A device and method for measuring the transverse resistivity of a fiber bundle

Abstract

The present invention relates to a device for measuring the transverse resistivity of a fiber bundle, comprising a conductive metal foil plate, a concave groove provided at the centerline of the conductive metal foil plate, a circular groove provided at each end of the concave groove, and through holes symmetrically provided on both sides of the concave groove of the conductive metal foil plate. The through holes are fixedly connected to wire electrodes. A fiber bundle sample is placed in the concave groove, and a resistance meter collects resistance data of the conductive loop. The transverse resistance of the fiber bundle of the present invention is obtained by an indirect measurement method. By coating the fiber bundle with conductive silver glue, an effective conductive path is ensured between the fiber bundle and the copper foil. The entire test loop is connected to the resistance meter through the wire electrodes, thereby solving the problem of difficulty in measuring resistance due to the small transverse distance of the fiber bundle. The test operation steps are simple and the test cost is low.

Description

Technical Field

[0001] The present invention belongs to the field of fiber bundle resistance measurement, and in particular relates to a method and a device for measuring the transverse resistivity of a fiber bundle. Background Art

[0002] Fiber-reinforced composite materials have the characteristics of high specific strength and high specific modulus, and are ideal materials for aerospace, automotive and other fields. However, since the service environment of such materials is usually relatively harsh, their structures are prone to internal damage, which requires structural health monitoring of fiber-reinforced composite structural parts to ensure their safety and reliability. Electrical impedance imaging technology is currently a research hotspot in non-destructive testing of composite structural parts. As a real-time damage monitoring method, this technology requires the composite material itself to be conductive. By passing an excitation current through the boundary area of ​​the test piece, collecting the boundary voltage, and outputting a resistivity distribution cloud map, the damage inside the test piece is analyzed. At present, the accuracy of electrical impedance imaging is not high enough, and it is necessary to use finite element simulation to study the factors that affect the accuracy of electrical impedance imaging. Material resistivity is an important parameter in the simulation process, so obtaining the actual resistivity of the material is of great significance for the simulation of electrical impedance imaging.

[0003] A fiber bundle is composed of multiple fiber filaments, and its longitudinal resistivity (along the fiber axis) is easy to obtain by measurement. However, the transverse distance of the fiber bundle is too small, which makes it extremely difficult to arrange the electrodes. Therefore, the conventional longitudinal resistivity measurement method is not applicable to the transverse resistivity measurement. In the paper "Flexible Integrated Sensors: Transverse Piezoresistance and Longitudinal Thermal Resistance of One Single Carbon Fiber Beam", two nanoprobes were used to detect the transverse resistance of the fiber bundle under a scanning electron microscope. In the paper "Single carbon fiber transverse electrical resistivity measurement via the van der Pauw method", the transverse resistance of the fiber filament was measured using an atomic force microscope based on the van der Pauw method. However, the above methods all perform in-situ resistance measurements under a microscope. Although this method is intuitive and accurate, it is complicated to operate, has a long sample preparation cycle, and has a high testing cost. It cannot quickly obtain the required transverse resistance parameters of the fiber bundle sample.

[0004] Therefore, it is necessary to provide a device that can quickly obtain the transverse resistance of a fiber bundle to achieve the measurement and analysis of the transverse resistivity of the fiber bundle. Summary of the Invention

[0005] The present invention addresses the shortcomings of existing technologies and provides a device and method for measuring the transverse resistivity of fiber bundles. This method eliminates measurement errors caused by wire resistance, conductive adhesive resistance, and other factors when measuring fiber bundles. The method offers advantages such as strong operability, high measurement accuracy, and low cost.

[0006] The technical solution adopted in the present invention is:

[0007] A device for measuring the transverse resistivity of a fiber bundle comprises a fiberglass board, the surface of the fiberglass board being covered with a layer of conductive metal foil, a concave groove being provided at the centerline of the fiberglass board on the side covered with the conductive metal foil, a circular groove having the same depth as the concave groove being connected to each end of the concave groove, the diameter of the circular groove being greater than the width of the concave groove, through holes being symmetrically provided on both sides of the fiberglass board, the through holes being fixedly connected to wire electrodes via conductive silver glue to ensure contact between the wire electrodes and the conductive metal foil, a fiber bundle sample being placed in the concave groove, the ends of the fiber bundle sample being fixed in the circular groove with glue, a layer of conductive silver glue being evenly applied along the direction of the concave groove to fix the fiber bundle sample, ensuring contact between the conductive silver glue and the conductive metal foil, and a measuring device preform being formed after the conductive silver glue is dried and cured, a resistor being connected to the wire electrodes, and the resistor collecting resistance data of a conductive loop formed by the wire electrodes, the conductive metal foil, the fiber bundle sample, and the conductive silver glue.

