Ferromagnetic metal stress and fatigue measurement method and device based on magnetic induction chain

Abstract

The invention relates to a ferromagnetic metal stress and fatigue measurement method and device based on a magnetic induction chain, and the device comprises an external magnetic field generation device, a magnetic induction chain detection device, and a data processing system. The magnetic induction chain detection device is used for detecting the magnetic induction intensity value and the change of the magnetic induction intensity value at a surface detection point, and the data processing system is used for receiving and processing magnetic intensity data, analyzing the stress and fatigue damage condition of the ferromagnetic metal material and monitoring the stress and fatigue state of the ferromagnetic metal material; a magnetic induction chain is excited by an external magnetic field, stress and fatigue damage conditions of a material are observed in real time by monitoring a magnetic induction intensity value and changes of the magnetic induction intensity value, and the method has the advantages of high sensitivity, high reliability, high real-time performance, capability of solving the dispersion problem existing in an existing method and the like, realizes stress and fatigue measurement of ferromagnetic metal, and is suitable for large-scale popularization and application. And an effective stress and fatigue measurement means can be provided for ferromagnetic metal in engineering application.

Description

Technical Field

[0001] The present invention belongs to the field of material science and nondestructive testing technology, and relates to a method and device for measuring stress and fatigue of ferromagnetic metal based on a magnetic induction chain, and in particular to a method and an implementation device for detecting the stress and fatigue state of ferromagnetic materials by using an external magnetic field generating device and a magnetic induction chain detection device. Background Art

[0002] Metal fatigue is a potential major safety hazard in structures. It may cause equipment or structures to fail suddenly when subjected to continuous or repeated stress, leading to serious safety accidents. Fatigue safety accidents are often sudden and unpredictable. Once they occur, they often cause significant casualties and property losses.

[0003] As the most widely used material in engineering, ferromagnetic metals (mainly including iron, nickel and their alloys, etc.) often become the hardest hit areas for fatigue fracture accidents. At present, in order to prevent the occurrence of fatigue failure accidents in various fields, researchers have proposed the SN (σ-N or ε-N) curve that takes into account both elastic and plastic strains. The establishment of the SN curve is the beginning of fatigue life observation and prediction research. Until now, the method of obtaining models and multiple deformations through fatigue test analysis is still a conventional means of observing and predicting material fatigue. Almost all components that need to withstand large cyclic loads for a long time must first undergo SN fatigue test evaluation before they can be put into use.

[0004] Unfortunately, the fatigue prediction models such as the SN curve, which are widely used at present, obtained through a large amount of fatigue test data, have large errors in fatigue life prediction, even exceeding one order of magnitude, due to the large dispersion of factors such as materials, dimensions and loads in actual engineering. In addition, the widely used mechanical parameters are very insensitive to the fatigue development process. Before the cracks appear (accounting for more than 90% of the entire life cycle), there is almost no obvious change. Once the cracks appear, the structure will fail and break quickly, especially in medium and low cycle fatigue.

[0005] In addition, after conducting a post-test on components that were replaced regularly based on the SN curve, it was found that many components that were disassembled due to reaching the replacement cycle still had a certain service life. In addition, in order to reduce the failure risk caused by low prediction accuracy, material fatigue strength design often adopts an overly redundant design strategy. These do not meet the requirements of green development.

[0006] Compared with the macro scale, the current micro-scale technologies such as SEM, TEM, HR-DIC, etc. have been used to observe material fatigue, providing more detailed information, revealing the internal microstructure of the material, the crack propagation path, and the phenomenon of micro crack initiation and expansion to form fracture. By observing the behavior of micro defects such as dislocations, grain boundaries and phase boundaries, we can gain a deep understanding of the changes and evolution of materials during fatigue. And according to the relevant parameters of micro observation, the existing evaluation methods can be modified.

[0007] However, microscopic observation faces many limitations in the measurement of fatigue state of ferromagnetic metals, such as limited observation range, potentially destructive sample preparation process, expensive equipment and complex operation. These factors together make it difficult to apply it in the prediction of fatigue life of ferromagnetic metals. In addition, microscopic observation usually relies on very precise instruments and is performed on carefully prepared samples. However, in actual structures, due to the lack of effective monitoring methods, fatigue failure often manifests as sudden fracture without signs, which makes the promotion of microscopic observation in actual engineering applications challenging. Therefore, there is no report on the actual engineering application of microscopic observation to predict material stress and fatigue life. Summary of the invention

[0008] In view of this, the present invention provides a ferromagnetic metal stress and fatigue measurement method and device based on a magnetic induction chain in order to solve the problems of using the above-mentioned microscopic observation method in the measurement of ferromagnetic metal stress and fatigue state, such as limited observation range, potentially destructive sample preparation process, expensive equipment and complicated operation, and reliance on precision instruments, which makes it difficult to apply it in the prediction of ferromagnetic metal stress and fatigue life.

[0009] In order to achieve the above object, the present invention provides the following technical solutions:

[0010] A ferromagnetic metal stress and fatigue measuring device based on a magnetic induction chain comprises an external magnetic field generating device, a magnetic induction chain detecting device and a data processing system. The external magnetic field generating device is placed on the surface of the ferromagnetic metal to be detected to apply a stable magnetic field. The magnetic induction chain detecting device is used to detect the magnetic induction intensity value and its change at the measuring point on the surface of the ferromagnetic metal. The data processing system is used to receive and process the magnetic intensity data of the magnetic induction chain detecting device, analyze the stress and fatigue damage of the ferromagnetic metal material, and monitor the stress and fatigue state of the ferromagnetic metal material.

[0011] Furthermore, the transmitting unit in the external magnetic field generating device is a magnetic material, preferably a neodymium iron boron magnet, the magnetic induction chain detection device is a magnetic sensor, preferably a linear Hall sensor, the distance between the external magnetic field generating device and the magnetic induction chain detection device is constant, and the external magnetic field generating device and the corresponding magnetic induction chain detection device are respectively placed at both ends of the ferromagnetic metal to be detected.

[0012] The measurement method of the ferromagnetic metal stress and fatigue state measurement device based on magnetic induction chain detection comprises the following steps:

[0013] S1: placing an external magnetic field generating device near the ferromagnetic metal material to be detected, and keeping the external magnetic field generating device stationary during the detection period, so as to apply a stable magnetic field;

[0014] S2: Start the magnetic induction chain detection device, keep the magnetic induction chain detection device still during the detection, keep the distance between the external magnetic field generating device and the magnetic induction chain detection device constant, and continuously monitor the magnetic induction intensity value and its change on the surface of the ferromagnetic metal material to be detected;

[0015] S3: applying an external load to the ferromagnetic metal material, and observing and recording the change of magnetic intensity of the magnetic induction chain in real time when the ferromagnetic metal material is subjected to the external load;

[0016] S4: Analyze the magnetic intensity data obtained in step S3 using a data processing system to obtain the change trend of the magnetic intensity of the magnetic induction chain, the relationship between the change value of the magnetic induction intensity and the stress, and the relationship between the peak-to-peak change of the magnetic intensity and the fatigue life;

[0017] S5: According to the analysis results of step S4, the stress state and fatigue damage of the material are evaluated, and the possible number of fatigue fractures is predicted to achieve early warning before fatigue fracture.

[0018] Furthermore, the main cause of fracture and fatigue of the material under external stress in step S3 is the slip and dislocation of the crystal between atoms, which is manifested by the change of the atomic spacing of the weakest cross-section layer. For ferromagnetic materials, atoms are mainly bound together by metal bonds, so the change of atomic spacing will cause the change of the atomic binding force. In the fatigue process of ferromagnetic materials, when the change of atomic spacing is small, it can be deduced that the change of the average atomic binding force between the metal material layers is approximately linearly related to the change of the average atomic spacing:

[0019]

[0020] Where ΔF C is the average atomic bonding force between layers, is the average interatomic distance change, K C is a constant related to the material. Therefore, it can be seen that in the absence of an external magnetic field, the fracture of ferromagnetic materials is mainly related to the change in the atomic distance. When ferromagnetic materials are subjected to fatigue loads, the atomic distance continues to increase, and the atomic bond fractures that cannot be observed macroscopically will also continue to increase. At this time, the interatomic bonding force will continue to weaken. When the interatomic bonding force is less than the external load, the material will break, and it will manifest as a sudden fracture that is difficult to observe and without signs. The schematic diagram of atomic dislocation is shown in Figure 1As shown. It is certain that the fracture is definitely caused by the fact that the bonding force of the weakest section is insufficient to resist the external load. Therefore, the essence of the fracture failure of the material under external force is the process in which the atomic distance of the weakest section continues to accumulate and increase, and the bonding force continues to weaken until the bonding force is less than the external load.

