Strain gauge pasting and pressurizing method based on large flat plate test piece

Abstract

The invention discloses a strain gauge pasting and pressurizing method based on a large flat plate test piece. The strain gauge pasting and pressurizing method comprises the step that a strain gauge is pasted to the large flat plate test piece through an adhesive to obtain stress average distribution for pasting. Pressure applied to the strain gauge by the pressurizing pad is uniformly transmitted and distributed, so that uniform stress of the strain gauge is ensured, the strain gauge is attached to the large flat plate test piece, and the problem that the strain gauge is attached to the large flat plate test piece due to non-uniform stress of the strain gauge is solved.

Description

Technical Field

[0001] This invention relates to a method for bonding and pressurizing strain gauges on large flat plate specimens, belonging to the field of aero-engine component testing technology. Background Technology

[0002] Stress analysis is fundamental to the structural strength design analysis of components. Stress measurement methods include electrical strain gauge measurement, fiber optic grating method, vibrating wire strain gauge measurement, electronic speckle interferometry, and optical information digital image processing. Among these, electrical strain gauge measurement is the most widely used due to its mature technology, simple equipment requirements, ease of implementation, and convenient and intuitive data acquisition. Strain gauge bonding is the most basic, important, and crucial technique in electrical strain gauge measurement, playing a decisive role in the validity and accuracy of the measurement results.

[0003] After the strain gauge is attached to the specimen, it needs to be pressurized between 0.1 MPa and 0.3 MPa. The existing technology can be found in Chinese Patent Publication No. CN113532259A. For large flat specimens, sandbags or metal sheets are used for spot welding to apply pressure, which cannot achieve an even distribution of the stress on the strain gauge. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a method for bonding and pressurizing strain gauges onto large flat plate specimens.

[0005] The present invention is achieved through the following technical solutions.

[0006] This invention provides a method for bonding and pressurizing strain gauges on large flat plate specimens, comprising: The strain gauge is bonded to a large flat plate specimen using adhesive to achieve a uniform stress distribution through a pressure application method.

[0007] The pressurization method includes a pressurization process in which the strain gauge is subjected to uniform force distribution on the back and adheres to a large flat plate specimen by covering the back of the strain gauge with a pressure pad supported by a silicone plate.

[0008] The pressurization process includes four steps in sequence: determining the pressurization area of ​​the strain gauge, selecting the isolation membrane, determining the pressurization material, and determining the applied pressure.

[0009] The steps for determining the strain gauge pressure zone are as follows: When the strain gauge is pasted, the area of ​​the large flat plate specimen coated with adhesive is the pressure zone. This is determined before pasting the strain gauge based on the location of the measuring points and the geometric dimensions of the selected strain gauge. After determination, the pressure zone is drawn with a marker. The area of ​​the pressure zone is not less than 2 to 4 times the area of ​​the strain gauge.

[0010] The selection steps for the isolation membrane are as follows: the isolation membrane is a polytetrafluoroethylene film with a thickness of 0.04mm ± 0.01mm, and the area of ​​the isolation membrane is larger than the adhesive area when the strain gauge is pasted.

[0011] The steps for determining the pressure material are as follows: the pressure pad is a silicone plate with a thickness of 2mm±0.5mm, the area of ​​the pressure pad should not be less than the area of ​​the pressure area of ​​the strain gauge, and the pressure pad 3 is placed directly above the strain gauge; The pressure plate should be twice the length of the pressure pad, and its width should not be less than the width of the pressure pad. Its thickness should be between 1mm and 0.5mm. It should be placed directly above the pressure pad.

[0012] The thickness of the pressure band is no more than 0.1 mm. One end of the pressure band is connected to the large flat plate specimen through a welding point. After the pressure plate is fixed by pressing it down, another pressure band is used to press down the other end of the pressure plate and is connected to the large flat plate specimen through a welding point.

[0013] The pressure plate and pressure belt are made of the same material as the large flat plate specimen or of a material with a similar coefficient of thermal expansion that is compatible with it and can be welded together.

[0014] The steps for determining the applied pressure are as follows: following the steps for selecting the isolation membrane, the strain value is measured during the spot welding of the pressure band at the welding point. When the pressure reaches the required level, the effective stress position is marked on the pressure plate and the pressure band, and the distances L1 and L2 are measured.

