A method and system for predicting fatigue life of a shaft coupling bolt of a Francis turbine generator set

Abstract

The application discloses a kind of shaft flow type hydroelectric generator unit coupling bolt fatigue life prediction method and system, belong to the technical field of hydroelectric generator bolt fatigue assessment.This application introduces secondary iteration calculation in the calculation of primary coupling bolt fatigue life, and according to the K value of secondary iteration running time and the calculation time of before and after two times, weighted operation is carried out, so as to obtain the actual bolt fatigue life, the error of initial calculation prediction can be corrected, to reduce the final calculation prediction error, compared with the bolt fatigue life of traditional stress spectrum calculation, the calculation prediction result of the application can significantly improve the reliability and accuracy of coupling bolt fatigue life prediction result.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of hydroelectric generator bolt fatigue evaluation, and particularly relates to a shaft-flow type hydroelectric generator set shaft coupling bolt fatigue life prediction method and system. BACKGROUND

[0002] The connecting component used by the shaft-flow type hydroelectric generator set includes a shaft coupling bolt. Since the hydroelectric generator rotates at high speed and is frequently started and stopped, the shaft coupling bolt used for connection is prone to fatigue cracks. The fatigue cracks gradually develop in depth with the action time, causing crack propagation and degradation of the mechanical properties of the shaft coupling bolt. When the length of the fatigue crack is greater than the critical crack size, fatigue instability occurs without any forewarning if the cross-section effective bearing capacity is less than the cyclic load, and finally leads to complete fracture.

[0003] In the field, in order to ensure the safe working performance of the shaft coupling bolt, fatigue prediction needs to be performed on the shaft coupling bolt, and the prediction of the fatigue crack propagation life of the shaft coupling bolt is one of important means of the fatigue prediction of the shaft coupling bolt. In the prior art, the prediction of the fatigue crack propagation life of the shaft coupling bolt generally adopts stress spectrum calculation to predict the fatigue crack propagation life, which belongs to standardized calculation prediction. However, the actual operation conditions of the shaft-flow type hydroelectric generator set are complex and different, which leads to poor reliability and accuracy of the prediction result of the prediction of the fatigue crack propagation life of the shaft coupling bolt by using stress spectrum calculation. SUMMARY

[0004] In order to solve the defects existing in the prior art, the purpose of the present application is to provide a shaft-flow type hydroelectric generator set shaft coupling bolt fatigue life prediction method and system, which can significantly improve the reliability and accuracy of the shaft coupling bolt fatigue life prediction result.

[0005] The present application is realized by the following technical solutions:

[0006] A shaft-flow type hydroelectric generator set shaft coupling bolt fatigue life prediction method, comprising:

[0007] S1: constructing a shaft coupling bolt fatigue prediction mathematical model;

[0008] S2: obtaining a first fatigue crack size of the shaft coupling bolt and inputting the first fatigue crack size into the shaft coupling bolt fatigue prediction mathematical model constructed in S1 to obtain a first fatigue propagation life N1 of the shaft coupling bolt;

[0009] S3: after a continuous operation time T, obtaining a second fatigue crack size of the shaft coupling bolt and inputting the second fatigue crack size into the shaft coupling bolt fatigue prediction mathematical model constructed in S1 to obtain a second fatigue propagation life N2 of the shaft coupling bolt;

[0010] S4: calculating a K value according to the following formula:

[0011]

[0012] If K > 1, then N1 and N2 are weighted separately and then summed to obtain the actual bolt fatigue expansion life of the coupling bolt; if K ≤ 1, then N2 is represented as the actual bolt fatigue expansion life.

[0013] Preferably, in S1, the mathematical model for predicting fatigue of the coupling bolts is:

[0014]

[0015] In the formula, α0 is the measured value of the fatigue crack size of the coupling bolt, α L The critical crack size of the coupling bolt. The crack propagation rate is the value of the coupling bolt.

[0016] More preferably, the critical crack size α of the coupling bolt L The calculation formula is as follows:

[0017]

[0018] In the formula, K IC Let f be the fracture toughness of the coupling bolt material, f be the shape factor, and σ be the tensile strength. x This represents the maximum value of the cyclic stress.

[0019] More preferably, the crack propagation rate of the coupling bolt. The calculation formula is as follows:

[0020]

[0021] In the formula, α is the crack depth or width, C and m are material-related parameters, ΔK is the range of stress intensity factor, and N is the number of stress cycles.

[0022] Preferably, in S3, N1 / 10 ≤ T ≤ N1 / 2.

