CN109884126B

CN109884126B - Crack propagation measurement system and method and inspection method and device thereof

Info

Publication number: CN109884126B
Application number: CN201910134596.7A
Authority: CN
Inventors: 薛河; 魏其深; 倪陈强; 张亮; 徐鹏超
Original assignee: Xian University of Science and Technology
Current assignee: Xian University of Science and Technology
Priority date: 2019-02-23
Filing date: 2019-02-23
Publication date: 2021-08-17
Anticipated expiration: 2039-02-23
Also published as: CN109884126A

Abstract

The invention discloses a crack propagation measuring system and a method and a checking method and a device thereof, wherein the crack propagation measuring system comprises a constant current source, a direct current turnover circuit, an operational amplifier module, a single chip microcomputer controller, an upper computer, an isolation circuit, a current connecting line and a voltage connecting line; the inspection device comprises a stator crack length change system, a single chip microcomputer and a relay set control module; the measuring method is a direct current potential drop method, the potential field of the sample changes when the crack expands, the voltage drop at two ends of the crack of the sample gradually increases along with the increase of the length of the crack, and the crack expansion value of the sample can be obtained by measuring the potential difference at two ends of the crack on the sample; the test method verifies the accuracy of the measurement system by comparing the relationship between the measured values and the known values of the test sample. The measuring system has the advantages of simple structure, integrated device, high measuring precision, convenient carrying and moderate price, and the checking device has the advantages of low cost and repeated use.

Description

Crack propagation measurement system and method and inspection method and device thereof

Technical Field

The invention belongs to the technical field of safety analysis of engineering parts, and particularly relates to a crack propagation measuring system and method and a crack propagation measuring inspection method and device.

Background

Many engineering parts in the aviation, nuclear power, power and metallurgy industries, such as shafts, crankshafts, connecting rods, gears, pressure vessels, turbine blades and the like, are subjected to mechanical stress generated by cyclic load and cyclic stress caused by periodic changes of temperature, pressure and the like due to continuous changes of severe environments such as environmental temperature, pressure and the like during service. In particular, microcracks are generated in stress concentration parts of parts in the long-term service process, and the generation of the microcracks can cause a series of changes of material properties of the parts, such as reduction of strength and rigidity. The microcracks gradually accumulate to form macrocracks and expand to finally cause material failure and damage, and the metal parts not only completely lose service capacity after being broken, but also possibly cause great economic loss and catastrophic accidents. The 20 th century and 70 th sweden investigated the damage of 85 large-sized ships at that time, and the result showed that the damage rate due to fatigue cracks reached 70.45%; research and study are carried out on sea damage accidents of 186 bulk carriers in 1980 and 1996, and the results show that an important reason for the sea damage accidents is that the fatigue strength of the ships is insufficient, so that the ships are damaged and sink into the sea; further studies have shown that significant accidents of airplane crashes due to fatigue fractures have occurred in the 80 s, on average 100 times per year. In order to ensure that the cracks existing or expanding in the equipment and parts are not irremediably catastrophic when the equipment and the parts are used, the subcritical crack expansion condition of the parts under the fatigue condition must be reliably determined, and the subcritical crack expansion condition is one of the characteristic indexes for determining the fatigue life of the parts. The DCPD method is a direct current potential drop measurement method, and is used for measuring the crack length based on the conductivity of a sample, the potential field of the sample changes when the crack grows, the voltage drop at two ends of the crack of the sample gradually increases along with the growth of the crack length, and the crack growth numerical value of the measured sample can be obtained by measuring the potential difference at two ends of the crack of the sample. At present, the domestic crack growth measurement system based on the DCPD method is built by several instruments, and there are not highly integrated device and influence factor more, lead to measurement accuracy relatively poor, and the volume is great, carry inconvenient, also builds temporarily to the verifying attachment of the crack growth measurement system's based on the DCPD method degree of accuracy moreover, and there is not one set of complete and verifying attachment that can used repeatedly.

Disclosure of Invention

The invention aims to overcome the defects in the prior art and provide a crack propagation measuring system which has the advantages of simple structure, integrated device, high measuring precision, portability and moderate price.

In order to achieve the purpose, the invention adopts the technical scheme that: a crack propagation measurement system, characterized by: the device comprises a constant current source for outputting constant direct current, a direct current turnover circuit for turning over the direction of the constant direct current output by the constant current source, an operational amplifier module for amplifying a received voltage signal, a single-chip microcomputer controller for converting a received voltage analog signal into a digital signal and analyzing and calculating the digital signal, an upper computer for displaying a measured value, an isolating circuit for isolating the electrical connection between the constant current source and the single-chip microcomputer controller, a current connecting wire for connecting and outputting the constant direct current and a voltage connecting wire for connecting and inputting a voltage signal to be measured, wherein the constant current source is connected with an external 24V battery, the current signal end of the constant current source is connected with the input end of the direct current turnover circuit, the output end of the direct current turnover circuit is connected with the current connecting wire and transmits the constant direct current signal to a measurement sample connected with the current connecting wire, the voltage connecting line is connected with the input end of the operational amplifier module, the voltage connecting line is connected with a measurement sample to transmit a voltage signal to the operational amplifier module, the output end of the operational amplifier module is connected with the input end of the single chip microcomputer controller and transmits the acquired voltage signal to the single chip microcomputer controller after amplification, the operational amplifier module is connected with an external 12V battery, the output end of the single chip microcomputer controller is connected with the input end of an upper computer and displays a measurement value after analysis and calculation on the upper computer, a data transmitting end of the constant current source is connected with a data receiving end of the single chip microcomputer controller and transmits a constant current source data signal to the single chip microcomputer controller, the data receiving end of the constant current source is connected with the data transmitting end of the single chip microcomputer controller to receive a command of the single chip microcomputer controller, the power end of the constant current source is connected with an isolation circuit, and the isolation circuit is connected with the power end of the The single chip microcomputer controller is connected with the direct current flip circuit and transmits a flip command to the direct current flip circuit to control the flip of the current direction.

The crack propagation measurement system is characterized in that: the isolating circuit includes that two models are opto-coupler 1 and opto-coupler 2 of PC817, No. 1 pin of opto-coupler 1 is connected with VCC end of access circuit, No. 2 pin is connected with single chip microcomputer controller's IO mouth, No. 3 pin is connected with single chip microcomputer controller's VCC end, No. 4 pin is connected with the VCC end of constant current source, No. 1 pin and VCC end of opto-coupler 2 are connected, No. 2 pin is connected with single chip microcomputer controller's IO mouth, No. 3 pin is connected with single chip microcomputer controller's GND end, No. 4 pin is connected with the GND end of constant current source.

