An equivalent modeling method for characterizing the anisotropic electrical conductivity of carbon fiber composites

Abstract

This invention relates to the field of electrical conductivity measurement technology for composite materials, and discloses an equivalent modeling method for characterizing the anisotropic electrical conductivity of carbon fiber composites. The method includes the following steps: treating carbon fiber filaments as equivalent conductive filament groups; calculating the equivalent resistance of a single conductive filament based on the radius of each filament in the conductive filament group; fixing the conductive filament group using a set of parallel vertical skeletons; replacing the resin matrix region with an air dielectric domain to eliminate the resin insulation effect; ensuring that the conductive filament groups are connected only by air or vacuum in the model settings; and adding conductive elements between several groups of conductive filaments in the conductive filament group to simulate the overlap resistance between carbon fiber filaments. This invention uses a finite-volume resistance wire to replace micron-sized carbon fiber filaments, overcoming the problem of uncontrollable micron-sized carbon fiber filaments; it uses an air domain to replace the resin domain; and it also uses overlap rings to simulate the overlap between fibers, overcoming the problem of unattainable overlap resistance when fibers are submerged in a resin matrix.

Description

Technical Field

[0001] This invention relates to the fields of composite materials and electrical conductivity measurement, and more specifically, to an equivalent modeling method for characterizing the anisotropic electrical conductivity of carbon fiber composite materials. Background Technology

[0002] The formation mechanism of anisotropic electrical conductivity in carbon fiber composites is relatively well understood. After curing, the carbon fibers undergo slight bending within the matrix, creating numerous contact points between them. All fibers connect to each other through these contact points, forming a fiber network. This fiber network structure provides a conductive path for lateral current conduction in the composite material, thus establishing a lateral conductivity mechanism where current is conducted along the fiber network.

[0003] However, the large number of fibers and their small diameter make quantitative analysis in engineering difficult, which limits in-depth research on the anisotropic conductivity of carbon fiber composites. Summary of the Invention

[0004] This invention provides an equivalent modeling method for characterizing the anisotropic electrical conductivity of carbon fiber composites, solving the technical problems in related technologies where traditional carbon fiber composites are not convenient for quantitative analysis in engineering and the analysis of contact points between fiber networks is uncontrollable.

[0005] This invention provides an equivalent modeling method for characterizing the anisotropic electrical conductivity of carbon fiber composites, comprising the following steps:

[0006] S100: Will Each carbon fiber filament is equivalent to a conductive filament assembly, where the radius of each conductive filament in the assembly is [missing information]. And calculate the equivalent resistance of a single conductive wire. Used for model calibration;

[0007] The conductive wire assembly is fixed using a set of parallel vertical frames;

[0008] S200: Replace the resin-based region with an air-dielectric region to eliminate the resin insulation effect. In the model settings, the conductive wire groups are connected only by air or vacuum.

[0009] S300: Add between one or more groups of conductive wires in a conductive wire assembly. A conductive component simulates the lap resistance between carbon fiber filaments;

[0010] S400: Use a set of horizontal skeletons fixed to the upper and lower ends of the vertical skeleton to ensure the stability of the model structure. Adjust the position of the horizontal skeleton and the transverse skeleton so that the conductive wires are arranged in parallel in the cavity enclosed between the horizontal skeleton and the transverse skeleton.

[0011] S500: A set of longitudinal electrodes is connected to the cross-sectional ends on both sides of the conductive wire assembly, and a test device is connected between the two longitudinal electrodes.

[0012] Longitudinal measurements based on testing equipment Calculate the longitudinal conductivity:

[0013] ;

[0014] ;

[0015] ;

[0016] in, This refers to the number of conductive wires. The length of the conductive wire, This is the cross-section of a single conductive wire. This represents the total cross-section of the conductive wire assembly. Longitudinal conductivity, This is a longitudinal measurement;

[0017] S600: A set of transverse electrodes is connected to the outer wall ends on both sides of the conductive wire assembly, and a test device is connected between the two transverse electrodes.

