CN101832970B - Device and method for reckoning fatigue crack propagation rate of flat alloy by AC potentiometry - Google Patents

Abstract

The invention provides a device and method for measuring and calculating the fatigue crack growth rate of a flat alloy by an AC potential method, and relates to the field of material fatigue performance detection. The method of the invention is two pairs of probes on the surface of a flat alloy sample. The AC potential method sensor on it monitors the potential changes on both sides of the crack in real time when the fatigue crack expands, and sends it to the dual-trace oscilloscope through the amplifier to display the potential waveform diagram of crack expansion at both ends, and input it into the computer through the A/D converter. Software analysis and processing, to obtain fatigue growth data such as fatigue crack growth rate. The device of the present invention mainly includes a fatigue testing machine, a sample fixture, an AC potentiometric sensor, a potential measuring probe, a wire, a signal amplifier, a dual trace oscilloscope, an A/D converter, a CCD image acquisition system and a computer. The invention is suitable for the research on the fatigue crack propagation behavior of the alloy.

Description

Apparatus and method for calculating fatigue crack growth rate of flat alloy by alternating current potential method

technical field

The invention relates to the field of material fatigue performance detection, in particular to a method and device for measuring and calculating the fatigue crack growth rate of flat alloys by an alternating current potential method, and is mainly applicable to the research on the fatigue crack growth behavior of alloys.

Background technique

The fatigue crack growth resistance of materials has become an important parameter in the design of real components. In order to ensure the safe use of components, it is necessary to study the fatigue and crack growth behavior of materials. The potential method can be used to derive the functional formula between the potential difference and the crack length during fatigue crack growth. Therefore, the potential difference can be used as a function of the crack position and size parameters to calculate the fatigue crack growth rate. The potential monitoring method is divided into direct current potential method (DCPD) and alternating current potential method (ACPD). The alternating current potential method is mainly used to monitor the occurrence and expansion of cracks on the conductor surface.

When the AC potential method monitors the fatigue crack growth, the external AC current is supplied to the component through a pair of current supply probes to provide continuous AC power, and a pair of potential measurement probes monitors the change in the potential difference between the two points when the fatigue crack grows, and the voltmeter displays the corresponding potential value . By monitoring and analyzing the potential difference signal, the formation and propagation of fatigue cracks on the surface of the component can be obtained, and finally the fatigue crack growth rate and other crack growth data can be obtained.

The rapid crack growth, especially in the high-rate area, the fatigue growth of small cracks, and the interference of various noises during the growth, coupled with the harsh external environment, have brought a lot of trouble to the real-time monitoring of surface fatigue crack growth. The AC potential method can automatically monitor the fatigue crack growth in real time for a long time, and is convenient and simple to operate. It is suitable as a method for studying the crack growth behavior of materials.

There are very few patents involving the AC potential method at home and abroad. The Chinese patent application number 03128293.8 "Ground Electrical Measurement Method for Detecting the Corrosion of Underground Metal Pipelines" uses the principle of the AC potential method to detect the corrosion of underground metal pipelines. Based on the method monitoring principle, the grounding power supply electrode and the measuring electrode are arranged along the measuring line perpendicular to the direction of the pipeline. The measuring electrode is connected to the broad-spectrum electrical measuring instrument instead of the voltmeter in the principle, and the broad-spectrum electrical measuring instrument is used to continuously change the frequency. Potential difference amplitude and phase measurement, and then determine whether the pipeline has been corroded and the degree of corrosion according to the magnitude of the abnormal amplitude of the pipeline on the phase-frequency spectrum curve. This method needs to constantly change the frequency of the broad-spectrum electric measuring instrument in the detection, and the automaticity and blindness are relatively large; the formula based on the theoretical formula of the amplitude and phase of the alternating electric field is more cumbersome and has a large amount of calculation; and the AC potential method The detection of corrosion degree does not involve other fatigue expansion, the application area is narrow, and the whole process of corrosion fatigue expansion cannot be automatically obtained.

Wang Liang ^[1] and others have discussed the method of measuring fatigue crack growth by direct current potential method at high temperature and the solution to the problems in use ([1] Wang Liang, Ding Chuanfu. Application of direct current potential method to measure crack length at high temperature [J ]. Physical and Chemical Testing-Physical Volume, 2006, 42(9): 454-456). This method is similar to the measuring principle of the alternating current potential method, the difference is that the applied current is direct current, and this method can measure the fatigue crack length, which improves the degree of automation. The integrity of the sample is destroyed, making it difficult to achieve non-destructive testing.

