A material flexoelectric property measurement device and method

Abstract

This invention discloses a device and method for measuring the flexural electrical properties of materials, belonging to the field of material electromechanical coupling performance testing. The device includes a mechanical loading module, a bending clamping assembly, and an electrical signal detection module. The upper and lower clamping members of the bending clamping assembly have arc-shaped working surfaces extending along the same bending direction, allowing the material under test to form a predetermined bending curvature and corresponding strain gradient under the clamping state. By changing the curvature of the clamps, the charge, current, or voltage responses under multiple strain gradient states are obtained under the same loading conditions, and the flexural electrical response parameters or flexural coefficient of the material are determined accordingly. The mechanical loading and electrical signal detection can be set independently or integrated into a quasi-static d-axis. 33 In the measuring instrument. This invention is applicable to thin films, sheets, or flexible block materials capable of forming a stable bending state.

Description

Technical Field

[0001] This invention relates to the field of material electrical property testing and electromechanical coupling performance characterization, specifically to a material flexural electrical property measuring device and method, and more particularly to a device and method for using a clamping structure with a predetermined curvature to form a determinable bending strain gradient in a bendable material, and detecting the charge, current or voltage response generated by the material under mechanical loading conditions to determine the material's flexural electrical response parameters or flexural electrical coefficient. Background Technology

[0002] Flexoelectricity is a mechanoelectric coupling effect between material polarization and strain gradient. Unlike the piezoelectric response typically caused by uniform strain, the flexoelectric response is related to the non-uniform spatial distribution of strain within the material. For thin films, sheet materials, and flexible bulk materials that can form a stable bending state under external force, the bending state can establish a strain gradient along the material thickness direction. Therefore, flexoelectric properties are an important parameter for evaluating the mechanoelectric conversion characteristics of such materials.

[0003] Current flexural electrical property measurements typically require establishing a deterministic strain gradient in the material under test before acquiring the corresponding charge, current, voltage, or polarization response. For different material morphologies, various methods exist, including cantilever beam bending, three- or four-point bending, roller bending, local loading, and microscopic testing. These methods can characterize flexural electrical properties, but the method of establishing the strain gradient, the actual deformation state, and the accuracy of its determination directly affect the final test results. Furthermore, different material morphologies often require different clamping and detection systems.

[0004] Taking the four-point bending test as an example, some methods require setting the test material between the matrix beam or supporting structure to form a laminated test structure, and then using an external loading device to cause it to bend. The strain gradient is then calculated by combining the loading force, span, sample and matrix dimensions, elastic parameters, etc. This type of method also needs to consider factors such as interlaminar force transmission, neutral layer position, and material mechanical parameters. When the test material is thin, soft, viscoelastic, or a bendable block material, the above factors may increase the uncertainty in the strain gradient determination process.

[0005] On the other hand, existing flexural electrical testing systems typically include mechanical loading, signal acquisition, and signal display components. Different schemes may use charge, current, or voltage as the electrical response quantity, but the mechanical loading device and the electrical signal detection device are often built separately. Differences in equipment connection, calibration, and testing conditions increase the complexity of the testing system. Therefore, it is necessary to provide a material flexural electrical property measurement scheme that can establish a strain gradient through clamping geometry and allows for the selection of different electrical signal detection methods based on actual testing conditions.

[0006] Quasi-static d 33The measuring instrument can apply periodic mechanical loads to the sample and read the corresponding electromechanical response. The equipment is mature and can serve as a preferred integrated testing platform for this invention. For testing systems employing independent mechanical loading mechanisms, the electrical response of the material can also be obtained through a charge meter, current detection device, or voltage detection device. Therefore, this invention does not necessarily limit itself to a specific electrical signal detection device, but focuses on establishing a controllable strain gradient using a clamping structure with a predetermined curvature and obtaining the corresponding electrical responses under different strain gradient states.

