A channel crack type flexible strain sensor based on non-through slot induction and pre-fatigue stabilization and a preparation method thereof

Abstract

The application belongs to the technical field of strain sensor preparation, and particularly relates to a channel crack type flexible strain sensor based on non-through slot induction and pre-fatigue stabilization and a preparation method thereof. The method comprises the following steps: forming a non-through slot structure extending along the width direction and arranged at intervals along the length direction on the surface of a conductive film; laying the conductive film in the middle of the upper and lower flexible substrates, and arranging electrodes at both ends of the conductive film to obtain an initial structure of the sandwich type flexible sensor; and applying a pre-fatigue cyclic load to the initial structure along the length direction of the conductive film, and stopping the load when the resistance response reaches a preset stable state to obtain the flexible strain sensor. The application limits the crack formation position and expansion direction through the non-through slot, and makes the channel crack complete stabilization before service through pre-fatigue treatment, so as to reduce the continuous evolution of the crack and signal baseline drift in the cycle process, and realize the combination of high sensitivity and high cycle stability.

Description

Technical Field

[0001] This invention belongs to the field of strain sensor fabrication technology, specifically relating to a channel crack type flexible strain sensor based on non-penetrating groove induction and pre-fatigue stabilization and its fabrication method. This flexible strain sensor has both high sensitivity and high cyclic stability. Background Technology

[0002] Flexible strain sensors, characterized by their lightweight, attachability, and ease of integration, have broad application prospects in wearable electronics, soft robotics, human-computer interaction, structural health monitoring, and intelligent equipment. Sensitivity and cyclic stability are two key indicators for evaluating the overall performance of flexible strain sensors. Sensitivity determines the accuracy of the sensor's signal response, while cyclic stability determines the long-term reliability of the sensor's signal. However, existing flexible strain sensors generally suffer from the difficulty of simultaneously achieving high sensitivity and high cyclic stability. Currently, most high-sensitivity flexible strain sensors are based on channel crack sensing. Because they can significantly amplify the resistance response through crack opening and closing, crack edge contact changes, and cross-crack tunneling effects, they can achieve high sensitivity within a small strain range. However, existing channel crack fabrication methods typically rely on overload stretching of a brittle conductive layer or weak interfacial bonding between the conductive layer and the flexible substrate, making it difficult to effectively control the final crack morphology. Furthermore, during subsequent cyclic loading, the crack may continue to propagate or induce local interfacial debonding, resulting in poor cyclic stability and difficulty in achieving good overall performance. Therefore, it is necessary to provide a method for fabricating flexible strain sensors that can simultaneously control crack morphology and service stability, so as to achieve a balance between high sensitivity and high cyclic stability. Summary of the Invention

[0003] The purpose of this invention is to overcome the problem that it is difficult to achieve both sensitivity and cyclic stability in existing flexible strain sensors. To this end, this invention provides a channel crack type flexible strain sensor based on non-penetrating groove induction and pre-fatigue stabilization, and its preparation method.

[0004] The present invention adopts the following technical solution: A method for fabricating a flexible strain sensor with a channel crack based on non-penetrating groove induction and pre-fatigue stabilization includes the following steps: (1) A non-through groove structure is formed on the surface of a rectangular conductive film, extending from its width direction to its length direction at two end faces and arranged in parallel intervals along the length direction, for setting a stress concentration area on the conductive film. (2) The conductive film forming the non-penetrating groove structure is placed between the upper and lower flexible substrates, so that the flexible substrates are attached around the perimeter. The conductive film is encapsulated in the middle of the flexible substrate, and electrode wires are connected to both ends of the conductive film along the length direction to obtain the initial structure of the sandwich flexible sensor. (3) Apply pre-fatigue cyclic loading to both ends of the initial structure of the flexible sensor along the length direction. When the resistance response of the initial structure of the sandwich flexible sensor reaches a preset stable state during the pre-fatigue cyclic loading process, stop the cyclic loading to obtain a flexible strain sensor. The strain range of the pre-fatigue cyclic loading is less than the fracture strain of the initial structure of the sandwich flexible sensor, preferably 0-1%; the frequency is 0.5-50 Hz, the strain ratio R=0, and the number of cycles is 10. 2 ~10 6 Week.

