A device and method for calibrating transverse effect coefficient of resistance strain gauge

Abstract

The application provides a kind of resistance strain gauge transverse effect coefficient calibration test device and calibration method, it is related to resistance strain gauge technical field.The device includes test piece, two tension-compression loading components, bending loading head, bending support head and base;The base is fixed on the lower side of biaxial testing machine;The bending support head is connected to the base;Two tension-compression loading components are respectively connected to the left and right sides of biaxial testing machine;Test piece is connected with two tension-compression loading components;The upper end of bending loading head is connected with the upper side of biaxial testing machine;The lower surface of test piece is in contact with the upper end of bending support head, in the case of no load, test piece is completely supported on bending support head, and test piece has no initial stress.The method based on the two loading modes that the calibration test device can realize can realize calibration test and simulate any ratio biaxial strain test;The device is simple in structure, easy to operate, used with biaxial testing machine, makes full use of existing equipment, and the test cost is low.

Description

Technical Field

[0001] This invention relates to the field of resistance strain gauge technology, and in particular to a test apparatus and calibration method for calibrating the transverse effect coefficient of resistance strain gauges. Background Technology

[0002] A strain gauge is an element used to measure strain, consisting of a sensitive grid, a substrate, and a capping layer. Resistance strain gauges are made based on the strain effect, which refers to the change in resistance of a conductor or semiconductor material when it undergoes mechanical deformation under external force. The rate of change of resistance is linearly related to strain, and the ratio of the rate of change of resistance to strain is called the sensitivity coefficient, which reflects the degree of change in the strain gauge's response to external strain.

[0003] Compared to other strain measurement methods, such as photoelasticity, brittle coating, moiré, speckle interferometry, and fiber optic and piezoelectric thin film methods, the electrical measurement method using resistance strain gauges offers advantages such as high sensitivity coefficient, high output accuracy, stable performance, fast response speed, and low cost, making it widely used in industrial fields. Strain gauges can be classified in various ways. Based on the sensing grid material, they can be categorized into metallic and semiconductor types. Metallic strain gauges can be further classified according to the sensing grid structure into wire-wound, short-circuited, and foil types. Different types of strain gauges need to be selected for different application scenarios.

[0004] In the aerospace field, high-precision dynamic strain measurement is very common. Dynamic strain measurement requires strain gauges with good fatigue resistance, fast response speed, and high sensitivity coefficient. Wire-wound strain gauges have good fatigue resistance and fast response speed, while foil strain gauges have high fatigue life, low transverse effect, and high heat dissipation efficiency. Both are widely used in dynamic measurement. However, wire-wound strain gauges have a larger transverse effect due to their semi-circular ends. To improve the fatigue life of foil strain gauges, the length or width of the measuring grid needs to be shortened or increased, which also increases the transverse effect. Therefore, strain gauges used for dynamic strain measurement generally suffer from a large transverse effect. The transverse effect reflects the degree of influence of transverse strain on the strain gauge output. An increase in the transverse effect will affect the measurement results, especially in the aerospace field where extremely high precision is required.

[0005] The transverse effect coefficient represents the ratio of the transverse sensitivity coefficient to the longitudinal sensitivity coefficient. It is an important parameter for measuring the magnitude of the transverse effect of a strain gauge and can also be used to correct strain gauge measurement results. Therefore, an accurate transverse effect coefficient can greatly improve the accuracy of measurement results. Currently, the widely used method for calibrating the transverse effect coefficient of strain gauges involves conducting calibration tests under planar uniaxial stress conditions and using the material's Poisson's ratio for theoretical calculations to obtain the transverse effect coefficient. However, since Poisson's ratio itself is not a precise constant value, and due to differences in the methods used for Poisson's ratio measurement, the environment, and the shape of the specimen, the value of Poisson's ratio fluctuates within a certain range. Therefore, the Poisson's ratio obtained from material handbooks has a relatively large error. Repeated use of Poisson's ratio in calculations further increases the error in the calculation results; researchers have even encountered instances where the calculated transverse effect coefficient error reached 100% in experiments.

[0006] To investigate the impact of transverse effects on the output, the values ​​of longitudinal and transverse sensitivity coefficients should be obtained separately to explore the variation patterns of these coefficients under different strains and sensitive grid structures. However, with existing calibration methods, it is not possible to obtain the values ​​of longitudinal and transverse sensitivity coefficients separately, making further research difficult.

[0007] The ideal environment for calibrating the transverse effect coefficient should be a standard planar uniaxial strain state, with high uniaxial strain degree and high strain uniformity in the calibration area. However, due to the existence of the Poisson effect, in general metallic materials, to create a uniaxial strain state, it is necessary to apply or constrain transverse strain in a certain form while applying longitudinal strain to counteract the transverse strain caused by the Poisson effect. Currently, there is no test environment that can perfectly meet the calibration requirements, mainly for the following reasons:

[0008] 1. The design of loading specimens is difficult. Currently, the most common biaxial loading method is biaxial tension / compression. Under this loading method, the specimen needs to be designed in a "+" shape. This type of specimen will produce significant stress concentration at the junction of the arms, causing the central region of the specimen to fail to achieve the expected strain effect, and may even fail at the junction. Based on the "+" shape, there is an improved biaxial tensile specimen that designs the junction with rounded corners or recesses to reduce stress concentration. However, the strain distribution in the central region still has the problem of uneven distribution. Furthermore, due to the presence of the recesses, the stress concentration changes with the applied strain, making the strain value in the central region difficult to calculate, and thus it is still unsuitable for calibration.

[0009] 2. The ratio of longitudinal and transverse loading is difficult to adjust flexibly. For example, in existing clamping equipment, there is a device for biaxial tensile and compressive loading, which achieves a certain ratio of bidirectional loading by changing the installation distance of certain components in the clamping device. However, the ratio is relatively fixed and cannot be continuously adjusted, making it unsuitable for calibration. Summary of the Invention

[0010] The technical problem to be solved by the present invention is to provide a calibration test device and a calibration method for the transverse effect coefficient of a resistance strain gauge in view of the deficiencies of the above-mentioned prior art, so as to achieve the calibration of the transverse effect coefficient of the resistance strain gauge.