[0008] To optimize the above technical solutions, specific measures taken also include:

[0009] The glass fiber board is square or rectangular, and the measuring device prefabricated body is immersed in epoxy resin and cured at room temperature to form the measuring device.

[0010] The conductive metal foil is specifically copper foil or aluminum foil.

[0011] The above-mentioned through holes are in multiple groups, which are symmetrically arranged near the boundary of the glass fiber board and along the concave groove. The measuring device can be divided into multiple groups, each of which contains a group of symmetrically arranged through holes. The wire electrodes of each measuring device are connected to the resistance meter and the resistance data of the conductive circuit composed of the wire electrodes, conductive metal foil, fiber bundle sample and conductive silver glue is collected through the resistance meter.

[0012] The resistance meter is connected to the lead electrodes via a Kelvin test clip.

[0013] The present invention also provides a method for measuring the transverse resistivity of a fiber bundle, comprising the following steps:

[0014] Step 1: Covering the surface of the fiberglass board with a layer of conductive metal foil, a concave groove is formed at the center line of the fiberglass board on the side covered with the conductive metal foil, and a circular groove with the same depth as the concave groove and a diameter greater than the width of the concave groove is formed at each end of the concave groove. The fiberglass board is symmetrically formed with multiple through holes at the edges of the fiberglass board on both sides of the concave groove, and the wire electrodes are fixedly connected to the through holes and in contact with the conductive metal foil;

[0015] Step 2: Place the fiber bundle sample in the concave groove, fix the two ends of the fiber bundle sample in the circular groove with glue, wait for the glue to cure, and evenly apply a layer of conductive silver glue along the direction of the concave groove to fix the fiber bundle sample, ensuring that the conductive silver glue is in contact with the conductive metal foil. The through hole and the wire electrode are fixedly connected by the conductive silver glue and ensure that the wire electrode is in contact with the conductive metal foil. After the conductive silver glue cures, the measuring device preform is completed.

[0016] Step 3: Place the measuring device preform in a silicone mold, pour epoxy resin into the mold and cure it at room temperature. After it is completely cured, remove the measuring device and place it in a laser cutting machine for cutting. Ensure that each piece has a set of through holes. Grind and mirror polish the cross section of the fiber bundle sample in each cut measuring device.

[0017] Step 4: Use a resistance meter to connect the polished wire electrode of the measuring device through a Kelvin test clip to obtain the conductive loop resistance value R of the measuring device. Eliminate the influence of the wire electrode resistance R0, the conductive metal foil resistances R1 and R4, and the conductive silver paste resistance R2 in the conductive loop, calculate the transverse resistance R3 of the fiber bundle sample in the measuring device, and then calculate the transverse resistivity of the fiber bundle sample;

[0018] Step 5: Measure the transverse resistivity of the fiber bundle sample in each measuring device, take the average value and finally obtain the transverse resistivity of the fiber bundle sample.

[0019] To optimize the above measurement methods, specific measures taken also include:

[0020] In step 1, the wire electrodes and through-holes are fixed to the edge of the fiberglass board by perforating and winding, and then conductive silver glue is applied to the wire electrodes and through-holes, which strengthens the wire electrodes and reduces the contact resistance between the wire electrodes and the conductive metal foil.

[0021] In step four,

[0022] The wire electrode resistance R0 is measured in advance before the test;

[0023] The measurement method of the conductive metal foil resistance R1 and R4 is as follows: First, measure the width w of the conductive metal foil in the measuring device, then measure the length L1 and L4 of the conductive metal foil on both sides of the concave groove, and then measure the average thickness h1 and h4 at both ends of the conductive metal foil to calculate the resistance of the conductive metal foil.

[0024] The measurement method of the conductive silver paste resistance R2 is as follows: the conductive silver paste in the measuring device and the fiber bundle sample are simplified into a parallel equivalent circuit, that is, the conductive silver paste resistance R2 and the transverse resistance R3 of the fiber bundle sample form a parallel resistance R'. The average thickness h2 and length L2 of the conductive silver paste are measured. The parallel resistance is calculated as R' = R-R0-R1-R4. The resistance of the conductive silver paste

[0025] Calculation method of the transverse resistance R3 of the fiber bundle sample: calculated according to the parallel formula of resistance

[0026] Method for calculating the transverse resistivity of a fiber bundle sample: simplify the transverse cross section of the fiber bundle sample (7) into a rectangular area, measure the length L3 and height h3 of the transverse cross section of the fiber bundle sample, and calculate the transverse resistivity of the fiber bundle sample (7).

