Coefficient calibration platform and method based on ring core method residual stress calculation

Abstract

The application relates to a coefficient calibration platform and method based on ring core method residual stress calculation. The coefficient calibration platform comprises a supporting bottom plate, a loading device and a clamping device. The loading device comprises a cross arm which can move linearly left and right and is installed on the supporting bottom plate, a loading power mechanism which drives the cross arm to move linearly left and right, a pressurizing pull rod which is installed on the cross arm, and a pressure sensor which is used for detecting the tension in the pressurizing pull rod. The clamping device comprises a first chuck which is fixed to the supporting bottom plate and a second chuck which is installed on the loading pull rod. The first chuck and the second chuck are opposite to each other. The coefficient calibration method is carried out by using the platform. The strain values at different depths of a test plate are obtained by using a method similar to the ring core method, and then the coefficients in the residual stress calculation formula are obtained. The coefficient calibration platform and method can popularize the application of the ring core method to different materials, have universality, and can effectively improve the application range and calculation precision of the ring core method.

Description

Technical Field

[0001] This invention relates to the field of residual stress measurement, and specifically to a coefficient calibration platform and method based on residual stress calculation using the ring core method. Background Technology

[0002] For rotating shaft components such as turbine and turbine generator rotors, residual stress is a crucial factor affecting their machining accuracy and service safety. Residual stress is the internal stress present in a component when no external force or torque is applied. The presence of residual stress not only affects the static strength, corrosion resistance, and fatigue strength of parts, but can also lead to deformation or damage during assembly and use, thus affecting the normal operation of the parts. Therefore, accurately understanding the distribution of residual stress in components is of paramount importance.

[0003] The ring core method has become the preferred method for measuring residual stress in rotor forgings due to its high accuracy and reliability. JB / T 8888-2018, "Test Method for Measuring Residual Stress in Steam Turbine and Steam Generator Rotor Forgings by Ring Core Method," details the operation of measuring residual stress in rotor forgings using the ring core method and provides calculation formulas for residual stress within a specified depth range. However, the calculation formulas in this standard are not applicable to all types of materials and are related to the ring groove diameter, ring groove depth, and strain gauge size. Existing calculation formulas are applicable to alloy steel with a ring groove outer diameter of 18mm, an inner diameter of 14mm, and a depth of 2-4mm, but may not be applicable to other situations. Summary of the Invention

[0004] In view of the shortcomings of the prior art described above, the technical problem to be solved by the present invention is to provide a calibration platform and method for residual stress calculation coefficients based on the ring core method, which has universality and can improve the applicability and calculation accuracy of the ring core method.

[0005] To achieve the above objectives, the present invention provides a coefficient calibration platform based on residual stress calculation using the ring core method, comprising a support base plate, a loading device, and a clamping device. The loading device includes a crossbeam mounted on the support base plate that can move linearly left and right, a loading power mechanism for driving the crossbeam to move linearly left and right, a pressure rod mounted on the crossbeam, and a pressure sensor for detecting the tension in the pressure rod. The clamping device includes a first clamp fixed to the support base plate and a second clamp mounted on the loading rod, wherein the first clamp and the second clamp are opposite each other left and right.

[0006] Furthermore, the support base plate is also provided with a guide structure, which is used to guide the left and right linear movement of the crossarm.

[0007] Furthermore, the guide structure includes guide posts arranged in the left-right direction, and the crossbeam is slidably fitted onto the guide posts.

[0008] Furthermore, the loading power mechanism includes a hydraulic jack, which is arranged in the left-right direction and its piston rod is fixedly connected to the crossbeam.

[0009] Furthermore, the clamping device also includes a liner plate mounted on the support base plate, the liner plate being located above the first clamp and the second clamp, and the liner plate having through holes.

[0010] Furthermore, the liner is made of magnetic material.

