CN109238526B - A resistance strain type tubular pressure sensor and pressure field testing method - Google Patents

Abstract

The invention discloses a resistance strain type tubular pressure sensor and a pressure field testing method. The sensor tube section includes a thin-walled circular tube section made of high-strength martensitic stainless steel and multiple foil-type resistance strain gauges pasted circumferentially along the inner wall of the tube section; the sensitive grids of the foil-type resistance strain gauges have the same specification, and the length of all sensitive grids The sum is equal to the circumference of the inner wall of the pipe joint. The length direction of the sensitive grid is parallel to the circumferential direction of the pipe joint, and they are connected end to end in sequence and staggered along the axial direction of the pipe joint in the width direction, forming a continuous 360-degree closed ring on the inner wall of the pipe joint. to the strain measurement area. The invention can measure the internal pressure field of the cable steel wire bundle, and eliminate the adverse influence of the "soil arch effect" that the traditional pressure sensor device receives during the pressure test; combined with the pressure test calculation method provided by the invention, the size of the confining pressure at the measuring point can be accurately obtained and its distribution along various directions; the sensor pipe section and the lead pipe are connected in series through flexible connectors to realize multi-point measurement.

Description

A resistance strain type tubular pressure sensor and pressure field testing method

technical field

The invention belongs to the technical field of pressure testing, and relates to pressure field measurement of solid media, in particular to a resistance strain type tubular pressure sensor and a pressure field testing method, which is suitable for the internal pressure of solid media such as granular bodies, cable wire bundles, and solid materials field test.

Background technique

With the functional requirements of modern buildings and bridge structures such as large space, large span, and durability, more and more attention has been paid to the refined research on the mechanical properties of key stress-bearing components such as prestressed cables and main cables of suspension bridges used in these structures. , the stay cable or the main cable needs to be fastened locally with prestressed high-strength bolts through the cable clamp, so there will be a huge radial extrusion effect between the parallel steel wires inside it. The measurement of the internal pressure field of the cable steel wire is this type. The basis for detailed research on components. At present, there are very few studies on the internal pressure of cable steel wires, and the research is carried out in the form of numerical simulation, and the actual measurement research has not been reported, which also reflects the difficulty of actual measurement. In the field of rock and soil mechanics, the research on the mechanical properties of granular materials such as soil-rock mixtures and high rockfill dam materials involves the measurement of the internal pressure field of the medium. All kinds of foundation projects also widely need to test the earth pressure of specific parts.

Due to the randomness of the internal arrangement of the cable steel wire bundle and the cylindrical contact between the steel wires, the specific contact position between the embedded pressure sensitive element and the steel wire is uncertain. After investigation, all types of pressure sensors are not suitable for other Measurement studies of internal pressure fields. At present, geotechnical tests in geotechnical mechanics and foundation engineering mainly use earth pressure cells for pressure measurement. The measurement principle of earth pressure cells leads to small measurement results due to the influence of soil arching effects. For details, see the paper "Model Calibration and Application of Membrane Earth Pressure Cells in Tests" ("Journal of Geotechnical Engineering" 2016 No. 5).

Contents of the invention

The purpose of the present invention is to solve the problem of steel wire bundle pressure field measurement in the fine research field of cable components in infrastructure construction. At the same time, the pressure sensor provided by the present invention has universal and flexible applicability to the type of solid medium to be measured. Including but not limited to soil-rock mixtures, granular materials such as storage grain accumulations, cable steel wire bundles, and continuous medium solid materials.

The technical scheme that realizes the object of the present invention is as follows:

A resistance strain type tubular pressure sensor, comprising a sensor pipe joint; the sensor pipe joint comprises a thin-walled circular pipe joint made of high-strength martensitic stainless steel and a plurality of foil resistance strain gauges pasted circumferentially along the inner wall of the pipe joint; the The sensitive grids of the above-mentioned foil resistance strain gauges have the same specifications, and the sum of the lengths of all sensitive grids is equal to the circumference of the inner wall of the pipe joint. The sections are axially staggered to form a continuous 360-degree closed circumferential strain measurement area on the inner wall of the pipe section.

Further, it includes more than one sensor pipe joint, and also includes more than one lead pipe and more than one insertable flexible connector; the insertable flexible connector includes round pipes at both ends and a middle flange, and the outer diameter of the round pipe is It is equal to the inner diameter of the sensor tube or the lead tube, and the outer diameter of the intermediate flange is equal to the sensor tube and the lead tube; between the sensor tubes, or between the lead tubes, or between the sensor tube and the lead tube All of them are connected in series through interpolated flexible connectors and then connected through, and the connecting wires of all foil resistance strain gauges are drawn out from the through continuous cavity.

