Method for synchronously measuring normal force and shear force of interface based on contact resistance

Abstract

The invention discloses a contact resistance-based method for synchronously measuring normal force and shear force of an interface, which comprises the following steps of: inspired by a yield criterion of material damage, establishing a relationship between normal stress and shear stress of the contact interface, thereby obtaining a relationship between a real contact area of the contact interface and the normal force and the shear force; obtaining the relationship between the contact resistance of the contact interface and the real contact area, and establishing the relationship between the contact resistance of the interface and the normal force and the shear force; according to the geometric deformation relation of the micro-convex bodies on the contact interface before and after the shearing force acts, the relation between the real contact area of the contact interface and the geometric deformation parameters of the micro-convex bodies is obtained, and the relation among the normal force of the contact interface, the shearing force and the geometric deformation parameters of the micro-convex bodies is obtained; and establishing a simultaneous equation set, measuring the contact resistance, and substituting the contact resistance into the equation set to calculate the normal force and the shear force. According to the invention, the normal force and shear force of the interface can be indirectly measured by measuring the contact resistance of the contact interface.

Description

Technical Field

[0001] The present invention relates to the technical field of interface contact force measurement, in particular to a method for synchronously measuring interface normal force and shear force based on contact resistance. Background Art

[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 aircraft engines. Measuring interfacial contact forces plays a key role in assessing the safety and stability of complex engineering structures. However, due to the strong randomness and complexity of rough interfaces, as well as their opacity, direct observation and measurement of contact forces (normal and shear forces) at these interfaces is difficult. Existing direct measurement methods, such as X-ray, magnetic measurement, and nanoindentation, struggle to detect rough contact interfaces. Therefore, indirect measurement methods are a way to overcome the limitations of direct measurement methods. This involves indirectly measuring interfacial contact forces by measuring another physical quantity, such as contact resistance. Existing studies have focused on the relationship between normal force and contact resistance, but have been unable to simultaneously consider the physical relationships between normal force and shear force and contact resistance. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for synchronously measuring the normal force and shear force of the interface based on contact resistance, so as to solve the defect that the existing technology cannot indirectly measure the contact force of the contact interface under the combined action of the normal force and the shear force.

[0004] To achieve the above object, the present invention provides the following technical solutions: The method for synchronously measuring interface normal force and shear force based on contact resistance includes the following steps: S1: Based on the yield criterion of material failure, the relationship between the normal stress and shear stress at the contact interface is established: ; Where, is the normal stress at the contact interface, is the contact interface shear stress, is the yield strength of the material under uniaxial stress, is a material-related constant; The relationship between the actual contact area of ​​the contact interface and the normal force and shear force is obtained from this relationship; S2: The contact interface is regarded as a collection 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 true contact area is established. The relationship between the true contact area of ​​the contact interface obtained in step S1 and the normal force and shear force is introduced into the established relationship between the total contact resistance and the true contact area, thereby establishing the relationship between the total contact resistance of the contact interface and the normal force and shear force. S3: Obtain the relationship between the true contact area of ​​the contact interface and the geometric deformation parameters of the asperities based on the geometric deformation relationship of the asperities on the contact interface before and after the shear force is applied; the geometric deformation relationship of the asperities on the contact interface before and after the shear force is: ; Where, is the bottom radius of the micro-convex body, is the contact radius of the asperity under the action of normal force alone, is the contact radius of the asperity under the combined action of normal force and shear force, is the bottom angle of the convex body under the action of normal force alone, is the bottom angle of the micro-convex body under the combined action of normal force and shear force; S4: combining the relationship between the true contact area of ​​the contact interface and the normal force and shear force obtained in step S1 and the relationship between the true contact area of ​​the contact interface and the geometric deformation parameters of the asperities obtained in step S3 to establish a relationship between the normal force and shear force of the contact interface and the geometric deformation parameters of the asperities; S5: Calculate the shear strain of the asperities based on the geometric deformation relationship of the asperities on the contact interface before and after the shear force acts, and obtain the relationship between the shear force magnitude of the contact interface and the geometric deformation parameters of the asperities by combining the existing shear force calculation formula; S6: jointly establish a system of equations by combining the relationship between the total contact resistance of the contact interface and the normal force and shear force established in step S2, the relationship between the normal force and shear force of the contact interface and the geometric deformation parameters of the asperities established in step S4, and the relationship between the shear force of the contact interface and the geometric deformation parameters of the asperities obtained in step S5; S7: Measure the contact resistance of the contact interface, substitute it into the equation set established in step S6, and obtain the normal force and shear force of the contact interface by solving them.

