A strain measurement method and a flexible sensor based on the shear stress transfer characteristic

Abstract

The present invention discloses a strain measurement method and a flexible sensor based on the shear stress transfer characteristic. By combining the characteristic of the quadratic curve transfer of the shear stress of the flexible material with the stress-strain relationship, an improved strain transfer model is obtained, which improves the accuracy of the strain transfer model, quantifies and visualizes the strain transfer process of the flexible sensor, improves the measurement accuracy of the flexible sensor, solves the problem of low strain measurement accuracy of the flexible sensor, and this method is applicable to both traditional strain gauges and flexible strain sensors. The calculation is simple and the accuracy is high, and it has strong engineering applicability.

Description

Technical Field

[0001] The present invention relates to the field of strain measurement, and particularly to a strain measurement method and a flexible sensor based on the shear stress transfer characteristic. Background Art

[0002] In traditional strain transfer models, since the sensitive layer materials are generally optical fibers, conductive metals, etc., their elastic moduli are relatively large, several orders of magnitude larger than those of other layer materials, and the elastic moduli of other layers are often ignored; however, for flexible sensors, the materials of each layer have good flexibility and compatibility, and their elastic moduli are often of the same order of magnitude, so they cannot be ignored.

[0003] In addition, in the process of establishing traditional strain transfer models, it is assumed that shear stress is linearly transferred in each layer of the sensor; however, due to the characteristics of flexible materials, shear stress is transferred in a quadratic curve in each layer, so the strain transfer rate calculated by traditional strain models is often on the high side.

[0004] In recent years, domestic and foreign scholars have tried to increase the problems that may be encountered in the actual application of strain transfer models by adding boundary conditions, considering interlayer bonding, etc., so as to improve the accuracy of displacement results, but these methods do not change the problem of insufficient accuracy of the model itself.

[0005] Therefore, at present, most flexible sensors are used to qualitatively measure some dynamic characteristics of structures, and insufficient accuracy is one of the main problems that prevent them from being applied to actual engineering strain measurement. Summary of the Invention

[0006] In order to solve the above problems, the present invention provides a strain measurement method and a flexible sensor device based on the shear stress transfer characteristic. By combining the characteristic of quadratic curve transfer of shear stress of flexible materials with the stress-strain relationship, an improved strain transfer model is obtained, the accuracy of the strain transfer model is improved, the strain transfer process of the flexible sensor is quantified and visualized, and the measurement accuracy of the flexible sensor is improved.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] In a first aspect, an embodiment of the present application provides a strain measurement method based on the shear stress transfer characteristic, including:

[0009] Based on the stress relationship of each layer structure of the flexible sensor, establish the axial tension / compression and shear force balance equations of each layer structure of the flexible sensor in combination with the stress state of each layer structure;

[0010] Obtain the mapping relationship between normal stress and shear stress from the axial tension / compression and shear force balance equations;

[0011] Based on the mapping relationship between the normal stress and the shear stress, combined with Hooke's theorem, the relationship equation between the shear stress and the strain of the sensitive layer of the flexible sensor is obtained;

[0012] According to the characteristic that the shear stress of the flexible material in the flexible sensor is transmitted in a quadratic curve between layers and the relationship between displacement, normal stress, and shear stress, and combined with the shear stress and sensitive layer strain equation, the displacement balance equation between the structural layer and the sensitive layer in the flexible sensor is obtained;

[0013] Based on the displacement balance equation and combined with the boundary conditions of the sensitive layer, the average strain transfer rate is obtained;

[0014] Dividing the strain measurement value by the average strain transfer rate to obtain the corrected strain value.

[0015] Optionally, each layer structure of the flexible sensor includes an adhesive layer, a base layer, a sensitive layer, and a cover layer stacked in sequence on the structural layer;

[0016] The cover layer surrounds the sensitive layer on three sides, isolating the sensitive layer from the air;

[0017] The sensitive layer is used to receive mechanical behavior and convert it into an electrical signal;

[0018] The base layer is located between the adhesive layer and the sensitive layer, and is used to prevent the sensitive layer from directly contacting the structural layer;

[0019] The adhesive layer is used to connect the flexible sensor to the structural layer.

