Dog-bone-shaped ultralow-temperature strain sensor protection device, manufacturing method thereof and strain sensor

Abstract

The invention provides a dog-bone-shaped ultralow-temperature strain sensor protection device, a manufacturing method of the dog-bone-shaped ultralow-temperature strain sensor protection device and a strain sensor using the dog-bone-shaped ultralow-temperature strain sensor protection device. The protection device provided by the invention is used for arranging and protecting the strain gauge, so that the strain force can detect the strain in an ultralow-temperature environment. The protection device comprises a chamber, the chamber is used for accommodating the strain gauges and the connecting wires of the strain gauges, the whole protection device is in the shape of a thin plate, and the main plane of the thin plate is in the shape of a dog bone with two wide ends and a narrow middle part. According to the invention, the monitoring precision and the application range can be improved, and the cold brittleness resistance, condensation resistance and ice crystal damage resistance of the strain gauge are improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of rock super-low temperature freeze-thaw cycle monitoring, which can be extended to the fields of tunnels and coal mining, and specifically relates to a dog bone-shaped low-temperature strain sensor protection device and a manufacturing method thereof, and a corresponding strain sensor. BACKGROUND

[0002] In rock super-low temperature freeze-thaw cycle monitoring and other super-low temperature monitoring, strain measurement is an important link for calculating stress and calculating compression and shear resistance. The traditional strain sensor protection device adopts passive protection methods such as silicone sealing, epoxy resin packaging or metal protective cover. Although these methods can isolate external interference to a certain extent, they still have problems such as response lag, complex installation and insufficient long-term stability, which greatly limit the monitoring.

[0003] Moreover, the existing strain sensor protection device performs well in a conventional environment, but has insufficient reliability in a super-low temperature environment. SUMMARY

[0004] (I) Technical problem to be solved

[0005] The technical problem to be solved by the present application is the response lag, complex installation, insufficient long-term stability and insufficient reliability in a super-low temperature environment of the existing strain sensor protection device.

[0006] (II) Technical solution

[0007] The first aspect of the present application proposes a dog bone-shaped super-low temperature strain sensor protection device for arranging and protecting a strain gauge so that the strain force can detect strain in a super-low temperature environment. The protection device includes a cavity for accommodating the strain gauge and the wiring of the strain gauge. The protection device is in the shape of a thin plate, and the main plane of the thin plate is in the shape of a dog bone with wide ends and a narrow middle part.

[0008] According to a preferred embodiment of the present application, the protection device includes a top plate and a bottom plate that match in shape. The bottom plate includes a recess that forms the cavity when the top plate is fastened to the bottom plate.

[0009] According to a preferred embodiment of the present application, the dog bone shape includes two end parts and a middle part between the two end parts in the length direction thereof, the width of the middle part is smaller than that of the end parts, and the middle part and the end parts are arcuately transitioned.

[0010] According to a preferred embodiment of the present application, the end faces of the two ends of the dog bone shape are flat.

[0011] According to a preferred embodiment of the present application, the width ratio of the end parts to the middle part is between 3:2 and 5:2.

[0012] According to a preferred embodiment of the present application, the length to width ratio of the dog bone shape is between 3:2 and 2:1.

[0013] The second aspect of the present application proposes a manufacturing method of a dog bone shaped ultra-low temperature strain sensor protection device, the protection device comprising a cavity for accommodating the strain gauge and the wiring of the strain gauge, and the protection device being in the shape of a thin plate with a dog bone shape of wide ends and narrow middle; the manufacturing method comprising the step of: manufacturing the dog bone shaped ultra-low temperature strain sensor protection device by 3D printing.

[0014] According to a preferred embodiment of the present application, the protection device comprises a top plate and a bottom plate with matching shapes; the top plate and the bottom plate are respectively made by 3D printing.

[0015] According to a preferred embodiment of the present application, the 3D printed material is a concrete material, which is the same as the concrete material of the ultra-low temperature geological model to be detected.