[0023] Preferably, in S4, the step of weighting N1 and N2 specifically involves:

[0024] S4.1: Determine the initial weighting coefficients for N1 and N2;

[0025] S4.2: Create a mapping table of running time T with weighted coefficients of N1 and N2;

[0026] S4.3: Weight N1 and N2 according to the weighted coefficient mapping table.

[0027] More preferably, in S4.1, if 1 < K ≤ 1.1, then the initial weighting coefficients of N1 and N2 are both determined to be 50%; if 1.1 < K ≤ 1.2, then the initial weighting coefficient of N1 is determined to be 45% and the initial weighting coefficient of N2 is determined to be 55%; if 1.2 < K, then the initial weighting coefficient of N1 is determined to be 40% and the initial weighting coefficient of N2 is determined to be 60%.

[0028] A fatigue life prediction system for coupling bolts of an axial-flow hydro-generator unit includes:

[0029] The module for constructing a mathematical model for predicting fatigue of coupling bolts is used to build such a model.

[0030] The fatigue crack acquisition module for coupling bolts acquires the fatigue crack size of the coupling bolts.

[0031] The fatigue propagation life acquisition module for coupling bolts inputs the fatigue crack size of the coupling bolts into the mathematical model for fatigue prediction of coupling bolts to obtain the fatigue propagation life of the coupling bolts.

[0032] The runtime timing module retrieves the runtime.

[0033] The K-value calculation module calculates the K-value.

[0034] The bolt fatigue extension life determination module determines the actual bolt fatigue extension life based on the K value.

[0035] Compared with the prior art, the present invention has the following beneficial technical effects:

[0036] The fatigue life prediction method for coupling bolts of axial-flow hydro-generator units disclosed in this invention introduces a second-order iterative calculation in the calculation of the fatigue extension life of the coupling bolts. The method performs a weighted calculation based on the running time of the second iteration and the K value of the two calculation times to obtain the actual fatigue extension life of the bolts. This method can correct the error of the initial calculation prediction and reduce the error of the final calculation prediction. Compared with the traditional stress spectrum calculation of bolt fatigue extension life, the calculation prediction results of this invention can significantly improve the reliability and accuracy of the fatigue life prediction results of coupling bolts.

[0037] The fatigue life prediction system for coupling bolts of axial-flow hydro-generator units disclosed in this invention is simple to construct, highly automated, and widely applicable. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the method flow of the present invention. Detailed Implementation

[0039] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. These descriptions are intended to explain the invention and not to limit it.

[0040] like Figure 1 As shown, the fatigue life prediction method for coupling bolts of axial-flow hydro-generator units of the present invention includes the following steps:

[0041] I. Constructing a mathematical model for fatigue prediction of coupling bolts; The mathematical model for fatigue prediction of coupling bolts is based on the Paris formula, and the formula for the mathematical model for fatigue prediction of coupling bolts is as follows: In the formula, α0 is the measured value of the fatigue crack size of the coupling bolt, α L The critical crack size of the coupling bolt. Let be the crack propagation rate of the coupling bolt, where α is the critical crack size of the coupling bolt. L The calculation formula is as follows: In the formula, K IC Let f be the fracture toughness of the coupling bolt material, f be the shape factor, and σ be the tensile strength. x This represents the maximum value of the cyclic stress.

[0042] Paris believed that the stress field intensity at the crack tip could be represented by the stress intensity factor K1. Therefore, only the stress intensity factor was the true driving force for crack propagation. He proposed a crack propagation formula directly related to the range of stress intensity factor variation ΔK. When ΔK at the crack tip > ΔKth, crack propagation begins, and lg(da / dN) and lg(ΔK) show a linear relationship, which is called the first stage of fatigue crack propagation. As ΔK continues to increase, after passing the inflection point B1, the second stage begins, where the propagation rate slows down, and lg(da / dN) and lg(ΔK) remain linearly related. When ΔK increases beyond the inflection point B2 of the second stage, Kmax is close to the material's K... 1c The crack propagation rate accelerates dramatically until fracture occurs. Since stages I and II are linear in a logarithmic coordinate system, this indicates an exponential relationship between da / dN and ΔK. Therefore, Paris proposed the following empirical formula for crack propagation rate. In the formula, α is the crack depth or width, C and m are material-related parameters, ΔK is the range of stress intensity factor, and N is the number of stress cycles.

[0043] 2. Obtain the primary fatigue crack size α1 of the coupling bolt. The fatigue crack of the coupling bolt can be obtained by using existing fatigue crack detection equipment to obtain matching data.