A pressure field testing method of a resistance strain type tubular pressure sensor, comprising

Place the sensor pipe joint in the position to be measured in the solid pressure field;

Collect strain measurements from all foil resistance strain gauges;

Calculate the average compressive stress at the measuring point

Among them, E is the Young's modulus of elasticity of the sensor tube material, is the average value of the measured strain values of all foil resistance strain gauges on the inner wall of the sensor tube; N is the total number of all foil resistance strain gauges on the inner wall of the sensor tube; εi is the measured value of the _i -th foil resistance strain gauge, where The tensile strain is positive, and the compressive strain is negative; K is the sensitivity coefficient of the sensor pipe joint, d ₁ is the outer diameter of the sensor pipe joint, and d ₂ is the inner diameter of the sensor pipe joint;

Using the finite element method, establish the sensor pipe joint under the confining pressure load Under the action of the plane strain model, the measured value of the foil resistance strain gauge at each azimuth position is taken as the target result, and the average value of the compressive stress As a known quantity, adjust Until the numerical calculation result of the circumferential strain value of the inner wall of the model agrees with the measured result, at this time That is, the distribution result of the compressive stress along the angle of the pressure field at the measuring point.

The beneficial effect of the present invention is that it can measure the internal pressure field of the cable steel wire bundle, and eliminate the adverse influence of the "soil arch effect" that the traditional pressure sensor device receives during the pressure test; the measurement mechanics principle of the sensor is clear, the manufacturing and calibration methods are simple, and the cost is relatively low. Low, less source of measurement error, sensitivity parameters and range can be flexibly selected and designed according to measurement needs; combined with the pressure test calculation method provided by the present invention, the size of the confining pressure at the measurement point and its distribution along various directions can be accurately obtained; the sensor tube Multi-point measurement can be realized after the joints and lead pipes are connected in series through flexible connectors; the sensor is externally connected with a dynamic stress acquisition instrument to realize dynamic testing of the pressure field.

Description of drawings

Figure 1 is a schematic diagram of the expansion of the inner wall of the sensor pipe joint, which shows the relationship between the sticking position of the strain gauge and the length of the sensitive grid of the strain gauge and the size of the pipe joint;

Fig. 2 is a three-dimensional schematic diagram of the sensor pipe joint;

Fig. 3 is a schematic diagram of an insertable flexible connector;

Fig. 4 is a schematic diagram of a combined pressure tube sensor;

In the picture:

1-Expansion of the inner wall of the sensor tube section, 2-Foil strain gauge base, 3-Foil strain gauge sensitive grid, 4-Interpolated flexible connector flange, 5-Lead round tube, 6-Interpolated flexible connector , 7-sensor pipe joint, 8-lead round pipe, 9-sensor pipe joint, 10-strain gauge lead wire, 11-solid medium for pressure to be measured.

Detailed ways

The pressure sensor provided by the present invention is a resistance strain type tubular pressure sensor. Its principle is: use the deformation of the inner wall of the circular tubular high-strength stainless steel elastomer to measure the size and distribution of the compressive stress around the medium where it is located. The two have mechanical principles. Consistent correspondence; deformation is measured by foil strain gauges bonded circumferentially on the inner wall of the tube.

The technical characteristics of the sensor are:

Thin-walled circular pipe joints are made of high-strength martensitic stainless steel (such as 17-4PH stainless steel, the yield strength can reach 1180MPa under the condition of aging treatment at 480°C), which can be used in a high equivalent stress strength pressure field without Plastic deformation of thin-walled circular steel pipe joints.

According to the measurement principle of the sensor, in order to obtain the compressive stress of the medium around the sensor and its distribution along the angular direction, it is necessary to know the circumferential strain at different azimuth angles within the 360° circumferential closed range of the inner wall of the steel pipe section, so the foil type on the inner wall of the steel pipe The arrangement of the resistance strain gauges needs to meet the following conditions: (1) The strain gauges are along the circumferential direction of the circular steel pipe joint, that is, the length direction of the sensitive grid of the foil resistance strain gauge is parallel to the circumferential direction of the steel pipe joint. (2) Each strain gauge is staggered back and forth in the longitudinal direction of the pipe joint; their sensitive grid areas are connected end to end in the ring direction. (3) Each resistance strain gauge adopts the length of the sensitive grid area of the same specification, and the sum of the length of the sensitive grid area of each resistance strain gauge is consistent with the inner wall circumference of the steel pipe section, so as to ensure that the inner wall ring of the steel pipe section is reached when pasting. The effect of forming a continuous 360-degree closed ring strain measurement area upward. In theory, reducing the length dimension of a single strain gauge sensitive grid and increasing the number of strain gauges can obtain a finer result of the distribution of compressive stress along the angular direction. In practice, eight strain gauges are sufficient.