[0007] Therefore, it is necessary to provide a material flexural electrical property measurement scheme that allows the strain gradient of the material under test to be mainly established by predetermined clamping geometry, transforming the strain gradient adjustment from a complex load-deformation inversion process into a direct geometric curvature adjustment; at the same time, it allows mechanical loading and electrical signal detection to adopt integrated or split structures to adapt to thin films, sheet materials and flexible block materials that can be stably bent. Summary of the Invention

[0008] In view of this, the present invention proposes a material flexural electrical property measurement device and method to solve the problems in existing flexural electrical testing, such as the large dependence of strain gradient establishment and determination on complex loading structures and multiple material mechanical parameters, limited adaptability to different material morphologies, and relatively fixed mechanical loading and electrical signal detection methods.

[0009] The technical solution of this invention is implemented as follows: This invention provides a material flexural electrical property measuring device, including a mechanical loading module, a bending clamping assembly, and an electrical signal detection module. The mechanical loading module has two loading ends arranged opposite to each other; the bending clamping assembly includes an upper clamping member and a lower clamping member respectively connected to the two loading ends, with arc-shaped working surfaces extending along the same bending direction formed on opposite sides of the upper and lower clamping members, and a bending clamping area for clamping the material to be tested formed between the two arc-shaped working surfaces, so that the material to be tested forms a predetermined bending state with the arc-shaped working surfaces under clamping conditions. The two signal input terminals of the electrical signal detection module are electrically connected to the test electrodes or electrical contacts on both sides of the material to be tested.

[0010] In some embodiments, the upper and lower clamping members constitute a detachable clamping assembly, and the measuring device is equipped with two or more sets of clamping assemblies with different radii of curvature. Different clamping member sets maintain the same thickness, length, and width of the clamping members while changing the radius of curvature of the arc-shaped working surface. By replacing clamping assemblies with different radii of curvature, the same material to be measured can be made to form different bending curvatures.

[0011] In some embodiments, the two arc-shaped working surfaces of the same clamping assembly can be configured as concentric arc surfaces with a common center of curvature, and their radii of curvature are R1 and R2, respectively. |R2-R1| is adapted to the total clamping thickness of the material under test within the clamping area; the total clamping thickness includes the thickness of the material under test body and the thickness of the test electrode when the surface test electrode is set. For the material under test that can be continuously attached and meets the approximate arc bending condition, the nominal radius of curvature r of its neutral surface can be approximately taken as (R1+R2) / 2. The above-mentioned concentric arc structure is a preferred structure, and the arc-shaped working surfaces can also adopt other curved surface mating forms that can make the material under test form a predetermined bending state.

[0012] In some implementations, a flat clamping assembly with zero curvature can be provided to obtain a reference electrical response of the material under test in a flat state; other clamping methods that can put the material under test in a zero curvature state can also be used for benchmark testing.

[0013] In some implementations, the mechanical loading module and the electrical signal detection module can be set up independently. The mechanical loading module applies a predetermined mechanical load to the material under test in a bent state, preferably a periodic load or a time-varying mechanical load; when using charge or voltage detection, the electrical response can also be obtained after the material under test has formed a predetermined bent state or during the load change process. The electrical signal detection module can be a charge detection unit, a current detection unit, or a voltage detection unit. When using current detection, it is preferable to collect the current signal during loading, unloading, or periodic excitation, and integrate the current signal over a predetermined time period or one or more complete loading cycles to obtain the equivalent charge; when using voltage detection, the equivalent charge or polarization response can be obtained based on the equivalent capacitance of the material under test and the test circuit or a calibrated voltage-charge conversion relationship.

[0014] In some embodiments, a first test electrode and a second test electrode are respectively disposed on two opposite surfaces of the material under test. The two test electrodes at least cover a predetermined effective test area and are respectively connected to two signal input terminals of the electrical signal detection module. The test electrodes may be conductive layers, conductive paste layers, metal films, or flexible conductive sheets that can bend with the material under test. When independent surface test electrodes are used, the effective test area A is the effective overlap area of ​​the two opposite test electrodes in the thickness direction of the material under test. In another embodiment, at least the arc-shaped working surfaces of the upper and lower clamping members that contact the material under test are conductive structures and are respectively connected to two signal input terminals of the electrical signal detection module, so that the upper and lower clamping members also serve as the first and second electrical contact terminals. In this case, the effective test area A is the area of ​​the effective electrical contact region defined by the arc-shaped working surfaces and determined or calibrated by geometric dimensions. An electrical isolation structure is provided between the two electrical signal acquisition paths. The electrical isolation structure may be disposed between the clamping member and the mechanical loading end, at the force transmission connector, or at the electrical signal lead-out position to avoid bypassing through the mechanical connector, instrument frame, or other conductive structures.

