Cantilever beam specimen crack extension device and method

Abstract

The present invention relates to a cantilever beam specimen crack extension test device and method, comprising a base, a cantilever beam specimen, a specimen fixing seat, two vibration motors, two leaf springs, a leaf spring support seat, and a signal acquisition and analysis system. The fixed end of the cantilever beam specimen is mounted on the specimen fixing seat, an upper motor seat and a lower motor seat are relatively mounted above and below the free end of the cantilever beam specimen, and two vibration motors are respectively mounted on the upper motor seat and the lower motor seat. Since the two vibration motors are relatively mounted above and below the cantilever beam specimen, the two vibration motors rotate simultaneously and in the same direction, and the exciting forces generated by the eccentric blocks thereof cancel each other out in the horizontal direction, and a resultant force is superimposed in the vertical direction, forcing the beam specimen to perform approximately linear reciprocating excitation along the vertical direction. The vibration motor can run continuously for a long time without stopping for a rest, thereby improving the efficiency of the crack beam specimen extension test; at the same time, compared with the use of an exciter, the vibration motor is not easy to burn out after long-term operation, which reduces the test results.

Description

Technical Field

[0001] The invention relates to a testing device, in particular to a cantilever beam sample crack extension device and method thereof. Background Art

[0002] In engineering practice, many structures can be simplified into cantilever beam models, such as wind turbine blades, helicopter wings, and long blades of aircraft engines. In actual practice, due to the influence of various factors such as the service environment and temperature fluctuations, these beam structures are prone to fatigue cracks under dynamic loads. Under the action of cyclic stress, fatigue cracks will continue to expand and lead to fractures. The sudden fracture of the beam structure not only affects the stable operation of production, but may also induce disasters and accidents, causing casualties and economic losses. According to statistics, more than 70% of engineering failure accidents are caused by fatigue failure, and they are often sudden and catastrophic. It can be seen that fatigue cracks seriously threaten the safety and reliability of beam structures.

[0003] In order to ensure the safety of beam structures, it is usually necessary to monitor the life of beam structures. Life monitoring is another important part of structural health monitoring. This method is to monitor the load / environment spectrum, conduct damage tolerance analysis, and determine the crack initiation and crack propagation time. Among them, the crack propagation time analysis mainly determines the life of the structure from the detectable crack size to the critical crack size under the use load, providing a basis for determining the structural maintenance cycle. From this perspective, in order to ensure the safety of key beam structures, it is necessary to conduct damage tolerance analysis, determine the crack propagation life, and provide a basis for formulating maintenance cycles.

[0004] The existing crack extension test machine products mainly use electro-hydraulic servo fatigue test machines. This type of fatigue test machine can only perform unidirectional bending loading tests on beam specimens, and cannot achieve symmetrical bending periodic loading of beam specimens. In order to conduct crack extension tests on beam specimens, some scholars have developed crack extension test devices for cracked beam specimens. For example, the journal "Structural Strength Research" published an article entitled "Analysis of Vibration Fatigue Test of Aircraft Horizontal Tail" in the second issue of 2009, which disclosed a certain type of aircraft horizontal tail test device. The test device includes an exciter, a sensor, a counterweight, a horizontal tail and a rigid base. One end of the horizontal tail is fixed on the rigid base, and the other end is excited by an exciter. The vibration fatigue test of the R area of ​​the horizontal tail counterweight is carried out. The journal Experimental Mechanics published an article entitled "Resonance Fatigue Test and Analysis of Unidirectional Double-Stiffened Plate Structural Members" in Volume 27, Issue 3, 2012. The vibration fatigue test system in the article includes an exciter, a unidirectional double-stiffened plate specimen, a push rod, a force sensor, and an acceleration sensor. One end of the specimen is fixed by a clamp, and the other end is connected to the exciter through the exciter to excite the push rod. During the experiment, the author found that the fatigue test time was long and the exciter could not bear it, so the exciter stopped for 1 minute every 20 minutes. In September 2019, the inventor published an article entitled "Nonlinear Vibration Analysis of a Beam with a Breathing Crack" in the journal Applied Sciences. The inventor built a vibration excitation device for a cracked cantilever beam, which includes a cracked beam specimen, a push rod, an exciter, a force sensor, and an acceleration sensor. The exciter is connected to the cracked beam specimen through a push rod. During the experiment, the inventor found that the exciter would automatically stop after working for 2 hours. Since the vibrator cannot operate continuously, the experiment must be interrupted for a period of time after running for two hours. After the vibrator cools down, the crack extension test can be carried out again. Under long-term operation conditions, the vibrator is very easy to burn out, the test cost is expensive, and the test time is long. In addition, since the push rod and the specimen are usually connected by threads, which is a rigid connection, the push rod is very easy to deform, resulting in a decrease in accuracy and damage, resulting in large errors in the crack extension test results of the beam specimen. Summary of the invention