[0011] This invention also provides a coefficient calibration method based on the residual stress calculation using the ring core method, used to obtain the coefficients of a workpiece of a certain material in the residual stress calculation. The workpiece includes shaft-type rotating parts. The calibration is performed using the aforementioned coefficient calibration platform and includes the following steps:

[0012] Step a, Test plate preparation: Select a test plate that has undergone complete stress relief heat treatment. The test plate material is the same as the material of the workpiece to be tested. The test plate is a cuboid, and the length L, width W, and height H of the test plate satisfy: L≥X / 30+40, W≥X / 30+40, H≥X / 40+10. The units of length L, width W, and height H are all mm, where X is the maximum allowable loading stress when applying tensile force to the test plate in step c, and the unit is MPa.

[0013] Step b, test plate clamping: Clamp the two short sides of the test plate in the first and second clamps of the coefficient calibration platform respectively, and the first and second clamps can clamp the short sides of the test plate completely. The main surface of the test plate formed by the long side and the wide side is facing upward.

[0014] Step c, Loading: Loading is performed using a loading power mechanism. The first clamp applies a certain tension to the test plate and stabilizes it at the specified load through a pressure sensor. The maximum loading stress in the test plate does not exceed X MPa.

[0015] Step d, Ring-core method measurement: Attach strain gauges to the main surface of the test plate, and use a milling ring groove device to cut a ring groove of a specified size on the main surface of the plate. Use a method similar to the ring-core method to measure the strain values ​​at different depths. The strain values ​​include at least those along the stress direction and perpendicular to the stress direction, and the maximum milling depth is not less than 4mm.

[0016] Step e, Formula coefficient calculation: Using the measurement results from step d, calculate the formula σ. y =A*Δε y +B*Δε x The coefficients A and B in the figure are the coefficients for calculating the residual stress of the workpiece under test of this material.

[0017] Furthermore, in step d, the strain gauge is a triaxial strain rosette, and the strain gauge direction includes the direction along the stress direction, perpendicular to the stress direction, and at a 45° angle to the stress direction.

[0018] Furthermore, in step d, strain values ​​are measured at at least four depth points.

[0019] Further, in step e, the strain value difference within the target depth range is obtained by direct subtraction or curve fitting, and coefficients A and B are calculated using the following formula. , Where σ is the uniformly distributed stress on the test plate during loading, determined by pressure sensor data and test plate dimensions, and ∆ε x ∆ε represents the difference in strain values ​​along the stress direction within the target depth range. y This represents the difference in strain values ​​along the vertical stress direction within the target depth range.

[0020] As described above, the coefficient calibration platform and method of the present invention have the following beneficial effects:

[0021] The coefficient calibration platform, equipped with a support base plate, loading device, and clamping device, is used to stably stretch a test plate to induce stable and uniform deformation, thereby obtaining the coefficients for residual stress calculation of a shaft-like rotating component made of a certain material. In use, the two short sides of the test plate are clamped in the first and second clamps of the coefficient calibration platform, respectively. Then, a loading power mechanism applies pressure, causing the first clamp to apply a certain tensile force to the test plate. A pressure sensor stabilizes the load at a specified level, ensuring that the stress in the test area of ​​the test plate is uniformly distributed uniaxial stress, resulting in uniform strain. Based on this, strain values ​​at different depths are measured using a method similar to the ring-core method. Coefficients A and B are then calculated using the measured strain values. By first determining coefficients A and B, the ring-core method can be extended to different materials, especially non-magnetic materials such as austenitic and nickel-based alloys. It can also be applied to different ring groove sizes, demonstrating universality and effectively improving the applicability and calculation accuracy of the ring-core method. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the residual stress calculation coefficient calibration platform of the present invention.

[0023] Figure 2 This is a fitted curve of strain along the stress direction in the residual stress calculation coefficient calibration method of the present invention.

[0024] Figure 3 This is a fitted curve of strain in the direction perpendicular to stress in the residual stress calculation coefficient calibration method of the present invention.

[0025] Component designation explanation:

[0026] 1-Support base plate

[0027] 11-Guide Post

[0028] 12-Slide

[0029] 2-Loading device

[0030] 21-Crossarm

[0031] 22-Pressure Sensor

[0032] 23-Compression Tie Rod

[0033] 24-Hydraulic Jack

[0034] 25-Monitor

[0035] 3-Clamping device

[0036] 31-First Clamp

[0037] 32-Second clamp

[0038] 33-Liner

[0039] 34-Through Hole

[0040] 4-Milling ring groove device Detailed Implementation

[0041] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification.