[0005] Furthermore, in step S1, the relationship between the actual contact area of ​​the contact interface and the normal force and shear force is: ; in, ; ; In the interface contact relationship of the present invention, the contact micro-protrusions on the contact interface are "averaged" so that the forces and geometric conditions of all micro-protrusions are equal. Refers to a single asperity on the contact interface and has no specific physical meaning; For the sake of simplicity, let ,make ; The relationship between the true contact area of ​​the contact interface and the normal force and shear force is expressed as: ; Where, is the normal force, is the shear force, is the true contact area of ​​the contact interface under the combined action of normal force and shear force, is the actual contact area of ​​the contact interface under the action of normal force alone, is the actual contact area of ​​a single asperity under the action of normal force alone, is the contact radius of the asperity under the action of normal force alone, is the actual number of contact points on the contact interface, is the initial height of the asperity, is a constant, is the creep activation energy, is the Boltzmann constant, is the temperature, is the normal load on a single convex body, is the stress index, For contact time.

[0006] Furthermore, in step S2, the relationship between the total contact resistance of the contact interface and the actual contact area is: ; Where, is the total contact resistance of the contact interface, is the material resistivity.

[0007] Furthermore, in step S3, the relationship between the actual contact area of ​​the contact interface and the geometric deformation parameter of the micro-asperity is: .

[0008] Furthermore, in step S4, the relationship between the normal force and shear force of the contact interface and the geometric deformation parameters of the asperities is: .

[0009] Furthermore, in step S5, the shear strain calculation formula of the micro-convex is: ; Where, is the shear strain of the asperity; The relationship between the shear force of the contact interface and the geometric deformation parameters of the asperity is: ; Where, is the shear modulus.

[0010] Furthermore, in step S7, the contact resistance of the contact interface is measured using a four-wire method, and the measuring equipment includes a direct shear device, an M81 synchronous source measurement system, a loading device, and a wire.

[0011] Compared with the prior art, the present invention has the following beneficial effects: The present invention establishes a force-electric contact model of the contact interface under the combined action of compression and shear, and based on the model, proposes an electrical measurement method for synchronously measuring the normal force and shear force of the interface by contact resistance. The present invention can easily and accurately calculate the magnitude of the contact force of the contact interface through an indirect measurement method, 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is the single asperity creep model of the present invention; Figure 2 Schematic diagram of the current path and equivalent circuit diagram of the rough contact interface of the present invention; Figure 3 Schematic diagram of geometric deformation of micro-asperities on the contact interface under the action of shear force and projection diagram of geometric deformation of micro-asperities; Figure 4 Schematic diagram of the connection between the contact interface electromechanical coupling shear experimental device and the "four-wire method" for measuring interface contact resistance in an embodiment of the present invention; Figure 5 Graphs showing the relationship between normalized true contact resistance and normal force under different shear forces, and graphs showing the relationship between normalized true contact resistance and shear force under different normal loads in an embodiment of the present invention; Figure 6 This is a comparison chart of the contact force values ​​calculated by the method proposed in the present invention and the experimental loading values. DETAILED DESCRIPTION

[0013] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0014] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0015] It will be understood that when used in this specification and the appended claims, the terms “comprises” and “comprising” indicate the presence of described features, integers, steps, operations, elements and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or groups thereof.

[0016] 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 present invention. As used in the specification and appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms unless the context clearly indicates otherwise.

[0017] It should be further understood that the term "and / or" used in the present description and the appended claims refers to and includes any and all possible combinations of one or more of the associated listed items.