[0011] To solve the above technical problem, the technical solution adopted by the present invention is as follows:

[0012] On the one hand, the present invention provides a calibration test device for the transverse effect coefficient of a resistance strain gauge, including: a specimen, two tensile and compressive loading components, a bending loading head, a bending support head and a base; the base is fixed on the lower side of a biaxial testing machine; the bending support head is connected to the base; the two tensile and compressive loading components are respectively connected to the left and right sides of the biaxial testing machine; the specimen is connected to the two tensile and compressive loading components; the upper end of the bending loading head is connected to the upper side of the biaxial testing machine;

[0013] The lower surface of the specimen contacts the upper end of the bending support head. In the case of no load, the specimen is completely supported on the bending support head, and the specimen has no initial stress.

[0014] Preferably, the specimen includes a working section, two transition sections and two contact sections; the working section is a rectangular thin plate, and both ends of the working section are respectively connected to the two contact sections through the two transition sections; the transition section is composed of several rectangular metal sheets, and the total height of the metal sheets is the same as the thickness of the rectangular thin plate, which plays a role in connecting the working section and the contact section; the contact section is also composed of several rectangular metal sheets, and the number of metal sheets in the contact section is the same as that in the transition section; the two contact sections are respectively in direct contact with the two tensile and compressive loading components, and a number of balls are arranged on the contact surface between the contact section and the tensile and compressive loading components. The purpose is to reduce the friction at the boundary between the specimen and the tensile and compressive loading components, so that the boundary can rotate freely during bending deformation.

[0015] Preferably, the tensile and compressive loading component adopts a "C"-shaped chute structure, and the chute size matches the contact section of the specimen; lubricating oil is applied on the inner surface of the chute and the balls on the contact section of the specimen. The contact sections of the specimen are respectively installed in the tensile and compressive loading components on the left and right sides of the biaxial testing machine, and the balls on the contact section just contact the inner wall of the chute of the tensile and compressive loading component. The end face of the contact section of the specimen is allowed to have an angular displacement in the chute, and the end face remains flat after the rotation.

[0016] Preferably, the cross section of the bending loading head is in the shape of "冂", and the thickness is greater than the length of the working section of the specimen. The lower end of the bending loading head is semi-circular; the lower end of the bending loading head contacts the upper surface of the specimen and is used for loading force during the bending deformation of the specimen. A connecting component is provided at the upper end of the bending loading head, which is adapted to the biaxial testing machine to achieve the loading of vertical force.

[0017] Preferably, the bending support head is in a "U" shape, with a thickness greater than the length of the working section of the specimen. The upper end of the bending support head is semi-circular. The upper end of the bending support head contacts the lower surface of the specimen and is used for supporting the specimen during bending deformation. A plurality of through holes are provided at the lower end of the bending support head for connection with the base.

[0018] Preferably, the base is in a "square with a hole in the middle" shape, and through holes are provided on all four sides. The two tension-compression loading components are respectively connected to the left and right sides of the biaxial testing machine through screw rods. The two screw rods respectively pass through the through holes on the left and right sides of the base. The tension-compression loading components and the screw rods can displace along the directions of the through holes on the left and right sides of the base. The upper end of the bending loading head is connected to the upper side of the biaxial testing machine through a screw rod. The screw rod passes through the through hole on the upper side of the base. The bending loading head and the screw rod can displace along the direction of the through hole on the upper side. The lower through hole is used to connect the bending support head and the base.

[0019] Preferably, the device can achieve the following two strain state loading modes:

[0020] Loading mode 1: Create a plane uniaxial strain state; when the marked strain used for calibration reaches the maximum calibration value in this strain state, the corresponding transverse strain is less than 0.1 microstrain, which is lower than the minimum strain that the strain gauge can reflect. The strain accuracy in the calibration area fully meets the calibration requirements, and the longitudinal sensitivity coefficient and the transverse sensitivity coefficient can be accurately calibrated.

[0021] For this loading mode 1, the direction along the tensile / compressive direction of the specimen is called the transverse direction, and the direction perpendicular to the transverse direction is called the longitudinal direction.

[0022] Loading mode 2: Simulate a biaxial strain state with any ratio to study the influence of different strain environments on the transverse effect coefficient; for this loading mode 2, the direction along the tensile / compressive direction of the specimen is set as the longitudinal direction, and the direction perpendicular to the longitudinal direction is called the transverse direction.

[0023] On the other hand, a test method for calibrating the transverse effect coefficient of a resistance strain gauge, based on the two loading modes that the calibration test device can achieve, respectively realizes the calibration test and the simulation of a biaxial strain test with any ratio.

[0024] Among them, the process of the calibration test is as follows:

[0025] [[ID=****]](1) Determine the calibration area of the specimen that meets the calibration requirements; the calibration area meets the requirements of unidirectionality degree and uniformity degree.

[0026] For the unidirectionality degree, it is set that when the longitudinal direction reaches the maximum calibration strain of 10,000 microstrains, the area where the transverse strain is less than 0.1 microstrain meets the calibration requirements.

[0027] For the uniformity degree, it is set that the area with a relative range less than 0.1% meets the calibration requirements.

[0028] (2) Attach the strain gauges to be calibrated.

[0029] A strain gauge along the longitudinal direction and a strain gauge along the transverse direction are called a pair of strain gauges. The axes of the two strain gauges are perpendicular and they are of the same model and batch. The strain gauge along the longitudinal direction is used to measure the longitudinal sensitivity coefficient, and the strain gauge along the transverse direction is used to measure the transverse sensitivity coefficient. Multiple pairs of strain gauges from the same batch are selected and pasted along the transverse direction in the calibration area of ​​the specimen. If the parameters of the strain gauge under longitudinal tension are to be calibrated, the strain gauge is pasted on the lower surface of the specimen. If the parameters of the strain gauge under longitudinal compression are to be calibrated, the strain gauge is pasted on the upper surface of the specimen.

[0030] (3) Set tensile / compression and bending loads on the specimen.

[0031] Set the displacement of the tension / compression loading component to zero, i.e., fix it; keep the tension / compression loading component fixed, and apply longitudinal strain by applying the bending loading head vertically downward; the biaxial testing machine adopts force control mode;

[0032] (4) Read bending load data and strain gauge output signals and perform data processing.