Contents of the invention

The purpose of the present invention is to overcome the limitations of potential measurement probes embedded in the sample that damage the integrity of the sample, the complete recording of data, the constraints of environmental factors in monitoring the fatigue crack growth of various alloy samples, and the improvement of the accuracy of the system device. An improved AC potential method sensor is developed, and the potential change at both ends of the crack is monitored by the improved potential measurement probe, and the direct image of the crack growth on the sample surface is taken online by the CCD, so an AC potential method is proposed to measure the fatigue crack growth of flat alloys Method and apparatus for speed.

The method adopted in the present invention is as follows: during the whole process of tensile fatigue test of the flat alloy sample with prefabricated cracks, the AC potentiometric sensor installed at the crack on the surface monitors the potential signal when the two ends of the crack expand in real time through the potential measurement probe. After being amplified by the amplifier, two potential waveforms are displayed on the dual-trace oscilloscope. The monitored potential signal is finally stored in the computer. Through the supporting integrated software, the fatigue crack growth data of the sample is obtained from the computer, such as fatigue crack growth. In order to specifically express the whole process of fatigue crack growth, a CCD image acquisition system is used in the present invention to record the crack growth process and store it in the computer, so as to comprehensively photograph the visual situation of fatigue crack growth from another angle, so as to avoid the important research details of fatigue crack growth omissions.

The device for implementing the method includes a fatigue testing machine and a sample fixture, a prefabricated crack flat alloy sample, an AC potentiometric sensor, a potential measurement probe, a lead wire, a signal amplifier, a dual-trace oscilloscope, an A/D converter, and a CCD image acquisition system and a computer with accompanying integrated software. A pair of rectangular induction coils of the AC potentiometric sensor and two pairs of potential measurement probes are installed on the surface of a flat alloy sample with a prefabricated crack, and the two pairs of potential measurement probes are located at both ends of the prefabricated crack and the crack is included in the middle Position, the two induction coils of the AC potential method sensor are respectively located at the two ends of the prefabricated crack on the surface of the tested alloy sample and include two pairs of potential measuring probes, which are placed on the fatigue testing machine as a whole, and the two ends of the alloy sample are fixed with clamps; The wire on the flat top cover of one probe of each pair of potential measurement probes is connected to the input end of a signal amplifier, while the wire on the other flat top cover is connected to the output end of the dual-trace oscilloscope; The output terminals of the two signal amplifiers are connected with the two input terminals of the dual-trace oscilloscope, the output terminals of the dual-trace oscilloscope are connected with the input terminals of the A/D converter, and finally the output terminals of the A/D converter are connected with the supporting A computer with integrated software. The CCD image acquisition system and the fatigue testing machine are also connected with the computer.

Potentiometric measuring probes consist of two parts, a cylindrical housing and a flat-topped cover with embedded leads. The cylindrical shell is connected by a spring buckle in the middle, and two pairs of cylindrical conductive adhesives are molded in the two ends of the prefabricated crack on the flat alloy sample, and the cylindrical shell is used to cover the two pairs of cylindrical conductive adhesives, and then Continue to inject conductive glue into the two pairs of cylindrical shells, so that the cylindrical conductive glue and the shell are tightly combined, so that the potential measurement probe can be fixed in the measurement area, and finally cover the flat top cover with embedded wires.

The cylindrical shell is easy and free to disassemble without destroying the integrity of the sample and can be used repeatedly. The flat top cover is designed in a flat top shape, which can ensure that the conductive glue fills the shell, and at the same time, the metal wire in the wire runs through the shell to ensure the best conductive effect. The cylindrical shell and the flat top cover are made of two materials. The outer layer is made of insulating material such as insulating rubber, which can shield the interference of external large resistance. The inner layer is made of conductive material, such as copper, to ensure electrical conductivity. Good sex. The potential measurement probe designed in this way can not only be fixed in the fatigue crack growth measurement area to monitor the potential change, but also does not need to destroy the sample, such as punching holes for the sample to embed the probe, etc., and the insulation design can prevent external high-resistance objects from affecting fatigue. Interference during crack monitoring.

The two induction coils of the AC potential method sensor are respectively located at the two ends of the prefabricated cracks on the surface of the tested alloy sample and include two pairs of potential measurement probes. The induction coils are wound in a rectangle to a height of 22mm-25mm. The rectangle is 55mm-59mm long. Width 25mm-29mm, Δ=35-39mm. An external excitation current flows through the pair of induction coils, and the changing electric field generates an induction magnetic field, which induces an induction current between the two pairs of potential measurement probes, and provides an external current to the sensor. The induction coil in this improved AC potential method gathers the induced current to the local test range, the current spread becomes smaller, the monitored potential value is relatively clear, and the accuracy is improved.