[0005] In view of the deficiencies in the prior art, the present invention provides a cantilever beam specimen crack extension device and method with continuous testing and high testing efficiency.

[0006] To achieve the above-mentioned purpose, the present invention adopts the following technical scheme: a cantilever beam specimen crack extension test device, comprising a base, a cantilever beam specimen, a specimen fixing seat, two vibration motors, two leaf springs, a leaf spring support seat, and a signal acquisition and analysis system, the fixed end of the cantilever beam specimen is installed on the specimen fixing seat, the upper motor seat and the lower motor seat are relatively installed above and below the free end of the cantilever beam specimen, the two vibration motors are respectively installed on the upper motor seat and the lower motor seat, the upper motor seat is fixedly connected to the upper clamping block and clamps the end of one leaf spring, the lower motor seat is fixedly connected to the lower clamping block and clamps the end of the other leaf spring, the upper clamping block and the lower clamping block clamp the cantilever beam specimen through the clamping block connecting bolts; the other ends of the two leaf springs are respectively fixed to the leaf spring support seat, and the leaf spring support seat It includes an upper clamping block for a leaf spring, an intermediate block for a leaf spring, and a lower clamping block for a leaf spring. The upper clamping block for the leaf spring is fixedly connected to the intermediate block for the leaf spring and clamps the upper leaf spring. The lower clamping block for the leaf spring is fixedly connected to the intermediate block for the leaf spring and clamps the lower leaf spring. The lower clamping block for the leaf spring is connected to a supporting seat, which is fixed on a base. The signal acquisition and analysis system includes a strain gauge, an acceleration sensor, and a dynamic signal acquisition instrument. The acceleration sensor is installed on a cantilever beam specimen, the strain gauge is attached to the back of the notch of the specimen, the strain gauge and the acceleration sensor are electrically connected to the dynamic signal acquisition instrument, the dynamic signal acquisition instrument is connected to a computer via a network cable, and data acquisition and signal analysis software is installed on the computer. The data acquisition and signal analysis software can acquire measurement data of the acceleration sensor and the strain gauge in real time.

[0007] Furthermore, the specimen fixing seat includes an upper specimen chuck, a lower specimen chuck and a bracket seat, the lower specimen chuck and the bracket seat are connected by screws, the upper specimen chuck and the lower specimen chuck are connected by screws, the beam specimen is clamped by the upper specimen chuck and the lower specimen chuck, and the middle parts of the upper chuck and the lower chuck of the beam specimen fixing bracket are provided with elongated protrusions, the end faces of the elongated protrusions are flat, the elongated protrusions of the upper chuck are pressed on the top plane of the beam specimen, and the protrusions of the lower chuck are pressed on the bottom plane of the beam specimen.

[0008] In order to facilitate the adjustment of the sample fixing seat and the leaf spring support seat, the base is provided with two long grooves, the first long groove is located below the sample fixing seat, and the bottom of the sample fixing seat is fixedly connected to the first long groove by bolts; the second long groove is located below the leaf spring support seat, and the bottom of the leaf spring support seat is fixedly connected to the second long groove by bolts.