[0027] Compared with the prior art, the present invention has the following advantages:

[0028] 1. The present invention uses an indirect measurement method to obtain the transverse resistance of a fiber bundle. By coating the fiber bundle with conductive silver glue, an effective conductive path is formed between the fiber bundle and the copper foil. A connection between the wire electrodes and the resistance meter forms a complete test circuit, solving the problem of resistance measurement difficulties caused by the small transverse distance between the fiber bundles. The measurement device involved is simple in structure, the test procedure is simple, and the test cost is low.

[0029] 2. In the present invention, epoxy resin is used to solidify the entire measuring device and the device is cut into multiple measurement samples, which effectively improves the measurement efficiency and reduces the measurement error by taking the average value of multiple measurements of different sections of the same fiber bundle.

[0030] 3. This invention uses an equivalent circuit method to simplify the resistance model of the entire conductive circuit. The fiber bundle and conductive silver paste are considered a parallel circuit, which forms a series circuit with the copper foil and wire electrodes. Ohm's law is used to calculate the transverse resistance of the fiber bundle. The transverse cross-section of the fiber bundle is simplified into a rectangular area, and the transverse resistivity of the fiber bundle is calculated.

[0031] 4. The wire electrodes in the present invention are arranged in a perforated winding manner, and the contact resistance between the wire electrodes and the copper foil surface is reduced by applying conductive silver glue, which effectively reduces the influence of the contact resistance of the wire electrodes on the measurement error. The wire electrodes can be better connected to the resistance meter for resistance measurement, and the influence of the wire resistance can be well eliminated during the calculation process. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Schematic diagram of the structure of the device for measuring the transverse resistance of a fiber bundle of the present invention;

[0033] Figure 2 This is a schematic diagram of the structure of the measuring device of the present invention after the fiber bundle is placed;

[0034] Figure 3 Schematic diagram of resistance collection after the measuring device of the present invention is cut into multiple samples;

[0035] Figure 4 Schematic diagram of an equivalent circuit of the measuring method of the present invention;

[0036] Figure 5 is a simplified schematic diagram of a transverse cross section of a fiber bundle of the present invention;

[0037] The reference numerals are as follows: glass fiber board-1, conductive metal foil-2, concave groove-3, circular groove-4, through hole-5, wire electrode-6, fiber bundle sample-7, glue-8, conductive silver glue-9. DETAILED DESCRIPTION

[0038] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer and more understandable, the present invention is further 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 intended to limit the present invention.

[0039] like Figure 1 As shown, the measuring device of the present invention includes a fiberglass board 1 and a conductive metal foil 2. In this embodiment, the conductive metal foil 2 is copper foil. The copper foil is bonded to the surface of the fiberglass board 1 to form a copper-clad laminate. A concave groove 3 is cut along the centerline of any side of the copper-clad laminate with the copper foil. A circular groove 4 with the same depth as the groove and a larger diameter than the groove is cut at each end of the concave groove 3. Ten through-holes 5 are cut near the edges of the concave groove 3. Twenty wires of equal length and diameter are taken and their resistance value, R0 = 0.026Ω, is measured using an ohmmeter. The wires are passed through the ten through-holes 5, bent to the side edge of the copper-clad laminate, and twisted 3 to 4 times around the wires to ensure they are firmly fixed at the top and bottom ends of the copper-clad laminate.

[0040] Cut a certain size of Toray 3K carbon fiber bundle prepreg as fiber bundle sample 7, as shown in Figure 2 The carbon fiber prepreg is placed in the concave groove 3 of the measuring device. AB glue is used to bond the two ends of the fiber bundle prepreg to the circular groove 4 of the measuring device and wait for the AB glue to cure. After the AB glue has completely cured, conductive silver glue 9 is evenly applied to the upper surface of the carbon fiber bundle prepreg along the direction of the concave groove 3, ensuring that the conductive silver glue 9 contacts the copper foil on the surface of the copper-clad laminate to form a conductive loop. Then, conductive silver glue 9 is applied to the ten through-holes 5 of the copper-clad laminate to complete the preparation of the wire electrodes 6. The conductive silver glue 9 used in this experiment is model 8813X fast-drying conductive silver glue. The entire measuring device preform is placed in a fume hood and waited for 24 hours until the glue is completely cured.

