Method for determining two-dimensional attribute of fatigue load
By using rainflow counting and stress-strain hysteresis loop analysis, the two-dimensional properties of fatigue loads are determined, which solves the problem of ignoring the load sequence order in existing methods and improves the fitting accuracy of the load spectrum and the accuracy of fatigue damage assessment.
Patent Information
- Application Number
- CN202511078760.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-08-01
- Publication Date
- 2025-11-14
AI Technical Summary
Existing methods for compiling fatigue load spectra rely solely on the cyclic amplitude and mean values obtained from rainflow counting, neglecting the sequential properties of the load in the time series. This results in a significant deviation between the compiled load spectrum and the actual fatigue damage, making it difficult to accurately reflect the true fatigue damage mechanism.
The statistical properties of fatigue loads are determined by rainflow counting, and the order properties, including the parent-child relationship of loads, load level and load direction, are extracted based on stress-strain hysteresis loops to form the two-dimensional properties of fatigue loads.
It achieves accurate reproduction of loading sequence and hierarchical effects in load spectrum, improves load spectrum fitting accuracy, and provides more accurate fatigue damage assessment and life prediction support.
Smart Images
Figure CN120951464A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of load spectrum compilation technology for aero-engine structural components, and in particular to a method for determining the two-dimensional properties of fatigue loads. Background Technology
[0002] With the rapid development of high-end equipment in aviation, aerospace, automotive, and wind power industries, structural components are subjected to complex and variable loads over long periods, leading to increasingly prominent issues of fatigue damage accumulation and lifespan degradation. Fatigue loads, as a significant external factor causing structural failure, directly affect the reliability and safety of components. Therefore, accurately and comprehensively characterizing and determining fatigue load properties has become a crucial prerequisite for fatigue design, lifespan prediction, and accelerated testing.
[0003] Currently, most fatigue load classification methods rely solely on the amplitude or mean values of cycles obtained from rainflow counting, grouping cycles with similar values into the same level. However, these methods only consider the statistical properties of the load while ignoring the chronological order of the loads in the time series, making it difficult to reflect the true sequence effect and leading to discrepancies between fatigue test results and actual service conditions. In the load spectrum compilation process, only by combining statistical and sequence attributes can we ensure accurate numerical fitting of the original load amplitude and mean while precisely reproducing the loading sequence and hierarchical effects at the sequence level. This significantly improves the fitting accuracy of the program spectrum, reflects the true fatigue damage mechanism, and provides solid and reliable technical support for accelerating fatigue test design and life assessment. When analyzing the load spectrum of a non-random aircraft process, the loading sequence of the load spectrum has a significant impact on fatigue life. Considering only the load magnitude without considering the load application location is unreasonable, and following the law of the influence of the load loading sequence on life is one of the basic principles of compiling test load spectra. However, it does not provide specific guidance on how to consider the statistical and sequence attributes of fatigue loads during the load spectrum compilation process.
[0004] Existing fatigue load spectrum compilation methods rely solely on single statistical attributes such as the cyclic amplitude and mean obtained from rainflow counting for load classification, resulting in a significant deviation between the discretized program spectrum and the amplitude and mean distribution of the original load. Furthermore, they neglect the hierarchical order attribute of fatigue loads. Therefore, providing a method that comprehensively considers both the statistical and order attributes of fatigue loads is crucial for ensuring that the compiled aero-engine load spectrum more closely approximates actual flight loads. Summary of the Invention
[0005] In view of the problems existing in the current method for determining the two-dimensional properties of fatigue load, this invention is proposed. Therefore, the problem to be solved by this invention is how to provide a method for determining the two-dimensional properties of fatigue load.
[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution:
[0007] In a first aspect, the present invention provides a two-dimensional property determination method for fatigue load, which includes pairing peak and valley points in the measured load time history according to the four-point rule using the rainflow counting method, calculating the stress amplitude, stress mean and stress range of each closed cycle, and obtaining the statistical properties of fatigue load.
[0008] Based on the rainflow counting results, the stress-strain hysteresis loop is reconstructed, and the order attributes, including the parent-child relationship of the load, the load level, and the load direction, are extracted from the hysteresis loop.
[0009] The statistical attribute and the order attribute are combined to form a two-dimensional attribute for each cycle.
[0010] As a preferred embodiment of the two-dimensional attribute determination method for fatigue load described in this invention, the step of pairing peak and valley points in the measured load time history according to the four-point rule using the rainflow counting method includes: applying the four-point rainflow judgment method to each pair of peak and valley points in the original load time history to identify all closed cycles; for each closed cycle, calculating its maximum stress and minimum stress respectively, and further calculating the amplitude, mean and range, and combining the three as the statistical attribute of the cycle.