[0044] 3. Import the initial fatigue crack size α1 into the fatigue prediction mathematical model of the coupling bolt to obtain the first fatigue propagation life N1 of the coupling bolt. When importing into the fatigue prediction mathematical model, take α1 = α0.

[0045] Fourth, after a further running time T, the predicted data is iterated. First, the secondary fatigue crack size α2 of the coupling bolt is obtained, using the same method as in step two. Existing fatigue crack detection devices can be used to obtain matching data. To ensure the consistency of the measurement data, the same instrument should be used for detection in steps two and four. In a further preferred embodiment, if there is a significant difference in the real-time temperature between the two detections, temperature compensation should also be performed. In this embodiment, the relationship between the running time T and the primary fatigue propagation life N1 is as follows: N1 / 10 ≤ T ≤ N1 / 2.

[0046] 5. Import the secondary fatigue crack size α2 into the fatigue prediction mathematical model of the coupling bolt to obtain the secondary fatigue propagation life N2 of the coupling bolt. When importing into the fatigue prediction mathematical model, take α2 = α0.

[0047] VI. Calculate the K value according to the formula: The actual bolt fatigue expansion life is determined based on the value of K. There are two cases: First, if K > 1, N1 and N2 are weighted separately and then summed to obtain the actual bolt fatigue expansion life of the coupling bolt; Second, if K ≤ 1, N2 is represented as the actual bolt fatigue expansion life.

[0048] This embodiment uses a weighted algorithm to weight N1 and N2. The specific method is as follows: First, determine the initial weighting coefficients of N1 and N2. If 1 < K ≤ 1.1, then the initial weighting coefficients of N1 and N2 are both determined to be 50%. If 1.1 < K ≤ 1.2, then the initial weighting coefficient of N1 is determined to be 45% and the initial weighting coefficient of N2 is determined to be 55%. If 1.2 < K, then the initial weighting coefficient of N1 is determined to be 40% and the initial weighting coefficient of N2 is determined to be 60%. Then, create a mapping table between the running time T in step four and the weighting coefficients of N1 and N2, as shown in Table 1. The design principle of the weighting coefficient mapping table is that the longer the running time, the lower the weighting coefficient of N1, and vice versa. Finally, weight N1 and N2 are weighted according to the weighting coefficient mapping table. For example: The initial weighting coefficients of N1 and N2, determined by the value of K, are N1 45% and N2 55%, respectively. Based on this, according to the weighting coefficient mapping table, if the running time T = N1 / 5, the actual weighting coefficients of N1 and N2 are the initial weighting coefficients plus the added weighting coefficients. The final weighting coefficient results are as follows: N1 30% and N2 70%.

[0049] Table 1

[0050] Run time T [weighting factor for N1 increase] [weighting factor for N2 increase] [N1 / 10] 0 0 [N1 / 9] -2.5％ 2.5％ [N1 / 8] -5％ 5％ [N1 / 7] -7.5％ 7.5％ [N1 / 6] -10％ 10％ [N1 / 5] -15％ 15％ [N1 / 3] -20％ 20％ [N1 / 2] -30％ 30％

[0051] This invention introduces a second-order iterative calculation in the calculation of the fatigue extension life of coupling bolts, and combines a weighted calculation based on the running time of the second iteration and the K value of the two calculation times to obtain the actual fatigue extension life of the bolts.

[0052] It should be noted that the above description is only a part of the embodiments of the present invention, and all equivalent changes made to the system described in this invention are included within the protection scope of this invention. Those skilled in the art can make similar substitutions to the specific examples described, as long as they do not deviate from the structure of the invention or exceed the scope defined in these claims, all of which fall within the protection scope of this invention.

