Online stress spectrum statistics and fatigue damage estimation method based on four-point rain flow counting method

Abstract

The invention belongs to the field of fatigue life estimation of equipment, and particularly relates to an online stress spectrum statistics and fatigue damage estimation method based on a four-point rain flow counting method, which comprises the following steps of: acquiring and recording stress data measured inside a mechanical structure of the equipment in real time according to fixed sampling time; judging whether a pole appears or not according to current data and previously recorded last point data, updating existing pole information, calculating fatigue damage, accumulating to accumulate fatigue damage, judging whether a four-point rain flow counting waveform appears or not, calculating fatigue damage of the four-point rain flow counting waveform, accumulating to accumulate fatigue damage, and updating the existing pole information. And finally, calculating the current fatigue damage between the recording points according to the current data and the previously recorded pole data, and outputting the total fatigue damage. According to the method, the problem of online estimation of the fatigue damage of the equipment is solved, and the accuracy and real-time performance of estimating the fatigue damage of the equipment are improved.

Description

Technical Field

[0001] The invention belongs to the field of equipment fatigue life estimation, and specifically relates to an online stress spectrum statistics and fatigue damage estimation method based on a four-point rain flow counting method. Background Art

[0002] Fatigue is one of the main factors causing failure of many infrastructures and key equipment, including common aircraft, bridges, pipelines, vehicles, machines, etc. Fatigue is caused by repeated external stimulation and is a cumulative damage process. When the accumulation exceeds a certain critical value, tiny cracks will first occur at the local stress concentration, then expand, and finally suddenly break, which can easily cause great loss of life and property.

[0003] Recent studies have also shown that fatigue of mechanical parts is caused by cyclic plastic strain in the local stress concentration area inside the parts, and the load time history is complex and randomly changes. Therefore, in order to reasonably predict the fatigue life of parts, it is necessary to perform statistical processing and cycle counting on the load time history or local stress and strain history, so as to calculate damage and complete life estimation. There are many counting methods, such as peak counting, level counting and rain flow counting.

[0004] Peak counting is used to analyze stress or strain cycles in load history to estimate fatigue damage of materials under repeated loads. The peak counting method is based on local extreme values ​​(i.e., peaks and valleys) in the load time series, and calculates key parameters such as stress or strain amplitude and number of cycles by analyzing these local extreme values. Peak counting greatly simplifies the complexity of fatigue analysis by only analyzing local extreme values ​​in the load. It is particularly suitable for the analysis of complex load spectra. For random load histories, it can effectively extract the main damage contribution cycles and ignore some small fluctuations that are not sensitive to damage.

[0005] Level counting is a technique used to analyze load histories, especially for evaluating the cyclic characteristics of stress or strain under random or complex loads. Level counting estimates the fatigue damage of materials under these loads by counting the number of times the stress or strain signal crosses a specific level in the load time history. Level counting is particularly suitable for analyzing random or non-periodic load signals because it does not require the load cycle to present a standard rise-fall pattern, but only focuses on the number of times the signal crosses a specific level. Under complex load histories, directly analyzing all local extreme values ​​may be too cumbersome, and setting a few key thresholds for level counting can effectively simplify the analysis process.

[0006] The rainflow counting method is the most commonly used and effective counting technique in fatigue analysis, and is particularly suitable for processing complex random load signals. It decomposes the complex load cycles in the stress or strain history and converts the load into a series of fatigue cycles, thereby estimating the fatigue damage of the material under multiple repeated loads. The rainflow counting method can effectively decompose complex stress-time histories, and can identify key fatigue cycles regardless of random or cyclic loads. It is more accurate in fatigue damage estimation than other methods (such as peak counting, level-crossing counting, etc.). The rainflow counting method is an internationally recognized standard method and is widely used in many fatigue analysis fields.

[0007] The rain flow counting method is limited by its algorithm structure. This method cannot be solved online in real time, and the problem of real-time estimation of structural fatigue damage remains to be solved. Summary of the invention

[0008] In view of the above problems, the purpose of the present invention is to provide an online stress spectrum statistics and fatigue damage estimation method based on the four-point rainflow counting method, so as to solve how to realize real-time calculation of fatigue damage and improve the accuracy of fatigue damage estimation.

