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Applications
The PAC acoustic emission system is used to study the law of acoustic emission signals generated by rock samples under the condition of external pressure until destruction.
Release time: 2020-01-14
First, the concept of acoustic emission system
One of the non-destructive testing methods.
        The phenomenon of localized stress concentration in materials, the rapid release of energy and the generation of transient elastic waves is called acoustic emission (AEoustic Emission, AE for short), and is sometimes called stress wave emission. Material deformation and crack growth under stress are important mechanisms for structural failure. This source, which is directly related to deformation and fracture mechanisms, is called an acoustic emission source. Another type of elastic wave source, such as fluid leakage, friction, impact, and combustion, which is not directly related to deformation and fracture mechanisms, is called other or secondary acoustic emission sources. Non-destructive testing using this "stress wave emission" has the effect that other non-destructive testing methods cannot replace.
History and development of acoustic emission
natural phenomenon
        Acoustic emission and micro-vibrations are natural phenomena that occur at any time in nature. Although it is impossible to verify when people first heard acoustic emission, fracture processes such as tree breaking, rock breaking and bone breaking are undoubtedly the earliest sounds that people have heard. transmit a signal. It can be concluded with certainty that "tin tin" is the first sound emission phenomenon observed in metal, because mechanical twins of pure tin produce audible acoustic emissions during plastic deformation, and the smelting of copper and tin dates back to AD Before 3700.
history record
        In the late 1950s, American Schofield and Tatro found that the acoustic emission of plastic deformation of metals was mainly caused by the movement of a large number of dislocations, and an important conclusion was reached that acoustic emission was mainly a volume effect rather than a volume effect. Surface effect. Tatro has carried out research on the physical mechanisms leading to acoustic emission phenomena. For the first time, acoustic emission can be used as a tool to study the behavioral problems of engineering materials, and predicts that acoustic emission has a unique potential advantage in nondestructive testing.
        In the first stage, in 1965, the United States Dunegan launched the first commercial acoustic emission instrument. Until 1983, it was basically an acoustic emission instrument implemented by pure analog technology, and it was also the first generation acoustic emission instrument;
        The second generation of acoustic emission instrument, from 1983 to 1994, SPARTAN-AT of PAC in the United States began to introduce microprocessors, and modularized and partially digitized the acoustic emission system;
        The third generation of acoustic emission instrument. From 1994 to 2003, the American DW, American PAC, and German Vallen fully digitized the acoustic emission instrument. The signal received by the acoustic emission sensor was amplified by an amplifier and directly passed to an AD converter for digital signals. Digital circuit hardware extracts characteristic parameters and extracts acoustic emission waveforms according to time constants such as PDT, HDT, HLT;
        The fourth generation of acoustic emission instrument, from 2003 to 2015, the PAC of the United States introduced an 18-bit high-speed ADC to the PCI bus acoustic emission card. It turned on 18-bit high-precision acquisition. In addition to the characteristic parameters and waveforms, it also enabled waveforms containing all the original information. Stream function. During this period, the sound emission instrument with USB interface also began to appear, and gradually developed from USB2.0 to USB3.0, and the bus transmission speed also increased from 40MB to 400MB;
        Fifth-generation acoustic emission instrument, 2015-present, the PAC company in the United States has launched a PCIE bus acoustic emission card, a single card 8 channels, each channel 18bit30M sampling, frequency bandwidth up to 1kHz ~ 5MHz, and using PCIE x8 speed transmission, board transmission bandwidth Up to 3GB / s, the transmission bottleneck of the fourth generation acoustic emission instrument has been solved. In addition to the hardware real-time extraction of acoustic emission characteristic parameters and waveforms, the waveform streaming function also enables full-speed acquisition and real-time transmission without bandwidth limitations. At the same time, a network acoustic emission instrument suitable for distributed detection with a gigabit network interface has begun to appear, and will gradually develop to optical fiber transmission to achieve long-distance distributed acoustic emission detection.

Divided by frequency:
        In the first stage, Dunegan et al. Increased the experimental frequency of acoustic emission to 100kHz-1MHz;
        In the second stage, the signal bandwidth of the acoustic emission instrument was increased to 100kHz ~ 1.2MHz;
        In the third stage, the signal bandwidth of the acoustic emission instrument was widened to 1kHz ~ 2MHz;
        In the fourth stage, the signal bandwidth of the acoustic emission instrument is increased to 1kHz ~ 3MHz;
        In the fifth stage, the signal bandwidth of the acoustic emission instrument is increased to 1kHz ~ 5MHz;
        With the development of PCIE bus technology and high-speed ADCs, acoustic emission instruments with a 10MHz signal frequency or higher may appear in the future. In fact, as early as October 1989, Fuji Ceramics Japan produced a standard 10MHz acoustic emission sensor (model REF10M).

