Fiber bragg grating strain gauge device suitable for early-age concrete

Abstract

The invention discloses a fiber bragg grating strain gauge device suitable for early-age concrete. The fiber bragg grating strain gauge device comprises a strain gauge, an optical fiber thermometer, a silica gel soft package body and sensor end covers, wherein the optical fiber thermometer and the strain gauge are arranged side by side; the silica gel soft package body is used for wrapping the strain gauge and the optical fiber thermometer; the two ends of the strain gauge are respectively and fixedly connected with an armored optical cable, and the armored optical cables extend out of a wire outlet of the sensor end cover and are fixed on the sensor end cover; wherein the strain gauge and the silica gel soft package body are in a non-adhesive free deformation state. According to the invention, the strain gauge realizes the fidelity transmission and measurement of the structural strain under any rigidity condition after the concrete is solidified, and the temperature of the sensing element is automatically compensated.

Description

Technical Field

[0001] The present invention relates to the technical field of strain gauges, and particularly to a fiber Bragg grating strain gauge device suitable for early-age concrete. Background Art

[0002] After the casting of mass concrete, due to the hydration reaction of the matrix material, the internal temperature of the structure rises sharply and the moisture content drops sharply, causing non-uniform deformation, crack initiation, and internal damage of the structure under the coupling of temperature, humidity, and stress, posing a huge hidden danger to the safety and durability of the structure. Therefore, accurately detecting and scientifically evaluating the deformation and damage of mass concrete structures in the early age is an extremely important technical link in mass concrete structure engineering.

[0003] A main parameter for evaluating the initial damage of concrete is the strain during the concrete curing process. Due to the characteristics of early-age concrete such as small stiffness and high hydration temperature, it is very difficult to measure the strain. For various existing strain sensors, since their own stiffness is much greater than that of early-age concrete, the deformation cannot be faithfully transmitted, and the measurement results are much smaller than the actual values or even seriously distorted.

[0004] In summary, there is an urgent need to develop a high-precision strain sensing device with an axial deformation stiffness matching that of early-age concrete, automatic elimination of temperature influence, and real-time monitoring function. Summary of the Invention

[0005] Aiming at the deficiencies existing in the prior art, the purpose of the present invention is to provide a fiber Bragg grating strain gauge device suitable for early-age concrete, which has water and corrosion resistance, high precision, good stability, and can synchronously monitor the temperature of concrete. To achieve the above-mentioned purpose and other advantages of the present invention, there is provided a fiber Bragg grating strain gauge device suitable for early-age concrete, including: A strain gauge, a fiber optic thermometer arranged side by side with the strain gauge, a silica gel soft package for wrapping the strain gauge and the fiber optic thermometer, and a sensor end cap for encapsulating both ends of the silica gel soft package; Armor cables are fixedly connected to both ends of the strain gauge, and the armor cables extend out from the sensor end cap and are fixed on the sensor end cap; Wherein, a non-bonded free deformation state exists between the strain gauge and the silica gel soft package.

[0006] A wavelength adapted to the strain sensor (1528 - 1568 nm) is selected and connected to the strain gauge and then encapsulated in a silica gel cylinder simultaneously as the automatic temperature compensation of the strain gauge to ensure the reliability and high precision of the strain monitoring data. At the same time, the built-in thermometer can separately monitor the temperature change of the concrete to obtain the temperature data for evaluating the concrete damage.

[0007] The sensor end caps are axially limited and movable, and are connected by guide rods circumferentially arranged at equal intervals of 120°. A 4-mm sliding between the sensor end caps is allowed, and the lateral bending deformation of the fiber Bragg grating strain gauge is avoided.

