Method for simultaneous measurement of normal force and shear force based on contact resistance

Abstract

This invention discloses a method for simultaneously measuring interfacial normal force and shear force based on contact resistance, comprising the following steps: Inspired by the yield criterion for material failure, establishing the relationship between normal stress and shear stress at the contact interface, thereby obtaining the relationship between the actual contact area of ​​the contact interface and the normal force and shear force, obtaining the relationship between the contact resistance of the contact interface and the actual contact area, and establishing the relationship between the interface contact resistance and the normal force and shear force; Based on the geometric deformation relationship of the micro-protrusions on the contact interface before and after the application of shear force, obtaining the relationship between the actual contact area of ​​the contact interface and the geometric deformation parameters of the micro-protrusions, obtaining the relationship between the normal force and shear force of the contact interface and the geometric deformation parameters of the micro-protrusions; Solving a system of equations, and calculating the normal force and shear force by measuring the contact resistance and substituting it into the system of equations. This invention enables the indirect measurement of the magnitude of the interface normal force and shear force by measuring the contact resistance of the contact interface.

Description

Technical Field

[0001] This invention relates to the field of interface contact force measurement technology, and in particular to a method for simultaneously measuring interface normal force and shear force based on contact resistance. Background Technology

[0002] Contact interfaces serve as bridges for force transmission, electrical conduction, and heat transfer in engineering structures, such as superconducting magnets in fusion reactors and bearings in aero-engines. Measuring interfacial contact forces plays a crucial role in assessing the safety and stability of complex engineering structures. However, due to the strong randomness and complexity of rough interfaces, and their opacity, it is difficult to directly observe and measure the contact forces (normal and shear forces) at the interface. Existing measurement methods, such as X-ray, magnetic measurement, and nanoindentation, are insufficient for detecting rough contact interfaces. Therefore, indirect measurement methods are an approach to overcome the limitations of direct methods. This involves measuring another physical quantity, such as contact resistance, to indirectly measure the interfacial contact forces. Current research only considers the relationship between normal force and contact resistance, failing to simultaneously consider the physical relationships between both normal force and shear force and contact resistance. Summary of the Invention

[0003] The purpose of this invention is to provide a method for simultaneously measuring the normal force and shear force at an interface based on contact resistance, so as to solve the defect that the magnitude of the contact force at the contact interface under the combined action of normal force and shear force cannot be indirectly measured by existing technology.

[0004] To achieve the above objectives, the present invention provides the following technical solution:

[0005] The method for simultaneously measuring interface normal force and shear force based on contact resistance includes the following steps:

[0006] S1: Based on the yield criterion for material failure, establish the relationship between the normal stress and shear stress at the contact interface:

[0007] ;

[0008] In the formula, For the normal stress at the contact interface, For the shear stress at the contact interface, The yield strength of the material under uniaxial stress. These are material-related constants;

[0009] This relationship allows us to obtain the relationship between the actual contact area of ​​the contact interface and the normal force and shear force.

[0010] S2: The contact interface is regarded as an assembly of a large number of tiny contact points. Each contact point on the contact interface is an independent conductive path. The relationship between the total contact resistance of the contact interface and the actual contact area is established. The relationship between the actual contact area of ​​the contact interface and the normal force and shear force obtained in step S1 is introduced into the relationship between the total contact resistance and the actual contact area, thereby establishing the relationship between the total contact resistance of the contact interface and the normal force and shear force.

[0011] S3: Based on the geometric deformation relationship of the micro-protrusions on the contact interface before and after the shear force, obtain the relationship between the actual contact area of ​​the contact interface and the geometric deformation parameters of the micro-protrusions; the geometric deformation relationship of the micro-protrusions on the contact interface before and after the shear force is as follows:

[0012] ;

[0013] In the formula, The radius of the bottom of the micro-convex body is . The contact radius of the micro-protrusion under the action of normal force alone. The contact radius of the micro-protrusion under the combined action of normal force and shear force. The base angle of the micro-convex body under the action of normal force alone. The base angle of the micro-convex body under the combined action of normal force and shear force;

[0014] S4: Combine the relationship between the actual contact area of ​​the contact interface and the normal force and shear force obtained in step S1 and the relationship between the actual contact area of ​​the contact interface and the geometric deformation parameters of the micro-protrusion obtained in step S3 to establish the relationship between the normal force and shear force of the contact interface and the geometric deformation parameters of the micro-protrusion.

