A high-speed train structural health monitoring method based on CFRP structure

Abstract

The invention discloses a high-speed train structural health monitoring method based on a CFRP structure. A rectangular coordinate system is established based on the structural characteristics of a CFRP laminate in a carriage plate, with any point on the inner wall of the CFRP laminate as the coordinate origin, the length direction of the single-layer CFRP plate as the X-axis, the thickness direction of the stacked single-layer CFRP plate as the Y-axis, and the width direction of the single-layer CFRP plate as the Z-axis; a plurality of monitoring points are selected on the CFRP laminate, and each monitoring point is equipped with monitoring electrodes in the X-direction, the Y-direction and the Z-direction; the monitoring electrodes are arranged in combination with the conductive characteristics of the CFRP laminate in the X-direction, the Y-direction and the Z-direction; the conductivity data at the monitoring point is collected through the monitoring electrodes; the conductivity data at each monitoring point is obtained, the actually detected conductivity data is compared with the conductivity threshold, and the structural health detection result at each monitoring point is output.

Description

Technical Field

[0001] The present invention belongs to the field of structural health monitoring, and in particular relates to a high-speed train structural health monitoring method based on a CFRP structure. Background Art

[0002] With the increase in the speed of high-speed trains and the number of trains in operation, how to effectively prevent safety accidents during operation has become a key issue to consider during design and maintenance. At present, the technologies commonly used for high-speed train structural health monitoring include optical method, acoustic emission, strain gauge, eddy current detection, smart coating, etc. These commonly used methods have shortcomings such as long operation time, damage to the structure, increase in structural deadweight, and inability to monitor the entire field and time domain.

[0003] At the same time, CFRP (carbon fiber composite material) is widely used in the field of high-speed trains due to its high specific stiffness, high specific strength, good corrosion resistance, small thermal expansion coefficient, light weight, high strength, good conductivity and non-metallic properties. CFRP material not only has good mechanical properties and can be used to prepare train structural components, but also has conductivity. Therefore, after the train structure is prepared, a stable conductivity can be obtained in the system. When the monitored component is damaged or the damage expands, its conductivity will change. After data collection and calculation, the number and shape of damage are analyzed and inferred, and the relationship between conductivity and damage state is established to achieve real-time monitoring of components. This intelligent monitoring method that uses its own electrical characteristics can be integrated with the structure to be measured, is easy to operate, does not increase dead weight, is suitable for complex structures, and has high cost performance. At the same time, it can also realize full-field and full-time domain monitoring, providing a reliable basis for the safety and maintenance of high-speed trains, and has good application prospects.

[0004] However, CFRP materials are usually laminated structures connected by adhesives. The presence of adhesives between adjacent layers will affect the conductivity, resulting in inaccurate monitoring results and affecting the accuracy of damage judgment. Therefore, based on the structural characteristics of CFRP materials, how to achieve high-precision monitoring of the structural health of high-speed trains is still a key technical problem that needs to be solved. Summary of the invention

[0005] In order to address the deficiencies in the prior art, the present invention proposes a high-speed train structural health monitoring method based on a CFRP structure. The present application arranges monitoring electrodes according to the structural characteristics of the CFRP laminate and the conductive characteristics in various directions, and improves the accuracy of the monitoring results and the monitoring accuracy of the high-speed train structural health by optimizing the monitoring points and the positions of the monitoring electrodes at the monitoring points.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] A high-speed train structural health monitoring method based on a CFRP structure comprises the following steps:

[0008] Step 1: Establish a rectangular coordinate system based on the structural characteristics of the CFRP laminate in the car body panel, with any point on the inner wall of the CFRP laminate as the coordinate origin, the length direction of the single-layer CFRP plate as the X-axis, the thickness direction of the stacked single-layer CFRP plate as the Y-axis, and the width direction of the single-layer CFRP plate as the Z-axis;

[0009] Step 2, selecting a number of monitoring points on the CFRP laminate, and each monitoring point is equipped with monitoring electrodes in the X direction, Y direction and Z direction; arranging the monitoring electrodes in combination with the conductive characteristics of the CFRP laminate in the X direction, Y direction and Z direction; collecting the conductivity data at the monitoring points through the monitoring electrodes;

[0010] Step 3: Obtain the conductivity data at each monitoring point, compare the actually detected conductivity data with the conductivity threshold, and output the structural health detection results at each monitoring point.