[0033] Record the magnitude of the bending load. Under this load, read and record the electrical signal (ΔR / R)1 output by the longitudinally attached strain gauge and the electrical signal (ΔR / R)2 output by the transversely attached strain gauge. Calculate the longitudinal sensitivity coefficient, transverse sensitivity coefficient, and transverse effect coefficient. Then, use these three parameters to calculate the true strain in the measurement of practical engineering problems. Here, ΔR is the change in resistance of the strain gauge under load, R is the nominal resistance of the strain gauge, and ΔR / R is the rate of change of resistance.

[0034] Preferably, the process of calculating the longitudinal sensitivity coefficient, the transverse sensitivity coefficient, and the transverse effect coefficient is as follows:

[0035] Based on the output of the strain gauges pasted longitudinally:

[0036] (ΔR / R)1=K x ε x =K x ε 标

[0037] Obtain the longitudinal sensitivity coefficient K x As shown in the formula below:

[0038]

[0039] Where, ε 标 To indicate strain;

[0040] Based on the output of the strain gauges pasted laterally:

[0041] (ΔR / R)²=K y ε y =K y ε 标

[0042] Obtain the transverse sensitivity coefficient K y As shown in the formula below:

[0043]

[0044] Furthermore, the horizontal effect coefficient H is obtained, as shown in the following formula:

[0045]

[0046] In actual engineering measurements, the true strain is measured using calibrated strain gauges, as shown in the following formula:

[0047]

[0048]

[0049] Where, ε x ε represents the longitudinal strain generated by the strain gauge. y ε′ represents the transverse strain occurring at the strain gauge. x , ε′ y All of these are the actual strains to be measured in actual engineering projects. (ΔR / R)′1 is the electrical signal output by a strain gauge in actual engineering measurement, and (ΔR / R)′2 is the electrical signal output by a strain gauge in the direction perpendicular to the aforementioned strain gauge.

[0050] The process of simulating an arbitrary scale biaxial strain test is as follows:

[0051] 1) Determine the test area; the test area shall meet the same requirements as the calibration test in terms of uniformity and the accuracy of changes in longitudinal and transverse strain.

[0052] The uniformity requirement is the same as that of the calibration test. The purpose of this test is to investigate the variation law of strain gauge output with transverse strain under the same longitudinal strain. The test can ensure that the accuracy of the changes in longitudinal and transverse strain is the same as that of the calibration test. Therefore, the accuracy requirement for the specific value of transverse strain is lower than that of the calibration test. It is specified that the uncertainty of transverse strain is less than 0.1% to meet the experimental requirements.

[0053] 2) Attach strain gauges

[0054] Multiple strain gauges from the same batch are selected and pasted longitudinally within the test area of ​​the specimen; if the effect of strain gauge output increasing with transverse strain is to be investigated, the strain gauges are pasted on the lower surface of the specimen; if the effect of strain gauge output decreasing with transverse strain is to be investigated, the strain gauges are pasted on the upper surface of the specimen.

[0055] 3) Set tensile / compression and bending loads on the specimen.

[0056] Both tensile / compression loading and bending loading adopt force-controlled mode. First, the longitudinal strain value to be investigated is calculated, and the load to be applied is calculated. Tensile / compression load is set and applied. Tensile / compression loading is maintained, and the tensile and compressive directions of the biaxial testing machine are fixed at this position. The bending loading head applies bending deformation vertically downward to change the transverse strain and obtain a biaxial strain state. After one test, the bending deformation is unloaded, the tensile / compression load is adjusted, and bending deformation is applied again.

[0057] 4) Read the bending load and strain gauge output signals and perform data processing.

[0058] Record the initial tensile / compression load magnitude, continuously change the bending load, record the bending load magnitude, and under each bending load, read and record the electrical signal (ΔR / R) output by each strain gauge to obtain the strain gauge output changing with transverse strain.

[0059] Preferably, the process of obtaining the strain gauge output image as a function of transverse strain is as follows:

[0060] (1) Based on the recorded bending load, and combined with the formula for calculating the indicated strain ε,

[0061] The finite element simulation results of the bending load process are used to obtain the transverse strain under each bending load.

[0062] (2) Using the electrical signal (ΔR / R) output by the strain gauge as the vertical axis and the transverse strain as the horizontal axis, we obtain a graph showing the change of the strain gauge output with the transverse strain under a specific longitudinal strain.

[0063] The beneficial effects of the above technical solution are as follows: The present invention provides a test device and calibration method for calibrating the transverse effect coefficient of a resistance strain gauge. (1) The device adopts a coaxial tension-bending combination deformation method, which is different from the general tension-bending combination. The axial direction of the bending moment of this device is parallel to the axial direction of the tension (compression), which makes it convenient to apply force and the load is continuously adjustable. It can flexibly realize any proportion of loading within the test range, solving the problem of difficult biaxial arbitrary proportion loading. (2) The loading specimen designed by this device can realize simultaneous tension (compression) and bending, avoiding the problem of stress concentration in the "+" shaped specimen, so that the strain in the specimen calibration area has extremely high unidirectionality and uniformity. (3) The planar uniaxial strain state created by this device, as well as the calibration method based on the device, avoid the use of Poisson's ratio, which greatly reduces the calculation error of the transverse effect coefficient. (4) Through the calibration method provided by the present invention, the longitudinal sensitivity coefficient and the transverse sensitivity coefficient can be obtained respectively. Not only can the transverse effect coefficient be calculated, but the variation law of the longitudinal sensitivity coefficient and the transverse sensitivity coefficient with strain can also be further studied. (5) This device has a simple structure and is easy to operate. When used in conjunction with a biaxial testing machine, it makes full use of existing equipment and reduces testing costs. (6) The uniaxial strain state and biaxial strain state of arbitrary proportion created by this device are not limited to calibration tests and can be extended to actual industrial scenarios that require similar strain states. Attached Figure Description

[0064] Figure 1 This is a front view of the structure of a test device for calibrating the transverse effect coefficient of a resistance strain gauge, provided in an embodiment of the present invention.