[0016] The third aspect of the present application proposes a dog bone shaped ultra-low temperature strain sensor, comprising a strain gauge and a protection device, the protection device being the aforementioned dog bone shaped ultra-low temperature strain sensor protection device.

[0017] (Three) beneficial effects

[0018] The strain sensor protection device of the present application adopts the same material as the test piece, has the same material, high tensile and compressive strength, high shear strength compared with other protection covers, improves the monitoring accuracy and application range, improves the cold brittleness and cold condensation resistance of the strain gauge, and resists the damage of ice crystals. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 is a schematic diagram of the shape of an embodiment of the dog bone shaped ultra-low temperature strain sensor protection device of the present application.

[0020] Figure 2 is Figure 1 is a perspective view of an embodiment of the dog bone shaped ultra-low temperature strain sensor protection device of the present application.

[0021] Figure 3 and Figure 4 are respectively Figure 1 are respectively the structural schematic diagrams of the top plate and the bottom plate of an embodiment of the dog bone shaped ultra-low temperature strain sensor protection device of the present application.

[0022] Figure 5 and Figure 6 are respectively the force analysis diagrams of the conventional strain sensor protection device and the ultra-low temperature strain sensor protection device of the present application.

[0023] Figure 7 and Figure 8 is a size design drawing of the dog bone shaped ultra-low temperature strain sensor protection device of the present application.

[0024] Figure 9 is an example drawing of one specific size of the top plate of the dog bone shaped ultra-low temperature strain sensor protection device of the present application.

[0025] Figure 10 is an example drawing of one specific size of the bottom plate of the dog bone shaped ultra-low temperature strain sensor protection device of the present application.

[0026] Figure 11 is a schematic drawing of area A3 of one example of the dog bone shaped ultra-low temperature strain sensor protection device of the present application.

[0027] Figure 12 is a schematic drawing of area A4 of one example of the dog bone shaped ultra-low temperature strain sensor protection device of the present application.

[0028] Figure 13 is a structural schematic drawing of one embodiment of the dog bone shaped ultra-low temperature strain sensor of the present application. DETAILED DESCRIPTION

[0029] To solve the above technical problems, the present application proposes a dog bone shaped ultra-low temperature strain sensor protection device. It should be noted that the ultra-low temperature referred to in the present application is an extremely low temperature, usually referring to an environmental temperature below -190℃. For example, the present application can be applied to measure geological strain or model strain in underground LNG storage and its test model, and accordingly the stress can be calculated.

[0030] The protection device of the present application is a thin plate in the shape of a dog bone as a whole. The surface area of one face of the thin plate is the largest, which is its main plane. From the main plane, the two ends are wide and the middle part is narrow, thus it is called "dog bone shaped". More specifically, the "dog bone shaped" is a symmetrical shape, having two symmetry axes, respectively parallel to the length direction and the width direction. The length direction of the dog bone shaped includes two end parts and a middle part between the two end parts, and the width of the middle part is smaller than that of the end parts.

[0031] As a preferred embodiment, the end faces of the two ends of the length direction of the dog bone shaped are flat, and an arc transition is adopted between the middle part and the end parts.

[0032] The strain sensor protection device mainly bears tension in traditional application, but needs to bear shrinkage under ultra-low temperature test. The rectangular strain sensor protection device mainly resists damage by contact surface friction. The dog bone shaped strain sensor protection device, compared with the rectangular strain sensor protection device, has the same friction resistance to damage, and the arc surface is under compression, the side arc surface can provide tension, cooperative deformation, the arc surface is under compression, and is not prone to failure.

[0033] The protection device of the application comprises a cavity for accommodating the strain gauge and the wiring of the strain gauge. For this purpose, the application designs a top plate and a bottom plate with matching shapes to constitute the protection device. Specifically, the application proposes that the top plate and the bottom plate can be printed by 3D printing, and a recess is designed on the bottom plate. When the top plate is buckled on the bottom plate, the recess forms the cavity.