[0011] Furthermore, the arrangement characteristics of the monitoring electrodes of the CFRP laminate in the X and Y directions are as follows: since the fibers in the X and Z directions are in continuous contact with each other, the circuit is relatively stable; therefore, only one monitoring electrode needs to be provided at the monitoring point in the X and Z directions.

[0012] Furthermore, the characteristics of the monitoring electrode layout of CFRP laminates in the Y direction are as follows: the fibers in the same single-layer CFRP plate are in continuous contact and the circuit is relatively stable; however, the contact between adjacent single-layer CFRP plates is unstable due to the bonding layer. Only when subjected to external force will the bonding layer deform, resulting in more fiber contact points on both sides of the bonding layer, forming a good circuit; therefore, in view of the conductive characteristics in the Y direction, it is necessary to use the principles of molecular dynamics to describe the electron migration mode in the CFRP laminate to determine the layout of the monitoring electrodes in the Y direction.

[0013] Furthermore, the molecular dynamics principle is used to describe the electron migration mode in the CFRP laminate to determine the arrangement process of the Y-direction monitoring electrode:

[0014] Step 2.1, according to the stress characteristics of the high-speed train during operation, a dynamic equation of the high-speed train during operation is constructed to characterize the external force acting on the CFRP laminate during the operation of the high-speed train;

[0015] Step 2.2, based on the external force on the CFRP laminate during train operation obtained in step 2.1, the electron migration response of the CFRP laminate in the Y direction under the external force is derived, which is expressed as:

[0016]

[0017] Among them, u(lz ) is the migration function of electrons under external force, u 1 is the component of the displacement function, C 1 ,C 2 is a constant, l z is the radial distance between two micro-elements;

[0018] Step 2.3, based on the migration function, calculate the number of layers of electrons that migrate through the bonding layer in the CFRP laminate under the action of external force, expressed as:

[0019] In mm, electrons cannot pass through 1 Monitoring electrodes are arranged in each of the bonding layers, and the remaining bonding layer is close to the interior of the vehicle compartment.

[0020] Furthermore, a method for determining the conductivity threshold is as follows: by conducting a damage experiment on the CFRP laminate in advance, recording the damage level of the CFRP laminate during the experiment and its corresponding conductivity, and selecting the conductivity threshold therefrom.

[0021] Furthermore, the monitoring electrodes are coaxially arranged in the Y direction.

[0022] Furthermore, the monitoring points are arranged coaxially or staggered along the X direction.

[0023] Furthermore, the monitoring points are arranged with equal spacing or variable spacing along the X direction.

[0024] The beneficial effects of the present invention are as follows:

[0025] 1. The present invention proposes a method for monitoring the structural health of high-speed trains based on a CFRP structure. In this method, the fluid mechanics and solid kinematics characteristics exhibited by the train during operation are described by using the Euler and Lagrange equations respectively to construct its kinematic equations, which is convenient for directly determining the stress state of the train in practical applications.

[0026] 2. The present invention proposes a high-speed train structural health monitoring method based on a CFRP structure. In this method, the migration path of electrons in the CFRP laminate under the action of external force is analyzed, and molecular dynamics is used to describe the cohesive energy and migration function between adjacent electrons, providing theoretical support for the conductive path and subsequent electrode distribution.

[0027] 3. A high-speed train structural health monitoring method based on CFRP structure. Compared with other monitoring methods, this method constructs a CFRP conductive path through theoretical deduction to determine the location of sensor layout points and the number of electrode layouts, which can reduce the number of sensors installed, save the cost of engineering inspection, and the workload of data processing; it can also ensure the accuracy of monitoring data.