[0020] Optionally, the mapping relationship between the normal stress and the shear stress is:

[0021]

[0022]

[0023]

[0024]

[0025] Where W c 、W g 、W b 、W p are the lateral widths of the cover layer, the sensitive layer, the base layer, and the adhesive layer respectively; h c 、h g 、h b 、h p are the thicknesses of the cover layer, the sensitive layer, the base layer, and the adhesive layer respectively; τ cg 、τ gb 、τbp , τ ph are the shear stresses of the covering layer and the sensitive layer, the sensitive layer and the base layer, the base layer and the cementing layer, and the cementing layer and the structural layer respectively, and σ c , σ g , σ b , σ p are the normal stresses of the covering layer, the sensitive layer, the base layer, and the cementing layer, and dx is an infinitesimal element arbitrarily taken along the length direction of the sensitive layer.

[0026] Optionally, the relationship equation between the shear stress of the flexible sensor and the strain of the sensitive layer is:

[0027]

[0028] Wherein,

[0029]

[0030]

[0031]

[0032]

[0033] ε g is the strain of the sensitive layer, and E c , E g , E b , E p are the elastic moduli of the covering layer, the sensitive layer, the base layer, and the cementing layer respectively.

[0034] Optionally, after obtaining the relationship equation between the shear stress of the flexible sensor and the strain of the sensitive layer, the method further includes:

[0035] According to the characteristic that the shear stress of the flexible material is transmitted in a quadratic curve between layers, the transfer function of the shear stress is obtained:

[0036]

[0037] Wherein, τ1 is the shear stress on the lower surface of each layer, τ2 is the shear stress on the upper surface of each layer, and h is the thickness of each layer of material.

[0038] Optionally, the relationship between the displacement and the normal stress and shear stress is:

[0039]

[0040]

[0041] Among them, u is displacement, σ is stress, ε is strain, E is elastic modulus, Δ is the displacement of this layer structure relative to the lower layer structure, τ is shear stress, and G is shear modulus.

[0042] Optionally, the displacement balance equation of the structural layer and the sensitive layer is:

[0043]

[0044] Among them,

[0045] Optionally, the boundary conditions of the sensitive layer are:

[0046]

[0047] Among them, L g is half of the length of the sensitive layer.

[0048] Optionally, the improved strain transfer model and the average strain transfer rate are:

[0049]

[0050]

[0051] Among them, L is the length of the sensitive layer.

[0052] In a second aspect, an embodiment of the present application provides a flexible sensor for measuring a strain value by using any of the above methods.

[0053] It can be seen that the strain measurement method and the flexible sensor device based on the shear stress transfer characteristic provided by the embodiment of the present invention improve the measurement accuracy of the flexible sensor and solve the problem of low strain measurement accuracy of the flexible sensor. Description of the Drawings

[0054] Figure 1 is a schematic diagram of a flexible sensor and a structural layer provided by an embodiment of the present invention;

[0055] Figure 2 is a flowchart for establishing a strain measurement method based on the shear stress transfer characteristic provided by an embodiment of the present invention;

[0056] Figure 3(a) is a stress distribution diagram of each layer of a flexible sensor provided by an embodiment of the present invention;

[0057] Figure 3(b) is a displacement analysis diagram of each layer of a flexible sensor provided by an embodiment of the present invention;

[0058] Figure 4 is a shear stress quadratic curve transfer analysis diagram based on the shear stress transfer characteristic provided by an embodiment of the present invention;

[0059] Figure 5 It is a comparison diagram of the strain transfer coefficients of the traditional model, the model of the embodiment of the present invention, and the simulation results;

[0060] Figure 6 It is a comparison diagram of the average strain transfer coefficients of the traditional model, the model of the embodiment of the present invention, and the simulation results;

[0061] Figure 7(a) is a comparison diagram of the strain transfer coefficients of the traditional model, the model of the embodiment of the present invention, and the simulation results when the substrate thickness is 0 mm;

[0062] Figure 7(b) is a comparison diagram of the strain transfer coefficients of the traditional model, the model of the embodiment of the present invention, and the simulation results when the substrate thickness is 0.25 mm;

[0063] Figure 7(c) is a comparison diagram of the strain transfer coefficients of the traditional model, the model of the embodiment of the present invention, and the simulation results when the substrate thickness is 2 mm;

[0064] Figure 7(d) is a comparison diagram of the strain transfer coefficients of the traditional model, the model of the embodiment of the present invention, and the simulation results when the substrate thickness is 4 mm; Detailed implementation manners

[0065] Next, the technical solutions in the embodiments of the present disclosure will be clearly and completely described in conjunction with the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present disclosure, rather than all of the embodiments. Based on the embodiments provided by the present disclosure, all other embodiments obtained by those of ordinary skill in the art belong to the scope of protection of the present disclosure.