[0018] 1. Establish a contact resistance-contact force model under the combined action of normal force and shear force Inspired by the yield criterion of material failure, the sliding behavior of micro-asperities between rough surfaces is considered to be a similar failure mechanism. Under this condition, the normal stress and shear stress at the contact interface satisfy the following yield criterion relationship: (1) Where, is the normal stress at the contact interface, is the contact interface shear stress, is the yield strength of the material under uniaxial stress, is a constant related to the material and is calibrated by experiment. The contact force on the asperity of the contact interface satisfies: (2) Where, 、 are the normal load and tangential load on the single convex body, is the actual contact area of ​​a single asperity under the combined action of normal force and shear force, is the actual contact area of ​​a single micro-convex body under the action of normal force alone. In the interface contact relationship of the present invention, the contact micro-convex bodies on the contact interface are "averaged" and the force and geometric conditions of all micro-convex bodies are equal. Therefore, the subscript It refers to a single asperity on the contact interface and has no specific physical meaning. For the entire rough contact interface, the contact normal force and shear force satisfy: (3) Where, is the normal force, is the shear force, is the true contact area of ​​the contact interface under the combined action of normal force and shear force, is the actual contact area of ​​the contact interface under the action of normal force alone. Since the forces and geometric conditions of all asperities on the contact interface are equal, the are the same, then: (4) (5) Where, is the actual number of contact points on the contact interface.

[0019] According to formula (3), the real contact area of ​​the contact interface under the combined action of normal force and shear force can be deduced as: (6) in, (7); where is the actual number of contact points on the contact interface, is the actual contact area of ​​a single asperity under normal force, is the contact radius of the asperity under the action of normal force alone.

[0020] Asperity contact radius under normal force alone The calculation is carried out by constructing a single asperity creep constitutive model. The specific description and derivation process are as follows: When two rough metal surfaces come into contact under the action of external force, the actual contact does not occur on the entire surface, but is concentrated between a few micro-protrusions distributed on the surface micro-concave-convex structure. Therefore, the contact characteristics of the micro-protrusions directly affect the overall mechanical behavior of the contact interface. In the initial contact stage, only a few of the highest micro-protrusion tips participate in the contact. At this time, the actual contact area is extremely small, and the local pressure within the unit contact area is much higher than the average stress level, thereby inducing significant plastic deformation. As the loading continues, more micro-protrusions with lower heights gradually participate in the contact until the cumulative contact area can balance the applied load. According to the statistical distribution of the micro-geometric characteristics of the rough surface, the shape of a single contact micro-protrusion can be simplified to a conical pyramid structure (such as Figure 1 Considering the progressive deformation characteristics of metal materials under high local stress, these asperities exhibit creep-like gradual compression behavior during the plastic contact stage. Therefore, the following creep constitutive relation can be used to describe the nonlinear deformation behavior of asperities at the metal interface during contact deformation: (8) Where, is the creep rate, is a constant that depends on the material and creep mechanism, is the normal stress at the contact interface, is the stress index, is the creep activation energy, is the Boltzmann constant, is temperature; According to the geometric relationship of the micro-convex body (such as Figure 1 As shown in Figure 2), the expressions of the normal creep rate, normal stress and contact radius of the contact asperity with respect to the contact time can be expressed as follows: (9) Where, is the creep rate as a function of contact time, is the rate of change of the asperity height as a function of the contact time, is the initial height of the asperity, is the normal load on a single convex body, is the function of the contact radius change rate of the asperity under the action of normal force alone with respect to the contact time, t is the contact time, is the bottom angle of the micro-convex body under the action of normal force alone. The geometric model size of the micro-convex body is the average geometric size (such as contact radius and micro-convex body height); Substituting Equation (9) into Equation (8), the derivative of the asperity contact radius is obtained as: (10) Integrating Equation (10) with respect to time yields the following expression for the contact radius of the asperity as a function of contact time: (11) Where, for When the asperity radius is small enough, it can be ignored, and the relationship between the contact radius of a single asperity and the contact time is obtained as follows: (12); In the formula, for the sake of simplicity, let (13), where (14); make (15) Substituting equations (13) and (15) into equation (12), we can obtain ; The contact radius of the asperity under the action of normal force alone is obtained based on the creep constitutive model. for: (16).