[0011] As a preferred embodiment of the two-dimensional property determination method for fatigue load described in this invention, the reconstructing of stress-strain hysteresis loop based on rainflow counting results includes: interpolating and connecting each set of peak-valley pairing points and their original time history trajectories to form a closed path; mapping the closed path to the corresponding stress-strain hysteresis loop curve according to the known stress-strain mapping relationship, and retaining the key semi-loop node information on the path, and extracting directional and hierarchical features.
[0012] As a preferred embodiment of the two-dimensional property determination method for fatigue load described in this invention, the parent-child relationship of the load includes: for any two hysteresis loops A and B, if the maximum stress of A is greater than the maximum stress of B and the minimum stress of A is less than the minimum stress of B, then A is regarded as the parent loop that encompasses B, and B is regarded as the child loop; for multiple child loops under the same parent loop, they are sorted in descending order of average stress.
[0013] As a preferred embodiment of the two-dimensional property determination method for fatigue load described in this invention, the load direction includes: in a hysteresis loop, if the loop half-cycle first experiences stress increase and then unloading, the loop direction is defined as negative; if it first experiences stress decrease and then reverse loading, the loop direction is defined as positive.
[0014] As a preferred embodiment of the two-dimensional property determination method for fatigue load according to the present invention, the load level includes: defining the largest main loop that is not contained by any other hysteresis loop as a first-level load; defining the closed sub-loop directly contained by the first-level load as a second-level load; defining the closed sub-loop further contained by the second-level load as a third-level load; and so on, defining higher-level loads in sequence according to the increasing containment depth.
[0015] In a second aspect, the present invention provides a computer device, including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the steps of a method for determining the two-dimensional properties of fatigue load.
[0016] Thirdly, the present invention provides a computer-readable storage medium having a computer program stored thereon, wherein: when the computer program is executed by a processor, it implements the steps of a method for determining the two-dimensional properties of fatigue load.
[0017] The beneficial effects of this invention are as follows: Based on traditional rainflow counting statistical attributes, this invention also determines the order attribute of fatigue loads based on the rainflow hysteresis loop containment relationship. This order attribute allows the program spectrum to reproduce the "parent-child" nesting relationship and the loading direction of "increase first, then decrease" or "decrease first, then increase." This method of constructing a program block spectrum that takes into account the two-dimensional attributes of fatigue loads can realistically reproduce the sequence effect and amplitude-mean situation of the measured load spectrum. While ensuring fatigue damage equivalence within the error range, it also helps to enrich the methods for life prediction research. Attached Figure Description
[0018] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0019] Figure 1 This is a flowchart of the method of the present invention.
[0020] Figure 2 A schematic diagram for determining the order properties of fatigue loads.
[0021] Figure 3 This is a schematic diagram of a certain load history of an aero-engine.
[0022] Figure 4 This is a schematic diagram of a certain load history of an aero-engine.
[0023] Figure 5 This is a schematic diagram of an experiment on a notched specimen under the load sequence effect. Detailed Implementation
[0024] To make the above-mentioned objects, features, and advantages of the present invention more readily understood, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the protection scope of the present invention.
[0025] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.
[0026] Secondly, the term "an embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places throughout this specification does not necessarily refer to the same embodiment, nor is it a single embodiment or an embodiment selectively excluded from other embodiments.
[0027] Example 1
[0028] Reference Figure 1 This is the first embodiment of the present invention, which provides a method for determining the two-dimensional properties of fatigue load, including:
[0029] 1. By matching the peak and valley points in the measured load time history using the rainflow counting method according to the four-point rule, the stress amplitude, mean stress, and stress range of each closed cycle are calculated to obtain the statistical properties of the fatigue load.
[0030] Specifically, the four-point rainflow determination method is applied to each pair of peaks and valleys in the original load time history to identify all closed cycles; for each closed cycle, its maximum stress and minimum stress are calculated, and the amplitude, mean and range are further calculated, and the three are combined as the statistical attributes of the cycle.
[0031] 2. Reconstruct the stress-strain hysteresis loop based on the rainflow counting results, and extract the order attributes from the hysteresis loop, including the parent-child relationship of the load, the load level, and the load direction;
[0032] Specifically, each pair of peak and valley points and their original time history trajectories are interpolated and connected to form a closed path; based on the known stress-strain mapping relationship, the closed path is mapped to the corresponding stress-strain hysteresis loop curve, and the key semi-loop node information on the path is retained, and directional and hierarchical features are extracted.