[0009] In order to further adjust the speed of the vibration motor, the vibration motor is a variable frequency speed regulating motor, and the variable frequency speed regulating motor is electrically connected to a frequency converter.

[0010] In order to further adjust the speed of the vibration motor, the vibration motor is a single-phase series-excited motor, and the single-phase series-excited motor is electrically connected to the contactor voltage regulator.

[0011] In order to form cracks better, a notch is provided on the cantilever beam specimen, and the notch is a straight-through notch.

[0012] In order to better form cracks, the cantilever beam specimen is provided with a notch, which is a notch cut by a molybdenum wire.

[0013] In order to better form cracks, the cantilever beam specimen is provided with a notch, and the curvature radius of the notch root is less than or equal to 0.08 mm.

[0014] A test method for a cantilever beam specimen crack growth test device, the steps of the test method are as follows:

[0015] Step 1: First, a notch is cut on the cantilever beam sample, and the curvature radius of the notch root is less than or equal to 0.08 mm;

[0016] Step 2: fix the notched cantilever beam sample on the sample fixing seat, install the free end of the notched cantilever beam sample between the upper clamping block and the lower clamping block, and fix the notched cantilever beam sample;

[0017] Step 3: Install the acceleration sensor on the cantilever beam sample, attach the strain gauge to the center of the back of the notch, and electrically connect the strain gauge and the acceleration sensor to a dynamic signal acquisition instrument. The dynamic signal acquisition instrument is connected to a computer via a network cable. The computer is installed with data acquisition and signal analysis software. The data acquisition and signal analysis software can collect measurement data of the acceleration sensor and strain gauge in real time, and analyze the collected acceleration and strain gauge data;

[0018] Step 4, using a hammer or other stick-like object to hit the free end of the cantilever beam to induce free vibration of the cantilever beam, and measuring the fixed frequency of the cantilever beam;

[0019] Step 5, start the two vibration motors, control the two vibration motors to rotate synchronously and in the same direction, select a suitable sampling frequency, observe and record the acceleration value and strain value in real time, adjust the vibration motor excitation frequency to a preset loading frequency, keep the vibration motor in stable motion, and subject the notched cantilever beam specimen to steady-state forced excitation until the cantilever beam specimen is completely broken;

[0020] Step six, based on the measured data of notch back strain and time, and according to the corresponding relationship between back strain and crack depth, the relationship between the crack extension length and time of the cantilever beam specimen is obtained.

[0021] The beneficial effects of the present invention are as follows: since the two vibration motors are relatively installed above and below the cantilever beam specimen, the two vibration motors rotate simultaneously and in the same direction, and the exciting forces generated by their eccentric blocks cancel each other out in the horizontal direction, and a resultant force is superimposed in the vertical direction, forcing the beam specimen to perform approximately linear reciprocating excitation along the vertical direction. The vibration motor can run continuously for a long time without stopping for a rest, thereby improving the efficiency of the crack beam specimen expansion test; at the same time, compared with the use of an exciter, the vibration motor is not easy to burn out after long-term operation, which reduces the test results. In addition, the vibration motor directly excites the beam specimen, avoiding the use of a rigid connection between the push rod and the specimen to transmit the excitation. The exciting force generated by the vibration motor will not be affected by factors such as the deformation and rigidity of the push rod, and the cantilever beam specimen crack expansion test results are highly accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic structural diagram of a cantilever beam specimen crack extension device of the present invention;

[0023] Figure 2 yes Figure 1 A schematic diagram of the structure enlargement in the middle;

[0024] Figure 3 yes Figure 1 Front view of the structure of the crack extension device for the cantilever beam specimen;

[0025] Figure 4 yes Figure 1 Schematic diagram of the structure of the leaf spring support seat in the crack extension device of the cantilever beam specimen;

[0026] Figure 5 yes Figure 1 Schematic diagram of inertial excitation of two vibration motors;

