CN107830950A - A kind of adjusting method of pressure measxurement sensitivity - Google Patents

Abstract

The invention discloses a method for adjusting pressure measurement sensitivity. This method targets a novel distributed pressure-sensing element with fiber-reinforced composites as the sensitive material to adjust the sensitive relationship between its resistance change and external pressure. Firstly, in the process of fabricating fiber-reinforced fabrics on fiber looms, the degree of closeness between carbon fibers in fabrics is changed by adjusting the yarn tension of the yarn carrier; secondly, in the process of polymer matrix injection molding, the carbon nanotubes or Conductive particles such as carbon black are uniformly dispersed in the polymer fluid in proportion, and the density of conductive particles in the gaps between carbon fibers can be changed by adjusting the filling amount. Based on the above adjustments, this method can effectively change the relationship between the initial resistance value between carbon fibers and the pressure-resistance change, and then change the measurement sensitivity of the pressure sensing element. The invention can effectively adjust the pressure measurement sensitivity of the composite material without substantially changing the overall strength of the composite material.

Description

A method for adjusting pressure measurement sensitivity

technical field

The invention relates to a method for adjusting the sensitivity of a sensor, in particular to a method for adjusting the pressure measurement sensitivity of a fiber-reinforced composite material.

Background technique

In the field of force sensing, silicon-based piezoresistive materials and metal-based strain gauges have always been the mainstream of industrial applications, but their use in non-planar contact pressure distribution detection applications is limited by the hardness and brittleness of the materials themselves. The advantages of fiber-reinforced composite materials in the "integration of structure and function" make it begin to develop into the field of sensing and testing. The deformation of the carbon fiber reinforced composite material will lead to the change of the internal carbon fiber resistance, so there is no need to add other equipment, and the force of the composite material can be effectively judged only by measuring the resistance value of the carbon fiber. Therefore, the surface adaptability and self-sensitivity properties of fiber reinforced composites can be used to design curved surface pressure sensing devices that can work stably on complex curved surfaces for a long time.

In practical applications, the measurement range and sensitivity of the force sensor are generally designed according to the requirements of the application to optimize the use efficiency of the sensor. Sensors based on silicon-based piezoresistive materials or metal-based strain gauges can adjust the range and sensitivity through the strength of the sensitive structure. While fiber reinforced composites are sensitive materials, they also often play the role of structural support. Therefore, although methods such as changing the number of filaments and changing the polymer matrix material can change its sensitivity, it also tends to reduce its strength, so it is not suitable for use.

Starting from the microstructure of fiber reinforced composite materials, it can be found that the measured resistance value between carbon fibers in the composite material will change under the action of external force. distance, which ultimately changes the resistance measurement between the carbon fibers.

Based on this, in the composite material manufacturing stage, the present application artificially designs the gap distance between the carbon fiber tow and the tow to change the measurement sensitivity of the pressure sensing unit, that is, to realize the adjustment of the piezoresistive sensitivity.

Contents of the invention

Aiming at the above-mentioned defects in the use of fiber-reinforced composite materials as the pressure sensor of the sensitive element, this application provides a method capable of adjusting the measurement sensitivity of its contact pressure. This method can effectively adjust the pressure detection of the fiber-reinforced composite material pressure sensor. Sensitivity without having a large impact on the structural strength of the composite material itself.

To achieve the above object, the technical scheme adopted in the present invention is as follows:

A method for adjusting pressure measurement sensitivity, aiming at fiber-reinforced composite materials as a new type of distributed pressure sensing element as a sensitive material: During the weaving process of fiber fabrics, the yarn tension of the yarn carrier in the knitting machine is adjusted to change The degree of tension of the carbon fibers in the fabric, which in turn adjusts the contact area between two carbon fibers that intersect at nodes. When the contact area increases, the measured resistance value between the two carbon fibers decreases, and vice versa, it increases. When the polymer matrix is prepared, conductive fillers are added to it, so that the conductive fillers are evenly dispersed in the polymer matrix, so as to change the resistance characteristics of the polymer matrix, and then affect the sensitivity of the resistance value of carbon fibers in fiber reinforced composites to external forces. .