The crack propagation measurement system is characterized in that: the current connecting wire consists of a current output wire and a current input wire, the voltage connecting wire consists of two wires, the direct current turnover circuit comprises a solid state relay SSR1, a solid state relay SSR2, a solid state relay SSR3, a solid state relay SSR4 and a transistor array with the model number of ULN2003A, a No. 9 pin of the transistor array is connected with an external 5V battery, a No. 1 pin and a No. 2 pin are connected with an instruction output end of the single chip microcomputer controller, a No. 15 pin of the transistor array is connected with a No. 4 pin of the solid state relay SSR2 and a No. 4 pin of the solid state relay SSR4, a No. 16 pin is connected with a No. 4 pin of the solid state relay SSR1 and a No. 4 pin of the solid state relay SSR3, a No. 3 pin of the solid state relay SSR1, a No. 3 pin of the solid state relay SSR2, a No. 3 pin of the solid state relay SSR3 and a No. 3 pin of the solid state relay SSR4 are connected with an external 5V battery, the pin No. 2 of the solid-state relay SSR1 and the pin No. 2 of the solid-state relay SSR2 are both connected with the current positive output end of the constant current source, the pin No. 1 of the solid-state relay SSR3 and the pin No. 1 of the solid-state relay SSR4 are both connected with the current negative input end of the constant current source, the pin No. 1 of the solid-state relay SSR1 and the pin No. 2 of the solid-state relay SSR4 are both connected with current output leads, and the pin No. 1 of the solid-state relay 2 and the pin No. 2 of the solid-state relay SSR3 are both connected with current input leads.

The crack propagation measurement system is characterized in that: the distance from the welding point of the current output lead and the measurement sample to the crack of the measurement sample and the distance from the welding point of the current input lead and the measurement sample to the crack of the measurement sample are both larger than the distance from the lead of the voltage connecting wire and the welding point of the measurement sample to the crack of the measurement sample.

The crack propagation measurement system is characterized in that: the constant current source is a program-controlled power supply with the model number ZXY-6005S.

The invention also provides a method for measuring crack propagation by using the system, which is characterized by comprising the following steps:

step one, starting a power switch of a crack propagation measurement system, respectively spot-welding a current output lead and a current input lead to two sides of a crack surface of a measurement sample, and respectively spot-welding a voltage connecting wire to two sides of a crack of the measurement sample;

setting an output constant direct current value and an output voltage value of a constant current source in an upper computer, transmitting a set constant direct current value command to a data receiving end of the constant current source through a data transmitting end of a single chip microcomputer controller by the upper computer, outputting constant direct current set by the upper computer by the constant current source, transmitting the constant direct current to a direct current overturning circuit, overturning the direction of the current continuously by the direct current overturning circuit under the control of the single chip microcomputer controller, enabling the constantly overturned constant direct current to flow through a current output wire into a measurement sample, and flowing to the direct current overturning circuit through a current input wire after the measurement sample is output;

thirdly, the operational amplifier module receives the measurement voltage signal transmitted by the voltage connecting line and amplifies the collected voltage signal, the operational amplifier module transmits the amplified voltage signal to the single chip microcomputer controller, the single chip microcomputer controller converts the received voltage analog signal into a digital signal and carries out analysis and calculation, the single chip microcomputer controller uploads the data after the analysis and calculation to an upper computer, an operator can check the crack propagation length data of the measurement sample in the upper computer,

the analysis calculation formula of the singlechip controller is as follows:

a＝15.153*u²+83.408u+3.2361

wherein a is the crack propagation length of the measurement sample and has a unit of mm, and u is the voltage signal data of the measurement sample and has a unit of muV;

and finishing the measurement of the crack propagation data of the measured sample.

The invention also provides a low-cost and reusable inspection device for inspecting the crack propagation measurement accuracy of the measurement system, which is characterized in that: including stationary blade crackle length change system that is fixed with a plurality of inspection samples and the singlechip and the relay group control module that are used for controlling inspection sample measurement order, singlechip and relay group control module and stationary blade crackle length change headtotail and be used for selecting the inspection sample that needs output voltage signal, current output wire and current input wire all are connected with the inspection sample in the stationary blade crackle length change system and transmit the current signal after the upset of direct current flip circuit to the inspection sample in the stationary blade crackle length change system respectively, singlechip and relay group control module's output and voltage connecting wire are connected and will inspect sample voltage signal transmission to the operational module.

The above-mentioned inspection device, its characterized in that: the fixing piece crack length change system comprises ten inspection samples and five wiring terminals, wherein the five wiring terminals are four-position wiring terminals, the five wiring terminals are wiring terminals 1, wiring terminals 2, wiring terminals 3, wiring terminals 4 and wiring terminals 5 respectively, the ten inspection samples are 304 steel inspection samples, the crack propagation lengths of the ten inspection samples are known and are sequentially arranged from short to long according to the crack lengths, the crack length of the inspection sample 1 is shortest, the crack length of the inspection sample 10 is longest, the other end of a current output lead is in spot welding connection with one side of a crack surface of the inspection sample 1, the other side of the crack surface of the inspection sample 1 is in spot welding connection with one side of the crack surface of the inspection sample 2 through a lead, the other side of the crack surface of the inspection sample 2 is in spot welding connection with one side of the crack surface of the inspection sample 3 through a lead, the other side of the crack surface of the test sample 3 is connected with one side of the crack surface of the test sample 4 by wire spot welding, the other side of the crack surface of the test sample 4 is connected with one side of the crack surface of the test sample 5 by a lead spot welding, the other side of the crack surface of the test sample 5 is connected with one side of the crack surface of the test sample 6 by a lead spot welding, the other side of the crack surface of the test sample 6 is connected with one side of the crack surface of the test sample 7 by a lead spot welding, the other side of the crack surface of the test sample 7 is connected with one side of the crack surface of the test sample 8 by wire spot welding, the other side of the crack surface of the test sample 8 is connected with one side of the crack surface of the test sample 9 by wire spot welding, the other side of the crack surface of the test sample 9 is connected with one side of the crack surface of the test sample 10 in a spot welding mode through a lead, and the other side of the crack surface of the test sample 10 is connected with a current input lead;

the crack side of the inspection sample 1 is connected with the front end No. 1 interface of the wiring terminal 1, the crack other side of the inspection sample 1 is connected with the front end No. 2 interface of the wiring terminal 1, the crack side of the inspection sample 2 is connected with the front end No. 1 interface of the wiring terminal 2, the crack other side of the inspection sample 2 is connected with the front end No. 2 interface of the wiring terminal 2, the crack side of the inspection sample 3 is connected with the front end No. 1 interface of the wiring terminal 3, the crack other side of the inspection sample 3 is connected with the front end No. 2 interface of the wiring terminal 3, the crack side of the inspection sample 4 is connected with the front end No. 1 interface of the wiring terminal 4, the crack side of the inspection sample 5 is connected with the front end No. 1 interface of the wiring terminal 5, and the crack other side of the inspection sample 5 is connected with the front end No. 2 interface of the wiring terminal 5, one side of the crack of the inspection sample 6 is connected with a No. 4 interface at the rear end of the wiring terminal 5, the other side of the crack of the inspection sample 6 is connected with a No. 3 interface at the rear end of the wiring terminal 5, one side of the crack of the inspection sample 7 is connected with a No. 4 interface at the rear end of the wiring terminal 4, the other side of the crack of the inspection sample 7 is connected with a No. 3 interface at the rear end of the wiring terminal 4, one side of the crack of the inspection sample 8 is connected with a No. 4 interface at the rear end of the wiring terminal 3, the other side of the crack of the inspection sample 8 is connected with a No. 3 interface at the rear end of the wiring terminal 3, one side of the crack of the test sample 9 is connected with a No. 4 interface at the rear end of the wiring terminal 2, the other side of the crack of the test sample 9 is connected with a No. 3 interface at the rear end of the wiring terminal 2, the crack side of the inspection sample 10 is connected with the interface No. 4 at the rear end of the wiring terminal 1, and the other crack side of the inspection sample 10 is connected with the interface No. 3 at the rear end of the wiring terminal 1.