[0021] The microscopic essence of the magnetism of ferromagnetic metals is the exchange interaction between spin magnetic moment, orbital magnetic moment and electrons; the most complex mechanism is the exchange interaction, which is also the key to the generation of magnetic interaction force between atoms. Like the binding force, it is also directly related to the atomic distance. When the atomic distance changes slightly, it is inferred that the change in the average magnetic force between atoms in the ferromagnetic material layer is approximately linearly related to the change in the average atomic distance:

[0022]

[0023] Where ΔF m is the average magnetic force between atoms in the layer, is the average interatomic distance change, K m is a constant related to the material, and the relationship between the binding force and the magnetic force is obtained as follows:

[0024] ΔF C =KΔF m

[0025] Obviously, magnetic force and binding force exist simultaneously in atoms, and both are functions related to the change of interatomic distance.

[0026] Furthermore, in step S3, the atomic binding force, magnetic interaction force and the relationship between the atomic distance are theoretically derived, specifically: the binding energy is expressed as Coulomb repulsion energy and attraction energy. When the distance between atoms is close, the repulsion between negatively charged electrons is dominant, and the dominant energy is expressed as repulsion energy; when the distance between atoms is far, the main energy is expressed as attraction energy; in the free state, the energy is at the equilibrium point where the repulsion energy and attraction energy are combined to a minimum value;

[0027] In the study, only the tension state of the material starting from the free state was considered, and only the case where the change in the distance between atoms was relatively small was considered;

[0028] From the measurement and simulation images of the electron cloud of the iron atom, it can be seen that the electrons are distributed around the atom in the form of a probability density function of a wave function. According to the representation method in solid state physics (Schrödinger equation), the binding energy is expressed in the form of a wave function:

[0029]

[0030] where R is the distance between atoms, r 12 is the distance between electrons, r b1 and ra2 is the distance between an atom and its neighboring electrons, ψ ab , They are the wave function and conjugate matrix of the electrons that form the binding energy, and e represents the charge distribution between the electrons that form the binding energy and the atoms. Currently, there are many models for the binding energy between iron atoms, such as the localized electron model, the itinerant electron model, and the energy band model. However, the basic forms can all be expressed by the above formula with only minor differences.

[0031] If it is the binding energy between multiple pairs of atoms, equation (1) is changed to the following:

[0032]

[0033] Where R ij is the distance between atoms i and j, r ij is the distance between electrons i and j, r aj and r bi are the distances between atom a and its adjacent electron i and the lengths between atom b and its adjacent electron j, respectively;

[0034] Note that when the material is stretched, its binding energy increases monotonically from the lowest energy point. The average atomic spacing function between the two layers of the stretched cross section of the material (denoted as ) to simplify the equivalent overall wave function:

[0035]

[0036] in In fact, it represents the average Coulomb interaction distance between two layers of atoms; Substituting equation (3) into equation (2), we get equation (4):

[0037]

[0038] Because under other constant conditions, as long as the average interatomic distance is determined There is only one value, and take U C Relative to The derivative of gives:

[0039]

[0040] where F C Represents the average binding force between two layers of atoms;

[0041] By using Taylor series expansion Expand to get:

[0042]

[0043] Among them CC0 ,C C1 and C C2 is a constant;

[0044] Ignoring higher-order terms, we consider only the case where the interatomic distance increases slightly from its lowest energy position, where Relative to Linear change, we get:

[0045]

[0046] in are all constants;

[0047] Therefore, a function of the interatomic distance is used to represent the change in the average interatomic bonding force during tensile fatigue;

[0048] The magnetic interaction is relatively more complicated and is calculated here in the same form as the binding force; the magnetic exchange energy is generated by the exchange interaction between the electrons of two atoms and between the electrons and the nuclei, and is represented by the wave function;

[0049]

[0050] The wave functions of the electrons contributing to the magnetic exchange energy are respectively given by Its conjugate matrix is ​​represented by represents; m represents the combined charge and magnetic moment of electrons and atoms that form magnetic exchange energy;

[0051] For the magnetic exchange energy between multiple pairs of atoms, equation (8) can be written as:

[0052]

[0053] where r ij is the distance between electrons i and j, r bi and r aj are the distances between atom a and its adjacent electron i, and between atom b and its adjacent electron j, respectively;

[0054] For the double-layer atomic structure, we get:

[0055]

[0056] By substituting equation (10) into equation (9), we obtain:

[0057]

[0058] Overline symbol In fact, it represents the equivalent magnetic interaction distance between two layers of atoms; similarly, is the average distance between the atoms in these two layers function; under other constant conditions, once the average distance between layers is determined , It will take a unique value;

[0059] By taking U m exist The derivative on , that is:

[0060]

[0061] where F m represents the average magnetic force between two layers of atoms;

[0062] By using Taylor series expansion Expand to get:

[0063]

[0064] Among them C m0 ,C m1 and C m2 is a constant;

[0065] Again, ignoring higher-order terms, we only consider Relative to The linear change of , we get:

[0066]

[0067] in and is a constant;

[0068] Therefore, it is believed that the average binding force and magnetic interaction force between adjacent atomic layers in ferromagnetic materials are homologous effects, both of which are inversely proportional to the square of the average atomic distance between layers; therefore, When the change is small, The increase of will lead to the decrease of binding force and magnetic force (only considering increased impact);

[0069] When there is an external cyclic load, the force exerted by the load on the two-layer atoms is expressed as f(σ), and the interlayer magnetic force caused by the load is expressed as g(σ); the function form of g(σ) is relatively complicated, and since it is omitted in the subsequent derivation, its specific form is not considered here;

[0070] During cyclic loading, the stress gradually increases to a maximum level and then decreases to zero, repeating the cycle near an intermediate stress value;

[0071] When the initial load is σ m -σ L hour;

[0072] The combined effect of bonding and load is as follows:

[0073] F C0 -f(σ m -σ L ) (15)

[0074] The combined effect of magnetic force and loading is as follows:

[0075] F m0 -g(σ m -σ L ) (16)

[0076] in

[0077] When the initial load is σ m +σ L hour;

[0078] The combined effect of bonding and load is as follows:

[0079] F C1 -f(σ m +σ L ) (17)

[0080] The combined effect of magnetic force and loading is as follows:

[0081] F m1 -g(σ m +σ L ) (18)

[0082] in

[0083] where σ m represents the average force during external cyclic loading, σ L is the fluctuation value of the internal force of the cycle; F C0 When the initial load is σ m -σ L The initial average bonding force inside the material, F C1 When the initial load is σ m +σ L The initial average bonding force inside the material at that time; similarly, F m0 When the initial load is σ m -σ L The initial average magnetic force in the material, F m1 When the initial load is σ m +σ L The initial average magnetic force in the material at the time Denotes the initial load as σ m -σ Lis the initial average atomic distance inside the material, and Indicates that the initial load is σ m +σ L The initial average atomic spacing within the post-material;

[0084] Subtracting equation (15) from equation (17) yields the difference in bond force, which represents the peak-to-peak value of the initial bond force during loading:

[0085]

[0086] Subtracting equation (16) from equation (18) gives the magnetic force difference, which is actually the peak-to-peak value of the initial magnetic force during loading:

[0087]

[0088] Since the diameter of the middle of the specimen is smaller than that of the periphery, fatigue is most likely to occur. It is assumed that the fatigue dislocation occurs between the two layers of atoms in the middle (in fact, there may be more than that, but it can be assumed that the dislocations in the weakest two layers determine the fracture);

[0089] When the initial load is σ m -σ L When considering that the distance between the two layers of atoms changes from their initial equilibrium position ΔR is added. ΔR represents the fatigue dislocation change of the specimen under external cyclic load.

[0090] Then, the combined effect of bonding and loading is as follows:

[0091]

[0092] The combined effect of magnetic force and loading is as follows:

[0093]

[0094] In the formula

[0095] When the initial load is σ m +σ L When considering that the two layers of atoms are moving from their initial equilibrium positions The distance between them increases by ΔR, and The combined effect of bonding force and loading is as follows:

[0096]

[0097] The combined effect of magnetic force and loading is as follows:

[0098]

[0099] In the formula

[0100] The difference obtained by subtracting (21) from (23) represents the actual change in bonding force due to fatigue, which is actually the peak-to-peak value of bonding force when fatigue dislocation occurs during loading:

[0101]

[0102] The difference obtained by subtracting (22) from (24) represents the actual change in magnetic force due to fatigue, which is actually the peak-to-peak value of the magnetic force when fatigue dislocation occurs during loading:

[0103]

[0104] Subtracting equation (25) from equation (19) yields the relationship between the change in fatigue dislocation ΔR and the change in average bonding force during actual loading:

[0105]

[0106] because Ignore the higher-order terms and ignore ΔR in the above equation 2 ; Therefore, equation (27) is simplified to:

[0107]

[0108] Simplifying equation (28) to:

[0109] ΔF C =K C ΔR (29)

[0110] in ΔF C is the average change in the bonding forces between atoms;

[0111] because and It is related to the initial force magnitude and the inherent properties of the material during the loading process. Once the material and loading force are specified, and The average value of has a unique value; given ΔR vs K C The influence of the denominator in is negligible, so k C Approximately a constant, when the material undergoes fatigue dislocation, the change in average bonding force depends only on the change in average interatomic distance;

[0112] Similarly, subtracting equation (26) from equation (20) yields the relationship between the change in fatigue dislocation ΔR and the change in average magnetic force during actual loading:

[0113]

[0114] Simplifying equation (30) to:

[0115]

[0116] Simplifying equation (31) to:

[0117] ΔF m =K m ΔR (32)

[0118] in, Also considered a constant; ΔF m represents the average change in magnetic force; then, when the material undergoes fatigue dislocations, the change in average magnetic force is also related only to the change in average atomic spacing;

[0119] Combining equation (29) and equation (32), we get the relationship between the binding force and the magnetic force:

[0120] ΔF C =KΔF m (33)

[0121] in

[0122] Furthermore, after applying an external magnetic field to the ferromagnetic metal in step S3, a magnetic flux linkage effect is formed inside the ferromagnetic material. This effect is manifested in the metal as the characteristic of magnetic intensity change being transmitted layer by layer. It depends on the interlayer magnetic interaction. These magnetic flux linkages are transmitted layer by layer in the metal, and the magnetic intensity change of each layer of magnetic flux linkage will affect the next layer. The magnetic induction relationship between each layer is as follows: Figure 2 shown.