[0042] It should be understood that the structures, proportions, sizes, etc., depicted in the accompanying drawings of this specification are merely for illustrative purposes to aid those skilled in the art in understanding and reading the content disclosed herein, and are not intended to limit the conditions under which the invention can be implemented. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in proportions, or adjustments to the size, without affecting the effects and objectives achieved by the invention, should still fall within the scope of the technical content disclosed herein. Furthermore, the terms such as "upper," "lower," "left," "right," and "middle" used in this specification are merely for clarity and are not intended to limit the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention's implementation.

[0043] See Figure 1The present invention provides a coefficient calibration platform based on residual stress calculation using the ring core method, comprising a support base plate 1, a loading device 2, and a clamping device 3. The loading device 2 includes a crossbeam 21 that is linearly movable to the left and right on the support base plate 1, a loading power mechanism that drives the crossbeam 21 to move linearly to the left and right, a pressure rod 23 installed on the crossbeam 21, and a pressure sensor 22 for detecting the tension in the pressure rod 23. The clamping device 3 includes a first clamp 31 fixed to the support base plate 1 and a second clamp 32 installed on the loading rod, with the first clamp 31 and the second clamp 32 facing each other to the left and right.

[0044] The basic working principle of the coefficient calibration platform involved in this invention is as follows: The coefficient calibration platform is used to stably stretch a test plate to induce stable and uniform deformation, thereby obtaining the coefficients of a certain material shaft-type rotating component in residual stress calculation. Specifically, in use, a test plate is first selected according to regulations, and the two short sides of the test plate are clamped in the first clamp 31 and the second clamp 32 of the coefficient calibration platform, respectively. The dimensions of the first clamp 31 and the second clamp 32 are determined according to the dimensions of the test plate, and the width of the first clamp 31 and the second clamp 32 is required to be greater than or equal to the width of the test plate, that is, to be able to completely clamp both ends of the test plate, so that the stress in the test area of ​​the test plate is uniformly distributed uniaxial stress. After clamping, the main surface of the test plate formed by the long side and the wide side faces upward, and then pressure is applied using a loading power mechanism, so that the first clamp 31 applies a certain tensile force to the test plate, and stabilizes it at a specified load through the pressure sensor 22, thereby making the test plate have uniform stress and forming uniform strain.

[0045] See Figure 1 In this embodiment, as a preferred design, the support base plate 1 is also provided with a guide structure. The guide structure is used to guide the left and right linear movement of the crossarm 21. Specifically, the guide structure includes guide posts 11 arranged in the left and right direction. The crossarm 21 is slidably fitted onto the guide posts 11. Of course, other suitable structures can also be used for the guide structure.

[0046] See Figure 1 In this embodiment, pressure sensor 22 is mounted on crossarm 21, and the tail end of pressure rod 23 is mounted on pressure sensor 22. The axial direction of pressure rod 23 is along the left-right direction, and second clamp 32 is mounted on the end of pressure rod 23. Of course, the mounting method of pressure rod 23 and pressure sensor 22 can also be other forms, as long as it ensures that pressure rod 23 can apply tension and be accurately detected by pressure sensor 22. The loading power mechanism includes a hydraulic jack 24, which has an operating handle for easy loading. The hydraulic jack 24 is arranged along the left-right direction, and its piston rod is fixedly connected to crossarm 21. Furthermore, the loading device 2 also includes a display 25, which is connected to pressure sensor 22 and used to read pressure values ​​to facilitate determination that the applied tension can be stabilized at a specified value.