The above-mentioned inspection device, its characterized in that: the single motor and relay group control module consists of 8 relay groups A, 8 relay groups B, 8 relay groups C and a single chip microcomputer chip with the model number of STM32F103C8T6, wherein an IN1 pin to an IN8 pin of the 8 relay groups A are sequentially connected with an A6 pin, an A12 pin, an A11 pin, an A8 pin, a B15 pin, a B14 pin, a B13 pin and a B9 pin of the single chip microcomputer chip respectively, an IN1 pin to an IN8 pin of the 8 relay groups B are sequentially connected with an A5 pin, an A4 pin, a B5 pin, a B6 pin, a B7 pin, a B8 pin and a B8 pin of the single chip microcomputer chip respectively, and A8 pin to an IN8 pin of the 8 relay groups C are sequentially connected with a VCC 72 pin, A8 pin and A8 pin of the single chip respectively, A8 pin and A8 end of the single chip microcomputer chip respectively, The VCC end of the 8-path relay group B and the VCC end of the 8-path relay group C are connected with a 5v pin of the single chip microcomputer chip, the GND end of the 8-path relay group A, the GND end of the 8-path relay group B and the GND end of the 8-path relay group C are connected with the GND end of the single chip microcomputer chip, and the single chip microcomputer chip is connected with the input end of the operational amplifier module;

the front end No. 3 interface of the wiring terminal 1 is connected with the No. 1 pin of the 10B of the 8-way relay group C, the front end No. 4 interface is connected with the No. 1 pin of the 10A of the 8-way relay group C, the rear end No. 1 interface is connected with the No. 1 pin of the 1A of the 8-way relay group A, and the rear end No. 2 interface is connected with the No. 1 pin of the 1B of the 8-way relay group A; the front end No. 3 interface of the wiring terminal 2 is connected with the No. 1 pin of the 9B of the 8-way relay group C, the front end No. 4 interface is connected with the No. 1 pin of the 9A of the 8-way relay group C, the rear end No. 1 interface is connected with the No. 1 pin of the 2A of the 8-way relay group A, and the rear end No. 2 interface is connected with the No. 1 pin of the 2B of the 8-way relay group A; the front end No. 3 interface of the wiring terminal 3 is connected with the No. 1 pin of the 8B relay of the 8-way relay group B, the front end No. 4 interface is connected with the No. 1 pin of the 8A of the 8-way relay group B, the rear end No. 1 interface is connected with the No. 1 pin of the 3A of the 8-way relay group A, and the rear end No. 2 interface is connected with the No. 1 pin of the 3B of the 8-way relay group A; the front end No. 3 interface of the wiring terminal 4 is connected with the No. 1 pin of the 7B of the 8-path relay group B, the front end No. 4 interface is connected with the No. 1 pin of the 7A of the 8-path relay group B, the rear end No. 1 interface is connected with the No. 1 pin of the 4A of the 8-path relay group A, and the rear end No. 2 interface is connected with the No. 1 pin of the 4B of the 8-path relay group A; the front end No. 3 interface of the wiring terminal 5 is connected with the No. 1 pin of the 6B of the 8-path relay group B, the front end No. 4 interface is connected with the No. 1 pin of the 6A of the 8-path relay group B, the rear end No. 1 interface is connected with the No. 1 pin of the 5A of the 8-path relay group B, and the rear end No. 2 interface is connected with the No. 1 pin of the 5B of the 8-path relay group B; no. 2 pin of 1A of 8 way relay set A, No. 2 pin of 2A of 8 way relay set A, No. 2 pin of 3A of 8 way relay set A, No. 2 pin of 4A of 8 way relay set A, No. 2 pin of 5A of 8 way relay set B, No. 2 pin of 6A of 8 way relay set B, No. 2 pin of 7A of 8 way relay set B, No. 2 pin of 8A of 8 way relay set B, No. 2 pin of 9A of 8 way relay set C and No. 2 pin of 10A of 8 way relay set C are connected together, No. 2 pin of 1B of 8 way relay set A, No. 2 pin of 2B of 8 way relay set A, No. 2 pin of 3B of 8 way relay set A, No. 2 pin of 4B of 8 relay set A, No. 2 pin of 5B of 8 relay set B, No. 2 pin of 6B of 8 relay set B, Pin No. 2 of 7B of the 8-way relay group B, pin No. 2 of 8B of the 8-way relay group B, pin No. 2 of 9B of the 8-way relay group C, and pin No. 2 of 10B of the 8-way relay group C are connected together.

In addition, the invention also provides a method for testing the crack propagation measurement accuracy of the measurement system by using the testing device, which is characterized by comprising the following steps:

step one, turning on power switches of a crack propagation measurement system and a detection device of the crack propagation measurement system;

step two, setting an output constant direct current value and an output voltage value of a constant current source in an upper computer, transmitting a set constant direct current value command to a data receiving end of the constant current source through a data transmitting end of a single-chip microcomputer controller by the upper computer, outputting constant direct current set by the upper computer by the constant current source, transmitting the constant direct current to a direct current overturning circuit, continuously overturning the current direction of the direct current overturning circuit under the control of the single-chip microcomputer controller, transmitting the continuously overturned constant direct current to ten test samples of a stator crack length change system through an over-current output wire, and flowing back to the direct current overturning circuit through a current input wire, wherein the ten test samples are test samples with known crack lengths, and the crack lengths of the ten test samples are different;

step three, the singlechip and the singlechip chip of the relay group control module control the corresponding 8 relay groups according to the instruction of connecting the test sample 1 loop to connect the voltage signal loop of the test sample 1 and transmit the voltage signal to the operational amplifier module, the singlechip chip transmits the voltage signal of the collected test sample 1 to the operational amplifier module, the operational amplifier module amplifies the received voltage signal and transmits the voltage signal into the singlechip controller, the singlechip controller converts the received analog voltage signal into a digital signal and carries out analysis and calculation, the singlechip controller uploads the data after the analysis and calculation to an upper computer, an operator can check the crack extension length data of the test sample 1 in the upper computer,

the analysis calculation formula of the singlechip controller is as follows:

a＝15.153*u²+83.408u+3.2361

wherein a is the crack propagation length of the test specimen and is in mm, and u is the measured voltage signal data of the test specimen and is in μ V;

step four, repeating the step three to respectively finish the data acquisition from the test sample 2 to the test sample 10;

and step five, comparing the collected data of the test samples 1 to 10 with the known crack data of the corresponding test samples respectively, and testing the measurement accuracy of the crack propagation measurement system by comparing the relation between the test data of the ten test samples and the known crack data.

