A strain sensor that deforms in concert with asphalt pavement material

Abstract

The application discloses a strain sensor which can be deformed with asphalt pavement material, and relates to the technical field of sensors.The technical scheme is characterized by comprising an elastic sensitive element, a resistance strain gauge, an end flange, a packaging shell and a flexible layer.The packaging shell is wrapped with the flexible layer, and the packaging shell and the end flange are connected in an assembled manner.The packaging shell and the end flange can slide freely in the measuring direction and are constrained with each other in the vertical measuring direction, so that the stiffening effect of the packaging shell is eliminated.The size of the packaging shell is determined according to the same tensile stiffness principle of the elastic sensitive element and the strain sensor in the pavement material, so that the elastic sensitive element is deformed with the pavement material, the limitation that the traditional strain sensor and the pavement material are difficult to be deformed coordinately is made up, and the measurement result can directly and truly reflect the actual state of the pavement structure without the need of secondary calibration of the sensor.

Description

Technical Field

[0001] This invention relates to the field of sensor technology, and more specifically to a strain sensor that deforms in tandem with asphalt pavement materials. Background Technology

[0002] Under repeated traffic loads, asphalt pavements gradually exhibit various forms of damage such as fatigue damage, reflective cracks, and rutting. Ultimately, this is due to the accumulation of stress and strain in the pavement structure, leading to the degradation of material properties. Therefore, obtaining the stress and strain response of the structural layer under actual traffic loads during the service of asphalt pavements can guide pavement structure design, explain the mechanism of pavement mechanical failure, and formulate pavement maintenance decisions. It is an important component in establishing a long-life pavement structure design system, and embedded strain sensors have become the main observation method for monitoring the health of pavement structures.

[0003] Currently, the embedded strain sensors used in asphalt pavements typically use steel with a high modulus as the sensor casing to prevent damage to the internal sensitive elements caused by the vibration and compaction of the steel wheels of the road roller during construction and the heavy traffic during service. This makes the sensor act as reinforcement in the pavement structure, which restricts the deformation of the asphalt mixture around the sensor. As a result, the measurement output results are inconsistent with the actual pavement structure, affecting the understanding of the true state of the pavement structure.

[0004] Meanwhile, due to the constraint effect of the sensor, stress concentration occurs at the interface between the sensor and the surrounding road surface material. Under repeated traffic loads, the sensor is prone to separation from the surrounding road surface material.

[0005] In Chinese invention patent publication number CN101592474A, an evaluation method for the coordinated deformation of asphalt pavement material and fiber optic grating sensor is proposed. This method is based on the assumption of a small deformation pure elastic beam and corrects the output result of the strain sensor according to theoretical strain calculation. However, it requires that the embedded strain sensor must first be implanted into a four-point bending beam for secondary calibration before it can be used for actual pavement structure monitoring. Its operation process is cumbersome and complicated, making it difficult to promote.

[0006] Therefore, there is an urgent need for a strain sensor that can provide a realistic understanding of the road surface structure, has a simple calculation process, and is easy to promote. Summary of the Invention

[0007] The purpose of this invention is to provide a strain sensor that deforms in tandem with asphalt pavement materials. In order to solve the problem that existing strain sensors for asphalt pavement cannot deform in tandem with the pavement materials, resulting in discrepancies between the measurement results and the actual state of the pavement, this invention proposes a strain sensor that deforms in tandem with asphalt pavement materials, ensuring that the sensor output truly reflects the actual state of the pavement structure and achieving the goal of accurately measuring pavement strain.

[0008] The above-mentioned technical objective of the present invention is achieved through the following technical solution:

[0009] A strain sensor that deforms in tandem with asphalt pavement material, comprising:

[0010] The elastic sensing element, located inside the strain sensor, is a flat rectangular sheet structure used to sense changes in the shape of the asphalt pavement and deform synchronously with it.

[0011] Resistance strain gauges are attached and fixed in the middle of the elastic sensing element to collect and transmit deformation data generated by the elastic sensing element;

[0012] The end flanges are rectangular in shape and two are symmetrically arranged at both ends of the elastic sensitive element;

[0013] The encapsulation shell is in the shape of a flat cuboid, and two are symmetrically provided on the flat two sides of the elastic sensing element, which are used to cooperate with the end flange to complete the fixed encapsulation of the elastic sensing element and the resistance strain gauge.

[0014] A flexible layer, nested within the surface of the encapsulation housing, is used to protect the interior of the strain sensor.

[0015] Further configuration: A rectangular groove extending along the length of the elastic sensitive element is provided on one side of the package housing that is attached to the elastic sensitive element, and the rectangular grooves on the two package housings cooperate with each other to accommodate the elastic sensitive element.