[0015] S5: Calculate the shear strain of the micro-protrusions based on the geometric deformation relationship of the micro-protrusions on the contact interface before and after the shear force is applied, and obtain the relationship between the magnitude of the shear force at the contact interface and the geometric deformation parameters of the micro-protrusions by combining the existing shear force calculation formula.

[0016] S6: Combine the relationships between the total contact resistance of the contact interface and the normal force and shear force established in step S2, the relationships between the normal force and shear force of the contact interface and the geometric deformation parameters of the micro-protrusion established in step S4, and the relationships between the magnitude of the shear force of the contact interface and the geometric deformation parameters of the micro-protrusion obtained in step S5 to establish a system of equations.

[0017] S7: Measure the contact resistance of the contact interface and substitute it into the equation set established in step S6. Solve the equations to obtain the magnitudes of the normal force and shear force at the contact interface.

[0018] Furthermore, in step S1, the relationship between the actual contact area of ​​the contact interface and the normal force and shear force is as follows:

[0019] ;

[0020] in, ;

[0021] ;

[0022] In the interface contact relationship of this invention, the contact micro-protrusions on the contact interface are "averaged," ensuring that the force and geometric conditions of all micro-protrusions are equal. Therefore, the subscript... It refers to a single micro-protrusion on the contact interface and has no specific physical meaning;

[0023] For ease of abbreviation, let ,make The relationship between the actual contact area of ​​the contact interface and the normal force and shear force is expressed as:

[0024] ;

[0025] In the formula, For normal force, Shear force, This represents the actual contact area of ​​the interface under the combined action of normal and shear forces. This represents the actual contact area of ​​the contact interface under the action of normal force alone. This represents the actual contact area of ​​a single micro-protrusion under the action of a single normal force. The contact radius of the micro-protrusion under the action of normal force alone. This represents the actual number of contact points on the interface. The initial height of the micro-convex body. It is a constant. The creep activation energy, Boltzmann's constant, For temperature, For the normal load on a single micro-convex body, Stress index For contact time.

[0026] Furthermore, in step S2, the relationship between the total contact resistance of the contact interface and the actual contact area is as follows:

[0027] ;

[0028] In the formula, This represents the total contact resistance at the contact interface. The resistivity of the material.

[0029] Furthermore, in step S3, the relationship between the actual contact area of ​​the contact interface and the geometric deformation parameters of the micro-protrusion is as follows:

[0030] .

[0031] Furthermore, in step S4, the relationship between the normal force and shear force of the contact interface and the geometric deformation parameters of the micro-protrusion is as follows:

[0032] .

[0033] Furthermore, in step S5, the formula for calculating the bulk shear strain of the micro-convexity is:

[0034] ;

[0035] In the formula, The shear strain of the micro-convexity;

[0036] The relationship between the magnitude of the shear force at the contact interface and the geometric deformation parameters of the micro-protrusion is as follows:

[0037] ;

[0038] In the formula, This is the shear modulus.

[0039] Furthermore, in step S7, the contact resistance of the contact interface is measured using the four-wire method. The measuring equipment includes a direct shearing device, an M81 synchronous source measuring system, a loading device, and wires.

[0040] Compared with the prior art, the present invention has the following advantages:

[0041] This invention establishes a force-electric contact model of the contact interface under combined compression and shear, and proposes an electrical measurement method for simultaneously measuring the normal force and shear force of the interface by combining the stress-strain equations of the geometric deformation of the micro-protrusions of the contact interface based on the model. Using this invention, the magnitude of the contact force of the contact interface can be easily and accurately calculated by indirect measurement. That is, the magnitude of the normal force and shear force loaded on the contact interface can be calculated by measuring the contact resistance of the contact interface. Attached Figure Description

[0042] Figure 1 This is the single micro-convexity creep model of the present invention;

[0043] Figure 2 This is a schematic diagram and equivalent circuit diagram of the current path at the rough contact interface of the present invention;

[0044] Figure 3 This is a schematic diagram and a projection diagram of the geometric deformation of the micro-protrusions at the contact interface under shear force according to the present invention.

