In-situ imaging monitoring device and method for fatigue test of additive manufacturing metal materials

Abstract

The present invention discloses an in-situ imaging monitoring device and method for fatigue tests of additive manufacturing metal materials, including a signal generator, a power amplifier, an excitation coil, an infrared thermal imaging module, an optical camera module, and a monitoring computer; the output end of the signal generator is electrically connected to the input end of the power amplifier; the output end of the power amplifier is electrically connected to the input end of the excitation coil; the excitation coil is wound around the upper and lower sides of the axial center position of the fatigue specimen; the shooting direction of the infrared thermal imaging module is directly opposite to the monitoring area of the gauge section of the fatigue specimen; the position of the optical camera module is adjacent to the infrared thermal imaging module, and the shooting direction and shooting area are the same as those of the infrared thermal imaging module. The present invention can perform high-resolution in-situ imaging on the surface layer of the monitoring area online, at low cost, and non-contact, quickly realize the monitoring of damage and the dynamic evolution process of damage near the surface of the gauge section of the fatigue specimen, and improve the online monitoring accuracy and monitoring efficiency of micro-damage on the surface layer of the fatigue specimen.

Description

Technical Field

[0001] The present invention relates to the technical field of non-destructive testing, and particularly to an in-situ imaging monitoring device and method for fatigue tests of additively manufactured metal materials. Background Art

[0002] Problems such as the fatigue resistance, fatigue performance dispersion, and defect sensitivity of metal materials after additive manufacturing are hot issues that need to be studied urgently at present, and are also key problems restricting the engineering application of additively manufactured metal materials in main load-bearing structures. Due to defects or anomalies such as micro pores, lack of fusion, inclusions, material anisotropy, and non-uniformity that may exist in the metal materials after forming, the fatigue fracture failure analysis problem of additively manufactured metal materials becomes very complicated.

[0003] To better explore the fatigue failure law of additively manufactured metal materials, as well as the correlation between factors such as metallurgical defects and the mechanical properties of fatigue and damage tolerance, and further provide a reliable theoretical basis for the life design of additively manufactured metal components, it is very necessary to obtain macroscopic quantitative mechanical parameters of additively manufactured metal materials under alternating loads through fatigue tests, and combine advanced sensing and detection technologies to conduct in-situ observations on internal damage and microstructural organizations of the materials.

[0004] The combination of existing microscopic optical imaging monitoring technology and material fatigue testing can conduct in-situ tests and observations on the propagation of microcracks during mechanical loading and fatigue testing. However, due to the limitations of its resolution and magnification, the test effect of this technology has great limitations; the combination of existing scanning electron microscope in-situ observation and fatigue loading device can observe the microstructural morphology and damage of materials with high resolution, but only two-dimensional images of the material surface can be obtained and the sample size is limited greatly; the existing fatigue testing machine technology that can use synchrotron radiation sources for in-situ imaging can clearly and accurately obtain three-dimensional stereoscopic images inside the materials during fatigue tests. However, the technical system of this technology is complex, the penetration ability of synchrotron radiation sources is limited, and there are potential radiation hazards. Existing technologies have deficiencies in the in-situ imaging monitoring of the surface layer, especially near-surface damage, of metal materials, and it is difficult to discover the micro-damage state information on the surface layer of materials during fatigue tests online, at low cost, and efficiently. In order to realize the in-situ imaging monitoring of the surface layer, especially near-surface damage, of fatigue specimens, improve the observation ability of near-surface damage and the dynamic evolution process of damage of materials, analyze the correlation between damage and fatigue performance, and the damage failure evolution law, it is of great significance to develop a new type of visual in-situ imaging monitoring device and method for fatigue tests of additively manufactured metal materials. Summary of the Invention

[0005] The present invention provides an in-situ imaging monitoring device and method for fatigue tests of additively manufactured metal materials to solve the problems raised in the above background art.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] An in-situ imaging monitoring device for fatigue testing of additive manufacturing metal materials, comprising a signal generator, a power amplifier, an excitation coil, an infrared thermal imaging module, an optical camera module, and a monitoring computer;

[0008] The output end of the signal generator is electrically connected to the input end of the power amplifier;

[0009] The output end of the power amplifier is electrically connected to the input end of the excitation coil;

[0010] The excitation coil is coupled to the monitoring area of the fatigue specimen through an electromagnetic field;

[0011] The output end of the infrared thermal imaging module is electrically connected to the input end of the monitoring computer;

[0012] The output end of the optical camera module is electrically connected to the input end of the monitoring computer.