[0027] Figure 6 is a flow chart of the steps of the experimental method of the present invention; DETAILED DESCRIPTION

[0028] The preferred embodiments of the present invention are described below in conjunction with the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0029] Example 1: Figure 1-4As shown, the present invention provides a technical solution, a cantilever beam sample crack extension test device, including a base 1, a cantilever beam sample 2, a sample fixing seat 3, a leaf spring support seat 4, an upper leaf spring 5, a lower leaf spring 6, an upper vibration motor 51, a lower vibration motor 61, and a signal acquisition and analysis system. The fixed end of the cantilever beam sample 2 is installed on the sample fixing seat 3, the upper motor seat 52 is installed above the free end of the cantilever beam sample, the upper vibration motor 51 is installed on the upper motor seat 52, and the upper motor seat 52 is fixedly connected to the upper clamping block 53 and clamps the end of the upper leaf spring 5. In order to adjust the speed of the vibration motor, two vibration motors use single-phase series-excited motors, and the single-phase series-excited motors are electrically connected to the contact voltage regulator. The lower motor seat 62 is relatively installed below the free end of the cantilever beam sample, and the lower vibration motor 61 is installed below the lower motor seat 62, and the upper part of the lower motor seat 62 is fixedly connected to the lower clamping block 63 and clamps the end of the lower leaf spring 6. The upper clamp block 53 and the lower clamp block 63 clamp the cantilever beam specimen 2 via the clamp block connecting bolts 64 .

[0030] The signal acquisition and analysis system includes an acceleration sensor 71, a strain gauge 72, a dynamic signal acquisition instrument 73 and a computer 74. The acceleration sensor 71 is installed on the cantilever beam sample. The acceleration sensor 71 uses an IEPE type acceleration sensor. The acceleration sensor belongs to a piezoelectric velocity sensor. The 1A101 type acceleration sensor of Jiangsu Donghua Vibration Testing Co., Ltd. can be selected. The strain gauge 72 is attached to the back of the notch of the sample. The strain gauge 72 and the acceleration sensor 71 are electrically connected to the dynamic signal acquisition instrument 73. The dynamic signal acquisition instrument 73 adopts a distributed dynamic signal test and analysis system. The DH5981 type distributed dynamic signal test and analysis system of Jiangsu Donghua Vibration Testing Co., Ltd. can be selected. The dynamic signal acquisition instrument 73 is connected to the computer through a network cable. The computer 74 is installed with data acquisition and signal analysis software. The data acquisition and signal analysis software can collect the measurement data of the acceleration sensor and the strain gauge in real time. The data acquisition and signal analysis software uses the DHDAS software of Jiangsu Donghua Vibration Testing Co., Ltd.

[0031] The other ends of the upper leaf spring 5 and the lower leaf spring 6 are respectively fixed on the leaf spring support seat 4, which includes an upper leaf spring clamping block 41, a leaf spring middle block 42, and a lower leaf spring clamping block 43. The upper leaf spring clamping block 41 and the leaf spring middle block 42 are fixedly connected and clamp the upper leaf spring 5. The lower leaf spring clamping block 43 and the leaf spring middle block 42 are fixedly connected and clamp the lower leaf spring 6. The lower leaf spring clamping block 43 is connected to a support seat 44, which is fixed on the base 1.

[0032] The specimen fixing seat 3 includes an upper specimen chuck 31, a lower specimen chuck 32 and a bracket seat 33. The lower specimen chuck 32 and the bracket seat 33 are connected by a lower countersunk screw 34. The upper specimen chuck 31 and the lower specimen chuck 32 are connected by an upper countersunk screw 35. The cantilever beam specimen 2 is clamped by the upper specimen chuck 31 and the lower specimen chuck 32. The middle parts of the upper specimen chuck 31 and the lower specimen chuck 32 of the specimen fixing seat 3 are provided with a long strip protrusion 311. The end face of the long strip protrusion 311 is a plane. The long strip protrusion of the upper chuck is pressed on the top plane of the beam specimen, and the protrusion of the lower chuck is pressed on the bottom plane of the beam specimen.