[0065] Figure 2 A side sectional view of a test device for calibrating the transverse effect coefficient of a resistance strain gauge, provided in an embodiment of the present invention;

[0066] Figure 3 This is a structural diagram of the specimen provided in an embodiment of the present invention;

[0067] Figure 4 A structural diagram of a bending loading head provided in an embodiment of the present invention;

[0068] Figure 5 A structural diagram of a bending support head provided in an embodiment of the present invention;

[0069] Figure 6 The following diagram illustrates the longitudinal and transverse specification methods under different loading modes provided in the embodiments of the present invention, wherein (a) shows the longitudinal and transverse specification under loading mode 1, and (b) shows the longitudinal and transverse specification under loading mode 1.

[0070] Figure 7 This is a schematic diagram showing the longitudinal cross-sectional dimensions of the working section of the specimen and the force applied by the bending loading head, provided in an embodiment of the present invention.

[0071] Figure 8 Schematic diagram of strain gauge pasting under Loading Mode 1 provided by an embodiment of the present invention;

[0072] Figure 9 Simulation result diagram of calibrating test simulation in finite element software provided by an embodiment of the present invention, where (a) is the longitudinal strain distribution diagram of the working section of the specimen, (b) is the transverse strain distribution diagram of the working section of the specimen, and (c) is the selected calibration area;

[0073] Figure 10 Schematic diagram of strain gauge pasting under Loading Mode 2 provided by an embodiment of the present invention.

[0074] In the figure: 1. Specimen; 2. Tensile and compressive loading component; 3. Bending loading head; 4. Bending support head; 5. Base; 1-1. Working section; 1-2. Transition section; 1-3. Contact section; 3-1. "冂"-shaped bending loading head; 3-2. Lower end of the bending loading head; 4-1. "凵"-shaped bending support head; 4-2. Lower end of the bending support head; 6. Pair of strain gauges; 7. Strain gauge; 8. Calibration area. Detailed implementation manners

[0075] The following combines the drawings and embodiments to further describe in detail the specific implementation manners of the present invention. The following embodiments are used to illustrate the present invention, but are not used to limit the scope of the present invention.

[0076] In this embodiment, a calibration test device for the transverse effect coefficient of a resistance strain gauge is as Figure 1 、 2 shown, and includes: a specimen 1, two tensile and compressive loading components 2, a bending loading head 3, a bending support head 4, and a base 5; the base 5 is fixed to the lower side of a biaxial testing machine; the bending support head 4 is connected to the base 5 through bolts and nuts; the two tensile and compressive loading components 2 are respectively connected to the left and right sides of the biaxial testing machine; the specimen 1 is connected to the two tensile and compressive loading components 2; the upper end of the bending loading head 3 is connected to the upper side of the biaxial testing machine;

[0077] The lower surface of the specimen 1 contacts the upper end of the bending support head 4. In the case of no load, the specimen 1 is completely supported on the bending support head 4, and the specimen 1 has no initial stress.

[0078] In this embodiment, the specimen is as Figure 3As shown in the figure, it includes a working section 1-1, two transition sections 1-2, and two contact sections 1-3; the working section 1-1 is a rectangular thin plate, and both ends of the working section 1-1 are connected to the two contact sections 1-3 through the two transition sections 1-2 respectively; the transition section 1-2 is composed of several rectangular metal sheets, and the total height of the metal sheets is the same as the thickness of the rectangular thin plate, which plays a role in connecting the working section and the contact section; the contact section 1-3 is also composed of several rectangular metal sheets, and the number of metal sheets in the contact section 1-3 is the same as that in the transition section 1-2; the two contact sections 1-3 are in direct contact with the two tension-compression loading components 2 respectively, and a number of ball bearings are distributed on the contact surfaces between the contact section 1-3 and the tension-compression loading components 2. The purpose is to reduce the friction at the boundary between the specimen and the tension-compression loading components, so that the boundary can rotate freely during bending deformation; the transition section 1-2 and the contact section 1-3 are both secondary boundaries. Due to the complex shape and contact method, the stress and strain are also very complex. However, according to Saint-Venant's principle, they do not affect the strain state in the central region of the working section 1-1 of the specimen and do not interfere with the accuracy of the test environment.

[0079] In this embodiment, the two tension-compression loading components 2 adopt a "C"-shaped chute structure, and the chute size matches the contact section 1-3 of the specimen; lubricating oil is applied to both the inner surface of the chute and the ball bearings on the contact section 1-3 of the specimen 1. The contact sections 1-3 of the specimen are respectively installed in the tension-compression loading components 2 on the left and right sides of the biaxial testing machine, and the ball bearings on the contact section 1-3 just contact the inner wall of the chute of the tension-compression loading component 2. The end face of the contact section 1-3 of the specimen is allowed to have an angular displacement in the chute, and the end face remains flat after the angular displacement occurs.

[0080] In this embodiment, the tension-compression loading component 2, the bending loading head 3, and the bending support head 4 of the device are all made of materials (high-carbon steel) with relatively high hardness and strength, and the specimen 1 is made of a material (low-carbon steel) with relatively low stiffness.

[0081] In this embodiment, the cross-section of the bending loading head 3 is as Figure 4 shown, presenting a "冂"-shaped 3-1, with a thickness greater than the length of the working section 1-1 of the specimen. The lower end 3-2 of the bending loading head is semi-circular; the lower end 3-2 of the bending loading head contacts the upper surface of the specimen 1 and is used for loading force during the bending deformation of the specimen 1. A connecting component is provided at the upper end of the bending loading head 3, which is adapted to the biaxial testing machine to achieve vertical force loading.

[0082] In this embodiment, the bending support head 4 is as Figure 5 shown, presenting a "凵"-shaped 4-1, with a thickness greater than the length of the working section 1-1 of the specimen. The upper end 4-2 of the bending support head is semi-circular; the upper end 4-2 of the bending support head contacts the lower surface of the specimen 1 and is used for supporting the specimen 1 during bending deformation. A number of through holes are provided at the lower end of the bending support head 4 for connection with the base 1.