[0005] Further, the conductive film in step (1) is one or more composite conductive films selected from carbon nanotube film, graphene film and near-zero temperature resistivity hybrid film, which maintains conductive continuity and structural integrity at 0 ℃ to -196 ℃, has a thickness of 50 μm ~ 1 mm, and the aspect ratio of the rectangular conductive film is ≥1. The near-zero temperature resistivity hybrid film is a hybrid film between conductive fillers or a hybrid film between conductive fillers and a polymer matrix; the hybrid film between conductive fillers is one or more of the following: carbon nanotube / graphene hybrid film, carbon nanotube / MXene hybrid film, graphene / silver nanowire hybrid film, or carbon nanotube / metal nanowire hybrid film; the hybrid film between conductive fillers and the polymer matrix is ​​one or more of the following: carbon nanotube / polymer composite film, graphene / polymer composite film, MXene / polymer composite film, or carbon nanotube / graphene / polymer composite film; after designing different component ratios, the conductive film achieves a near-zero temperature resistivity.

[0006] The non-penetrating trench structure is formed by local removal, local pressing, local etching, or local thinning; the specific preparation method of the non-penetrating trench structure is one or more of the following: laser processing, mechanical cutting, mold imprinting, ion beam etching, photolithography-etching-transfer, or patterned film formation. The non-penetrating groove structure is a V-shaped groove, a U-shaped groove, a rectangular groove, a trapezoidal groove, an arc groove, or a combination of the above groove shapes; preferably, the non-penetrating groove structure is a V-shaped groove.

[0007] The geometric parameters of the non-penetrating groove structure include one or more of the following: groove spacing, groove depth, groove width, groove angle, groove bottom curvature radius, and groove edge morphology; by adjusting the geometric parameters, the degree of local stress concentration in the conductive film can be controlled.

[0008] The surface groove depth of the non-through groove structure is 1 / 10 to 1 / 3 of the conductive film thickness; the surface groove width is 1 μm to 300 μm; and the surface groove spacing is 1 / 60 to 1 / 6 of the conductive film length.

[0009] Further, the flexible substrate in step (2) is a low-temperature resistant polymer substrate, specifically including one or more of polyimide, polytetrafluoroethylene, fluorinated ethylene propylene, perfluoroalkoxy resin, ethylene-tetrafluoroethylene copolymer, polyether ether ketone, polyetherimide, and liquid crystal polymer; the electrode wire is a copper wire with a diameter of 0.1-0.3 mm.

[0010] Further, the pre-fatigue cyclic loading load in step (3) is a sine wave, triangular wave, trapezoidal wave or other periodic tensile load; the pre-fatigue cyclic loading process causes cracks to preferentially initiate and propagate along the root of the non-penetrating groove structure, forming multiple channel cracks with consistent orientation and spacing limited by the non-penetrating groove structure in the conductive film.

[0011] The preset stable state is defined as follows: within a continuous preset fatigue cycle loading period, the relative change rate of the peak resistance and baseline resistance between the two wires of the initial structure of the flexible sensor does not exceed a preset threshold; preferably, the preset cycle number is 10. 2 ~10 6 Each cycle, the preset threshold is 1% to 10%.

[0012] A flexible strain sensor includes upper and lower flexible substrates and a conductive film encapsulated between the two flexible substrates. Electrodes are respectively provided at both ends of the conductive film along its length for connecting to an external resistance signal acquisition device. The surface of the conductive film is provided with a plurality of non-penetrating groove structures that extend from its width direction to its two end faces along its length direction and are arranged in parallel and spaced apart along its length direction. After pre-fatigue cyclic loading, channel cracks preferentially initiate from the root of the non-penetrating groove structure and extend along the extension direction of the groove structure, thereby forming a stable channel crack structure with consistent orientation, controlled spacing, and reversible opening and closing with external strain.

