Integrated crack sensor for structural part strain measurement and in-situ transfer manufacturing method

Abstract

A co-integrated crack sensor for measuring strain of a structural part and an in-situ transfer manufacturing method, the sensor comprises a NOA ultraviolet curing agent adhered to a surface to be measured, a conductive sensitive material with a grid structure adhered to the upper surface of the NOA ultraviolet curing agent to form a conductive network, and localized generated cracks are distributed on the conductive network; the manufacturing method firstly performs preparation and surface treatment of an imprinting mold, then performs surface treatment of a PDMS substrate, then performs constrained printing of a conductive sensitive material, then generates localized generated cracks, and then performs an in-situ transfer process to form a co-integrated crack sensor; when used, a constant voltage value is applied to the co-integrated crack sensor, when strain occurs on the surface to be measured, the resistance changes accordingly, the current signal is collected, and the change information of different strains on the surface to be measured is distinguished through signal analysis and processing; the sensor of the present invention is more sensitive and has more stable performance, the conductive grid is directly bonded to the surface to be measured, and the strain transmission rate is higher.

Description

Technical Field

[0001] The present invention belongs to the field of micro-nano manufacturing technology, and in particular relates to a common crack sensor for measuring the strain of a structural part and an in-situ transfer manufacturing method. Background Art

[0002] As the basic unit for sensing deformation and mechanical information, strain has important measurement significance in the fields of intelligent robots, industrial inspection, and medical rehabilitation. Traditional optical measurement methods such as speckle measurement and DIC measurement are too large to achieve portable and lightweight measurement equipment; for surface-mounted sensors, fiber optic measurement has too high environmental requirements such as temperature, strain gauge measurement has problems such as low sensitivity and inability to array for high-density gradient measurement, and flexible strain sensors have problems such as low strain transfer rate and insufficient lightweight integration, which cannot meet the measurement requirements of surface strain of some equipment.

[0003] The existing strain gauge (application number: CN201880086299.3, name: strain gauge) is measured by sticking the strain gauge on the measured surface with an adhesive. The strain gauge is divided into three layers: substrate, sensing unit, and covering layer. Through strain transfer theory, strain analysis can be performed on it. It can be concluded that the lower the material thickness between the sensing unit and the measured surface, the greater the elastic modulus, the higher the strain transfer rate, and the higher the measurement accuracy. Existing strain sensors generally have the disadvantages of being unable to measure with high sensitivity in situ, low transmission efficiency, and insufficient lightweight integration. Summary of the invention

[0004] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide an integrated crack sensor and an in-situ transfer manufacturing method for structural part strain measurement, adopting a crack structure and controlling the crack morphology to improve the sensor sensitivity, and adopting an in-situ transfer process to reduce strain transmission losses and improve the lightweight integration of the sensor.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] A commensurate crack sensor for measuring strain of structural parts comprises a NOA ultraviolet curing agent adhered to a surface to be measured, a conductive sensitive material with a grid structure adhered to the upper surface of the NOA ultraviolet curing agent to form a conductive network, and localized generated cracks are distributed on the conductive network.

[0007] An in-situ transfer manufacturing method of a common crack sensor for measuring strain of a structural part comprises the following steps:

[0008] The first step is to prepare the imprint mold and treat the surface: prepare a mold 1 on the surface of the silicon wafer, place the mold 1 on the lower glass sheet 3-1, pour PDMS on the mold 1, press the upper glass sheet 3-2 on the PDMS in a vacuum box, press the PDMS into a thin film, let it stand at room temperature to solidify the PDMS, demold, and form a constrained microcavity on the surface of the PDMS substrate 2;

[0009] The second step is surface treatment of the PDMS substrate 2: treating the PDMS substrate 2 with the constrained microcavity in an oxygen plasma environment to make its surface hydrophilic;

[0010] The third step is constrained printing of conductive sensitive materials: drip a carbon nanotube aqueous solution 4 on the surface of the PDMS substrate 2, and scrape it back and forth with a scraper to fill the constrained microcavity with the carbon nanotube aqueous solution 4, then dry it, and wipe off the dry carbon nanotube film on the surface; repeat the scraping and drying until the conductive material in the grid-shaped constrained microcavity is evenly and continuously distributed;

[0011] The fourth step is to generate localized cracks: the PDMS substrate 2 filled with carbon nanotubes is pre-stretched, and the local strain drives the cracks in the carbon nanotube network to expand in a controllable manner, and cracks are generated only at the stress concentration point, and the cracks are customized to be generated locally to form a conductive grid 5;

[0012] The fifth step is the in-situ transfer process: apply a drop of NOA ultraviolet curing agent 6 on the surface to be tested 7, cover the PDMS substrate 2 with the conductive grid 5 on the NOA ultraviolet curing agent 6, apply pressure on the PDMS substrate 2, irradiate with ultraviolet light, peel off the PMDS substrate 2, and the conductive grid 5 containing carbon nanotubes is transferred to the NOA curing agent 6 to form an integrated transfer, and connect the wires at both ends to form a co-integrated crack sensor.