[0018] Lateral measurements based on testing equipment Calculate the transverse conductivity:

[0019] ;

[0020] in, Transverse conductivity, This is a lateral measurement.

[0021] S700: Comparison of longitudinal conductivity and transverse conductivity Calculate the anisotropy ratio of conductivity in each direction:

[0022] ;

[0023] Repeat steps S300-S700 to reduce error.

[0024] Furthermore, the vertical frame includes a frame body, a first insert plate, and a second insert plate. A first insert plate groove is formed between the two outer walls of the frame body, and a second insert plate groove is formed between the top and bottom outer walls of the frame body. The first insert plate is inserted into the first insert plate groove, and the second insert plate is inserted into the second insert plate groove.

[0025] Furthermore, both the first and second insert plates have a comb-like structure, and several sets of limiting grooves consistent with the insertion direction are opened in the insertion direction of the first and second insert plates.

[0026] Furthermore, conductive component placement grooves are formed on one outer wall of both the first and second insert plates. The conductive component placement grooves are used to install conductive components, and the conductive components are used to connect the conductive wires in the adjacent limiting grooves.

[0027] Furthermore, the conductive element includes a first conductive element and a second conductive element. The first conductive element is used to short-circuit adjacent horizontal or vertically upward conductive wires, and the second conductive element is used to short-circuit adjacent diagonally upward conductive wires.

[0028] Furthermore, conductive grooves are formed at both ends of one side outer wall of the first and second conductive components, and the groove opening direction of the limiting groove is consistent with the insertion direction of the first and second insert plates.

[0029] Furthermore, when the first and second insert plates are inserted into the frame, the limiting grooves of the first and second insert plates intersect to form several limiting slots, and the conductive wire assembly is limited within the limiting slots.

[0030] Furthermore, both the first and second conductive components are made of high-purity copper, and the thickness of both the first and second conductive components is less than or equal to the depth of the conductive component placement groove.

[0031] Furthermore, the end face of the skeleton frame has matrix-distributed insertion interfaces, the diameter of which is adapted to the diameter of the cross-section of the conductive wire.

[0032] Furthermore, pin holes are opened on both the upper and lower ends of the vertical frame, and mating holes are opened on the horizontal frame, with a pull-out pin inserted between the pin holes and the mating holes.

[0033] The beneficial effects of this invention are as follows:

[0034] This invention ingeniously uses a resistance wire of limited volume to replace a carbon fiber filament with a diameter of micrometers, overcoming the engineering challenge of the uncontrollable nature of micrometer-sized carbon fiber filaments. It uses an air domain to replace a resin domain and simulates the overlap between fibers through an overlap ring, thus overcoming the problem of unachievable overlap resistance when fibers are submerged in a resin matrix.

[0035] Meanwhile, by using standard conductive parts to clamp onto the conductive wire, the problems of inaccurate positioning, inconsistent parameters such as spacing and overlap tightness, and the influence of model geometry deviation on current distribution are solved. Attached Figure Description

[0036] Figure 1 This is a flowchart of an equivalent modeling method for characterizing the anisotropic electrical conductivity of carbon fiber composite materials according to the present invention.

[0037] Figure 2 This is a schematic diagram of the structure of the equivalent model of the present invention;

[0038] Figure 3 This is the invention Figure 2 A schematic diagram of the test structure for the transverse conductivity of the model (with test equipment connected between A and B).

[0039] Figure 4 This is the invention Figure 2 A schematic diagram of the test structure for the longitudinal conductivity of the model.

[0040] Figure 5 This is the invention Figure 2 A schematic diagram of the vertical frame structure;

[0041] Figure 6 This is the invention Figure 5 A schematic diagram of the connection structure between the middle insert plate and the conductive components.

[0042] In the figure: 100, first horizontal frame; 200, vertical frame; 210, frame body; 220, first insert plate; 221, comb teeth; 222, conductive component placement groove; 223, limiting groove; 224, snap-fit ​​groove; 225, first conductive component; 226, second conductive component; 230, second insert plate; 240, insertion interface; 300, second horizontal frame; 400, conductive wire assembly; 500, transverse electrode; 600, longitudinal electrode. Detailed Implementation

[0043] The subject matter described herein will now be discussed with reference to exemplary embodiments. It should be understood that these embodiments are discussed only to enable those skilled in the art to better understand and implement the subject matter described herein, and changes may be made to the function and arrangement of the elements discussed without departing from the scope of this specification. Various processes or components may be omitted, substituted, or added as needed in the examples. Furthermore, features described in some examples may be combined in other examples.