[0123] Due to the layer-by-layer transmission characteristics of the magnetic flux effect, the change in magnetic intensity at a certain measuring point is actually the cumulative effect of the change in magnetic intensity of each layer before it. Since there is a certain relationship between the change in magnetic intensity of each layer of magnetic flux and the magnetic intensity of the previous layer, this relationship is expressed in the form of a continuous product; therefore, even if the change in magnetic intensity of each layer of magnetic flux is very small, after being transmitted through multiple layers, these tiny changes will be continuously amplified at the measuring point, forming a significant change in magnetic intensity;

[0124]

[0125] As fatigue develops, changes in magnetic intensity will continue to accumulate and manifest themselves macroscopically as a significant amplification of changes in magnetic intensity at the measurement point; this cumulative effect means that even if the value of the applied magnetic intensity remains unchanged, as the magnetic induction intensity is transmitted deeper into the material, the magnetic intensity sensed by each layer will gradually increase. It is worth noting that this amplification effect is not evenly distributed throughout the material. Since changes in atomic spacing mainly occur on the persistent slip band during the fatigue process of the material, it can be considered that this amplification factor corresponds exactly to the number of layers of the persistent slip band. This means that by monitoring the amplification effect of magnetic induction intensity, we can not only understand the microstructural changes inside the material, but also predict the fatigue life and performance of the material.

[0126] Furthermore, the theoretical derivation and amplification of the magnetic linkage effect in step S3 are specifically as follows:

[0127] When an external magnetic field is applied to a ferromagnetic metal, the magnetic induction intensity is transmitted layer by layer along a certain direction due to the (virtual) magnetic interaction between layers. Assuming that the magnetic interaction between layers is the only determining factor for the induction transmission of magnetic field intensity in the magnetic flux chain, and ignoring the magnetic intensity of the external magnetic field transmitted by the air, the relationship between the induced magnetic intensity value after the external magnetic field passes through a layer, the external magnetic intensity value, and the magnetic interaction force between layers is:

[0128] B1=B0·f(F m0 ) (34)

[0129] Where B0 is the external magnetic intensity value, B1 is the induced magnetic intensity value of the first layer, F m0 Interlayer magnetic interaction, f(F m0 ) is a continuous function of the interlayer magnetic interaction force.

[0130] The magnetic intensity of the next layer is induced by the magnetic intensity of the previous layer through the interlayer magnetic interaction force, so:

[0131]

[0132] Where B2 is the induced magnetic intensity value of the second layer, F m1 is the interlayer magnetic interaction of the second layer;

[0133] By analogy, we get:

[0134] B i =B i-1 ·f(F m(i-1) ) (36)

[0135] Among them B i is the induced magnetic intensity value of the i-th layer, F m(i) is the interlayer magnetic interaction of the i-th layer.

[0136] Thus, the induced magnetic intensity value of the nth layer (measurement layer) is obtained as follows:

[0137]

[0138] When the average interatomic distance between layers changes due to stress or fatigue, the magnetic interaction between the layers will change accordingly ΔF mi ; At this time, the induced magnetic intensity value of the nth layer is expressed as:

[0139]

[0140] When ΔF mi When I was very young, I had:

[0141] f(F mi +ΔF mi )≈f(F mi )+f / (F mi )·ΔF mi (39)

[0142] where f / (F mi ) means that the function f is in F mi Substituting the derivative at In the result:

[0143]

[0144] To B n and Taking the logarithm respectively, we get:

[0145]

[0146]

[0147] get:

[0148]

[0149] Simplifying equation (43) yields ΔB n :

[0150]

[0151] Considering that when x is very small, exp(x)≈1+x. Formula (43) is simplified to:

[0152]

[0153] Since ΔF mi The change in the interatomic distance between layers ΔR i Correlation (ΔF mi =K m ΔR i),get:

[0154]

[0155] If the entire material is subjected to uniform force or uniform fatigue, the change in the atomic spacing of each layer tends to be consistent, and the magnetic interaction of each layer inside it will also show similar effects. To simplify the derivation, we simply assume that the change in the atomic spacing of each layer (ΔR i ) are equal, that is, ΔR i =ΔR; and the magnetic interaction function f(F mi ) are also equal, that is, f(F mi )=f(F m ).

[0156] Formula (46) is simplified to:

[0157]

[0158] The same derivation is used to obtain the change in magnetic intensity of any single layer:

[0159]

[0160] Given that changes in atomic spacing during material fatigue mainly occur on persistent slip bands (PSBs), it is believed that this amplification factor n corresponds exactly to the number of PSB layers; as fatigue progresses, the magnetic intensity changes caused by changes in each layer of PSBs will continue to accumulate and manifest themselves macroscopically as a significant amplification of the magnetic intensity changes at the measurement point.

[0161] HR-DIC observations at the microscopic level have revealed that there is a clear linear relationship between the maximum slip strength of PSB during initial cyclic loading, the average value of the slip mark spacing and its 5% highest value distribution and the fatigue strength of the material, indicating that the magnification factor n is also strongly correlated with the fatigue strength of the material.

[0162] Since the distance between atoms does not change much, ΔF C It is also linearly related to ΔR (ΔF C =K c ΔR), substituting the relationship between the interlayer bonding force and the change in the interlayer atomic distance into formula (47), we obtain:

[0163] ΔB n =K B ΔF C (49)

[0164]

[0165] The magnetic intensity ΔB measured by the external Hall sensor H Actually, ΔB n A component of:

[0166] ΔB H =K E ΔB n (50)

[0167] When the measurement distance and environmental factors remain unchanged, K E As a constant, we get:

[0168] ΔB H =K H ΔF C (51)

[0169] Where K H =K E K B .

[0170] Therefore, through the great amplification effect of the magnetic flux caused by the external magnetic strength on the tiny internal changes, the fatigue process of ferromagnetic materials caused by the gradual cumulative weakening of the binding force is observed.

[0171] Further, the specific method for predicting the fatigue fracture time of the material in step S5 is as follows: fatigue tests are performed on all ferromagnetic metals under different stresses using the magnetic induction chain detection method, and the magnetic peak-to-peak value is calculated after the magnetic intensity change value of the metal during the entire fatigue process is obtained, and a curve diagram of the relationship between the magnetic peak-to-peak value and the number of cycles is drawn; the slope of the change of the magnetic peak-to-peak value of each metal specimen with the number of cycles is calculated using the univariate linear fitting of the least squares method; the relationship between the number of fatigue fractures under different stresses and the slope of the change of the magnetic peak-to-peak value is drawn into a scatter plot, and the relationship diagram between the magnetic peak-to-peak value change rate of each specimen and the number of fractures is called the MN curve, and the linear fitting formula of the MN curve is obtained by linear fitting:

[0172]

[0173] where k av is the magnetic intensity peak-to-peak slope, k c is the slope of the MN curve, C is the intercept of the MN curve; where k c =-1.261, C = -0.167, k av Obtained by linear fitting of magnetic intensity variation data;

[0174] The slope k of the linear fit of the peak magnetic intensity at the early stage of the loading cycle of all ferromagnetic metals is av Substitute into the above formula to calculate the fatigue failure life of each metal; calculate the correlation between the calculated fatigue failure life and the actual fatigue failure life of all specimens using the following formula;

[0175]

[0176] Where x is the calculated fatigue failure life and y is the actual fatigue failure life.

[0177] Furthermore, the specific method for material fatigue fracture warning in step S5 is: according to the two changing trends of the peak value of the magnetic intensity of ferromagnetic metal under external fatigue load, two early warning methods before fatigue fracture are proposed; two windows are set, wherein B med is the median value of magnetic drift in the first window, A med , A max , A min are the median, maximum, and minimum values ​​of the magnetic drift in the second window;

[0178] When the number of cycles does not exceed 300,000, starting from the 5000th cycle, the first window is 60 cycles before the current time, and the second window is 1000 cycles before 3000 cycles before the current 60 cycles; take B med -A med + (S1 is a constant obtained through fatigue testing. When the number of cycles does not exceed 300,000, S1 is 4.8, A max -A min Take 0.0132) as the alarm threshold. When the alarm threshold is less than 0 for more than four consecutive times, the alarm is triggered.