[0016] Further configuration: The package housing has horizontal semi-circular grooves located on both sides of the rectangular groove and parallel to the rectangular groove. Two sets of horizontal semi-circular grooves are symmetrically arranged about the centerline of the elastic sensitive element. The end flange has a convex cylinder corresponding to the position of the horizontal semi-circular groove. The shape and number of the convex cylinders are adapted to the horizontal semi-circular groove to complete the fitting connection between the two.

[0017] Further configuration: A longitudinal semi-circular groove perpendicular to the length direction of the sensitive element is formed on the side of the package housing. A wire is connected to the resistance strain gauge, and the wire is led out through the longitudinal semi-circular groove and extends to the outside.

[0018] Further settings: Height H of the package housing f ≤10mm, the width W of the package shell f The calculation is based on the principle that the elastic sensing element has the same tensile stiffness as the road surface material occupied by the strain sensor along its length. The specific calculation formula is as follows:

[0019]

[0020] Among them, W b H is the width of the elastic sensing element. b H represents the thickness of the elastic sensing element.f T is the height of the package housing. b E represents the thickness of the flexible layer. a E represents the elastic modulus of the road surface material. b The elastic modulus of the elastic sensitive element

[0021] Further details: The package housing has several threaded holes that penetrate the package housing. The threaded holes on two package housings are located at corresponding positions and are connected to each other by bolts.

[0022] Preferably, the flexible layer is made of butadiene rubber.

[0023] In summary, the present invention has the following beneficial effects:

[0024] 1. The encapsulation shell and end flange of this invention adopt an assembly-type connection method, which allows the encapsulation shell and end flange to slide freely in the measurement direction and constrain each other in the perpendicular measurement direction. The encapsulation shell is wrapped with a flexible layer, eliminating the reinforcing effect of the encapsulation shell. The size of the encapsulation shell is determined according to the principle that the road surface material occupied by the elastic sensitive element and the strain sensor has the same tensile stiffness, ensuring that the deformation of the elastic sensitive element and the road surface material is consistent. This makes up for the limitation of traditional strain sensors that are difficult to coordinate with the deformation of the road surface material. The measurement results can directly and truly reflect the actual state of the road surface structure without the need for secondary calibration of the sensor.

[0025] 2. The strain sensor designed in this invention adopts a flat shape, which reduces the height of the sensor in the vertical direction, reduces the influence of the strain response of different road layers on the sensor measurement output, and further ensures the consistency between the sensor measurement output and the actual road layer structure state.

[0026] 3. The sensor designed in this invention can deform in coordination with the road surface material. The stress concentration at the interface between the sensor and the road surface material is smaller than that of traditional sensors, resulting in a longer lifespan of adhesion failure with the road surface material during long-term dynamic response monitoring of the road structure. Attached Figure Description

[0027] The invention will be further described below with reference to the accompanying drawings.

[0028] Figure 1 This is a schematic diagram of the overall three-dimensional structure of the present invention;

[0029] Figure 2 This is a three-dimensional schematic diagram of each element in this invention;

[0030] Figure 3 This is a schematic diagram of the four-point bending load test in Examples 1 and 2 and Comparative Examples 1 and 2 of the present invention.

[0031] In the figure, 1. Elastic sensing element; 2. Resistance strain gauge; 3. End flange; 4. Encapsulation shell; 5. Flexible layer; 6. Convex cylinder; 7. Rectangular groove; 8. Transverse semi-circular groove; 9. Longitudinal semi-circular groove; 10. Screw hole; 11. Bolt; 12. Wire; 13. Bending test sensor; 14. Bending test strain gauge; 15. Bending test indenter; 16. Bending test asphalt mixture specimen; 17. Support. Detailed Implementation

[0032] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0033] The technical solution adopted in this invention is:

[0034] A strain sensor that deforms in tandem with asphalt pavement material specifically includes: an elastic sensing element 1, a resistance strain gauge 2, an end flange 3, a housing 4, and a flexible layer 5.

[0035] When designing strain sensors that deform in tandem with asphalt pavement materials, key considerations include:

[0036] a. Asphalt pavement material is a composite material with an uneven distribution of internal strain field. The strain sensor measures the average strain of the pavement material. The strain sensor is required to use two end flanges 3 to generate displacement as the pavement material deforms. Therefore, the two end flanges 3 are connected by an elastic sensitive element 1. A resistance strain gauge 2 is attached to the elastic sensitive element 1. The strain of the elastic sensitive element 1 is the output result of the strain sensor.