[0021] From formulas (6), (7), and (16), we can obtain: (17) Since the contact points on the rough surface are independent of each other, according to the resistance law of conductors, the following relationship exists for each micro-convex body: (18) Where, is the contact resistance of a single contact asperity, is the resistivity, is the length of a single asperity, is the actual contact area of ​​a single contact micro-convex body under the combined action of normal force and shear force. It should be noted that those skilled in the art generally believe that the micro-convex bodies on the contact interface are evenly distributed, so the length and resistivity of each micro-convex body on the contact interface are consistent, that is, Is a fixed value.

[0022] like Figure 2 As shown ( Figure 2 (a) is a schematic diagram of the current path at the rough contact interface. Figure 2 (b) is an equivalent circuit diagram. The rough contact interface is considered to be a collection 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 solely 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 equated to a parallel relationship. According to the superposition principle of parallel resistance, for all contact points, the following relationship holds: (19) Where, is the total contact resistance of the contact interface.

[0023] From formulas (18) and (19), we can get: ,because , then: (20) Considering that the micro-convex body has been deformed, the length of a single micro-convex body is Initial height of micro-protrusion The relationship is: (twenty one) Where, is the bottom angle of the micro-convex body under the action of normal force alone. According to equations (17), (20), and (21), the contact resistance of the rough interface under the combined action of pressure and shear force can be obtained as follows: (twenty two) Based on this, a contact resistance-contact force model under the combined action of normal force and shear force was established.

[0024] 2. Establish stress-strain equation based on the geometric deformation relationship of the micro-convex body In order to achieve the simultaneous measurement of normal force and shear force by a single contact resistance, it is necessary to supplement the stress-strain equation based on geometric deformation on the basis of the electromechanical contact equation. 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-convex body. Under the action of shear force, the contact radius of the micro-convex body increases, and the following relationship is satisfied before and after deformation: (twenty three) Where, is the bottom radius of the micro-convex body, is the contact radius of the asperity under the normal force alone, is the contact radius of the asperity under the combined action of normal force and shear force, is the bottom angle of the micro-convex body under the combined action of normal force and shear force.

[0025] From formula (23), the real contact area under the combined action of normal force and shear force can be obtained as: (twenty four) Equations (17) and (24) are the true contact areas calculated from the stress relationship and geometric deformation relationship under the yield criterion, respectively. From the deformation coordination condition, it can be seen that the two are equal, thus obtaining: (25) At the same time, the shear strain of the micro-convex body can also be calculated based on the geometric deformation relationship of the micro-convex body. ; Combine and , we can get: (26) Where, is the shear modulus, is the asperity shear stress, is the asperity shear strain, is the shear force.

[0026] 3. Construct a set of equations to calculate the interface normal force and shear force The following equations are formed by equations (13), (14), (15), (16), (22), (25), and (26): ; The unknown quantity in this system of equations is the normal force , shear force and contact resistance , other parameters are known or measurable, among which, 、 、 All can be measured by surface measuring instrument. 、 、 , are intermediate parameters that can be calculated from known quantities. The actual number of contact points n on the contact interface is calculated using the existing calculation formula. In this embodiment, stainless steel is used as the contact interface material. The determination of the model calculation parameters is determined by referring to Table 1. Specifically, the solution to this set of equations is: First, the total contact resistance of the contact interface is obtained through experimental detection , then Substitute into formula (22) and calculate , then Substitute into formula (24) to calculate the intermediate parameters , intermediate parameters The unknown quantity can be obtained by equation (16): Indicates that the intermediate parameters 、 Substitute into formula (23) and replace the intermediate parameter With unknown quantity With intermediate parameters Indicates that the intermediate parameters 、 、 Substitute into equation (26), and then combine equations (22), (25), and (26) to calculate the normal force and shear force .

[0027] Table 1. Model calculation parameters

[0028] 4. Measurement of contact resistance In this embodiment, a 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. This method can accurately measure the contact resistance. The M81 synchronous source measurement system is used to record and analyze the measured voltage data, and ultimately calculate the resistance value.

