Method for measuring stress
Through the combination of numerical methods and strain gauge, the maximum stress of the centrifugal compressor impeller during resonance is accurately measured, which solves the problem of measurement difficulties in the prior art, improves measurement accuracy and reduces costs.
Patent Information
- Application Number
- CN202510131050.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-02-05
- Publication Date
- 2025-05-06
AI Technical Summary
It is difficult to accurately measure the maximum stress of centrifugal compressor impeller during resonance, especially when the curvature of the stress concentration area is large and the stress changes dramatically.
By selecting failed parts and unfailed parts with cracks, the target test position is determined, and the test modality is obtained numerical methods, and the stress at the target test position is calculated. At the same time, select the measurement position that avoids the stress concentration area, use the strain gauge to measure, and determine the linear coefficient by the ratio of the calculated value to the measured value, and calculate the stress at the target test position.
Improves the accuracy of stress measurement, reduces test costs, and reduces calculation errors.
Smart Images
Figure CN119935377A_ABST
Abstract
Description
Technical Field
[0001] The present disclosure relates to a method for measuring stress. Background Art
[0002] During the operation of centrifugal compressors, vibration problems are inevitable. Impellers (especially open impellers) often crack due to vibration, which leads to blade breakage. The chamfered transition position at the root of the blade (i.e., the transition position between the blade and the hub) is a stress concentration area in structure and is prone to resonance, so cracks usually occur at this position. In order to analyze the cause of blade breakage and improve the design of the impeller, it is necessary to determine the resonant stress level of the crack position under working conditions, that is, to obtain the maximum stress when the impeller resonates.
[0003] It is known that the magnitude of stress can be directly measured by pasting strain gauges at the above-mentioned transition positions. However, the stress changes sharply at the transition position, and the strain gauge can only measure the average level of stress in the area it covers, resulting in the maximum stress being difficult to measure. In addition, the curvature at the transition position is large, making it difficult to accurately paste the strain gauge at the predetermined position and difficult to firmly hold it at the predetermined position. Furthermore, the measurement needs to be repeated many times, and then the maximum value of the multiple measured values is taken as the test result, resulting in high test costs.
[0004] Another method is to calculate the stress magnitude at the transition position by simulation method (e.g., finite element method). However, this method has great difficulty in simulating the actual working load, resulting in large calculation errors. Although the calculation results can be calibrated by the first method mentioned above (i.e., the method using strain gauges), if the first method has the problems mentioned above, the calibrated results still have certain errors. Summary of the invention
[0005] In order to solve the above technical problems, the present disclosure provides a method for measuring stress, which comprises the following steps:
[0006] S1: selecting a failed part with cracks and a corresponding non-failed part without cracks, taking the non-failed part as a test part, and determining a corresponding position on the test part as a target test position according to the crack position on the failed part;
[0007] S2: obtaining different modes of the test part at different natural frequencies by a numerical method, and selecting a test mode from each of the modes according to the stress concentration position in each of the modes, wherein at least one stress concentration position under the test mode coincides with the target test position;
[0008] S3: Obtaining a calculated value A of the stress at the target test position in a direction perpendicular to the propagation direction of the crack according to the test modal calculation;
[0009] S4: selecting a measurement position on the test part according to the test mode, wherein the measurement position avoids any stress concentration position under the test mode;
[0010] S5: Obtaining a calculated value B of the stress at the measuring position in a direction perpendicular to the propagation direction of the crack according to the test modal calculation;
[0011] S6: obtaining, based on a strain gauge test, a measured value b of the stress at the measuring position in a direction perpendicular to the propagation direction of the crack at the natural frequency of the test mode; and
[0012] S7: Calculate a measured value a of the stress at the target test position in a direction perpendicular to the propagation direction of the crack according to the calculated value A, the calculated value B and the measured value b.