[0045] Figure 4 This is a schematic diagram showing the connection between the contact interface force-electric coupling shear test device and the "four-wire method" for measuring the interface contact resistance in an embodiment of the present invention.

[0046] Figure 5 The diagrams show the relationship between normalized true contact resistance and normal force under different shear forces and under different normal loads in the embodiments of the present invention.

[0047] Figure 6 This is a comparison chart of the contact force value calculated by the method proposed in this invention and the experimental loading value. Detailed Implementation

[0048] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0049] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0050] It should be understood that, when used in this specification and the appended claims, the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0051] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0052] It should also be further understood that the term "and / or" as used in this specification and the appended claims refers to any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0053] 1. Establish a contact resistance-contact force model under the combined action of normal force and shear force.

[0054] Inspired by the yield criterion for material failure, the micro-protrusion slippage behavior between rough surfaces is considered a similar failure mechanism. Under these conditions, the normal stress and shear stress at the contact interface satisfy the following yield criterion relationship:

[0055] (1)

[0056] In the formula, For the normal stress at the contact interface, For the shear stress at the contact interface, The yield strength of the material under uniaxial stress. These are material-related constants, determined experimentally. Further, the contact forces on the micro-protrusions at the contact interface satisfy:

[0057] (2)

[0058] In the formula, , These represent the normal load and tangential load acting on a single micro-convex body, respectively. This represents the actual contact area of ​​a single micro-protrusion under the combined action of normal and shear forces. This represents the actual contact area of ​​a single micro-protrusion under the action of a normal force alone. In the interface contact relationship of this invention, the contact micro-protrusions on the contact interface are "averaged," ensuring that the force and geometric conditions of all micro-protrusions are equal. Therefore, the subscript... This refers to a single micro-protrusion on the contact interface and has no specific physical meaning; for the entire rough contact interface, the contact normal force and shear force satisfy:

[0059] (3)

[0060] In the formula, For normal force, Shear force, This represents the actual contact area of ​​the interface under the combined action of normal and shear forces. This represents the actual contact area of ​​the contact interface under the action of a single normal force. Since all micro-protrusions on the contact interface experience the same force and geometric conditions, the area of ​​each micro-protrusion... If they are all the same, then:

[0061] (4)

[0062] (5)

[0063] In the formula, This represents the actual number of contact points on the interface.

[0064] According to equation (3), the actual contact area of ​​the contact interface under the combined action of normal force and shear force can be derived as follows:

[0065] (6)

[0066] in, (7); where, This represents the actual number of contact points on the interface. This represents the actual contact area of ​​a single micro-protrusion under normal force. The contact radius of the micro-convex body under the action of normal force alone.

[0067] Contact radius of micro-convexity under normal force alone The calculation is performed by constructing a single micro-convexity creep constitutive model, and the specific explanation and derivation process are as follows:

[0068] When two rough metal surfaces come into contact under external force, the actual contact does not occur across the entire surface, but rather is concentrated between a few micro-protrusions distributed on the surface's micro-uneven structure. Therefore, the contact characteristics of these micro-protrusions directly affect the overall mechanical behavior of the contact interface. In the initial contact stage, only the tips of a few of the tallest micro-protrusions participate in the contact. At this point, the actual contact area is extremely small, and the local pressure within a unit contact area is much higher than the average stress level, thus inducing significant plastic deformation. As loading continues, more micro-protrusions with lower heights gradually participate in the contact until the accumulated contact area can balance the applied load. Based on the statistical distribution of the rough surface's micro-geometric features, the shape of a single contacting micro-protrusion can be simplified to a conical truncated pyramid structure (such as...). Figure 1 (As shown). Considering the progressive deformation characteristics of metallic materials under high local stress, these micro-protrusions exhibit progressive compression behavior similar to creep during the plastic contact stage. Therefore, the following creep constitutive relation can be used to describe the nonlinear deformation behavior of micro-protrusions at the metal interface during contact deformation:

[0069] (8)

[0070] In the formula, For creep rate, It is a constant, depending on the material and the creep mechanism. For the normal stress at the contact interface, Stress index The creep activation energy, Boltzmann's constant, For temperature;

