Equivalent modeling method for representing anisotropic conductivity of carbon fiber composite material

Abstract

The invention relates to the technical field of conductivity measurement of composite materials, and discloses an equivalent modeling method for characterizing anisotropic conductivity of a carbon fiber composite material, which comprises the following steps: enabling carbon fiber filaments to be equivalent to a conductive filament group, calculating the resistance of a single equivalent conductive filament according to the radius of each conductive filament in the conductive filament group, and calculating the anisotropic conductivity of the carbon fiber composite material according to the resistance of the equivalent conductive filament. A group of parallel vertical frameworks are used for fixing the conductive wire group; a resin-based area is replaced by an air medium area, the resin insulation effect is eliminated, in model setting, only air or vacuum passes through conductive wire groups, conductive pieces are added among a plurality of groups of conductive wires in the conductive wire groups, and lap resistance among carbon fiber wires is simulated. According to the invention, the resistance wire with limited volume is used for replacing the diameter micron-sized carbon fiber yarn, the problem that the micron-sized carbon fiber yarn cannot be controlled is solved, the air domain is used for replacing the resin domain, and the lap joint between the fibers is simulated through the lap joint ring, so that the problem that the lap joint resistance cannot be reached when the fibers are submerged in the resin matrix is solved.

Description

Technical Field

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

[0002] The mechanism for the anisotropic conductivity of carbon fiber composites is relatively clear. After curing, the carbon fibers are slightly bent within the matrix, creating numerous contact points between them. These points connect the fibers to form a fiber network. This fiber network provides a conductive path for lateral current conduction within the composite, creating a transverse conductive mechanism where current is conducted along the fiber network.

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

[0004] The present invention provides an equivalent modeling method for characterizing the anisotropic conductivity of carbon fiber composite materials, which solves the technical problems in related technologies that traditional carbon fiber composite materials are not convenient for quantitative analysis in engineering and the analysis of contact points between fiber networks is uncontrollable.

[0005] The present invention provides an equivalent modeling method for characterizing the anisotropic conductivity of carbon fiber composite materials, comprising the following steps:

[0006] S100: A carbon fiber wire is equivalent to a conductive wire group, and the radius of each conductive wire in the conductive wire group is , and calculate the equivalent conductive wire resistance of a single wire , used for model calibration;

[0007] A set of parallel vertical skeletons are used to fix the conductive wire group;

[0008] S200: Replace the resin-based region with an air dielectric domain to eliminate the resin insulation effect. In the model setting, only air or vacuum passes between the conductive filament groups.

[0009] S300: Add between one or more groups of conductive threads in the conductive thread group A conductive part to simulate the lap resistance between carbon fiber filaments;

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

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

[0012] Longitudinal measurements based on test equipment , calculate the longitudinal conductivity:

[0013] ;

[0014] ;

[0015] ;

[0016] in, is the number of conductive filaments, is the length of the conductive wire, is the cross section of a single conductive wire, is the total cross-section of the conductive filament group, is the longitudinal conductivity, is the longitudinal measurement;

[0017] S600: Connect a set of transverse electrodes to the outer wall ends of both sides of the conductive wire group, and connect a test device between the two transverse electrodes;

[0018] Based on lateral measurements of the test equipment , calculate the transverse conductivity:

[0019] ;

[0020] in, is the transverse conductivity, is the horizontal measurement;

[0021] S700: Comparing longitudinal conductivity and transverse conductivity , calculate the anisotropic ratio of conductivity in each direction:

[0022] ;

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

[0024] Furthermore, the vertical skeleton includes a skeleton frame, a first plug-in board and a second plug-in board. A first plug-in board groove is opened between the outer walls on both sides of the skeleton frame, and a second plug-in board groove is opened between the top outer wall and the bottom outer wall of the skeleton frame. The first plug-in board is inserted into the first plug-in board groove, and the second plug-in board is inserted into the second plug-in board groove.

[0025] Furthermore, the first plug-in plate and the second plug-in plate are both comb-tooth structures, and a plurality of groups of limiting grooves that are consistent with the insertion direction are opened in the insertion direction of the first plug-in plate and the second plug-in plate.

[0026] Furthermore, conductive member placement grooves are provided on one side outer wall of the first plug board and the second plug board. The conductive member placement grooves are used to install conductive members, and the conductive members are used to connect the conductive wires in adjacent limiting grooves.