[0041] Place the entire measuring device prefabricated body in a silicone mold, pour in room temperature curing epoxy resin, wait for 48 hours to completely cure, and then remove the measuring device from the mold. Place the entire measuring device in a laser cutting machine and cut it into equal parts, such as Figure 3 shown.

[0042] Take any measuring device and use a metallographic sample grinder to polish the fiber bundle cross section. Use 1000-grit sandpaper for light polishing, and then use 2000 or 3000-grit sandpaper for mirror polishing.

[0043] The polished measuring device was measured using a resistance meter (Keithley DAQ6510) with a Kelvin test clip, obtaining a resistance value of R = 0.16196 Ω. A vernier caliper was used to measure the width of the polished measuring device (w = 7.35 mm). The lengths of the copper foil on both sides of the groove (L1 = L4 = 20.00 mm) were also measured.

[0044] The polished surface of the sample was photographed using a scanning electron microscope, and the average thickness of the copper foil on both ends of the copper clad laminate was measured to be h1 = h4 = 0.1 mm. Figure 4 As shown, the conductive silver paste and the carbon fiber bundle are simplified into a parallel equivalent circuit, that is, the conductive silver paste resistor R2 and the carbon fiber bundle transverse resistor R3 form a parallel resistor R'.

[0045] The cross section of the conductive silver paste and carbon fiber bundle is simplified into a rectangular area as follows Figure 5 As shown, the average thickness of the conductive silver paste obtained by scanning electron microscope is h2 = 0.12 mm, and the length is L2 = 1.2 mm.

[0046] The resistance of the copper foil at both ends is calculated by the following formula Parallel resistance R′=R-R0-R1-R4=0.135Ω, resistance of conductive silver glue According to the parallel formula of resistance, the transverse resistance of carbon fiber bundle can be calculated

[0047] The length L3 of the carbon fiber bundle cross section is 1.2 mm, and the average thickness h3 is 0.2 mm. The transverse resistivity of the carbon fiber bundle is calculated by the following formula:

[0048] Repeat the above measurement and calculation process for other measuring devices and take the average value of the transverse resistivity of the carbon fiber bundle to reduce the measurement error.

[0049] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions based on the principles of the present invention are within the scope of protection of the present invention. It should be noted that for those skilled in the art, various improvements and modifications that do not depart from the principles of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A device for measuring the transverse resistivity of a fiber bundle, comprising a glass fiber board (1), characterized in that: The surface of the glass fiber board (1) is covered with a layer of conductive metal foil (2), and a concave groove (3) is provided at the center line position of the glass fiber board (1) on one side covered with the conductive metal foil (2). The two ends of the concave groove (3) are respectively connected to a circular groove (4) with the same depth as the concave groove (3), and the diameter of the circular groove (4) is greater than the width of the concave groove (3). The glass fiber board (1) is symmetrically provided with through holes (5) on both sides of the concave groove (3). The through holes (5) and the wire electrodes (6) are fixedly connected by conductive silver glue (9) to ensure that the wire electrodes (6) are in contact with the conductive metal foil (2). The fiber bundle sample (7) is placed in the concave groove (3). The two ends of the fiber bundle sample (7) are fixed in the circular groove (4) with glue (8), and a layer of conductive silver glue (9) is evenly applied along the direction of the concave groove (3) to fix the fiber bundle sample (7) to ensure that the conductive silver glue (9) is in contact with the conductive metal foil (2). After the conductive silver glue (9) is dried and solidified, a measuring device preform is formed. The resistor is connected to the wire electrode (6). The resistor collects resistance data of the conductive circuit composed of the wire electrode (6), the conductive metal foil (2), the fiber bundle sample (7) and the conductive silver glue (9); the glass fiber board (1) is square or rectangular, and the measuring device preform is immersed in epoxy resin and solidified at room temperature to form a measuring device.

2. The device for measuring the transverse resistivity of a fiber bundle according to claim 1, wherein: The conductive metal foil (2) is specifically copper foil or aluminum foil.

3. The device for measuring the transverse resistivity of a fiber bundle according to claim 1, wherein: The through holes (5) are arranged in groups, close to the boundary of the glass fiber board (1) and symmetrically along the concave groove (3). The measuring device can be divided into multiple groups, each measuring device includes a group of symmetrically arranged through holes. The wire electrode (6) of each measuring device is connected to the resistance meter and the resistance data of the conductive circuit composed of the wire electrode (6), the conductive metal foil (2), the fiber bundle sample (7) and the conductive silver glue (9) are collected through the resistance meter.