Compared with the prior art, the invention has the following advantages:

1. the crack propagation measuring system adopts the constant direct current as the input current of the measuring sample, avoids the influence of residual alternating voltage and current skin effect after alternating current is rectified and filtered on a real signal, and improves the measuring precision of the measuring system.

2. The crack propagation measurement system adopts the direct current turnover circuit consisting of the transistor array and the four solid-state relays to continuously turn over the direction of the input current, eliminates the interference of thermoelectric force generated by contact resistance between a current input lead and a measurement sample on an output voltage signal, eliminates the influence of amplified bias voltage of the output voltage signal on real data, and improves the measurement precision of the measurement system.

3. The crack propagation measurement system adopts a design method of internal modularization and system integral integration, has the advantages of high measurement precision, simple operation, convenient carrying and automatic control, is suitable for high-temperature and high-pressure measurement environments, such as nuclear power loop pipelines, nuclear power reactor high-pressure kettles, chemical reaction kettles and the like, which need to be monitored but are difficult to monitor, and solves the problem that metal pipeline cracks in the high-temperature and high-pressure environment are difficult to measure.

4. The crack propagation measurement system is additionally provided with the isolation circuit, so that the electrical connection between the constant current source and the single chip microcomputer controller is successfully isolated, and the interference of the constant current source on the acquisition signal of the single chip microcomputer controller is effectively avoided.

5. The fixed plate crack length change system in the inspection device of the crack propagation measurement system is provided with ten inspection samples with different crack lengths, and the ten inspection samples are placed in the order of the crack lengths from small to large, so that the ten inspection samples can simulate the crack propagation process of the measurement samples, the fatigue stretcher can be used for replacing the stretching process to measure the crack propagation condition, the cost for purchasing the fatigue stretcher is reduced, the danger possibly generated in the operation and running of the fatigue stretcher is eliminated, and the possibility of experiments is provided for researchers who are temporarily weak to purchase the fatigue stretcher.

6. The numerical range of the crack lengths of the ten inspection samples in the crack length change system of the fixing piece in the inspection device of the crack propagation measurement system covers the whole range of the crack propagation of the measurement sample, so that the accuracy of the crack measurement system can be completely and comprehensively inspected, the crack length change system of the fixing piece does not need to be supplied with power from the outside, only a power line needs to be led out from the crack monitoring system, and the crack propagation measurement system has the advantages of simple structure and low cost and can be repeatedly used.

7. The invention breaks through the current situation that no integrated crack propagation measurement system based on a DCPD method and no reusable crack propagation measurement system inspection device exist in China, and the crack propagation measurement system provided by the invention has a power supply inside and has the advantages of low voltage, low power consumption, low noise and low power consumption.

The invention is described in further detail below with reference to the figures and examples.

Drawings

FIG. 1 is a schematic diagram of the energization of a 304 steel coupon in accordance with the present invention.

FIG. 2 is a schematic block diagram of the electrical circuit of the crack propagation measurement system of the present invention.

FIG. 3 is a circuit diagram of a crack propagation measurement system of the present invention.

Fig. 4 is a diagram showing the connection between the crack propagation measuring system and the measurement specimen according to the present invention.

FIG. 5 is a graph of experimental data for crack propagation length measurements for test specimens of the stator crack length variation system of the present invention.

Fig. 6 is a schematic block circuit diagram of an inspection apparatus of the crack propagation measurement system of the present invention.

FIG. 7 is a block diagram of the connection of the crack propagation measurement system and the inspection device of the measurement system of the present invention.

FIG. 8 is a circuit diagram of a stator crack length variation system of the present invention.

Fig. 9 is a circuit diagram of the single chip microcomputer and the relay set control module of the invention.

FIG. 10 is a circuit diagram of a relay set connected to a stator crack change system.

FIG. 11 is a schematic diagram of the connection circuit of the crack propagation measurement system and the inspection device of the measurement system of the present invention.

Description of reference numerals:

1-constant current source; 2-a direct current flip circuit;

3, a stator crack length change system; 4, a singlechip and relay group control module;

5, an operational amplifier module; 6, a singlechip controller; 7, an upper computer;

8-an isolation circuit; 9-measuring the sample; 10-current connection line;

10-1-current output lead; 10-2-current input leads; 11-voltage connection line;

12-24V batteries; 13-12V batteries; 14-5V batteries;

15—VCC。

Detailed Description

As shown in fig. 1, the crack measuring system of the present invention is based on the DCPD (direct current potential drop) method, which measures the crack length based on the electrical conductivity of a metal member, and on a crack-containing specimen, the potential field is a function of the specimen geometry and the crack length, and the specimen potential field changes during crack propagation, and by measuring this change, the crack propagation can be obtained, and when a constant current (I) is passed through the specimen 304, the cross section through which the current passes is reduced due to the presence of the crack, resulting in an increase in the electrical resistance of the material itself, i.e., the measurement potential (V) increases with the specimen crack length.

As shown in fig. 2 and fig. 3, a crack propagation measuring system includes a constant current source 1 for outputting a constant direct current, a direct current flipping circuit 2 for flipping the direction of the constant direct current output by the constant current source 1, an operational amplifier module 5 for amplifying a received voltage signal, a single chip microcomputer controller 6 for converting a received voltage analog signal into a digital signal and analyzing and calculating the digital signal, an upper computer 7 for displaying a measured value, an isolation circuit 8 for isolating the electrical connection between the constant current source 1 and the single chip microcomputer controller 6, a current connection line 10 for connecting and outputting the constant direct current, and a voltage connection line 11 for connecting and inputting a voltage signal to be measured, wherein the constant current source 1 is connected to an external 24V battery 12, a current signal end of the constant current source 1 is connected to an input end of the direct current flipping circuit 2, an output end of the direct current flipping circuit 2 is connected to the current connection line 10, and the constant direct current signal is transmitted to and current is transmitted to a current source 1 The measuring device comprises a measuring sample 9 connected with a connecting wire 10, a voltage connecting wire 11 is connected with the input end of an operational amplifier module 5, the voltage connecting wire 11 is connected with the measuring sample 9 to transmit a voltage signal to the operational amplifier module 5, the output end of the operational amplifier module 5 is connected with the input end of a single chip microcomputer controller 6 and transmits an acquired voltage signal to the single chip microcomputer controller 6 after amplifying the voltage signal, the operational amplifier module 5 is connected with an external 12V battery 13, the output end of the single chip microcomputer controller 6 is connected with the input end of an upper computer 7 and displays a measured value after analysis and calculation on the upper computer 7, a data transmitting end of a constant current source 1 is connected with a data receiving end of the single chip microcomputer controller 6 and transmits a data signal of the constant current source 1 to the single chip microcomputer controller 6, and the data receiving end of the constant current source 1 is connected with the data transmitting end of the single chip microcomputer controller 6 to receive a command of the single chip microcomputer controller 6, the power end of the constant current source 1 is connected with the isolation circuit 8, the isolation circuit 8 is connected with the power end of the single chip microcomputer controller 6 and is used for preventing the signals of the constant current source 1 from interfering with the signals received by the single chip microcomputer controller 6, and the single chip microcomputer controller 6 is connected with the direct current turnover circuit 2 and transmits turnover instructions to the direct current turnover circuit 2 to control the turnover of the current direction.