[0033] In order to facilitate the adjustment of the positions of the sample fixing seat 3 and the leaf spring support seat 4, the base 1 is provided with two long grooves at corresponding positions. The first long groove is located below the bracket seat 33 of the sample fixing seat 3. The sample fixing seat 3 is fixed to the base 1 by the connecting bolt 36. The position of the sample fixing seat 3 on the base can be adjusted by loosening the connecting bolt 36, moving the sample fixing seat to a predetermined position, and then tightening the connecting bolt 36.

[0034] The second long groove is located below the leaf spring support seat. The support seat 44 of the leaf spring support seat is fixedly connected to the base 2 through a connecting bolt 45 that passes through the second long groove. By loosening the connecting bolt 45, moving the sample fixing seat to a predetermined position and then tightening the connecting bolt 45, the position of the leaf spring support seat 4 on the base can be adjusted.

[0035] In order to facilitate the prefabrication of qualified fatigue cracks, the cantilever beam specimens are subjected to wire cutting after heat treatment. The cutting notch is a straight-through notch, and the curvature radius of the notch root is less than or equal to 0.08 mm.

[0036] The speed regulation of the vibration motor is not limited to the above-mentioned speed regulation method. The vibration motor can also be a variable frequency speed regulation motor, and the variable frequency speed regulation motor is electrically connected to the frequency converter.

[0037] When this embodiment is used for the crack extension test of the cantilever beam specimen, firstly, the four upper countersunk screws 35 on the specimen upper clamp 31 and the specimen lower clamp 32 of the specimen fixing seat are loosened, and the specimen upper clamp 31 and the specimen lower clamp 32 are loosened. Then, the clamp block connecting bolt 64 is loosened for a certain length, and a certain space can be formed between the upper clamp block 53 and the lower clamp block 63, and the length of the space distance is greater than the height of the cantilever beam specimen; then, one end of the notched cantilever beam specimen 2 is installed between the upper clamp block 53 and the lower clamp block 63, and the other end is installed between the specimen upper clamp 31 and the specimen lower clamp 32, and then the upper countersunk screws 35 and the clamp block connecting bolt 64 are tightened respectively, and one end of the notched cantilever beam specimen is fixed on the specimen fixing seat 3, and the other end is installed with the upper clamp block 53 and the lower clamp block 63, and the upper clamp block 53 is installed with the upper motor seat 52 and the upper vibration motor 51 in sequence, and the lower motor seat 62 and the lower vibration motor 61 are installed below the lower clamp block 63 in sequence. When the upper vibration motor 51 and the lower vibration motor 61 rotate, the cantilever beam with a notch will be caused to reciprocate up and down.

[0038] An acceleration sensor 71 and a strain gauge 72 are installed on the cantilever beam specimen with a notch. The strain gauge 72 is attached to the back of the notch. The acceleration sensor 71 and the strain gauge 72 are connected to a dynamic signal acquisition instrument 73 through a signal line. The dynamic signal acquisition instrument 73 is then connected to a computer through a network line. The computer 74 is installed with data acquisition and signal analysis software, which can collect measurement data of the acceleration sensor and the strain gauge in real time.

[0039] Finally, start the two vibration motors and control them to rotate synchronously and in the same direction. Figure 5 It can be seen that the upper vibration motor 51 and the lower vibration motor 61 are arranged symmetrically up and down to form a two-axis inertial exciter. When the two vibration motors are controlled to rotate synchronously and in opposite directions, the exciting forces generated by their eccentric blocks cancel each other out in the horizontal direction and a resultant force is superimposed in the vertical direction. Therefore, the cantilever beam with a notch is excited as a straight line along the vertical direction. Figure 4 The vibration motor excitation force at three different positions is shown. When the two semi-disc eccentric blocks are at the lowest position, the two eccentric blocks generate a centrifugal force F in the vertical direction. As the vibration motor rotates, at the other two positions, when the two semi-disc eccentric blocks of the vibration motor rotate, the centrifugal force F generated by the two eccentric blocks, the horizontal force Fx always cancels each other, and the vertical force Fy always superimposes each other, and the generated excitation force 2Fy forces the vibration table to reciprocate in an approximately linear direction in the vertical direction. The vertical centrifugal forces of the upper vibration motor and the lower vibration motor are completely superimposed, causing the cantilever beam with crack notch to reciprocate.