[0044] like Figure 1 As shown, an equivalent modeling method for characterizing the anisotropic electrical conductivity of carbon fiber composites includes the following steps:

[0045] S100: Will Each carbon fiber filament is equivalent to a conductive filament group 400, and the radius of each conductive filament in the conductive filament group 400 is [missing information]. And calculate the equivalent resistance of a single conductive wire. A set of parallel vertical skeletons 200 is used to fix the conductive wire group 400.

[0046] S200: Replace the resin-based region with an air-dielectric region to eliminate the resin insulation effect. In the model settings, make the conductive wire groups 400 pass through only air or vacuum.

[0047] S300: Add between one or more groups of conductive wires in the conductive wire group 400 A conductive component simulates the lap resistance between carbon fiber filaments;

[0048] S400: Use a set of horizontal skeletons to fix on the upper and lower ends of the vertical skeleton 200 to ensure the stability of the model structure. Adjust the position of the horizontal skeleton and the transverse skeleton so that the conductive wires are arranged in parallel in the cavity enclosed between the horizontal skeleton and the transverse skeleton.

[0049] S500: A set of longitudinal electrodes 600 are connected to the cross-sectional ends on both sides of the conductive wire group 400, and a test device is connected between the two longitudinal electrodes 600.

[0050] Longitudinal measurements based on testing equipment Calculate longitudinal conductivity ;

[0051] S600: A set of transverse electrodes 500 are connected to the outer wall ends on both sides of the conductive wire assembly 400, and a test device is connected between the two transverse electrodes 500.

[0052] Lateral measurements based on testing equipment Calculate the transverse conductivity ;

[0053] S700: Comparison of longitudinal conductivity and transverse conductivity Calculate the anisotropy ratio of conductivity in each direction:

[0054] ;

[0055] Reusing conductivity ratio Analyze the degree of electrical anisotropy of the material.

[0056] like Figures 2-6 As shown, the equivalent model used to characterize the anisotropic electrical conductivity of carbon fiber composites is as follows:

[0057] In one embodiment of the present invention, the model includes a horizontal skeleton, a vertical skeleton 200 and a conductive wire group 400. The conductive wire group 400 is arranged in a matrix and parallel, and is inserted into the vertical skeleton 200. The horizontal skeleton is set at the upper and lower ends of the vertical skeleton 200. Pin holes are opened on the upper and lower end surfaces of the vertical skeleton 200. A mating port is opened on the horizontal skeleton, and a pluggable pin is inserted between the pin hole and the mating port.

[0058] The horizontal skeleton includes a first horizontal skeleton 100 and a second horizontal skeleton 300, which are arranged parallel to each other.

[0059] The end face of the skeleton frame 210 has matrix-distributed through-hole interfaces 240. The diameter of the interface 240 is adapted to the diameter of the cross-section of the conductive wire. The vertical skeleton 200 includes the skeleton frame 210, the first insert plate 220 and the second insert plate 230. The first insert plate groove is opened between the two outer walls of the skeleton frame 210, and the second insert plate groove is opened between the top outer wall and the bottom outer wall of the skeleton frame. The first insert plate 220 is inserted into the first insert plate groove, and the second insert plate 230 is inserted into the second insert plate groove.

[0060] The first insert plate 220 and the second insert plate 230 are both comb-shaped structures. Several sets of limiting grooves 223 are opened in the insertion direction of the first insert plate 220 and the second insert plate 230, which are consistent with the insertion direction. The number of limiting grooves 223 is related to the number of longitudinal conductive wires and the number of transverse conductive wires in the conductive wire group 400. The comb-shaped part 221 is located between the limiting grooves 223.