From the way of signal acquisition and analysis:
        In the first stage, the acoustic emission instrument uses purely analog technology;
        In the second stage, the microprocessor was introduced into the acoustic emission instrument and began to form a mixture of analog and digital circuits. The signal analysis mainly analyzed the characteristic parameters;
        In the third stage, the acoustic emission instrument was fully digitized after the signal was amplified and entered the ADC. In addition to the characteristic parameters, an analysis method of acoustic emission waveforms appeared;
        In the fourth stage, the acoustic emission instruments began to be PCI and USB buses. The sampling accuracy and sampling rate of the ADC were greatly improved. In addition to the characteristic parameters and waveforms, the waveform stream signals containing all the original information were also stored. It is not possible to obtain all the multi-channel waveform stream files only due to the bus bandwidth limitation;
        In the fifth stage, the acoustic emission instrument began to use the PCIE bus, and the bus bandwidth bottleneck of the fourth-generation instrument was broken. In addition to the characteristic parameters and acoustic emission waveforms, the original waveform stream files were all transmitted and saved in real time.
        As a typical virtual instrument, the acoustic emission instrument is also inevitable with the development of computer bus technology.
Third, the basic principles of acoustic emission
        The principle of acoustic emission detection is shown in the following figure. The elastic wave emitted from the acoustic emission source finally propagates to the surface of the material, causing surface displacement that can be detected by acoustic emission sensors. These detectors convert the mechanical vibration of the material into electrical signals, and then It is then enlarged, processed and recorded. Changes in internal stress in solid materials generate acoustic emission signals. There are many factors that can cause changes in internal stress during material processing, processing, and use, such as dislocation movement, twinning, crack initiation and propagation, fracture, non-diffusive phase transitions. , Magnetic domain wall motion, thermal expansion and contraction, changes in applied load, and so on. People analyze and infer based on the observed acoustic emission signals to understand the mechanism by which materials emit acoustic emissions.



