Composite material fiber monofilament radial resistance testing device and resistivity calculation method

Abstract

The invention discloses a composite material fiber monofilament radial resistance testing device and a resistivity calculation method, and belongs to the technical field of composite material performance testing and structure health monitoring. The device comprises a base, a cross beam, a micrometer caliper type push rod and a plate-shaped electrode. The cross beam is an elastic component, the two ends of the cross beam are installed on stand columns of the base, plate-shaped electrodes on the cross beam can be driven by a push rod to move in parallel and opposite directions, and parallel and lossless clamping of fiber monofilaments is achieved. The base is provided with a monofilament fixing mechanism used for straightening and fixing fibers. During testing, after fiber monofilaments are straightened and aligned, a to-be-tested section of the fiber monofilaments is clamped in parallel by a plate-shaped electrode, constant current is applied, voltage drop is measured, and radial resistance is calculated. Furthermore, based on the actually measured resistance value, a finite element model of the corresponding size is established, and the radial conductivity of the fiber is inverted by adopting a bisection iteration method. The problem that the radial resistance of the micron-sized fiber monofilament is difficult to accurately measure is solved, the device is simple in structure, convenient to operate, low in cost and accurate and reliable in measurement result, and a key parameter acquisition means is provided for composite material microcosmic conductive network modeling and structure health monitoring.

Description

Technical Field

[0001] This invention belongs to the field of composite material structural health monitoring, specifically involving a radial resistance testing device for fiber monofilaments and a resistivity calculation method. By accurately characterizing the radial resistance of fibers, it provides core parameters for impedance response-based composite material structural health monitoring. Background Technology

[0002] Fiber-reinforced composite materials, due to their superior properties such as high strength, high modulus, and low density, have been widely used in various fields. However, harsh working environments can lead to extremely complex damage modes. If damage is not identified and assessed in a timely manner after it occurs, failure during operation can have catastrophic consequences. Therefore, it is crucial to detect the health status of fiber-reinforced composite components and predict their failure. It is noteworthy that some fiber-reinforced composite materials possess inherent electrical conductivity, and their resistance response is closely related to various factors such as temperature, load, and failure mode. Therefore, they can act as "sensors," providing in-situ feedback on the operating temperature and load of components, and offering a basis for reliability assessment and failure prediction.

[0003] The anisotropy of fiber-reinforced composites is not only reflected in their mechanical properties but also significantly in their electrical properties. Therefore, resistivity parameters in different directions are particularly important for establishing the overall model. Axial resistivity is relatively easy to measure, while radial resistivity measurement is more difficult, and resistivity derivation is also challenging. Currently, only Lu Wei et al. from Nanjing University of Aeronautics and Astronautics have invented a device and method for measuring the transverse resistivity of fiber bundles, realizing the measurement of the transverse resistance of fiber bundles (A device and method for measuring the transverse resistivity of fiber bundles, CN116338312).

[0004] However, the morphology of the monofilaments within fiber bundles is extremely complex. The monofilaments are not in ideal parallel contact, and their resistance network is not a simple parallel connection. Therefore, the macroscopic transverse resistance parameters measured based on the fiber bundle cannot be directly applied to the monofilament scale. When constructing a microscopic conductive network in composite materials, the transverse resistance (radial resistance) of the monofilament is a crucial parameter. However, the size of the fiber monofilament is small, and traditional resistance measurement methods cannot accurately measure its transverse resistance. Therefore, it is necessary to design a device to measure the transverse resistance of fiber monofilaments, solving the problem of measuring the transverse resistance of monofilaments and providing accurate parameters for subsequently establishing a microscopic conductive network in composite materials by combining the morphology of the fiber bundle. Summary of the Invention

[0005] This invention addresses the shortcomings of existing technologies by providing a device for testing the radial resistance of composite fiber monofilaments and a method for calculating resistivity.

[0006] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is as follows:

[0007] A device for testing the radial resistance of a single composite fiber filament includes a base, a crossbeam, a micrometer-type push rod, and a plate electrode.