[0027] Furthermore, the conductive member includes a first conductive member and a second conductive member, the first conductive member is used to short-circuit adjacent horizontally or vertically upward conductive threads, and the second conductive member is used to short-circuit adjacent diagonally upward conductive threads.

[0028] Furthermore, conductive grooves are formed at both ends of the outer walls of one side of the first conductive member and the second conductive member, and the directions of the groove openings of the limiting grooves are consistent with the insertion directions of the first plug-in board and the second plug-in board.

[0029] Furthermore, when the first plug-in board and the second plug-in board are inserted into the skeleton frame, the limiting grooves of the first plug-in board and the second plug-in board intersect to form a plurality of limiting slot holes, and the conductive wire group is limited in the limiting slot holes.

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

[0031] Furthermore, the end surface of the skeleton frame is provided with plug-in interfaces distributed in a matrix, and the diameter of the plug-in interfaces is adapted to the diameter of the cross section of the conductive wire.

[0032] Furthermore, pin openings are provided on the upper end surface and the lower end surface of the vertical frame, and a matching opening is provided on the horizontal frame, and a pluggable pin is inserted between the pin opening and the matching opening.

[0033] The beneficial effects of the present invention are:

[0034] The present invention cleverly uses a finite volume of resistance wire to replace micron-sized carbon fiber wire, overcoming the engineering difficulty of micron-sized carbon fiber wire being unmanageable. It uses an air domain to replace the resin domain and uses a lap ring to simulate the lap joint between fibers, overcoming the problem of unattainable lap resistance when the fibers are submerged in the resin matrix.

[0035] At the same time, by clamping the standard conductive parts on the conductive wire, it solves the problems of inaccurate positioning, inconsistent parameters such as spacing and overlap tightness, and model geometric shape deviation affecting current distribution. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a flow chart of an equivalent modeling method for characterizing anisotropic conductivity of carbon fiber composite materials of the present invention;

[0037] Figure 2 It is a structural schematic diagram of the equivalent modeling model of the present invention;

[0038] Figure 3 The present invention Figure 2 Schematic diagram of the test structure of the transverse conductivity of the middle model (the test equipment is connected between AB);

[0039] Figure 4 The present invention Figure 2 Schematic diagram of the test structure of the longitudinal conductivity of the middle model;

[0040] Figure 5 The present invention Figure 2 Schematic diagram of the structure of the vertical skeleton;

[0041] Figure 6 The present invention Figure 5 Schematic diagram of the connection structure between the middle plug board and the conductive part.

[0042] In the figure: 100, first horizontal skeleton; 200, vertical skeleton; 210, skeleton frame; 220, first plug board; 221, comb tooth portion; 222, conductive member placement slot; 223, limit slot; 224, buckle slot; 225, first conductive member; 226, second conductive member; 230, second plug board; 240, plug interface; 300, second horizontal skeleton; 400, conductive wire group; 500, horizontal electrode; 600, vertical electrode. DETAILED DESCRIPTION

[0043] The subject matter described herein will now be discussed with reference to exemplary embodiments. It should be understood that these embodiments are discussed solely to enable those skilled in the art to better understand and implement the subject matter described herein, and that the functions and arrangements of the elements discussed may be varied without departing from the scope of this specification. Various examples may omit, substitute, or add various processes or components as needed. In addition, features described with respect to some examples may also be combined in other examples.

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

[0045] S100: The carbon fiber filaments are equivalent to the conductive filament group 400, and the radius of each conductive filament in the conductive filament group 400 is , and calculate the equivalent conductive wire resistance of a single wire , using a set of parallel vertical frames 200 to fix the conductive thread group 400;

[0046] S200: replacing the resin-based region with an air dielectric region to eliminate the resin insulation effect. In the model setting, only air or vacuum passes between the conductive filament groups 400.