The lead wire steel round tube is connected in series with the sensor tube joint, and the strain gauge wire leads out the pressure medium to be measured from the through inner cavity formed by the two, so as to connect with the strain collector to form a Wheatstone bridge circuit, which has high Sensitivity to accurately measure resistance changes.

In order to facilitate the installation of the sensor, the sensor pipe section and the lead pipe should be connected in series with an interposed flexible connector. The connector should not affect the free deformation of the sensor steel joint. For this reason, aluminum alloy, plastic, rubber and other flexible connectors can be used. Material manufacturing. In order not to affect the original distribution of the stress field of the medium to be measured, the outer diameter of the lead pipe and the flange diameter of the connector should be consistent with the outer diameter of the sensor tube.

When multiple sensor pipe joint units are connected in series through flexible joints and lead pipes, a combined pressure pipe sensor is formed, which can perform multi-point synchronous measurement of the pressure field of the solid medium to be measured; when the external dynamic strain collector is connected, the pressure field can be Take dynamic measurements.

The first physical quantity measured by the pressure sensor provided by the present invention is the hoop strain generated by the steel pipe joint under pressure, and the present invention provides a corresponding compressive stress calculation method. First, calculate the average value of the measured values of each strain gauge according to formula (2) Then calculate according to formula (1) to obtain the average value of compressive stress at the measuring point Among them, the sensitivity coefficient K of the pressure sensor pipe joint is determined by its geometric size, calculated according to formula (3), and the geometric parameters of the sensor pipe joint can be flexibly adjusted according to the pressure measurement range requirements; when the compressive stress of different azimuth angles around the sensor pipe joint When q(θ) is uneven, the circumferential compressive strain ε(θ) of the inner wall will also be uneven, and the distribution of the compressive stress q(θ) has a consistent correspondence with the distribution of the circumferential compressive strain ε(θ) of the inner wall, so , conveniently, the compressive stress q(θ) can be obtained by inverse calculation from the measured values ε _i of each strain gauge with the help of the finite element plane strain calculation model of the pressure sensor pipe joint.

The formula for calculating the average value of compressive stress at the measuring point is as follows:

in is the average value of compressive stress at the measuring point, E is the Young's modulus of elasticity of the pressure sensor tube material, is the average value of the strain measurements of all strain gauges on the inner wall of the pressure sensor pipe joint, that is,

Where εi is the measured value of the _i -th strain gauge on the inner wall of the pressure sensor pipe joint, where the tensile strain is positive and the compressive strain is negative, and N is the total number of strain gauges on the inner wall of the pressure sensor pipe joint unit.

K is the sensitivity coefficient of the pressure sensor pipe joint, which is calculated by the following formula:

Among them, d ₁ is the outer diameter of the pressure sensor pipe joint, and d ₂ is the inner diameter of the pressure sensor pipe joint.

The compressive stress q(θ) along the circumferential coordinate θ angle direction of the pressure sensor pipe joint at the measuring point is obtained through a simple finite element plane strain calculation model of the pressure sensor pipe joint.

Example 1

The resistance strain type circular tubular pressure sensor includes a circular steel pipe section and a foil resistance strain gauge adhered circumferentially along its inner wall. The circular steel pipe section is shown in Figure 2, and the sticking position of the strain gauge is shown in Figure 1. The specific manufacturing process is carried out as follows:

(1) Manufacturing of circular steel pipe joints for sensor sensitive elements. The 17-4PH martensitic stainless steel rod is subjected to solid solution treatment, and then processed by turning to form a round thin-walled steel pipe section of predetermined size, and then subjected to vacuum aging treatment at 450°C to 480°C. Experimental research shows that aging in this temperature range is 3-4 hours, and the sample structure can obtain tempered martensite, making the hardness reach 39-42HRC, and the yield strength reaches 1180MPa.

(2) Manufacturing of foil strain gauges. As shown in Figure 1, two sensitive grids can be integrated on a substrate, the product of the length and number of the sensitive grids is equal to the circumference of the inner wall of the circular pipe section, and the terminals leading out the wires are insulated.