[0013] In the present disclosure, by fixing the strain gauge to the measurement position, the strain gauge can avoid the stress concentration area where the stress changes sharply, thereby improving the accuracy of the present method. In addition, compared with the target test position, the curvature of the measurement position is usually smaller, so that the strain gauge can be accurately and firmly fixed to the target test position, thereby further improving the accuracy of the present method. Furthermore, when there are multiple target test positions and the crack propagation direction is the same, since the measurement position does not need to change with the change of the target test position, the measurement values at all different target test positions can be obtained in one test, thereby reducing the cost of the present method.
[0014] Further, in step S2, the test part has a plurality of alternative test modes, at least one stress concentration position under each of the alternative test modes coincides with the target test position, and the test mode is the mode with the lowest order among the plurality of alternative test modes.
[0015] In the present disclosure, by selecting the candidate test mode with the lowest order as the test mode, since cracks are usually generated under low-frequency resonance, a suitable test mode can be quickly selected, thereby reducing the cost of the method.
[0016] Further, step S4 includes the following steps:
[0017] S41: selecting a candidate measurement area for determining the measurement position on the test part according to the test mode, wherein the candidate measurement area avoids any stress concentration position under the test mode;
[0018] S42: Selecting a plurality of inspection positions in the candidate measurement area;
[0019] S43: Obtaining a calculated value C of the stress at the inspection position in a direction perpendicular to the propagation direction of the crack according to the test modal calculation;
[0020] S44: determining whether the difference between any two of the calculated values C is less than or equal to a first threshold, and if so, taking the candidate measurement area as the measurement area; and
[0021] S45: Select a position in the measurement area as the measurement position.
[0022] In the present disclosure, by judging whether the difference between any two calculated values C is less than or equal to the first threshold, it is possible to ensure that the stress variation in the measurement area is sufficiently gentle, thereby improving the accuracy of the method.
[0023] Further, in step S42, the inspection position is located at the edge of the candidate measurement area.
[0024] In the present disclosure, by selecting the inspection position from the edge of the alternative measurement area, since the stress level at the edge of the alternative measurement area is usually greatly different from the average stress level of the alternative measurement area, the difference between the calculated values C can more effectively reflect the distribution of stress, thereby improving the accuracy of the present method.
[0025] Further, in step S42, the candidate measurement area is a rectangular area, and at least one of the plurality of inspection positions is located at a corner of the rectangular area.
[0026] In the present disclosure, when the candidate measurement area is a rectangular area, by selecting the inspection position from the corner of the rectangular area, the difference between the calculated values C can better reflect the stress distribution, thereby improving the accuracy of the method.
[0027] Further, step S6 includes the following steps:
[0028] S61: Fix the strain gauge to the test part so that the strain gauge covers the measurement position and the entire strain gauge is located within the range of the measurement area.
[0029] In the present disclosure, by making the strain gauge cover the measurement position and making the entire strain gauge located within the range of the measurement area, the strain gauge can more accurately measure the stress at the measurement position, thereby improving the accuracy of the method.
[0030] Further, step S7 includes the following steps:
[0031] S71: Determine a linear coefficient k according to the ratio of the calculated value B to the measured value b; and
[0032] S73: Obtain the measured value a according to the calculated value A and the linear coefficient k, so that the ratio of the calculated value A to the measured value a is equal to the linear coefficient k.
[0033] In the present disclosure, by obtaining the linear coefficient k, since the calculated value A and the measured value a can be associated with the calculated value B and the measured value b through the linear coefficient k, the measured value a can be simply and accurately calculated according to the linear coefficient k, making the method easy to implement while having high accuracy.
[0034] Further, in step S71, the linear coefficient k is determined according to an average value of a plurality of ratios obtained from a plurality of the calculated values B and a plurality of the measured values b at a plurality of the measuring positions.
[0035] In the present disclosure, by taking the average value of multiple ratios as the linear coefficient k, the measurement error can be reduced in the process of data processing of multiple ratios, thereby improving the accuracy of the method.