[0008] The elastic modulus of the silicone rubber soft package body is ≤1 MPa, which encapsulates the bare fiber Bragg grating, and keeps the fiber Bragg grating element in a non-bonded free deformation state with the silicone rubber soft package body. The stiffness matching between the strain gauge and the measured concrete medium is realized to ensure the faithful transmission of the early-age concrete strain. Description of the Drawings

[0009] Figure 1 It is a schematic structural diagram of a fiber Bragg grating strain gauge device applicable to early-age concrete according to the present invention; Figure 2 It is a schematic structural diagram of the sensor end cap of a fiber Bragg grating strain gauge device applicable to early-age concrete according to the present invention; Figure 3 It is a schematic structural diagram of the cylindrical silicone rubber soft package body of a fiber Bragg grating strain gauge device applicable to early-age concrete according to the present invention; Figure 4 It is a schematic structural diagram of the stainless steel bending-resistant guide rod of a fiber Bragg grating strain gauge device applicable to early-age concrete according to the present invention. Detailed Embodiment

[0010] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0011] Refer to Figure 1 , a fiber Bragg grating strain gauge device applicable to early-age concrete, comprising: a strain gauge 3, a fiber optic thermometer 1 arranged side by side with the strain gauge 3, a silicone rubber soft package body 2 for wrapping the strain gauge 3 and the fiber optic thermometer 1, and sensor end caps 6 for encapsulating both ends of the silicone rubber soft package body 2; Armor cables 5 are fixedly connected to both ends of the strain gauge 3, and the armor cables 5 extend from the sensor end caps 6 and are fixed to the sensor end caps 6; Among them, a non-bonded free deformation state exists between the strain gauge 3 and the silicone rubber soft package body 2. The sensing element in the strain gauge 3 uses a fiber Bragg grating with a wavelength of 1528~1568 nm as the sensing element, the range requirement is 8000 με~10000 με, the length of the fiber Bragg grating is 5 mm, and an armor cable 5 with a diameter of 6 mm is connected.

[0012] The strain gauge 3 of the present application adopts an assembled structure. After the fiber Bragg grating and the fiber Bragg grating sensing element of the thermometer 1 are positioned and connected to the armored optical cable 5, they are encapsulated with a cylindrical silicone soft package 2. The encapsulated strain gauge 3 and the thermometer 1 are coaxially fixed through two sensor end caps 6, and the two sensor end caps 6 are connected by a stainless steel guide rod 4 that can be limited and moved axially; a 6 mm armored optical cable 5 is used and passes out through the wire outlet holes at both ends of the sensor end cap 6 and is bonded and fixed with strong glue. The structural assembly form is as Figure 2 shown. The design drawing of the sensor end cap is as Figure 3 shown. The sensor end cap 6 is made of Q235 ordinary carbon steel. The internal cavity of the sensor end cap 6 is used to access the silicone soft package 2; f3 mm guide holes are evenly arranged along the 28 mm circumference of the sensor end cap 6 at 120°; an f8 mm optical cable outlet hole is provided axially on the sensor end cap 6. The outlet hole and the optical cable are sealed with strong glue.

[0013] The present application uses a silicone soft package 2 to encapsulate the bare fiber Bragg grating, and makes the fiber Bragg grating element and the silicone soft package 2 in a non-bonded free deformation state. To achieve the stiffness matching between the strain gauge and the measured concrete medium and ensure the faithful transmission of the early-age concrete strain. As Figure 3 shown. The fiber Bragg grating and the silicone soft package 2 are designed to be in a non-bonded state with relative slippage, ensuring that the temperature deformation of the silicone soft package 2 will not have an adverse effect on the fiber Bragg grating sensing element. The length of the silicone soft package 2 is 94 mm and the nominal diameter is 20 mm; a 1 mm deformation gap is reserved between the silicone soft package 2 and the inner side of the sensor end cap 6 to avoid additional strain on the fiber Bragg grating caused by the lateral compression or thermal expansion of the silicone soft package 2.

[0014] In the present application, the two sensor end caps 6 are connected by a stainless steel guide rod circumferentially at equal intervals of 120°, and there is a 4 mm sliding space between the two sensor end caps, and the lateral bending deformation of the fiber Bragg grating strain gauge is avoided. To avoid damage to the fiber Bragg grating caused by excessive tensile elongation of the strain gauge during concrete pouring construction, a 4 mm stroke limit is designed at the connection part between the guide rod 4 and the sensor end cap 6. To improve the lateral bending stiffness of the strain gauge, 3 equally spaced positioning guide rods 4 are arranged axially, that is, the cross-section is equally divided into 120° of the circumferential circle.