[0013] The sensor exhibits stable mechanical response and baseline resistance output in cryogenic environments below -100°C; the sensor's sensitivity factor reaches 10. 5 The above; a stable cycle count of 10 is achieved. 5 above.

[0014] Compared with the prior art, the present invention has the following advantages and outstanding technical effects: 1. The present invention can realize the controllable construction of channel crack structure and reduce the performance dispersion caused by the uncontrollable morphology of random cracks.

[0015] 2. This invention achieves pre-service stabilization of channel cracks through pre-fatigue cyclic loading, reducing baseline drift of the resistance signal during sensor service.

[0016] 3. The flexible strain sensor prepared by this invention has both high sensitivity and high cycling stability, and its sensitivity factor can reach 10.5 The above; meanwhile, in the cyclic strain sensor 10 5 Even after several cycles, the resistance strain response can still maintain a stable level.

[0017] 4. The non-penetrating groove structure and pre-fatigue parameters of the present invention are adjustable, enabling customized design of sensing performance.

[0018] 5. With the support of a low-temperature resistant material system, this invention can extend the sensing advantages of stable channel crack structures to deep low-temperature environments below -100℃. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the flexible strain sensor prepared according to Embodiment 1 of the present invention; in the figure, 1 is a conductive thin film; 2 is a flexible substrate; 3 is an electrode; 4 is a V-groove; and 5 is a channel crack.

[0020] Figure 2 The test curve of room temperature strain sensing of the flexible strain sensor prepared in Example 1 of the present invention is shown.

[0021] Figure 3 The image shows the room temperature cycling stability test curve and a partial magnified view of the flexible strain sensor prepared in Example 1 of this invention.

[0022] Figure 4 The strain sensing test curve of the flexible strain sensor prepared in Example 1 of the present invention in a liquid nitrogen environment.

[0023] Figure 5 The image shows the cyclic stability test curve and a magnified view of the flexible strain sensor prepared in Example 1 of this invention under liquid nitrogen environment.

[0024] Figure 6 The strain sensing test curve is shown for the flexible strain sensor prepared in Comparative Example 1 of this invention.

[0025] Figure 7 The strain sensing test curve is shown for the flexible strain sensor prepared in Comparative Example 2 of this invention. Detailed Implementation

[0026] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0027] Example 1: This embodiment describes the fabrication of a flexible strain sensor for channel cracks based on non-penetrating groove induction and pre-fatigue stabilization. A schematic diagram of the flexible strain sensor is shown below. Figure 1As shown, the flexible strain sensor includes upper and lower flexible substrates 2 and a conductive film 1 encapsulated between the two flexible substrates 2. Electrodes 3 are respectively provided at both ends of the conductive film 1 along its length for connecting to an external resistance signal acquisition device. The surface of the conductive film 1 is provided with a plurality of non-penetrating V-shaped grooves 4 extending from its width direction to its two end faces along its length direction and arranged in parallel and spaced order along its length direction. After pre-fatigue cyclic loading, channel cracks 5 preferentially initiate from the root of the non-penetrating V-shaped grooves 4 and extend along the extension direction of the groove structure, thereby forming a stable channel crack structure with consistent orientation, controlled spacing, and reversible opening and closing with external strain.

[0028] The specific fabrication steps of the flexible strain sensor are as follows: Step 1: Weigh 100 mg of multi-walled carbon nanotube powder (MWCNTs, model TNM3, purity >98%, diameter 10–20 nm, length 10–30 μm) and add it to 1 mL of Triton X-100 surfactant in a mortar and grind thoroughly. Then, wash with 200 mL of deionized water to obtain a MWCNTs dispersion. Stir the dispersion magnetically at 1200 r / min for 30 min, then sonicate for 2 h to improve dispersion uniformity. Centrifuge the dispersion at 3500 r / min for 30 min to remove coarse particles and insufficiently dispersed agglomerates. After standing for 1 h, take 150 mL of the supernatant and filter it in a vacuum filter, continuously adding deionized water during filtration to thoroughly wash away residual surfactant. After filtration, the obtained MWCNTs filter cake was placed in a vacuum oven at 60 °C and dried for 3 h. After drying, it was carefully peeled off from the surface of the filter membrane to obtain a MWCNTs film with a thickness of about 100 μm, which served as the initial conductive film for the sensor.