[0009] In order to achieve the above object, the technical solution of the present invention is as follows:

[0010] S1. Collect and record stress data measured inside the mechanical structure of the equipment in real time at a fixed sampling time;

[0011] S2. Determine whether a pole appears according to the current data and the previous data recorded. If a new pole appears, calculate the fatigue damage between the last two poles in the pole queue and add it to the cumulative fatigue damage. At the same time, kick out the pole data at the end of the queue and insert the new pole data at the head of the queue. If no new pole appears, insert the new pole at the head of the queue.

[0012] S3. Determine whether a four-point rain flow counting waveform appears according to the current data and the previously recorded pole data. If a four-point rain flow counting waveform appears, use the data difference between the first two poles as the amplitude, calculate the fatigue damage of the four-point rain flow counting waveform, add it to the cumulative fatigue damage, kick out the first two poles, and insert the last pole to the first pole;

[0013] S4. Calculate the current fatigue damage between the recorded points according to the current data and the previously recorded extreme point data;

[0014] S5. Calculate and output the total fatigue damage.

[0015] In S1, the stress data measured inside the mechanical structure of the equipment is collected and recorded in real time at a fixed sampling time, and the recorded data includes information of the current point and the previous point.

[0016] In S1, the stress data measured inside the mechanical structure of the equipment is collected and recorded in real time at a fixed sampling time. The collected stress data can be used to reflect other types of data of fatigue damage.

[0017] In S2, whether a pole appears is determined based on the current data and the previously recorded pole data. The poles include both maximum and minimum points. The positive and negative data difference between the head pole in the pole queue and the previous point and the positive and negative data difference between the current data and the previous point are used to determine whether a new pole appears. If the positive and negative values ​​of the two data differences are opposite, a new pole appears, otherwise not.

[0018] In S2, note that the size of the pole queue is three, and can only store three pole data at most.

[0019] In S2, the fatigue damage between the two poles at the end of the queue is calculated and added to the cumulative fatigue damage. The data difference between the two poles at the end of the queue is used as the amplitude, and the fatigue damage of the structure is calculated according to the corresponding SN curve in half a cycle.

[0020] In S3, the four-point rain flow counting waveform requires that the pole data at the end of the team is greater than the pole data at the beginning of the team, the pole data in the middle of the team is greater than the current point data, and the pole data in the middle of the team is less than the pole data at the beginning of the team, or the pole data at the end of the team is less than the pole data at the beginning of the team, the pole data in the middle of the team is less than the current point data, and the pole data in the middle of the team is greater than the pole data at the beginning of the team.

[0021] In S3, the four-point rain flow counting waveform needs to be composed of four points. If the pole queue is not full, the judgment link is skipped.

[0022] In S3, the fatigue damage of the four-point rain flow counting waveform is calculated, and the data difference between the two poles at the head of the queue is taken as the amplitude. The fatigue damage of the structure is calculated according to the corresponding SN curve in one cycle.

[0023] In 0022, the SN curve is one of the most commonly used tools in fatigue analysis. It is used to describe the fatigue life of materials under repeated cyclic loads. It helps engineers predict the fatigue life of materials under specific stress conditions by indicating the number of fatigue cycles that materials can withstand under different stress amplitudes. The limit of the number of stress cycles that a material can withstand is N times (obtained through the SN curve method). If it has actually experienced n stress cycles (manually counted according to the definition), its cumulative fatigue damage value can be expressed as D=n / N.

[0024] In S4, the current fatigue damage between the recording points is calculated. The recording points include the current point and the poles in the pole queue. The data difference between adjacent points is used as the amplitude. The fatigue damage of the structure is calculated according to the corresponding SN curve in half a cycle and accumulated as the current fatigue damage.

[0025] In S5, the total fatigue damage is the sum of the accumulated fatigue damage and the current fatigue damage.