[0047] S300: Adding between one or more groups of conductive threads in the conductive thread group 400 A conductive part to simulate the lap resistance between carbon fiber filaments;

[0048] S400: Using a set of horizontal frames fixed to the upper and lower ends of the vertical frame 200 to ensure the stability of the model structure, the positions of the horizontal frames and the transverse frames are adjusted so that the conductive wires are arranged in parallel in the cavity enclosed between the horizontal frames and the transverse frames;

[0049] S500: Connect a set of longitudinal electrodes 600 to the cross-sectional ends on both sides of the conductive filament group 400, and connect a test device between the two longitudinal electrodes 600;

[0050] Longitudinal measurements based on test equipment , calculate the longitudinal conductivity ;

[0051] S600: Connect a set of transverse electrodes 500 to the outer sidewall ends of both sides of the conductive wire group 400, and connect a test device between the two transverse electrodes 500;

[0052] Based on lateral measurements of the test equipment , calculate the transverse conductivity ;

[0053] S700: Comparing longitudinal conductivity and transverse conductivity , calculate the anisotropic ratio of conductivity in each direction:

[0054] ;

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

[0056] like Figure 2-Figure 6 As shown in Figure 2, the equivalent model used to characterize the anisotropic conductivity of carbon fiber composite materials is as follows:

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

[0058] The horizontal frame includes a first horizontal frame 100 and a second horizontal frame 300, and the first horizontal frame 100 and the second horizontal frame 300 are arranged parallel to each other;

[0059] The end surface of the skeleton frame 210 is provided with a matrix-distributed through-hole plug-in port 240. The diameter of the plug-in port 240 is adapted to the cross-sectional diameter of the conductive wire. The vertical skeleton 200 includes the skeleton frame 210, a first plug-in board 220, and a second plug-in board 230. A first plug-in board slot is provided between the outer walls of the skeleton frame 210 on both sides, and a second plug-in board slot is provided between the top and bottom outer walls of the skeleton frame. The first plug-in board 220 is inserted into the first plug-in board slot, and the second plug-in board 230 is inserted into the second plug-in board slot.

[0060] The first plug-in board 220 and the second plug-in board 230 are both comb-tooth-shaped structures. A plurality of limiting grooves 223 are provided in the insertion direction of the first plug-in board 220 and the second plug-in board 230, which are consistent with the insertion direction. The number of limiting grooves 223 is related to the number of longitudinal conductive threads and the number of transverse conductive threads in the conductive thread group 400. The comb-tooth portions 221 are located between the limiting grooves 223.

[0061] It should be noted that the first plugboard 220 and the second plugboard 230 have buckle grooves 224 on the outer walls of the board ends;

[0062] Conductive member placement slots 222 are formed on the outer walls of the comb-tooth portions 221 of the first plugboard 220 and the second plugboard 230. The conductive member placement slots 222 are used to install conductive members, which are used to connect the conductive wires in adjacent limiting slots 223. The conductive members include a first conductive member 225 and a second conductive member 226. The first conductive member 225 is used to short-circuit adjacent horizontally or vertically upward conductive wires, and the second conductive member 226 is used to short-circuit adjacent diagonally upward conductive wires.

[0063] Conductive grooves are formed at both ends of the outer wall of one side of the first conductive member 225 and the second conductive member 226. The groove direction of the conductive groove is consistent with the insertion direction of the first plugboard 220 and the second plugboard 230. When the first plugboard 220 and the second plugboard 230 are inserted into the skeleton frame 210, a plurality of limiting slots are formed between the limiting slots 223 of the first plugboard 220 and the second plugboard 230. The conductive wire group 400 is limited in the limiting slots. The first conductive member 225 and the second conductive member 226 are both made of high-purity copper. The thickness of the first conductive member 225 and the second conductive member 226 is less than or equal to the groove depth of the conductive member placement groove 222. When the first conductive member 225 and / or the second conductive member 226 are placed in the conductive member placement groove 222, the groove wall of the conductive groove is pressed against the outer wall of the conductive wire.

[0064] like Figure 6 As shown, the remaining portion after the conductive member placement groove 222 is opened on the comb tooth portion 221 is a protrusion, which is used to clamp the conductive member;

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

[0066] Transverse resistance Impact: the number of conductive parts increases, the overlap points increase, the current transfer between fibers is smoother, resulting in a decrease in the lateral equivalent resistance;

[0067] Transverse resistance and the number of conductive elements Roughly inversely proportional, that is:

[0068] ;

[0069] However, the actual relationship is affected by the quality of the overlap, contact resistance, etc. and may be nonlinear;

[0070] The increase in conductive parts also reduces local current concentration and hot spots, improving the overall stability and uniformity of the material;

[0071] Longitudinal resistance Influence: Longitudinal resistance is mainly conducted along the direction of carbon fiber filaments, and conductive parts have little effect on longitudinal resistance. However, in extreme cases, too many conductive parts may introduce additional contact resistance, which has a slight impact.