[0047] See Figure 1 In this embodiment, as a preferred design, the clamping device 3 further includes a liner 33 mounted on the supporting base plate 1. The liner 33 is located above the first chuck 31 and the second chuck 32, and a through hole 34 is provided on the liner 33. After the test plate is clamped in the first chuck 31 and the second chuck 32, it is located below the liner 33. The liner 33 is used to fix the milling ring groove device 4. The milling cutter in the milling ring groove device 4 extends into the test plate through the through hole 34. The size of the through hole 34 is preferably greater than 20mm × 20mm. The bottom of the existing milling ring groove device 4 is generally provided with a magnetic chuck. When using the ring core method for measurement, the rotating shaft being measured is generally made of magnetic alloy steel material, which is directly adsorbed onto the rotating shaft by the magnetic chuck. In this embodiment, preferably, the liner 33 is made of magnetic metal material. When working with test plates made of non-magnetic materials, the magnetic chuck at the bottom of the milling ring groove device 4 can be firmly attracted to the liner 33, which is convenient for installation and operation. Furthermore, the liner 33 can be composed of multiple sub-plates, and at least one sub-plate is installed in the slide groove 12 on the support base plate 1, which can move back and forth along the slide groove 12, thereby adjusting the position and area of ​​the liner 33, facilitating the installation and use of the milling ring groove device 4, and also facilitating the clamping and removal of the test plate.

[0048] This invention also provides a coefficient calibration method based on residual stress calculation using the ring core method, used to obtain the coefficients for residual stress calculation of a workpiece made of a certain material, including shaft-type rotating parts. Currently, the ring core method is mainly applied to shaft-type rotating parts; however, in some cases, it can also be applied to workpieces such as plates. This invention focuses on shaft-type rotating parts. The standard ring core method given in "JB / T 8888-2018 Test Method for Measuring Residual Stress of Steam Turbine and Steam Turbine Generator Rotor Forgings using the Ring Core Method" is related to the material and ring groove size of the shaft-type rotating part and is not applicable to all types of materials; the coefficients for residual stress calculation also differ. For shaft-type rotating parts made of other materials, the coefficients are unknown under different ring groove sizes and cannot be directly measured and calculated using the standard ring core method.

[0049] The coefficient calibration method of the present invention, using the above-mentioned coefficient calibration platform, includes the following steps:

[0050] Step a, Test Plate Preparation: Select a test plate that has undergone complete stress-relief heat treatment. The test plate material is the same as that of the rotating shaft to be tested. The test plate is a cuboid, and its length L, width W, and height H satisfy the following conditions: L≥X / 30+40, W≥X / 30+40, H≥X / 60+10. The units for length L, width W, and height H are all mm, where X is the maximum allowable loading stress value when applying tensile force to the test plate in step c, in MPa. The maximum loading stress is determined based on the material of the test plate and must be lower than the yield strength of the material. In this embodiment, the test plate material is 617 nickel-based alloy; the complete stress-relief heat treatment is: 980℃×3h, furnace cooling.

[0051] The ring-core method is generally used for rotating shafts with a diameter greater than 600mm. To approximate the measurement structure of the ring-core method, if the test plate is cylindrical, its size must be close to that of the rotating shaft being tested, resulting in a very large test plate that is inconvenient to operate. In the ring-core method, when a ring groove is cut on the outer circumference of the rotating shaft, the radius of the groove is much smaller than that of the shaft, approaching the effect of cutting a ring groove on a plane. In this invention, a cuboid plate is used as the test plate, and its size is determined according to the above method. The size of the test plate no longer affects the test results. At this point, the test plate most closely approximates the actual results and is convenient for experimental operation.

[0052] Step b, clamping the test plate: clamp the two short sides (i.e. the sides with width W) of the test plate in the first clamp 31 and the second clamp 32 of the coefficient calibration platform respectively, and the first clamp 31 and the second clamp 32 can clamp the short sides of the test plate completely, so as to ensure that the strain in the test plate is uniformly distributed uniaxial stress when the tensile force is applied later. The main surface of the test plate formed by the long side (i.e. the side with length L) and the wide side faces upward.

[0053] Step c, Loading: Loading is performed using a loading power mechanism. The first clamp 31 applies a certain tensile force to the test plate, and the load is stabilized at a specified level by the pressure sensor 22, wherein the maximum load stress in the test plate does not exceed X MPa. Specifically, the load is stabilized by the reading on the display 25.