[0179] When the number of cycles exceeds 300,000, the first window is 60 cycles before the current time, and the second window is 2,000 cycles before the current 60 cycles and 40,000 cycles before the current time. (Where S2 is a constant obtained through fatigue testing; when the number of cycles exceeds 300,000, S2 is set to 1.2, A max -A min Take 0.0132) as the alarm threshold. When the alarm threshold is greater than 0 for more than four consecutive times, an alarm is triggered.

[0180] The beneficial effects of the present invention are:

[0181] 1. The method for measuring ferromagnetic metal stress and fatigue state by magnetic induction chain detection disclosed in the present invention has the following advantages:

[0182] (1) Since the magnetic induction chain is an induction conduction from one section to another, the magnetic strength is most affected by the change in the atomic spacing between the weakest sections of the metal structure. The material is subjected to external forces and fatigue failure mainly manifests as fractures between the weakest sections. Therefore, the sensitivity of the magnetic induction chain change to stress and fatigue damage is much higher than that of traditional mechanical variables.

[0183] (2) The corresponding relationship between the slope of the peak value of the magnetic intensity of each ferromagnetic metal and the number of cycles and the number of fracture loading is drawn into a scatter plot, and the scatter plot between the peak value change rate of the magnetic intensity and the number of fractures is called the MN curve. The drawn MN curve (where M represents the peak value change rate of the magnetic intensity, and N represents the number of cycles) is not affected by the doping of other elements, and also does not affect the relationship between the peak value slope of the magnetic intensity and the fatigue life. Therefore, compared with the SN curve, the magnetic induction chain method proposed in the present invention is more likely to solve the current dispersion problem when evaluating fatigue life.

[0184] (3) Although the existing microscopic observation method can observe the appearance of cracks before fatigue fracture, it cannot evaluate the overall fatigue state of the structure and cannot be applied to in-service structures. The magnetic induction chain detection method proposed in the present invention can clearly observe the gradual development of fatigue by eliminating the magnetic intensity changes caused by external loading, leaving only the peak value of the magnetic intensity that considers fatigue changes. It also means that the slow change of bonding force during fatigue can be observed.

[0185] (4) Compared with the existing methods that use limited data to predict the fatigue life of ferromagnetic metals with low accuracy, the magnetic induction linkage method used in the present invention achieves accurate prediction of the fatigue life of the material. Only by performing less fatigue loading on the structure based on the method of the present invention, the fatigue life of the ferromagnetic material can be accurately and reliably predicted, thereby greatly improving the prediction efficiency and accuracy. And as the number of cyclic loading increases, the prediction accuracy is also continuously improved.

[0186] (5) There has been no scientific and effective early warning method for ferromagnetic metal fatigue fracture before. The present invention is based on the obvious mutation trend of the magnetic induction chain before the material fracture, and monitors the stress and fatigue state of the ferromagnetic material in real time, so as to achieve effective early warning before the fracture occurs.

[0187] (6) This method is applicable to all ferromagnetic metals, including but not limited to soft magnets, 45 steel, Q235 steel, etc., and has broad application prospects.

[0188] (7) In the design of ferromagnetic metals, the present invention can help optimize the material structure and predict the fatigue life of ferromagnetic metals during the design process, thereby avoiding potential design defects and repairing the materials in a timely manner. In addition, compared with traditional structural detection methods, the present invention can non-destructively detect the fatigue state of metal structures, timely discover and warn of potential fracture risks, and ensure the safety and reliability of the structure.

[0189] 2. The present invention discloses a method for measuring the stress and fatigue state of ferromagnetic metals by means of magnetic induction chain detection. A well-designed external magnetic field device (which remains stationary during the process) is attached to the surface of the ferromagnetic metal to magnetize the entire ferromagnetic metal in a non-invasive manner, thereby forming a continuous and sensitive magnetic induction chain inside the structure. The stress change and fatigue state of the structure are reflected by detecting the magnetic intensity value and change of the magnetic induction chain of the metal.

[0190] Under an external magnetic field, when the ferromagnetic structure is subjected to external stress and fatigue load, its internal microscopic defects will gradually develop, resulting in the rearrangement of the internal magnetic domains and subtle changes in the magnetic field strength. The magnetic induction chain will have a great amplification effect on the internal micro changes as the metal continues to slip under the external load, and it will be manifested as a significant amplification of the change in magnetic intensity at the measurement point on a macro scale. In addition, the change in the magnetic intensity of this magnetic chain actually reflects the change or redistribution of the internal binding force of the material. Therefore, the change in magnetic intensity detected by the magnetic induction chain detection device can reflect the change in binding force and realize the measurement of fatigue state.

[0191] The magnetic induction intensity transfer phenomenon and its amplification effect of ferromagnetic materials under the action of an external magnetic field provide us with a new perspective to observe and understand the stress changes and fatigue processes of materials. By monitoring the changes in magnetic induction intensity, we can indirectly understand the microstructural changes inside the material, and then predict the stress state, fatigue performance and remaining life of the material. The advantages of this method are its non-destructive, real-time and high sensitivity, which provides new possibilities and opportunities for research and application in the field of materials science and engineering. Based on magnetic induction chain detection, it is possible to achieve accurate quantitative evaluation of stress and fatigue damage of ferromagnetic structures, fatigue life estimation and early warning before fatigue fracture. This method has the advantages of high sensitivity, strong reliability, easy digital output, and the ability to solve the problem of material dispersion, and realizes the effective observation of the fatigue state of ferromagnetic metals.

[0192] 3. The method for measuring the stress and fatigue state of ferromagnetic metals through magnetic induction chain detection disclosed in the present invention utilizes an external magnetic field to excite the magnetic induction chain, and monitors the fatigue damage of the material in real time by monitoring the changes in the magnetic induction chain. It has the advantages of high sensitivity, strong reliability, and strong real-time performance, and can solve the dispersion problem existing in the existing methods. It realizes the stress and fatigue measurement of ferromagnetic metals and can provide an effective stress and fatigue measurement method for ferromagnetic metals in engineering applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0193] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:

[0194] Figure 1 It is a schematic diagram of interatomic dislocation of the present invention;

[0195] Figure 2 This is a schematic diagram of the relationship between the interlayer induced magnetic intensity values ​​of the present invention;

[0196] Figure 3 It is a diagram of the detection device of the present invention and a diagram of the internal magnetic induction line distribution and magnetic domain orientation (front view);

[0197] Figure 4 It is a diagram of the detection device of the present invention and a diagram of the internal magnetic induction line distribution and magnetic domain orientation (side view);

[0198] Figure 5 (a) is a comparison chart of displacement and magnetic intensity change trends at 385Mpa. Figure 5 (b) is a comparison chart of the peak-to-peak displacement and peak-to-peak magnetic intensity trends at 385 MPa; Figure 5 (c) is a comparison chart of displacement and magnetic intensity change trends at 395Mpa. Figure 5 (d) is a comparison chart of the peak-to-peak displacement and peak-to-peak magnetic intensity trends at 395 MPa; Figure 5 (e) is a comparison chart of displacement and magnetic intensity change trends at 425Mpa. Figure 5 (f) is a comparison chart of the peak-to-peak displacement and peak-to-peak magnetic intensity trends at 425 MPa;

[0199] Figure 6 (a) is a comparison diagram of the MN curve and the SN curve based on magnetic induction linkage. Figure 6 (b) is a comparison diagram of the logarithmic MN curve and SN curve based on magnetic induction linkage;

[0200] Figure 7 This is a diagram showing the fatigue prediction and analysis of ferromagnetic materials of the present invention;

[0201] Figure 8 This is a diagram for analyzing the fatigue prediction effect of the ferromagnetic material of the present invention;

[0202] Fig. 9 This is a diagram of the fatigue prediction method of ferromagnetic materials of the present invention;

[0203] Fig.10 The figure is a distribution curve of the magnetic strength value and stress change of the ferromagnetic metal of the present invention. DETAILED DESCRIPTION

[0204] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0205] like Figure 3 and Figure 4 The ferromagnetic metal stress and fatigue measuring device shown is based on a magnetic induction chain, comprising an external magnetic field generating device, a magnetic induction chain detection device and a data processing system, wherein the external magnetic field generating device is placed on the surface of the ferromagnetic metal to be detected to apply a stable magnetic field, the magnetic induction chain detection device is used to detect the magnetic induction intensity value and its change at the measuring point on the surface of the ferromagnetic metal, and the data processing system is used to receive and process the magnetic intensity data of the magnetic induction chain detection device, analyze the stress and fatigue damage of the ferromagnetic metal material, and monitor the stress and fatigue state of the ferromagnetic metal material. The transmitting unit in the external magnetic field generating device is a magnetic material, preferably a neodymium iron boron magnet, the magnetic induction chain detection device is a magnetic sensor, preferably a linear Hall sensor, the distance between the external magnetic field generating device and the magnetic induction chain detection device is constant, and the linear Hall sensor and the corresponding neodymium iron boron magnet are respectively placed at both ends of the ferromagnetic metal to be detected.