[0072] Usually ignored Direct impact on longitudinal resistance.

[0073] Quantitative model diagram:

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

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

[0076] The transverse path is composed of multiple conductive members connected in parallel;

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

[0078] ;

[0079] along with increases, and the overall lateral resistance gradually decreases;

[0080] Longitudinal resistance It is mainly determined by the carbon fiber filaments equivalent to the conductive filaments themselves, and:

[0081] ;

[0082] Conductive wire resistance: resistance of a single conductive wire By material resistivity And the geometric dimensions determine:

[0083] ;

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

[0085] Total cross-sectional area:

[0086] ;

[0087] Longitudinal conductivity and transverse conductivity , which is calculated as follows:

[0088] ;

[0089] ;

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

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

[0092] Use wires or metal foil to connect the left and right ends of all conductive wires to ensure that all wire ends have the same potential, forming a unified electrode surface;

[0093] The endpoints of each conductive wire at the right / left end are connected to the other pole of the test instrument respectively, or the endpoints of each wire at the right end are connected together to form a common end as the other electrode;

[0094] The short circuit should be firm and the contact resistance should be very low to avoid affecting the measurement;

[0095] Measure the resistance between the two ends through the test equipment;

[0096] Assume that the conductive threads in the conductive thread group 400 are numbered ,but:

[0097] Left / right short circuit:

[0098] ;

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

[0100] The steps for testing the conductivity in the orthogonal direction (transverse direction) are as follows:

[0101] Use wires or copper foil to directly connect the left end points of all conductive wires to form an equipotential surface to ensure that all wire ends have the same potential;

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

[0103] The connection should be in close contact to avoid extra contact resistance caused by poor contact, which may affect the measurement accuracy;

[0104] Assume that the conductive threads in the conductive thread group 400 are numbered ,but:

[0105] Left / right short circuit:

[0106] ;

[0107] Right / left short circuit:

[0108] ;

[0109] The current flows into the common electrode on the left / right side, is conducted laterally between the conductive wire group 400 and the conductive member, and flows out of the common electrode on the right / left side. The voltage and current at both ends are measured to calculate the resistance. .

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

[0111] ;

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

[0113] in Quantified the degree of electrical anisotropy of the material, It means that the conductivity in the fiber direction is much stronger than that in the transverse direction, which is typical of carbon fiber composite materials with highly ordered arrangement and good contact. It indicates that the material conductivity is close to isotropic, which may be due to disordered fiber arrangement or large contact resistance;

[0114] use Quantitative analysis of influencing factors:

[0115] Influence of carbon fiber arrangement:

[0116] Orderly arrangement: When the carbon fiber fibers are highly arranged in a certain direction, the longitudinal conductivity Significantly improved, the lateral conductive path is limited, resulting in Large, by measurement , the uniformity and directionality of fiber arrangement can be evaluated;

[0117] Disordered or random arrangement: fiber orientation is dispersed, making the transverse conductivity Raise, lower , reflecting the isotropic conductivity trend of the material;

[0118] Quantitative method: Combine microscopy, CT scanning and other means to obtain 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 (number and quality of contact points between carbon fiber filaments):

[0120] Many and good contact points: Increased lateral current conduction paths, improving , thereby reducing k;

[0121] This shows that the overlap density and contact resistance between fibers in the composite material have a significant impact on the lateral conductivity.

[0122] Sparse contact points or high contact impedance: limited lateral conductivity, low, k increases;

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

[0124] The above describes the embodiments of the present invention, but the present invention is not limited to the above specific implementation methods. The above specific implementation methods are merely illustrative and not restrictive. Ordinary technicians in this field can also make many forms under the guidance of the present invention, all of which are protected by the present invention.