[0066] In the description of the present disclosure, it should be understood that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing the present disclosure and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation to the present disclosure.

[0067] Unless otherwise required by the context, throughout the specification and claims, the term "comprising" is interpreted as an open, inclusive meaning, that is, "including, but not limited to". For example, a process, method, system, product or device that includes a series of steps or units is not limited to the listed steps or units, but may optionally further include steps or units not listed, or may optionally further include other steps or units inherent to these processes, methods, products or devices.

[0068] In the context of the present disclosure, the meanings of "on", "above", and "over" should be construed in the broadest possible manner such that "on" not only means "directly on something", but also includes "on something" with intermediate features or layers therebetween, and "above" or "over" not only means "above" or "over" something, but also includes "above" or "over" something with no intermediate features or layers therebetween (i.e., directly on something).

[0069] Exemplary embodiments are described herein with reference to cross-sectional views and / or plan views that are idealized exemplary drawings. In the drawings, the thickness of layers and regions is exaggerated for clarity. Accordingly, variations in shape relative to the drawings due to, for example, manufacturing techniques and / or tolerances are contemplated. Thus, exemplary embodiments should not be construed as limited to the shapes of the regions shown herein, but rather include shape deviations due to, for example, manufacturing. Accordingly, the regions shown in the drawings are schematic in nature, and their shapes are not intended to show the actual shape of the regions of the device, and are not intended to limit the scope of the exemplary embodiments.

[0070] Regarding the above-mentioned problem of insufficient measurement accuracy of flexible sensors, the reason is that the traditional strain transfer model is not applicable to flexible sensors. In the sensor structure, the sensitive layer of the sensor is an important part that converts structural changes into electrical signal changes. The sensitive layer is protected by the covering layer and the substrate. The sensitive layer materials of traditional sensors such as fiber Bragg grating sensors and strain gauges are generally optical fibers, conductive metals, etc., and their elastic moduli are relatively large, several orders of magnitude larger than those of other layer materials. In practical applications, the elastic moduli of other layers are often ignored. Therefore, in the traditional model, the displacement at the bottom layer of the sensitive layer is used as the overall displacement of the layer; however, for flexible sensors, the materials of each layer have good flexibility and compatibility, and their elastic moduli are often in the same order of magnitude. Due to the relatively small elastic moduli of the materials of each layer of the flexible sensor, there will be a large loss of strain during the process of transferring the strain from the measured structure to the sensitive layer of the sensor, resulting in inaccurate measurement results.

[0071] In addition, during the establishment of the traditional strain transfer model, it is assumed that the shear stress is linearly transferred in each layer of the sensor; however, due to the characteristics of flexible materials, the shear stress is transferred in a quadratic curve manner in each layer. Therefore, the strain transfer rate calculated by applying the traditional strain model to flexible sensors is often too large.

[0072] The strain measurement method and flexible sensor device based on the shear stress transfer characteristic provided by the embodiments of the present application combine the characteristic of the quadratic curve transfer of the shear stress of the flexible material with the stress-strain relationship to obtain an improved strain transfer model, improve the accuracy of the strain transfer model, quantify and visualize the strain transfer process of the flexible sensor, improve the measurement accuracy of the flexible sensor, solve the problem of low strain measurement accuracy of the flexible sensor, and this method is applicable to both traditional strain gauges and flexible strain sensors. The calculation is simple and the accuracy is high, and it has strong engineering applicability.

[0073] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0074] Please refer to Figure 1 , Figure 1 which is a schematic diagram of a flexible sensor and a structural layer provided by the embodiments of the present application. The flexible sensor is simplified into a structure stacked layer by layer. As Figure 1 shown, the flexible sensor 1 includes a cover layer 2, a sensitive layer 3, a base layer 4, and a cementing layer 5. The flexible sensor 1 is connected to the structural layer 6 through the cementing layer 5. As described above, the materials of each layer of the flexible sensor 1 are all linear elastic materials and isotropic.