[0015] In some implementations, the mechanical loading module and the electrical signal detection module are integrated into a quasi-static d 33 In the measuring instrument. During testing, the bending clamping assembly determines the bending geometry of the material under test, d 33 The measuring instrument applies a periodic mechanical load to the material under test via a clamping assembly and reads the corresponding effective force-electric response. This allows for the establishment of strain gradients, mechanical loading, and acquisition of electrical responses all to be performed on the same testing platform.

[0016] In some implementations, measurements are performed under zero curvature and multiple non-zero curvature states, with the material under test, effective test area, mechanical load, and electrical signal acquisition conditions kept consistent or within a predetermined allowable deviation range in each measurement. The electrical response under zero curvature is used as a benchmark, and the electrical response under non-zero curvature states is corrected accordingly. The flexural electrical performance parameters are then determined based on the relationship between the corrected electrical response and the strain gradient.

[0017] In some implementations, at least three different non-zero nominal strain gradients are set, and the charge, current, or voltage response is directly or calibrated and converted into equivalent charge, polarization response, or other comparable electrical response quantities. The relationship between the electrical response quantities and the nominal strain gradients is then fitted. When the slope of the fitting between the polarization response and the strain gradient is used as the characterization, the effective flexural coefficient of the material under test can be obtained.

[0018] In some embodiments, the material to be tested can be a thin film, sheet, or flexible block material, which can form a stable bending state and a deterministic strain gradient under selected clamping curvature and load conditions; the material can be a polymer, composite material, or other flexible material with flexural electrical response. For samples of different thicknesses, shapes, and flexibility, by selecting clamping components with appropriate radii of curvature, clamping spacing, and loading conditions, the area to be tested can be kept stably attached and cracked or irreversibly deformed can be avoided.

[0019] In some implementations, finite element analysis can be used to assist in verifying the stress and strain distribution under different curvature states. For the test material that is continuously attached within the clamping area and meets the approximate circular arc bending condition, the nominal strain gradient can be determined by C=1 / r according to the actual or nominal radius of curvature r of its neutral surface. For the test material that is thicker, has local slippage, wrinkles, obvious shear deformation, or other deviations from the approximate circular arc bending state, the corresponding strain gradient can be determined according to the actual deformation profile, finite element analysis, or the calibrated curvature-strain gradient relationship.

[0020] In some embodiments, the material to be tested is preferably a polymer film, including polyvinylidene fluoride film and copolymer films thereof; such materials and forms are used to illustrate a preferred test method of the present invention and do not constitute a limitation on the type and form of the material to be tested.

[0021] In some implementations, the bending clamping assembly can be positioned within the temperature-controlled area via a force-transmitting connector, while the main body of the mechanical loading module and / or electrical signal detection module remains outside the temperature-controlled area for extended testing under different temperature conditions; when using quasi-static d 33 When measuring, the clamp can be fed into the adjustable temperature control device through the force transmission connector.

[0022] The present invention also provides a method for measuring the flexural electrical properties of materials: a bending clamping assembly with a first predetermined curvature is selected, and the material to be tested is clamped between upper and lower arc-shaped working surfaces extending along the same bending direction, so that the material to be tested forms a first strain gradient, and the corresponding electrical response is obtained under mechanical loading; then the curvature of the clamping assembly is changed, and different strain gradients and their corresponding electrical responses are obtained under predetermined test conditions; the flexural electrical response parameters or flexural electrical coefficients of the material to be tested are determined according to the correspondence between the strain gradient and the electrical response.