Claims

1. A method for predicting the fatigue life of coupling bolts in an axial-flow hydro-generator unit, characterized in that, include: S1: Construct a mathematical model for predicting fatigue in coupling bolts. The mathematical model for predicting fatigue in coupling bolts is as follows: In the formula, α0 is the measured value of the fatigue crack size of the coupling bolt, α L The critical crack size of the coupling bolt. The crack propagation rate of the coupling bolt; S2: Obtain the primary fatigue crack size α1 of the coupling bolt and substitute it into the fatigue prediction mathematical model of the coupling bolt constructed in S1 to obtain the primary fatigue propagation life N1 of the coupling bolt; S3: After running for a further time T, obtain the secondary fatigue crack size α2 of the coupling bolt and substitute it into the coupling bolt fatigue prediction mathematical model constructed in S1 to obtain the secondary fatigue propagation life N2 of the coupling bolt, N1 / 10≤T≤N1 / 2; S4: Calculate the value of K according to the following formula: If K > 1, then N1 and N2 are weighted separately, and then summed to obtain the actual bolt fatigue expansion life of the coupling bolt; if K ≤ 1, then N2 is represented as the actual bolt fatigue expansion life, and the specific steps for weighting N1 and N2 are as follows: S4.1: Determine the initial weighting coefficients of N1 and N2. If 1 < K ≤ 1.1, then determine that the initial weighting coefficients of N1 and N2 are both 50%. If 1.1 < K ≤ 1.2, then determine that the initial weighting coefficient of N1 is 45% and the initial weighting coefficient of N2 is 55%. If 1.2 < K, then determine that the initial weighting coefficient of N1 is 40% and the initial weighting coefficient of N2 is 60%. S4.2: Create a mapping table of running time T and weighted coefficients of N1 and N2. The longer the running time, the lower the weight coefficient of N1, and vice versa. S4.3: Weight N1 and N2 according to the weighting coefficient mapping table and the initial weighting coefficients.

2. The method for predicting the fatigue life of coupling bolts in an axial-flow hydro-generator unit as described in claim 1, characterized in that, Critical crack size α of coupling bolts L The calculation formula is as follows: In the formula, For the fracture toughness of the coupling bolt material, For shape factor, This represents the maximum value of the cyclic stress.

3. The method for predicting the fatigue life of coupling bolts in an axial-flow hydro-generator unit as described in claim 1, characterized in that, Crack propagation rate of coupling bolts The calculation formula is as follows: In the formula, α is the crack depth or width, and C and m are material-related parameters. Where represents the range of stress intensity factor variation, and N represents the number of stress cycles.

4. A fatigue life prediction system for coupling bolts of an axial-flow hydro-generator unit, characterized in that, include: The module for constructing a mathematical model for fatigue prediction of coupling bolts builds a mathematical model for fatigue prediction of coupling bolts. The mathematical model for fatigue prediction of coupling bolts is as follows: In the formula, α0 is the measured value of the fatigue crack size of the coupling bolt, α L The critical crack size of the coupling bolt. The crack propagation rate of the coupling bolt; The fatigue crack acquisition module for coupling bolts acquires the fatigue crack size α1 of the coupling bolts. The fatigue propagation life acquisition module of the coupling bolt inputs the fatigue crack size α1 of the coupling bolt into the fatigue prediction mathematical model of the coupling bolt to obtain the fatigue propagation life N1 of the coupling bolt, where N1 / 10≤T≤N1 / 2; The running time timing module, after continuing to run for time T, obtains the secondary fatigue crack size α2 of the coupling bolt and substitutes it into the coupling bolt fatigue prediction mathematical model constructed by S1 to obtain the secondary fatigue propagation life N2 of the coupling bolt, N1 / 10≤T≤N1 / 2; K-value calculation module, calculates the K-value: ; The bolt fatigue extension life determination module determines the actual bolt fatigue extension life based on the K value. If K > 1, N1 and N2 are weighted separately and then summed to obtain the actual bolt fatigue extension life of the coupling bolt. If K ≤ 1, N2 is represented as the actual bolt fatigue extension life. The specific steps for weighting N1 and N2 are as follows: Determine the initial weighting coefficients for N1 and N2. If 1 < K ≤ 1.1, then determine that the initial weighting coefficients for N1 and N2 are both 50%. If 1.1 < K ≤ 1.2, then determine that the initial weighting coefficient for N1 is 45% and the initial weighting coefficient for N2 is 55%. If 1.2 < K, then determine that the initial weighting coefficient for N1 is 40% and the initial weighting coefficient for N2 is 60%. Create a mapping table of running time T and weighted coefficients of N1 and N2. The longer the running time, the lower the weight coefficient of N1, and vice versa. N1 and N2 are weighted according to the weighting coefficient mapping table and the initial weighting coefficients.

5. The fatigue life prediction system for coupling bolts of axial-flow hydro-generator units as described in claim 4, characterized in that, Critical crack size α of coupling bolts L The calculation formula is as follows: In the formula, For the fracture toughness of the coupling bolt material, For shape factor, This represents the maximum value of the cyclic stress.

6. The fatigue life prediction system for coupling bolts of axial-flow hydro-generator units as described in claim 4, characterized in that, Crack propagation rate of coupling bolts The calculation formula is as follows: In the formula, α is the crack depth or width, and C and m are material-related parameters. Where represents the range of stress intensity factor variation, and N represents the number of stress cycles.

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