[0075] The cover layer 2 is located above the sensitive layer 3. In an embodiment of the present application, the cover layer 2 is located above the sensitive layer 3 and surrounds the sensitive layer from three sides, that is, the top surface and the side surface of the sensitive layer 3 are wrapped, so that the sensitive layer 3 is isolated from the air, preventing the components in the air from reacting with the materials in the sensitive layer 3, resulting in unstable measurement results or reducing the service life of the sensor. It should be noted that the positional relationship between the cover layer 2 and the sensitive layer 3 and the way the cover layer 2 surrounds the sensitive layer 3 are a possible implementation manner of the present application. The present application does not limit this, and any way of isolating the sensitive layer 3 from the air is within the protection scope of the present application.

[0076] The main function of the sensitive layer 3 is to convert the received mechanical behavior into an electrical signal. Taking a piezoresistive strain sensor as an example, the sensitive layer 3 is a conductive layer. In an embodiment of the present application, the sensitive layer can be a composite material, which has a certain resistance. When the structural layer 6 undergoes strain, it will cause the sensitive layer 3 to undergo strain at the same time, which makes the resistance value of the sensitive layer 3 change, and the change amount of the resistance value is related to the strain magnitude. By detecting the resistance change of the sensitive layer 3 with an instrument, the strain magnitude of the structural layer 6 can be calculated. In an embodiment of the present application, the sensitive layer is a MXene / PDMS composite material, where PDMS (polydimethylsiloxane) is polydimethylsiloxane.

[0077] The base layer 4 is located below the sensitive layer 3. The material of the base layer 4 is PDMS, but it is not limited thereto. The base layer 4 can prevent the sensitive layer 3 from directly contacting the structural layer 6. The structural layer 6 usually has a certain electrical conductivity. When the sensitive layer 3 directly contacts the structural layer 6, since the sensitive layer 3 is a conductive layer, an electrical interaction will occur between the structural layer 6 and the sensitive layer 3, thereby affecting the resistance value of the sensitive layer 3 and the magnitude of the strain value of the structural layer 6 finally measured.

[0078] The flexible sensor 1 is adhesively attached to the structure to be measured, that is, the structural layer 6, through the bonding layer 5. In an embodiment of the present application, the bonding layer 5 is PDMS, but it is not limited thereto. The structural stress and strain state are transmitted to the sensitive layer 3 through the bonding layer 5 and the base layer 4.

[0079] The physical property parameters of each of the above-mentioned material layers, such as the elastic modulus and Poisson's ratio, are shown in Table 1 below.

[0080] Physical property parameters of each layer of the flexible strain sensor

[0081]

[0082] Table 1

[0083] Next, the strain transfer mechanism of the flexible sensor will be specifically analyzed in combination with embodiments. In the embodiments of the present application, each material layer of the flexible sensor uses a linear elastic material and is isotropic; the elastomer is only uniformly stretched along the axial direction, that is, the Figure 1 X direction in, the sensor deforms the strain gauge through the bonding layer, and the sensor does not directly bear external forces; the interfaces between the covering layer, the sensitive layer, the base layer, the bonding layer and the structural layer are tightly combined and do not undergo relative slip; the above-mentioned material layers are respectively subjected to shear stresses on the upper and lower surfaces and normal stresses of this layer; the deformations of each material layer caused by temperature changes are not within the scope considered in the embodiments of the present application.

[0084] Specifically, please refer to Figure 2 , Figure 2 is a flowchart established for a strain measurement method based on the shear stress transfer characteristic. The present invention will be combined with Figure 2 to elaborate in detail on the establishment of the strain model and the measurement of strain.