[0008] The base is equipped with several columns and push rod mounting seats;

[0009] The crossbeam is an elastic component, with both ends detachably mounted on the column. The two crossbeams are parallel to each other and located on both sides of the fiber monofilament; an installation structure is provided in the middle of the crossbeam.

[0010] The plate-shaped electrode is mounted on the beam mounting structure, with the plate surface of the plate-shaped electrode parallel to the beam.

[0011] The micrometer-type push rod is mounted on the push rod mounting base. Its telescopic end acts on the crossbeam to push the two crossbeams to bend in parallel towards each other, so that the two plate-shaped electrodes clamp the fiber monofilament in parallel.

[0012] The base is also equipped with a monofilament fixing mechanism to fix the two ends of the fiber monofilament to be tested, so that the fiber monofilament is straightened and located at the center line position between the two plate electrodes.

[0013] To optimize the above technical solution, the specific measures also include:

[0014] The top of the column is provided with a T-shaped mounting groove, and the two ends of the crossbeam are T-shaped structures that match the T-shaped mounting groove. The installation and positioning of the crossbeam are achieved through the T-shaped fit.

[0015] The plate electrode is made of copper, with an electrode post perpendicular to the plate surface at one end. The mounting structure in the middle of the crossbeam is a sleeve that matches the electrode post. The plate electrode is installed by inserting the electrode post into the sleeve.

[0016] The monofilament fixing mechanism includes at least two threaded holes on the base, bolts that mate with the threaded holes, and threaded washers that are fitted onto the bolts and mate with the bolt threads. The fiber monofilaments are pressed and fixed to the base by the tightened threaded washers.

[0017] A method for testing the radial resistance of a single composite fiber filament, using the aforementioned device for testing the radial resistance of a single composite fiber filament, includes the following steps:

[0018] S1: Install the plate electrode on the crossbeam, install the crossbeam on the base, and install the micrometer screw rod on the base;

[0019] S2: Straighten the fiber monofilament and fix its two ends to the base using the monofilament fixing mechanism, so that the fiber monofilament is aligned with the center line of the two plate electrodes;

[0020] S3: Connect the measuring leads to the two plate electrodes and connect them to the resistance measuring device;

[0021] S4: Operate the micrometer type push rod to push the crossbeam to bend, so that the two plate-shaped electrodes clamp the fiber monofilament in parallel, and cut off the redundant fiber monofilament outside the electrodes.

[0022] S5: Apply a constant current I to the two plate-shaped electrodes through a resistance measuring device, measure the voltage drop V between the two electrodes, and calculate the radial resistance value r = V / I of the fiber monofilament in the clamped section between the two electrodes.

[0023] The fiber monofilament is a silicon carbide fiber monofilament or a carbon fiber monofilament.

[0024] A method for calculating the radial conductivity of a composite material fiber monofilament includes the following steps:

[0025] P1: Based on the radial resistance value r of the fiber monofilament measured by the method for testing the radial resistance of the composite material fiber monofilament as claimed in claim 5, establish a cylindrical finite element model with the same geometric dimensions as the clamped section of the actually measured fiber monofilament.

[0026] P2: Apply the same constant current I as the excitation measured in the area of the finite element model corresponding to the contact position of the plate-shaped electrodes, and set a ground boundary condition at the other end of the model.

[0027] P3: Use the dichotomy iteration method to calculate the radial conductivity of the fiber monofilament: set the conductivity search interval [A, B], so that the model calculation resistance values a and b corresponding to this interval satisfy r ∈ [a, b]; take the midpoint conductivity value C = (A + B) / 2 of the interval for calculation to obtain the model resistance value c; if c < r, then let B = C, otherwise let A = C; repeat this iteration process until the error between the calculated resistance value c and the actually measured resistance value r meets the preset standard, and then the corresponding conductivity C at this time is the radial conductivity of the fiber monofilament.