As shown in fig. 3, isolating circuit 8 includes that two models are opto-coupler 1 and opto-coupler 2 of PC817, No. 1 pin of opto-coupler 1 is connected with VCC (voltage of access circuit) 15 end connection, No. 2 pin and single chip microcomputer controller 6's I/O mouth, No. 3 pin and single chip microcomputer controller 6's VCC end connection, No. 4 pin and constant current source 1's VCC end connection, No. 1 pin and VCC (voltage of access circuit) 15 end connection, No. 2 pin and single chip microcomputer controller 6's I/O mouth connection, No. 3 pin and single chip microcomputer controller 6's GND (ground wire) end connection, No. 4 pin and constant current source 1's GND (ground wire) end connection of 1 of opto-coupler.

As shown in fig. 3, the current connection line 10 is composed of a current output wire 10-1 and a current input wire 10-2, the voltage connection line 11 is composed of two wires, the dc flip circuit 2 includes a solid-state relay SSR1, a solid-state relay SSR2, a solid-state relay SSR3, a solid-state relay SSR4 and a transistor array with a model number ULN2003A, a pin 9 of the transistor array is connected to an external 5V battery 14, a pin 1 and a pin 2 are connected to an instruction output end of the mcu 6, a pin 15 of the transistor array is connected to a pin 4 of the solid-state relay SSR2 and a pin 4 of the solid-state relay 4, a pin 16 is connected to a pin 4 of the solid-state relay SSR1 and a pin 4 of the solid-state relay SSR3, a pin 3 of the solid-state relay SSR1, a pin 3 of the solid-state relay SSR2, a pin 3 of the solid-state relay SSR3 and a pin 3 of the solid-state relay 4 are connected to an external 5V battery 14 The pin 2 of the solid-state relay SSR1 and the pin 2 of the solid-state relay SSR2 are both connected with the current anode output end of the constant current source 1, the pin 1 of the solid-state relay SSR3 and the pin 1 of the solid-state relay SSR4 are both connected with the current cathode input end of the constant current source 1, the pin 1 of the solid-state relay SSR1 and the pin 2 of the solid-state relay SSR4 are both connected with the current output lead 10-1, and the pin 1 of the solid-state relay SSR2 and the pin 2 of the solid-state relay SSR3 are both connected with the current input lead 10-2.

As shown in FIG. 4, the distances from the welding point of the current output lead 10-1 and the measurement sample 9 to the crack of the measurement sample 9 and the distances from the welding point of the current input lead 10-2 and the measurement sample 9 to the crack of the measurement sample 9 are larger than the distances from the welding point of the voltage connecting wire 11 and the measurement sample 9 to the crack of the measurement sample 9.

In this embodiment, the constant current source 1 is a program-controlled power supply with a model number ZXY-6005S.

Referring to fig. 4, the method for measuring crack propagation includes the steps of:

step one, starting a power switch of a crack propagation measurement system, respectively spot-welding a current output lead 10-1 and a current input lead 10-2 to two sides of a crack surface of a measurement sample 9, and respectively spot-welding a voltage connecting wire 11 to two sides of the crack of the measurement sample 9;

step two, setting an output constant direct current value and an output voltage value of the constant current source 1 in the upper computer 7, transmitting a set constant direct current value command to a data receiving end of the constant current source 1 through a data transmitting end of the single chip microcomputer controller 6 by the upper computer 7, outputting a constant direct current set by the upper computer 7 by the constant current source 1, transmitting the constant direct current to the direct current overturning circuit 2, overturning the direction of the current ceaselessly by the direct current overturning circuit 2 under the control of the single chip microcomputer controller 6, transmitting the ceaselessly overturned constant direct current to a measurement sample 9 through a current output lead 10-1, and outputting the constant direct current from the measurement sample and then flowing to the direct current overturning circuit 2 through a current input lead 10-2;

thirdly, the operational amplifier module 5 receives the measurement voltage signal transmitted by the voltage connecting line 11 and amplifies the collected voltage signal, the operational amplifier module 5 transmits the amplified voltage signal to the single chip microcomputer controller 6, the single chip microcomputer controller 6 converts the received voltage analog signal into a digital signal and carries out analysis and calculation, the single chip microcomputer controller 6 uploads the data after the analysis and calculation to the upper computer 7, an operator can check the crack propagation length data of the measurement sample 9 in the upper computer 7,

the analysis and calculation formula of the singlechip controller 6 is as follows:

a＝15.153*u²+83.408u+3.2361

wherein a is the crack propagation length of the measurement specimen 9 and is in mm, and u is the voltage signal data of the measurement specimen 9 and is in μ V;

the crack propagation data of the test specimen 9 was measured.

The crack propagation measurement system breaks through the current situation that no integrated crack propagation measurement system exists in China at present, and therefore the crack propagation measurement system is also very important for testing the accuracy and the measurement repeatability of the crack propagation measurement system. The inspection device of the crack propagation measurement system is more domestic initiative, the inspection device greatly improves the measurement precision of the crack propagation measurement system, and in the early development work of the inspection device, the measurement data of the inspection device of the crack propagation measurement system is analyzed, so that the feasibility of the inspection device is verified. The experimental data of the crack propagation length measurement of the inspection sample of the stator crack length variation system is shown in fig. 5, and it can be seen from fig. 5 that the error value between the actual data and the known data of the corresponding inspection sample is within the measurement precision range of the measurement system, so that the device is feasible for inspecting the accuracy and measurement repeatability of the crack propagation system.

As shown in FIGS. 6 and 7, the testing device for testing the accuracy of the crack propagation measuring system comprises a fixed plate crack length changing system 3 fixed with a plurality of test samples and a singlechip and relay group control module 4 for controlling the measuring sequence of the test samples, the single chip microcomputer and relay group control module 4 is connected with the stator crack length change system 3 and is used for selecting a test sample needing to output a voltage signal, the current output lead 10-1 and the current input lead 10-2 are connected with the inspection sample in the stator crack length change system 3 and respectively transmit the current signals after the direct current turnover circuit 2 is turned over into the inspection sample in the stator crack length change system 3, the output end of the single chip microcomputer and relay group control module 4 is connected with the voltage connecting line 11 and transmits the voltage signal of the test sample to the operational amplifier module 5.