[0033] The parent-child relationship of loads includes: for any two hysteresis loops A and B, if the maximum stress of A is greater than the maximum stress of B and the minimum stress of A is less than the minimum stress of B, then A is regarded as the parent loop that encompasses B, and B is regarded as the child loop; for multiple child loops under the same parent loop, they are sorted in descending order of average stress.
[0034] The load direction includes: in a hysteresis loop, if the loop half-cycle first experiences stress increase and then unloading, the loop direction is defined as negative; if it first experiences stress decrease and then reverse loading, the loop direction is defined as positive.
[0035] The load levels are as follows: the largest main loop that is not contained by any other hysteresis loop is defined as a first-level load; the closed sub-loop that is directly contained by a first-level load is defined as a second-level load; the closed sub-loop that is further contained by a second-level load is defined as a third-level load; and so on, with higher load levels defined in order of increasing containment depth.
[0036] 3. Combine the statistical attribute with the order attribute to form a two-dimensional attribute for each cycle.
[0037] Example 2
[0038] Reference Figures 2-5 This is a second embodiment of the present invention, which provides a method for determining the two-dimensional properties of fatigue load, including:
[0039] Assume that the payload trajectories of a certain aero-engine are as follows: Figure 3 and Figure 4 As shown, the difference lies in the load loading order of the cycle "2–3–2′" and the cycle "5–6–5′".
[0040] Rainflow counting analysis of two load histories: The four-point rule of rainflow counting method can be used to match segments one by one to find all closable loops.
[0041] Identify separately Figure 3 and Figure 4 The closed stress-stress cycle pairs (peak-valley pairs) were identified, and their statistical properties of fatigue load were statistically analyzed. Figure 3 First load history statistics and Figure 4 The statistical attributes of the second load history are summarized below, and the statistical results are shown in Table 1 and Table 2.
[0042] Table 1 Summary of Statistical Attributes of the First Load History
[0043]
[0044] Table 2 Summary of Statistical Attributes of the Second Load History
[0045]
[0046] As shown above, the statistical properties of the two load histories are exactly the same.
[0047] The two hysteresis loops are determined based on the load history: Figure 3 and Figure 4 The load time history on the left can be used to establish its corresponding hysteresis loop through the rainflow counting method: point 1→8→1′ constitutes the maximum main loop; within this main loop, points 2→3→2′ and 4→7→4′ are paired to form two secondary loops respectively; within the 4→7→4′ loop, a tertiary loop 5→6→5′ can be formed.
[0048] Although the statistical attributes have been determined, in reality, even if the damage statistical attributes are the same, their order attributes may be different.
[0049] like Figure 4 As shown, while maintaining Figure 3 Under the premise that the amplitudes of each level of hysteresis loop (such as the main loop and the sub-loop) remain unchanged, a new load sequence is formed by adjusting the insertion position of a certain level of small loop in its parent loop. The possible damage situations are comprehensively considered by taking into account the possible loading order.
[0050] The specific operation is as follows: During the continuous repetition of the random spectrum, the entire process involves the continuous repetition of the stress-strain curve from point 1 to point 8, forming three fixed cyclic periods in the reference cycle. The magnitude and position of each period remain unchanged. Figure 3 As shown, the interaction between the loads stabilizes in the current state;
[0051] Adjusting the positions of the 5-6-5' and 2-3-2' loads creates a new load sequence and stress-strain curve, as shown below. Figure 4 As shown, during the continuous repetition process, three fixed cycle periods are also formed in the baseline cycle.
[0052] Comparative analysis revealed that the magnitude and position of the baseline cycle and the 4-7-4' cycle remained unchanged, and the change in the load sequence had no impact on the inherent damage and interaction effects of the three cycles. While the magnitude of the 5-6-5' cycle remained the same, its position within the 4-7-4' cycle changed. Similarly, while the magnitude of the 2-3-2' cycle remained the same, its position within the 1-8-1' cycle changed. Taking the 5-6-5' cycle as an example, the shift from a large tensile load to a large compressive load altered the sequence effect of the 4-7-4' cycle on the 5-6-5' cycle, resulting in different actual damage in the 5-6-5' cycle. Figure 4 The damage changes.
[0053] Extract the order attribute of fatigue loads; further, determine the parent-child relationship based on the hysteresis loop inclusion relationship:
[0054] 4.1, such as Figure 2 In the hysteresis loop diagram shown, each stress cycle corresponds to a closed loop. To determine the parent-child relationship between two loops, a hierarchical parent-child nested structure can be formed based on the rules of "peak-valley inclusiveness" and "unique parent loop selection".