[0040] Example 2: Figure 6 As shown, a test method for a cantilever beam specimen crack growth test device, the steps of the test method are as follows:

[0041] Step 1: First, a notch is cut on the cantilever beam sample 2, and the curvature radius of the notch root is less than or equal to 0.08 mm;

[0042] Step 2: fix the notched cantilever beam sample 2 on the sample fixing seat 3, install the free end of the notched cantilever beam sample 2 between the upper clamping block 31 and the lower clamping block 32, and fix the notched cantilever beam sample 2;

[0043] Step 3: Install the acceleration sensor 71 on the cantilever beam specimen 2 with a notch, attach the strain gauge 72 to the center of the back of the notch, and electrically connect the strain gauge 72 and the acceleration sensor 71 to the dynamic signal acquisition instrument 73. The dynamic signal acquisition instrument 73 is connected to the computer 74 via a network cable. The computer 74 is installed with data acquisition and signal analysis software. The data acquisition and signal analysis software can collect measurement data of the acceleration sensor 71 and the strain gauge 72 in real time, and analyze the collected acceleration and strain gauge data;

[0044] Step 4, using a hammer or other stick-like object to hit the free end of the cantilever beam with a notch, inducing the cantilever beam to generate free vibration, and measuring the fixed frequency of the cantilever beam with a notch;

[0045] Step 5, start the upper vibration motor 51 and the lower vibration motor 61, the upper vibration motor 51 and the lower vibration motor 61 rotate synchronously and in the same direction (counterclockwise or clockwise at the same time), select a suitable sampling frequency, observe and record the acceleration value and the strain value in real time, adjust the vibration motor excitation frequency to the preset loading frequency, keep the vibration motor in stable motion, and subject the notched cantilever beam sample 2 to steady-state forced excitation until the cantilever beam sample 2 is completely broken;

[0046] Step six, based on the measured data of notch back strain and time, and according to the corresponding relationship between back strain and crack depth, the relationship between the crack extension length and time of the cantilever beam specimen is obtained.