[0029] Step 2: A VMSP0202-GL-25 (CCD) green femtosecond galvanometer dicing machine was used as the non-penetrating groove processing equipment to laser etch the surface of the initial conductive film to form multiple V-shaped grooves 4 extending along the width direction of the film. These V-shaped grooves 4 are non-penetrating grooves and are spaced apart along the length direction of the initial conductive film. During processing, the idle speed was set to 5000 mm / s, the laser frequency was set to 30 kHz, and the duty cycle was set to 50%. The depth of the V-shaped grooves was controlled by adjusting the number of laser scans, the scanning speed, and the laser energy ratio to avoid local melting. In this embodiment, the following parameters were used: 1 scan, 100 mm / min scanning speed, 10% laser energy ratio, and -3.2 mm Z-axis focal position. The depth of the V-shaped grooves formed after etching was approximately 20 μm, the width was approximately 15 μm, and the groove spacing D was 1.0 mm. Subsequently, the laser-etched initial conductive film was cut into rectangular samples of 12 mm × 3 mm as conductive film 1. During cutting, the length direction of the rectangular sample is parallel to the length direction of the initial conductive film, and the width direction is the same as the width direction of the initial conductive film. The cutting edge in the length direction is preferably located between two adjacent V-grooves.

[0030] Step 3: Place the conductive film 1 on the flexible substrate 2, which is a 30 μm thick polyimide low-temperature tape (purchased from Tianjin Duoweilaibo Technology Co., Ltd., 30 mm in length and 6 mm in width). Connect copper wires (0.1 mm in diameter) with conductive silver paste (purchased from SPI Supplies, silver solid content 43% ± 3%) at both ends of the conductive film along its length to serve as the leads for electrode 3, and cure at 70 °C for 10 min. Then, cover the sample surface with the same polyimide low-temperature tape to complete the device encapsulation, obtaining the initial structure of the sandwich-type flexible sensor.

[0031] Step 4: Fix both ends of the initial structure of the sandwich-type flexible sensor along its length in the fixture of the Shimadzu Microforce Testing System (MMT-101NV-10). Apply a sinusoidal cyclic load along the length of the sensor at a frequency of 10 Hz, a strain range of 0-1%, and a strain ratio R=0. Set the total number of cycles to 10,000. During the pre-fatigue process, connect an Agilent 34410 high-precision multimeter to both ends of the sensor via electrodes 3 to synchronously acquire the sensor resistance signal. When the changes in peak resistance, valley resistance, or response amplitude during cyclic loading tend to stabilize, stop the pre-fatigue treatment. After this pre-fatigue treatment, cracks preferentially initiate and propagate along the root position of the prefabricated V-groove 4, forming stable channel cracks 5 with consistent orientation (cracks extend along the width direction of the conductive film), spacing limited by the V-groove, and reversibly opening and closing with the load. After this pre-fatigue treatment, the flexible strain sensor of this embodiment is obtained.

[0032] Figure 2 The results show the room-temperature sensing performance test results of the flexible strain sensor prepared in this embodiment. The sensing performance of the flexible strain sensor was tested using a Shimadzu microforce testing system. A unidirectional tensile load was applied along the length of the sensor, and the loading was performed at a rate of 1 mm / min within the 0-5% strain range. The two ends of the sensor were connected to an Agilent 34410 high-precision multimeter via electrodes 3 for resistance measurement. The test was conducted at room temperature, and the obtained strain-resistance curves were used to calculate the sensor's sensitivity (GF = ΔR / R0 / ε). The test results show that the sensor's sensitivity factors are as high as 2348, 22854, and 197472 in the 0-2%, 2-4%, and 4-5% strain ranges, respectively.