The specific steps of the method for calculating the fatigue crack growth rate of flat alloys by alternating current potential method are as follows:

(6) Install two pairs of potential measuring probes on the two ends of the prefabricated crack on the flat alloy sample, include the prefabricated crack in the middle position, and then wind the induction coil at both ends of the crack to form an AC potential sensor, and place it on the fatigue testing machine as a whole , the external excitation current flows in the induction coil, and the wire on one of the flat-topped covers of each pair of potential measurement probes is connected to a signal amplifier, while the wire on the other flat-topped cover is connected to the output terminal of the dual-trace oscilloscope, Then turn on the signal amplifier, dual-trace oscilloscope, A/D converter, CCD image acquisition system, computer with supporting integrated software and other devices connected by wires in the system, and put the fatigue testing machine in working condition.

(7) The AC potentiometric sensor uses two pairs of potential measuring probes to monitor the signal of the potential change at both ends of the crack caused by fatigue crack growth in real time.

(8) Two signal amplifiers amplify the potential change signal at both ends of the crack monitored by two pairs of potential measuring probes, and transmit it to the dual-trace oscilloscope, which simultaneously displays the potential data and measurable waveforms when the crack expands at both ends.

(9) The electric signal collected by the above-mentioned double-trace oscilloscope is input into the computer through two A/D converters, and the potential data is processed by the computer to obtain crack growth data such as the fatigue crack growth rate. The computer software is based on Johnson's derivation of the functional relationship between the potential change and the fatigue crack growth parameter.

(10) The CCD is used to take images of the entire fatigue crack growth process, record the information and store it in a computer with supporting software, to avoid omission of important research details of fatigue crack growth, and make a backup for the follow-up processing of fatigue crack growth.

Compared with the existing potential method for monitoring fatigue crack growth, the present invention has the following advantages:

(1) The potential measurement probe designed in the present invention not only has the function of transmitting alternating current, but also can isolate possible high resistance interference from the outside. The probe is composed of two parts, namely a cylindrical shell and a flat top cover. The cylindrical shell is made of two materials. First use; flat top cover design, the purpose is to make the cylindrical shape of the injected conductive glue completely conform to the shell, and improve the conductive efficiency.

(2) In the present invention, the general AC potential method is improved, and the electromagnetic field theory of "magnetoelectricity" is adopted to excite the magnetic field with the excitation current, and the induced current is generated in the local monitoring area. Compared with the general AC potential method, the induced current diverges less , can be gathered in the monitoring area, improving the accuracy of monitoring potential signals.

(3) Set up two pairs of potential measurement probes at both ends of the crack, and send the monitored potential signal of fatigue crack growth at both ends of the sample to the dual-trace oscilloscope after being amplified by the amplifier, so that not only the magnitude of the potential signal can be read at the same time , which can more intuitively display the waveform diagram of the potential signal monitored by the two pairs of potential measuring probes.

(4) The CCD image acquisition system is used for the fatigue crack growth on the surface of the alloy sample, which can capture the growth of the fatigue crack on the surface of the alloy sample in real time. Through the software designed in this system, the follow-up research and processing of the fatigue crack growth on the surface can be carried out , understand the fatigue crack growth from many aspects and angles, and it is not easy to ignore the important details of fatigue crack growth.

(5) The computer is equipped with fatigue testing machine control software, fatigue crack growth analysis software and CCD image acquisition system software integration system. The fatigue crack growth analysis software is based on the functional relationship between Johnson potential and fatigue crack growth parameters, and can obtain fatigue growth data such as fatigue crack growth rate online, including numerical values and graphics.

Description of drawings

Figure 1 is a schematic diagram of the closed control system for measuring and calculating the fatigue crack growth rate of flat alloys by AC potential method.

Fig. 2 is a schematic diagram of an AC potentiometric sensor (4) installed at a crack on the surface of an alloy sample.

Fig. 3 is a three-view view of the AC potentiometric sensor (4) system device placed at the crack on the surface of the alloy sample.

Fig. 4 is a structural design diagram of the potential measuring probe (6).

Fig. 5 is a flat top cover (17) with lead wires (7) embedded in the potential measurement probe (6)

Fig. 6 is a structural diagram of a probe (6) cylindrical casing (18) for monitoring potential signals.