[0206] The measurement method of the ferromagnetic metal stress and fatigue state measurement device based on magnetic induction chain detection comprises the following steps:

[0207] S1: placing an external magnetic field generating device near the ferromagnetic metal material to be detected, and keeping the external magnetic field generating device stationary during the detection period to apply a stable magnetic field; the transmitting unit in the external magnetic field generating device is a magnetic material, preferably a neodymium iron boron magnet;

[0208] S2: starting the magnetic induction chain detection device, the magnetic induction chain detection device remains stationary during the detection period, the distance between the external magnetic field generating device and the magnetic induction chain detection device remains constant, and the magnetic induction intensity on the surface of the ferromagnetic metal material to be detected is continuously detected; the magnetic induction chain detection device is a magnetic sensor, preferably a linear Hall sensor;

[0209] S3: applying an external load to the ferromagnetic metal material, and observing and recording the change of magnetic intensity of the magnetic induction chain in real time when the ferromagnetic metal material is subjected to the external fatigue load;

[0210] S4: Analyze the magnetic intensity data obtained in step S3 using a data processing system to obtain the change trend of the magnetic intensity of the magnetic induction chain, the relationship between the change of the magnetic induction intensity value and the stress, and the relationship between the peak-to-peak change of the magnetic intensity and the fatigue life;

[0211] S5: According to the analysis results of step S4, the stress state and fatigue damage of the material are evaluated, and the possible fatigue fracture time is predicted to achieve early warning before fatigue fracture.

[0212] Among them, (1) calibration device: construct and calibrate the external magnetic field generating device to ensure that it can generate a stable and uniform magnetic field in the specified area. At the same time, assemble and calibrate the magnetic induction chain detection device, which contains a high-precision magnetic induction sensor array (such as Hall sensor). The magnetic induction chain detection device and the external magnetic field generating device are separated by a certain distance from the ferromagnetic metal to accurately capture the magnetic field changes. Finally, build a data processing system that integrates data acquisition, analysis and storage to prepare for subsequent data processing and analysis.

[0213] (2) Fix the external magnetic field generator: Fix the ferromagnetic material, demagnetize the material, and then place the external magnetic field generator near the ferromagnetic material to be tested and keep it still. Adjust the magnetic field strength to the preset value and keep it constant to establish the basis of the testing environment. Ensure that all measurements are performed under uniform and stable magnetic field conditions to improve the accuracy and reliability of the data.

[0214] (3) Real-time detection of magnetic induction chain detection device: Fix the magnetic induction chain detection device and keep it still. Start the magnetic induction chain detection device. When the ferromagnetic material is subjected to an external load, the magnetic induction intensity on the surface of the ferromagnetic material is continuously and non-contactly monitored in real time. The sensor array records the changes in the magnetic field at the measuring points on the surface of the material in real time. These changes are closely related to the stress and fatigue state and the change in the bonding force inside the material. The monitoring process ensures that there is no interference from the external magnetic field to ensure the purity of the data.

[0215] (4) Data transmission and analysis: The data collected by the magnetic induction chain detection device is transmitted to the data processing system in real time. The system first cleans the data to remove noise and outliers, and then uses a preset algorithm to perform in-depth analysis on the cleaned data. The focus is on analyzing the change trend of the magnetic induction chain, focusing on the relationship between the change in magnetic induction intensity value and stress, the relationship between the peak-to-peak change of magnetic strength and the fatigue state, and the mapping relationship between the average change rate of magnetic strength peak-to-peak and the final fatigue life. The corresponding relationship between the slope of the peak-to-peak value of the magnetic strength of each ferromagnetic metal and the number of fracture loadings is plotted as a scatter plot, and the scatter plot between the peak-to-peak change rate of magnetic strength and the number of fractures is called the MN curve (where M represents the peak-to-peak change rate of magnetic strength, and N represents the number of cycles), which solves the order of magnitude dispersion problem existing in existing methods.

[0216] (5) Evaluation and feedback based on the analysis results of magnetic induction chain changes: Based on the analysis results of the data processing system, the current stress state and fatigue damage degree of the ferromagnetic material are evaluated. Detailed evaluation results are provided, including magnetic intensity value change and stress distribution curve, material fatigue damage curve based on magnetic intensity peak-peak change, material fatigue life evaluation table and material fracture failure warning information. Based on the evaluation results, maintenance suggestions and warning information are provided in a timely manner to guide subsequent material use or maintenance decisions. At the same time, the monitoring and evaluation model is continuously optimized to improve detection accuracy and efficiency.

[0217] Specific method for fatigue life prediction: First, fatigue tests are performed on all ferromagnetic metals under different stresses using the magnetic induction chain detection method. After obtaining the magnetic intensity change value of the metal during the entire fatigue process, its magnetic intensity peak-to-peak value is calculated, and a curve chart showing the relationship between the magnetic intensity peak-to-peak value and the number of cycles is drawn. The slope of the change in the magnetic intensity peak-to-peak value of each metal specimen with the number of cycles is calculated using the univariate linear fitting method of the least squares method. The relationship between the number of fatigue fractures under different stresses and the slope of the change in the magnetic intensity peak-to-peak value is plotted as a scatter plot. We call the relationship between the change rate of the magnetic intensity peak-to-peak value and the number of fractures for each specimen the MN curve. The linear fitting formula for the MN curve is obtained by linear fitting:

[0218]

[0219] where k av is the magnetic intensity peak-to-peak slope, k c is the slope of the MN curve, and C is the intercept of the MN curve. c =-1.261, C =-0.167. av Obtained by linear fitting of magnetic intensity variation data.

[0220] The slope k of the linear fit of the peak-to-peak magnetic intensity of all ferromagnetic metals in the early stage of the loading cycle (5%, 6%, 7%, 8%, 9%, 10%, 20%, 30%, 40%, 50%, 60% of the fatigue failure life) is av Substitute into the above formula to calculate the fatigue failure life of each metal. Then use the following formula to calculate the correlation between the calculated fatigue failure life and the actual fatigue failure life of all specimens.

[0221]

[0222] Where x is the calculated fatigue failure life, and y is the actual fatigue failure life. It can be concluded that the correlation between the fatigue life calculated by 5%, 6%, 7%, 8%, 9%, 10%, 20%, 30%, 40%, 50%, and 60% before cyclic loading and the actual life is 0.737, 0.763, 0.834, 0.886, 0.907, 0.912, 0.961, 0.977, 0.986, 0.993, and 0.994, respectively.

[0223] In this regard, in actual application, the slope k obtained by linear fitting between the peak value of magnetic intensity and the number of cycles in early fatigue cycle loading can be used. av A correlation table is established between the actual failure life and the fatigue life of the next new metal specimen or in-service structure, as shown in Table 1. When the fatigue life of the next new metal specimen or in-service structure needs to be evaluated, the new specimen is subjected to a small amount of cyclic loading using the magnetic induction chain detection method, or the magnetic induction chain detection device is installed on the structure to be tested and operated for a period of time. The magnetic intensity peak-to-peak slope k is fitted according to the measured magnetic induction chain magnetic intensity. av The fatigue life value is determined by comparing it with the correlation table obtained from the test. av Values ​​are constantly revised, allowing for a more accurate assessment of the specimen or structure.

[0224] Table 1 Correlation between the peak slope of magnetic intensity and actual fatigue life at different cyclic loading stages

[0225]

[0226] When predicting the fatigue life of a new ferromagnetic material or structure, the magnetic induction linkage method can be used to apply less fatigue loading to it, and then the actual fatigue life can be determined with high accuracy by looking up the table. The number of fatigue loadings can also be appropriately increased to continuously improve the prediction accuracy.

[0227] Specific methods for early warning of fatigue fracture:

[0228] According to the two changing trends of the peak value of magnetic intensity of ferromagnetic metal under external fatigue load, two early warning methods before fatigue fracture are proposed. Two windows are set up, and the specific method steps are as follows: Fig. 9 As shown, B med is the median value of magnetic drift in the first window, A med , A max , A min are the median, maximum, and minimum values ​​of the magnetic drift in the second window.

[0229] When the number of cycles does not exceed 300,000, starting from the 5000th cycle, the first window is 60 cycles before the current time, and the second window is 1000 cycles before 3000 cycles before the current 60 cycles.med -A med + (Where S1 is a constant obtained through fatigue testing. When the number of cycles does not exceed 300,000 times, S1 is 4.8, A max -A min Take 0.0132) as the alarm threshold. When the alarm threshold is less than 0 for more than four consecutive times, an alarm is triggered.

[0230] Once the number of cycles exceeds 300,000, the first window is 60 cycles before the current time, and the second window is 2,000 cycles before the current 60 cycles and 40,000 cycles before the current time. (Where S2 is a constant obtained through fatigue testing. When the number of cycles exceeds 300,000, S2 is 1.2, A max -A min Take 0.0132) as the alarm threshold. When the alarm threshold is greater than 0 for more than four consecutive times, an alarm is triggered.