4. The device for measuring the transverse resistivity of a fiber bundle according to claim 1, wherein: The resistance meter is connected to the wire electrode (6) via a Kelvin test clip.

5. A method for measuring the transverse resistivity of a fiber bundle, characterized in that: The following steps are involved: Step 1: Covering the surface of the glass fiber board (1) with a layer of conductive metal foil (2), opening a concave groove (3) at the center line position of the glass fiber board (1) on one side covered with the conductive metal foil (2), and opening a circular groove (4) with the same depth as the concave groove (3) and a diameter greater than the width of the concave groove (3) at each end of the concave groove (3); the glass fiber board (1) symmetrically opens a plurality of through holes (5) at both sides of the concave groove (3) near the boundary position of the glass fiber board (1); and the wire electrode (6) is fixedly connected to the through hole (5) and contacts the conductive metal foil (2); Step 2: Place the fiber bundle sample (7) in the concave groove (3), fix the two ends of the fiber bundle sample (7) in the circular groove (4) with glue (8), wait for the glue (8) to solidify, evenly apply a layer of conductive silver glue (9) along the direction of the concave groove (3) to fix the fiber bundle sample (7), ensure that the conductive silver glue (9) is in contact with the conductive metal foil (2), and the through hole (5) and the wire electrode (6) are fixedly connected by the conductive silver glue (9) and ensure that the wire electrode (6) is in contact with the conductive metal foil (2). After the conductive silver glue (9) is solidified, a measuring device preform is manufactured; Step 3: Place the measuring device preform in a silicone mold, pour epoxy resin into the mold and cure it at room temperature, take out the measuring device after it is completely cured, place the measuring device in a laser cutting machine and cut it, ensuring that each part has a group of through holes (5), and grind and mirror-polish the cross section of the fiber bundle sample (7) in each cut measuring device; Step 4: Use a resistance meter to connect the polished wire electrode (6) of the measuring device through a Kelvin test clip to obtain the conductive circuit resistance value R of the measuring device, eliminate the influence of the wire electrode (6) resistance R0, the conductive metal foil (2) resistance R1 and R4, and the conductive silver glue (9) resistance R2 in the conductive circuit, calculate the transverse resistance R3 of the fiber bundle sample (7) in the measuring device, and then calculate the transverse resistivity of the fiber bundle sample (7); Step 5: measuring the transverse resistivity of the fiber bundle sample (7) in each measuring device, taking the average value to finally obtain the transverse resistivity of the fiber bundle sample (7).

6. The method for measuring the transverse resistivity of a fiber bundle according to claim 5, wherein: In the step 1, the wire electrode (6) and the through hole (5) are fixed to the edge of the glass fiber board (1) by perforating and winding, and then the conductive silver glue (9) is applied to the wire electrode (6) and the through hole (5), thereby reinforcing the wire electrode (6) and reducing the contact resistance between the wire electrode (6) and the conductive metal foil (2).

7. The method for measuring the transverse resistivity of a fiber bundle according to claim 5, wherein: In the step 4, The resistance R0 of the wire electrode (6) is measured in advance before the test; Method for measuring the resistance R1 and R4 of the conductive metal foil (2): first, measure the width w of the conductive metal foil (2) in the measuring device, then measure the length L1 and L4 of the conductive metal foil (2) on both sides of the concave groove (3), and then measure the average thickness h1 and h4 at both ends of the conductive metal foil (2) to calculate the resistance of the conductive metal foil (2). Method for measuring the resistance R2 of the conductive silver paste (9): simplify the conductive silver paste (9) and the fiber bundle sample (7) in the measuring device into a parallel equivalent circuit, that is, the resistance R2 of the conductive silver paste (9) and the transverse resistance R3 of the fiber bundle sample (7) form a parallel resistance R′, measure the average thickness h2 and length L2 of the conductive silver paste (9), and calculate the parallel resistance formula as R′=R-R0-R1-R4. The resistance of the conductive silver paste (9) The calculation method of the transverse resistance R3 of the fiber bundle sample (7) is as follows: The transverse resistivity of the fiber bundle sample (7) is calculated by simplifying the transverse cross section of the fiber bundle sample (7) into a rectangular area, measuring the length L3 and height h3 of the transverse cross section of the fiber bundle sample (7), and calculating the transverse resistivity of the fiber bundle sample (7).

Images