[0015] The beneficial effects of this invention are as follows: the pressure pad applies pressure to the strain gauge and distributes it evenly, ensuring that the strain gauge is subjected to uniform force, and making the strain gauge fit closely with the large plate specimen, thus solving the problem of uneven pressure on the strain gauge leading to the strain gauge fitting closely with the large plate specimen. Attached Figure Description

[0016] Figure 1 This is a top view of the present invention; Figure 2 This is a top view schematic diagram of the solder joint distribution of the present invention; Figure 3 This is a schematic diagram showing the distribution of the effective force-bearing position distances L1 and L2 of the present invention; Figure 4 This is a schematic diagram of the actual distribution of the solder joints during electric welding according to the present invention; In the figure: 1-Strain gauge; 2-Isolation membrane; 3-Pressure pad; 4-Pressure plate; 5-Pressure belt; 51-Weld joint. Detailed Implementation

[0017] The technical solution of the present invention is further described below, but the scope of protection is not limited to what is described.

[0018] like Figures 1 to 4 As shown.

[0019] This application discloses a method for bonding and pressurizing strain gauges on large flat plate specimens, comprising the following steps: Step 1: Determine the strain gauge pressurization zone When attaching strain gauge 1, the area of ​​the large flat plate specimen coated with adhesive is the pressure zone. This zone is generally determined before attaching strain gauge 1 based on the measurement point locations and the selected strain gauge geometry. After determination, the pressure zone is marked with a marker. The area of ​​the pressure zone is generally not less than 2 to 4 times the area of ​​the strain gauge.

[0020] Step 2: Selection of the separating membrane Polytetrafluoroethylene (PTFE) film is resistant to acids and alkalis, and is not easily corroded. It can be used for extended periods at high temperatures without being adhered to by adhesives. Using a PTFE film with a thickness of 0.04mm ± 0.01mm as the release liner 2 can prevent the pressure pad 3 from being adhered to by adhesives. The area of ​​the release liner is larger than the adhesive application area during strain gauge bonding.

[0021] Step 3: Determine the pressurizing material (1) Pressure pad A silicone sheet with a thickness of 2mm ± 0.5mm is selected as the pressure pad 3. The area of ​​the pressure pad 3 should not be less than the area of ​​the pressure zone of the strain gauge. Cut the silicone sheet to the determined dimensions and place it directly above the strain gauge.

[0022] (2) Pressure plate The length of pressure plate 4 is approximately twice the length of the long side of pressure pad, and its width should not be less than the width of pressure pad 3. Cut it to the determined dimensions. Taking GH2150 specimen material as an example, use 45# stainless steel with a thickness between 1mm ± 0.5mm. After cutting, remove the burrs with a file and place it directly above the pressure pad.

[0023] (3) Pressure belt A thin sheet of the same material as the specimen (or a material that fuses with the specimen at high temperatures) is selected as the pressure band 5. Its thickness is generally no more than 0.1 mm. Using a spot welding machine, the pressure band 5 is first spot-welded to one end of the large flat specimen. Then, it is used to press down on the pressure plate and fix it. Another pressure band is then used to press down on the other end of the pressure plate, and spot-welded to form weld point 51, connecting it to the large flat specimen. Based on the pressure plate pressure distance determined in step four, the pressure bands at both ends are further spot-welded until the target is achieved. The fixing positions of the pressure bands are as follows: Figure 1 As shown.

[0024] Step 4: Determine the magnitude of the applied pressure. Determined through preliminary testing. Specifically: Strain gauges are attached to large flat plate specimens using fast-drying strain adhesive, and then strain values ​​are measured during spot welding of the pressure band according to section (3). When the pressure reaches the required level, the effective stress positions are marked on the pressure plate and pressure band, and the distances L1 and L2 are measured. Figure 2 As shown. Produce the required number of sheets as needed, and mark the solder joint positions on the pressure plate and pressure belt according to the measured dimensions.

[0025] 1. Pressurization method This invention utilizes high-temperature fusion welding technology to fix the pressure plate 4 to a large flat plate specimen by spot welding with a pressure band 5, thereby applying force to the strain gauge bonding area. At the same time, the pressure is determined through pre-testing, ensuring the target pressure value and controlling the dispersion of the bonding and pressurization quality of batch strain gauges.

[0026] 2. Selection of pressure pad material The main function of the pressure pad 3 is to transmit the applied pressure and distribute the stress evenly on the strain gauge. Traditionally, wool felt pads are used. Wool felt pads are relatively expensive, easily contaminate the strain gauge with capillary action, have lower elasticity than silicone, and their temperature resistance generally does not exceed 200℃. They yellow and harden after high temperatures and cannot be reused. They are only suitable for pressure curing of strain gauges with an operating temperature below 150℃ (adhesive curing temperature is approximately 160℃). Conventional silicone, on the other hand, has a temperature resistance of around 300℃, good elasticity, is easily deformable, has high adhesion to large flat specimens, and its chemical properties remain largely unchanged after high temperatures. It can be reused repeatedly and is suitable for pressure curing of strain gauges with an operating temperature below 300℃ (adhesive curing temperature is approximately 280℃). This effectively controls testing costs and ensures the quality of strain gauge bonding.