[0071] Based on the geometric relationship of micro-convexities (such as...) Figure 1 As shown), the expressions for the normal creep rate, normal stress, and contact radius of the contact micro-protrusion with respect to contact time can be expressed as follows:

[0072] (9)

[0073] In the formula, It is a function of creep rate with respect to contact time. Let be the rate of height change of the micro-protrusion creep as a function of contact time. The initial height of the micro-convex body. For the normal load on a single micro-convex body, Let be the rate of change of the contact radius of the micro-protrusion under the action of normal force alone, as a function of contact time, where t is the contact time. This refers to the base angle of the micro-protrusion under the action of normal force alone. The geometric model dimensions of the micro-protrusion are the average geometric dimensions (such as contact radius and micro-protrusion height).

[0074] Substituting equation (9) into equation (8), we obtain the derivative of the contact radius of the micro-protrusion as follows:

[0075] (10)

[0076] Integrating equation (10) over time yields the following expression for the change of the contact radius of the micro-protrusion with contact time:

[0077] (11)

[0078] In the formula, for When the radius of the micro-protrusion is sufficiently small, it can be ignored, and the relationship between the contact radius of a single micro-protrusion and the contact time is obtained as follows:

[0079] (12);

[0080] In the formula, for the sake of simplicity, let (13), of which (14);

[0081] make (15)

[0082] Substituting equations (13) and (15) into equation (12), we get ;

[0083] Therefore, the contact radius of the micro-convexity under the action of normal force alone is obtained based on the creep constitutive model. for: (16).

[0084] From equations (6), (7), and (16), we can obtain:

[0085] (17)

[0086] Since the contact points on the rough surface are independent of each other, according to the law of resistance of a conductor, the following relationship exists for each micro-protrusion:

[0087] (18)

[0088] In the formula, The contact resistance of a single contact micro-protrusion. Resistivity The length of a single micro-protrusion, This represents the actual contact area of ​​a single contact micro-protrusion under the combined action of normal and shear forces. It should be noted that those skilled in the art generally assume that the micro-protrusions on the contact interface are evenly distributed, therefore each micro-protrusion on the contact interface has the same length and resistivity. It is a constant value.

[0089] like Figure 2 As shown ( Figure 2 (a) is a schematic diagram of the current path at a rough contact interface. Figure 2 (b) is an equivalent circuit diagram, where the rough contact interface is considered as an assembly of numerous tiny contact points, and each contact point on the interface is assumed to be an independent conductive path. This assumption means that the resistance characteristics of each contact point are determined only by its local geometry, material properties, and load state, and are not affected by other micro-protrusions. Therefore, within the total contact area, the resistance of each contact point can be equivalent to a parallel relationship. According to the principle of superposition of parallel resistances, the following relationship holds for all contact points:

[0090] (19)

[0091] In the formula, This represents the total contact resistance at the contact interface.

[0092] From equations (18) and (19), we can obtain:

[0093] ,because Then we have:

[0094] (20)

[0095] Considering that the micro-protrusions have already deformed, the length of a single micro-protrusion Initial height of the micro-protrusion The relationship is:

[0096] (twenty one)

[0097] In the formula, Given the bottom angle of the micro-convex body under the action of normal force alone, the contact resistance of the rough interface under the combined action of pressure and shear force can be obtained from equations (17), (20), and (21):

[0098] (twenty two)

[0099] This led to the establishment of a contact resistance-contact force model under the combined action of normal force and shear force.

[0100] 2. Establishing stress-strain equations based on the geometric deformation relationship of micro-convex bodies

[0101] To achieve simultaneous measurement of normal and shear forces using a single contact resistance, it is necessary to supplement the electromechanical contact equation with a stress-strain equation based on geometric deformation. For example... Figure 3 As shown ( Figure 3 (a) is a schematic diagram of the geometric deformation of the micro-convex body under shear force. Figure 3 (b) is a projection diagram of the geometric deformation of the micro-protrusion. Under the action of shear force, the contact radius of the micro-protrusion increases, and the following relationship is satisfied before and after deformation:

[0102] (twenty three)

[0103] In the formula, The radius of the bottom of the micro-convex body is . The contact radius of the micro-protrusion under the action of normal force alone. The contact radius of the micro-protrusion under the combined action of normal force and shear force. The bottom angle of the micro-convex body under the combined action of normal force and shear force.