[0013] Preferably, the signal generator outputs short-time pulse excitations periodically.

[0014] Preferably, the excitation coil is composed of two coaxially wound toroidal air-core solenoids with the same shape, size, number of coil turns, and wire diameter.

[0015] Preferably, the two toroidal air-core solenoids of the excitation coil are equidistantly wound around the upper and lower sides of the axial center position of the fatigue specimen and are coaxial with the fatigue specimen.

[0016] Preferably, the infrared thermal imaging module is composed of four infrared thermal imaging modules, which are equidistantly distributed along the circumferential direction of the fatigue specimen, and the shooting direction is directly opposite to the gauge section monitoring area near the axial center position of the fatigue specimen, and the shooting area completely covers the circumferential surface of the fatigue specimen at the monitoring area.

[0017] Preferably, the optical camera module is composed of four optical imaging modules, which are placed adjacent to the infrared thermal imaging modules, and the shooting directions and shooting areas of the four optical imaging modules are the same as those of the infrared thermal imaging modules.

[0018] The present invention also discloses an in-situ imaging monitoring method for fatigue testing of additive manufacturing metal materials, based on the in-situ imaging monitoring device for fatigue testing of additive manufacturing metal materials described in any one of the above, and the method includes the following steps:

[0019] S1: Before the fatigue test begins, install the fatigue specimen on the fixture of the fatigue testing machine. At the same time, install the above-mentioned in-situ imaging monitoring device for the fatigue test of additive manufacturing metal materials at the monitoring area of the gauge section of the fatigue specimen. Before applying the alternating load to the fatigue specimen, conduct the first electromagnetic-thermal-optical multi-physical field in-situ imaging on the monitoring area;

[0020] S2: When implementing the electromagnetic-thermal-optical multi-physical field in-situ imaging, the signal generator outputs short-time pulse excitations periodically. After being amplified in power by the power amplifier, the short-time pulse excitations drive the excitation coil. The short-time pulse current flowing through the excitation coil generates a transient excitation magnetic field inside and outside the two toroidal hollow solenoids. The transient excitation magnetic field is transmitted to the surface layer of the gauge section monitoring area near the axial center position of the fatigue specimen and induces eddy currents through electromagnetic induction. The induced eddy currents cause temperature distribution information by inductively heating the surface layer of the monitoring area based on the Joule heat effect. The infrared thermal imaging module converts the circumferential surface temperature distribution information at the gauge section monitoring area of the fatigue specimen into a visible thermal image monitoring signal and transmits it to the monitoring computer;

[0021] S3: The optical camera module conducts optical imaging on the circumferential surface of the gauge section monitoring area of the fatigue specimen and transmits the converted optical image monitoring signal to the monitoring computer;

[0022] S4: The monitoring computer stores the received circumferential surface visible thermal image monitoring signal and optical image monitoring signal of the gauge section monitoring area of the fatigue specimen and draws the monitoring result diagram of the electromagnetic-thermal-optical multi-physical field in-situ imaging at the gauge section monitoring area of the fatigue specimen;

[0023] S5: The monitoring computer displays the monitoring result diagram of the electromagnetic-thermal-optical multi-physical field in-situ imaging at the gauge section monitoring area of the fatigue specimen drawn in real time on the monitoring display screen for the monitoring personnel to observe and evaluate;

[0024] S6: During the fatigue test process, starting from the first application of the alternating load to the fatigue specimen, repeat the operations of S2 to S5 above at regular intervals of a certain number of cycles until the set number of cycles for completing the fatigue test is reached;

[0025] S7: After the fatigue test ends, analyze the damage and the dynamic evolution law of the damage at the gauge section monitoring area of the fatigue specimen based on the electromagnetic-thermal-optical multi-physical field in-situ imaging monitoring results obtained at different numbers of cycles throughout the fatigue test process.