Further, as a preference:

The method for adjusting the yarn output tension of the yarn carrier includes: adjusting the spring on the guide rail of the pulley block of the yarn carrier for the circular knitting process, and changing the springs of different strengths can change the yarn output tension of the yarn carrier. For the three-dimensional weaving process, adjust the spring connected to the brake pad on the yarn carrier, and the yarn output tension of the yarn carrier can be changed by tightening the spring. Since other links in the process will also affect the yarn outlet tension, the adjusted yarn carrier outlet tension needs to be calibrated by the yarn tension measuring instrument to ensure that the tension of all fibers remains consistent.

The process of adding conductive filler to the polymer matrix includes: the conductive filler is carbon nanotubes, carbon black or a mixture of the two, the ratio of the volume of the polymer matrix to the total volume of the conductive filler is between 100:1 and 100:15; the content of the conductive filler The higher the value, the smaller the initial value of resistance between carbon fibers in the composite material, and the higher the pressure measurement sensitivity. The polymer matrix is epoxy resin, which is composed of two liquids, the main agent and the curing agent, and the ratio of the two liquids is subject to the preparation requirements of the epoxy resin. First, add the conductive filler to the epoxy resin main agent, stir with a stirrer at a speed of 500-1000rpm for 10-30 minutes, seal it and put it in an ultrasonic cleaner for 10-30 minutes, then add the curing agent, and then use the stirrer Stir at a speed of 500-1000rpm for 5-10 minutes. After the conductive filler is evenly dispersed, put it into a vacuum box to evacuate to 0.1 atmosphere and keep it for 2 minutes to remove air bubbles, and then you can carry out injection molding.

Finally, the adjustment effect of piezoresistive sensitivity needs to be fed back, which includes: the yarn tension in the weaving process and the proportion of conductive filler in the polymer matrix are two adjustable parameters. Samples of distributed pressure sensing elements under different parameter combinations were prepared, and the corresponding relationship between the pressure and the resistance change between carbon fibers was obtained through pressure testing. Through the above corresponding relationship, it can be determined how to adjust the adjustable parameters to manufacture the distributed pressure sensing element with required piezoresistive sensitivity.

The beneficial effects that the present invention has are:

The invention concentrates the sensitivity adjustment of the composite material sensor on the preparation stage of the reinforced fabric and the polymer matrix, so the operation is simple and does not require special modification of the existing fiber-reinforced composite material manufacturing equipment, and can basically not change the overall structure of the composite material. The intensity of the situation, effectively adjust the sensitivity of its pressure measurement.

Description of drawings

Figure 1 is a structural diagram of the middle layer of a fiber-reinforced fabric.

Figure 2 is a schematic diagram of the structure based on two intersecting carbon fibers in the composite material at the node.

Figure 3 is the response of a group of carbon fiber resistance values to external pressure in the composite material pressure sensor.

In the figure: 1. Test point, 2. Resistance measurement, 3. Warp carbon fiber tow, 4. Warp to Kevlar tow, 5. Weft carbon fiber tow, 6. Weft tow Kevlar tow, 7. Current path, 8. Warp carbon fiber tow, 9. Weft carbon fiber tow, 10. Carbon nanotube particles.

Detailed ways

The present invention will be further described below in conjunction with accompanying drawings and examples.

A typical example of the inventive method is: adopt the three-dimensional weaving method to manufacture the multi-layer composite fiber fabric that has binding yarn, as shown in Figure 1, fabric middle layer adopts Toray T700-12K carbon fiber as sensitive fiber except part warp yarn and weft yarn Besides, the other fiber is Kevlar-29. The polymer matrix adopts vinyl resin RF1001, and the conductive filler adopts multi-walled carbon nanotubes (outer diameter 50 nanometers, length 10-20 microns).

In the fabric manufacturing stage, adjust the tension control spring of the yarn carrier so that the yarn tension of all warp and weft yarns is controlled at 80 centinewtons, and verify the actual tension of each yarn with a hand-held yarn tension tester.