[0028] 4. A high-speed train structural health monitoring method based on CFRP structure. The whole set of sensor deployment based on the concept of distributed sensing has good feasibility, excellence and reliability. In the future, it can realize monitoring and early warning in intercity train / subway systems and provide technical support for intelligent operation and maintenance. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a schematic diagram of high-speed train coordinates;

[0030] Figure 2 This is a schematic diagram of aerodynamic loads on high-speed trains;

[0031] Figure 3 This is a schematic diagram of the CFRP car panel and circuit of a high-speed train;

[0032] Figure 4 This is a schematic diagram of the stress migration of electrons in the internal circuit of CFRP;

[0033] Figure 5 This is a schematic diagram of the monitoring points and electrode layout of the CFRP car body panel;

[0034] In the figure: 21, car body panel, 22, aerodynamic load; 31, CFRP laminate, 32, CFRP monofilament, 33, bonding layer, 34, X-direction circuit, 35, Y-direction circuit; 41, electrons in CFRP circuit; 51, monitoring point, 52, origin of the coordinate system of the monitoring point electrode, 53, electrode. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solution and advantages of the present invention clear, the present invention will be described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0036] Combined with Figure 1-5 , this application proposes a high-speed train structural health monitoring method based on a CFRP structure, comprising the following steps:

[0037] Step 1: Establish a rectangular coordinate system based on the structural characteristics of the CFRP laminate 31 in the car body panel 21.

[0038] First, the CFRP laminate 31 is formed by bonding a plurality of CFRP single-layer panels together through an adhesive layer 33, and each single-layer CFRP panel is formed by pressing a plurality of CFRP filaments 32; and when the CFRP laminate 31 is used as a car body panel 21, from the cross-sectional view of the CFRP laminate 31, the CFRP single-layer panels are stacked in sequence around the car body outward.

[0039] Based on the structural characteristics of the above-mentioned CFRP laminate 31 and its state when used as the compartment panel 21, for the convenience of description, in this embodiment, any point on the inner wall surface of the CFRP laminate 31 is taken as the coordinate origin, the length direction of the single-layer CFRP plate is taken as the X-axis, the thickness direction of the stacked single-layer CFRP plate is taken as the Y-axis, and the width direction of the single-layer CFRP plate is taken as the Z-axis to establish a rectangular coordinate system as shown in the figure below: Figure 3 shown.

[0040] Combined with the structural characteristics of the CFRP laminate 31, the internal circuit of the CFRP laminate 31 can be simplified for reference Figure 3 Specifically, since the fibers in the length direction (X direction) and the width direction (Z direction) of the CFRP laminate 31 are in continuous contact, the circuits in the X direction and Z direction are relatively stable. In the thickness direction (Y direction), the fibers in a single-layer CFRP plate are in continuous contact, so the circuit is relatively stable. However, due to the presence of the bonding layer 33 between adjacent single-layer CFRP plates, the fibers on both sides of the bonding layer 33 are less in contact. When the CFRP laminate 31 is subjected to external force, the bonding layer 33 in the CFRP laminate 31 is deformed under the extrusion of the external force, so that the fiber contact points on both sides of the bonding layer 33 increase, forming a good circuit.

[0041] Step 2: Select several monitoring points on the CFRP laminate 31 according to monitoring needs, and each monitoring point is equipped with monitoring electrodes in the X, Y and Z directions; the monitoring electrodes need to be arranged in combination with the conductive characteristics of the CFRP laminate 31 in the X, Y and Z directions; and collect the conductivity data at the monitoring points through the monitoring electrodes.

[0042] (1) Since the fibers in the X direction and the width direction Z direction are in continuous contact and the circuit is relatively stable, only one monitoring electrode is needed in the X direction and the Z direction to meet the monitoring requirements.