[0061] It should be noted that the first insert plate 220 and the second insert plate 230 have snap-fit ​​grooves 224 on the outer wall of the plate end;

[0062] Conductive component placement grooves 222 are provided on the outer walls of the comb teeth 221 of the first insertion plate 220 and the second insertion plate 230. The conductive component placement grooves 222 are used to install conductive components. The conductive components are used to connect the conductive wires in the adjacent limiting grooves 223. The conductive components include a first conductive component 225 and a second conductive component 226. The first conductive component 225 is used to short-circuit adjacent horizontal or vertically upward conductive wires. The second conductive component 226 is used to short-circuit adjacent diagonally upward conductive wires.

[0063] Conductive grooves are formed at both ends of the outer wall of the first conductive element 225 and the second conductive element 226. The groove opening direction is consistent with the insertion direction of the first insert plate 220 and the second insert plate 230. When the first insert plate 220 and the second insert plate 230 are inserted into the skeleton frame 210, the limiting grooves 223 of the first insert plate 220 and the second insert plate 230 intersect to form a number of limiting slot holes. The conductive wire group 400 is limited in the limiting slot holes. The first conductive element 225 and the second conductive element 226 are both made of high-purity copper. The thickness of the first conductive element 225 and the second conductive element 226 is less than or equal to the depth of the conductive element placement groove 222. When the first conductive element 225 and / or the second conductive element 226 are placed in the conductive element placement groove 222, the groove wall of the conductive element abuts against the outer wall of the conductive wire.

[0064] like Figure 6 As shown, the remaining part after the conductive component placement groove 222 is opened on the comb tooth part 221 is a protrusion, which is used to hold the conductive component.

[0065] The influence of conductive components on resistance measurement:

[0066] For lateral resistance The increased number of conductive parts and overlapping points leads to smoother current transfer between fibers, resulting in a decrease in the lateral equivalent resistance.

[0067] lateral resistance and the number of conductive parts They are roughly inversely proportional, that is:

[0068] ;

[0069] However, the actual relationship may be nonlinear due to factors such as the quality of the overlap and contact resistance.

[0070] The increased number of conductive components also reduces local current concentration and hot spots, improving the overall stability and uniformity of the material;

[0071] For longitudinal resistance Impact: The longitudinal resistance is mainly conducted along the direction of the carbon fiber filament. The conductive components have little effect on the longitudinal resistance, but in extreme cases, too many conductive components may introduce additional contact resistance, which has a slight impact.

[0072] Generally negligible Direct impact on longitudinal resistance.

[0073] Quantitative model illustration:

[0074] The longitudinal resistance of a single conductive wire is ;

[0075] The contact resistance of a single conductive component is ;

[0076] The lateral path consists of multiple conductive components connected in parallel;

[0077] The lateral resistance is then approximately equal to the parallel combination of the resistances of the conductive wire contacts:

[0078] ;

[0079] along with As the resistance increases, the overall transverse resistance gradually decreases.

[0080] Longitudinal resistance It is mainly determined by the carbon fiber filament itself, which is equivalent to the conductive filament, and:

[0081] ;

[0082] Resistance of a single conductive wire: Based on the resistivity of the material Determined by geometry:

[0083] ;

[0084] in, For the equivalent radius, The resistivity of the conductive wire (such as nickel-chromium alloy).

[0085] Total cross-sectional area:

[0086] ;

[0087] Longitudinal conductivity and transverse conductivity The calculation formula is as follows:

[0088] ;

[0089] ;

[0090] in and These are the measured longitudinal and transverse resistances, respectively.

[0091] The specific steps for testing fiber conductivity (longitudinal direction) are as follows:

[0092] Connect the left and right ends of all conductive wires with wires or metal foil to ensure that all wire ends have the same potential and form a uniform electrode surface.

[0093] The endpoints of each conductive wire on the right / left end are connected to the other pole of the testing instrument, or the endpoints of each wire on the right end are connected together to form a common end, which serves as another electrode.