[0028] In step P1, the finite element model is a cylinder with the same diameter as the fiber monofilament and a length equal to the distance between the clamping points of the two plate-shaped electrodes.

[0029] The device for testing the radial resistance of the composite material fiber monofilament of the present invention can conveniently carry out the test of the temperature-sensitive effect of the radial resistivity by adding auxiliary experimental equipment such as a high-temperature furnace and a thermocouple on the basis of changing the materials of the base, crossbeam, etc.

[0030] The present invention has the following beneficial effects:

[0031] 1. This invention provides a device for testing the radial resistance of composite fiber monofilaments. This device is specifically designed to address the technical challenges of the small size of the fiber monofilaments and the difficulty in parallel clamping of the samples, thus effectively solving the problems existing in traditional measurement methods. The testing device of this invention not only enables accurate measurement of the radial resistance of fiber monofilaments, but also features a simple and quick assembly process and easy-to-master operation steps. Furthermore, the testing device of this invention significantly reduces manufacturing and usage costs and provides stable and reliable measurement data, thereby ensuring the accuracy and repeatability of the test results.

[0032] 2. This invention provides a method for calculating the radial resistivity of composite material monofilaments. It utilizes computer finite element simulation to solve the problem of measuring the radial resistance distribution of fiber monofilaments due to factors such as small filament size and uneven microstructure. It uses experimentally measured voltage drop as a benchmark for iterative conductivity calibration, ensuring a high degree of consistency between the resistance distribution results and the electrical properties of the monofilament, significantly improving analytical accuracy. Calculations using the finite element model can efficiently output the spatial distribution characteristics of the monofilament's radial resistance, greatly reducing subjective errors caused by manual intervention, effectively reducing operating costs, and demonstrating high engineering feasibility. Attached Figure Description

[0033] Figure 1 This is an exploded schematic diagram of a composite material fiber monofilament radial resistance testing device according to the present invention;

[0034] Figure 2 This is a schematic diagram showing the fiber monofilaments after being loaded onto the device;

[0035] Figure 3 This is a schematic diagram of the divided grid;

[0036] Figure 4 It is the calculated radial potential distribution diagram;

[0037] Figure 5 This is a flowchart of the operation of the present invention.

[0038] In the diagram, 1 is the base; 11 is the column; 12 is the push rod mounting seat; 13 is the T-shaped mounting groove; 2 is the micrometer-type push rod; 3 is the plate electrode; 4 is the crossbeam; 5 is the bolt; 6 is the threaded washer; and 7 is the fiber monofilament. Detailed Implementation

[0039] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and should not be used to limit the scope of protection of the present invention.

[0040] like Figure 1As shown, the measuring device of the present invention includes a 3D-printed plastic base 1, a micrometer-type push rod 2, a plate electrode 3, a 3D-printed plastic crossbeam 4, a metal bolt 5, and a threaded washer 6.

[0041] The base 1 has four columns 11 at its four corners. The top of each column 11 has a T-shaped mounting groove 13 with the same geometric shape as the end of the crossbeam 4 and a depth of 10mm. This groove is used for the installation and positioning of the crossbeams to ensure that the crossbeams 4 are relatively parallel.

[0042] The base 1 has two columns 11 at the midpoint of both sides for mounting the micrometer push rod 2. The columns have holes with the same size as the mounting sleeve at the front end of the push rod (5mm). The center height of the holes is the same as the center line height of the installed crossbeam, ensuring that the push rod can push the crossbeam's center point when it extends, causing it to bend inward in parallel.

[0043] The base 1 is designed with two monofilament placement platforms for mounting bolts 5. The internal threaded holes can be matched with M10 bolts. The top is flush with the center line of the crossbeam. The threaded washer 6 can be matched with the bolts 5 to fix the monofilament on the placement platform.

[0044] Micrometer type push rod 2, the push rod can be extended in the range of 0-13mm.

