Research And Desigh Of Multi-channel Brittle Material Fracture Online Monitoring System Based On Acoustic Emission

With good physical and chemical properties, brittle material is widely used in geological exploration, oil drilling, metallurgical machinery, industrial chemicals, and even aerospace, biomedical, microelectronics and other high-tech fields, especially in extreme environments. In the process of internal micro-cracks growth, fracture development, it will engender acoustic emission. Therefore, the acoustic emission nondestructive testing technology is a powerful tool for the study of brittle material fracture evolution.The subject comes from the National Natural Science Foundation of scientific instruments basic research project "5GPa high temperature and high pressure rheometer technology research and equipment development".5GPa high temperature and high pressure rheometer is a precision scientific instruments consisting of mechanical systems, hydraulic systems, heating systems and electronic control system. The internal high-pressure cavity and the deformation rods are made of ultra-high strength tungsten carbide. The rheometer cavity may rupture and the lever may crack after working in ultra-high pressure high temperature environment for a long time. It will not only have a bad impact on the experimental results, but also endanger the lives and safety of the experimental staff.Therefore, this paper proposes the use of acoustic emission nondestructive testing technology to achieve intelligent damage diagnosis system based on real-time monitoring is of great significance and practical application prospects. By acquiring the acoustic emission signals, removing the noise and extracting the characteristics of the acoustic emission signals cracks in brittle materials, we can know the stage of development of material injury, the causes and the corresponding performance. It is an effective way to prevent the vicious experiments accidents and it provides a basis for the rheometer maintenance and the judgment of potential failure. It will gradually narrow the gap between our country and international advanced level in the study of high temperature high pressure rheology.By comparison with the existing acoustic emission acquisition system this paper design a multi-channel brittle material fracture online monitoring system based on acoustic emission combining the functional requirements of the subject and the advantages of the embedded processor.The system is designed in modular design concept. The hardware includes acoustic emission sensor, pre-amplifier, acoustic emission data acquisition card and communication module. Acoustic emission data acquisition card is the core of the entire design. It mainly consists of a control module, a signal conditioning module, A/D converter module, the data storage module,485communication module, the alarm module, a user interface module and the power module. The software includes lower computer program, PC interface program and PC-side data processing program.Acoustic emission sensors use the PXR series resonant high sensitivity sensor to collect the acoustic emission signals of the brittle materials crack. Preamplifier module select Linear Technology’s LTC6241dual low noise, rail-to-rail CMOS operational amplifier chip to designe single-supply level uplift amplifier circuit and the amplifier gain is20dB. The control module of the acoustic emission data acquisition card uses a high-performance ARM Cortex-M3core chip STM32F103VET as a core processor to achieve the intelligent control of the system. Signal conditioning module uses two dual-channel low-noise, rail-to-rail operational amplifier LTC6241to achieve the second-order band-pass filter and AC amplifier. The A/D converter module uses the STM32internal built-in A/D. And the micro-power comparator LTC6702is used to trigger the A/D sampling to avoid excessive consumption of the controller resources. The data storage module uses SD card to storage the sampling data. The communication module uses485bus communication and ADI’s ADM2483isolated half-duplex RS485transceiver to achieve multi-channel acoustic emission data transmission. Alarm module uses sound and light alarm. The user interface module uses8-bit DIP switch to set the trigger threshold of acoustic emission signals. The system uses the+12V DC power supply. The power modules uses MORSUN’s wide voltage input DC-DC isolation power module VFB1205₆W to produce the voltage of+5V. High-performance integrated voltage regulator AMS1117-3.3and ultra-low noise, low dropout linear regulator TPSA4901are used to output+3.3V. It achieves the separated power supply of digital and analogue circuit. The main functions of the PC interface are to communicate with the lower computer in485bus, receive the acoustic emission data and store them on the local hard disk. The user can also query each acquisition channel through the PC interface. PC-side data processing includes acoustic emission signal recovery, time domain analysis, frequency domain analysis, energy spectrum analysis, wavelet denoising.The system hardware development platform uses Altium Designer Summer09and PSpice software to complete system hardware schematics desogn, PCB design and analog circuit hardware emulation. Lower computer software design integrated development environment is IAR Systems’s IAR Embedded Workbench for ARM （EWARM）. The host computer interface software design platform is Microsoft Visual Studio2010. PC-side data processing is realized in MATLAB software.After design we debug each module, the whole system. And we apply the system in the tungsten carbide pressure hammer high pressure rupture experiment. Through the data analysis the system is able to achieve performance parameters and the expected design goals. And it proved to be working stability and has a good performance.