[0034] As a specific design size ratio of the dog bone shape, the application preferably has a width ratio of the end part to the middle part of 3:2 to 5:2, and a length to width ratio of 3:2 to 2:1.

[0035] The 3D printed material of the application is preferably a concrete material, which is the same as the concrete material of the ultra-low temperature geological model to be detected. Since the same material is used, the protection device has the same elastic modulus as the material to be detected, has a more stable stress shape than other shapes, stabilizes the measurement environment, and improves the accuracy.

[0036] The application also proposes a strain sensor using the above dog bone shaped ultra-low temperature strain sensor protection device.

[0037] The protection device with the above design can effectively resist external mechanical forces such as collision, friction and extrusion, prevent the sensitive grid and substrate of the strain gauge from being damaged, and prolong the service life. Moreover, the application can effectively block dust, water vapor and other pollutants from entering the strain gauge, avoid changes in resistance value caused by moisture or dust accumulation, and ensure the stability of measurement accuracy.

[0038] To make the purpose, technical scheme and advantages of the application clearer and more apparent, the application will be further described in detail below with reference to the specific embodiments and the accompanying drawings.

[0039] Figure 1 is a schematic diagram of the shape of an embodiment of the dog bone shaped ultra-low temperature strain sensor protection device of the application. As Figure 1As shown, the protective device includes a top plate 1 and a bottom plate 2, which interlock to form a thin plate shape. The figure shows that the main plane of the thin plate is shaped like a dog bone, wider at both ends and narrower in the middle, with the width at both ends greater than the width in the middle. The two ends along its length are rectangular planes, while the two ends along its width bulge inwards. That is, the middle and ends of the dog bone shape have an arc-shaped transition, and the overall shape resembles the letter "I".

[0040] from Figure 1 It can also be seen that one end of the base plate in the width direction has an opening 21, which is the opening for the wiring of the strain gauge.

[0041] Figure 2 yes Figure 1 An internal perspective view of one embodiment of the dog-bone-shaped cryogenic strain sensor protection device of the present invention is shown. Figure 2 As shown, a recess 22 is provided in the middle of the interior of the base plate, which is used to accommodate the strain gauge and one end of the strain gauge's wiring, and is connected to the opening 21.

[0042] Figure 3 and Figure 4 They are Figure 1 The diagram shows the structural schematic of the top and bottom plates of one embodiment of the dog-bone-shaped cryogenic strain sensor protection device of the present invention. Figure 3 and Figure 4 As shown, both the top plate 1 and the bottom plate 2 are thin plates, and their main planes have identical shapes to ensure a perfect fit. Furthermore, in this embodiment, their thicknesses are also the same.

[0043] like Figure 4 As shown, the recess 22 includes two regions: a central region 221 and a wiring region 222. The central region 221 is located in the center of the base plate 2, and its main plane is rectangular in shape, used to accommodate a rectangular strain gauge. The wiring region 222 is located on one side of the central region 221, and is also rectangular in shape, used to accommodate one end of the strain gauge's wiring.

[0044] Figure 5 and Figure 6 These are force analysis diagrams of a traditional strain sensor protection device and the cryogenic strain sensor protection device of this invention, respectively. Figure 5 and Figure 6As shown, when the traditional rectangular main plane strain sensor protection device is under the action of stresses σ1 and σ2, and S1 and S2 are both broken, S1 and S2 only rely on friction to resist damage, and when all four surfaces are broken, they cannot deform cooperatively. However, when the ultra-low temperature strain sensor protection device of the present application is under the action of stress σ1, and S1 is broken, S1-1 and S1-2 are subjected to stress together with friction, S1-1 and S1-2 provide tensile and compressive forces, and the arc surface is subjected to tension and compression. Similarly, under the action of σ2, the arc surface is also subjected to tension and compression, and resists damage together with friction. That is, when S1 and S2 are broken, they can still deform cooperatively and work normally.