[0085] S101. First, based on the stress relationships of each material layer of the flexible sensor, such as the covering layer, the sensitive layer, the base layer, and the bonding layer, combined with the stress states of each material layer, establish the axial tension / compression and shear force balance equations for each layer structure of the flexible sensor. The magnitude of the axial tension / compression is the normal stress multiplied by the microelement length, and the magnitude of the shear force is the shear stress multiplied by the contact area between microelements. Specifically as follows:

[0086] Take an infinitesimal element \(dx\) along the length direction of the sensitive layer of the flexible sensor, and conduct a force analysis on each layer. Specifically, according to the principle of force balance, establish the axial tension / compression and shear force balance equations for each material layer as follows:

[0087] (W c h c -W g h g )dσ c +τ cg (2h g +W g )dx=0 (1.1)

[0088] h g W g dσ g +τ gb W g dx-τ cg (2h g +W g )dx=0 (1.2)

[0089] h b W b dσ b +τ bp W b dx-τ gb W g dx=0 (1.3)

[0090] h p W p dσ p +τ ph W p dx-τ bp W b dx=0 (1.4)

[0091] In the above equations, \(W\) c , \(W\) g , \(W\) b , \(W\) p are the transverse widths of the cover layer, sensitive layer, base layer, and cementing layer respectively; \(h\) c , \(h\) g , \(h\) b , \(h\) p are the thicknesses of the cover layer, sensitive layer, base layer, and cementing layer respectively; \(\tau\) cg , \(\tau\) gb , \(\tau\) bp , \(\tau\) ph are the shear stresses between the cover layer and the sensitive layer, the sensitive layer and the base layer, the base layer and the cementing layer, and the cementing layer and the structural layer respectively, and \(\sigma\) c , \(\sigma\) g , \(\sigma\) b , \(\sigma\)p The normal stresses of the covering layer, the sensitive layer, the base layer, and the bonding layer;

[0092] S102. Further, according to the above axial tension / compression and shear force balance equations, obtain the mapping relationships of normal stress and shear stress, which are specifically as follows:

[0093]

[0094]

[0095]

[0096]

[0097] S103. Further, according to Hooke's law, introduce the relationship between stress and strain and the elastic modulus of each layer material, which is specifically as follows:

[0098] σ = Eε (3)

[0099] Let:

[0100]

[0101] In the above formula, σ is stress, ε is strain, and E is the elastic modulus. E c 、E g 、E b 、E p are the elastic moduli of the covering layer, the sensitive layer, the base layer, and the bonding layer, respectively.

[0102] Since the covering layer, the sensitive layer, the base layer, and the bonding layer deform synchronously, the strain gradients of the three are close. Therefore, it can be considered that:

[0103]

[0104] In the formula, ε c 、ε g 、ε b 、ε p are the strains of the covering layer, the sensitive layer, the base layer, and the bonding layer, respectively.

[0105] Substitute formulas (3)-(5) into formulas (2.1)-(2.4), and in order to simplify the expression, let

[0106]

[0107]

[0108]

[0109]

[0110] The relationship equations between the shear stresses of each layer and the strain of the sensitive layer are as follows:

[0111]

[0112] S104. As known from the characteristics of the flexible material, the shear stress is transmitted in a quadratic curve between layers. Let its transfer function be y = ax 2 . The quadratic curve graph is as shown in Figure 4 . In the figure, h is the thickness of the material layer, τ1 is the shear stress on the lower surface of the material layer, τ2 is the shear stress on the upper surface of the material layer, and the difference between the two, τ1 - τ2, is the coordinate of the x-axis at the end of the curve. Substituting the coordinates (τ1 - τ2, h) into the quadratic curve equation, the transfer function of the shear stress is obtained as follows:

[0113]

[0114] According to the mechanics of materials, the relationships between displacement, normal stress, and shear stress are as follows:

[0115]

[0116]

[0117] In the above formulas (10) - (11), u is the displacement, σ is the stress, ε is the strain, E is the elastic modulus, Δ is the displacement of this layer structure relative to the lower layer structure, τ is the shear stress, and G is the shear modulus;

[0118] From formulas (9), (10), and (11), the displacement calculation formulas for each layer of the flexible sensor relative to the lower layer structure are calculated as follows:

[0119]

[0120] In the formula, Δ 12 is the relative displacement between each layer structure and the lower layer structure, u1 is the displacement of this layer structure, u2 is the displacement of the lower layer structure, G is the shear modulus, h is the thickness of each layer of material, ε is the strain, τ1 is the shear stress on the lower surface of each layer, and τ2 is the shear stress on the upper surface of each layer;

[0121] Substituting the parameters corresponding to each layer into the relative displacement calculation formula (12), we get:

[0122]

[0123]

[0124]