[0104] From equation (23), the actual contact area under the combined action of normal force and shear force can be obtained as:

[0105] (twenty four)

[0106] Equations (17) and (24) represent the actual contact areas calculated from the stress and geometric deformation relationships under the yield criterion, respectively. According to the deformation compatibility condition, they are equal, thus yielding:

[0107] (25)

[0108] Furthermore, the shear strain of the micro-convexity can also be calculated from its geometric deformation relationship. ; combination and We can obtain:

[0109] (26)

[0110] In the formula, Shear modulus For micro-convex body shear stress, For the shear strain of the micro-convex body, This is the shear force.

[0111] 3. Construct a system of equations to calculate the normal and shear forces at the interface.

[0112] The following system of equations is formed by equations (13), (14), (15), (16), (22), (25), and (26):

[0113] ;

[0114] The unknowns in this system of equations have a normal force. Shear force and contact resistance All other parameters are known or measurable quantities, among which, , , All of these can be measured using a surface measuring instrument. , , Both and are intermediate parameters that can be calculated from known quantities. The actual number of contact points n at the contact interface is calculated using existing formulas. In this embodiment, stainless steel is used as the contact interface material, and the model calculation parameters are determined according to Table 1. Specifically, the solution method for this system of equations is as follows:

[0115] First, the total contact resistance of the contact interface is obtained through experimental testing. Then Substituting into equation (22) yields the following results: Then The intermediate parameters are obtained by substituting them into equation (24). intermediate parameters The unknown quantity can be obtained through equation (16). This indicates that the intermediate parameters will be used. , Substitute the intermediate parameters into equation (23). Using unknown quantities With intermediate parameters This indicates that the intermediate parameters will be used. , , Substituting into equation (26), and then combining equations (22), (25), and (26), the normal force can be calculated. With shear force .

[0116] Table 1. Model Calculation Parameters

[0117]

[0118] 4. Measurement of contact resistance

[0119] In this embodiment, the four-wire method is used to measure the interface contact resistance. One pair of test wires provides current, and the other pair of test wires measures voltage, which can accurately measure the contact resistance. The measured voltage data is recorded and analyzed using the M81 synchronous source measurement system, and the resistance value is finally calculated.

[0120] 5. Experimental verification of accuracy

[0121] To verify the accuracy and feasibility of the proposed method for synchronously measuring normal force and shear force based on contact resistance, a force-electric contact experiment was conducted on a rough interface. Under a given constant normal load, the interface shear force and the corresponding changes in contact resistance were measured.

[0122] (1) Experimental apparatus and samples

[0123] Construct a mechanical-electric coupling shear test apparatus for rough interfaces (e.g.) Figure 4 (a) shows the experimental setup, which includes a direct shearing device, an M81 synchronous source measurement system, a loading device, and wires. Under a constant normal load, the tangential load and corresponding contact resistance changes at the interface are measured. The tangential load (shear force) on the rough interface is measured by the displacement of the force sensor in the direct shearing test device, with a stiffness of 453 N / mm. The contact resistance of the rough interface is measured using the voltage-current method: under applied normal and tangential loads, current is transmitted through the contact interface. The voltage difference across the interface is measured using the synchronous source measurement system (M81), and the contact resistance is calculated based on Ohm's law. Specifically, the contact resistance of the interface is measured using the "four-wire method." The connection method for measuring the contact resistance of the interface using the "four-wire method" is as follows: Figure 4 As shown in (b), one pair of test leads provides current, and another pair measures voltage. The sample material is stainless steel. Holes are drilled on the sides of both samples and aligned at the ends. The two leads are connected to the M81 synchronous source measurement system. During the experiment, a normal load is applied via a direct shear device, with a load range of 0-1000N. (Since the maximum load capacity of the strain-controlled direct shear device is 1000N, the experimental load is strictly controlled within 0-1000N to avoid damaging the instrument.) During the load holding phase, if the voltage fluctuation range is 0.5μV, the system is considered to have reached a steady state. At this point, the M81 synchronous source measurement system begins to continuously record voltage changes. Based on the tested voltage and the applied rated current, the formula for calculating the contact resistance using Ohm's law is as follows:

[0124] In the formula, It is contact resistance. It's voltage. It is electric current.