[0045] The size design of the top plate 1 will be described below with reference to Figure 7 and Figure 8

[0046] Here, the length of the top plate 1 is represented by a, the width by b, and the thickness by c. Since the dog bone shape of this embodiment is a symmetrical figure, the length direction includes a middle part and two end parts, and the lengths of the middle part and the end parts are a1 and a2, respectively, i.e. a = a1 + 2a2. Correspondingly, the width direction also includes a middle part and two end parts, and the lengths of the middle part and the end parts are b1 and b2, respectively, i.e. b = b1 + 2b2. Through simulation and experiments of the present application, the ratio a:b of the length a and the width b is preferably between 3:2 and 2:1, and more preferably 5:3.

[0047] The ratio of the lengths of the middle part and the end part in the length direction, i.e. a1:a1+2a2, is preferably between 3:2 and 5:2, and more preferably 2:1. Similarly, the ratio of the lengths of the middle part and the end part in the width direction, i.e. b1:b1+2b2, is also preferably between 3:2 and 5:2, and more preferably 2:1.

[0048] Figure 9 An example of a specific size of the top plate 1 is given. Figure 9 The length unit in the above table is mm. The total length of the top plate 1 is 20 mm, the width is 12 mm, and the thickness is 3 mm. The width of the middle part in the length direction is 6 mm, and the length of the middle part in the width direction is 10 mm. The size of the curved section of the dog bone shape: the radii of all the curved sections of the dog bone are set to a transition arc with a radius of 5 mm.

[0049] Figure 10 An example of a specific size of the bottom plate 2 is given. The size design of the bottom plate 2 will be described below with reference to Figure 10 ​The dimensions of the base plate 2 will be explained below. Since the top plate 1 and the base plate 2 have identical external dimensions, the external dimensions of the base plate 2 can be referenced from the top plate 1 and will not be described further. The dimensions of the recess 22 on the base plate 2 are matched with the strain gauge; depending on the size of the strain gauge, the dimensions of the recess 22 can be varied accordingly. In this example, the length, width, and thickness of the central region 221 of the recess 22 are 6.0 mm, 4.0 mm, and 1.5 mm, respectively, and the width of the wiring area is 2.0 mm, and the thickness is 1.5 mm.

[0050] The following diagram illustrates the performance of this protective device in ultra-low temperature environments using its dimensions as an example.

[0051] I. Calculation of the safe load-bearing capacity of dog bones.

[0052] 1. Consider the compressive strength of the dog bone-shaped protective device under temperature changes.

[0053] б t =E·α·ΔT·K

[0054] in:

[0055] E is the elastic modulus of the C30 concrete used in this example, taken as 3.0 × 10⁻⁶. 4 MPa;

[0056] α is the coefficient of linear expansion of C30 concrete, taken as 1.0 × 10⁻⁶. -5 / ℃;

[0057] ΔT is the temperature change, taking the maximum change, i.e. -196℃ to 30℃, with a temperature interval of 226℃;

[0058] K is the constraint coefficient, which is set to 1.

[0059] Calculation yields: б t The maximum is 67.8 MPa. It is also known that the applied stress is б. 施 Approximately 1 GPa.

[0060] (б 施 Represents: the stress applied by the press. (Along the direction of the force applied by the press.)

[0061] Assuming shear failure occurs longitudinally (along the longest direction in the top view of the dog bone protective cover), the most critical cross-sectional area of ​​the vertical (length direction) bending segment of the cover plate and base plate is taken as...

[0062] A1 = 5mm × 3m = 15mm 2

[0063] A1 is Figure 7 The area of ​​the cross section shown in the yellow box of the top plate 1 is similar in position to that in the bottom plate 2.