[0043] (2) In the Y direction, the fibers in the same single-layer CFRP plate are in continuous contact and the circuit is relatively stable; however, the contact between adjacent single-layer CFRP plates is unstable due to the bonding layer 33. Only when subjected to external force, the bonding layer 33 deforms, so that the fiber contact points on both sides of the bonding layer 33 increase, forming a good circuit. Therefore, in view of the conductive characteristics in the Y direction, it is necessary to use the principle of molecular dynamics to describe the electron migration mode in the CFRP laminate 31 to determine the arrangement of the monitoring electrodes in the Y direction, as follows:

[0044] Step 2.1, according to the force characteristics of the high-speed train during operation, a dynamic equation of the high-speed train during operation is constructed to characterize the external force acting on the CFRP laminate 31 during operation of the high-speed train.

[0045] according to Figure 1 , 2The force characteristics of the high-speed train during operation are shown in the figure, and its force control equation is constructed. For fluid mechanics and solid kinematics, Euler and Lagrange equations are used to describe them respectively, and their constitutive equations are:

[0046]

[0047] Among them, ρ f is the fluid density, v s is the solid velocity, t is the time, is the divergence operator, μ f is the fluid viscosity, T is the temperature, I is the unit matrix, F is the external force, v f is the fluid velocity and σ is the stress.

[0048] Based on the above equations (1) and (2), we can get the fluid velocity v f , and further calculate the load F generated by the fluid when the train is running f for:

[0049]

[0050] Among them, I′ is the feature matrix, F p is the pressure, and l is the external normal vector on the fluid-solid coupling interface.

[0051] The high-speed train is subjected to aerodynamic loads (fluid generation) during its travel. The aerodynamic matrix of the object can be further calculated using the aerodynamic loads and the scaling factors dn and dN of the space frame and material frame of the grid unit:

[0052]

[0053] At the same time, when the train operation produces a coupling effect, the speed of the rigid motion of the object needs to be considered.

[0054]

[0055] Among them, H u is the rigid body displacement matrix when the train is running.

[0056] During the operation of the train, the rigid body motion displacement and deformation jointly determine the solid node displacement of the train at the fluid-solid coupling interface, so the main dynamic equation is:

[0057]

[0058] Among them, H s is the mass matrix, H c is the damping matrix, H k is the stiffness matrix, H u is the displacement matrix, Hs,f is the aerodynamic matrix, H F This is the load matrix other than aerodynamic loads.

[0059] Step 2.2, based on the external force applied to the CFRP laminate 31 during train operation obtained in step 2.1, derive the electron migration response of the CFRP laminate 31Y under the external force.

[0060] exist Figure 4 In the coordinate system shown, an atom is taken on each side of the bonding layer 33 between the CFRP laminates 31 as a microelement, assuming that ω is the X-axis angle, β is the Y-axis angle, and r e is the radius, l z is the radial distance between the two micro-element bodies, micro-element A 1 (r e sinωcosβ,r e sinωsinβ,r e cosω), microelement body A 2 (0,0,l z ), the distance between the two infinitesimal bodies is:

[0061]

[0062] According to the principle of molecular dynamics, the cohesive energy between two micro-elements is:

[0063]

[0064] In the formula,

[0065] Among them, ρ e is the single electron density, V e is the volume of a single electron, V A1A2 A 1 A 2 The volume, α e ,γ e is the volume of a single electron.

[0066] When the CFRP laminated plates 31 are subjected to external force, compression occurs between the plates, and the thickness of the bonding layer 33 between the CFRP laminated plates 31 is l h will change, so the cohesive energy between the infinitesimal elements can be expressed as:

[0067]

[0068] By taking the derivative of the above formula, we can get the cohesive force on the interface between the two infinitesimals:

[0069]

[0070] From the above equations (9) and (10), we can get the radial distance l between the two micro-element bodies: z Cohesive energy of the surface:

[0071]

[0072] According to formula (11), the resultant force on the interface can be obtained:

[0073]