[0054] Step d, Ring Core Method Measurement: Strain gauges are attached to the main surface of the test plate, and a ring groove of specified dimensions is cut into the main surface using the ring groove milling device 4. Strain values ​​at different depths are measured using a method similar to the standard ring core method. The strain values ​​include at least those along the stress direction and perpendicular to the stress direction, with a maximum milling depth of not less than 4 mm. The measurement method in this step is basically the same as the standard ring core method, except that the dimensions of the ring groove are determined as needed, and are not limited to the standard ring core method's outer diameter of 18 mm, inner diameter of 14 mm, and depth of 2-4 mm.

[0055] In this step, the strain gauge is preferably a triaxial strain rosette. The strain gauge direction includes the direction along the stress direction, perpendicular to the stress direction, and at a 45° angle to the stress direction. That is, the measured strain values ​​include those along the stress direction, perpendicular to the stress direction, and at a 45° angle to the stress direction. Preferably, strain values ​​are measured at at least four depth points with the same depth gradient. Specifically, see [link to documentation]. Figure 2 and Figure 3 In this embodiment, strain values ​​at 11 depth points were measured within the range of 0 to 5 mm, with a depth interval gradient of 0.5 mm.

[0056] Step e, Formula coefficient calculation: Using the measurement results from step d, calculate the formula σ. y =A*Δε y +B*Δε x The coefficients A and B in the formula are the coefficients for calculating the residual stress of the rotating shaft components of this material.

[0057] Specifically, the strain difference within the target depth range can be obtained through direct subtraction or curve fitting. In this embodiment, curve fitting is used. The fitted curves of the measured strain values ​​along the stress direction and the strain values ​​perpendicular to the stress direction are respectively shown in [reference 1]. Figure 2 and Figure 3 Then, the coefficients A and B are calculated using the following formula. , Where σ is the uniformly distributed stress on the test plate during loading, determined by data from pressure sensor 22 and the dimensions of the test plate, and ∆ε x ∆ε represents the difference in strain values ​​along the stress direction within the target depth range. y This refers to the difference in strain values ​​along the vertical stress direction within the target depth range. For example, in this embodiment, when the target depth is 2~4mm, see [reference needed]. Figure 2 and Figure 3 Through curve fitting calculations, we obtained the following: at a depth of 2 mm, the strain value along the stress direction is approximately -1063 με, and the strain value perpendicular to the stress direction is -33 με; at a depth of 4 mm, the strain value along the stress direction is approximately -1548 με, and the strain value perpendicular to the stress direction is -49 με. Therefore, ∆ε... x =(-1063)-(-1548)=485με, Δε y =(-33)-(-49)=16με. The final calculated coefficients within the target depth range of 2~4mm are: A=0.372, B=-0.012. Therefore, the formula for calculating the residual stress of shaft-type rotating parts made of 617 nickel-based alloy material under a specified annular groove size is σ. y =0.372*Δε y -0.012*Δε x , where σt The unit is MPa, Δε y and Δε x The unit is με.

[0058] After calculating coefficients A and B using the above method, the standard ring-core method can be extended to different materials. For example, when measuring rotating shafts made of 617 nickel-based alloy, the ring-core method can be used, but the ring groove size is taken from the ring groove size in step d above. Then, the measurement can be performed using the above formula σ. y =0.372*Δε y -0.012*Δε x The residual stress can be obtained through calculation.

[0059] The coefficient calibration platform and method of this invention, by first determining coefficients A and B, can extend the application of the ring core method to different materials, especially to non-magnetic materials such as austenitic and nickel-based alloys. It can also be applied to different ring groove sizes, has universality, and can effectively improve the applicability and calculation accuracy of the ring core method.

[0060] In summary, this invention effectively overcomes the various shortcomings of the prior art and has high industrial application value.