[0023] The present invention has the following advantages over the prior art: This invention utilizes a pair of co-directional arc-shaped working surfaces with predetermined curvature to apply bending constraints to the material under test. This transforms the main control quantity of the strain gradient from complex load-deformation inversion to directly settable fixture geometric curvature, reducing the dependence of synchronous deformation of the matrix beam, interlayer force transfer, and inversion of multiple mechanical parameters on the testing process. The mechanical loading module and electrical signal detection module can be set independently or integrated into a quasi-static d 33 In the measuring instrument, the electrical response can be characterized by charge, current, or voltage, thereby improving the adaptability of the testing system to different detection conditions. The test object is not limited to polymer films, but can also be extended to sheet materials and flexible block materials that can form a stable bending state. By setting multiple curvature states, the correspondence between strain gradient and electrical response can be established; at the same time, it can be combined with a temperature control structure to realize extended testing under different temperature conditions. Attached Figure Description

[0024] To more clearly illustrate the technical solution of the present invention, the accompanying drawings used in the embodiments are briefly described below.

[0025] Figure 1 A preferred embodiment of the present invention employs quasi-static d 33 Schematic diagram of the material flexural electrical properties measuring device and bending clamping assembly of the measuring instrument; Figure 2 The theoretical strain distribution along the thickness direction of a 70 μm PVDF film under different nominal strain gradients; Figure 3 To obtain strain distribution maps along the thickness direction of thin films under different curvature conditions through finite element simulation; Figure 4 This is a schematic diagram of a preferred variable temperature testing structure of the present invention; Figure 5 The graph shows the relationship between the effective electromechanical response and the nominal strain gradient of PVDF films of different thicknesses.

[0026] Figure reference numeral: 1-quasi-static d 33 1-Measuring instrument; 2-Upper clamp; 3-Lower clamp; 4-Material to be tested; 5-First test electrode; 6-Second test electrode; 7-Electrically isolated structure; 8-Temperature control device; 9-Force transmission connector. Detailed Implementation

[0027] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. The following embodiments are used to illustrate the technical solution of the present invention, and not to limit the scope of protection. The higher-level solution of the present invention can employ an independently configured mechanical loading module and an electrical signal detection module. The electrical signal detection module can detect charge, current, or voltage; the following embodiments mainly use quasi-static d 33The measuring instrument is described as an integrated mechanical loading and charge response reading platform, using a PVDF thin film as the material to be tested. This specific embodiment does not constitute a limitation on the measuring device, material type, or material form.

[0028] The "effective flexural electrical coefficient" referred to in this embodiment is a coefficient denoted as μeff, determined by the electromechanical response corresponding to the preset bending strain gradient and mechanical excitation of the material under test under the test configuration and boundary conditions of this embodiment. It is used to characterize the flexural electrical response under this test configuration and is not directly equivalent to a single intrinsic flexural electrical tensor component independent of boundary conditions. For implementation schemes using independent current or voltage detection methods, comparable equivalent charge or polarization responses can be obtained first based on integral relationships, equivalent capacitance, or calibration conversion relationships, and then evaluated according to the same strain gradient-electrical response relationship.

[0029] Example 1 Quasi-static d 33 Preferred testing equipment and basic testing methods for measuring instruments like Figure 1 As shown, this embodiment uses commercial quasi-static d 33 As an integrated mechanical loading and electrical response reading platform, the measuring instrument removes the original upper and lower point-type clamps and installs upper and lower clamping components. Both the upper and lower clamping components are made of 304 stainless steel, with opposing sides forming arc-shaped working surfaces extending in the same bending direction and cooperating with each other. The PVDF film to be tested is directly placed between the two arc-shaped working surfaces and, after clamping, bends along the arc-shaped working surfaces. The upper and lower clamping components are connected to the electrical contact paths on both sides of the film to be tested, while maintaining electrical isolation between the two electrical contact paths. In this embodiment, an insulating connecting sleeve is provided at the connection position between the clamping components and the original test end of the instrument to form the aforementioned electrical isolation structure.