[0055] like Figure 2 In (b), based on the inclusion and contained states of the hysteresis loop, the hysteresis loop is decomposed into three different hysteresis loop levels. The engine's base cycle (0-max-0) is necessarily the largest hysteresis loop (1-8-1'), and the second-level (2-3-2' and 4-7-4') and third-level (5-6-5') cycles are determined sequentially. According to the subordinate relationship, the 1-8-1' cycle is called the parent cycle of the 2-3-2' and 4-7-4' cycles, and the 2-3-2' and 4-7-4' cycles are the child cycles of the 1-8-1' cycle; similarly, the 4-7-4' cycle is called the parent cycle of the 5-6-5' cycle, and the 5-6-5' cycle is the child cycle of the 4-7-4' cycle.
[0056] 4.2 Determining load direction based on hysteresis loop loading and unloading;
[0057] exist Figure 2 In the hysteresis loop shown in (b), each loop contains two half-cycles: "load → unload" and "unload → reload". The positive load direction marking rule described above ensures the reproduction of the original load loading and unloading sequence. For example... Figure 2 In (b), the first-level longitudinal load 1-8-1' and the third-level longitudinal load 5-6-5' are negative loads; the second-level longitudinal loads 2-3-2' and 4-7-4' are positive loads.
[0058] 4.3 Determining load levels based on the hierarchical structure of hysteresis loops.
[0059] exist Figure 2 In the hysteresis loop structure shown, the load cycles at each level naturally form a hierarchical nesting due to their containment relationships: the outermost "0–max–0" main loop is defined as a first-level load because it is not contained by any other loop; the loops directly contained by the main loop (such as "2–3–2′" and "4–7–4′" in the figure) are second-level loads; the smaller loops contained by the second-level loops (such as "5–6–5′") are third-level loads; and so on. All loops can be numbered sequentially according to their nesting depth to form first-level, second-level, third-level, and so on load levels.
[0060] For ease of understanding, Figure 3 and Figure 4 For example, the two-dimensional properties of its fatigue load are statistically analyzed in the table below:
[0061] Table 3 Summary of Two-Dimensional Attributes of the First Load History
[0062]
[0063] Table 4 Summary of Two-Dimensional Attributes of the Second Load History
[0064]
[0065] As shown above, the statistical properties of the two load histories are the same; the parent-child relationship and load level in the order properties are also the same, but the load direction of cycle B and cycle D has changed, which causes the loading and unloading process to change accordingly, and ultimately the damage also changes.
[0066] To further investigate the influence of the sequence effect on damage, this invention conducts variable amplitude fatigue tests on dual-hole specimens. Figure 2 Taking the four-level load sequence in (a) as an example, the cyclic stress history from point 1 to point 8 forms three stable cyclic cycles in the main cycle. Figure 5 As shown in (a), by adjusting the position of the 5-6-5' load, a new load sequence and a stable stress-strain curve were formed, as shown in (a). Figure 5 As shown in (b), comparative analysis shows that the size and position of the main cycle, the 2-3-2', and the 4-7-4' cycles remain unchanged, indicating that changes in the load sequence do not affect the damage and interaction effects of these three cycles. Although the size of the 5-6-5' cycle remains unchanged, its position within the 4-7-4' cycle changes, transferring the effect of the large load from the previous tensile load to the compressive load. Therefore, the sequence effect of the 4-7-4' cycle on the 5-6-5' cycle changes, which in turn affects the fatigue damage of the 5-6-5' cycle and sequence 2. To illustrate the effect of layering order on fatigue damage, Figure 2 (c) shows an example of an instructive experimental result. It involves two VA fatigue tests, in which the first block, subjected to a high amplitude load, induced cyclic plasticity at the notch root. Figure 2 There are subtle differences between the two sequences in (c). In the first case, the last maximum stress before the amplitude decreases is positive, while in the second case it is negative. This corresponds to... Figure 2 (a) and Figure 2 The 5-6-5' cyclic sequence effect observed in (b) is shown. The first sequence produces favorable compressive residual stress at the notch root, while the second sequence produces unfavorable tensile residual stress. These effects are clearly reflected in the cumulative damage ratios of the experimental results: 2.04 for the first case and 0.90 for the second. This plasticity-induced sequence effect was not identified by Miner's rule and rainflow count.
[0067] As the above examples demonstrate, when two load histories have the same statistical properties, changes in their order properties can alter the damage. Therefore, when compiling fatigue load information, both the statistical and order properties of the fatigue load must be considered to achieve a more accurate life assessment.