[0026] The beneficial effects of the present invention are as follows:

[0027] The online stress spectrum statistics and fatigue damage estimation method based on the four-point rain flow counting method of the present invention collects and records the stress data measured inside the mechanical structure of the equipment in real time according to the fixed sampling time; judges whether a pole appears according to the current data and the previous point data recorded previously; if a new pole appears, the fatigue damage between the two poles at the end of the pole queue is calculated and accumulated to the cumulative fatigue damage, and the pole data at the end of the queue is kicked out at the same time, and the new pole data is inserted at the head of the queue; if no new pole appears, a new pole is inserted at the head of the queue; judges whether a four-point rain flow counting waveform appears according to the current data and the pole data recorded previously; if a four-point rain flow counting waveform appears, the amplitude is calculated by taking the difference between the two poles at the head of the queue as the amplitude, and the fatigue damage of the four-point rain flow counting waveform is accumulated to the cumulative fatigue damage, the two poles at the head of the queue are kicked out, and the pole at the end of the queue is inserted into the head of the queue; according to the current data and the pole data recorded previously, the current fatigue damage between the recorded points is calculated; and finally the total fatigue damage is output. It can more accurately identify and process cyclic loads, especially in the case of rapid load changes, and can better capture stress history. It can better handle complex stress cycles, such as multiple peaks and valleys, which makes it more robust in some irregular load sequences. Compared with existing fatigue damage estimation methods, it can achieve real-time calculation of quantitative indicators of cumulative fatigue damage degree in any period. It has a short calculation time and can calculate real-time fatigue damage within one round of sampling, which can ensure the real-time performance of the algorithm. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the implementation of the present invention or the existing technical solutions, the following briefly introduces the drawings required to be used in the embodiments or the description of the prior art.

[0029] Figure 1 This is a schematic diagram of the first four-point rain flow counting waveform, which requires that the pole data at the end of the team is greater than the pole data at the beginning of the team, the pole data in the team is greater than the current point data, and the pole data in the team is less than the pole data at the beginning of the team meet the following three conditions at the same time.

[0030] Figure 2 This is a schematic diagram of the second four-point rain flow counting waveform, which requires that the pole data at the end of the team is less than the pole data at the beginning of the team, the pole data in the middle of the team is less than the current point data, and the pole data in the middle of the team is greater than the pole data at the beginning of the team meet the following three conditions at the same time.

[0031] Figure 3 The present invention provides a flowchart of an online stress spectrum statistics and fatigue damage estimation method based on a four-point rain flow counting method. DETAILED DESCRIPTION

[0032] The present invention will be described below with reference to specific embodiments. Those skilled in the art can understand that these embodiments are only used to illustrate the present invention and do not limit the scope of the present invention in any way.

[0033] As Figure 3 shown, an online stress spectrum statistics and fatigue damage estimation method based on the four-point rainflow counting method is disclosed in an embodiment of the present invention, including the following steps:

[0034] (1) Collect and record the internal measurement of the mechanical structure of the device in real time at a fixed sampling time;

[0035] (2) Determine whether a pole appears according to the current data and the previous data recorded at the previous point. If a new pole appears, calculate the fatigue damage between the last two poles in the pole queue and accumulate it to the cumulative fatigue damage. At the same time, kick out the data of the last pole in the queue and insert the new pole data at the head of the queue. If no new pole appears, insert the new pole at the head of the queue;

[0036] (3) Determine whether a four-point rainflow counting waveform appears according to the current data and the pole data recorded previously. If a four-point rainflow counting waveform appears, use the difference between the two pole data at the head of the queue as the amplitude, calculate the fatigue damage of the four-point rainflow counting waveform, accumulate it to the cumulative fatigue damage, kick out the two poles at the head of the queue, and insert the pole at the end of the queue to the head of the queue;

[0037] (4) Calculate the current fatigue damage between the recording points according to the current data and the pole data recorded previously;

[0038] (5) Calculate and output the total fatigue damage.

[0039] As a preferred implementation of the present invention, in step (1), the process of collecting and recording the stress data of the internal measurement of the mechanical structure of the device is as follows:

[0040] Collect the stress data of the internal measurement of the mechanical structure at a cycle time greater than the algorithm operation time, and record the pole information, the previous point information, and the current time information in the pole queue.

[0041] As a preferred implementation of the present invention, in step (2), the process of determining whether a pole appears is as follows:

[0042] Determine whether a pole appears according to the current data F(t) and the pole data F(t-1) recorded previously. Use the positive and negative of the data difference between the pole P 1 at the head of the pole queue and the previous point and the positive and negative of the data difference between the current data and the previous point to determine whether a new pole appears. If F(t)>F(t-1) and F(P 1 )>F(t-1), or F(t)<F(t-1) and F(P 1) If <F(t - 1), then new poles appear; otherwise, no.