[0030] In this embodiment, the effective working width of both the upper and lower clamping members is 10 mm, and the length of the arc-shaped working area along the bending direction is 12 mm. Clamping member groups with different curvatures maintain consistent thickness, length, and width. Different bending states are obtained by changing the radius of curvature r of the arc-shaped working surface. For PVDF films of different thicknesses, the clamping distance between the upper and lower arc-shaped working surfaces is adjusted accordingly, ensuring continuous adhesion of the film within the effective testing area without significant wrinkles or irreversible compression deformation. As a further lower-level implementation, the upper and lower arc-shaped working surfaces can be made into concentric arc surfaces with a common curvature center, with curvature radii R1 and R2, respectively. |R2-R1| is adapted to the total clamping thickness of the film body and its surface test electrodes within the clamping area, and the nominal radius of curvature r of the neutral surface can be approximately taken as (R1+R2) / 2.

[0031] For a homogeneous PVDF film with a thickness much smaller than the bending radius and continuously bonded within the test area, the nominal strain gradient is C = 1 / r. Under ideal circular arc bending conditions, the axial strain along the film thickness direction (z) satisfies εx(z) = z / r, therefore... εx / z=1 / r. Six clamping states are set, and their nominal strain gradients and corresponding nominal radii of curvature are shown in Table 1.

[0032] Table 1

[0033] During testing, the film to be tested is placed between the upper and lower clamping components, and the handwheel is adjusted to ensure continuous contact between the film and the upper and lower clamping surfaces. To reduce clamping variations, this embodiment uses a thin force sensor to calibrate the clamping position once before formal testing, and a reset mark is made at the handwheel position to control the static clamping force within the range of 1.40 to 1.60 N under various curvature states. After calibration, each set of tests is performed at the same reset position.

[0034] After starting the piezoelectric coefficient measuring instrument, first switch to the force display mode. After installing the corresponding clamping assembly and the film to be tested, adjust the loading mechanism to keep the dynamic force displayed by the instrument at 0.250±0.010 N, then switch to d... 33 Measurements were taken under the reading conditions; the frequency of the periodic mechanical load was 110 Hz. The clamping and dynamic force verification results for the six clamping conditions are shown in Table 2.

[0035] Table 2

[0036] In this embodiment, commercially available PVDF films from the same batch are used, and no additional electric field polarization treatment is performed before testing. A first test electrode and a second test electrode are respectively set on the upper and lower surfaces of the film under test. The test electrode is located in the center of the film, with an effective size of 8 mm × 8 mm. The effective overlap area A of the two opposing test electrodes is 64 mm². The electrodes are formed using conductive silver paste that can bend with the film. The first test electrode is connected to the instrument signal terminal via the upper clamp or an independent lead, and the second test electrode is connected to the instrument reference terminal via the lower clamp or an independent lead. The two electrical signal acquisition paths are electrically isolated by an insulating connecting sleeve located at the clamp mounting position, avoiding bypassing through the instrument's mechanical frame. In other embodiments, the arc-shaped working surfaces of the upper and lower clamps can be conductive surfaces that also serve as two electrical contact ends. In this case, the effective test area A is the area of ​​the effective electrical contact region defined by the arc-shaped working surface and determined or calibrated by geometric dimensions. For each curvature state, after the reading stabilizes, three consecutive readings are recorded, each 10 s apart. The average of the three readings is taken as the electrical response value di for that curvature state.

[0037] First, a flat clamping assembly J0 was used for testing to obtain the reference electrical response value d0 in the zero curvature state; then, J1 to J5 were used for testing in sequence. The electrical response in the non-zero curvature state was corrected for the reference by Δdi=di-d0 to reduce the influence of the instrument zero point, the conventional piezoelectric background of the film under test, and the fixed contact background on the results.

[0038] Based on the dynamic force F and the effective test area A, the effective electromechanical response under the i-th non-zero nominal strain gradient, after reference correction, is converted into the effective polarization response Pi. In this embodiment, when independent surface test electrodes are used, A is the effective overlap area of ​​the first and second test electrodes: Pi = ΔdiF / A Linearly fit Pi to the corresponding nominal strain gradient Ci: Pi = μeffCi + b In the formula, the slope μeff of the fitted straight line is taken as the effective flexural coefficient of the film under test in this test configuration, and b is the fitting intercept. Using multi-curvature fitting instead of direct calculation based on a single test point can reduce the impact of single clamping error and instantaneous reading fluctuation on the final result.