[0094] The short circuit should be secure, with extremely low contact resistance to avoid affecting the measurement;

[0095] Measure the resistance at both ends using testing equipment;

[0096] Let the conductive wires in the conductive wire group 400 be numbered as follows: ,but:

[0097] Left / right end shorted:

[0098] ;

[0099] The right / left end is connected individually or together to the measuring terminal. Current enters from the common terminal of the left / right end and flows longitudinally along each carbon fiber filament to the right / left end. The voltage and current at both ends are measured, and the resistance is calculated. .

[0100] The steps for testing orthogonal (lateral) conductivity are as follows:

[0101] Connect the left ends of all conductive wires directly with wires or copper foil to form an equipotential surface, ensuring that all wire ends have the same potential.

[0102] Similarly, connect the right ends of all carbon fiber filaments to form another common end;

[0103] The connection points should be in tight contact to avoid additional contact resistance caused by poor contact, which could affect the accuracy of the measurement.

[0104] Assume the conductive wires in conductive wire group 400 are numbered as follows: ,but:

[0105] Left / right short circuit:

[0106] ;

[0107] Right / left short circuit:

[0108] ;

[0109] Current flows in from the common electrode on the left / right side, is transversely conducted between the conductive wire group 400 and the conductive element, and flows out from the common electrode on the right / left side. The resistance is calculated by measuring the voltage and current across the two ends. .

[0110] Anisotropy ratio It is usually defined as the ratio of the electrical conductivity of a material along the fiber direction (longitudinal direction) to the electrical conductivity perpendicular to the fiber direction (transverse direction):

[0111] ;

[0112] in, It is the longitudinal conductivity. It is the transverse conductivity.

[0113] in The degree of electrical anisotropy of the material was quantified. This indicates that the electrical conductivity along the fiber direction is much stronger than that in the transverse direction, typically seen in highly ordered carbon fiber composites with good contact. This indicates that the material's electrical conductivity is close to isotropic, which may be due to disordered fiber arrangement or high contact resistance.

[0114] use Quantitative analysis of influencing factors:

[0115] The effect of carbon fiber filament arrangement:

[0116] Ordered arrangement: When carbon fiber filaments are arranged vertically along a certain direction, the longitudinal conductivity is... Significantly improved, but lateral conductive paths are limited, leading to Large, through measurement It can assess the uniformity and orientation of fiber arrangement;

[0117] Disordered or random arrangement: the fiber orientation is dispersed, resulting in lower transverse conductivity. Increase, decrease This reflects the isotropic electrical conductivity tendency of the material;

[0118] Quantitative methods: Combine microscopy, CT scanning and other means to obtain the fiber orientation distribution, use conductivity measurement to obtain k, and establish a mathematical model or empirical formula for the arrangement of carbon fiber filaments and k.

[0119] Contact density (the number and mass of contact points between carbon fiber filaments):

[0120] Multiple and well-maintained contact points increase the lateral current conduction path, improving... This reduces k;

[0121] This reflects the significant impact of fiber overlap density and contact resistance on the transverse conductivity of composite materials;

[0122] Sparse contact points or high contact resistance: limited lateral conductivity. Low, k increases;

[0123] Quantitative analysis: By adjusting experimental parameters such as the number of conductive components, contact pressure, and surface treatment, the changed k is measured to quantify the contribution of contact density to anisotropy.

[0124] The embodiments of the present invention have been described above, but the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention, all of which are within the protection scope of the present invention.