Fig. 7 is the diagram of the CCD image acquisition system (12) for real-time shooting of fatigue crack growth at the sample surface

Fig. 8 is a schematic diagram of a computer (11) installed with fatigue testing machine control software, fatigue crack growth analysis software and CCD image acquisition system software.

In the figure, 1. Fatigue testing machine 2. Sample fixture 3. Flat alloy sample 4. AC potentiometric sensor 5. Prefabricated surface crack 6. Potential measurement probe 7. Wire 8. Signal amplifier 9. Dual trace oscilloscope 10. A/D converter 11. Computer 12. CCD image acquisition system 13. Induction coil 14. Excitation current 15. Induction current 16. Induction magnetic field 17. Flat top cover 18. Cylindrical shell 19. Metal wire 20. Spring buckle.

Detailed ways

The details and working conditions of the specific device proposed by the present invention will be described in detail below in conjunction with the accompanying drawings.

The device for measuring and calculating the fatigue crack growth rate of flat alloys by using the AC potential method of the present invention includes a fatigue testing machine (1), a sample clamp (2) and a flat sample (3) between them, and an AC potential sensor on the sample. (4), prefabricated surface crack (5), potential measurement probe (6), lead wire (7), signal amplifier (8), dual trace oscilloscope (9), A/D converter (10), CCD image acquisition system (12) and the computer (11) that installs supporting software control program.

Figure 1 is a schematic diagram of the closed control system for measuring and calculating the fatigue crack growth rate of flat alloys by AC potential method. First, the sensor (4) based on the principle of AC potential method is installed on the sample (3), and then placed on the fatigue testing machine (1) as a whole, and the sample is in the tension fatigue test state during the whole monitoring process. On the one hand, the AC potentiometric sensor (4) provides the sample with an external AC current (15) with high aggregation ability, and on the other hand, it cooperates with two pairs of potential measurement probes (6) placed at both ends of the surface crack (5), each pair of potential measurement probes The probes (6) contain the crack (5) in the middle position, and monitor the potential changes on both sides of the crack caused by the fatigue crack growth in real time. The potentials detected by the two pairs of electrode probes (6) are respectively passed through two amplifiers (8 ) to be amplified, and then sent to the dual-trace oscilloscope (9), by which the oscilloscope (9) can simultaneously display the potential waveform diagrams of crack expansion at both ends, through the A/D converter (10), input in the computer (11), and carry out The data processing of fatigue crack growth can obtain crack growth data such as fatigue crack growth rate. CCD (12) is used to take images of the entire fatigue crack growth process, and its image recording and fatigue testing machine (1) load loading are also controlled and stored by the computer (11), paving the way for the follow-up processing of fatigue crack growth , thus forming a closed control system for real-time monitoring of fatigue crack growth.

Fig. 2 is a schematic diagram of an AC potentiometric sensor (4) installed at a crack on the surface of an alloy sample. Build a pair of rectangular induction coils (13) on the surface of the tested alloy sample. The induction coils are wound to a height of 22mm-25mm in a rectangle. The rectangle is 55mm-59mm long and 25mm-29mm wide. -39mm. An external excitation current (14) flows in the pair of induction coils, and the changing electric field produces an induction magnetic field (16), and the direction of the induction magnetic field can be determined according to the right-hand rule and the direction of the induction coil current loop, as shown in Figure 2, the induction magnetic field direction is perpendicular to the sample surface. The changing magnetic field generates an electric field, thereby generating a concentrated induced current (15) between the pair of induced coils.

Fig. 3 is a three-view view of the AC potentiometric sensor (4) system installed at the crack on the surface of the alloy sample. The upper left image is a top view of the modified AC potentiometric technique, and the lower left and right images are side views. Improve the general AC potential method, build a pair of rectangular induction coils (13) on the tested sample, a=25mm-29mm, b=55mm-59mm, c=22mm-25mm, h=5～12mm, H=0mm , feed the excitation current (14) to the induction coil, so that the induction current (15) is induced in the middle of the two coils, and the induction current flows through the crack, which is equivalent to the external AC current directly introduced by the wire in the above schematic diagram 2. The induced current in the improved AC potential method is not directly introduced by wires, but induced. The potential value monitored by this improved AC potential method is much larger than that of the general potential method technology, especially for the monitoring of stress corrosion crack growth. The monitored potential value is dozens of times larger than that of the general potential method, and its accuracy is also It is more technical than the general potentiometric method. Compared with the current used in the general potentiometric method, the improved AC potentiometric method, because the induction coil gathers the induced current to the local test range, the current diffusion becomes smaller, the monitored potential value is relatively clear, and the accuracy is improved. It can be seen that the alternating current potential method in the present invention can also be used to monitor the propagation of surface fatigue cracks in the depth direction.