[0013] The first step of film thickness control is achieved by placing objects of different thicknesses between the upper glass sheet 3-2 and the lower glass sheet 3-1.

[0014] The application of the integrated crack sensor for measuring the strain of structural parts is as follows: a constant voltage value is applied to the integrated crack sensor. When the surface to be measured is strained, the NOA adhesive 6 is strained accordingly, causing the conductive grid 5 containing carbon nanotubes to deform, and the microcracks open and close accordingly, and the resistance changes accordingly. The current signal in this process is collected, and after signal analysis and processing, the change information of different strains of the surface to be measured is distinguished.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] The integrated crack sensor of the present invention is based on the principle of microcracks, which greatly improves the sensitivity of the sensor and can effectively detect the tiny strain of the surface to be measured; at the same time, the integrated crack sensor of the present invention is manufactured by in-situ transfer printing, and the regular conductive network formed by the constrained microcavity is completely transferred to the NOA ultraviolet curing agent, eliminating the PDMS substrate, and there is less medium between the conductive network and the surface to be measured, so that the strain transfer rate is higher, there is no hysteresis effect of the substrate, the response recovery time is shorter, and it has good dynamic response. The integrated crack sensor of the present invention has good application prospects in machine surface strain detection, human-computer interaction, medical rehabilitation, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a schematic diagram of the integrated crack sensor detecting the strain of the surface to be measured according to an embodiment of the present invention.

[0018] Figure 2 This is a schematic diagram of PDMS molding by die extrusion according to an embodiment of the present invention.

[0019] Figure 3 Schematic diagram of the constrained printing process of conductive sensitive materials according to an embodiment of the present invention.

[0020] Figure 4 Schematic diagram of localized cracks generated by pre-stretching in an embodiment of the present invention.

[0021] Figure 5 Schematic diagram of the in-situ transfer process according to an embodiment of the present invention.

[0022] Figure 6 This is a microscopic morphology of carbon nanotubes after in-situ transfer of the integrated crack sensor according to an embodiment of the present invention.

[0023] Figure 7 This is a real picture of the integrated crack sensor of the present invention being in-situ transferred to different objects. DETAILED DESCRIPTION

[0024] The manufacturing method of the present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0025] Reference Figure 1 A compositive crack sensor for measuring strain of structural parts includes a NOA ultraviolet curing agent 6 adhered to a surface to be measured 7, a conductive sensitive material with a grid structure adhered to the upper surface of the NOA ultraviolet curing agent to form a conductive network, and localized cracks are distributed on the conductive network as a sensing mechanism.

[0026] An in-situ transfer manufacturing method of a common crack sensor for measuring strain of a structural part comprises the following steps:

[0027] The first step is to prepare the imprint mold and treat the surface: prepare the mold 1 on the surface of the silicon wafer by photolithography and etching process, put the mold 1 on the lower glass sheet 3-1, pour PDMS on the mold 1, and after evacuating in a vacuum box for 10 minutes, press the upper glass sheet 3-2 on the PDMS to press the PDMS into a thin film. The film thickness is controlled by placing objects of different thicknesses between the upper glass sheet 3-2 and the lower glass sheet 3-1; let it stand at room temperature for 10 hours to solidify the PDMS, demold it, and form a constrained microcavity on the surface of the PDMS substrate 2, such as Figure 2 As shown;

[0028] The second step is surface treatment of the PDMS substrate 2: the PDMS substrate 2 with the constrained microcavity is treated in a 40W oxygen plasma environment for 30s to make its surface hydrophilic, which is conducive to the printing of conductive sensitive materials;

[0029] The third step is the constrained printing of the conductive sensitive material: drop a carbon nanotube aqueous solution 4 on the surface of the PDMS substrate 2, and scrape it back and forth with a scraper. The carbon nanotube aqueous solution 4 fills the constrained microcavity under the drive of capillary force, and then bakes it on a drying table at 85°C for 1 minute, and wipes off the dry carbon nanotube film on the surface; repeat the above scraping and drying steps 3 to 4 times until the conductive material in the grid-like constrained microcavity is evenly and continuously distributed, such as Figure 3 As shown;

[0030] The fourth step is to generate localized cracks: the PDMS substrate 2 filled with carbon nanotubes is pre-stretched with a certain strain. Under the pre-stretching effect, the redistributed local strain will drive the cracks in the carbon nanotube network to expand in a controllable manner, and finally cracks will only be generated at the stress concentration point. Customizable localized cracks are generated to form a conductive grid 5, such as Figure 4 shown.

[0031] The fifth step is the in-situ transfer process: a certain amount of NOA ultraviolet curing agent 6 is dripped on the surface to be tested 7, and then the PDMS substrate 2 with the conductive grid 5 is covered on the NOA ultraviolet curing agent 6, a certain pressure is applied on the PDMS substrate 2, and 150W ultraviolet rays are irradiated for 1 minute, and then the PMDS substrate 2 is slowly peeled off. Due to the principle of adhesion energy, the conductive grid 5 containing carbon nanotubes is transferred to the NOA curing agent 6 to form an integrated transfer, and wiring is connected at both ends to form a co-integrated crack sensor, such as Figure 5 shown.