[0043] As a preferred embodiment of the present invention, in step (2), the process of calculating the fatigue damage accumulation between the last two poles in the pole queue and adding it to the cumulative fatigue damage is as follows:

[0044] The last two poles in the pole queue are P 2 and P 3 . The amplitude between the two points is S = |F(P 2 ) - F(P 3 )|. According to the S - N curve S m × N = C, the maximum cyclic load number N corresponding to the load is obtained, where m is the Wohler index.

[0045] Calculate the fatigue damage of the structure according to the corresponding S - N curve in half a cycle and add it to the cumulative fatigue damage D F (t) = D F (t - 1) + 0.5 / N.

[0046] As a preferred embodiment of the present invention, in step (3), the process of determining whether a four - point rain - flow counting waveform appears is as follows:

[0047] Judge according to three poles P 1 , P 2 , P 3 in the pole queue and the current data. If F(P 3 ) > F(P 1 ), F(P 2 ) > F(t), F(P 1 ) > F(P 2 ), the waveform as shown in Figure 1 appears, or F(P 3 ) < F(P 1 ), F(P 2 ) < F(t), F(P 1 ) < F(P 2 ), the waveform as shown in Figure 2 appears. If there are less than three poles, skip the judgment link.

[0048] As a preferred embodiment of the present invention, in step (3), the process of calculating the fatigue damage of the four - point rain - flow counting waveform and adding it to the cumulative fatigue damage is as follows:

[0049] The first two poles in the pole queue are P 2 and P 1 . The amplitude is S = |F(P 2 ) - F(P 1 )|. According to the S - N curve S m×N=C, and the maximum number of cyclic loads N corresponding to the load is obtained, where m is the Wohler index.

[0050] The fatigue damage of the structure is calculated according to the corresponding SN curve in one cycle and accumulated to the cumulative fatigue damage D F (t) = D F (t-1)+1 / N.

[0051] As a preferred embodiment of the present invention, in step (4), the process of calculating the current fatigue damage between the recording points is as follows:

[0052] According to the three poles P in the pole queue 1 , P 2 , P 3 And the current data get the amplitude S=|F(t)-F(P 1 )|、S=|F(P 2 )-F(P 1 )|、S=|F(P 3 )-F(P 2 )|, according to the SN curve S m ×N=C, get the maximum number of cyclic loads N corresponding to the load 1 、N 2 、N 3 , where m is the Wohler index.

[0053] The fatigue damage of the structure is calculated according to the corresponding SN curve in half a cycle, and the current fatigue damage is calculated as D now (t)=0.5 / N 1 +0.5 / N 2 +0.5 / N 3 .

[0054] As a preferred embodiment of the present invention, in step (5), the process of calculating and outputting the total fatigue damage is as follows:

[0055] The current fatigue damage and the accumulated fatigue damage are D now (t) and D F (t), calculate the total fatigue damage D(t)=D now (t)+D F (t).

[0056] It should be understood that the application of the invention is not limited to the above examples. For ordinary technicians in this field, improvements or changes can be made based on the above description. All these improvements and changes should fall within the scope of protection of the claims attached to this new use model.

Claims

1. An online stress spectrum statistics and fatigue damage estimation method based on a four-point rain flow counting method, characterized in that: The steps include: S1. Collect and record stress data measured inside the mechanical structure of the equipment in real time at a fixed sampling time; S2. Determine whether a pole appears according to the current data and the previous data recorded. If a new pole appears, calculate the fatigue damage between the last two poles in the pole queue and add it to the cumulative fatigue damage. At the same time, kick out the pole data at the end of the queue and insert the new pole data at the head of the queue. If no new pole appears, insert the new pole at the head of the queue. S3. Determine whether a four-point rain flow counting waveform appears according to the current data and the previously recorded pole data. If a four-point rain flow counting waveform appears, use the data difference between the first two poles as the amplitude, calculate the fatigue damage of the four-point rain flow counting waveform, add it to the cumulative fatigue damage, kick out the first two poles, and insert the last pole to the first pole; S4. Calculate the current fatigue damage between the recorded points according to the current data and the previously recorded extreme point data; S5. Calculate and output the total fatigue damage.