[0231] Specific method of stress detection:

[0232] Based on the close relationship between the magnetic intensity value and stress state of ferromagnetic materials under an external magnetic field, the magnetic intensity measured by the flux detection device under external stress is compared with the magnetic intensity when the stress is zero, and then the magnitude of the structural stress is calculated to determine its stress state.

[0233] Since the change of magnetic intensity of ferromagnetic materials under external force is related to the change of stress, when the steel bar is strained, the magnetic induction intensity of the magnetic induction chain detection device also changes. Fig.10 As shown in the figure, the force-magnetic coupling formula for ferromagnetic materials can be established based on this phenomenon. Therefore, the force-magnetic coupling relationship of the magnetic induction chain detection device is calibrated on this basis.

[0234] When it is necessary to evaluate the stress state of a new metal specimen or an in-service structure, the calibrated magnetic induction chain detection device is installed on the ferromagnetic material. First, the magnetic induction intensity value when the stress is zero is measured. When the stress and strain of the material change, the magnetic properties of the material will also change. At this time, the magnetic induction intensity value under different forces measured by the calibrated magnetic induction chain detection device can be used, and compared with the magnetic intensity value when the stress is zero, the stress of the structure can be calculated and the stress state of the structure can be determined.

[0235] Implementation Effect

[0236] ① Stronger sensitivity than traditional mechanical variables:

[0237] The magnetic intensity data collected by the magnetic induction chain detection device under different fatigue loads are extracted, and the magnetic intensity value of each cycle is subtracted from the initial magnetic intensity value and divided by the initial magnetic intensity value to obtain the magnetic intensity change rate data under different fatigue loads. The displacement data under different fatigue loads collected by the extraction system are extracted, and the displacement of each cycle is subtracted from the initial displacement and divided by the initial magnetic intensity to obtain the strain under different fatigue loads.

[0238] In order to remove the change in magnetic flux density caused by loading, the change in magnetic flux density caused by fatigue during cyclic loading is directly observed. We obtain the peak-to-peak value of magnetic flux density by subtracting the valley value of magnetic flux density from the peak value of magnetic flux density under fatigue load, and obtain the peak-to-peak value of displacement by subtracting the peak value of displacement from the valley value. The relationship between the rate of change of magnetic flux density, strain, peak-to-peak value of magnetic flux density and peak-to-peak value of displacement under different fatigue loads and the number of cycles is plotted as follows: Figure 5 shown. Figure 5 (b) is a comparison chart of the peak-to-peak displacement and peak-to-peak magnetic intensity trends at 385 MPa; Figure 5 (c) is a comparison chart of displacement and magnetic intensity change trends at 395Mpa. Figure 5 (d) is a comparison chart of the peak-to-peak displacement and peak-to-peak magnetic intensity trends at 395 MPa; Figure 5 (e) is a comparison chart of displacement and magnetic intensity change trends at 425Mpa. Figure 5 (f) is a comparison chart of the peak-to-peak displacement and peak-to-peak magnetic intensity trends at 425 MPa;

[0239] It can be seen from the figure that compared with the slight changes in the peak-to-peak values ​​of strain and displacement during the entire fatigue process, the change rate of magnetic intensity and the peak-to-peak value of magnetic intensity change very obviously. With the increase in the number of cycles, it can be observed that the rate of change of magnetic intensity of the flux linkage has a significant gradual decrease. A long time before fatigue fracture, the rapid decrease in the rate of change of magnetic intensity can be observed again, which is significantly earlier than the time when the strain changes rapidly. The peak-to-peak value of magnetic intensity also shows a significant upward trend with the increase in the number of cyclic loading, and it can be seen from the figure that the peak-to-peak value of magnetic intensity before fracture changes significantly earlier than the peak-to-peak value of displacement. Obviously, the sensitivity of magnetic intensity to fatigue changes is much greater than the sensitivity of mechanical quantities to fatigue changes. It also further verifies the effectiveness of the method of detecting the fatigue state of ferromagnetic metals based on magnetic induction chains.

[0240] ②Solve the order of magnitude dispersion problem of existing methods

[0241] A linear fit is performed on the curve of each ferromagnetic metal displacement peak-to-peak value changing with the number of cycles, and the corresponding relationship between the slope of each metal peak-to-peak value changing with the number of cycles and the number of fracture loadings is drawn into a scatter plot, a SN curve is drawn, and the corresponding 95% confidence interval and prediction interval are fitted.

[0242] In a similar way, the slope of the peak value of the magnetic strength of each ferromagnetic metal with the number of cycles and the corresponding relationship between the number of fracture loadings are plotted as a scatter plot, called the MN curve, and the corresponding 95% confidence interval and prediction interval are fitted as follows: Figure 6 shown. Figure 6 (a) is a comparison diagram of the MN curve and the SN curve based on magnetic induction linkage. Figure 6 (b) is a comparison diagram of the logarithmic MN curve and SN curve based on magnetic induction linkage;

[0243] It can be seen that the fitted magnetic intensity peak-to-peak slope is highly correlated with the scatter distribution of fracture times, with a fitting degree of up to 0.956, which is much larger than the fitting degree of 0.796 of the SN curve for the stress scatter distribution.

[0244] The logarithms of the displacement peak-to-peak slope and the magnetic intensity peak-to-peak slope were taken respectively, and their corresponding relationships with the number of fracture loadings were plotted as scatter plots to obtain the LogS-N curve and the LogM-N curve.

[0245] It can be found that the fitting degree of the LogS-N curve is 0.812, while the fitting degree of the LogM-N curve is as high as 0.974. Therefore, the order of magnitude dispersion problem of SN may be solved by the MN curve.

[0246] ③Fatigue life prediction effect:

[0247] Using the fatigue prediction method adopted by the present invention, it is found that the correlation between the fatigue life calculated by using only the peak value data of the magnetic intensity before 9% of the cyclic loading and the actual life can reach 0.907. The correlation between the estimated life and the actual life is as follows Figure 7 As shown. However, due to the large dispersion caused by material doping, specimen processing, load differences, etc., there will be a large error in the fatigue life assessment of a new component using the SN curve. The correlation between its stress and fatigue life is only -0.73. The effect achieved by the magnetic induction chain method is far better than the SN curve, and as the data increases, the peak-to-peak change rate of magnetic intensity is constantly being revised. The correlation between the fatigue life and the final life estimated by it is also increasing and approaching 1, and the prediction accuracy is also constantly improving.

[0248] ④Fatigue fracture warning effect:

[0249] We analyzed the warning effect by using the early warning method based on magnetic induction chain and found that when this method is used to warn ferromagnetic metals, when the number of fatigue cycle fractures is less than 300,000 times, the residual life of the early warning is 860-3570 times, and the corresponding proportion of the residual life to the total fatigue life is 1.64%-3.28%. When the number of cycles is greater than 300,000 times, the residual life of the early warning is 1700-38540 times, and the corresponding proportion is 0.04%-7.54%. The prediction effect is as follows Figure 8 Therefore, it is entirely possible to monitor the fatigue state of ferromagnetic materials through the magnetic induction chain method and provide effective early warning before fracture occurs.

Claims

1. A ferromagnetic metal stress and fatigue measurement device based on a magnetic induction chain, characterized in that: It includes an external magnetic field generating device, a magnetic induction chain detection device and a data processing system. The external magnetic field generating device is placed on the surface of the ferromagnetic metal to be detected to apply a stable magnetic field. The magnetic induction chain detection device is used to detect the magnetic induction intensity value and its change at the measuring point on the ferromagnetic metal surface. The data processing system is used to receive and process the magnetic induction intensity value and its change of the magnetic induction chain detection device, analyze the stress and fatigue damage of the ferromagnetic metal material, and monitor the stress and fatigue state of the ferromagnetic metal material.

2. The ferromagnetic metal stress and fatigue measuring device according to claim 1, characterized in that: The transmitting unit in the external magnetic field generating device is a magnetic material, preferably a neodymium iron boron magnet, the magnetic induction chain detection device is a magnetic sensor, preferably a linear Hall sensor, the distance between the external magnetic field generating device and the magnetic induction chain detection device is constant, and the external magnetic field generating device and the corresponding magnetic induction chain detection device are respectively placed at both ends of the ferromagnetic metal to be detected.

3. A detection method based on the ferromagnetic metal stress and fatigue measurement device according to any one of claims 1 to 2, characterized in that: The following steps are involved: S1: placing an external magnetic field generating device near the ferromagnetic metal material to be detected, and keeping the external magnetic field generating device stationary during the detection period, so as to apply a stable magnetic field; S2: Start the magnetic induction chain detection device, keep the magnetic induction chain detection device still during the detection period, keep the distance between the external magnetic field generating device and the magnetic induction chain detection device constant, and continuously monitor the magnetic induction intensity value and its change on the surface of the ferromagnetic metal material to be detected; S3: applying an external load to the ferromagnetic metal material, and observing and recording the magnetic induction chain magnetic intensity value and its change in real time during the process of the ferromagnetic metal material being subjected to the external load; S4: Analyze the magnetic intensity data obtained in step S3 using a data processing system to obtain the magnetic intensity change trend of the magnetic induction chain, the relationship between the magnetic induction intensity value and the stress, and the relationship between the peak-to-peak change of the magnetic intensity and the fatigue life; S5: According to the analysis results of step S4, the stress state and fatigue damage of the material are evaluated, and the possible fatigue fracture time is predicted to achieve early warning before fatigue fracture.