[0033] Figure 3 This figure shows the room temperature cyclic stability test curve and a partial magnified view of the flexible strain sensor prepared in this embodiment. The stability test of the flexible strain sensor was conducted using a Shimadzu microforce testing system to apply cyclic fatigue loads at a frequency of 20 Hz within a strain range of 0-1%. Resistance was measured by connecting the two ends of the sensor to an Agilent 34410 high-precision multimeter via electrodes 3. The test was performed at room temperature. The figure shows the sensor under cyclic loading of 5 × 10⁻⁶ Hz. 5 The stable resistance response curves and magnified views within the cycle indicate that the sensor has cyclic stability with an ultra-long service life at room temperature.

[0034] Figure 4 This image shows the strain sensing test curve of the flexible strain sensor prepared in this embodiment under liquid nitrogen conditions. The cryogenic sensing performance test of the flexible strain sensor was conducted using an E3000 fatigue testing machine equipped with a self-built liquid nitrogen cryogenic chamber. A uniaxial tensile load was applied within the 0-5% strain range under liquid nitrogen conditions at a strain of 2.78 × 10⁻⁶. -3 s -1 The strain rate was applied. Liquid nitrogen was added to the cryogenic chamber and kept at that temperature for 5 minutes before testing began at approximately -196 °C. The sensor was connected to an Agilent 34410 high-precision multimeter via electrode 3 for resistance measurement. The resulting cryogenic strain-resistance curves were used to calculate the sensor's sensitivity at low temperatures. Test results show that the sensor maintains a good segmented high-sensitivity strain response under liquid nitrogen cryogenic conditions. Sensitivity factors in the strain ranges of 0-2%, 2-4%, and 4-5% reach 2430, 22695, and 205738, respectively. This indicates that the channel crack structure constructed in this invention can effectively retain the amplification effect on the strain signal in a deep cryogenic environment, thus achieving high-sensitivity cryogenic strain sensing.

[0035] Figure 5This image shows the cyclic stability test curve and a magnified portion of the flexible strain sensor fabricated in this embodiment under liquid nitrogen conditions. The cryogenic cyclic stability test of the flexible strain sensor was conducted using an E3000 fatigue testing machine equipped with a self-built liquid nitrogen cryogenic chamber. Cyclic fatigue loads were applied at a frequency of 20 Hz within a strain range of 0-1% under liquid nitrogen conditions. Liquid nitrogen was added to the cryogenic chamber and held for 5 minutes before the test began. Resistance data was collected by connecting the two ends of the sensor to an Agilent 34410 high-precision multimeter via electrode 3. The test was performed under liquid nitrogen cryogenic conditions. Figure 5 The image shows the sensor being cyclically loaded 10 times. 5 The stable resistance response curves and magnified local images within the cycle show that the magnified local curves at the beginning and end of the test are basically consistent, with no obvious baseline drift or signal attenuation. This indicates that the sensor can maintain a stable cyclic strain response over a long period of time in a deep cryogenic environment.

[0036] Comparative Example 1: This comparative example demonstrates the fabrication of a flexible strain sensor without the non-penetrating V-groove 4 and without pre-fatigue treatment. The specific fabrication steps of the flexible strain sensor are as follows: Step 1: Weigh 100 mg of multi-walled carbon nanotube powder (MWCNTs, model TNM3, purity >98%, diameter 10–20 nm, length 10–30 μm) and add it to 1 mL of Triton X-100 surfactant in a mortar and grind thoroughly. Then wash with 200 mL of deionized water to obtain a MWCNT dispersion. Stir the dispersion magnetically at 1200 r / min for 30 min, then sonicate for 2 h to improve dispersion uniformity. Centrifuge for 30 min to remove coarse particles and insufficiently dispersed agglomerates. After standing for 1 h, take 150 mL of the supernatant and filter it in a vacuum filter, continuously adding deionized water during filtration to thoroughly wash away residual surfactant. After filtration, the obtained MWCNTs filter cake was placed in a vacuum oven at 60 °C and dried for 3 h. After drying, it was carefully peeled off from the surface of the filter membrane to obtain a MWCNTs film with a thickness of about 100 μm. It was then cut into rectangular samples of 12 mm × 3 mm as conductive film 1 for later use.