Fig. 4 is a structural design diagram of the potential measuring probe (6). The probe consists of two parts, a cylindrical shell (18) and a flat top cover (17) embedded with wires. Two pairs of conductive adhesives in the shape of cylinders are molded in the regions at both ends of the prefabricated cracks (5) on the flat alloy sample (3), and the two pairs of conductive adhesives in the shape of cylinders are covered with a cylindrical shell (18), and then continue to These two pairs of cylindrical shells (18) are injected with conductive glue, so that the cylindrical conductive glue and the shell (18) are tightly combined, so that the potential measurement probe (6) can be fixed in the measurement area, and finally the cover is embedded with wires The flat top cover (17); the distance between a pair of potential measuring probes (6) is 5 mm to 12 mm. The conductive adhesive can be copper-plated silver conductive rubber and the like. The potential measurement probe (6) designed in this way can be fixed in the fatigue crack growth measurement area to monitor the potential change, and there is no need to destroy the sample (3), such as punching holes for the sample to embed the probe, etc., and the insulation design can avoid The interference of external high-resistance objects on fatigue crack monitoring.

Fig. 5 is a flat top cover (17) with lead wires (7) embedded in the potential measuring probe (6). The flat top cover (17) is made of two kinds of materials, and the outer layer is made of insulating material, such as insulating rubber, and the inner layer is made of conductive material, such as copper. The needle shell (18) is filled, and the metal wire (19) in the lead wire (7) runs through the potentiometric probe shell (18) simultaneously to ensure the best conduction effect.

Fig. 6 is a structural diagram of a probe (6) cylindrical casing (18) for monitoring potential signals. The cylindrical shell (18) is connected by a spring buckle (20) in the middle, and covers two pairs of cylindrical conductive glue molded in the two ends of the prefabricated crack (5) on the flat alloy sample (3). The shell (18) is easy and free to disassemble, without destroying the integrity of the sample, and can be reused. It is made of two kinds of materials. The outer layer is made of insulating material such as insulating rubber, which can shield the interference of external large resistance, etc. The inner layer is made of conductive material, such as copper, to ensure good conductivity.

Fig. 7 is a diagram of a CCD image acquisition system (12) for real-time shooting of fatigue crack growth on the surface of the sample. The system includes a shooting system and a storage system, and the shooting system is composed of two parts, i.e. an image input part composed of an optical microscope, a CCD camera and a video capture card, and an image output part of a high-resolution display, and the computer in Fig. 1 ( 11) It can be used as image storage, processing and analysis equipment. Among them, the CCD camera needs to be driven by pulsed laser pulses to form video signals. The video capture card inputs the video signal collected by the camera into the computer. This card is equipped with an A/D converter and an image display circuit, which can quickly input dynamic images and real objects. The high-resolution display output device can quickly display the image of the entire process, and is connected to the input device.

Fig. 8 is a schematic diagram of a computer (11) installed with fatigue testing machine control software, fatigue crack growth analysis software and CCD image acquisition system software. The fatigue crack growth analysis software is based on the functional relationship between the potential and the fatigue crack growth parameters derived by Johnson, and the fatigue crack growth rate data can be obtained online, including numerical values and diagrams, and there are various national standard sample fatigue tests The data can be regarded as a reference and comparison object, making the invention purposeful and comparable.

The AC potential method sensor monitors the potential signal of fatigue crack growth in real time, and obtains the fatigue crack growth rate and other parameters through computer software processing. The CCD image acquisition system shoots dynamic images of fatigue crack growth online to fully understand the fatigue crack growth from multiple angles.