4. The detection method of the ferromagnetic metal stress and fatigue measurement device as claimed in claim 3, characterized in that: The main cause of fracture and fatigue of materials under external stress is the slip and dislocation of crystals between atoms, which is manifested by the change of atomic spacing in the weakest cross-section layer. For ferromagnetic materials in step S3, atoms are mainly bound together by metal bonds, so the change of atomic spacing will cause the change of interatomic binding force. In the process of ferromagnetic materials under external stress and fatigue load, when the change of atomic spacing is small, it is deduced that the change of average atomic binding force between metal material layers is linearly correlated with the change of average atomic spacing: Where ΔF C is the average atomic bonding force between layers, is the average interatomic distance change, K C is a constant related to the material; The microscopic essence of the magnetism of ferromagnetic metals is the exchange interaction between spin magnetic moment, orbital magnetic moment and electrons. in The most complex mechanism is the exchange interaction, which is also the key to the generation of magnetic interaction between atoms. Like the binding force, it is also directly related to the atomic distance. When the atomic distance changes slightly, the linear relationship between the change in the average magnetic force between atoms in the ferromagnetic material layer and the change in the average atomic distance is deduced as follows: Where ΔF m is the average magnetic force between atoms in the layer, is the average interatomic distance change, K m is a constant related to the material, and the relationship between the binding force and the magnetic force is obtained as follows: ΔF C =KΔF m Obviously, magnetic force and binding force exist simultaneously in atoms, and both are functions related to the change of interatomic distance.

5. The detection method of the ferromagnetic metal stress and fatigue measurement device as claimed in claim 4, characterized in that: In step S3, the atomic binding force, magnetic interaction force and the relationship between the atomic distance are theoretically derived, specifically: the binding energy is expressed as Coulomb repulsion energy and attraction energy. When the distance between atoms is close, the repulsion between negatively charged electrons is dominant, and the dominant energy is expressed as repulsion energy. When the distance between atoms is far, the main energy is attractive energy; in the free state, the energy is at the equilibrium point where the combined value of repulsive energy and attractive energy is the minimum; Only the state of tension of the material starting from the free state is considered, and only the case where the change in the distance between atoms is relatively small is considered; From the measurement and simulation images of the electron cloud of the iron atom, it can be seen that the electrons are distributed around the atom in the form of a probability density function of a wave function. According to the representation method in solid state physics (Schrödinger equation), the binding energy is expressed in the form of a wave function: where R is the distance between atoms, r 12 is the distance between electrons, r b1 and r a2 is the distance between an atom and its neighboring electrons, ψ ab , They are the wave function and conjugate matrix of the electrons that form the binding energy, and e represents the charge distribution between the electrons that form the binding energy and the atoms; If it is the binding energy between multiple pairs of atoms, equation (1) is changed to the following: Where R ij is the distance between atoms i and j, r ij is the distance between electrons i and j, r aj and r bi are the distances between atom a and its adjacent electron i and between atom b and its adjacent electron j, respectively; The average atomic spacing function between the two layers of the material tensile cross section is used (denoted as ) to simplify the equivalent overall wave function: in In fact, it represents the average Coulomb interaction distance between two layers of atoms; Substituting equation (3) into equation (2), we get equation (4): Because under other constant conditions, as long as the average interatomic distance is determined There is only one value, and take U C Relative to The derivative of gives: where F C Represents the average binding force between two layers of atoms; By using Taylor series expansion Expand to get: Among them C C0 ,C C1 and C C2 is a constant; Ignoring higher-order terms, we consider only the case where the interatomic distance increases slightly from its lowest energy position, where Relative to Linear change, we get: in are all constants; Therefore, a function of the interatomic distance is used to represent the change in the average interatomic bonding force during tensile fatigue; The magnetic interaction is relatively more complicated and is calculated here in the same form as the binding force; the magnetic exchange energy is generated by the exchange interaction between the electrons of two atoms and between the electrons and the nuclei, and is represented by the wave function; The wave functions of the electrons contributing to the magnetic exchange energy are respectively given by Its conjugate matrix is ​​represented by represents; m represents the combined charge and magnetic moment of electrons and atoms that form magnetic exchange energy; For the magnetic exchange energy between multiple pairs of atoms, equation (8) can be written as: where r ij is the distance between electrons i and j, r bi and r aj are the distances between atom a and its adjacent electron i, and between atom b and its adjacent electron j, respectively; For the double-layer atomic structure, we get: By substituting equation (10) into equation (9), we obtain: Overline symbol In fact, it represents the equivalent magnetic interaction distance between two layers of atoms; similarly, is the average distance between the atoms in these two layers function; under other constant conditions, once the average distance between layers is determined It will take a unique value; By taking U m exist The derivative on , that is: where F m represents the average magnetic force between two layers of atoms; By using Taylor series expansion Expand to get: Among them C m0 ,C m1 and C m2 is a constant; Again, ignoring higher-order terms, we only consider Relative to The linear change of , we get: in and is a constant; Therefore, it is believed that the average binding force and magnetic interaction force between adjacent atomic layers in ferromagnetic materials are homologous effects, both of which are inversely proportional to the square of the average atomic distance between layers; therefore, When the change is small, The increase of will lead to the decrease of binding force and magnetic force (only considering increased impact); When there is an external cyclic load, the force exerted by the load on the two-layer atoms is expressed as f(σ), and the interlayer magnetic force caused by the load is expressed as g(σ); the function form of g(σ) is relatively complicated, and since it is omitted in the subsequent derivation, its specific form is not considered here; During cyclic loading, the stress gradually increases to a maximum level and then decreases to zero, repeating the cycle near an intermediate stress value; When the initial load is σ m -σ L hour; The combined effect of bonding and load is as follows: F C0 -f(s m -s L ) (15) The combined effect of magnetic force and loading is as follows: F m0 -g(s m -s L ) (16) in When the initial load is σ m +σ L hour; The combined effect of bonding and load is as follows: F C1 -f(s m +s L ) (17) The combined effect of magnetic force and loading is as follows: F m1 -g(s m +s L ) (18) among them where σ m represents the average force during external cyclic loading, σ L is the fluctuation value of the internal force of the cycle; F C0 When the initial load is σ m -σ L The initial average bonding force inside the material, F C1 When the initial load is σ m +σ L The initial average bonding force inside the material at that time; similarly, F m0 When the initial load is σ m -σ L The initial average magnetic force in the material, F m1 When the initial load is σ m +σ L The initial average magnetic force in the material at Denotes the initial load as σ m -σ L is the initial average atomic distance inside the material, and Indicates that the initial load is σ m +σ L The initial average atomic spacing within the post-material; Subtracting equation (15) from equation (17) yields the difference in bond force, which represents the peak-to-peak value of the initial bond force during loading: Subtracting equation (16) from equation (18) gives the magnetic force difference, which is actually the peak-to-peak value of the initial magnetic force during loading: Since the diameter in the middle of the specimen is smaller compared to the periphery, fatigue is most likely to occur, assuming that fatigue dislocations occur between the two layers of atoms in the middle; When the initial load is σ m -σ L When considering that the distance between the two layers of atoms changes from their initial equilibrium position ΔR is added; ΔR represents the fatigue dislocation change of the specimen under external cyclic load. Then, the combined effect of bonding and loading is as follows: The combined effect of magnetic force and loading is as follows: In the formula When the initial load is σ m +σ L When considering that the two layers of atoms are moving from their initial equilibrium positions The distance between them increases by ΔR, and The combined effect of bonding force and loading is as follows: The combined effect of magnetic force and loading is as follows: In the formula The difference obtained by subtracting (21) from (23) represents the actual change in bonding force due to fatigue, which is actually the peak-to-peak value of bonding force when fatigue dislocation occurs during loading: The difference obtained by subtracting (22) from (24) represents the actual change in magnetic force due to fatigue, which is actually the peak-to-peak value of the magnetic force when fatigue dislocation occurs during loading: Subtracting equation (25) from equation (19) yields the relationship between the change in fatigue dislocation ΔR and the change in average bonding force during actual loading: because Ignore the higher-order terms and ignore ΔR in the above equation 2 ; Therefore, equation (27) is simplified to: Simplifying equation (28) to: ΔF C =K C ΔR (29) in ΔF C is the average change in the bonding forces between atoms; because and It is related to the initial force magnitude and the inherent properties of the material during the loading process. Once the material and loading force are specified, and The average value of has a unique value; given ΔR vs K C The influence of the denominator in is negligible, so k C Approximately a constant, when the material undergoes fatigue dislocation, the change in average bonding force depends only on the change in average interatomic distance; Similarly, subtracting equation (26) from equation (20) yields the relationship between the change in fatigue dislocation ΔR and the change in average magnetic force during actual loading: Simplifying equation (30) to: Simplifying equation (31) to: ΔF m =K m ΔR (32) in, Also considered a constant; ΔF m represents the average change in magnetic force; then, when the material undergoes fatigue dislocations, the change in average magnetic force is also related only to the change in average atomic spacing; Combining equation (29) and equation (32), we get the relationship between the binding force and the magnetic force: ΔF C =KΔF m (33) in 6. The detection method of the ferromagnetic metal stress and fatigue measurement device as claimed in claim 5, characterized in that: After applying an external magnetic field to the ferromagnetic metal in step S3, a magnetic flux linkage effect is formed inside the ferromagnetic material. This effect is manifested in the metal as a layer-by-layer transmission of magnetic intensity changes. Relying on the interlayer magnetic interaction, these magnetic flux linkages are transmitted layer by layer in the metal, and the magnetic intensity changes of each layer of magnetic flux linkages will affect the next layer. Due to the layer-by-layer transmission characteristics of the magnetic flux effect, the change in magnetic intensity at a certain measuring point is actually the cumulative effect of the change in magnetic intensity of each layer before it. Since there is a certain relationship between the change in magnetic intensity of each layer of magnetic flux and the magnetic intensity of the previous layer, this relationship is expressed in the form of a continuous product; therefore, even if the change in magnetic intensity of each layer of magnetic flux is very small, after being transmitted through multiple layers, these tiny changes will be continuously amplified at the measuring point, forming a significant change in magnetic intensity; As the stress on the structure gradually increases and material fatigue develops, the changes in magnetic intensity will continue to accumulate and manifest themselves macroscopically as a significant amplification of the changes in magnetic intensity at the measurement point; this cumulative effect means that even if the value of the applied magnetic intensity remains unchanged, as the magnetic induction intensity is transmitted deeper into the material, the magnetic intensity sensed in each layer will gradually increase.