[0037] Step 2: The conductive film 1, which has not undergone laser etching, is directly placed on the surface of a 30 μm thick polyimide low-temperature adhesive tape flexible substrate 2. Copper wires are connected at both ends of the conductive film along its length to serve as electrode leads 3, and the film is cured at 70 °C for 10 min. Then, the same polyimide low-temperature adhesive tape is used to cover the upper surface of the sample to complete the device encapsulation, resulting in a flexible strain sensor.

[0038] Step 3: The encapsulated flexible strain sensor is used directly for subsequent strain sensing tests without pre-fatigue training.

[0039] Figure 6 The strain sensing test curve of the flexible strain sensor prepared in Comparative Example 1 is shown. The sensing performance test conditions of this flexible strain sensor are the same as those in Example 1, that is, a uniaxial tensile load is applied using a Shimadzu microforce testing system, and the loading is carried out at a speed of 1 mm / min within the strain range of 0-5%. The two ends of the sensor are connected to an Agilent 34410 high-precision multimeter through electrodes 3 for resistance acquisition. The test process is carried out at room temperature, and the obtained strain-resistance curve is used to calculate the sensitivity of the sensor. The test results show that the maximum sensitivity factor of this sensor in the strain range of 0-5% is only 47, which is significantly lower than that of Example 1. This result indicates that without the non-through-groove structure, it is difficult for the conductive film to form an effective orientation channel crack structure, thus resulting in a weak strain response.

[0040] Comparative Example 2: This comparative example demonstrates the fabrication of a flexible strain sensor with a non-penetrating V-groove 4, which underwent only a single pre-stretching treatment without pre-fatigue treatment. The specific fabrication steps of the flexible strain sensor are as follows: Step 1: Weigh 100 mg of multi-walled carbon nanotube powder (MWCNTs, model TNM3, purity >98%, diameter 10–20 nm, length 10–30 μm) and add it to 1 mL of Triton X-100 surfactant in a mortar and grind thoroughly. Then wash with 200 mL of deionized water to obtain a MWCNT dispersion. Stir the dispersion magnetically at 1200 r / min for 30 min, then sonicate for 2 h to improve dispersion uniformity. Centrifuge for 30 min to remove coarse particles and insufficiently dispersed agglomerates. After standing for 1 h, take 150 mL of the dispersion and pour it into a vacuum filter for filtration, continuously adding deionized water during filtration to thoroughly wash away residual surfactant. After filtration, place the obtained MWCNT filter cake in a vacuum oven at 60℃ and dry for at least 3 h. After drying, carefully peel it off from the filter membrane surface to obtain a MWCNT film with a thickness of approximately 100 μm, which serves as the initial conductive film for the sensor.

[0041] Step 2: A VMSP0202-GL-25 (CCD) green femtosecond galvanometer dicing machine was used as the non-penetrating groove processing equipment to laser etch the surface of the initial conductive film to form multiple V-shaped grooves 4 extending along the width direction of the film. These V-shaped grooves 4 are non-penetrating grooves and are spaced apart along the length direction of the initial conductive film. During processing, the idle speed was set to 5000 mm / s, the laser frequency was set to 30 kHz, and the duty cycle was set to 50%. The depth of the V-shaped grooves was controlled by adjusting the number of laser scans, the scanning speed, and the laser energy ratio to avoid local melting. The following parameters were used in this comparative example: 1 scan, 100 mm / min scanning speed, 10% laser energy ratio, and Z-axis focal position set to -3.2 mm. The depth of the V-shaped grooves formed after etching was approximately 20 μm, the width was approximately 15 μm, and the groove spacing D was set to 1.0 mm. Subsequently, the laser-etched initial conductive film was cut into rectangular samples of 12 mm × 3 mm as conductive film 1 for later use.