Claims (4)

1. the device of reckoning fatigue crack propagation rate of flat alloy by AC potentiometry; It is characterized in that, comprise fatigue tester (1) and specimen holder (2), ac potential method sensor (4), potential measurement probe (6), lead (7), signal amplifier (8), dual trace oscilloscope (9), A/D converter (10), ccd image acquisition system (12) and computing machine (11); The a pair of rectangle of said ac potential method sensor (4) induces coil (13) and two pairs of described potential measurement probes (6) to be installed in the surface of the flat alloy sample (3) that has precrack; Two tops that said two pairs of potential measurement probes (6) are positioned at the precrack of alloy sample (3) are contained in the centre position with this crackle; Induce coil (13) to lay respectively at two tops of the surperficial precrack of tested alloy sample (3) and two pairs of potential measurement probes (6) are comprised wherein for said two, alloy sample (3) places on the fatigue tester (1); The lead (7) of one of them probe of every pair of potential measurement probe (6) links to each other with the input end of a signal amplifier (8), and the lead of another probe (7) then links to each other with the output terminal of dual trace oscilloscope (9); The output terminal of two said signal amplifiers (8) is connected with two input ends of dual trace oscilloscope (9) through lead (7); The output terminal of dual trace oscilloscope (9) links to each other with the input end of A/D converter (10) through lead (7), and the output terminal of A/D converter (10) links to each other with computing machine (11) through lead (7); Said ccd image acquisition system (12) links to each other with this computing machine (11) through lead (7) with fatigue tester (1); The crack Propagation analysis software that said computing machine (11) is installed is the basis with the potential change of Johnson derivation and the functional relation between the crack Propagation parameter.

2. the device of reckoning fatigue crack propagation rate of flat alloy by AC potentiometry according to claim 1; It is characterized in that; Said potential measurement probe (6) is made up of cylinder blanket (18) and flat deck roof (17); Said flat-top lid (17) is the flat-top shape, is embedded with lead, and the tinsel (19) in the said lead is applied in the cylinder blanket (18); Said cylinder blanket (18) can freely be opened, through snap lock (20) connection of centre; Said cylinder blanket (18) and flat deck roof (17) are to be composited by two kinds of materials, and skin all adopts insulating material, and internal layer all adopts conductive material to process.

3. the device of reckoning fatigue crack propagation rate of flat alloy by AC potentiometry according to claim 1 and 2; It is characterized in that; Two of said ac potential method sensor (4) induce coil (13) to press rectangle around to the 22mm-25mm height; The long 55mm-59mm of said rectangle, wide 25mm-29mm, the centreline spacing Δ=35-39mm of two said rectangles; To said coil (13) the extrinsic motivated electric current (14) of inducing, the electric field of variation produces induced magnetic field (16), between two pairs of potential measurement probes (6), induces to produce induced current (15), impressed current is provided for this sensor.

4. implement the method for the device of reckoning fatigue crack propagation rate of flat alloy by AC potentiometry according to claim 2, it is characterized in that, concrete steps are following:

(1) precrack two head region on flat alloy sample (3) are installed two pairs of potential measurement probes (6), and precrack is contained in the centre position, again crackle two around on induce coil (13) to form ac potential method sensor (4); The conducting resinl of two pairs of cylindrical shapes in last precrack (5) two head region of flat alloy sample (3), moulding; Entangle with the conducting resinl of cylinder blanket (18) two pairs of cylindrical shapes; Continue in these two pairs of cylinder blankets (18), to inject conducting resinl again; Let the conducting resinl and the shell (18) of cylindrical shape combine closely, make potential measurement probe (6) can be fixed in the measurement zone, cover the flat-top lid (17) that is embedded with lead at last; Integral body places on the fatigue tester (1); Extrinsic motivated electric current (14) flows in inducing coil (13); Lead on one of them flat-top lid (17) of every pair of potential measurement probe (6) is linked to each other with a signal amplifier (8); Lead on another flat-top lid (17) then is connected with the output terminal of dual trace oscilloscope (9), opens the device of described reckoning fatigue crack propagation rate of flat alloy by AC potentiometry;

(2) signal of crackle two potential change of causing of two pairs of potential measurement probes (6) the on-line real time monitoring crack Propagation through said ac potential method sensor (4);

(3) said two signal amplifiers (8) amplify crackle two potential change signal that two pairs of potential measurement probes (6) monitor; Be sent in the dual trace oscilloscope (9), the potential data that shows crackle two when expansion through dual trace oscilloscope (9) simultaneously with can survey oscillogram;

(4) in electric signal two A/D converters of warp (10) input computing machines (11) that said dual trace oscilloscope (9) is collected, potential data is handled through computing machine (11) and is drawn fatigue crack growth rate;

(5) said ccd image acquisition system (12) is used for taking the image of whole Fatigue Cracks Propagation; Recorded information also is stored in the computing machine (11) that contains software kit; Avoid the careless omission of crack Propagation research details, carry out subsequent use the subsequent treatment of crack Propagation.

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