In the polymer matrix preparation stage, the dosage of each material is: the mass ratio of resin main agent, curing agent and accelerator is 100:2:2, and the volume ratio of the whole resin and carbon nanotubes is 100:5. First, add the resin main agent to the container, then add the carbon nanotube powder, and stir with a mixer at a speed of 800rpm for 20 minutes; then, seal the container, put it into an ultrasonic cleaner, and continue to disperse for 20 minutes; next, open the container and Add curing agent and accelerator, and stir again with a mixer at 800rpm for 5 minutes; finally, put the container in a vacuum drying oven, evacuate to 0.2 atmospheric pressure and keep it for 2 minutes. Put the prepared liquid into the injection molding machine to perform injection molding on the woven fabric.

The microstructure of the two intersecting carbon fibers at the joint position of the final composite pressure sensor is shown in Figure 2 (only the carbon nanotubes near the intersection point are shown). The gap between carbon nanotubes as bridges will change, and the measured resistance actually includes a combination of two parts: carbon fiber resistance and gap resistance. Obviously, the gap resistance is the main part of the measured resistance value. When the gap size changes, the overall resistance The value can also change significantly.

Put the sensor on the three-point press brake, measure the pressure, and measure the resistance change at the carbon fiber node under the pressure position. The results are shown in Figure 3. It can be seen that the resistance change rate is basically linear with the pressure.

Claims (4)

1. A method for adjusting pressure measurement sensitivity, characterized in that, for fiber-reinforced composite materials as a novel distributed pressure sensing element of sensitive material: (1) During the weaving process of the fiber fabric, the yarn tension of the yarn carrier in the weaving machine is adjusted to change the tension degree of the carbon fiber in the fabric, and then adjust the contact between the two carbon fibers intersecting at the node area; (2) When the polymer matrix is prepared, conductive fillers are added to it, so that the conductive fillers are evenly dispersed in the polymer matrix to change the resistance characteristics of the polymer matrix, thereby affecting the external force of the carbon fiber resistance value in the fiber reinforced composite material sensitivity. 2. The method for adjusting the pressure measurement sensitivity of the fiber-reinforced composite material according to claim 1, wherein the method for adjusting the yarn output tension of the yarn carrier comprises the following: (1) For the circular knitting process, adjust the spring on the guide rail of the pulley block of the yarn carrier, and replace the spring with different strength to change the yarn output tension of the yarn carrier; (2) For the three-dimensional weaving process, adjust the spring connected to the brake pad on the yarn carrier and tighten the spring to change the yarn output tension of the yarn carrier; (3) The adjusted yarn delivery tension of the yarn carrier needs to be calibrated by the yarn tension measuring instrument to ensure that the tension of all fibers remains consistent. 3. The adjustment method of the pressure measurement sensitivity of the fiber reinforced composite material according to claim 1, wherein the process of adding conductive filler to the polymer matrix includes the following content: (1) The conductive filler is carbon nanotubes, carbon black or a mixture of the two, and the ratio of the volume of the polymer matrix to the overall volume of the conductive filler is between 100:1 and 100:15; (2) The polymer matrix is epoxy resin, which is composed of two liquids, the main agent and the curing agent, and the ratio of the two is subject to the preparation requirements of epoxy resin; (3) First, add the conductive filler to the epoxy resin main agent, stir with a stirrer at a speed of 500-1000rpm for 10-30 minutes, seal it and put it into an ultrasonic cleaner for 10-30 minutes, then add the curing agent, and then Stir with a stirrer at a speed of 500-1000rpm for 5-10 minutes. After the conductive filler is evenly dispersed, put it in a vacuum box to evacuate to 0.1-0.3 atmospheres and keep it for 2 minutes to discharge air bubbles, and then injection molding can be performed. 4. The adjustment method of the pressure measurement sensitivity of fiber reinforced composite material according to claim 1, is characterized in that, needs to feedback the adjustment effect of piezoresistive sensitivity, and its content comprises: (1) The yarn tension in the weaving process and the ratio of the conductive filler in the polymer matrix are two adjustable parameters; (2) Prepare distributed pressure sensing element samples under different parameter combinations, and obtain the corresponding relationship between the pressure and the resistance change between the carbon fibers through the pressure test; (3) Through the above corresponding relationship, it can be determined how to adjust the adjustable parameters to manufacture the distributed pressure sensing element with required piezoresistive sensitivity.