[0039] Example 2: Strain gradient verification under different curvature conditions To illustrate the relationship between the clamping geometry curvature and the strain gradient along the thickness of the test material, a geometric force check is performed using a 70 μm thick PVDF film as an example. For a homogeneous sample with a circular arc curvature, taking the neutral plane as z=0, the axial strain at any position z along the thickness direction is εx(z)=z / r; therefore, its strain gradient along the thickness direction is... εx / z=1 / r, consistent with the curvature of the sample.

[0040] Figure 2 The theoretical strain distributions of a 70 μm PVDF film under five nominal strain gradients of 30.8, 47.3, 61.7, 76.9, and 92.7 m⁻¹ are presented, where the x-axis represents the thickness direction (z) and the y-axis represents the axial strain (εx). Each curve has the neutral plane as its zero point, with the upper and lower surfaces exhibiting tensile and compressive strains of opposite signs, respectively. The slope of the curve increases with increasing nominal curvature. At the maximum nominal strain gradient of 92.7 m⁻¹, the absolute value of the theoretical strain on the upper and lower surfaces of the 70 μm film is approximately 0.324%, still within the small deformation range.

[0041] In addition, COMSOL Multiphysics was used to simulate the arc-shaped clamping state. In the simulation, the elastic modulus of PVDF was taken as 2.0 GPa and Poisson's ratio as 0.34, while the elastic modulus of 304 stainless steel was taken as 193 GPa and Poisson's ratio as 0.30. Figure 3As shown, under different curvature conditions of 0, 30.8, 47.3, 61.7, 76.9, and 92.7 m⁻¹, the equivalent stress distribution on the stressed surface of the component changes significantly with increasing curvature, and its trend is consistent with the aforementioned relationship of circular arc bending. In this embodiment, the nominal strain gradient is determined by geometric curvature. The finite element results are used to assist in checking the stress and deformation trends under different curvature conditions, and are not a necessary prerequisite for determining C=1 / r.

[0042] Example 3: Measurement of flexural conductivity of 40 μm PVDF film A commercially available PVDF film of the same batch with a thickness of 40 μm was taken and cut into rectangular samples of 15 mm × 10 mm. No additional electric field polarization treatment was performed before testing. 8 mm × 8 mm test electrodes were formed at the center of the upper and lower surfaces of the samples, respectively. The test environment temperature was 23 ± 2 ℃, and the relative humidity was 45%–55%. Tests were conducted sequentially using clamping states J0–J5, with the dynamic load frequency maintained at 110 Hz, and the dynamic force controlled according to the force display verification method in Example 1.

[0043] Three parallel readings were performed according to the method in Example 1, and the average results under each nominal strain gradient are shown in Table 3.

[0044] Table 3

[0045] After subtracting the zero curvature reference, a linear fit was performed between the effective polarization response P and the nominal strain gradient C, and the correlation coefficient R was obtained. 2 The effective flexural coefficient of the 40 μm PVDF film was 0.41 nC / m, with a value of 0.991. Only a small reference output was observed at zero curvature. With increasing nominal strain gradient, the effective mechanical-electrical response generally increased and exhibited a stable linear relationship.

[0046] Example 4 Measurement of PVDF films of different thicknesses PVDF films with thicknesses of 40 μm, 70 μm, and 155 μm were selected for testing. Except for the film thickness, the effective test area, dynamic force, loading frequency, and nominal strain gradient sequence of each group of samples remained consistent. Clamping components with matching film clamping gaps were selected for samples of different thicknesses to ensure that each sample could be continuously attached to the arc-shaped working surface in the effective test area.

[0047] d for each group of samples under different nominal strain gradients 33 The instrument readings are shown in Table 4.

[0048] Table 4

[0049] The results of the three groups of samples were corrected for the baseline and linearly fitted, and the fitting results are shown in Table 5.

[0050] Table 5

[0051] like Figure 5 As shown, all three thicknesses of PVDF films can achieve quasi-static d in this embodiment. 33 A stable nominal strain gradient-effective mechanical-electrical response relationship is established on the test platform. The effective flexural coefficients obtained from samples of different thicknesses vary. This embodiment is primarily used to verify the applicability of the preferred embodiment of the present invention to flexible films of different thicknesses and does not constitute a limitation on the type and form of the material to be tested in this invention.