[0036] Further, step S7 includes the following steps:
[0037] Step S72 between step S71 and step S73: determine whether the difference between any two of the ratios is less than or equal to a second threshold; if so, allow step S73 to be executed.
[0038] In the present disclosure, by judging whether the difference between any two ratios is less than or equal to the second threshold, it is possible to ensure that the linear coefficient k is reliable, thereby improving the accuracy of the method.
[0039] Further, in step S1, the failed part and the test part are impellers. BRIEF DESCRIPTION OF THE DRAWINGS
[0040] The drawings described herein are used to provide a further understanding of the present disclosure and constitute a part of the present disclosure. The exemplary embodiments of the present disclosure and their descriptions are used to explain the present disclosure and do not constitute an improper limitation on the present disclosure. In the drawings:
[0041] Figure 1 is a perspective view of a test part for a method of measuring stress according to an embodiment of the present disclosure;
[0042] Figure 2 yes Figure 1 Stress cloud diagram of the partial structure of the test part;
[0043] Figures 3 to 6is a flow chart of a method for measuring stress according to an embodiment of the present disclosure.
[0044] Description of Figure Numbers:
[0045] 100. Test parts;
[0046] T, target test location;
[0047] M, measurement area;
[0048] P. Measurement location. DETAILED DESCRIPTION
[0049] The following will be combined with the drawings in the embodiments of the present disclosure to clearly and completely describe the technical solutions in the embodiments of the present disclosure. Obviously, the described embodiments are only part of the embodiments of the present disclosure, rather than all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present disclosure and its application or use. Based on the embodiments in the present disclosure, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present disclosure.
[0050] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present disclosure. As used herein, unless the context clearly indicates otherwise, the singular form is intended to include the plural form as well.
[0051] Refer to the following Figures 1 to 6 An embodiment according to the present disclosure is introduced.
[0052] Figure 1 is a perspective view of a test part for a method of measuring stress according to an embodiment of the present disclosure. Figure 2 yes Figure 1 Stress cloud diagram of the partial structure of the test part. Figures 3 to 6 is a flow chart of a method for measuring stress according to an embodiment of the present disclosure.
[0053] Reference Figures 1 to 3 The present disclosure provides a method for measuring stress, the method comprising the following steps:
[0054] S1: Select a failed part with cracks and a corresponding non-failed part without cracks, use the non-failed part as a test part 100, and determine the corresponding position on the test part 100 as a target test position T according to the crack position on the failed part;
[0055] S2: obtaining different modes of the test part 100 at different natural frequencies by a numerical method, selecting a test mode from each mode according to the stress concentration position in each mode, and at least one stress concentration position under the test mode coincides with the target test position T;
[0056] S3: Obtaining a calculated value A of the stress at the target test position T in a direction perpendicular to the crack propagation direction according to the test modal calculation;
[0057] S4: selecting a measurement position P on the test part 100 according to the test mode, wherein the measurement position P avoids any stress concentration position under the test mode;
[0058] S5: Obtain a calculated value B of the stress at the measuring position P in a direction perpendicular to the crack propagation direction according to the test modal calculation;
[0059] S6: at the natural frequency of the test mode, obtaining a measured value b of the stress at the measuring position P in a direction perpendicular to the propagation direction of the crack based on a strain gauge (not shown); and
[0060] S7: Calculate the measured value a of the stress at the target test position T in a direction perpendicular to the crack propagation direction according to the calculated value A, the calculated value B and the measured value b.
[0061] Here, the "test part" may be the same as the "failed part" before it failed. In other words, the "test part" may be in the state of the "failed part" before it failed. For example, the "failed part" and the "test part" may be parts from the same production batch.
[0062] As an example, in step S1, the failed part and the test part 100 may be an impeller, for example, an impeller in a centrifugal compressor. In this case, in step S6, in order to make the test part 100 vibrate at a certain frequency, the test part 100 may be rotated at the frequency. Of course, in other embodiments, the failed part and the test part 100 are not limited to being an impeller, and the method of applying vibration is not limited to rotating the test part 100.