[0061] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A coefficient calibration method based on the ring-core method for calculating residual stress, used to obtain the coefficients of a workpiece of a certain material in the calculation of residual stress, wherein the workpiece includes a shaft-like rotating component, characterized in that: The coefficient calibration is performed using a coefficient calibration platform, which includes a support base plate (1), a loading device (2), and a clamping device (3). The loading device (2) includes a crossbeam (21) that can be linearly moved left and right on the support base plate (1), a loading power mechanism that drives the crossbeam (21) to move linearly left and right, a pressure rod (23) installed on the crossbeam (21), and a pressure sensor (22) for detecting the tension in the pressure rod (23). The clamping device (3) includes a first clamp (31) fixed to the support base plate (1) and a second clamp (32) installed on the loading rod (23). The first clamp (31) and the second clamp (32) are opposite each other left and right. The coefficient calibration method includes the following steps: Step a, Test plate preparation: Select a test plate that has undergone complete stress relief heat treatment. The test plate material is the same as the material of the workpiece to be tested. The test plate is a cuboid, and the length L, width W, and height H of the test plate satisfy: L≥X / 30+40, W≥X / 30+40, H≥X / 40+10. The units of length L, width W, and height H are all mm, where X is the maximum allowable loading stress when applying tensile force to the test plate in step c, and the unit is MPa. Step b, test plate clamping: clamp the two short sides of the test plate in the first clamp (31) and the second clamp (32) of the coefficient calibration platform respectively, and the first clamp (31) and the second clamp (32) can clamp all the short sides of the test plate, with the main plate surface formed by the long side and the wide side of the test plate facing upwards. Step c, Loading: Loading is performed using a loading power mechanism. The first clamp (31) applies a certain tension to the test plate and stabilizes it at the specified load through the pressure sensor (22), wherein the maximum loading stress in the test plate does not exceed XMPa; Step d, Ring-core method measurement: Strain gauges are attached to the main surface of the test plate, and a ring groove of a specified size is cut on the main surface using a milling ring groove device (4). The milling ring groove device (4) is fixed on the liner (33), and the milling cutter extends into the test plate through the through hole (34). The size of the ring groove is determined as needed. The strain values ​​at different depths are measured using a method similar to the ring-core method, and the strain values ​​at at least 4 depth points are measured. The strain values ​​include at least those along the stress direction and perpendicular to the stress direction, and the maximum milling depth is not less than 4m. m; The liner (33) is made of magnetic material, and the bottom of the milling ring groove device (4) has a magnetic chuck. The magnetic chuck is attached to the liner (33) to fix the milling ring groove device (4) to the liner (33). The liner (33) is made of multiple sub-plates, and at least one sub-plate is installed in the slide groove (12) on the support base plate (1) and can move back and forth along the slide groove (12) to adjust the position and area of ​​the liner (33) so that the milling cutter in the milling ring groove device (4) extends from the through hole into the test plate; Step e, Formula coefficient calculation: Using the measurement results from step d, calculate the formula σ. y =A*Δε y +B*Δε x The coefficients A and B in the formula are the coefficients for calculating the residual stress of the workpiece under test for this material. The strain value difference within the target depth range is obtained by direct subtraction or curve fitting, and the coefficients A and B are calculated according to the following formula. , Where σ is the uniformly distributed stress on the test plate during loading, determined by the data from the pressure sensor (22) and the dimensions of the test plate, and Δε x Δε represents the difference in strain values ​​along the stress direction within the target depth range. y This represents the difference in strain values ​​along the vertical stress direction within the target depth range.

2. The coefficient calibration method according to claim 1, characterized in that: In step d, the strain gauge is a triaxial strain rosette, and the strain gauge direction includes the direction along the stress direction, perpendicular to the stress direction, and at a 45° angle to the stress direction.

3. The coefficient calibration method according to claim 1, characterized in that: The supporting base plate (1) is also provided with a guide structure, which is used to guide the left and right linear movement of the crossarm (21).

4. The coefficient calibration method according to claim 3, characterized in that: The guide structure includes guide posts (11) arranged in the left-right direction, and the crossbeam (21) is slidably fitted onto the guide posts (11).

5. The coefficient calibration method according to claim 1, characterized in that: The loading power mechanism includes a hydraulic jack (24), which is arranged in the left-right direction and whose piston rod is fixedly connected to the crossbeam (21).

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