[0037] b. The elastic sensitive element 1 and the resistance strain gauge 2 are directly exposed to the road surface material and are easily damaged. They need to be protected by an encapsulation shell 4. Therefore, an encapsulation shell 4 is provided.

[0038] c. The modulus of the encapsulation shell 4 is much higher than that of the road material, which constrains the deformation of the surrounding road material and thus restricts the movement of the two end flanges 3. This will cause the deformation of the elastic sensitive element 1 to be less than the actual deformation of the road material. Therefore, a flexible material is used to wrap the surface of the encapsulation shell 4 to eliminate the reinforcing effect of the encapsulation shell 4 on the surrounding road material.

[0039] d. The end flange 3 is connected by the elastic sensitive element 1. After eliminating the reinforcing effect of the encapsulation shell 4 on the surrounding road surface material and the end flange 3, in order to ensure that the deformation of the elastic sensitive element 1 is consistent with the actual road surface material, the tensile stiffness of the elastic sensitive element 1 in the measurement direction is consistent with the tensile stiffness of the road surface material in the space occupied by the strain sensor.

[0040] e. The strain response varies at different depths of the road surface. The vertical height of the strain sensor should be as small as possible to reduce the impact of the strain response at different depths of the road structure on the sensor measurement results.

[0041] like Figure 1-2 As shown, in this invention, the elastic sensitive element 1 is disposed inside the strain sensor and is a flat rectangular sheet structure, used to sense changes in the shape of the asphalt pavement and deform synchronously with it.

[0042] The resistance strain gauge 2 is attached and fixed in the middle of the elastic sensing element 1 to collect and transmit the deformation data generated by the elastic sensing element 1;

[0043] The end flange 3 has a cuboid structure and two flanges are symmetrically provided at both ends of the elastic sensitive element 1;

[0044] The encapsulation shell 4 is in the shape of a flat cuboid, and two are symmetrically provided on the flat sides of the elastic sensitive element 1 to cooperate with the end flange 3 to complete the fixed encapsulation of the elastic sensitive element 1 and the resistance strain gauge 2. A rectangular groove 7 extending along the length direction of the elastic sensitive element 1 is provided on one side of the encapsulation shell 4 that is in contact with the elastic sensitive element 1. The rectangular grooves 7 on the two encapsulation shells 4 cooperate with each other to accommodate the elastic sensitive element 1.

[0045] The encapsulation housing 4 has horizontal semi-circular grooves 8 located on both sides of the rectangular groove 7 and parallel to the rectangular groove 7. Two sets of horizontal semi-circular grooves 8 are symmetrically arranged about the center line of the elastic sensitive element 1. The end flange 3 has a convex cylinder 6 corresponding to the position of the horizontal semi-circular groove 8. The shape and number of the convex cylinder 6 are adapted to the horizontal semi-circular groove 8 to complete the fitting connection between the two.

[0046] The side of the encapsulation housing 4 has a longitudinal semi-circular groove 9 perpendicular to the length direction of the sensitive element. A wire 12 is connected to the resistance strain gauge 2. The wire 12 is led out through the longitudinal semi-circular groove 9 and extends to the outside. The encapsulation housing 4 is also provided with several screw holes 10 penetrating the encapsulation housing 4. The screw holes 10 on two encapsulation housings 4 are located at corresponding positions and are connected to each other by bolts 11.

[0047] When the upper and lower encapsulation shells 4 are installed, the elastic sensitive element 1 and the resistance strain gauge 2 are placed in the rectangular groove 7 of the encapsulation shell 4. The wire 12 of the resistance strain gauge 2 is led out from the semi-circular groove perpendicular to the measurement direction at the center of the side of the encapsulation shell 4. The convex cylinder 6 of the end flange 3 is embedded in the semi-circular groove at the end of the encapsulation shell 4 so that the encapsulation shell 4 and the end flange 3 can slide freely in the measurement direction and constrain each other in the perpendicular measurement direction.

[0048] The flexible layer 5 is nested on the surface of the encapsulation shell 4 to protect the inside of the strain sensor. The flexible layer 5 is made of butadiene rubber to eliminate the reinforcing effect of the encapsulation shell 4 on the road surface material.

[0049] The height Hf of the enclosure 4 should not exceed 10mm to reduce the influence of strain response at different depths of the road surface on the sensor measurement results; the width W of the enclosure 4... f The width of the encapsulation shell 4 is calculated based on the principle that the elastic sensing element 1 has the same tensile stiffness as the road surface material occupied by the strain sensor in the measurement direction. The specific calculation formula is as follows:

[0050] A b E b =A s E a (1)

[0051] Among them, A b E is the cross-sectional area of ​​the flat rectangular sheet in the middle of the elastic sensing element perpendicular to the measurement direction. b Let A be the elastic modulus of the elastic sensing element. s E represents the cross-sectional area of ​​the road material occupied by the strain sensor perpendicular to the measurement direction. a This refers to the elastic modulus of the road surface material.