As shown in fig. 8, the fixed piece crack length change system 3 includes ten inspection samples and five connection terminals, the five connection terminals are four-bit connection terminals, the five connection terminals are respectively a connection terminal 1, a connection terminal 2, a connection terminal 3, a connection terminal 4 and a connection terminal 5, the ten inspection samples are 304 steel inspection samples, the crack propagation lengths of the ten inspection samples are known and are sequentially arranged from short to long according to the crack lengths, the crack length of the inspection sample 1 is the shortest and the crack length of the inspection sample 10 is the longest, the other end of the current output lead 10-1 is connected with one side of the crack surface of the inspection sample 1 by spot welding, the other side of the crack surface of the inspection sample 1 is connected with one side of the crack surface of the inspection sample 2 by spot welding, the other side of the crack surface of the inspection sample 2 is connected with one side of the crack surface of the inspection sample 3 by spot welding, the other side of the crack surface of the test sample 3 is connected with one side of the crack surface of the test sample 4 by wire spot welding, the other side of the crack surface of the test sample 4 is connected with one side of the crack surface of the test sample 5 by a lead spot welding, the other side of the crack surface of the test sample 5 is connected with one side of the crack surface of the test sample 6 by a lead spot welding, the other side of the crack surface of the test sample 6 is connected with one side of the crack surface of the test sample 7 by a lead spot welding, the other side of the crack surface of the test sample 7 is connected with one side of the crack surface of the test sample 8 by wire spot welding, the other side of the crack surface of the test sample 8 is connected with one side of the crack surface of the test sample 9 by wire spot welding, the other side of the crack surface of the test sample 9 is connected with one side of the crack surface of the test sample 10 by wire spot welding, the other side of the crack surface of the test sample 10 is connected with a current input lead 10-2;

As shown IN fig. 9, the single motor and relay group control module 4 is composed of 8 relay groups a, 8 relay groups B, 8 relay groups C and a single chip microcomputer chip with model number STM32F103C8T6, the pins IN1 to IN8 of the 8 relay groups a are sequentially and respectively connected with the pins a6, a12, a11, A8, B15, B14, B13 and B12 of the single chip microcomputer chip, the pins IN1 to IN8 of the 8 relay groups B are sequentially and respectively connected with the pins A5, A4, B5, B6, B7, B8 and B8 of the single chip microcomputer chip, the pins IN8 to IN 72 of the 8 relay groups C are sequentially and respectively connected with the pins VCC, B8, VCC, A8 and A8 of the single chip microcomputer chip, and the terminal of the relay groups A8 and VCC, The VCC end of the 8-path relay group B and the VCC end of the 8-path relay group C are connected with a 5v pin of the single chip microcomputer chip, the GND end of the 8-path relay group A, the GND end of the 8-path relay group B and the GND end of the 8-path relay group C are connected with the GND end of the single chip microcomputer chip, and the single chip microcomputer chip is connected with the input end of the operational amplifier module 5;

as shown in fig. 10, the front end No. 3 interface of the connection terminal 1 is connected to the pin No. 1 of the 10B of the 8-way relay group C, the front end No. 4 interface is connected to the pin No. 1 of the 10A of the 8-way relay group C, the rear end No. 1 interface is connected to the pin No. 1 of the 1A of the 8-way relay group a, and the rear end No. 2 interface is connected to the pin No. 1 of the 1B of the 8-way relay group a; the front end No. 3 interface of the wiring terminal 2 is connected with the No. 1 pin of the 9B of the 8-way relay group C, the front end No. 4 interface is connected with the No. 1 pin of the 9A of the 8-way relay group C, the rear end No. 1 interface is connected with the No. 1 pin of the 2A of the 8-way relay group A, and the rear end No. 2 interface is connected with the No. 1 pin of the 2B of the 8-way relay group A; the front end No. 3 interface of the wiring terminal 3 is connected with the No. 1 pin of the 8B relay of the 8-way relay group B, the front end No. 4 interface is connected with the No. 1 pin of the 8A of the 8-way relay group B, the rear end No. 1 interface is connected with the No. 1 pin of the 3A of the 8-way relay group A, and the rear end No. 2 interface is connected with the No. 1 pin of the 3B of the 8-way relay group A; the front end No. 3 interface of the wiring terminal 4 is connected with the No. 1 pin of the 7B of the 8-path relay group B, the front end No. 4 interface is connected with the No. 1 pin of the 7A of the 8-path relay group B, the rear end No. 1 interface is connected with the No. 1 pin of the 4A of the 8-path relay group A, and the rear end No. 2 interface is connected with the No. 1 pin of the 4B of the 8-path relay group A; the front end No. 3 interface of the wiring terminal 5 is connected with the No. 1 pin of the 6B of the 8-path relay group B, the front end No. 4 interface is connected with the No. 1 pin of the 6A of the 8-path relay group B, the rear end No. 1 interface is connected with the No. 1 pin of the 5A of the 8-path relay group B, and the rear end No. 2 interface is connected with the No. 1 pin of the 5B of the 8-path relay group B; no. 2 pin of 1A of 8 way relay set A, No. 2 pin of 2A of 8 way relay set A, No. 2 pin of 3A of 8 way relay set A, No. 2 pin of 4A of 8 way relay set A, No. 2 pin of 5A of 8 way relay set B, No. 2 pin of 6A of 8 way relay set B, No. 2 pin of 7A of 8 way relay set B, No. 2 pin of 8A of 8 way relay set B, No. 2 pin of 9A of 8 way relay set C and No. 2 pin of 10A of 8 way relay set C are connected together, No. 2 pin of 1B of 8 way relay set A, No. 2 pin of 2B of 8 way relay set A, No. 2 pin of 3B of 8 way relay set A, No. 2 pin of 4B of 8 relay set A, No. 2 pin of 5B of 8 relay set B, No. 2 pin of 6B of 8 relay set B, Pin No. 2 of 7B of the 8-way relay group B, pin No. 2 of 8B of the 8-way relay group B, pin No. 2 of 9B of the 8-way relay group C, and pin No. 2 of 10B of the 8-way relay group C are connected together.

