezoelectric non-destructive testing device.
First, a signal generator and a piezoelectric exciter are selected as the excitation portion and the signal emission portion. The core device of the excitation part is a piezoelectric ceramic, and the specific operation is as follows: First, the piezoelectric ceramic is pasted or buried on the surface or inside of the composite test piece. In this way, the sensing and excitation components can be connected at the same time; then a typical voltage signal-square wave signal is generated by the signal generator, and the square wave voltage signal is easy to generate and has high analysis precision. According to the inverse piezoelectric effect, the piezoelectric ceramic subjected to voltage excitation will be deformed to drive the composite test piece to generate a periodic vibration signal. The internal structure energy also changes. The periodic vibration of the structure will in turn drive the deformation of the piezoelectric ceramic ; according to the positive piezoelectric effect, the piezoelectric sensor will generate a periodically varying voltage signal, collect the signal, amplify it with an amplifier, and then filter out some interference. The signal is sent to the resistance strain gauge, and then the digital acquisition instrument is used to digitize the collected signal, and finally connected to the computer to analyze and process the signal. This allows analysis of the internal structural parameters of the composite.The electronic tensile testing machine is mainly used for the tensile test of materials. The model selected is the WDW300 electronic tensile testing machine. The advantages are as follows:
1) It is possible to load and measure the test piece with high precision;
2) DC motor and thyristor stepless speed regulation system can realize stepless adjustment.
The instrument for sensing the load selects the BLR42 type pull load sensor. The connection method is in the form of Wheatstone bridge. The resistance strain gauge and sensitive elastic components are attached to the test piece. The sticking method can be full bridge mode, which can improve the sensitivity;This instrument is cheaper and can generate arbitrary waveforms and wide-band signals. The oscilloscope uses the dual-track oscilloscope and dual-track display to observe the excitation signal and response signal simultaneously. By comparing the signal record by the collector with the signal displayed on the oscilloscope, you can determine whether the acquired signal is distorted and the degree of distortion; you can also observe the signal display on the oscilloscope to ensure that the signal voltage sent to the collector does not exceed the maximum allowable of the collector.
The PZT8 material piezoceramic ring in the piezoelectric sensor has a very high internal resistance, and the output signal power is small. Generally, it cannot be directly displayed, recorded, and used, and needs to undergo impedance transformation and signal amplification. Therefore, the measurement circuit used with the hard material piezoelectric ceramics ring must be a high input impedance preamplifier, which has two functions: the first is to amplify the weak signal of the piezoelectric sensor; the second is to output the sensor with high impedance. Transformed to a low-impedance output. The charge amplifier can be selected from the DHF2A charge amplifier produced .The resistance strain gauge of the device is YD28 type. The strain gauge has a feedback circuit inside, which can automatically zero and eliminate zero drift. The strain gauge also has the advantages of low noise, wide frequency response and high stability. An internal power-off protection circuit eliminates some unsafe factors.
The WSUSB data acquisition instrument used in this paper has 16 channels. The instrument is a relatively advanced device with automatic channel scanning technology and FIF0 buffer memory, so data can be automatically collected and processed, and the processing speed is also quite high. The signal acquisition uses software. The signal analysis and processing software uses the V.0205 software, which is compatible with the operating system. Therefore, the installation is convenient, and it can be self-learned according to the instructions. In the course of the experiment, some unrelated factors will always interfere with the test, such as the high and low voltage, the interference of external electric and magnetic fields. Therefore, it is very necessary to regulate the input signal. After repeated trials and tests, I found that the SM7801J AC voltage regulator can achieve this goal.
Signal collection needs to pay attention to:
1) The measuring signal should not exceed the maximum value;
2) The signal-to-noise ratio of the input signal is relatively high. If there are more noise signals, it must be processed by the filter;
3) Test and analyze the conversion speed of the collector, the processing speed of the computer, and the transmission speed of the interface.
The experimental design steps of this paper are divided into:
1) The piezoelectric ceramic crystal is welded and fixed on the surface of the carbon fiber-based composite beam sample. And testing the performance of this homemade sensor;
2) Checking the performance of the instrument used in the test. Debug the instrument and set the parameters;
3) A healthy composite sample is tested and the signal is recorded in a single channel;
4) Put the test piece on the electronic tensile machine, add increasing pressure to the test piece, signal test and record in the loading process (ie, the damage process of the sample), and double-channel acquisition;
5) Input the collected signal into the computer, use software for data conversion, and then perform spectrum analysis.