[0026] Compared with the prior art, the beneficial effects of the present invention are:

[0027] After adopting an in-situ imaging monitoring device and method for fatigue tests of additive manufacturing metal materials according to the present invention, the observation of surface damage and the dynamic evolution process of damage in the gauge section of a fatigue specimen can be realized through in-situ imaging monitoring of multi-physical fields such as electromagnetic, thermal, and optical. Compared with the prior art, the in-situ imaging monitoring device has a simple structure and convenient operation, and can perform high-resolution in-situ imaging on the surface layer of the monitoring area online, at low cost, and non-contact, quickly realizing the observation of damage and the dynamic evolution process of damage near the surface of the gauge section of the fatigue specimen, improving the online monitoring accuracy and monitoring efficiency of micro-damage on the surface layer of the fatigue specimen, and providing monitoring data support for damage evaluation and analysis of the dynamic evolution process of damage at different stages during the fatigue test;

[0028] The present invention is applicable to fatigue tests and defect sensitivity analysis of metal materials including but not limited to additive manufacturing, as well as traditional casting, forging, powder metallurgy, etc., and is applicable to the analysis of surface and near-surface damage and the dynamic evolution law of damage of standard specimens, characteristic structures, and typical components of metal materials during fatigue tests.

[0029] The above description is only an overview of the technical solution of the present invention. In order to understand the technical means of the present invention more clearly and implement it in accordance with the content of the description, the following takes the preferred embodiments of the present invention and describes them in detail in conjunction with the accompanying drawings. The specific implementation manners of the present invention are given in detail by the following embodiments and their accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The drawings described herein are used to provide a further understanding of the present invention, form a part of this application, and the schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0031] Figure 1 Schematic diagram of the system composition of an embodiment of the device of the present invention;

[0032] Figure 2 Schematic diagram of the exciting coil toroidal solenoid of an embodiment of the device of the present invention;

[0033] Figure 3 Schematic diagram of the infrared thermal imaging and optical camera module of an embodiment of the device of the present invention;

[0034] Figure 4 Schematic diagram of the induced eddy current distribution in the monitoring area during the implementation of the device and method of the present invention;

[0035] Figure 5 Schematic diagram of the temperature distribution information in the monitoring area during the implementation of the device and method of the present invention.

[0036] In the drawings, the list of components represented by each reference numeral is as follows:

[0037] 1. Signal generator; 2. Power amplifier; 3. Excitation coil; 4. Infrared thermal imaging module; 401. First infrared thermal imaging module; 402. Second infrared thermal imaging module; 403. Third infrared thermal imaging module; 404. Fourth infrared thermal imaging module; 5. Optical camera module; 501. First optical imaging module; 502. Second optical imaging module; 503. Third optical imaging module; 504. Fourth optical imaging module; 6. Monitoring computer; 7. Fatigue specimen; 8. Monitoring area; 9. Discontinuity; 10. Fixture; 11. Inductive eddy current; 12. Temperature distribution information. Specific embodiments

[0038] The principles and features of the present invention will be described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention. In the following paragraphs, the present invention will be described more specifically by way of example with reference to the accompanying drawings. The advantages and features of the present invention will be clearer according to the following description and claims. It should be noted that the accompanying drawings are all in a very simplified form and use non-precise scales, only for the purpose of facilitating and clearly assisting in explaining the purpose of the embodiments of the present invention.

[0039] It should be noted that when a component is referred to as being "fixed to" another component, it can be directly on the other component or there can also be an intermediate component. When a component is considered to be "connected" to another component, it can be directly connected to the other component or there may be an intermediate component at the same time. When a component is considered to be "disposed on" another component, it can be directly disposed on the other component or there may be an intermediate component at the same time. The terms "vertical", "horizontal", "left", "right" and similar expressions used herein are only for the purpose of illustration.

[0040] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0041] See Figure 1 , an in-situ imaging monitoring device for fatigue testing of additive manufacturing metal materials, the device includes a signal generator 1, a power amplifier 2, an excitation coil 3, an infrared thermal imaging module 4, an optical camera module 5 and a monitoring computer 6;

[0042] The output end of the signal generator 1 is electrically connected to the input end of the power amplifier 2;

[0043] The output end of the power amplifier 2 is electrically connected to the input end of the excitation coil 3;

[0044] The excitation coil 3 is composed of two coaxially wound toroidal air-core solenoids, and the two toroidal air-core solenoids are equidistantly arranged on the upper and lower sides of the axial center position of the fatigue specimen 7;

[0045] The excitation coil 3 is coupled with the monitored area 8 of the gauge section of the fatigue specimen 7 through an electromagnetic field;

[0046] The output end of the infrared thermal imaging module 4 is electrically connected to the input end of the monitoring computer 6;

[0047] The output end of the optical camera module 5 is electrically connected to the input end of the monitoring computer 6.