Claims

1. An equivalent modeling method for characterizing the anisotropic conductivity of carbon fiber composite materials, characterized in that: The following steps are involved: S100: A carbon fiber wire is equivalent to a conductive wire group, and the radius of each conductive wire in the conductive wire group is , and calculate the equivalent conductive wire resistance of a single wire , used for model calibration; A set of parallel vertical skeletons are used to fix the conductive wire group; S200: Replace the resin-based region with an air dielectric domain. In the model settings, the conductive filament groups are conducted only through air or vacuum. S300: Add between several groups of conductive threads in the conductive thread group A conductive part to simulate the lap resistance between carbon fiber filaments; S400: Use a set of horizontal frames to fix the upper and lower ends of the vertical frames to ensure the stability of the model structure. Adjust the positions of the horizontal and transverse frames so that the conductive wires are arranged in parallel in the cavity enclosed between the horizontal and transverse frames. S500: A set of longitudinal electrodes is connected to the cross-sectional ends on both sides of the conductive wire group, and a test device is connected between the two longitudinal electrodes; Longitudinal measurements based on test equipment , calculate the longitudinal conductivity; S600: Connect a set of transverse electrodes to the outer wall ends of both sides of the conductive wire group, and connect a test device between the two transverse electrodes; Based on lateral measurements of the test equipment , calculate the transverse conductivity; S700: Comparing longitudinal conductivity and transverse conductivity , calculate the anisotropic ratio of conductivity in each direction: ; Repeat S300-S700 to reduce the error.

2. The equivalent modeling method for characterizing the anisotropic conductivity of carbon fiber composite materials according to claim 1, characterized in that: The calculation formula of longitudinal conductivity is as follows: ； ； ； in, is the number of conductive filaments, is the length of the conductive wire, is the cross section of a single conductive wire, is the total cross-section of the conductive filament group, is the longitudinal conductivity, is the longitudinal measurement; The calculation formula of transverse conductivity is as follows: ； in, is the transverse conductivity, The values ​​are measured in the horizontal direction.

3. The equivalent modeling method for characterizing the anisotropic conductivity of carbon fiber composite materials according to claim 1, characterized in that: The vertical skeleton includes a skeleton frame, a first plug-in plate and a second plug-in plate. A first plug-in plate groove is opened between the outer walls of both sides of the skeleton frame, and a second plug-in plate groove is opened between the top outer wall and the bottom outer wall of the skeleton frame. The first plug-in plate is inserted into the first plug-in plate groove, and the second plug-in plate is inserted into the second plug-in plate groove. The first plug-in plate and the second plug-in plate are both comb-tooth structures, and several groups of limit grooves consistent with the insertion direction are opened in the insertion direction of the first plug-in plate and the second plug-in plate.

4. The equivalent modeling method for characterizing the anisotropic conductivity of carbon fiber composite materials according to claim 3, characterized in that: Conductive member placement grooves are provided on one side outer wall of the first plug board and the second plug board. The conductive member placement grooves are used to install conductive members, and the conductive members are used to connect the conductive wires in 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 member includes a first conductive member and a second conductive member. The first conductive member is used to short-circuit adjacent horizontal or vertical conductive threads, and the second conductive member is used to short-circuit adjacent diagonally upward conductive threads.

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 formed at both ends of the outer walls of one side of the first conductive member and the second conductive member, and the directions of the slot openings of the limiting grooves are consistent with the insertion directions of the first plug-in board and the second plug-in board.

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 plug-in board and the second plug-in board are inserted into the skeleton frame, the limiting grooves of the first plug-in board and the second plug-in board intersect to form a plurality of limiting slot holes, and the conductive wire group is limited in the limiting slot holes.

8. The equivalent modeling method for characterizing the anisotropic conductivity of carbon fiber composite materials according to claim 7, characterized in that: The first conductive member and the second conductive member are both made of high-purity copper, and the thickness of the first conductive member and the second conductive member is less than or equal to the depth of the groove where the conductive member is 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 surface of the skeleton frame is provided with matrix-distributed plug-in interfaces, and the diameter of the plug-in interfaces is adapted to the diameter of the cross section of the conductive wire.

10. An equivalent modeling method for characterizing the anisotropic conductivity of carbon fiber composite materials according to claim 9, characterized in that: Pin openings are provided on the upper end surface and the lower end surface of the vertical frame, and a matching opening is provided on the horizontal frame. A pluggable pin is inserted between the pin opening and the matching opening.

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