[0063] As an example, in step S2 , the numerical method may include a finite element method.
[0064] In the present disclosure, by fixing the strain gauge to the measurement position P, the strain gauge can avoid the stress concentration area where the stress changes sharply, thereby improving the accuracy of the present method. In addition, compared with the target test position T, the curvature of the measurement position P is usually smaller, so that the strain gauge can be accurately and firmly fixed to the target test position T, thereby further improving the accuracy of the present method. Furthermore, when there are multiple target test positions T (which can correspond to cracks on the same failed part or cracks on different failed parts) and the cracks have the same propagation direction, since the measurement position P does not need to change with the change of the target test position T, the measurement values at all different target test positions T can be obtained in one test, thereby reducing the cost of the present method.
[0065] Reference Figures 1 to 3 In step S2, the test part 100 has multiple alternative test modes, at least one stress concentration position under each alternative test mode coincides with the target test position T, and the test mode is the lowest order mode among the multiple alternative test modes.
[0066] Here, “the lowest-order mode” means that the natural frequency of the mode is the smallest among multiple candidate test modes.
[0067] In the present disclosure, by selecting the candidate test mode with the lowest order as the test mode, since cracks are usually generated under low-frequency resonance, a suitable test mode can be quickly selected, thereby reducing the cost of the method.
[0068] Reference Figures 1 to 4 , step S4 comprises the following steps:
[0069] S41: selecting a candidate measurement area for determining a measurement position P on the test part 100 according to the test mode, wherein the candidate measurement area avoids any stress concentration position under the test mode;
[0070] S42: Selecting a plurality of inspection positions in the candidate measurement area;
[0071] S43: Obtaining a calculated value C of the stress at the inspection position in a direction perpendicular to the crack propagation direction according to the test modal calculation;
[0072] S44: determining whether the difference between any two calculated values C is less than or equal to a first threshold, and if so, taking the candidate measurement area as the measurement area M; and
[0073] S45: Select a position in the measurement area M as the measurement position P.
[0074] As an example, in step S44, the difference between any two calculated values C may be a relative difference. For example, the first threshold may be 10%, preferably 5%. In other examples, the difference between any two calculated values C may also be an absolute difference.
[0075] As an example, in step S44, if the judgment is no, return to step S41.
[0076] As an example, in step S45 , the measurement position P may be located inside the measurement region M, for example, may be located at the geometric center of the measurement region M.
[0077] In the present disclosure, by judging whether the difference between any two calculated values C is less than or equal to the first threshold, it is possible to ensure that the stress variation in the measuring area M is sufficiently gentle, thereby improving the accuracy of the method.
[0078] Reference Figure 4 , in step S42, the verification position is located at the edge of the candidate measurement area.
[0079] In other embodiments, the inspection position is not limited to being located at the edge of the candidate measurement region, and may be located inside the candidate measurement region, for example.
[0080] In the present disclosure, by selecting the inspection position from the edge of the alternative measurement area, since the stress level at the edge of the alternative measurement area is usually greatly different from the average stress level of the alternative measurement area, the difference between the calculated values C can more effectively reflect the distribution of stress, thereby improving the accuracy of the present method.
[0081] Reference Figure 4 In step S42, the candidate measurement area is a rectangular area, and at least one of the multiple inspection positions is located at a corner of the rectangular area.
[0082] As an example, in step S42 , the number of the inspection positions may be four, and the four inspection positions may be located at four corners of the rectangular area, respectively.
[0083] In other embodiments, the candidate measurement area is not limited to being a rectangle, and may be a circle, for example.
[0084] In the present disclosure, when the candidate measurement area is a rectangular area, by selecting the inspection position from the corner of the rectangular area, the difference between the calculated values C can better reflect the stress distribution, thereby improving the accuracy of the method.