[0048] See Figure 2 , the toroidal air-core solenoid of the excitation coil 3 is coaxial with the fatigue specimen 7.

[0049] See Figure 3 , the infrared thermal imaging module 4 is composed of a first infrared thermal imaging module 401, a second infrared thermal imaging module 402, a third infrared thermal imaging module 403, and a fourth infrared thermal imaging module 404. The four infrared thermal imaging modules are equidistantly distributed along the circumferential direction of the fatigue specimen 7, and the shooting direction is facing the monitored area 8 near the axial center position of the fatigue specimen 7. The shooting area completely covers the circumferential surface of the fatigue specimen 7 at the monitored area 8 of the gauge section.

[0050] See Figure 3 , the optical camera module 5 is composed of a first optical imaging module 501, a second optical imaging module 502, a third optical imaging module 503, and a fourth optical imaging module 504. The placement positions of the four optical imaging modules are adjacent to the infrared thermal imaging modules, and the shooting directions and shooting areas of the four optical imaging modules are the same as those of the infrared thermal imaging modules.

[0051] During specific implementation, the signal generator 1 outputs a short-time pulse excitation periodically.

[0052] During specific implementation, the two toroidal air-core solenoids of the excitation coil 3 have the same shape, size, number of coil turns, and wire diameter.

[0053] The present invention also discloses a method for in-situ imaging monitoring of the fatigue test of an additive manufacturing metal material, which is a method for in-situ imaging monitoring of the fatigue specimen 7 by using the above device. The method includes the following steps:

[0054] S1: Before the fatigue test starts, install the fatigue specimen 7 on the fixture 10 of the fatigue testing machine. At the same time, install the above device at the monitored area 8 of the gauge section of the fatigue specimen 7. Before applying an alternating load to the fatigue specimen 7, perform the first electromagnetic-thermal-optical multi-physical-field in-situ imaging on the monitored area 8;

[0055] S2: When implementing in-situ imaging of electromagnetic, thermal, and optical multi-physical fields, the signal generator outputs short-pulse excitations periodically. After being amplified in power by the power amplifier 2, it drives the excitation coil 3. The short-pulse current flowing through the excitation coil 3 generates a transient excitation magnetic field inside and outside the two toroidal air-core solenoids. The transient excitation magnetic field reaches the surface layer of the gauge section monitoring area 8 near the axial center position of the fatigue specimen 7 and generates induced eddy currents 11 through electromagnetic induction. The induced eddy currents 11 cause temperature distribution information 12 by inductively heating the surface layer of the gauge section monitoring area 8 of the fatigue specimen 7 based on the Joule heating effect. The infrared thermal imaging module 4 converts the circumferential surface temperature distribution information 12 at the gauge section monitoring area 8 of the fatigue specimen 7 into a visible thermal image monitoring signal and transmits it to the monitoring computer 6;

[0056] S3: The optical camera module 5 performs optical imaging on the circumferential surface of the gauge section monitoring area 8 of the fatigue specimen 7 and transmits the converted optical image monitoring signal to the monitoring computer 6;

[0057] S4: The monitoring computer 6 stores the received circumferential surface visible thermal image monitoring signal and optical image monitoring signal of the gauge section monitoring area 8 of the fatigue specimen 7 and draws the in-situ imaging monitoring result diagram of the electromagnetic, thermal, and optical multi-physical fields at the gauge section monitoring area 8 of the fatigue specimen 7;

[0058] S5: The monitoring computer 6 displays the drawn in-situ imaging monitoring result diagram of the electromagnetic, thermal, and optical multi-physical fields at the gauge section monitoring area 8 of the fatigue specimen 7 on the monitoring display screen in real time for the monitoring personnel to observe and evaluate;

[0059] S6: During the fatigue test, starting from the first application of the alternating load to the fatigue specimen 7, the operations of S2 to S5 above are repeated at regular intervals of a certain number of cycles until the set number of cycles for completing the fatigue test is reached;

[0060] S7: After the fatigue test is completed, based on the in-situ imaging monitoring results obtained at different numbers of cycles throughout the fatigue test process, the damage and the dynamic evolution law of the damage at the gauge section monitoring area 8 of the fatigue specimen 7 are analyzed.