[0015] In the present application, a fiber optic thermometer 1 with a wavelength adapted to the strain sensor is selected and connected to the strain gauge 3 and then encapsulated in the silicone soft package 2 at the same time. The fiber optic thermometer 1 is used as the temperature automatic compensation of the strain gauge 3 to ensure the reliability and high precision of the strain monitoring data. At the same time, the built-in thermometer can monitor the concrete temperature change separately and obtain the temperature data for concrete damage evaluation.

[0016] During the production and monitoring use process of the device for the strain gauge, the specific implementation method is as follows: Process the components separately according to the design drawings and technical specifications of each component of the strain gauge.

[0017] After the technical parameters of the components are inspected and qualified, the factory assembles them into a prefabricated fiber Bragg grating strain gauge and sets the product number.

[0018] Conduct technical calibration of the wavelengths of the strain sensing element and the temperature sensing element, and determine the sensing element coefficients {K, a, b} through tests.

[0019] Set up a temperature simulation environment to study the temperature sensitivity of the soft package during the whole process of temperature rise and fall of the strain gauge and its influence on the strain sensing element. The specific method is as follows: i) According to the engineering characteristics, set the temperature peak value, temperature rise period, and temperature fall period; ii) Place the sensor in a standard temperature chamber and lead out the signal line to connect to a data acquisition instrument; iii) Simulate the temperature environment parameters to conduct tests under the condition of no external load, and automatically record the temperature and the strain of the sensor; v) Obtain the strain-temperature function relationship through least squares regression.

[0020] Establish a temperature compensation and correction method for the strain gauge. It specifically includes three steps: i) Select the thermal strain-temperature relationship curve of the strain gauge base; ii) Calculate the thermal strain of the strain gauge base according to the temperature data measured in the test Calculate the thermal strain of the strain gauge base ; iii) Calculate the strain of the concrete structure according to the correction model calculated from the aforementioned thermal strain of the base .

[0021] After the product is inspected and qualified, it is provided for on-site monitoring or test applications in the project.

[0022] The equipment quantities and processing scales described here are used to simplify the description of the present invention, and it is obvious to those skilled in the art for the application, modification, and variation of the present invention.

[0023] Although the embodiments of the present invention have been disclosed as above, it is not limited to the applications listed in the specification and embodiments. It can be fully applied to various fields suitable for the present invention. For those familiar with the field, additional modifications can be easily achieved. Therefore, without departing from the general concept defined by the claims and the equivalent scope, the present invention is not limited to specific details and the illustrated examples described here.

Claims

1. An optical fiber grating strain gauge device applicable to early-age concrete, characterized in that, Including: A strain gauge, an optical fiber thermometer arranged side by side with the strain gauge, a silica gel soft package for wrapping the strain gauge and the optical fiber thermometer, and a sensor end cap for encapsulating both ends of the silica gel soft package; [[ID=K2]]Both ends of the strain gauge are fixedly connected with armored optical cables, and the armored optical cables extend out from the wire outlet of the sensor end cap and are fixed on the sensor end cap; Wherein, a non-bonded free deformation state exists between the strain gauge and the silica gel soft package.

2. The fiber Bragg grating strain gauge device applicable to early-age concrete as described in claim 1, wherein The sensing element in the strain gauge is an optical fiber grating with a wavelength of 1528 - 1568 nm, and the measuring range is 8000 με - 10000 με, and the length of the optical fiber grating is 5 mm.

3. The fiber Bragg grating strain gauge device applicable to early-age concrete according to claim 1, wherein, A plurality of guide rods are arranged between the sensor end caps on the two end faces of the silica gel soft package, and the two sensor end caps can be axially limited and moved through the plurality of guide rods.

4. The fiber Bragg grating strain gauge device applicable to early-age concrete according to claim 3, wherein The plurality of guide rods between the two sensor end caps are arranged at equal intervals of 120° in the circumferential direction, and the sliding between the sensor end caps is 4 mm.

5. The fiber Bragg grating strain gauge device applicable to early-age concrete according to claim 1, wherein The structure of the silica gel soft package is cylindrical, and the length of the silica gel soft package is 94 mm, the nominal diameter is φ20 mm, and a deformation gap of 1 mm is reserved respectively between one end face of the silica gel soft package and the inner side of the sensor end cap.

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