[0052] Example 5: Test repeatability Using a 70 μm PVDF film, five independent full-clamping and multi-curvature measurements were performed under the test conditions described in Examples 1–4. After each test, the sample was removed, repositioned, clamped, and the test was repeated for all curvature states to examine the effect of reclamping on the measurement results.

[0053] The effective flexural coefficients obtained from five independent tests were 0.641, 0.659, 0.648, 0.667, and 0.653 nC / m, respectively, with an average of 0.654 nC / m, a standard deviation of 0.010 nC / m, and a relative standard deviation of 1.53%. The results indicate that, when the fixture curvature, effective test area, and dynamic loading conditions remain consistent, the testing method using a geometrically pre-set strain gradient demonstrates good repeatability.

[0054] Example 6: Temperature Variation Test like Figure 4 As shown, for materials requiring evaluation of their variable-temperature flexural electrical properties, the bending clamping assembly can be connected to the loading end of the mechanical loading module via a rigid force-transmitting connector. This allows the bending clamping assembly and the material under test to be located within the constant-temperature zone of the temperature control device, while the main body of the mechanical loading module and / or the electrical signal detection module is located outside the temperature control zone. This embodiment still uses a quasi-static d... 33 The measuring instrument is described as a preferred integrated testing platform.

[0055] During variable temperature testing, the zero curvature benchmark test and loading condition verification can be repeated at each set temperature, and multi-curvature measurements can be performed after the temperature stabilizes. Force transmission connectors, insulation structures, and electrode leads are selected from materials that meet the corresponding temperature requirements.

[0056] The variable temperature test can determine the flexural electrical properties parameters at the corresponding temperature according to the same benchmark correction and multi-curvature fitting steps as in Example 1; the specific temperature range is determined according to the temperature resistance of the material to be tested and the loading and testing accessories used, and a specific temperature change law is not a necessary condition for the implementation of this invention.

[0057] The above embodiments are used to illustrate the technical concept and implementation path of the present invention and do not constitute a limitation on the scope of protection of the present invention. Based on the disclosure of the present invention, those skilled in the art can make conventional adjustments to the clamping material, number of curvatures, type of detection signal, mechanical loading method, test electrode form, or temperature control structure, as long as the predetermined curvature clamping is still used to establish the bending strain gradient of the material under test, and the flexural electrical performance parameters are determined based on the electrical response under different strain gradient states. All of these adjustments can be implemented according to the technical solution disclosed in the present invention.

Claims

1. A device for measuring the flexural electrical properties of materials, characterized in that, The device includes a mechanical loading module, a bending clamping assembly, and an electrical signal detection module. The mechanical loading module includes a first loading end and a second loading end disposed opposite to each other, and a loading mechanism for driving at least one loading end to apply a mechanical load along the loading direction. The bending clamping assembly includes an upper clamping member and a lower clamping member respectively connected to the first loading end and the second loading end. The upper clamping member and the lower clamping member respectively form arc-shaped working surfaces extending along the same bending direction on opposite sides. A bending clamping area for clamping the material to be tested is formed between the two arc-shaped working surfaces, so that the material to be tested forms a predetermined bending state with the arc-shaped working surfaces. The electrical signal detection module has two signal input terminals respectively electrically connected to test electrodes or electrical contacts on both sides of the material to be tested. The electrical signal detection module includes at least one of a charge detection unit, a current detection unit, or a voltage detection unit.

2. The material flexural electrical property measuring device according to claim 1, characterized in that, The bending clamping assembly includes at least two sets of upper and lower clamping parts with different radii of curvature. The thickness, length and width of the clamping parts in different clamping parts sets are consistent, and the bending curvature of the material to be tested can be changed by changing the clamping parts sets with different radii of curvature.