[0083] In this embodiment, the base 1 is in a "hui" shape, and through holes are provided on all four sides; two tension-compression loading components 2 are respectively connected to the left and right sides of the biaxial testing machine through screw rods. The two screw rods respectively pass through the through holes on the left and right sides of the base. The tension-compression loading component 2 and the screw rod can displace along the direction of the through holes on the left and right sides of the base; the upper end of the bending loading head 3 is connected to the upper side of the biaxial testing machine through a screw rod. The screw rod passes through the through hole on the upper side of the base. The bending loading head 3 and the screw rod can displace along the direction of the through hole on the upper side; the through hole on the lower side is used to realize the connection between the bending support head 4 and the base.

[0084] In this embodiment, the assembly method of the calibration test device is as follows:

[0085] ① The base 1 is fixed to the biaxial testing machine by a certain method;

[0086] ② The bending support head 4 is connected to the base 1 by bolts and nuts;

[0087] ③ The two tension-compression loading components 2 are respectively connected to the biaxial testing machine through screw rods. The two screw rods respectively pass through the through holes on the left and right sides of the base. The tension-compression loading component 2 and the screw rod can displace along the direction of the through holes on the left and right sides.

[0088] ④ The upper end of the bending loading head 3 is connected to the biaxial testing machine through a screw rod. The screw rod passes through the through hole on the upper side of the base 5. The bending loading head 3 and the screw rod can displace along the direction of the through hole on the upper side.

[0089] ⑤ Lubricating oil is applied to both the sliding groove of the tension-compression loading component 2 and the ball on the contact section 1-3 of the test piece. The contact sections 1-3 of the test piece are respectively installed in the two tension-compression loading components 2. The balls on the contact section 1-3 just contact the inner wall of the groove of the tension-compression loading component 2. The end surface of the contact section 1-3 of the test piece is allowed to have an angular displacement in the sliding groove, and the end surface remains flat after the angular displacement.

[0090] ⑥ The lower surface of the test piece 1 contacts the upper end 4-2 of the bending support head. In the case of no load, the test piece 1 is completely supported on the bending support head 4, and the test piece has no initial stress.

[0091] In this embodiment, the calibration test device can achieve the following two strain state loading modes:

[0092] Loading mode 1: Create a high-precision plane uniaxial strain state; when the marked strain for calibration reaches the maximum calibration value in this strain state, the corresponding transverse strain is less than 0.1 microstrain, which is lower than the minimum strain that the strain gauge can reflect. The strain accuracy in the calibration area fully meets the requirements of calibration, and can accurately calibrate the longitudinal sensitivity coefficient and the transverse sensitivity coefficient;

[0093] For this loading mode 1, it is set that the direction along the tension / compression direction of the test piece is called the transverse direction, and the direction perpendicular to the transverse direction is called the longitudinal direction, as Figure 6As shown in (a).

[0094] Loading mode 2: Simulates biaxial strain states of arbitrary scale to study the influence of different strain environments on the transverse effect coefficient; for this loading mode 2, the direction along the tensile / compression direction of the specimen is defined as the longitudinal direction, and the direction perpendicular to the longitudinal direction is defined as the transverse direction.

[0095] The principle behind the resistance strain gauge transverse effect coefficient calibration test device of the present invention for creating a uniaxial strain state is as follows:

[0096] The device achieves bidirectional strain loading through a coaxial tension-bending combination. Bending deformation is applied vertically, while tensile / compressive deformation is applied horizontally. Unlike typical tension-bending combinations, the bending moment axis of this device is parallel to the tensile / compressive axis. Four-point bending induces compressive strain on the upper surface and tensile strain on the lower surface of the specimen. Simultaneously, due to the Poisson effect, transverse strain occurs. This device constrains the transverse strain by limiting the transverse displacement of the boundary. The strains on the upper and lower surfaces of the specimen under four-point bending deformation are derived below. In the following descriptions, the longitudinal and transverse directions are those specified in loading mode 1.

[0097] Since the cross-sections of the working sections of the specimen are all identical rectangles and the force is uniformly distributed along the transverse direction, the force, displacement, and strain of the working sections of the specimen can be approximately deduced as a rectangular beam of unit width. The accurate values ​​will be obtained using finite element simulation.

[0098] The portion between the specimen and the contact point with the bending loading head is a pure bending segment, with a bending moment M per unit width of...

[0099]

[0100] Longitudinal bending strain ε is

[0101]

[0102] The marked strain generated on the upper and lower surfaces of the working section of the specimen after the calibration test device is loaded is shown in the following formula:

[0103]

[0104] Where b is the distance between the contact point between the bending support head and the specimen and the contact point between the bending loading head and the specimen, t is the length of the working section of the specimen along the tensile / compression direction, y is the distance from a point on the cross section to the neutral layer, E is the elastic modulus of the specimen material, I is the moment of inertia of the longitudinal section of the working section of the specimen about the neutral layer, F is the force applied to one side of the bending loading head, f is the force applied per unit length to one side of the bending loading head, ε is the longitudinal bending strain, and ε 标 To indicate strain;

[0105] In this embodiment, the longitudinal cross-sectional dimensions of the working section of the specimen and the force applied by the bending loading head are as follows: Figure 7 As shown, and with b = 20 mm, h = 4 mm, t = 200 mm, E = 200 GPa,

[0106] Because the derivation of the specified strain formula involves some assumptions and simplifications, the theoretical value deviates somewhat from the actual value. Therefore, finite element method (FEM) software is used to simulate the loading process, correct the theoretical value, and obtain the accurate specified strain ε. 标 .

[0107] To ensure that there is no additional moment on the transverse end face during bending, the transverse end face of the specimen must be allowed to undergo angular displacement. At the same time, to constrain the transverse strain caused by the Poisson effect, the transverse end face of the specimen must not undergo transverse displacement.

[0108] The principle behind the test device for calibrating the transverse effect coefficient of resistance strain gauges to create arbitrary biaxial strain states is as follows:

[0109] The loading process consists of two steps. In the first step, tensile (compressive) deformation is applied, at which point longitudinal strain occurs and transverse strain caused by the Poisson effect occurs. After loading to a predetermined value, the load is fixed. Here, the longitudinal and transverse directions are specified in loading mode 2.