[0085] Reference Figures 1 to 3 as well as Figure 5 , step S6 comprises the following steps:
[0086] S61: Fix the strain gauge to the test part 100 so that the strain gauge covers the measurement position P and the entire strain gauge is located within the measurement area M.
[0087] As an example, in step S61 , the strain gauge may be bonded to the test part 100 by, for example, an adhesive, and the shape and size of the strain gauge may be the same as the shape and size of the measurement area M. In other examples, the area of the measurement area M may be larger than the area of the strain gauge.
[0088] In the present disclosure, by making the strain gauge cover the measurement position P and making the entire strain gauge located within the measurement area M, the strain gauge can more accurately measure the stress at the measurement position P, thereby improving the accuracy of the present method.
[0089] Reference Figure 3 and Figure 6 , step S7 comprises the following steps:
[0090] S71: Determine a linear coefficient k according to a ratio of the calculated value B and the measured value b; and
[0091] S73: Obtain the measured value a according to the calculated value A and the linear coefficient k, so that the ratio of the calculated value A to the measured value a is equal to the linear coefficient k.
[0092] As an example, in step S73 , the calculated value A, the linear coefficient k, and the measured value a may satisfy A / a=k.
[0093] In the present disclosure, by obtaining the linear coefficient k, since the calculated value A and the measured value a can be associated with the calculated value B and the measured value b through the linear coefficient k, the measured value a can be simply and accurately calculated according to the linear coefficient k, making the method easy to implement while having high accuracy.
[0094] Reference Figure 1 , Figure 2 as well as Figure 6 In step S71, the linear coefficient k is determined based on the average value of multiple ratios obtained from multiple calculated values B and multiple measured values b at multiple measurement positions P.
[0095] As an example, in step S4, multiple measurement positions P can be selected on the test part 100 according to the test mode, for example, three measurement positions P can be selected. In step S5, the calculated value B of each measurement position P can be obtained, for example, the calculated values B of the three measurement positions P can be B1, B2, and B3 respectively. In step S6, the measured value b of each measurement position P is obtained, for example, the measured values b of the three measurement positions P can be b1, b2, and b3 respectively. In step S71, the linear coefficient k can be obtained, for example, the linear coefficient k can satisfy k=(B1 / b1+B2 / b2+B3 / b3) / 3.
[0096] As an example, when the test part 100 is in a first-order mode with a natural frequency of 430 Hz, specific values of the calculated value A, the calculated value B, and the measured value b may be as shown in Table 1.
[0097] Table 1
[0098] A 280MPa B1 170MPa B2 65MPa B3 50MPa b1 50MPa b2 20MPa b3 15MPa
[0099] In other embodiments, the linear coefficient k is not limited to being determined based on an average value of multiple ratios, and may be determined, for example, based on a minimum value, a maximum value, or a median value of multiple ratios.
[0100] In the present disclosure, by taking the average value of multiple ratios as the linear coefficient k, the measurement error can be reduced in the process of data processing of multiple ratios, thereby improving the accuracy of the method.
[0101] Reference Figure 3 and Figure 6 , step S7 comprises the following steps:
[0102] Step S72 between step S71 and step S73: determine whether the difference between any two ratios is less than or equal to a second threshold, and if so, allow step S73 to be executed.
[0103] As an example, in step S72, the difference between any two ratios may be a relative difference. For example, the second threshold may be 10%, preferably 5%. In other examples, the difference between any two ratios may also be an absolute difference.
[0104] As an example, in step S72, if the judgment is no, then return to step S6. In other examples, if the judgment is no, then return to step S4.
[0105] In the present disclosure, by judging whether the difference between any two ratios is less than or equal to the second threshold, it is possible to ensure that the linear coefficient k is reliable, thereby improving the accuracy of the method.