With reference to fig. 7 and 11, the method for checking the crack propagation measurement accuracy by the measurement system comprises the following steps:

step two, setting an output constant direct current value and an output voltage value of a constant current source 1 in an upper computer 7, transmitting a set constant direct current value command to a data receiving end of the constant current source 1 through a data transmitting end of a single chip microcomputer controller 6 by the upper computer 7, outputting a constant direct current set by the upper computer 7 by the constant current source 1, transmitting the constant direct current to a direct current turnover circuit 2, continuously turning over the current direction by the direct current turnover circuit 2 under the control of the single chip microcomputer controller 6, transmitting the continuously turned over constant direct current to ten test samples of a stator crack length change system 3 through a current output lead, and returning the constant direct current to the direct current turnover circuit 2 through a current input lead 10-2, wherein the ten test samples are test samples with known crack lengths, and the crack lengths of the ten test samples are all unequal;

step three, the singlechip and the singlechip chip of the relay group control module 4 control the corresponding 8-path relay group according to the instruction of switching on the loop of the test sample 1 to switch on the voltage signal loop of the test sample 1 and transmit the voltage signal of the test sample 1 to the operational amplifier module 5, the operational amplifier module 5 amplifies the collected voltage signal and transmits the voltage signal to the singlechip controller 6, the singlechip controller 6 converts the received analog voltage signal into a digital signal and carries out analysis and calculation, the singlechip controller 6 uploads the data after the analysis and calculation to the upper computer 7, an operator can check the crack extension length data of the test sample 1 in the upper computer 7,

a＝15.153*u²+83.408u+3.2361

Since the test specimens 1 to 10 can simulate the crack propagation of a specimen under the action of a fatigue stretcher, the measured data of the test specimens 1 to 10 which have been tested can also be analyzed to simulate the experimental conclusion of the fatigue stretcher.

The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and all simple modifications, changes and equivalent structural changes made to the above embodiment according to the technical spirit of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A crack propagation measurement system, characterized by: comprises a constant current source (1) for outputting constant direct current, a direct current turnover circuit (2) for reversing the direction of the constant direct current output by the constant current source (1), an operational amplifier module (5) for amplifying a received voltage signal, a singlechip controller (6) for converting a received voltage analog signal into a digital signal and analyzing and calculating the digital signal, an upper computer (7) for displaying a measured value, an isolating circuit (8) for isolating the electrical connection between the constant current source (1) and the singlechip controller (6), a current connecting wire (10) for outputting the constant direct current and a voltage connecting wire (11) for inputting a voltage signal to be measured, wherein the constant current source (1) is connected with an external 24V battery (12) and the current signal end of the constant current source (1) is connected with the input end of the direct current turnover circuit (2), the output and the current connection line (10) of direct current upset circuit (2) are connected and will invariable direct current signal transmission to the measurement sample (9) of being connected with current connection line (10), voltage connection line (11) are put module (5) input with fortune and voltage connection line (11) are through being connected with measurement sample (9) and put module (5) with voltage signal transmission to fortune, the output of fortune is put module (5) and is connected with the input of singlechip controller (6) and transmit to singlechip controller (6) after the voltage signal who gathers is enlargied, fortune is put module (5) and is connected with external 12V battery (13), the output and the host computer (7) input of singlechip controller (6) are connected and show the measurement value after the analysis calculation on host computer (7), the data sending end of constant current source (1) is connected with the data receiving end of singlechip controller (6) and with constant current source (1) data letter The signal is transmitted to the single chip microcomputer controller (6), a data receiving end of the constant current source (1) is connected with a data sending end of the single chip microcomputer controller (6) to receive a command of the single chip microcomputer controller (6), a power end of the constant current source (1) is connected with the isolating circuit (8), the isolating circuit (8) is connected with the power end of the single chip microcomputer controller (6) and is used for preventing signals of the constant current source (1) from interfering with signals received by the single chip microcomputer controller (6), and the single chip microcomputer controller (6) is connected with the direct current overturning circuit (2) and transmits an overturning instruction to the direct current overturning circuit (2) to control overturning of the current direction.

2. The crack propagation measurement system of claim 1, wherein: isolator circuit (8) are opto-coupler 1 and opto-coupler 2 of PC817 including two models, 1 pin of opto-coupler 1 and VCC (15) end connection, 2 pin and singlechip controller (6) of access circuit the IO mouth be connected, 3 pin and the VCC end connection of singlechip controller (6), 4 pin and the VCC end connection of constant current source (1), 1 pin of opto-coupler 2 and VCC (15) end connection, 2 pin and singlechip controller (6) the IO mouth be connected, 3 pin and the GND end connection of singlechip controller (6), 4 pin and the GND end connection of constant current source (1).

3. The crack propagation measurement system of claim 2, wherein: the current connecting line (10) consists of a current output conducting wire (10-1) and a current input conducting wire (10-2), the voltage connecting line (11) consists of two conducting wires, the direct current flip circuit (2) comprises a solid-state relay SSR1, a solid-state relay SSR2, a solid-state relay SSR3, a solid-state relay SSR4 and a transistor array with the model number of ULN2003A, a No. 9 pin of the transistor array is connected to an external 5V battery (14), a No. 1 pin and a No. 2 pin are connected with an instruction output end of a single-chip microcomputer controller (6), a No. 15 pin of the transistor array is connected with a No. 4 pin of a solid-state relay SSR2 and a No. 4 pin of a solid-state relay SSR4, a No. 16 pin is connected with a No. 4 pin of the solid-state relay SSR1 and a No. 4 pin of the solid-state relay SSR3, and a No. 3 pin of a solid-state relay SSR1, a No. 3 pin of the solid-state relay SSR2, a solid-state relay SSR3 and a transistor array are connected with a transistor array, and a transistor array connected with a transistor array connected, No. 3 pin of solid state relay SSR3 and No. 3 pin of solid state relay SSR4 all insert external 5V battery (14), No. 2 pin of solid state relay SSR1 and No. 2 pin of solid state relay SSR2 all are connected with the current positive output terminal of constant current source (1), No. 1 pin of solid state relay SSR3 and No. 1 pin of solid state relay SSR4 all are connected with the current negative input terminal of constant current source (1), No. 1 pin of solid state relay SSR1 and No. 2 pin of solid state relay SSR4 all are connected with current output wire (10-1), No. 1 pin of solid state relay SSR2 and No. 2 pin of solid state relay SSR3 all are connected with current input wire (10-2).

4. The crack propagation measurement system of claim 3, wherein: the distance from the welding point of the current output lead (10-1) and the measuring sample (9) to the crack of the measuring sample (9) and the distance from the welding point of the current input lead (10-2) and the measuring sample (9) to the crack of the measuring sample (9) are both larger than the distance from the welding point of the lead of the voltage connecting wire (11) and the measuring sample (9) to the crack of the measuring sample (9).

5. Crack propagation measurement system according to claim 1 or 2, characterized in that: the constant current source (1) is a program-controlled power supply with the model number ZXY-6005S.