Fourth, the introduction of the United States PAC physical acoustics company and Express8 products
Introduction of American Physical Acoustics Corporation (PAC)
        The American Physical Acoustics Corporation (PAC) belongs to the Mistras Group of Companies. The American Physical Acoustics Corporation (PAC) was founded in 1978. Its founder was Dr. Sotirios J. Vahaviolos, a scientist from Bell Laboratories. As a high-tech company, PAC relied on many talents and continuous innovation in the field of acoustic emission to enable the company to develop and grow rapidly. In 1985, it merged with the world's most famous acoustic emission technology company-Dunegan, USA The company (founded in 1968) makes PAC the world's largest R & D company in acoustic emission technology and a recognized leader in world acoustic emission technology. It is precisely because of PAC's technical breakthroughs and innovations in the field of acoustic emission that the acoustic emission technology has gradually stepped out of the laboratory and continuously entered the field of engineering applications. It has successfully solved engineering problems and led acoustic emission. Technology is moving deeper, higher, and more practically.
        PAC and its developed Mistras group of companies now employ more than 5,000 people worldwide and were listed on the New York Stock Exchange in 2009. Become one of the world's largest non-destructive testing companies with diversified NDT equipment, technology, services, training and standards.
        At present, PAC's acoustic emission products and technical services account for more than 85% of the global market.
        PAC's great achievements in the field of acoustic emission benefit from the company's outstanding talent team. PAC brings together a large number of world-class experts in acoustic emission research and applications, including many experts with doctoral and master's degrees, many experts in Several important academic organizations and institutions hold important positions, such as: Dr. Sotirios J. Vahaviolos, President of PAC Corporation, was the chairman of the American Society of Nondestructive Testing; Dr. Pollock, who is responsible for PAC training, is the director of the Education and Qualification Committee of the American Society of Nondestructive Testing and National Certification Important member of the working group. In terms of acoustic emission technology, PAC holds dozens of technology patents in this field worldwide and has published hundreds of academic papers.
Express8 Product Introduction
        Express8 is the latest AE-based acquisition card based on PCI-Express bus developed by PAC. Adopts new Express bus technology, which is much faster than PCI, VMI and USB bus processing speed. There are 8 channels on a card, but the size is only half that of a PCI-8 card. The board is shorter, stronger and more reliable. Like PCI-2 card, it has waveform streaming function, suitable for research and various field applications.
        Each Express card has 8 acoustic emission channels;
        Smaller size, board size: 16.5cmX10.7cmX1.8cm
        Lighter weight: only 0.1KG
        4 high-pass, 3 low-pass analog filters per channel;
        More than 500 freely combined digital filters;
        16-bit A / D accuracy, 10MHz sampling rate;
        8 external parameter channels;
        Real-time / synchronous acoustic emission feature extraction and waveform acquisition / analysis
        Continuous waveform stream acquisition without board memory limitations
        Alarm Output
        8 digital inputs, 8 digital outputs
        Support 5V, 28V amplifier
        Support oscilloscope mode (direct input without preamp signal)
        Easy-to-use SMB connector
        1KHz-1.2MHz bandwidth;
        Support all types of our company's amplifiers, including 26dB and 40dB amplifiers and integrated front sensors;
        With two new hosts: 32-channel machine and 96-channel host;
        Real-time synchronization can be achieved between different hosts through extended interfaces;
        Can provide Labview / C ++ driver development program.
V. Experimental background of Wuhan University of Science and Technology
        Wuhan University of Science and Technology's School of Resources and Environmental Engineering covers four first-level disciplines: mining engineering, safety science and engineering, environmental science and engineering, and geography. The mining engineering discipline was selected as the "double first-class" domestic first-class discipline construction in Hubei Province. The discipline setting of the college has obvious cross advantages, in the efficient extraction and deep processing of characteristic vanadium resources, deep processing and fine processing of minerals, deep underground metal mine mining and disaster prevention and control, mine safety and disaster prevention, reduction of mining and metallurgical process technology and resource recycling, Theoretical research and engineering applications in industrial flue gas pollution control, mining and metallurgical ecological environment restoration theory and technology, and mining and metallurgical wastewater treatment and resource utilization have distinctive characteristics.
        The purchase of the PAC acoustic emission system is to study the law of acoustic emission signals generated during the process of rock samples under external pressure conditions until destruction, and to simulate the acoustic emission process under mine pressure conditions. Use acoustic emission to continuously monitor the mining process, find dangerous signals and provide early warning to reduce the occurrence of mining disasters. It has positive guiding significance for mining engineering and mine production operations.
Composition of the system

        This system includes:
        Express8 8-channel digital PCIE bus acoustic emission processing card
        8-channel mini industrial computer
        Nano-30 300Hz sensor 8
        4 preamps
        AEwin 8-channel basic acquisition and analysis software
        AEwin 3D analysis software
        Several cables
Seven, the test process
  
        After the sensor is pasted, it is ready. The sample size is 50 × 100mm.


We are tested
  
测试结果 Test result of sample damage
             

        Data field analysis
Conclusion
        It can be seen from the figure that the positioning results of the acoustic emission software are in good agreement with the actual failure mode and location of the concrete sample.
Nine, rock concrete user configuration recommendations
        8chs Express-8 System

Item Model Description Qty
   8chs Express-8 System  
1 Express-8 The 8-channel PCI-Express bus acoustic emission processing card can be inserted into any standard modern PC to form an 8-channel multiple acoustic emission system. 16-bit A / D, 1KHz-1000KHz frequency range. Real-time acoustic emission characteristic parameter acquisition / analysis and waveform acquisition / analysis realized by hardware (FPGA-DSP). 1
2 AE-win for Express-8 8CH 8-channel basic acquisition / analysis software package in WINDOWS environment.
Enhanced interactive graphical interface for real-time acoustic emission signal acquisition / analysis
1
3 AEWIN 3D-LOC 3D positioning module 1
4 Nano30 300KHz resonant frequency sensor 8
5 2/4/6 preamp Pre-amplifier with 20/40 / 60db three magnifications to choose from 8
6 IPC Acoustic emission control computer, keyboard, mouse, monitor 1
7 P-Case On-site shipping box 1
8 1234-10 10-meter signal cable, connecting the capture card and preamp 8
9 SMB / BNC-0.3 0.3m adapter cable 8
        Specific configuration requirements can consult the sales staff of the European and American offices.
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