[0045] The crossbeam 4 has a certain degree of elasticity and can be pushed inward by the push rod. Both ends are T-shaped. After installation, the two crossbeams are parallel to each other. There are two sleeves in the middle of the crossbeam for installing copper electrodes. The outer diameter is 8mm, the inner diameter is 3mm, and the depth is 5mm.

[0046] The plate electrode 3 is made of copper, with a copper plate size of 10*10mm. One end of the plate is designed with a copper column that is 15mm long and 3mm in diameter, perpendicular to the copper plate. It is assembled with a sleeve designed on the crossbeam to ensure that the copper plate and the crossbeam are parallel to each other. During the bending process of the crossbeam, the fiber monofilament 7 is exactly at the center line of the copper plate.

[0047] like Figure 2 As shown, the operation method of a composite material fiber monofilament radial resistance testing device should include the following steps:

[0048] 1. Screw the M10 threaded washer onto the M10 bolt, and then screw the bolt into the pre-drilled mounting hole on the base;

[0049] 2. Install the plate electrode 3 into the pre-drilled hole on the crossbeam 4, and install the crossbeam into the pre-drilled mounting slot on the base 1, ensuring that the two crossbeams are parallel to each other;

[0050] 3. Take a 200mm long SiC fiber bundle, heat it to 600℃ and keep it at that temperature for 1 hour to remove the glue, and then extract the degummed fiber monofilaments from it;

[0051] 4. Place the monofilament under the threaded washer, straighten the monofilament, and tighten the two washers so that the two washers clamp the monofilament. At this time, the monofilament is parallel to the center line of the plate copper electrode.

[0052] 5. Wrap copper wire around the copper electrodes and connect it to a digital multimeter. The multimeter's measurement accuracy is 0.012%. 6. 1 / 2 Precise distribution rate source and measurement;

[0053] 6. Rotate the two spiral micrometer push rods 2 on both sides to make the two plate copper electrodes clamp the fiber monofilament in parallel. Cut off the excess monofilament outside the plate copper electrodes with scissors so that the length of the fiber monofilament in the passage is 10mm.

[0054] 7. Use a digital multimeter to apply a constant current I=100 to the two electrodes. The measured voltage drop was V = 0.4104V, and the radial resistance of the 10mm SiC fiber monofilament was determined to be r = 4.104V. .

[0055] like Figure 3 As shown, a method for calculating the radial resistivity of a composite fiber monofilament should include the following steps:

[0056] 8. Using numerical methods for resistivity calculation, establish a diameter of 13... A 10mm long cylindrical geometric model was created and meshed.

[0057] 9. Apply I=100 to one side of the model in step 8. A constant current source is provided, and a ground is provided on the opposite side. The conductivity of each source is set to A=1*10. -4 S / m and B=1*10 -2 S / m, using the bisection method, is obtained when the conductivity is C=8.5*10 - 4 At S / m, the voltage drop is v = 0.4093V, and the resistance is c = 4.093V. If the error standard is met, then the transverse conductivity of the fiber monofilament is C = 8.5 * 10⁻⁶. -4 S / m, from which the radial resistivity of the fiber monofilament is calculated to be R = 1.176. .

[0058] It will be understood by those skilled in the art that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. It should also be understood that terms such as those defined in general dictionaries should be understood to have the same meaning as in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless defined as herein.

[0059] 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 falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A device for testing the radial resistance of a single composite fiber filament, characterized in that, It includes a base (1), a crossbeam (4), a micrometer-type push rod (2), and a plate electrode (3); The base (1) is provided with several columns (11) and push rod mounting base (12); The crossbeam (4) is an elastic member, and its two ends are detachably installed on the column (11). The two crossbeams (4) are parallel to each other and located on both sides of the fiber monofilament (7). The crossbeam (4) is provided with an installation structure in the middle. The plate electrode (3) is mounted on the mounting structure of the crossbeam (4), and the plate surface of the plate electrode (3) is parallel to the crossbeam (4); The micrometer-type push rod (2) is mounted on the push rod mounting base (12), and its telescopic end acts on the crossbeam (4) to push the two crossbeams (4) to bend in parallel towards each other, so that the two plate electrodes (3) clamp the fiber monofilament (7) in parallel. The base (1) is also provided with a single filament fixing mechanism for fixing the two ends of the fiber filament to be tested, so that the fiber filament is straightened and located at the center line position between the two plate electrodes (3).