6. A method for crack propagation measurement using the system of claim 4, comprising the steps of:

step one, starting a power switch of a crack propagation measurement system, respectively welding a current output lead (10-1) and a current input lead (10-2) to two sides of a crack surface of a measurement sample (9) in a spot welding manner, and respectively welding a voltage connecting wire (11) to two sides of the crack of the measurement sample (9) in a spot welding manner;

step two, setting an output constant direct current value and an output voltage value of a constant current source (1) in an upper computer (7), transmitting a set constant direct current value command to a data receiving end of the constant current source (1) through a data transmitting end of a single chip microcomputer controller (6) by the upper computer (7), outputting a set constant direct current by the constant current source (1) and transmitting the constant direct current to a direct current turnover circuit (2), continuously turning over the direction of the constant direct current by the direct current turnover circuit (2) under the control of the single chip microcomputer controller (6), transmitting the continuously turned over constant direct current to a measurement sample (9) through a current output wire (10-1), and outputting the constant direct current from the measurement sample (9) and then flowing to the direct current turnover circuit (2) through a current input wire (10-2);

thirdly, the operational amplifier module (5) receives the measurement voltage signal transmitted by the voltage connecting line (11) and amplifies the acquired voltage signal, the operational amplifier module (5) transmits the amplified voltage signal into the single chip microcomputer controller (6), the single chip microcomputer controller (6) converts the received voltage analog signal into a digital signal and carries out analysis and calculation, the single chip microcomputer controller (6) uploads the data after the analysis and calculation to the upper computer (7), an operator can check the crack propagation length data of the measurement sample (9) in the upper computer (7),

the analysis and calculation formula of the singlechip controller (6) is as follows:

a＝15.153*u²+83.408u+3.2361

wherein a is the crack propagation length of the measurement sample (9) and has a unit of mm, and u is the voltage signal data of the measurement sample (9) and has a unit of μ V;

the crack propagation data of the test specimen (9) are measured.

7. An inspection apparatus for checking the crack propagation measurement accuracy of the measurement system of claim 4, wherein: comprises a fixed piece crack length change system (3) fixed with a plurality of test samples and a singlechip and relay group control module (4) used for controlling the measurement sequence of the test samples, the singlechip and relay group control module (4) is connected with the stator crack length change system (3) and is used for selecting a test sample needing to output a voltage signal, the current output lead (10-1) and the current input lead (10-2) are both connected with the inspection sample in the fixed sheet crack length change system (3) and respectively transmit the current signals after the direct current turnover circuit (2) is turned over into the inspection sample in the fixed sheet crack length change system (3), the output end of the single chip microcomputer and relay group control module (4) is connected with a voltage connecting line (11) and transmits a voltage signal of the test sample to the operational amplifier module (5).

8. The inspection device of claim 7, wherein: the fixing piece crack length change system (3) comprises ten inspection samples and five wiring terminals, wherein the five wiring terminals are four-position wiring terminals, the five wiring terminals are wiring terminals 1, wiring terminals 2, wiring terminals 3, wiring terminals 4 and wiring terminals 5 respectively, the ten inspection samples are 304 steel inspection samples, the crack propagation lengths of the ten inspection samples are known and are sequentially arranged from short to long according to the crack lengths, the crack length of the inspection sample 1 is shortest, the crack length of the inspection sample 10 is longest, the other end of a current output lead (10-1) is in spot welding connection with one side of a crack surface of the inspection sample 1, the other side of the crack surface of the inspection sample 1 is in spot welding connection with one side of the crack surface of the inspection sample 2 through a lead, the other side of the crack surface of the inspection sample 2 is in spot welding connection with one side of the crack surface of the inspection sample 3 through a lead, the other side of the crack surface of the test sample 3 is connected with one side of the crack surface of the test sample 4 by wire spot welding, the other side of the crack surface of the test sample 4 is connected with one side of the crack surface of the test sample 5 by a lead spot welding, the other side of the crack surface of the test sample 5 is connected with one side of the crack surface of the test sample 6 by a lead spot welding, the other side of the crack surface of the test sample 6 is connected with one side of the crack surface of the test sample 7 by a lead spot welding, the other side of the crack surface of the test sample 7 is connected with one side of the crack surface of the test sample 8 by wire spot welding, the other side of the crack surface of the test sample 8 is connected with one side of the crack surface of the test sample 9 by wire spot welding, the other side of the crack surface of the test sample 9 is connected with one side of the crack surface of the test sample 10 by wire spot welding, the other side of the crack surface of the test sample 10 is connected with a current input lead (10-2);

9. The testing device of claim 8, wherein: the single chip microcomputer and relay group control module (4) comprises 8 paths of relay groups A, 8 paths of relay groups B and 8 paths of relay groups C and a single chip microcomputer chip with the model number of STM32F103C8T6, pins from IN1 to IN8 of the 8 paths of relay groups A are sequentially and respectively connected with a6 pin, an A12 pin, an A11 pin, an A8 pin, a B15 pin, a B14 pin, a B13 pin and a B12 pin of the single chip microcomputer chip, pins from IN1 to IN8 of the 8 paths of relay groups B are sequentially and respectively connected with A5 pin, an 4 pin, a B5 pin, a B6 pin, a B7 pin, a B8 pin and a B8 pin of the single chip microcomputer chip, and pins from IN 72 to IN8 of the 8 paths of relay groups C are sequentially and respectively connected with A8 pin, B8 pin, A8 pin and A8 pin of the single chip VCC chip, A8 and A8 end of the single chip microcomputer chip, The VCC end of the 8-path relay group B and the VCC end of the 8-path relay group C are connected with a 5v pin of a single chip microcomputer chip, the GND end of the 8-path relay group A, the GND end of the 8-path relay group B and the GND end of the 8-path relay group C are connected with the GND end of the single chip microcomputer chip, and the single chip microcomputer chip is connected with the input end of the operational amplifier module (5);

10. A method for verifying the accuracy of a crack propagation measurement by a measurement system using the apparatus of claim 9, the method comprising the steps of:

step two, setting an output constant direct current value and an output voltage value of a constant current source (1) in an upper computer (7), transmitting a set constant direct current value command to a data receiving terminal of the constant current source (1) through a data sending terminal of a singlechip controller (6) by the upper computer (7), outputting the constant direct current set by the upper computer (7) by the constant current source (1), transmitting the constant direct current to a direct current turnover circuit (2), continuously turning over the current direction by the direct current turnover circuit (2) under the control of the singlechip controller (6), transmitting the continuously turned over constant direct current to ten inspection samples of a fixed sheet crack length change system (3) through an output lead (10-1), the test sample flows back to the direct current turnover circuit (2) through a current input lead (10-2), the ten test samples are test samples with known crack lengths, and the crack lengths of the ten test samples are different;

step three, the singlechip and the singlechip chip of the relay group control module (4) control the corresponding 8 relay groups according to the instruction of switching on the test sample 1 loop to switch on the voltage signal loop of the test sample 1 and transmit the voltage signal to the operational amplifier module (5), the operational amplifier module (5) amplifies the acquired voltage signal and transmits the voltage signal into the singlechip controller (6), the singlechip controller (6) converts the received analog voltage signal into a digital signal and carries out analysis and calculation, the singlechip controller (6) uploads the data after the analysis and calculation to the upper computer (7), an operator can check the crack extension length data of the test sample 1 in the upper computer (7),

a＝15.153*u²+83.408u+3.2361