3. The material flexural electrical property measuring device according to claim 1 or 2, characterized in that, The two arc-shaped working surfaces of the same clamping assembly are concentric circular arc surfaces with a common center of curvature, and their radii of curvature are R1 and R2, respectively; |R2-R1| is adapted to the total clamping thickness of the material under test in the clamping area, the total clamping thickness includes the thickness of the material under test body and the thickness of the test electrode when the surface test electrode is set; the nominal radius of curvature r of the neutral surface of the material under test under continuous contact and satisfying the approximate arc bending condition is approximately (R1+R2) / 2.

4. The material flexural electrical property measuring device according to claim 1, characterized in that, It also includes a temperature control device and a force transmission connector, wherein the force transmission connector is connected between the mechanical loading module and the bending clamping assembly, so that the bending clamping assembly is located within the temperature control area of ​​the temperature control device, while the main body of the mechanical loading module and / or the electrical signal detection module is located outside the temperature control area.

5. The material flexural electrical property measuring device according to claim 1, characterized in that, The mechanical loading module and the electrical signal detection module are integrated into the quasi-static d 33 In the measuring instrument, the upper clamp and the lower clamp replace the quasi-static d 33 The original point clamp of the measuring instrument is installed at its opposite test end.

6. A method for measuring the flexural electrical properties of a material, characterized in that, include: The material to be tested is clamped between upper and lower arc-shaped working surfaces with a first predetermined curvature and extending along the same bending direction, so that the material to be tested forms a first bending state with the arc-shaped working surfaces, and a first strain gradient is determined according to the first predetermined curvature; a mechanical load is applied to the material to be tested in the first bending state through a mechanical loading module, and the corresponding first electrical response is obtained through an electrical signal detection module; the curvature of the bending clamping assembly is changed so that the material to be tested forms a second bending state different from the first bending state, and the corresponding second electrical response is obtained under predetermined test conditions; the flexural electrical properties parameters of the material to be tested are determined according to the different strain gradient states and their corresponding electrical responses.

7. The method for measuring the flexural electrical properties of materials according to claim 6, characterized in that, For the material to be measured that is continuously attached to the arc-shaped working surface in the clamping area and meets the approximate circular arc bending condition, the nominal strain gradient C is determined by the nominal radius of curvature r of the neutral surface, C=1 / r; when the upper and lower arc-shaped working surfaces are concentric circular arc surfaces with a common curvature center and curvature radii R1 and R2 respectively, r is approximately taken as (R1+R2) / 2. For test materials that significantly deviate from the approximate circular arc curvature, the corresponding strain gradient is determined based on the actual deformation profile, finite element analysis, or the calibrated curvature-strain gradient relationship.

8. The method for measuring the flexural electrical properties of materials according to claim 6, characterized in that, The electrical response is at least one of charge, current, or voltage; when detecting charge, the corresponding surface charge density or polarization response is determined based on the detected charge quantity Q and the effective test area A; when detecting current, the equivalent charge Q is obtained by integrating the current signal over a predetermined time period or one or more complete loading cycles during the loading or unloading process; when detecting voltage, the voltage response is converted into an equivalent charge or polarization response based on the equivalent capacitance of the material under test and the test circuit or the calibrated voltage-charge conversion relationship.

9. The method for measuring the flexural electrical properties of materials according to claim 6, characterized in that, It also includes zero curvature reference measurements and acquires electrical responses under at least three different non-zero curvature states; The electrical response in the non-zero curvature state is corrected by the electrical response in the zero curvature state, and the flexural electrical properties parameters of the material under test are determined based on the relationship between the corrected electrical response and the nominal strain gradient.

10. The method for measuring the flexural electrical properties of materials according to claim 9, characterized in that, The mechanical loading module and the electrical signal detection module are integrated into the quasi-static d 33 In the measuring instrument, the frequency of the periodic mechanical load is 110 Hz, and the dynamic force is 0.250 ± 0.010 N; the material to be tested is a PVDF thin film, and the effective area of ​​the test electrode is A. The d-th non-zero nominal strain gradient Ci is applied... 33 The reference reading d0 in the zero curvature state is subtracted from the instrument reading di to obtain Δdi. The corresponding effective polarization response Pi is obtained according to Pi=ΔdiF / A, and the slope of the linear fitting between Pi and Ci is used as the effective flexural coefficient.

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