[0074] Combining the above formula, we can get the final resultant force on the interface of the two micro-elements as:

[0075]

[0076] It can be seen from equation (13) in step 2 that the migration of electrons in the conductive path of the CFRP laminate 31 under the action of external force is related to the thickness of the bonding layer l h It is related to the number of layers m (assuming that the bonding layer 33 has m layers, and the entire CFRP laminate 31 has m+1 layers of CFRP single-layer plates), so the displacement response expression of electrons under external force is constructed (the formula for breaking through the bonding layer), and then the number of electrodes in the Y direction is reasonably arranged. Since the direction of the resultant force is radial and has nothing to do with β and ω and is in the Y direction, according to the principle of elastic mechanics:

[0077]

[0078] According to the force on the microelement, its strain and stress tensor can be obtained as follows:

[0079]

[0080] Among them, i, j are the directions of the basis vector axes in the Cartesian coordinate system, ε ij is the electronic strain, u i ,u j is the displacement of the electron in each direction, σ ij is the electronic stress, is the radial distance l between the two micro-elements z The electronic stress at the position, E is the electronic elastic modulus, v′ is the electronic Poisson’s ratio, δ ij is the Kronecker operator, T j is the external force, x i ,x j ,y i ,y j are coordinate components.

[0081] Substituting equation (15) into equation (14), we can obtain the equilibrium equation in the coordinate system:

[0082]

[0083] According to the stress-strain relationship in elastic mechanics, equation (16) can be rewritten as:

[0084]

[0085] Substitute the resultant force H on the right side of equation (6) in step 2.1 s,f +H F Replace T on the right side of equation (17) j , then solving the differential equation (17) we can obtain the electron migration function u(l z ):

[0086]

[0087] In the formula,

[0088] Among them, u 1 is the component of the displacement function, C 1 ,C 2 ,C 3 is a constant.

[0089] Step 2.3, according to formula (18), the number of layers through which electrons migrate in the CFRP laminate under the action of external force through the bonding layer 33 can be calculated:

[0090]

[0091] This means that electrons can only pass through m 1 Adhesive layer 33, m 1 ∈[1,m]; the remaining mm 1 The remaining mm 1 The conductivity data cannot be monitored in the layer; in order to overcome this defect, it is necessary to monitor the conductivity data in the Y direction in the mm region where electrons cannot reach. 1 Monitoring electrodes are arranged in each single-layer CFRP plate. The full-field and full-time monitoring in the Y direction is achieved through these adjacently arranged monitoring electrodes.

[0092] Taking m=6 as an example, assuming that m calculated by equation (19) 1 If it is 2, it means that the remaining 4 layers of electrons cannot pass through, and monitoring electrodes need to be arranged in the remaining 4 layers of single-layer CFRP plates.

[0093] In this embodiment, electrons jump from the outside to the inside of the car, so the monitoring electrodes are arranged on the 4-layer single-layer CFRP plates close to the inside of the car, and the monitoring electrodes on the 4-layer single-layer CFRP plates need to be coaxially arranged.

[0094] More specifically, the monitoring points may be coaxially arranged or staggered along the length direction (X direction).

[0095] More specifically, the monitoring points may be arranged at reasonable intervals, such as equal intervals or variable intervals.

[0096] Step 3: Obtain the conductivity data at each monitoring point, set the conductivity threshold, compare the actually detected conductivity data with the conductivity threshold, and output the structural health detection results at each monitoring point.

[0097] By performing a damage experiment on the CFRP laminate 31 in advance and recording the damage level of the CFRP laminate 31 and its corresponding conductivity during the experiment, a conductivity threshold can be determined for structural health judgment.

[0098] The above embodiments are only used to illustrate the design ideas and features of the present invention, and their purpose is to enable scientific research and engineering technicians in the field to understand the content of the present invention and implement it accordingly. The protection scope of the present invention is not limited to the above embodiments, so all equivalent changes or modifications made based on the theories, technologies and methods disclosed in the present invention are within the protection scope of the present invention.