[0052] Expanding formula (1) further, we get:

[0053] W b ×H b ×E b =(W f +2×T b )×(2×(H f +T b ))×E a (2)

[0054] Among them, W b H represents the width of the flat rectangular sheet in the middle of the elastic sensing element. b H represents the thickness of the flat rectangular sheet in the middle of the elastic sensing element. f T is the height of the package housing. b This refers to the thickness of the flexible layer.

[0055] Further transforming formula (2), we obtain the specific formula for the width Wf of the encapsulation shell:

[0056]

[0057] Among them, W b H is the width of the elastic sensing element. b H represents the thickness of the elastic sensing element. f T is the height of the package housing. b E represents the thickness of the flexible layer. a E represents the elastic modulus of the road surface material. b This is the elastic modulus of the elastic sensitive element.

[0058] In this invention, two sets of embodiments and two sets of comparative examples are provided to compare the differences in measurement between this invention and other embodiments.

[0059] Example 1

[0060] In this embodiment, the elastic sensing element is made of aluminum alloy with an elastic modulus E. b The pressure is 72 GPa, and the thickness H of the flat rectangular sheet of the elastic sensing element is... b The strain gauge is 1mm thick, 5mm wide (Wb), and 80mm long. It is attached to the center of a flat rectangular plate in the middle of the elastic sensitive element.

[0061] The end flange is rectangular in shape, made of stainless steel, with a thickness of 7mm along the measuring direction, a height of 11mm, and a width equal to W. f +2xT b Two convex cylinders are positioned on the left and right sides, each with a diameter of 3mm and a length of 5mm. The encapsulation shell consists of upper and lower parts, both flat rectangular parallelepipeds made of stainless steel, with a height H. f It measures 4.5mm in diameter and 80mm in length.

[0062] The enclosure has a groove in the middle along the measurement direction to hold the elastic sensitive element and the resistance strain gauge. The groove is 7mm wide and 2.5mm deep. A semi-circular hole is provided in the center of the side to lead out the resistance strain gauge wire. Semi-cylindrical grooves are provided at both ends. The diameter of the semi-cylindrical grooves is 3.5mm and the depth is 5.5mm. The screw holes of the two enclosures are connected by screws. When the two enclosures are connected, the convex cylinder of the end flange can be inserted. The enclosure and the end flange can slide freely in the measurement direction and are mutually constrained in the perpendicular measurement direction.

[0063] A flexible layer is nested on the surface of the encapsulation shell to eliminate the reinforcing effect of the encapsulation shell. The material is butadiene rubber with an elastic modulus of 0.0061 GPa, exhibiting good wear resistance. The thickness is T. b The elastic modulus Ea of AC25 graded asphalt mixture was measured to be 2.1 GPa at room temperature (20℃). Based on the principle that the tensile stiffness of the flat rectangular sheet in the middle of the elastic sensing element is equal to the road material occupied by the strain sensor's encapsulation shell, the width W of the encapsulation shell was calculated. f The diameter is 13.58mm, and the width of the end flange is 15.58mm.

[0064] Example 2

[0065] In this embodiment, the difference from Embodiment 1 is that the elastic sensing element is made of cast aluminum bronze with an elastic modulus of 103.2 GPa. Therefore, except for the material of the elastic sensing element, the width of the encapsulation shell, and the width of the end flange, the materials and dimensions of all other sensor components are the same as in Embodiment 1. In Embodiment 2, the width of the encapsulation shell is calculated to be 20.34 mm, and the width of the end flange is 22.34 mm.

[0066] Comparative Example 1

[0067] In this comparative example, the difference from Example 1 is that the width W of the packaging shell... f The diameter is 18mm, the end flange width is 20mm, and the dimensions and materials of the other components of the sensor are the same as in Example 1.

[0068] Comparative Example 2

[0069] In this comparative example, unlike Example 1, the flexible layer is absent. The dimensions and materials of the remaining components of the sensor are identical to those of Example 1.

[0070] After setting up Example 1, Example 2, and Comparative Example 1 and Comparative Example 2, the actual usage effects of the above examples and comparative examples were tested.