[0064]

[0065] Since And the four most dangerous cross-sections are the four cross-sections of the cover plate and the four cross-sections of the base plate, then:

[0066]

[0067] Therefore, the total applied force F 总1 ≤120KN is the safe range, which protects the vertical (length direction) of the device from shear failure. (The applied force is the force of the applied load)

[0068] Assuming that the transverse (width direction) is subjected to shear failure, the most dangerous cross-sections are the transverse cross-sections of the top plate and the base plate, and the most dangerous cross-section area is:

[0069] A2 = 6mm x 6mm x 2 = 72mm 2

[0070] A2 is Figure 8-10 the area of the blue frame of the base plate and the top plate.

[0071]

[0072] In summary, the maximum safe stress of the dog bone-shaped base plate is 72KN.

[0073] 2. Consider the compressive strength of the dog bone-shaped protective device under the action of freezing and thawing.

[0074] f cu,n = f cu,0 × (1-D N )

[0075] According to the empirical formula, the damage coefficient is:

[0076] D N = 1-e -KN

[0077] f cu,n : the compressive strength after n times of freezing and thawing.

[0078] f cu,0 : the compressive strength without freezing and thawing cycles.

[0079] D N : the loss rate of compressive strength after n times of freezing and thawing.

[0080] Let the attenuation coefficient K be 0, then the compressive strength f cu,n after freezing and thawing is f cu,0 , and the compressive strength of C30 concrete is 30MPa. Then:

[0081]

[0082] (A is the surface area of the dog bone shape, б is the sum of the compressive strength of C30 concrete and the temperature stress and applied stress.)

[0083] In summary, for the additional load within the safety range of 135KN, there is a great safety reserve under the influence of freeze-thaw cycle and extreme temperature change.

[0084] 3. Consider the compressive strength of the dog bone-shaped protective device under pressure.

[0085] Because the middle rectangle of the dog bone-shaped protective device is pasted with strain gauges, and the compressive strength of the dog bone shape is higher than that of the rectangle, the more dangerous rectangle is used to replace the dog bone for theoretical demonstration.

[0086]

[0087] First consider single-sided compression

[0088] Front:

[0089] A = 135.1175mm 2

[0090] The surface area of the dog bone shape can be calculated to be 135.1175mm 2

[0091] F1 = б 总 × A = 1 GPa × 135.1175mm 2 ≈ 135KN

[0092] Side:

[0093] A3 = 6mm × 20mm = 36mm 2

[0094] Figure 11 The position of A3 is shown.

[0095] F2 = б 总 × A3 = 1 GPa × 36mm 2 = 36KN

[0096] In summary, the minimum stress is 36KN. (Meaning: After steps 1-3 above, the minimum stress is calculated to ensure the minimum safety stress)

[0097] 4. Consider the maximum stress of the dog bone-shaped protective device cover plate shear failure when demolding.

[0098] The most dangerous section of the cover plate of the dog bone-shaped protective device is the interface between the strain gauge pasting place and the rest of the concrete section.

[0099] The mold is composed of two aluminum alloy molds, which are coated with oil and bound with elastic ropes before pouring, and then demolded after solidification.

[0100] Shear area:

[0101] A4 = 1.5mm x 4mm x 2 + 1.5mm x 1mm x 2 + 1.5mm x 2mm + 1.5mm x 6mm x 2 = 36mm 2

[0102] A4 is Figure 12 the area of the middle shadow part.

[0103] According to the Code for Design of Concrete Structures, the shear strength design value of C30 concrete is about 1.43MPa.

[0104] F4 = τ·A4 = 1.43MPa x 36mm 2 = 51.48N

[0105] 42.9N is equivalent to 5.25kg of weight, and when the mold is removed, the dog bone-shaped protective device will not be damaged.

[0106] Core formula

[0107] б = E 实际 ·ε 实际 = E 理论 ·ε 理论

[0108] Parameter description:

[0109] E 实测 : actual elastic modulus

[0110] ε 实测 : actual strain

[0111] E 理论 : theoretical elastic modulus

[0112]

[0113] Figure 13 is a structural schematic diagram of an embodiment of the dog bone-shaped super-low temperature strain sensor of the application. As Figure 13 shown, in this embodiment, the strain gauge S of the super-low temperature strain sensor is placed in the middle area 221 of the recess 22 of the bottom plate 2, the wire T of the strain gauge S is located in the wiring area 222, and extends out through the opening 21.