[0125] The sensitive layer of the flexible sensor is made of a flexible material and has a certain thickness. It is inaccurate to directly represent the displacement of the entire sensitive layer with the displacement of the lower surface of the sensitive layer in the traditional model. Therefore, in the present invention, the relative displacement of half of the entire sensitive layer is introduced into the strain transfer formula. According to the relationship between the displacements of the structural layer and the sensitive layer in Fig. 3(b), where the displacement of the sensitive layer is taken as the relative displacement of half of the entire sensitive layer, the displacement balance equation between the structural layer and the sensitive layer in the flexible sensor is obtained as follows:

[0126]

[0127] In the above formula:

[0128]

[0129] S105. Differentiate the displacement balance equation 13.4 to obtain a second-order linear non-homogeneous differential equation with constant coefficients for strain, as follows:

[0130]

[0131] Introduce the boundary conditions of the sensor sensitive layer, as follows:

[0132]

[0133] In the formula, L g is half of the length of the sensitive layer;

[0134] Solve to obtain the second-order linear non-homogeneous differential equation with constant coefficients for strain, which is the improved strain transfer model, as follows:

[0135]

[0136] In the above formula, L is the length of the sensitive layer.

[0137] Through the ratio of the strain of the sensitive layer to the strain of the structural layer, the improved strain transfer coefficient β can be obtained, as follows:

[0138]

[0139] Integrate the strain transfer coefficient in Equation (12.8) to obtain the average strain transfer rate α, as follows:

[0140]

[0141] S106. Divide the actually measured strain value of the flexible sensor by the average strain transfer rate α to obtain a more accurate corrected strain value, that is,

[0142] Corrected strain value = Strain measurement value / α

[0143] The following describes the improved effect of the sensor strain transfer model based on the shear stress transfer characteristics in combination with specific embodiments. As shown in Fig. 3(a), the object is a finite element model of a flexible sensor. In this embodiment, the materials of the flexible sensor cover layer, base layer, and cementing layer are PDMS, and the material of the sensitive layer is MXene / PDMS composite material, but it is not limited thereto; in this embodiment, the size of the cover layer is 80 mm in length, 30 mm in width, and 2.1 mm in height, the size of the sensitive layer is 60 mm in length, 10 mm in width, and 2 mm in height, the size of the base layer is 80 mm in length, 30 mm in width, and 0.5 mm in height, and the size of the cementing layer is 80 mm in length, 30 mm in width, and 0.05 mm in height, but it is not limited thereto.

[0144] As shown in Fig. 3(a), the sensor is layered, and the stress states of each layer are marked. The strain transfer model is calculated by the improved method of the sensor strain transfer model based on the shear stress transfer characteristics. In an embodiment of the present application, the sensor can be pasted at the center position of the structure, and the structure can be a Q235 cantilever steel plate. A tensile strain of 0.2 is applied to the steel plate, and the strain of the sensitive layer of the sensor is measured as the strain transfer. Subsequently, the physical property parameters are input into the improved strain transfer model, and the strain transfer coefficient and the average strain transfer rate are calculated.

[0145] Furthermore, to verify that the present invention is applicable to calculating the strain transfer coefficient of the layered structure sensor, the calculation results of the traditional strain transfer model are also used for comparison. Figure 5 The comparison of the strain transfer curves of the traditional model, the optimized model, and the simulation results is given under the conditions that the length of the sensitive layer is 60 mm and 100 mm. Figure 6 The comparison of the results of the average strain transfer rate of the three models varying with the length of the sensitive layer is given. From Figure 5 and Figure 6 it can be seen that the error of the improved method of the strain transfer model proposed by the present invention is significantly smaller than that of the calculation method of the traditional strain transfer model, which shows the effectiveness of the present invention in improving the accuracy of the strain transfer model.

[0146] Furthermore, to verify the wide applicability of the method of the present invention, the results are compared using base layers with different thicknesses, which are 0 mm, 0.25 mm, 2 mm, and 4 mm respectively. Figure 7(a) - Figure 7(d) The comparison of the strain transfer coefficients under various base layer thicknesses is given. It can be seen from the figure that under the four conditions, the results of the optimized model are better than those of the traditional model, which also shows the applicability of the present invention to various layered sensors.