[0061] In-situ imaging monitoring principle and operation process of the fatigue test of additive manufacturing metal materials:

[0062] Assume that a discontinuity 9 appears on the surface layer of the gauge section monitoring area 8 of the additive manufacturing metal material fatigue specimen 7;

[0063] See Figure 4, which is a schematic diagram of the induced eddy current distribution in the monitoring area during the implementation of the present device and method. The two annular hollow solenoids of the excitation coil 3 generate induced eddy currents 11 on the surface layer of the monitoring area 8 in the gauge section of the fatigue specimen 7 through electromagnetic induction. The flow direction of the induced eddy currents 11 is parallel to the axial direction of the fatigue specimen 7. According to the skin effect, it can be known that the induced eddy currents 11 have a certain penetration depth on the surface layer of the monitoring area 8 in the gauge section of the fatigue specimen 7. When a discontinuity 9 appears on the surface layer of the monitoring area 8 in the gauge section of the fatigue specimen 7, the discontinuity 9 hinders and changes the flow direction and distribution of the induced eddy currents 11, and the induced eddy currents 11 cause temperature distribution information 12 near the discontinuity 9 on the surface layer of the monitoring area 8 in the gauge section of the fatigue specimen 7.

[0064] See Figure 5 , due to the interaction between the electromagnetic-thermal multi-physical field and the discontinuity 9, the temperature distribution information 12 caused near the discontinuity 9 on the surface layer of the monitoring area 8 in the gauge section of the fatigue specimen 7 can reflect the position, size, orientation and shape information of the discontinuity 9.

[0065] When a discontinuity 9 appears on the surface layer of the monitoring area 8 in the gauge section of the additive manufacturing metal material fatigue specimen 7, the visible thermal image monitoring signal monitored by the device will be different from the visible thermal image monitoring signal obtained before when there is no discontinuity 9 on the surface layer of the monitoring area 8; when the discontinuity 9 on the surface layer of the monitoring area 8 continues to grow and expand, the visible thermal image monitoring signal monitored by the device will change as the discontinuity 9 expands and evolves; when the discontinuity 9 grows and expands to a certain extent, and the defect geometric characteristics of the discontinuity 9 on the surface of the fatigue specimen enable the optical camera module 5 to distinguish, the optical image monitoring signal monitored by the device will be different from the optical image monitoring signal obtained before when there is no discontinuity 9 on the surface layer of the monitoring area 8; when the discontinuity 9 continues to grow and expand on the surface of the fatigue specimen 7, the optical image monitoring signal monitored by the device will change as the discontinuity 9 expands and evolves; all these differences will be synchronously displayed in the electromagnetic-thermal-optical multi-physical field in-situ imaging monitoring result diagram of the monitoring area 8 in the gauge section of the fatigue specimen 7 drawn by the monitoring computer 6; the monitoring computer 6 simultaneously intercepts and saves the visible thermal image monitoring signal and the optical image monitoring signal at the monitoring area 8 in the gauge section of the fatigue specimen 7 obtained at different cycle numbers during the whole process of the fatigue test for the monitoring personnel to observe and evaluate.

[0066] For the verification of the technical implementation feasibility, the technical solutions and embodiments provided by the present invention have been simulated and verified by using the multi-physical field finite element simulation analysis method, and the simulation analysis results are as Figure 5 shown, and the verification results show that the technical solution of this patent proposal is feasible.