2. The composite material fiber monofilament radial resistance testing device according to claim 1, characterized in that, The column (11) has a T-shaped mounting groove (13) at the top, and the two ends of the crossbeam (4) are T-shaped structures that match the T-shaped mounting groove (13). The crossbeam (4) is installed and positioned by the T-shaped fit.

3. The composite material fiber monofilament radial resistance testing device according to claim 1, characterized in that, The plate electrode (3) is a copper electrode with an electrode post perpendicular to the plate surface at one end. The mounting structure in the middle of the crossbeam (4) is a sleeve that matches the electrode post. The plate electrode (3) is installed by inserting the electrode post into the sleeve.

4. The composite material fiber monofilament radial resistance testing device according to claim 1, characterized in that, The monofilament fixing mechanism includes at least two threaded holes on the base (1), a bolt (5) that mates with the threaded holes, and a threaded washer (6) that is sleeved on the bolt (5) and mates with the bolt thread. The fiber monofilament is pressed and fixed on the base (1) by the threaded washer (6) that is tightened.

5. A method for testing the radial resistance of a single filament of a composite fiber, characterized in that, Using the composite fiber monofilament radial resistance testing device as described in any one of claims 1-4, the method includes the following steps: S1: Install the plate electrode (3) on the crossbeam (4), install the crossbeam (4) on the base (1), and install the micrometer push rod (2) on the base (1); S2: Straighten the fiber monofilament (7) and fix its two ends to the base (1) using the monofilament fixing mechanism, so that the fiber monofilament (7) is aligned with the center line of the two plate electrodes (3); S3: Connect the measuring leads to the two plate electrodes (3) and connect them to the resistance measuring device; S4: Operate the micrometer screw (2) to push the crossbeam (4) to bend, so that the two plate electrodes (3) clamp the fiber monofilament (7) in parallel, and cut off the excess fiber monofilament on the outside of the electrodes; S5: Apply a constant current I to the two plate electrodes (3) using a resistance measuring device, measure the voltage drop V between the two electrodes, and calculate the radial resistance value r = V / I of the fiber monofilament clamped between the two electrodes.

6. The method for testing the radial resistance of a single composite fiber filament according to claim 5, characterized in that, The fiber monofilament is a silicon carbide fiber monofilament or a carbon fiber monofilament.

7. A method for calculating the radial conductivity of a single filament of a composite material fiber, characterized in that, Includes the following steps: P1: Based on the radial resistance value r of the composite fiber monofilament measured by the method for testing the radial resistance of the composite fiber monofilament as described in claim 5, a cylindrical finite element model with the same geometric dimensions as the clamped section of the measured fiber monofilament is established; P2: A constant current I identical to the measured value is applied as an excitation in the region of the finite element model corresponding to the contact position of the plate-shaped electrode (3), and a ground boundary condition is set at the other end of the model; P3: The radial conductivity of the fiber monofilament is calculated by using the dichotomy iterative method: a conductivity search interval [A, B] is set, such that the model calculated resistance values a and b corresponding to this interval satisfy r ∈ [a, b]; the conductivity value C at the midpoint of the interval, C = (A + B) / 2, is taken for calculation to obtain the model resistance value c; if c < r, then B = C, otherwise A = C; this iterative process is repeated until the error between the calculated resistance value c and the measured resistance value r meets the preset standard, and at this time the corresponding conductivity C is the radial conductivity of the fiber monofilament.

8. The method for calculating the radial conductivity of composite fiber monofilaments according to claim 7, characterized in that, In step P1, the finite element model is a cylinder with the same diameter as the fiber monofilament and a length equal to the distance between the clamping points of the two plate-shaped electrodes (3).

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