Non-destructive testing of structures by ultrasonic method

Views: 11 Author: Site Editor Publish Time: 2019-10-23 Origin: Site

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With the propagation of ultrasonic vibration in the medium, its essence is the mechanical vibration is propagating in the elastic medium in the form of wave, it is generally considered that its frequency should be above 20 kHz. Ultrasonic non-destructive testing commonly used at 0 4 to 5 MHz. Ultrasonic is used for the damage detection:

1 When the ultrasonic wave propagates in the medium, the interface will be reversed.
2 The ultrasonic directivity is good, the higher the frequency, the better the directivity;
3 Ultrasonic propagation energy is large, and the penetration force of various materials is better and strong. The following mainly introduces pulse reflection ultrasonic nondestructive testing.

1 Ultrasonic signal (very narrow single-pulse signal) is generated. The GPIB interface and cable are used to store the editing single-pulse signal on the computer to the AFG320 signal generator. The piezo disc sensor is generally detected by a very narrow single pulse. Editing the required pulse signal on the computer using the US Tektronix proprietary signal editing software. Its frequency is corresponding to the time width of a single pulse,which belongs to the range of ultrasonic signal, and the time width of this single pulse is 0 625 . It can also be used in SONY's AFG320 signal generator panel: directly operate and edit some signals,signal waveform and frequency are limited and single pulse signals can only be generated to 100 kHz. Using the arbitrary function signal generator itself can not be moved to produce a sufficiently narrow single pulse signal required for the test, to solve this problem a very narrow single-pulse signal, and then store this very narrow coin pulse signal nj computer transmission meter into the memory of AFG320 signal puller through the GPIB cable and the GPIB interface on the PCI slot of the computer. The AFG320 signal has four independent signal memories. The edited signal can be stored in the memory. The test can be used to separate the four signals as needed. the main single-pulse signal of more than 1 MHz is used for the structure.

Type selection of single pulse signals

The pulse signal has different crack anti-injection wave effect in the aluminum plate and propagation. After several experiments, it is found that the ramp pulse is a better choice.

2 using the transducer for non-destructive testing

The A-scan crack detection and crack width determination fixes the two piezoelectric disc
transducers transmitted and received by the ten letters on the same straight line J so that they constitute a set of transducer devices for transmitting and receiving. Using the scanning method, the transmitting and receiving device group is moved from the left to the test riding member. By analyzing the collected test data, the crack existing on the test piece can be clearly detected, and the width of the crack is determined. The value of the crack moves the device from the left to the right on the test piece. When the device is moved to the left position , only one upper edge reflection can be received. The acquired signal continues to move the set to the right, when is moving to the left position near point 2 (the left vertex of the crack). The collected signal. It has a curved reflected wave, the first reflected wave is the crack reflected wave, and the reflected wave of the upper edge of the test piece of the j-ray wave is reflected. The reflection time of the crack reflected wave is shorter than the reflection time of the edge reflected wave. When the device continues to move to the 3 area, the acquiring signal can be collected, and the scanning continues, and the electric energy finds the right vertex of the crack. When the end of the crack is encountered, it is immediately available in the piezo piece. Marking the end position of the crack, and determine the crack width by the end of the crack indicated by the left. Testing data acquisition and analysis software Via GP. IB interface, the data collected by the computer can be stored in EXCEL file and other multi-data forms, which is very convenient for analysis and use. The GP-IB interface used is a GP-IB interface for the PCI slot on one end of the computer. The digital oscilloscope TDS3034B itself has a GP-IB interface module. The test system can also use a slow RS-232 serial interface.

The ultrasound wave that is transmitted and received is converted by wave mode, and the transverse wave (also called shearwave) is transmitted in the aluminum plate. The non-destructive testing that the transverse wave can only perform below is the non-destructive testing of the transverse wave flaw detection method. The shear wave flaw detection method is that the sound wave is incident on the workpiece at a certain angle to generate a wave pattern conversion, and the transverse wave propagates in the structure. A method of structural flaw detection using transverse waves. After the transverse wave is incident on the L-piece, the sound wave will be reflected when the defect is perpendicular to the sound beam or the angle is large. A defect wave appears on the display screen. The test piezo disks crystal used were mainly aluminum plate. The propagation speed of the transverse wave in the aluminum plate aluminum is 3100 m/s. The position of the crack can be calculated and determined based on the transmission time of the wave obtained by the GPIB connected to the computer.

Crack detection by using piezoelectric ceramic crystal materials

Non-destructive testing using piezoelectric ceramic crystal materials to make PZT (lead zirconate fitanafe oxide. Thickness 0.191 mm:430 nF capacitance; Conductive resin (conductive epoxv) wire and piezoelectric crystal test sheet, piezo ceramic test sheet. The distance from the crack to be shot is different.