[0068] This embodiment also provides a computer device applicable to a method for determining the two-dimensional properties of fatigue load, comprising: a memory and a processor; the memory is used to store computer-executable instructions, and the processor is used to execute the computer-executable instructions to implement all or part of the steps of the method described in the above embodiments of the present invention.
[0069] This embodiment also provides a storage medium on which a computer program is stored. When the computer program is executed by a processor, it performs the method in any optional implementation of the above embodiments. The storage medium can be implemented by any type of volatile or non-volatile storage device or a combination thereof, such as Static Random Access Memory (SRAM), Electrically Erasable Programmable Read-Only Memory (EEPROM), Erasable Programmable Read-Only Memory (EPROM), Programmable Red-Only Memory (PROM), Read-Only Memory (ROM), magnetic storage, flash memory, magnetic disk, or optical disk.
[0070] The storage medium proposed in this embodiment and the data storage method proposed in the above embodiments belong to the same inventive concept. Technical details not described in detail in this embodiment can be found in the above embodiments, and this embodiment has the same beneficial effects as the above embodiments.
[0071] In summary, this invention, based on traditional rainflow counting statistical attributes, further determines the order attribute of fatigue loads based on the rainflow hysteresis loop containment relationship. This order attribute allows the program spectrum to reproduce the "parent-child" nesting relationship and the loading direction of "increase first, then decrease" or "decrease first, then increase." This method of constructing a program block spectrum that takes into account the two-dimensional attributes of fatigue loads can realistically reproduce the sequence effect and amplitude-mean situation of the measured load spectrum. While ensuring fatigue damage equivalence within the error range, it also helps to enrich the methods for life prediction research.
[0072] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.
Claims
1. A method for determining the two-dimensional properties of fatigue load, characterized in that: include, By matching the peaks and valleys of the complete measured spectrum according to the four-point rule using the rainflow counting method, the stress amplitude, mean stress, and stress range of each closed cycle are calculated to obtain the statistical properties of fatigue load. Based on the rainflow counting results, the stress-strain hysteresis loop is reconstructed, and the order attributes, including the parent-child relationship of the load, the load level, and the load direction, are extracted from the hysteresis loop. The statistical attribute and the order attribute are combined to form a two-dimensional attribute for each cycle.
2. The method for determining the two-dimensional properties of fatigue load as described in claim 1, characterized in that: The method of pairing peak and valley points in the measured load time history using the rainflow counting method according to the four-point rule includes: applying the four-point rainflow judgment method to each pair of peak and valley points in the original load time history to identify all closed cycles; for each closed cycle, calculating its maximum stress and minimum stress, and further calculating the amplitude, mean and range, and combining the three as the statistical attributes of the cycle.
3. The method for determining the two-dimensional properties of fatigue load as described in claim 2, characterized in that: The reconstruction of stress-strain hysteresis loop based on rainflow counting results includes: interpolating and connecting each set of peak-valley pairing points and their original time history trajectories to form a closed path; mapping the closed path to the corresponding stress-strain hysteresis loop curve according to the known stress-strain mapping relationship, and retaining the key semi-loop node information on the path, and extracting directional and hierarchical features.
4. The method for determining the two-dimensional properties of fatigue load as described in claim 3, characterized in that: The parent-child relationship of the load includes: for any two hysteresis loops A and B, if the maximum stress of A is greater than the maximum stress of B and the minimum stress of A is less than the minimum stress of B, then A is regarded as the parent loop that encompasses B, and B is regarded as the child loop; for multiple child loops under the same parent loop, they are sorted in descending order of average stress.
5. The method for determining the two-dimensional properties of fatigue load as described in claim 4, characterized in that: The load direction includes: in a hysteresis loop, if the loop half-cycle first experiences stress increase and then unloading, the loop direction is defined as negative; if it first experiences stress decrease and then reverse loading, the loop direction is defined as positive.
6. The method for determining the two-dimensional properties of fatigue load as described in claim 5, characterized in that: The load levels include: defining the largest main loop that is not contained by any other hysteresis loop as a Level 1 load; defining a closed sub-loop that is directly contained by a Level 1 load as a Level 2 load; defining a closed sub-loop that is further contained by a Level 2 load as a Level 3 load; and so on, defining higher load levels in order of increasing containment depth.
7. A computer device comprising a memory and a processor, wherein the memory stores a computer program, characterized in that: When the processor executes the computer program, it implements the steps of the two-dimensional property determination method for fatigue load as described in any one of claims 1 to 6.
8. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by the processor, it implements the steps of the two-dimensional property determination method for fatigue load as described in any one of claims 1 to 6.