[0042] Step 3: Place the laser-etched conductive film 1 onto the flexible substrate 2, which is the surface of a 30 μm thick polyimide low-temperature adhesive tape. Connect copper wires with conductive silver paste at both ends of the conductive film as electrode leads 3, and cure at 70 °C for 10 min. Then cover the upper surface of the sample with the same polyimide low-temperature adhesive tape to complete the device encapsulation and obtain the initial structure of the sandwich-type flexible sensor.

[0043] Step 4: Replace the pre-fatigue cyclic loading in Example 1 with a single pre-tension loading. Specifically, fix both ends of the initial structure of the sandwich-type flexible sensor along its length in the fixture of the Shimadzu Microforce Testing System (MMT-101NV-10), and apply a single unidirectional tensile load along the length of the sensor. The tensile strain is 5%, and the strain rate is 0.3% s. -1 This yielded a flexible strain sensor that had only undergone pre-stretching treatment.

[0044] Figure 7The strain sensing test curve of the flexible strain sensor prepared in Comparative Example 2 is shown. The sensing performance test conditions of this flexible strain sensor are the same as those in Example 1, that is, a uniaxial tensile load is applied using a Shimadzu micro-force testing system, and the loading is carried out at a speed of 1 mm / min within the strain range of 0-5%. The two ends of the sensor are connected to an Agilent 34410 high-precision multimeter through electrodes 3 for resistance acquisition. The test process is carried out at room temperature, and the obtained strain-resistance curve is used to calculate the sensitivity of the sensor. The test results show that the sensitivity of the sensor is improved compared with Comparative Example 1, with a maximum sensitivity factor of 158 in the strain range of 0-5%. However, its strain response increase is still significantly lower than that of Example 1, and its sensitivity is also significantly lower than that of Example 1. This result shows that although a single pre-stretch can induce partial crack formation, it cannot replace the role of pre-fatigue cyclic loading in crack propagation and stabilization, and it is difficult to obtain a high-sensitivity response and stable channel crack structure comparable to Example 1.

Claims

1. A method for fabricating a flexible strain sensor with a channel crack based on non-penetrating groove induction and pre-fatigue stabilization, characterized in that, Includes the following steps: (1) A non-through groove structure is formed on the surface of a rectangular conductive film, extending from its width direction to its length direction at two end faces and arranged in parallel intervals along the length direction, for setting a stress concentration area on the conductive film. (2) The conductive film forming the non-penetrating groove structure is placed between the upper and lower flexible substrates, so that the flexible substrates are attached around the perimeter. The conductive film is encapsulated in the middle of the flexible substrate, and electrode wires are connected to both ends of the conductive film along the length direction to obtain the initial structure of the sandwich flexible sensor. (3) Apply pre-fatigue cyclic loading to both ends of the initial structure of the flexible sensor along the length direction. When the resistance response of the initial structure of the sandwich flexible sensor reaches a preset stable state during the pre-fatigue cyclic loading process, stop the cyclic loading to obtain a flexible strain sensor. The strain range of the pre-fatigue cyclic loading is less than the fracture strain of the initial structure of the sandwich flexible sensor, preferably 0-1%; The frequency is 0.5–50 Hz, the strain ratio R=0, and the number of cycles is 10. 2 ~10 6 Week.