[0114] From the above embodiment, the application has the following effects.

[0115] (1) The dog bone-shaped protective device of the application can improve the precision.

[0116] The dog bone-shaped protective device has the same material and elastic modulus as the experimental assembly, has a more stable stress state than other shapes, stabilizes the measurement environment, and improves the precision.

[0117] (2) The dog bone-shaped protective device can resist mechanical sprains.

[0118] Because the strain gauge protective device in the dog bone shape has better compression resistance and shear resistance than the circular, square and other shapes, it can resist external mechanical forces such as collision, friction and extrusion, prevent the sensitive grid and base of the strain gauge from being damaged, and prolong the service life.

[0119] (3) The dog bone-shaped protective device can prevent dust and moisture.

[0120] Because the strain gauge in the dog bone shape is spliced and bonded by a bottom plate and a top plate and has only one wire hole connected to the outside world, its airtightness is better than that of strain gauge protective devices in other shapes. It can effectively block dust, water vapor and other pollutants from entering the strain gauge, avoid changes in resistance value caused by moisture or dust accumulation, and ensure the stability of the measurement precision.

[0121] The above specific embodiments further illustrate the purpose, technical solutions and advantages of the present application. It should be understood that the above description is only a specific embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A dog bone shaped cryogenic strain sensor protection device for positioning and protecting a strain gauge for detecting strain under cryogenic conditions, characterized in that: the protection device comprises a cavity for accommodating the strain gauge and wires of the strain gauge; and the protection device is in the shape of a thin plate with a main plane in the shape of a dog bone with wider ends and a narrower middle.

2. The dog bone shaped cryogenic strain sensor protection device according to claim 1, characterized in that: the protection device comprises a top plate and a bottom plate with mating shapes; and the bottom plate comprises a recess forming the cavity when the top plate is fastened to the bottom plate.

3. The dog bone shaped cryogenic strain sensor protection device according to claim 1 or 2, characterized in that: the dog bone shape comprises two ends and a middle between the two ends, the width of the middle is smaller than the width of the ends, and the middle and the ends are connected by an arc.

4. The dog bone shaped cryogenic strain sensor protection device according to claim 3, characterized in that: the end faces of the two ends of the dog bone shape are flat; the ratio of the width of the ends to the width of the middle is between 3:2 and 5:2; and the ratio of the length of the dog bone shape to the width of the dog bone shape is between 3:2 and 2:

1.

7. A method for manufacturing a dog bone shaped cryogenic strain sensor protection device, characterized in that: the protection device comprises a cavity for accommodating the strain gauge and wires of the strain gauge, and the protection device is in the shape of a thin plate with a main plane in the shape of a dog bone with wider ends and a narrower middle; and the method comprises the step of: manufacturing the dog bone shaped cryogenic strain sensor protection device by 3D printing.

8. The method for manufacturing a dog bone shaped cryogenic strain sensor protection device according to claim 7, characterized in that: the protection device comprises a top plate and a bottom plate with mating shapes; and the top plate and the bottom plate are respectively manufactured by 3D printing.

9. The method for manufacturing a dog bone shaped cryogenic strain sensor protection device according to claim 7 or 8, characterized in that: the material of the 3D printing is a concrete material, which is the same as the concrete material of a cryogenic geological model to be detected; and the protection device is the dog bone shaped cryogenic strain sensor protection device according to any one of claims 1 to 6. ​ ​ ​ 5. The dog bone shaped ultra-low temperature strain sensor protection device of claim 3, wherein: ​ 6. The dog bone shaped ultra-low temperature strain sensor protection device of claim 3, wherein: ​ ​ ​ ​ ​ ​ ​ ​ ​ 10. A dog-bone shaped ultra-low temperature strain sensor comprising a strain gauge and a protective device, characterized in that, ​

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