[0071] like Figure 3 As shown, strain sensors required for Examples 1 and 2 and Comparative Examples 1 and 2 were prepared respectively. Four cuboid beams with lengths of 40cm, widths of 10cm, and heights of 10cm were prepared using AC25 asphalt mixture. During the beam forming process, the above four types of bending test sensors 13 were implanted at a position 2cm away from the bottom surface of the beam at the mid-span of the four beams, and bending test asphalt mixture specimens 16 were obtained.

[0072] All small beams were kept in a constant temperature chamber at 20℃ for 24 hours. Bending strain gauges 14 were attached to the sides of the beams at the same distance from the sensor to the bottom of the beam. A four-point bending load test was conducted. In the four-point bending test, the bottom surface of the beam was supported by two supports with a distance of 30cm between them, and the top surface of the beam had two bending test indenters 15 with a distance of 10cm between them. A step-by-step loading method was used to load the two indenters on the top surface. The sensor output results and strain gauge output results are shown in Table 1.

[0073] Table 1. Sensor output results and corresponding strain gauge output results in Examples 1 and 2 and Comparative Examples 1 and 2.

[0074]

[0075] Comparing the results in Table 1, it can be seen that the strain sensors prepared according to the present invention in Examples 1 and 2 have maximum relative measurement errors of 3.1% and 3.7%, respectively. The output results are basically consistent with the output results of the corresponding strain gauges, indicating that the sensors prepared according to the present invention can truly reflect the actual deformation of the road surface material.

[0076] Compared to the sensor in Example 1, the sensor in Comparative Example 1 has an increased encapsulation structure width. The tensile stiffness of the strain gauge is lower than the tensile stiffness of the asphalt mixture occupied by the sensor. The sensor measurement value in Comparative Example 1 is higher than the strain gauge output result, and the difference between the two gradually increases with the increase of load.

[0077] Compared to the sensor in Example 1, the sensor in Comparative Example 2 has the flexible layer removed, which causes the sensor output to be less than the output value of the strain gauge. Furthermore, the difference between the two gradually increases with the increase of the load. The maximum relative measurement errors of Comparative Examples 1 and 2 are 19.1% and 28.1%, respectively.

[0078] It can be seen that the measurement error is relatively large, indicating that whether the tensile stiffness of the strain sensor can be equal to the actual stiffness of the mixture, and whether the reinforcing effect of the encapsulation shell can be eliminated, are the key to accurately measuring the strain of asphalt mixture.

[0079] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention shall fall within the scope of the invention.

Claims

1. A strain sensor that deforms in concert with an asphalt pavement material, characterized by, The utility model relates to a kind of flexible pavement strain sensor, including: elastic sensitive element (1), resistance strain gauge (2), end flange (3), encapsulation shell (4) and flexible layer (5);The elastic sensitive element (1) is overall flat cuboid sheet structure;Resistance strain gauge (2) is fixed in the middle position of the elastic sensitive element (1);Two end flanges (3) are symmetrically provided at the two ends of the elastic sensitive element (1);Encapsulation shell (4) is flat cuboid, and two are symmetrically provided at the flat two sides of the elastic sensitive element (1);End flange (3) is provided with convex cylinder (6), encapsulation shell (4) is provided with transverse semicircular groove (8) embedded with the convex cylinder (6) connection, so that encapsulation shell (4) and end flange (3) are free to slide in measurement direction, and are mutually constrained in vertical measurement direction;Flexible layer (5) is nested on the surface of encapsulation shell (4);The width Wf of encapsulation shell satisfies the following formula: Wf = (Wb * Hb * Eb) / (2(Hf +Tb)* Ea) - 2Tb; Wherein, Wb is the width of elastic sensitive element, Hb is the thickness of elastic sensitive element, Hf is the height of encapsulation shell, Tb is the thickness of flexible layer, Ea is the elastic modulus of pavement material, Eb is the elastic modulus of elastic sensitive element. The side of encapsulation shell (4) is provided with rectangular groove (7) extending along its length direction, and the rectangular groove (7) on two encapsulation shells (4) is matched to accommodate the elastic sensitive element (1).

2. The strain sensor of claim 1, wherein: The side of encapsulation shell (4) is formed with longitudinal semicircular groove (9) perpendicular to the length direction of sensitive element, resistance strain gauge (2) is connected with wire (12), and wire (12) is led out through longitudinal semicircular groove (9).

3. The strain sensor of claim 1, wherein: Encapsulation shell (4) is provided with a plurality of screw holes (10) penetrating through encapsulation shell (4), and screw holes (10) on two encapsulation shells (4) are located in corresponding position and connected with each other by bolt (11).

4. The strain sensor of claim 1, wherein: Flexible layer (5) is made of butadiene rubber material.

5. The strain sensor of claim 1, wherein: ​

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