Claims

1. A high-speed train structural health monitoring method based on CFRP structure, characterized in that: The steps include: Step 1, based on the structural characteristics of the CFRP laminate (31) in the compartment panel (21), a rectangular coordinate system is established, with any point on the inner wall surface of the CFRP laminate (31) as the coordinate origin, the length direction of the single-layer CFRP plate as the X-axis, the thickness direction of the stacked single-layer CFRP plate as the Y-axis, and the width direction of the single-layer CFRP plate as the Z-axis; Step 2, select a number of monitoring points on the CFRP laminate (31), and each monitoring point is equipped with monitoring electrodes in the X direction, Y direction and Z direction; arrange the monitoring electrodes in combination with the conductive characteristics of the CFRP laminate (31) in the X direction, Y direction and Z direction; collect the conductivity data at the monitoring points through the monitoring electrodes; the arrangement characteristics of the monitoring electrodes in the Y direction of the CFRP laminate (31) are as follows: the fibers in the same single-layer CFRP plate are in continuous contact and the circuit is relatively stable; however, the contact between adjacent single-layer CFRP plates is unstable due to the bonding layer (33). Only when subjected to external force, the bonding layer (33) deforms, so that the fiber contact points on both sides of the bonding layer (33) increase, forming a good circuit; therefore, in view of the conductive characteristics in the Y direction, it is necessary to use the principle of molecular dynamics to describe the electron migration mode in the CFRP laminate (31) to determine the arrangement of the monitoring electrodes in the Y direction; Step 3: Obtain the conductivity data at each monitoring point, compare the actually detected conductivity data with the conductivity threshold, and output the structural health detection results at each monitoring point.

2. A high-speed train structural health monitoring method based on a CFRP structure according to claim 1, characterized in that: The monitoring electrode arrangement characteristics of the CFRP laminate (31) in the X direction and the Y direction are as follows: since the fibers in the X direction and the width direction and the Z direction are in continuous contact, the circuit is relatively stable; therefore, only one monitoring electrode needs to be provided at the monitoring point in the X direction and the Z direction.

3. A high-speed train structural health monitoring method based on a CFRP structure according to claim 1, characterized in that: The electron migration mode in the CFRP laminate (31) is described by using the principle of molecular dynamics to determine the arrangement process of the Y-direction monitoring electrode: Step 2.1, constructing a dynamic equation of the high-speed train when it is running according to the stress characteristics of the high-speed train when it is running, so as to characterize the external force acting on the CFRP laminate (31) when the high-speed train is running; Step 2.2, based on the external force applied to the CFRP laminate (31) during train operation obtained in step 2.1, the electron migration response of the CFRP laminate (31) in the Y direction under the external force is derived, which is expressed as: Among them, u(l z ) is the migration function of electrons under external force, u1 is the component of displacement function, C1, C2 are constants, l z is the radial distance between two micro-elements; Step 2.3, based on the migration function, the number of layers of electrons in the CFRP laminate that migrate through the bonding layer (33) under the action of external force is calculated, which is expressed as: Among them, l h The thickness of the bonding layer is 10 ...

4. A high-speed train structural health monitoring method based on a CFRP structure according to claim 1, characterized in that: The method for determining the conductivity threshold value is as follows: a damage experiment is performed on the CFRP laminate (31) in advance, the damage level of the CFRP laminate (31) and its corresponding conductivity are recorded during the experiment, and the conductivity threshold value is selected therefrom.

5. A high-speed train structural health monitoring method based on a CFRP structure according to claim 1, characterized in that: The monitoring electrodes are coaxially arranged in the Y direction.

6. A high-speed train structural health monitoring method based on a CFRP structure according to claim 1, characterized in that: The monitoring points are arranged coaxially or staggered along the X direction.

7. A high-speed train structural health monitoring method based on a CFRP structure according to claim 1, characterized in that: The monitoring points are arranged along the X direction with equal spacing or variable spacing.

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