[0125] (2) Experimental steps

[0126] To ensure the accuracy of experimental data measurements and minimize measurement errors, the experimental procedure follows these steps:

[0127] 1) Within 0-1800 seconds, start the M81 synchronous source measurement system to stabilize the test environment and reduce system errors;

[0128] 2) Within 1800-2000 seconds, place the sample in an unloaded experimental setup and let it stand for a period of time to minimize the initial error caused by creep effect;

[0129] 3) Within 2000-2180 seconds, connect the sample line to the SSM and apply a DC current of 0.1A while applying the specified load. This current value is intended to reduce the interference of external factors such as environmental noise and DC drift on the measurement in order to obtain a more stable electrical signal response.

[0130] 4) Start the shear test device and introduce a DC signal while continuously applying a normal load to ensure the formation of electrical contact, reduce the effects of material creep, and suppress the Branly effect (i.e., the phenomenon of a sudden drop in material resistance when the current increases), thereby improving the stability and repeatability of the measurement. To ensure measurement accuracy, multiple repeated measurements were performed using samples prepared in the same batch under the same experimental conditions, and the arithmetic mean of the results was used as the final output of the experimental data.

[0131] It is important to note that, to ensure the stability of the experimental environment and the consistency of the sample surface condition, a uniform pretreatment procedure is used before each test of the stainless steel samples. The specific procedure is as follows: wipe the sample surface with filter paper to remove contaminants such as dust and oil, and then blow cold air on the sample surface for 3-5 minutes to remove any remaining debris. This process ensures that the roughness of each sample is within the same range.

[0132] (3) Experimental results

[0133] The results calculated using the method proposed in this invention are compared with the experimental results, such as... Figure 5 As shown ( Figure 5 (a) is a graph showing the relationship between normalized true contact resistance and normal force under different shear forces. Figure 5(b) shows the relationship between normalized true contact resistance and shear force under different normal loads. Regardless of whether shear force is applied, the calculation results of the proposed method model agree well with the experimental measurements, verifying the effectiveness of the theoretical model. Under the combined action of normal and tangential forces, the contact area increases, thus reducing the contact resistance due to the weakening of the current contraction effect. Further applying tangential force under normal force leads to a decrease in contact resistance due to the increase in contact area. Furthermore, as the normal force increases, the maximum value of the applicable tangential force also increases, meaning a larger tangential force is required to induce sliding.

[0134] Furthermore, to verify the feasibility and accuracy of the proposed measurement method, we first measured the contact resistance values ​​under different normal and tangential forces, then substituted the resistance values ​​into the equations to calculate the normal and tangential forces, and compared them with the applied normal and tangential forces. Figure 6 The figure shows a comparison between the calculated normal and tangential forces obtained by the electrical measurement method proposed in this invention and the normal and shear forces applied by the experimental device. The figure shows that the theoretical values ​​of the normal and tangential forces calculated by this invention are in good agreement with the experimental values ​​of the normal and tangential forces applied in the experiment. This indicates that the measurement method proposed in this invention is feasible and has high accuracy.