7. The detection method of the ferromagnetic metal stress and fatigue measurement device as claimed in claim 6, characterized in that: The theoretical derivation and amplification of the magnetic linkage effect in step S3 are specifically as follows: When an external magnetic field is applied to a ferromagnetic metal, the magnetic induction intensity is transmitted layer by layer along a certain direction due to the (virtual) magnetic interaction between layers. Assuming that the magnetic interaction between layers is the only determining factor for the induction transmission of magnetic field intensity in the magnetic flux chain, and ignoring the magnetic intensity of the external magnetic field transmitted by the air, the relationship between the induced magnetic intensity value after the external magnetic field passes through a layer, the external magnetic intensity value, and the magnetic interaction force between layers is: B1=B0·f(F m0 ) (34) Where B0 is the external magnetic intensity value, B1 is the induced magnetic intensity value of the first layer, F m0 Interlayer magnetic interaction, f(F m0 ) is a continuous function of the interlayer magnetic interaction force; The magnetic strength of the next layer is induced by the magnetic strength of the previous layer through the interlayer magnetic interaction force, so: <h2 style=";text-align:left;direction:ltr">B2=B1·f(F<h2 style=";text-align:left;direction:ltr"> m1 <h2 style=";text-align:left;direction:ltr"> ) (35) Where B2 is the induced magnetic intensity value of the second layer, F m1 is the interlayer magnetic interaction of the second layer; By analogy, we get: B i =B i-1 ·f(F m(i-1) ) (36) Among them B i is the induced magnetic intensity value of the i-th layer, F m(i) is the interlayer magnetic interaction of the i-th layer; Thus, the induced magnetic intensity value of the nth layer (measurement layer) is obtained as follows: When the average interatomic distance between layers changes due to stress or fatigue, the magnetic interaction between the layers will change accordingly ΔF mi ; At this time, the induced magnetic intensity value of the nth layer is expressed as: When ΔF mi When I was very young, I had: f(F mi +ΔF mi )≈f(F mi )+f / (F mi )·ΔF mi (39) where f / (F mi ) means that the function f is in F mi Substituting the derivative at In the result: To B n and Taking the logarithm respectively, we get: get: Simplifying equation (43) yields ΔB n : Considering that when x is very small, exp(x)≈1+x; Formula (43) is simplified to: Since ΔF mi The change in the interatomic distance between layers ΔR i Correlation (ΔF mi =K m ΔR i ),get: If the entire material is subjected to uniform force or uniform fatigue, the change in the atomic spacing of each layer tends to be consistent, and the magnetic interaction of each layer inside it will also show similar effects. In order to simplify the derivation, it is assumed that the change in the atomic spacing of each layer (ΔR i ) are equal, that is, ΔR i =ΔR; and the magnetic interaction function f(F mi ) are also equal, that is, f(F mi )=f(F m ); Formula (46) is simplified to: The same derivation is used to obtain the change in magnetic intensity of any single layer: In view of the fact that the change in atomic spacing during the fatigue process of the material mainly occurs on the PSB, it is believed that this magnification factor n corresponds exactly to the number of PSB layers; as fatigue develops, the change in magnetic intensity caused by the change in each layer of PSB will continue to accumulate, and will be manifested macroscopically as a significant amplification of the change in magnetic intensity at the measurement point; HR-DIC observations at the microscopic level have revealed that there is a clear linear relationship between the maximum slip strength of PSB during initial cyclic loading, the average value of the slip trace spacing and its 5% highest value distribution and the fatigue strength of the material, indicating that the magnification factor n is also strongly correlated with the fatigue strength of the material; Since the distance between atoms does not change much, ΔF C It is also linearly related to ΔR (ΔF C =K c ΔR), substituting the relationship between the interlayer bonding force and the change in the interlayer atomic distance into formula (47), we obtain: ΔB n =K B ΔF C (49) in The magnetic intensity ΔB measured by the external Hall sensor H Actually, ΔB n A component of: ΔB H =K E ΔB n (50) When the measurement distance and environmental factors remain unchanged, K E As a constant, we get: ΔB H =K H ΔF C (51) Where K H =K E K B ; Therefore, through the great amplification effect of the magnetic flux caused by the external magnetic strength on the tiny internal changes, the fatigue process of ferromagnetic materials caused by the gradual cumulative weakening of the binding force is observed.

8. The detection method of the ferromagnetic metal stress and fatigue measurement device as claimed in claim 7, characterized in that: The specific method for predicting material fatigue fracture in step S5 is as follows: fatigue tests are performed on all ferromagnetic metals under different stresses using a magnetic induction chain detection method, and the magnetic peak-to-peak value is calculated after obtaining the magnetic intensity change value of the metal during the entire fatigue process, and a curve diagram of the relationship between the magnetic peak-to-peak value and the number of cycles is drawn; the slope of the change of the magnetic peak-to-peak value of each metal specimen with the number of cycles is calculated using a univariate linear fitting of the least squares method; the relationship between the number of fatigue fractures under different stresses and the slope of the change of the magnetic peak-to-peak value is drawn into a scatter plot, and the relationship between the magnetic peak-to-peak value change rate of each specimen and the number of fractures is called an MN curve, and the linear fitting formula of the MN curve is obtained by linear fitting: where k av is the magnetic intensity peak-to-peak slope, k c is the slope of the MN curve, C is the intercept of the MN curve; where k c =-1.261, C = -0.167, k av Obtained by linear fitting of magnetic intensity variation data; The slope k of the linear fit of the peak magnetic intensity at the early stage of the loading cycle of all ferromagnetic metals is av Substitute into the above formula to calculate the fatigue failure life of each metal; calculate the correlation between the calculated fatigue failure life and the actual fatigue failure life of all specimens using the following formula; Where x is the calculated fatigue failure life and y is the actual fatigue failure life.

9. The detection method of the ferromagnetic metal stress and fatigue measurement device as claimed in claim 8, characterized in that: The specific method for material fatigue fracture warning in step S5 is: according to the two changing trends of the peak value of magnetic intensity of ferromagnetic metal under external fatigue load, two early warning methods before fatigue fracture are proposed; two windows are set, wherein B med is the median value of magnetic drift in the first window, A med , A max , A min are the median, maximum, and minimum values ​​of the magnetic drift in the second window; When the number of cycles does not exceed 300,000, starting from the 5000th cycle loading, the first window is 60 cycles before the current time, and the second window is 1000 cycles before 3000 cycles before the current 60 cycles; (S1 is a constant obtained through fatigue testing. When the number of cycles does not exceed 300,000, S1 is 4.8, A max -A min Take 0.0132) as the alarm threshold. When the alarm threshold is less than 0 for more than four consecutive times, the alarm is triggered. When the number of cycles exceeds 300,000, the first window is 60 cycles before the current time, and the second window is 2,000 cycles before the current 60 cycles and 40,000 cycles before the current time. (Where S2 is a constant obtained through fatigue testing; when the number of cycles exceeds 300,000, S2 is set to 1.2, A max -A min Take 0.0132) as the alarm threshold. When the alarm threshold is greater than 0 for more than four consecutive times, an alarm is triggered.

Images