Claims

1. An equivalent modeling method for characterizing the anisotropic electrical conductivity of carbon fiber composites, characterized in that, Includes the following steps: S100: Will Each carbon fiber filament is equivalent to a conductive filament assembly, where the radius of each conductive filament in the assembly is [missing information]. And calculate the equivalent resistance of a single conductive wire. Used for model calibration; The conductive wire assembly is fixed using a set of parallel vertical frames; S200: Replace the resin-based region with an air-dielectric region, and in the model settings, make the conductive wire groups conduct only through air or vacuum; S300: Add between several groups of conductive wires in the conductive wire assembly. A conductive component simulates the lap resistance between carbon fiber filaments; S400: Use a set of horizontal skeletons fixed to the upper and lower ends of the vertical skeleton to ensure the stability of the model structure. Adjust the position of the horizontal skeleton and the transverse skeleton so that the conductive wires are arranged in parallel in the cavity enclosed between the horizontal skeleton and the transverse skeleton. S500: A set of longitudinal electrodes is connected to the cross-sectional ends on both sides of the conductive wire assembly, and a test device is connected between the two longitudinal electrodes. Longitudinal measurements based on testing equipment Calculate the longitudinal conductivity; S600: A set of transverse electrodes is connected to the outer wall ends on both sides of the conductive wire assembly, and a test device is connected between the two transverse electrodes. Lateral measurements based on testing equipment Calculate the transverse conductivity; S700: Comparison of longitudinal conductivity and transverse conductivity Calculate the anisotropy ratio of conductivity in each direction: ; Repeat steps S300-S700 to reduce error.

2. The equivalent modeling method for characterizing the anisotropic conductivity of carbon fiber composite materials according to claim 1, characterized in that, The formula for calculating longitudinal conductivity is as follows: ； ； ； in, This refers to the number of conductive wires. The length of the conductive wire, This is the cross-section of a single conductive wire. This represents the total cross-section of the conductive wire assembly. Longitudinal conductivity, This is a longitudinal measurement; The formula for calculating transverse conductivity is as follows: ； in, Transverse conductivity, This is a lateral measurement.

3. The equivalent modeling method for characterizing the anisotropic conductivity of carbon fiber composite materials according to claim 1, characterized in that, The vertical frame includes a frame body, a first insert plate, and a second insert plate. The first insert plate groove is formed between the two outer walls of the frame body, and the second insert plate groove is formed between the top and bottom outer walls of the frame body. The first insert plate is inserted into the first insert plate groove, and the second insert plate is inserted into the second insert plate groove. Both the first and second insert plates have a comb-like structure. Several sets of limiting grooves are formed in the insertion direction of the first and second insert plates, which are consistent with the insertion direction.

4. The equivalent modeling method for characterizing the anisotropic conductivity of carbon fiber composite materials according to claim 3, characterized in that, Conductive component placement grooves are provided on one outer wall of both the first and second insert plates. The conductive component placement grooves are used to install conductive components, and the conductive components are used to connect the conductive wires in the adjacent limiting grooves.

5. The equivalent modeling method for characterizing the anisotropic conductivity of carbon fiber composite materials according to claim 4, characterized in that, The conductive component includes a first conductive component and a second conductive component. The first conductive component is used to short-circuit adjacent horizontal or vertically upward conductive wires, and the second conductive component is used to short-circuit adjacent diagonally upward conductive wires.

6. The equivalent modeling method for characterizing the anisotropic conductivity of carbon fiber composite materials according to claim 5, characterized in that, Conductive grooves are opened at both ends of one side outer wall of the first and second conductive components, and the groove opening direction of the limiting groove is consistent with the insertion direction of the first and second insert plates.

7. The equivalent modeling method for characterizing the anisotropic conductivity of carbon fiber composite materials according to claim 6, characterized in that, When the first and second insert plates are inserted into the skeleton frame, the limiting grooves of the first and second insert plates intersect to form several limiting slots, and the conductive wire group is limited in the limiting slots.

8. The equivalent modeling method for characterizing the anisotropic conductivity of carbon fiber composite materials according to claim 7, characterized in that, Both the first and second conductive components are made of high-purity copper, and the thickness of both the first and second conductive components is less than or equal to the depth of the groove in which the conductive components are placed.

9. The equivalent modeling method for characterizing the anisotropic conductivity of carbon fiber composite materials according to claim 8, characterized in that, The end face of the skeleton frame has a matrix of insertion interfaces, the diameter of which is matched with the diameter of the cross-section of the conductive wire.

10. The equivalent modeling method for characterizing the anisotropic conductivity of carbon fiber composite materials according to claim 9, characterized in that, Pin holes are opened on both the upper and lower ends of the vertical frame, and mating holes are opened on the horizontal frame. A pull-out pin is inserted between the pin holes and the mating holes.

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