[0110] The second step is to apply bending deformation. The longitudinal strain generated by bending deformation is constrained by the boundary and is less than 0.1 micro-strain. It will not affect the longitudinal strain generated by tension / compression. The transverse strain generated by bending is superimposed on the transverse strain generated by tension / compression. By changing the load of bending deformation, it is possible to continuously change the transverse strain while keeping the longitudinal strain constant, and create longitudinal and transverse strains of any proportion.

[0111] The principle of this part involves Poisson's ratio, but this part aims to study the variation of transverse effect with transverse strain. Its accuracy requirements are much lower than those required during calibration. Furthermore, the accurate transverse effect coefficient determined in the calibration experiment can assist in the data processing of this part to obtain the variation image.

[0112] In this embodiment, a test method for calibrating the transverse effect coefficient of a resistance strain gauge is based on two loading modes that the calibration test device can achieve, respectively realizing the calibration test and simulating an arbitrary proportional biaxial strain test.

[0113] The calibration test process is as follows:

[0114] (1) Determine the calibration area of ​​the specimen that meets the calibration requirements; the calibration area meets the requirements of unidirectionality and uniformity;

[0115] Regarding the degree of unidirectionality, when the longitudinal direction reaches the maximum calibration strain of 10,000 micro-strains, the region with a transverse strain of less than 0.1 micro-strains meets the calibration requirements.

[0116] Regarding the degree of uniformity, the calibration requirements are met for areas where the relative range of longitudinal strain is less than 0.1%.

[0117] (2) Attach the strain gauges to be calibrated.

[0118] One strain gauge along the longitudinal direction and one strain gauge along the transverse direction are referred to as a pair of strain gauges (6). The axes of the two strain gauges are perpendicular, and they are of the same model and batch. The strain gauge along the longitudinal direction is used to measure the longitudinal sensitivity coefficient, and the strain gauge along the transverse direction is used to measure the transverse sensitivity coefficient. Six pairs of strain gauges from the same batch are selected and pasted transversely within the calibration area of ​​the specimen, such as... Figure 8 As shown; if the parameters of the strain gauge are to be calibrated under longitudinal tension, the strain gauge is attached to the lower surface of the specimen; if the parameters of the strain gauge are to be calibrated under longitudinal compression, the strain gauge is attached to the upper surface of the specimen.

[0119] In this embodiment, to eliminate the interference of temperature changes, the wiring method adopts the half-bridge wiring method, connecting one working plate and one compensation plate respectively. If there are other requirements for measurement, such as amplification sensitivity coefficient, the corresponding bridge circuit can be selected by oneself.

[0120] (3) Set tensile / compression and bending loads on the specimen.

[0121] Set the displacement of the tension / compression loading member to zero, i.e., fix it; keep the tension / compression loading member fixed, and apply longitudinal strain by applying the bending loading head vertically downward; the biaxial testing machine adopts force control mode;

[0122] (4) Read bending load data and strain gauge output signals and perform data processing.

[0123] Record the magnitude of the bending load. Under this load, read and record the electrical signal (ΔR / R)1 output by the longitudinally attached strain gauge and the electrical signal (ΔR / R)2 output by the transversely attached strain gauge. Calculate the longitudinal sensitivity coefficient, transverse sensitivity coefficient, and transverse effect coefficient. Then, use these three parameters to calculate the true strain in the measurement of practical engineering problems. Here, ΔR is the change in resistance of the strain gauge under load, R is the nominal resistance of the strain gauge, and ΔR / R is the rate of change of resistance.

[0124] The process of calculating the longitudinal sensitivity coefficient, transverse sensitivity coefficient, and transverse effect coefficient is as follows:

[0125] Based on the output of the strain gauges pasted longitudinally:

[0126] (ΔR / R)1=K xε x =K x ε 标

[0127] Obtain the longitudinal sensitivity coefficient K x As shown in the formula below:

[0128]

[0129] Where ε is the characteristic strain;

[0130] Based on the output of the strain gauges pasted laterally:

[0131] (ΔR / R)²=K y ε y =K y ε 标

[0132] Obtain the transverse sensitivity coefficient K y As shown in the formula below:

[0133]

[0134] Furthermore, the horizontal effect coefficient H is obtained, as shown in the following formula:

[0135]

[0136] In actual engineering measurements, the true strain is measured using calibrated strain gauges, as shown in the following formula:

[0137]

[0138]

[0139] Where, ε x ε represents the longitudinal strain generated by the strain gauge. y ε′ represents the transverse strain occurring at the strain gauge. x , ε′ y All of these are the actual strains to be measured in actual engineering projects. (ΔR / R)′1 is the electrical signal output by a strain gauge in actual engineering measurement, and (ΔR / R)′2 is the electrical signal output by a strain gauge in the direction perpendicular to the aforementioned strain gauge.

[0140] In this embodiment, the calibration test is simulated in finite element software, such as... Figure 9 As shown, the longitudinal strain distribution of the working section of the specimen is as follows: Figure 9 As shown in (a), it can be seen from the figure that the longitudinal strain uniformity in the middle of the specimen is extremely high.

[0141] Transverse strain distribution of the working section of the specimen as follows Figure 9As shown in (b), it can be seen from the figure that the uniformity of the transverse strain is worse than that of the longitudinal strain, but the degree of unidirectionality meets the requirements. The calibration area selected in the simulation results is as follows. Figure 9 As shown in (c), a rectangle with a longitudinal length of 40 and a transverse length of 60 is defined as the calibration area 8.

[0142] The longitudinal and transverse strain data of some measuring points within the calibration area are shown in Table 1:

[0143] Table 1. Longitudinal and transverse strain data at some measuring points within the calibration area.

[0144] Longitudinal strain Transverse strain -9.98670794E-03 -5.00692501E-08 -9.98670887E-03 -4.81283458E-08 -9.98670887E-03 -4.72881965E-08 -9.98670980E-03 -4.52617712E-08 -9.98670980E-03 -4.47446418E-08 -9.98671073E-03 -4.32133511E-08 -9.98671073E-03 -4.32133973E-08 -9.98670794E-03 -5.00696551E-08 -9.99497529E-03 -6.61831194E-08 -9.99497622E-03 -6.16329032E-08

[0145] The process of simulating an arbitrary scale biaxial strain test is as follows:

[0146] 1) Determine the test area; the test area shall meet the same requirements as the calibration test in terms of uniformity and the accuracy of changes in longitudinal and transverse strain.