[0135] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for simultaneously measuring interface normal force and shear force based on contact resistance, characterized in that, Includes the following steps: S1: Based on the yield criterion for material failure, establish the relationship between the normal stress and shear stress at the contact interface: ； In the formula, For the normal stress at the contact interface, For the shear stress at the contact interface, The yield strength of the material under uniaxial stress. These are material-related constants; This relationship allows us to obtain the relationship between the actual contact area of ​​the contact interface and the normal force and shear force. S2: The contact interface is regarded as an assembly of a large number of tiny contact points. Each contact point on the contact interface is an independent conductive path. The relationship between the total contact resistance of the contact interface and the actual contact area is established. The relationship between the actual contact area of ​​the contact interface and the normal force and shear force obtained in step S1 is introduced into the relationship between the total contact resistance and the actual contact area, thereby establishing the relationship between the total contact resistance of the contact interface and the normal force and shear force. S3: Based on the geometric deformation relationship of the micro-protrusions on the contact interface before and after the shear force, obtain the relationship between the actual contact area of ​​the contact interface and the geometric deformation parameters of the micro-protrusions; the geometric deformation relationship of the micro-protrusions on the contact interface before and after the shear force is as follows: ； In the formula, The radius of the bottom of the micro-convex body is . The contact radius of the micro-protrusion under the action of normal force alone. The contact radius of the micro-protrusion under the combined action of normal force and shear force. The base angle of the micro-convex body under the action of normal force alone. The base angle of the micro-convex body under the combined action of normal force and shear force; S4: Combine the relationship between the actual contact area of ​​the contact interface and the normal force and shear force obtained in step S1 and the relationship between the actual contact area of ​​the contact interface and the geometric deformation parameters of the micro-protrusion obtained in step S3 to establish the relationship between the normal force and shear force of the contact interface and the geometric deformation parameters of the micro-protrusion. S5: Calculate the shear strain of the micro-protrusions based on the geometric deformation relationship of the micro-protrusions on the contact interface before and after the shear force is applied, and obtain the relationship between the magnitude of the shear force at the contact interface and the geometric deformation parameters of the micro-protrusions by combining the existing shear force calculation formula. S6: Combine the relationships between the total contact resistance of the contact interface and the normal force and shear force established in step S2, the relationships between the normal force and shear force of the contact interface and the geometric deformation parameters of the micro-protrusion established in step S4, and the relationships between the magnitude of the shear force of the contact interface and the geometric deformation parameters of the micro-protrusion obtained in step S5 to establish a system of equations. S7: Measure the contact resistance of the contact interface and substitute it into the equation set established in step S6. Solve the equations to obtain the magnitudes of the normal force and shear force of the contact interface.

2. The method for synchronously measuring interface normal force and shear force based on contact resistance according to claim 1, characterized in that, In step S1, the relationship between the actual contact area of ​​the contact interface and the normal force and shear force is as follows: ； in, ; ； ； make ,make The relationship between the actual contact area of ​​the contact interface and the normal force and shear force is expressed as: ； In the formula, For normal force, Shear force, This represents the actual contact area of ​​the interface under the combined action of normal and shear forces. This represents the actual contact area of ​​the contact interface under the action of normal force alone. This represents the actual contact area of ​​a single micro-protrusion under the action of a single normal force. The contact radius of the micro-protrusion under the action of normal force alone. This represents the actual number of contact points on the interface. The initial height of the micro-convex body. It is a constant. The creep activation energy, Boltzmann's constant, For temperature, For the normal load on a single micro-convex body, It refers to a single micro-protrusion on the contact interface. Stress index For contact time.

3. The method for synchronously measuring interface normal force and shear force based on contact resistance according to claim 2, characterized in that, In step S2, the relationship between the total contact resistance of the contact interface and the actual contact area is as follows: ； In the formula, This represents the total contact resistance at the contact interface. The resistivity of the material.

4. The method for synchronously measuring interface normal force and shear force based on contact resistance according to claim 3, characterized in that, In step S3, the relationship between the actual contact area of ​​the contact interface and the geometric deformation parameters of the micro-protrusion is as follows: 。 5. The method for synchronously measuring interface normal force and shear force based on contact resistance according to claim 4, characterized in that, In step S4, the relationship between the normal force and shear force of the contact interface and the geometric deformation parameters of the micro-protrusion is as follows: 。 6. The method for synchronously measuring interface normal force and shear force based on contact resistance according to claim 5, characterized in that, In step S5, the formula for calculating the shear strain of the micro-protrusion is: ； In the formula, The shear strain of the micro-convexity; The relationship between the magnitude of the shear force applied to the contact interface and the geometric deformation parameters of the micro-protrusions on the contact interface before and after the shear force is applied is as follows: ； In the formula, This is the shear modulus.

7. The method for synchronously measuring interface normal force and shear force based on contact resistance according to claim 1, characterized in that, In step S7, the contact resistance of the contact interface is measured using the four-wire method. The measuring equipment includes a direct shearing device, an M81 synchronous source measuring system, a loading device, and wires.

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