2. The preparation method according to claim 1, characterized in that: The conductive film in step (1) is one or more composite conductive films selected from carbon nanotube films, graphene films and near-zero temperature resistivity hybrid films. It maintains conductive continuity and structural integrity at 0 ℃ to -196 ℃, with a thickness of 50 μm ~ 1 mm and an aspect ratio of ≥1 for rectangular conductive films. The near-zero temperature resistivity hybrid film is a hybrid film between conductive fillers or a hybrid film between conductive fillers and a polymer matrix; the hybrid film between conductive fillers is one or more of the following: carbon nanotube / graphene hybrid film, carbon nanotube / MXene hybrid film, graphene / silver nanowire hybrid film, or carbon nanotube / metal nanowire hybrid film; the hybrid film between conductive fillers and the polymer matrix is ​​one or more of the following: carbon nanotube / polymer composite film, graphene / polymer composite film, MXene / polymer composite film, or carbon nanotube / graphene / polymer composite film; after designing different component ratios, the conductive film achieves a near-zero temperature resistivity.

3. The preparation method according to claim 1, characterized in that: The non-penetrating trench structure in step (1) is formed by local removal, local pressing, local etching or local thinning; the specific preparation method of the non-penetrating trench structure is one or more of laser processing, mechanical cutting, mold imprinting, ion beam etching, photolithography-etching-transfer or patterned film formation. The non-penetrating groove structure is a V-shaped groove, a U-shaped groove, a rectangular groove, a trapezoidal groove, an arc groove, or a combination of the above groove shapes; preferably, the non-penetrating groove structure is a V-shaped groove.

4. The preparation method according to claim 3, characterized in that: The geometric parameters of the non-penetrating groove structure include one or more of the following: groove spacing, groove depth, groove width, groove angle, groove bottom curvature radius, and groove edge morphology; by adjusting the geometric parameters, the degree of local stress concentration in the conductive film can be controlled.

5. The preparation method according to claim 4, characterized in that: The surface groove depth of the non-through groove structure is 1 / 10 to 1 / 3 of the conductive film thickness; the surface groove width is 1 μm to 300 μm. The surface groove spacing is 1 / 60 to 1 / 6 of the length of the conductive film.

6. The preparation method according to claim 1, characterized in that: The flexible substrate in step (2) is a low-temperature resistant polymer substrate, specifically including one or more of polyimide, polytetrafluoroethylene, fluorinated ethylene propylene, perfluoroalkoxy resin, ethylene-tetrafluoroethylene copolymer, polyether ether ketone, polyetherimide, and liquid crystal polymer; the electrode wire is a copper wire with a diameter of 0.1-0.3 mm.

7. The preparation method according to claim 1, characterized in that: The pre-fatigue cyclic loading load in step (3) is a sine wave, triangular wave, trapezoidal wave, or other periodic tensile load; The pre-fatigue cyclic loading process causes cracks to preferentially initiate and propagate along the root of the non-penetrating groove structure, forming multiple channel cracks with consistent orientation and spacing limited by the non-penetrating groove structure in the conductive film.

8. The preparation method according to claim 1, characterized in that: The preset stable state in step (3) is: within a continuous preset fatigue cycle loading period, the relative change rate of the peak resistance and baseline resistance between the two wires of the initial structure of the flexible sensor does not exceed a preset threshold; preferably, the preset cycle number is 10. 2 ~10 6 Each cycle, the preset threshold is 1% to 10%.

9. A flexible strain sensor prepared by the preparation method according to any one of claims 1-8, characterized in that: The flexible strain sensor includes upper and lower flexible substrates and a conductive film encapsulated between the two flexible substrates. Electrodes are respectively provided at both ends of the conductive film along its length for connecting to an external resistance signal acquisition device. The conductive film surface is provided with multiple non-through groove structures that extend from its width direction to its two end faces in the length direction and are arranged in parallel and spaced apart along its length direction. After pre-fatigue cyclic loading, channel cracks preferentially initiate from the root of the non-penetrating groove structure and extend along the extension direction of the groove structure, thereby forming a stable channel crack structure with consistent orientation, controlled spacing, and reversible opening and closing with external strain.

10. The flexible strain sensor according to claim 9, characterized in that: The sensor exhibits stable mechanical response and baseline resistance output in cryogenic environments below -100°C; the sensor's sensitivity factor reaches 10. 5 The above; a stable cycle count of 10 is achieved. 5 above.

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