[0067] The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention; any ordinary technician in the industry can smoothly implement the present invention as shown in the accompanying drawings of the specification and described above; however, any slight changes, modifications, and equivalent variations made by those skilled in the art within the scope of the technical solution of the present invention by using the technical content disclosed above are all equivalent embodiments of the present invention; at the same time, any equivalent changes, modifications, and evolutions made to the above embodiments based on the essential technology of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. An in-situ imaging monitoring device for fatigue tests of additive manufacturing metal materials, characterized in that: It includes a signal generator (1), a power amplifier (2), an excitation coil (3), an infrared thermal imaging module (4), an optical camera module (5), and a monitoring computer (6); The output end of the signal generator (1) is electrically connected to the input end of the power amplifier (2); The output end of the power amplifier (2) is electrically connected to the input end of the excitation coil (3); The excitation coil (3) is coupled to the monitoring area (8) of the fatigue specimen (7) through an electromagnetic field; The output end of the infrared thermal imaging module (4) is electrically connected to the input end of the monitoring computer (6); The output end of the optical camera module (5) is electrically connected to the input end of the monitoring computer (6); The excitation coil (3) is composed of two coaxially wound toroidal air-core solenoids. The two toroidal air-core solenoids have the same shape, size, number of coil turns, and wire diameter; The two toroidal air-core solenoids of the excitation coil (3) are equidistantly wound around the upper and lower sides of the axial center position of the fatigue specimen (7) and are coaxial with the fatigue specimen (7); The infrared thermal imaging module (4) is composed of four infrared thermal imaging modules. The four infrared thermal imaging modules are equidistantly distributed along the circumferential direction of the fatigue specimen (7). The shooting direction is facing the gauge section monitoring area (8) near the axial center position of the fatigue specimen (7), and the shooting area completely covers the circumferential surface of the fatigue specimen (7) at the monitoring area (8); The optical camera module (5) is composed of four optical imaging modules. The placement positions of the four optical imaging modules are adjacent to the infrared thermal imaging modules. The shooting directions and shooting areas of the four optical imaging modules are the same as those of the infrared thermal imaging modules.

2. The in-situ imaging monitoring device for fatigue test of an additive manufacturing metal material according to claim 1, wherein, The signal generator (1) outputs a short-time pulse excitation periodically.

3. A method for in-situ imaging monitoring of fatigue tests of additive manufacturing metal materials, based on the in-situ imaging monitoring device for fatigue tests of additive manufacturing metal materials described in claim 1 or 2, characterized in that, The method includes the following steps: S1: Before the fatigue test starts, install the fatigue specimen (7) on the fixture (10) of the fatigue testing machine. At the same time, install the in-situ imaging monitoring device for additive manufacturing metal material fatigue test at the gauge section monitoring area (8) of the fatigue specimen (7). Before applying an alternating load to the fatigue specimen (7), perform the first electromagnetic-thermal-optical multi-physical field in-situ imaging on the monitoring area (8); S2: When performing the electromagnetic-thermal-optical multi-physical field in-situ imaging, the signal generator (1) outputs a short-time pulse excitation periodically. After being power-amplified by the power amplifier (2), it drives the excitation coil (3). The short-time pulse current flowing through the excitation coil (3) generates a transient excitation magnetic field inside and outside the two toroidal air-core solenoids. The transient excitation magnetic field is transmitted to the surface layer of the gauge section monitoring area (8) near the axial center position of the fatigue specimen (7) and generates an eddy current (11) through electromagnetic induction. The induced eddy current (11) induces heating of the surface layer of the monitoring area (8) based on the Joule heat effect, causing temperature distribution information (12). The infrared thermal imaging module (4) converts the circumferential surface temperature distribution information (12) of the gauge section monitoring area (8) of the fatigue specimen (7) into a visible thermal image monitoring signal and transmits it to the monitoring computer (6); S3: The optical camera module (5) performs optical imaging on the circumferential surface of the gauge section monitoring area (8) of the fatigue specimen (7) and transmits the converted optical image monitoring signal to the monitoring computer (6); S4: The monitoring computer (6) stores the circumferential surface visible thermal image monitoring signals and optical image monitoring signals at the monitoring area (8) of the gauge section of the fatigue specimen (7) that are received, and draws an in-situ imaging monitoring result graph of the electromagnetic-thermal-optical multi-physical field at the monitoring area (8) of the gauge section of the fatigue specimen (7); S5: The monitoring computer (6) displays the in-situ imaging monitoring result graph of the electromagnetic-thermal-optical multi-physical field at the monitoring area (8) of the gauge section of the fatigue specimen (7) that is drawn on the monitoring display screen in real time for the monitoring personnel to observe and evaluate; S6: During the fatigue test process, starting from the first application of the alternating load to the fatigue specimen (7), the operations of the above S2 to S5 are repeated at every certain number of cycles until the set number of cycles for completing the fatigue test is reached; S7: After the fatigue test is completed, based on the in-situ imaging monitoring results of the electromagnetic-thermal-optical multi-physical field obtained at different numbers of cycles throughout the fatigue test process, the damage and the dynamic evolution law of the damage at the monitoring area (8) of the gauge section of the fatigue specimen (7) are analyzed.

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