[0106] It should be understood that for the purpose of brevity and ease of understanding, each step of the method of the present disclosure is numbered, but unless explicitly indicated, these numbers are not used to limit the order between the steps and do not exclude the situation where multiple steps are performed simultaneously.
[0107] The above are only preferred embodiments of the present disclosure. It should be pointed out that, for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present disclosure. These improvements and modifications should also be regarded as the protection scope of the present disclosure.
Claims
1. A method for measuring stress, characterized in that The following steps are involved: S1: selecting a failed part with a crack and a corresponding non-failed part without a crack, taking the non-failed part as a test part (100), and determining a corresponding position on the test part (100) as a target test position (T) according to a crack position on the failed part; S2: obtaining different modes of the test part (100) at different natural frequencies by a numerical method, and selecting a test mode from each of the modes according to the stress concentration position in each of the modes, wherein at least one stress concentration position in the test mode coincides with the target test position (T); S3: Obtaining a calculated value A of the stress at the target test position (T) in a direction perpendicular to the propagation direction of the crack according to the test modal calculation; S4: selecting a measurement position (P) on the test part (100) according to the test mode, wherein the measurement position (P) avoids any stress concentration position under the test mode; S5: Obtaining a calculated value B of the stress at the measuring position (P) in a direction perpendicular to the propagation direction of the crack according to the test mode calculation; S6: obtaining, based on a strain gauge test, a measured value b of the stress at the measuring position (P) in a direction perpendicular to the propagation direction of the crack at the natural frequency of the test mode; and S7: Calculate the measured value a of the stress at the target test position (T) in a direction perpendicular to the propagation direction of the crack according to the calculated value A, the calculated value B and the measured value b.
2. The method according to claim 1, characterized in that In step S2, the test part (100) has a plurality of candidate test modes, at least one stress concentration position under each of the candidate test modes coincides with the target test position (T), and the test mode is the mode with the lowest order among the plurality of candidate test modes.
3. The method according to claim 1, characterized in that Step S4 includes the following steps: S41: selecting a candidate measurement area for determining the measurement position (P) on the test part (100) according to the test mode, wherein the candidate measurement area avoids any stress concentration position under the test mode; S42: Selecting a plurality of inspection positions in the candidate measurement area; S43: Obtaining a calculated value C of the stress at the inspection position in a direction perpendicular to the propagation direction of the crack according to the test modal calculation; S44: Determine whether the difference between any two of the calculated values C is less than or equal to a first threshold, and if so, use the candidate measurement area as the measurement area (M); and S45: Select a position in the measurement area (M) as the measurement position (P).
4. The method according to claim 3, characterized in that In step S42, the inspection position is located at the edge of the candidate measurement area.
5. The method according to claim 4, characterized in that In step S42, the candidate measurement area is a rectangular area, and at least one of the plurality of inspection positions is located at a corner of the rectangular area.
6. The method according to claim 3, characterized in that Step S6 includes the following steps: S61: Fixing the strain gauge to the test part (100) so that the strain gauge covers the measurement position (P) and the entire strain gauge is located within the measurement area (M).
7. The method according to claim 1, characterized in that Step S7 includes the following steps: S71: Determine a linear coefficient k according to the ratio of the calculated value B to the measured value b; and S73: Obtain the measured value a according to the calculated value A and the linear coefficient k, so that the ratio of the calculated value A to the measured value a is equal to the linear coefficient k.
8. The method according to claim 7, characterized in that In step S71, the linear coefficient k is determined based on the average value of a plurality of ratios obtained from a plurality of the calculated values B and a plurality of the measured values b at a plurality of the measurement positions (P).
9. The method according to claim 8, characterized in that Step S7 includes the following steps: Step S72 between step S71 and step S73: determine whether the difference between any two of the ratios is less than or equal to a second threshold, and if so, allow step S73 to be executed.
10. The method according to claim 1, characterized in that In step S1, the failed part and the test part (100) are impellers.