(3) Paste the foil strain gauge. Use sandpaper with a particle size of 200 to 400 mesh to polish the strain gauge pasting area on the inner surface of the circular steel pipe section, and grind out cross stripes at 45° to the patch direction, and then use a marking tool to draw a line at intervals of 45° along the circumference The positioning line ensures that the pasting position will not change. Then the surface is cleaned with an organic solvent such as acetone and the polished part. Then place it in an incubator and raise the temperature to 70° C., and keep it warm for 30 minutes. After taking it out, use H-610 glue to evenly coat the strain gauge attachment area on the inner surface of the pipe joint, then paste the strain gauges in sequence according to the positions shown in Figure 1, and fix them with internal support clamps with a pressure of 0.1~0.3MPa. Raise the temperature to 135°C in the incubator and keep it for 2.5 hours, then naturally cool to room temperature and release the pressure, then raise the temperature to 165°C, keep the temperature for 2 hours and then cool down to room temperature. Finally, use 704 glue to seal the surface of the pasted strain gauge.

Example 2

The combined pressure tube sensor is shown in Figure 4. It consists of a pressure sensor tube unit (7) (9), a lead pipe (5) (8), and an inserted flexible connector (6). The strain gauge wire ( 10) Lead out from the through internal cavity. According to the number of required measuring points and the spacing of measuring points, the number of sensor tube units of the combined pressure tube and the length of the lead round tube between each tube unit are selected. If it is necessary to connect the wires and the reserved terminals of the strain gauge at the test site, the connection part can be insulated and protected by a thermoplastic tube to avoid short circuits. The external wire and the strain collector form a Wheatstone bridge circuit.

Example 3

The present invention provides a pressure field test and calculation method corresponding to the sensor, the steps are as follows:

(1) The measured values ε _i of all the strain gauges in the pressure sensor tube unit at a certain measuring point are obtained by the strain collector, and then the average value According to the formula (1), the average value of the confining pressure at the measuring point is obtained

(2) Use numerical calculation methods such as finite element method to establish the confining pressure load of sensor pipe joints The plane strain model under the action takes the measured values of the strain gauges at each azimuth position as the target result, and takes the average value of the confining pressure load As a known quantity, adjust Until the numerical calculation result of the circumferential strain value of the inner wall of the model agrees with the measured result, at this time That is, the distribution result of the compressive stress along the angle of the pressure field at the measuring point.

Claims (2)

1. A resistance strain type tubular pressure sensor, comprising a sensor pipe joint (7); said sensor pipe joint (7) comprises a thin-walled circular pipe joint of high-strength martensitic stainless steel material and a plurality of rings pasted along the inner wall of the pipe joint foil resistance strain gauge; the sensitive grids (3) of the foil resistance strain gauges have the same specifications, and the sum of the lengths of all sensitive grids (3) is equal to the inner wall circumference of the pipe joint, and the length direction of the sensitive grids (3) Parallel to the ring direction of the pipe joint, connected end to end in sequence and staggered along the axial direction of the pipe joint in the width direction, a continuous 360-degree closed ring strain measurement area is formed on the ring direction of the inner wall of the pipe joint; It is characterized in that it includes more than one sensor pipe joint (7), and also includes more than one lead pipe (5) and more than one insertable flexible connector (6); the insertable flexible connector (6) includes two The outer diameter of the round tube is equal to the inner diameter of the sensor tube (7) or the lead tube (5), the middle flange (4) is connected with the sensor tube (7) and the lead tube (5) have the same outer diameter; between the sensor pipe joints (7), or between the lead pipes (5), or between the sensor pipe joints (7) and the lead pipes (5), there is an interpolation flexible The connectors (6) are connected in series and connected through, and the connecting wires of all the foil resistance strain gauges are led out from the through continuous cavity. 2. the pressure field testing method of a kind of resistance strain type tubular pressure sensor as claimed in claim 1, is characterized in that, comprises Place the sensor pipe joint (7) in the position to be measured in the solid pressure field; Collect strain measurements from all foil resistance strain gauges; Calculate the average compressive stress at the measuring point Wherein, E is the Young's modulus of elasticity of sensor tube joint (7) material, is the average value of the measured strain values of all the foil resistance strain gauges on the inner wall of the sensor tube (7); N is the total number of all the foil resistance strain gauges on the inner wall of the sensor tube (7); ε _i is the i-th foil resistance strain The measured value of the gauge, the tensile strain is positive, and the compressive strain is negative; K is the sensitivity coefficient of the sensor pipe joint (7), d ₁ is the outer diameter of the sensor pipe joint (7), and d ₂ is the sensor pipe joint (7) inner diameter; using the finite element method, establish the sensor pipe joint under the confining pressure load Under the action of the plane strain model, the measured value of the foil resistance strain gauge at each azimuth position is taken as the target result, and the average value of the compressive stress As a known quantity, adjust Until the numerical calculation result of the circumferential strain value of the inner wall of the model agrees with the measured result, at this time That is, the distribution result of the compressive stress along the angle of the pressure field at the measuring point.