[0029] 5. Experimental verification of accuracy To verify the accuracy and feasibility of the proposed method for simultaneously measuring normal and shear forces based on contact resistance, a mechanoelectric contact experiment was conducted on a rough interface. Under a given constant normal load, the interface shear force and the corresponding contact resistance change were measured.

[0030] (1) Experimental setup and samples

[0031] Build a rough interface electromechanical coupling shear experimental device (such as Figure 4(as shown in a), the experimental equipment includes a direct shear device, an M81 synchronous source measurement system, a loading device and a conductor. Under the condition of constant normal load, the interface tangential load and the corresponding contact resistance change are measured respectively. The measurement of the tangential load (shear force) on the rough interface is obtained by the displacement of the force sensor in the direct shear test device, and its stiffness is 453N / mm. The measurement of the contact resistance of the rough interface is based on the voltage-current method: under the condition of applying normal and tangential loads, the current is transmitted through the contact interface, and the synchronous source measurement system (M81) is used to measure the voltage difference across the interface, so that the contact resistance is calculated according to Ohm's law. Specifically, the "four-wire method" is used to measure the contact resistance of the contact interface. The connection method of the "four-wire method" for measuring the contact resistance of the contact interface is as follows Figure 4 As shown in (b), one pair of test wires provides current and the other pair of test wires measures voltage. The sample material is stainless steel. The two samples are drilled on the side and aligned at the end. The two wires are connected to the M81 synchronous source measurement system. During the experiment, a normal load is applied through a direct shear device with a load range of 0-1000N. (Since the maximum bearing capacity of the strain-controlled direct shear device is 1000N. Therefore, in order to avoid damage to the instrument, the experimental load is strictly controlled within 0-1000N.) During the load holding stage, if the voltage fluctuation range is 0.5μV, it is determined that the system has reached a stable state. At this time, the M81 synchronous source measurement system begins to continuously record voltage changes. According to the tested voltage and the rated current applied, the calculation expression of the contact resistance can be obtained according to Ohm's law as follows: , where is the contact resistance, is the voltage, It's electric current.

[0032] (2) Experimental steps To ensure the accuracy of experimental data measurement and minimize measurement errors, the experimental operation follows the following steps: 1) Start the M81 synchronous source measurement system within 0-1800 seconds to stabilize the test environment and reduce system errors; 2) Place the sample in an unloaded experimental device and let it rest for a period of time between 1800 and 2000 seconds to minimize the initial error caused by creep effects; 3) Connect the sample line to the SSM and apply a DC current of 0.1A for 2000-2180 seconds while applying the specified load. This current value is intended to reduce interference from external factors such as environmental noise and DC drift, thereby obtaining a more stable electrical signal response. 4) Start the shear test apparatus and, while continuously applying a normal load, introduce a DC signal to ensure electrical contact, mitigate material creep, and suppress the Branly effect (a sudden drop in material resistance when current increases), thereby improving measurement stability and repeatability. To ensure measurement accuracy, multiple repeated measurements are performed using samples prepared from the same batch under identical experimental conditions. The arithmetic mean of these measurements is used as the output data.

[0033] It's important to note that to ensure the stability of the experimental environment and the consistency of the sample surface condition, a unified pretreatment process is used for each stainless steel sample before testing. The specific process involves wiping the sample surface with filter paper to remove contaminants such as dust and oil, and then blowing cold air over the sample surface for 3-5 minutes to remove any remaining debris. This process ensures that the roughness of each sample remains within the same range.

[0034] (3) Experimental results The results calculated by the method proposed in this invention are compared with the experimental results. Figure 5 As shown ( Figure 5 (a) is the relationship between normalized true contact resistance and normal force under different shear forces. Figure 5 (b) Graph showing the relationship between normalized true contact resistance and shear force under different normal loads. The calculated results from the proposed model agree well with the experimental measurements, regardless of whether shear force is applied. This consistency validates the theoretical model. Under the combined action of normal and tangential forces, the contact area increases, resulting in a decrease in contact resistance due to a weakening of the current contraction effect. Further application of tangential force under the action of the normal force results in a decrease in contact resistance due to the increase in contact area. Furthermore, as the normal force increases, the maximum applicable tangential force also increases, meaning that a larger tangential force is required to induce sliding.