[0032] The PDMS is prepared by mixing the PDMS material and its curing agent at a mass ratio of 10:1, stirring for 5 minutes to completely mix them, placing them under negative pressure for 5 minutes, repeating twice, and removing bubbles.

[0033] The carbon nanotubes are 10%wt multi-walled carbon nanotube aqueous dispersion.

[0034] like Figure 1 As shown, the application of the integrated crack sensor for measuring the strain of structural parts is: a constant voltage value of 1V is applied to the integrated crack sensor. When the surface to be measured is strained, the NOA adhesive 6 is strained accordingly, causing the conductive grid 5 containing carbon nanotubes to deform, and the microcracks open and close accordingly, and the resistance changes accordingly. The current signal in this process is collected by a source meter 8, and the change information of different strains of the surface to be measured is distinguished through signal analysis and processing.

[0035] like Figure 6 As shown, Figure 6 This is a microscopic morphology of carbon nanotubes after in-situ transfer of the integrated crack sensor of an embodiment of the present invention. It can be seen that the crack morphology is good and is generated regularly at the designed designated positions, realizing the localized production of cracks, which is beneficial to improving the sensitivity and stability of the sensor.

[0036] like Figure 7 As shown, Figure 7 This is a real picture of the in-situ transfer of the integrated crack sensor of the present invention to different objects, which illustrates that the sensor can be transferred to equipment surfaces with different roughness, curvature and materials, proving that the transfer process has good environmental adaptability.

[0037] The integrated crack sensor of the present invention is based on the microcrack principle, and the in-situ transfer process greatly improves the sensitivity of the sensor, which can effectively detect the tiny strains of the surface to be measured; at the same time, the integrated crack sensor of the present invention removes the PDMS substrate, and there is less medium between the conductive material and the surface to be measured, so that the strain transfer rate is higher, there is no hysteresis effect of the substrate, the response recovery time is shorter, and it has good dynamic response, and has good application prospects in machine surface strain detection, human-computer interaction, medical rehabilitation and other aspects.

Claims

1. An in-situ transfer manufacturing method of a common crack sensor for measuring strain of a structural part, characterized in that: The integrated crack sensor includes a NOA ultraviolet curing agent adhered to the surface to be tested, and a conductive sensitive material with a grid structure is adhered to the upper surface of the NOA ultraviolet curing agent to form a conductive network, and localized cracks are distributed on the conductive network; The manufacturing method comprises the following steps: The first step is to prepare the imprint mold and treat the surface: prepare a mold (1) on the surface of a silicon wafer, place the mold (1) on the lower glass sheet (3-1), pour PDMS on the mold (1), press the upper glass sheet (3-2) on the PDMS in a vacuum box, press the PDMS into a thin film, let it stand at room temperature to solidify the PDMS, demold, and form a constrained microcavity on the surface of the PDMS substrate (2); The second step is surface treatment of the PDMS substrate (2): treating the PDMS substrate (2) with the constrained microcavity in an oxygen plasma environment to make its surface hydrophilic; The third step is constrained printing of conductive sensitive materials: dripping a carbon nanotube aqueous solution (4) on the surface of the PDMS substrate (2), scraping with a scraper to fill the constrained microcavity with the carbon nanotube aqueous solution (4), and then drying, wiping off the dry carbon nanotube film on the surface; repeating the scraping and drying until the conductive material in the grid-shaped constrained microcavity is evenly and continuously distributed; The fourth step is to generate localized cracks: the PDMS substrate (2) filled with carbon nanotubes is pre-stretched, and the local strain drives the cracks in the carbon nanotube network to expand in a controllable manner, and cracks are generated only at the stress concentration point, and the cracks are customized to be generated locally to form a conductive grid (5); The fifth step is the in-situ transfer process: a NOA ultraviolet curing agent (6) is dripped onto the surface to be tested (7), a PDMS substrate (2) having a conductive grid (5) is covered on the NOA ultraviolet curing agent (6), pressure is applied on the PDMS substrate (2), ultraviolet light is irradiated, the PMDS substrate (2) is peeled off, and the conductive grid (5) containing carbon nanotubes is transferred onto the NOA ultraviolet curing agent (6) to form an integrated transfer, and wiring is connected at both ends to form a co-integrated crack sensor; A constant voltage value is applied to the integrated crack sensor. When the surface to be measured is strained, the NOA ultraviolet curing agent (6) is strained accordingly, causing the conductive grid (5) containing carbon nanotubes to deform. The microcracks then open and close, and the resistance changes accordingly. The current signal in this process is collected, and after signal analysis and processing, the change information of different strains on the surface to be measured is distinguished.

2. The manufacturing method according to claim 1, characterized in that: The first step of film thickness control is achieved by placing objects of different thicknesses between the upper glass sheet (3-2) and the lower glass sheet (3-1).

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