[0047] Finally, it should be noted that the above description is only a preferred example of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A cantilever beam specimen crack growth test device, characterized in that: It includes a base, a cantilever beam specimen, a specimen fixing seat, two vibration motors, two leaf springs, a leaf spring support seat, and a signal acquisition and analysis system. The fixed end of the cantilever beam specimen is installed on the specimen fixing seat. The upper motor seat and the lower motor seat are relatively installed above and below the free end of the cantilever beam specimen. The two vibration motors are respectively installed on the upper motor seat and the lower motor seat. The upper motor seat is fixedly connected to the upper clamping block and clamps the end of one leaf spring. The lower motor seat is fixedly connected to the lower clamping block and clamps the end of the other leaf spring. The upper clamping block and the lower clamping block clamp the cantilever beam specimen through the clamping block connecting bolts; the other ends of the two leaf springs are respectively fixed on the leaf spring support seat. The leaf spring support seat includes a leaf spring upper clamping block, a leaf spring middle block, and a leaf spring The lower clamping block, the upper clamping block of the leaf spring is fixedly connected with the middle block of the leaf spring and clamps the upper leaf spring, the lower clamping block of the leaf spring is fixedly connected with the middle block of the leaf spring and clamps the lower leaf spring, the lower clamping block of the leaf spring is connected with a support seat, and the support seat is fixed on the base; the signal acquisition and analysis system includes a strain gauge, an acceleration sensor, and a dynamic signal acquisition instrument; the acceleration sensor is installed on the cantilever beam sample, the strain gauge is attached to the back of the notch of the sample, the strain gauge and the acceleration sensor are electrically connected to the dynamic signal acquisition instrument, the dynamic signal acquisition and analysis instrument is connected to the computer through a network cable, and the computer is installed with data acquisition and signal analysis software, and the data acquisition and signal analysis software can collect measurement data of the acceleration sensor and the strain gauge in real time; The sample fixing seat comprises an upper specimen chuck, a lower specimen chuck and a support seat, the lower specimen chuck and the support seat are connected by screws, the upper specimen chuck and the lower specimen chuck are connected by screws, the beam specimen is clamped by the upper specimen chuck and the lower specimen chuck, the middle parts of the upper chuck and the lower chuck of the beam specimen fixing support are provided with a long strip protrusion, the end faces of the long strip protrusion are planes, the long strip protrusion of the upper chuck is pressed on the top plane of the beam specimen, and the protrusion of the lower chuck is pressed on the bottom plane of the beam specimen; The base is provided with two long grooves, the first long groove is located below the sample fixing seat, and the bottom of the sample fixing seat is fixedly connected to the first long groove by bolts; the second long groove is located below the leaf spring support seat, and the bottom of the leaf spring support seat is fixedly connected to the second long groove by bolts.

2. The cantilever beam specimen crack extension test device according to claim 1, characterized in that The vibration motor is a variable frequency speed regulating motor, and the variable frequency speed regulating motor is electrically connected to the frequency converter.

3. The cantilever beam specimen crack extension test device according to claim 1, characterized in that The vibration motor is a single-phase series-excited motor, and the single-phase series-excited motor is electrically connected to a contactor voltage regulator.

4. The cantilever beam specimen crack growth test device according to claim 1, characterized in that The cantilever beam specimen is provided with a notch, and the notch is a straight-through notch.

5. The cantilever beam specimen crack extension test device according to claim 1, characterized in that The cantilever beam specimen is provided with a notch, which is a notch cut by a molybdenum wire.

6. The cantilever beam specimen crack growth test device according to claim 1, characterized in that The cantilever beam specimen is provided with a notch, and the curvature radius of the notch root is less than or equal to 0.08 mm.

7. A test method for a cantilever beam specimen crack extension test device according to any one of claims 1 to 6, characterized in that: The steps of this test method are as follows: Step 1: First, a notch is cut on the cantilever beam sample, and the curvature radius of the notch root is less than or equal to 0.08 mm; Step 2: fix the notched cantilever beam sample on the sample fixing seat, install the free end of the notched cantilever beam sample between the upper clamping block and the lower clamping block, and fix the notched cantilever beam sample; Step 3: Install the acceleration sensor on the cantilever beam sample, attach the strain gauge to the center of the back of the notch, electrically connect the strain gauge and the acceleration sensor to a dynamic signal acquisition instrument, connect the dynamic signal acquisition instrument to a computer via a network cable, and install data acquisition and signal analysis software on the computer. The data acquisition and signal analysis software can collect measurement data of the acceleration sensor and strain gauge in real time, and analyze the collected acceleration and strain gauge data; Step 4, using a hammer or other stick-like object to hit the free end of the cantilever beam to induce free vibration of the cantilever beam, and measuring the fixed frequency of the cantilever beam; Step 5, start the two vibration motors, control the two vibration motors to rotate synchronously and in the same direction, select a suitable sampling frequency, observe and record the acceleration value and strain value in real time, adjust the vibration motor excitation frequency to a preset loading frequency, keep the vibration motor in stable motion, and subject the notched cantilever beam specimen to steady-state forced excitation until the cantilever beam specimen is completely broken; Step six, based on the measured data of notch back strain and time, and according to the corresponding relationship between back strain and crack depth, the relationship between the crack extension length and time of the cantilever beam specimen is obtained.

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