[0035] 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 loaded normal and tangential forces. Figure 6 The figure shows a comparison between the normal force and tangential force calculation results obtained based on the electrical measurement method proposed in the present invention and the normal force and shear force loaded by the experimental device. It shows that the theoretical values ​​of the normal force and tangential force calculated by the present invention are in good agreement with the experimental values ​​of the normal force and tangential force loaded experimentally, which indicates that the measurement method proposed in the present invention is feasible and has high precision.

[0036] 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 in the scope of protection of the present invention.

Claims

1. A method for synchronously measuring interface normal force and shear force based on contact resistance, characterized in that: The following steps are involved: S1: Based on the yield criterion of material failure, the relationship between the normal stress and shear stress at the contact interface is established: ； Where, is the normal stress at the contact interface, is the contact interface shear stress, is the yield strength of the material under uniaxial stress, is a material-related constant; The relationship between the actual contact area of ​​the contact interface and the normal force and shear force is obtained from this relationship; S2: The contact interface is regarded as a collection 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 true contact area is established. The relationship between the true contact area of ​​the contact interface obtained in step S1 and the normal force and shear force is introduced into the established relationship between the total contact resistance and the true contact area, thereby establishing the relationship between the total contact resistance of the contact interface and the normal force and shear force. S3: Obtain the relationship between the true contact area of ​​the contact interface and the geometric deformation parameters of the asperities based on the geometric deformation relationship of the asperities on the contact interface before and after the shear force is applied; the geometric deformation relationship of the asperities on the contact interface before and after the shear force is: ； Where, is the bottom radius of the micro-convex body, is the contact radius of the asperity under the normal force alone, is the contact radius of the asperity under the combined action of normal force and shear force, is the bottom angle of the convex body under the action of normal force alone, is the bottom angle of the micro-convex body under the combined action of normal force and shear force; S4: combining the relationship between the true contact area of ​​the contact interface and the normal force and shear force obtained in step S1 and the relationship between the true contact area of ​​the contact interface and the geometric deformation parameters of the asperities obtained in step S3 to establish a relationship between the normal force and shear force of the contact interface and the geometric deformation parameters of the asperities; S5: Calculate the shear strain of the asperities based on the geometric deformation relationship of the asperities on the contact interface before and after the shear force acts, and obtain the relationship between the shear force magnitude of the contact interface and the geometric deformation parameters of the asperities by combining the existing shear force calculation formula; S6: jointly establish a system of equations by combining the relationship between the total contact resistance of the contact interface and the normal force and shear force established in step S2, the relationship between the normal force and shear force of the contact interface and the geometric deformation parameters of the asperities established in step S4, and the relationship between the shear force of the contact interface and the geometric deformation parameters of the asperities obtained in step S5; S7: Measure the contact resistance of the contact interface, substitute it into the equation set established in step S6, and obtain the normal force and shear force of the contact interface by solving them.

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: ； in, ; ； ； make ,make ; The relationship between the true contact area of ​​the contact interface and the normal force and shear force is expressed as: ； Where, is the normal force, is the shear force, is the true contact area of ​​the contact interface under the combined action of normal force and shear force, is the actual contact area of ​​the contact interface under the action of normal force alone, is the actual contact area of ​​a single asperity under the action of normal force alone, is the contact radius of the asperity under the normal force alone, is the actual number of contact points on the contact interface, is the initial height of the asperity, is a constant, is the creep activation energy, is the Boltzmann constant, is the temperature, is the normal load on a single convex body, Refers to a single asperity on the contact interface. is the 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: ； Where, is the total contact resistance of the contact interface, is the material resistivity.

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-asperities is: 。 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 asperity is: 。 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 shear strain calculation formula of the micro-convex body is: ； Where, is the shear strain of the asperity; The relationship between the magnitude of the shear force applied on the contact interface and the geometric deformation parameters of the asperities on the contact interface before and after the shear force is applied is: ； Where, 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 a four-wire method, and the measuring equipment includes a direct shear device, an M81 synchronous source measurement system, a loading device, and a wire.

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