[0147] The uniformity requirement is the same as that of the calibration test. The purpose of this test is to investigate the variation law of strain gauge output with transverse strain under the same longitudinal strain. The test can ensure that the accuracy of the changes in longitudinal and transverse strain is the same as that of the calibration test. Therefore, the accuracy requirement for the specific value of transverse strain is lower than that of the calibration test. It is specified that the uncertainty of transverse strain is less than 0.1% to meet the experimental requirements.

[0148] 2) Attach strain gauges

[0149] Six strain gauges 7 from the same batch were selected and pasted longitudinally within the test area of ​​the specimen, such as... Figure 10 As shown; if the effect of strain gauge output on the increase of transverse strain is investigated, the strain gauge is attached to the lower surface of the specimen; if the effect of strain gauge output on the decrease of transverse strain is investigated, the strain gauge is attached to the upper surface of the specimen.

[0150] 3) Set tensile / compression and bending loads on the specimen.

[0151] Both tensile / compression loading and bending loading adopt force-controlled mode. First, the longitudinal strain value to be investigated is calculated, and the load to be applied is calculated. Tensile / compression load is set and applied. Tensile / compression loading is maintained, and the tensile and compressive directions of the biaxial testing machine are fixed at this position. The bending loading head applies bending deformation vertically downward to change the transverse strain and obtain a biaxial strain state. After one test, the bending deformation is unloaded, the tensile / compression load is adjusted, and bending deformation is applied again.

[0152] 4) Read the bending load and strain gauge output signals and perform data processing.

[0153] Record the initial tensile / compression load magnitude, continuously change the bending load, record the bending load magnitude, and under each bending load, read and record the electrical signal (ΔR / R) output by each strain gauge to obtain the strain gauge output changing with transverse strain.

[0154] The process of obtaining the strain gauge output image as a function of transverse strain is as follows:

[0155] (1) Based on the recorded bending load, combined with the indicated strain ε 标 The calculation formula and finite element simulation results of the bending load loading process are used to obtain the transverse strain under each bending load.

[0156] (2) Using the electrical signal (ΔR / R) output by the strain gauge as the vertical axis and the transverse strain as the horizontal axis, we obtain a graph showing the change of the strain gauge output with the transverse strain under a specific longitudinal strain.

[0157] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope defined by the claims of the present invention.

Claims

1. A test apparatus for calibrating the transverse effect coefficient of a resistance strain gauge, characterized in that: include: The test specimen, two tension / compression loading components, a bending loading head, a bending support head, and a base; the base is fixed to the underside of the biaxial testing machine. The bending support head is connected to the base; two tension / compression loading components are respectively connected to the left and right sides of the biaxial testing machine; the specimen is connected to the two tension / compression loading components; the upper end of the bending loading head is connected to the upper side of the biaxial testing machine. The lower surface of the specimen is in contact with the upper end of the bending support head. Under no load, the specimen is fully supported on the bending support head and has no initial stress. The device can achieve the following two strain state loading modes: Loading Mode 1: Creates a planar uniaxial strain state; under this strain state, when the calibrated strain reaches the maximum calibration value, the corresponding transverse strain is less than 0.1 micro-strain, which is lower than the minimum strain that the strain gauge can reflect. The strain accuracy in the calibration area fully meets the calibration requirements and can accurately calibrate the longitudinal sensitivity coefficient and transverse sensitivity coefficient. For loading mode 1, the direction along the tensile / compression direction of the specimen is called the transverse direction, and the direction perpendicular to the transverse direction is called the longitudinal direction. Loading Mode 2: Simulates biaxial strain states of arbitrary scale to study the influence of different strain environments on the transverse effect coefficient; for this loading mode 2, the direction along the tensile / compression direction of the specimen is defined as the longitudinal direction, and the direction perpendicular to the longitudinal direction is defined as the transverse direction; Based on the two loading modes that the calibration test device can achieve, calibration tests and simulated biaxial strain tests of arbitrary scales can be realized respectively. The calibration test process is as follows: (1) Determine the calibration area of ​​the specimen that meets the calibration requirements; the calibration area meets the requirements of unidirectionality and uniformity; Regarding the degree of unidirectionality, when the longitudinal direction reaches the maximum calibration strain of 10,000 micro-strains, the region with a transverse strain of less than 0.1 micro-strains meets the calibration requirements. Regarding the degree of uniformity, areas with a relative range of less than 0.1% are considered to meet the calibration requirements; (2) Attach the strain gauges to be calibrated. A strain gauge along the longitudinal direction and a strain gauge along the transverse direction are called a pair of strain gauges. The axes of the two strain gauges are perpendicular and they are of the same model and batch. The strain gauge along the longitudinal direction is used to measure the longitudinal sensitivity coefficient, and the strain gauge along the transverse direction is used to measure the transverse sensitivity coefficient. Multiple pairs of strain gauges from the same batch are selected and pasted along the transverse direction in the calibration area of ​​the specimen. If the parameters of the strain gauge under longitudinal tension are to be calibrated, the strain gauge is pasted on the lower surface of the specimen. If the parameters of the strain gauge under longitudinal compression are to be calibrated, the strain gauge is pasted on the upper surface of the specimen. (3) Set tensile / compression and bending loads on the specimen. Set the displacement of the tension / compression loading member to zero, i.e., fix it; keep the tension / compression loading member fixed, and apply longitudinal strain by applying the bending loading head vertically downward; the biaxial testing machine adopts force control mode; (4) Read bending load data and strain gauge output signals and perform data processing. Record the magnitude of the bending load. Under this load, read and record the electrical signals output by the longitudinally attached strain gauges in each pair of strain gauges. Electrical signals output by strain gauges pasted laterally The longitudinal sensitivity coefficient, transverse sensitivity coefficient, and transverse effect coefficient are calculated, and then these three parameters are used to calculate the true strain in the measurement of practical engineering problems. R represents the change in resistance of the strain gauge under load, where R is the nominal resistance of the strain gauge. The rate of change of resistance; The process of simulating an arbitrary scale biaxial strain test is as follows: 1) Determine the test area; the test area shall meet the same requirements as the calibration test in terms of uniformity and the accuracy of changes in longitudinal and transverse strain. The degree of uniformity is the same as that required in the calibration test; the purpose of this test is to explore the variation law of the strain gauge output with the transverse strain under the same longitudinal strain. The test can ensure that the accuracy of the change amounts of the longitudinal strain and the transverse strain is the same as that in the calibration test. Therefore, the accuracy requirement for the specific value of the transverse strain is lower than that in the calibration test; it is stipulated that when the uncertainty of the transverse strain is less than 0.1%, it meets the experimental requirements; 2) Paste the strain gauges; Select multiple strain gauges of the same batch and paste them longitudinally in the test area of the specimen; if exploring the influence of the increase in the transverse strain on the strain gauge output, the strain gauges are pasted on the lower surface of the specimen; if exploring the influence of the decrease in the transverse strain on the strain gauge output, the strain gauges are pasted on the upper surface of the specimen; 3) Set tensile / compressive loading and bending loading for the specimen; Both the tensile / compressive loading and the bending loading adopt the force control mode; first, calculate the longitudinal strain value to be explored and calculate the load to be applied; set the tensile / compressive load and apply the load; maintain the tensile / compressive loading and set the tension / compression direction of the biaxial testing machine to be fixed at this position; the bending loading head applies bending deformation downward vertically to change the transverse strain and obtain the two-dimensional strain state; after one test is completed, unload the bending deformation, adjust the tensile / compressive load, and then apply the bending deformation loading again; 4) Read the bending load and the strain gauge output signal and perform data processing; Record the initial tensile / compression load magnitude, continuously change the bending load, record the bending load magnitude, and under each bending load, read and record the electrical signal output by each strain gauge. This yields an image showing the change in strain gauge output with lateral strain.