2. The method for online stress spectrum statistics and fatigue damage estimation based on the four-point rain flow counting method according to claim 1 is characterized in that: In S1, the stress data measured inside the mechanical structure of the equipment is collected and recorded in real time at a fixed sampling time, and the recorded data includes information of the current point and the previous point.

3. The method for online stress spectrum statistics and fatigue damage estimation based on four-point rain flow counting method according to claim 1 is characterized in that: In S1, the stress data measured inside the mechanical structure of the equipment is collected and recorded in real time at a fixed sampling time. The collected stress data can be used to reflect other types of data of fatigue damage.

4. The method for online stress spectrum statistics and fatigue damage estimation based on four-point rain flow counting method according to claim 1 is characterized in that: In S2, whether a pole appears is determined based on the current data and the previously recorded pole data. The poles include both maximum and minimum points. The positive and negative data difference between the head pole in the pole queue and the previous point and the positive and negative data difference between the current data and the previous point are used to determine whether a new pole appears. If the positive and negative values ​​of the two data differences are opposite, a new pole appears, otherwise not.

5. The method for online stress spectrum statistics and fatigue damage estimation based on four-point rain flow counting method according to claim 4 is characterized in that: Note that the size of the pole queue is three, and it can store at most three pole data.

6. The method for online stress spectrum statistics and fatigue damage estimation based on four-point rain flow counting method according to claim 1, characterized in that: In S2, the fatigue damage between the two poles at the end of the queue is calculated and added to the cumulative fatigue damage. The data difference between the two poles at the end of the queue is used as the amplitude, and the fatigue damage of the structure is calculated according to the corresponding SN curve in half a cycle.

7. The method for online stress spectrum statistics and fatigue damage estimation based on four-point rain flow counting method according to claim 1 is characterized in that: In S3, the four-point rain flow counting waveform requires that the pole data at the end of the team is greater than the pole data at the beginning of the team, the pole data in the middle of the team is greater than the current point data, and the pole data in the middle of the team is less than the pole data at the beginning of the team, or the pole data at the end of the team is less than the pole data at the beginning of the team, the pole data in the middle of the team is less than the current point data, and the pole data in the middle of the team is greater than the pole data at the beginning of the team.

8. The method for online stress spectrum statistics and fatigue damage estimation based on four-point rain flow counting method according to claim 1 is characterized in that: In S3, the four-point rain flow counting waveform needs to be composed of four points. If the pole queue is not full, the judgment link is skipped.

9. The method for online stress spectrum statistics and fatigue damage estimation based on four-point rain flow counting method according to claim 1, characterized in that: In S3, the fatigue damage of the four-point rain flow counting waveform is calculated, and the data difference between the two poles at the head of the queue is taken as the amplitude. The fatigue damage of the structure is calculated according to the corresponding SN curve in one cycle.

10. The method for online stress spectrum statistics and fatigue damage estimation based on four-point rain flow counting method according to claim 9, characterized in that: The SN curve is one of the most commonly used tools in fatigue analysis. It is used to describe the fatigue life of materials under repeated cyclic loads. It helps engineers predict the fatigue life of materials under specific stress conditions by indicating the number of fatigue cycles that the material can withstand under different stress amplitudes. The limit of the number of stress cycles that the material can withstand is N times (obtained through the SN curve method). If it has actually experienced n stress cycles (manually counted according to the definition), its cumulative fatigue damage value can be expressed as D=n / N.

11. The method for online stress spectrum statistics and fatigue damage estimation based on four-point rain flow counting method according to claim 1, characterized in that: In S4, the current fatigue damage between the recording points is calculated. The recording points include the current point and the poles in the pole queue. The data difference between adjacent points is used as the amplitude. The fatigue damage of the structure is calculated according to the corresponding SN curve in half a cycle and accumulated as the current fatigue damage.

12. The method for online stress spectrum statistics and fatigue damage estimation based on four-point rain flow counting method according to claim 1, characterized in that: In S5, the total fatigue damage is the sum of the accumulated fatigue damage and the current fatigue damage.

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