[0147] Through the above Figure 1- An improved strain transfer model based on the shear stress transfer characteristics in the embodiment shown in Figure 7 combines the characteristics of the quadratic curve transfer of the shear stress of the flexible material and the stress-strain relationship to obtain an improved strain transfer model, which improves the accuracy of the strain transfer model, quantifies and visualizes the strain transfer process of the flexible sensor, improves the measurement accuracy of the flexible sensor, solves the problem of low strain measurement accuracy of the flexible sensor, and this method is applicable to both traditional strain gauges and flexible strain sensors. The calculation is simple and the accuracy is high, and it has strong engineering applicability.

[0148] The embodiments described above are only used to describe the preferred embodiments of the present application, and do not limit the scope of the present application. Without departing from the design spirit of the present application, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present application shall fall within the protection scope determined by the claims of the present application.

Claims

1. A strain measurement method based on the shear stress transfer characteristic, characterized in that Including: Based on the stress relationship of each layer structure of the flexible sensor, establish the axial tension / compression and shear force balance equations of each layer structure of the flexible sensor by combining the stress states of each layer structure; Obtain the mapping relationship between normal stress and shear stress from the axial tension / compression and shear force balance equations; From the mapping relationship between normal stress and shear stress, combine Hooke's theorem to obtain the shear stress and sensitive layer strain relationship equation of the flexible sensor; According to the characteristic that the shear stress of the flexible material in the flexible sensor is transmitted in a quadratic curve between layers and the relationship between displacement and normal stress and shear stress, and combine the shear stress and sensitive layer strain equation to obtain the displacement balance equation between the structural layer and the sensitive layer of the flexible sensor; Obtain the average strain transfer rate from the displacement balance equation in combination with the boundary conditions of the sensitive layer; Divide the strain measurement value by the average strain transfer rate to obtain the corrected strain value.

2. The method according to claim 1, wherein Each layer structure of the flexible sensor includes a cement layer, a base layer, a sensitive layer, and a cover layer stacked on the structural layer in sequence; The cover layer surrounds the sensitive layer on three sides, isolating the sensitive layer from air; The sensitive layer is used to receive mechanical behavior and convert it into an electrical signal; The base layer is located between the cement layer and the sensitive layer, and is used to prevent the sensitive layer from directly contacting the structural layer; The cement layer is used to connect the flexible sensor and the structural layer.

3. The method according to claim 2, wherein The mapping relationship between normal stress and shear stress is: ， ， ， ， Wherein, , , , are the transverse widths of the covering layer, the sensitive layer, the base layer, and the cementing layer, respectively; , , , are the thicknesses of the covering layer, the sensitive layer, the base layer, and the cementing layer, respectively; , , , are the shear stresses between the covering layer and the sensitive layer, the sensitive layer and the base layer, the base layer and the cementing layer, and the cementing layer and the structural layer, respectively, c, g, b, p are the normal stresses of the covering layer, the sensitive layer, the base layer, and the cementing layer, and d x is an infinitesimal element taken arbitrarily along the length direction of the sensitive layer.

4. The method according to claim 3, wherein The shear stress and sensitive layer strain relationship equation of the flexible sensor is: ， ， ， ， Wherein, ， ， ， is the strain of the sensitive layer, , , , are the elastic moduli of the covering layer, the sensitive layer, the base layer, and the cementing layer respectively, , , .

5. The method according to claim 1, wherein After obtaining the shear stress and sensitive layer strain relationship equation of the flexible sensor, the method further includes: According to the characteristic that the shear stress of the flexible material is transmitted in a quadratic curve between layers, obtain the transfer function of the shear stress: ， Among them, is the shear stress on the lower surface of each layer, is the shear stress on the upper surface of each layer, h is the thickness of the material of each layer.

6. The method according to claim 4, wherein The relationship between displacement and normal stress and shear stress is: ， ， Among them, is displacement, is stress, is strain, is elastic modulus, is the displacement of this layer structure relative to the lower layer structure, is shear stress, is shear modulus.

7. The method according to claim 6, wherein The displacement balance equation between the structural layer and the sensitive layer is: ， Among them, 。 8. The method according to claim 7, wherein The boundary conditions of the sensitive layer are: ， Wherein, L g is half of the length of the sensitive layer.

9. The method according to claim 8, wherein The average strain transfer rate is: ， Among them, L is the length of the sensitive layer.

10. A flexible sensor, characterized in that, For measuring the strain value by using the method according to any one of claims 1-9.

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