[0027] 3. Selection of pressure plate material The function of pressure plate 4 is to receive external pressure and transfer it to pressure pad 3. Since the material undergoes thermal expansion during heating in the oven, both the material's temperature resistance and coefficient of thermal expansion must be considered. If the coefficient of thermal expansion of pressure plate 4 differs significantly from that of the specimen, the applied pressure will change significantly during heating, and the target pressure value cannot be guaranteed. Furthermore, if the selected material is too hard, it will not adhere well to the large flat specimen during pressure application, resulting in uneven stress on the strain gauge; if the selected material is too soft, force transmission will be poor, and the stress on the strain gauge may be insufficient. In the case study, for the GH2150 specimen, 45# stainless steel was used. Its coefficient of linear expansion is basically the same as that of GH2150. It not only has good temperature resistance, but more importantly, its good elasticity allows the thin plate to easily adhere to the large flat specimen, ensuring that the pressure is evenly transferred to the strain gauge and guaranteeing uniform stress on the strain gauge.

Claims

1. A method for bonding and pressurizing strain gauges on large flat plate specimens, characterized in that, include: The strain gauge (1) is bonded to a large flat plate specimen by adhesive to obtain a uniform force distribution through a pressure application method.

2. The method for bonding and pressurizing strain gauges on large flat plate specimens as described in claim 1, characterized in that: The pressurization method includes a pressurization process in which the strain gauge (1) is subjected to a uniform force distribution on the back of the strain gauge (1) and adheres to the large flat plate specimen by covering the back of the strain gauge (1) with a pressurization pad (3) supported by a silicone plate.

3. The method for bonding and pressurizing strain gauges on large flat plate specimens as described in claim 2, characterized in that, The pressurization process includes four steps in sequence: determining the pressurization area of ​​the strain gauge, selecting the isolation membrane, determining the pressurization material, and determining the applied pressure.

4. The method for bonding and pressurizing strain gauges on large flat plate specimens as described in claim 3, characterized in that, The steps for determining the strain gauge pressure area are as follows: When the strain gauge (1) is pasted, the area of ​​the large flat plate specimen coated with adhesive is the pressure area. Before pasting the strain gauge (1), the pressure area is determined according to the position of the measuring point and the geometric size of the selected strain gauge. After determination, the pressure area is drawn with a marker pen. The area of ​​the pressure area is not less than 2 to 4 times the area of ​​the strain gauge.

5. The method for bonding and pressurizing strain gauges on large flat plate specimens as described in claim 3, characterized in that, The selection steps for the isolation membrane are as follows: the isolation membrane (2) is a polytetrafluoroethylene film with a thickness of 0.04mm ± 0.01mm, and the area of ​​the isolation membrane is larger than the adhesive area when the strain gauge is pasted.

6. The method for bonding and pressurizing strain gauges on large flat plate specimens as described in claim 3, characterized in that, The steps for determining the pressurizing material are as follows: the pressurizing pad is a silicone plate with a thickness of 2mm±0.5mm, the area of ​​the pressurizing pad (3) should not be less than the area of ​​the pressurizing area of ​​the strain gauge, and the pressurizing pad (3) is placed directly above the strain gauge. The pressure plate (4) is twice the length of the pressure pad, and its width should not be less than the width of the pressure pad (3). Its thickness is between 1mm and 0.5mm. It is placed directly above the pressure pad. The thickness of the pressure band (5) is no more than 0.1 mm. One end of the pressure band (5) is connected to the large flat plate specimen through the welding point (51). Then, it is used to press down the pressure plate (4) and fix it. Another pressure band (5) is used to press down the other end of the pressure plate (4) and continue to be connected to the large flat plate specimen through the welding point (51).

7. The method for bonding and pressurizing strain gauges on large flat plate specimens as described in claim 6, characterized in that: The pressure plate (4) and pressure belt (5) are made of the same material as the large flat plate specimen or have similar thermal expansion coefficients and are compatible with each other.

8. The method for bonding and pressurizing strain gauges on large flat plate specimens as described in claim 3, characterized in that: The steps for determining the applied pressure are as follows: following the steps for selecting the isolation membrane, during the process of spot welding the pressure band (5) at the welding point (51), the strain value is measured. When the pressure reaches the required level, the effective stress position is marked on the pressure plate (4) and the pressure band (5), and the distances L1 and L2 are measured.

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