2. The test apparatus for calibrating the transverse effect coefficient of a resistance strain gauge according to claim 1, characterized in that: The specimen includes a working section, two transition sections, and two contact sections; the working section is a rectangular thin plate, and both ends of the working section are connected to the two contact sections through the two transition sections respectively; the transition section is composed of several rectangular metal sheets, and the total height of the metal sheets is the same as the thickness of the rectangular thin plate, which plays a role in connecting the working section and the contact section; the contact section is also composed of several rectangular metal sheets, and the number of metal sheets in the contact section is the same as that in the transition section; the two contact sections are in direct contact with the two tensile / compressive loading components respectively, and a number of balls are布满 on the contact surface between the contact section and the tensile / compressive loading components. The purpose is to reduce the friction at the boundary between the specimen and the tensile / compressive loading components, so that the boundary can rotate freely during bending deformation.

3. The test apparatus for calibrating the transverse effect coefficient of a resistance strain gauge according to claim 2, characterized in that: The tensile / compressive loading component adopts a "C"-shaped chute structure, and the chute size matches the contact section of the specimen; lubricating oil is applied on the inner surface of the chute and the balls on the contact section of the specimen. The contact sections of the specimen are respectively inserted into the tensile / compressive loading components on the left and right sides of the biaxial testing machine, and the balls on the contact section just contact the inner wall of the chute of the tensile / compressive loading component. The end face of the contact section of the specimen is allowed to have an angular displacement in the chute, and the end face remains flat after the angle change.

4. The test apparatus for calibrating the transverse effect coefficient of a resistance strain gauge according to claim 2, characterized in that: The cross-section of the bending loading head is in the shape of "冂", and the thickness is greater than the length of the working section of the specimen. The lower end of the bending loading head is semi-circular; the lower end of the bending loading head contacts the upper surface of the specimen and is used for applying force during the bending deformation of the specimen. A connecting component is provided at the upper end of the bending loading head, which is adapted to the biaxial testing machine to achieve the vertical force loading.

5. The test apparatus for calibrating the transverse effect coefficient of a resistance strain gauge according to claim 2, characterized in that: The bending support head is in the shape of "凵", and the thickness is greater than the length of the working section of the specimen. The upper end of the bending support head is semi-circular; the upper end of the bending support head contacts the lower surface of the specimen and is used for supporting the specimen during bending deformation. A number of through holes are provided at the lower end of the bending support head for connection with the base.

6. The test apparatus for calibrating the transverse effect coefficient of a resistance strain gauge according to claim 1, characterized in that: The base is in a "return" shape, and through holes are provided on all four sides; two tension-compression loading components are respectively connected to the left and right sides of the biaxial testing machine through screw rods, and the two screw rods respectively pass through the through holes on the left and right sides of the base. The tension-compression loading components and the screw rods can displace along the directions of the through holes on the left and right sides of the base; the upper end of the bending loading head is connected to the upper side of the biaxial testing machine through a screw rod, and the screw rod passes through the through hole on the upper side of the base. The bending loading head and the screw rod can displace along the direction of the through hole on the upper side; the lower through hole is used to connect the bending support head and the base.

7. The test apparatus for calibrating the transverse effect coefficient of a resistance strain gauge according to claim 1, characterized in that: The process of calculating the longitudinal sensitivity coefficient, the transverse sensitivity coefficient, and the transverse effect coefficient is as follows: According to the output of the strain gauges pasted longitudinally: ； Obtain the longitudinal sensitivity coefficient As shown in the formula below: ； in, To indicate strain; According to the output of the strain gauges pasted transversely: ； Obtain the transverse sensitivity coefficient As shown in the formula below: ； Furthermore, the horizontal effect coefficient is obtained. As shown in the formula below: 。 8. The test apparatus for calibrating the transverse effect coefficient of a resistance strain gauge according to claim 7, characterized in that: The process of obtaining the image of the change of the strain gauge output with the transverse strain is as follows: (1) Based on the recorded bending load, combined with the indicated strain The calculation formula and finite element simulation results of the bending load loading process are used to obtain the transverse strain under each bending load. (2) Electrical signals output by strain gauges The vertical axis is used, and the horizontal axis is used, to obtain a graph showing how the strain gauge output changes with the horizontal strain under a specific longitudinal strain.

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