High-precision prediction method for vibration fatigue life based on accelerated fatigue test

Abstract

The present invention proposes a high-precision prediction method for vibration fatigue life based on an accelerated fatigue test, which relates to the technical field of vibration fatigue life prediction, and includes: splitting the piecewise S-N curve into two independent S-N curves, and obtaining the complete fatigue damage of the two independent S-N curves based on the stress power spectral density function and vibration fatigue cumulative damage in the random vibration process; calculating the accelerated cumulative fatigue damage of the piecewise S-N curve based on the damage value of the assumed S-N curve; obtaining an improved inverse power law formula based on the original fatigue damage; calculating the stress probability function and performing numerical analysis to obtain the relationship curve between the acceleration ratio and the accelerated fatigue life; obtaining the accelerated vibration fatigue test value and correcting the relationship curve to obtain the original fatigue life; the present invention solves the problem of predicting the accelerated fatigue life of materials with a piecewise S-N curve by establishing and correcting an improved inverse power law formula for the piecewise S-N curve and obtaining the original fatigue life.

Description

Technical Field

[0001] The present invention relates to the technical field of vibration fatigue life prediction, and in particular, to a high-precision prediction method for vibration fatigue life based on an accelerated fatigue test. Background Art

[0002] Aerospace equipment widely has random excitation sources and has a great risk of vibration fatigue failure. How to effectively predict the fatigue life under a random vibration environment is a key technology for designing anti-fatigue configurations and improving structural reliability. Coffin and Manson established an inverse power law formula for estimating the original vibration fatigue life. Based on the life of the accelerated fatigue test and the acceleration ratio, the original vibration fatigue life of the structure can be predicted. However, this method only equally increases the load amplitude of the test load spectrum and is simple and convenient to apply. There are many existing technologies that have carried out experimental studies on the life prediction of accelerated vibration fatigue based on the inverse power law formula and predicted the vibration fatigue life.

[0003] However, all existing technologies have one thing in common, that is, they do not consider the characteristics of the material S-N curve and default that the S-N curve is in a straight line form in the logarithmic coordinate system. However, as more and more fatigue tests show, the S-N curves of a large number of materials show a segmented (two-segment) linear relationship. For materials with a segmented S-N curve, the results in relevant literature show that there are large errors in predicting the vibration fatigue life using the traditional inverse power law formula in the accelerated fatigue test. For the high-precision prediction method of the vibration fatigue life of such materials, there is still less research at present.

[0004] Based on this, the present application proposes a high-precision prediction method for vibration fatigue life based on an accelerated fatigue test to solve the above problems. Summary of the Invention

[0005] The purpose of the present invention is to provide a high-precision prediction method for vibration fatigue life based on an accelerated fatigue test, which can solve the problem of extremely large prediction errors for the fatigue life of materials with a segmented S-N curve in traditional technologies.

[0006] The technical solution of the present invention is as follows:

[0007] The present application provides a high-precision prediction method for vibration fatigue life based on an accelerated fatigue test, which includes the following steps:

[0008] S1. Split the segmented S-N curve into two independent S-N curves, and obtain the complete fatigue damage of the two independent S-N curves based on the stress power spectral density function and vibration fatigue cumulative damage during the random vibration process;

[0009] S2. Calculate the difference between the complete fatigue damage based on two independent S-N curves and the damage value of the assumed S-N curve to obtain the actual cumulative fatigue damage of the piecewise S-N curve;

[0010] S3. Calculate the ratio of the actual cumulative fatigue damage of the piecewise S-N curve to the original fatigue damage to obtain the improved inverse power law formula;

[0011] S4. Calculate the stress probability function based on the improved inverse power law formula by the Bendat method or the Dirlik method to obtain the characterized improved inverse power law formula, and conduct numerical analysis to obtain the relationship curve between the acceleration ratio and the accelerated fatigue life;

[0012] S5. Obtain the accelerated vibration fatigue test value and correct the relationship curve between the acceleration ratio and the accelerated fatigue life to obtain the original fatigue life under the original vibration load spectrum.

[0013] Further, the calculation formula for the complete fatigue damage of the above two independent S-N curves in step S1 is:

[0014]

[0015] Where are the complete fatigue damages of the two independent S-N curves respectively, and k1, C1, k2, and C2 are all fatigue parameters of the two independent S-N curves, E P is the peak crossing number of the random vibration stress power spectral density function, S is the stress amplitude in the vibration fatigue process, and P(S) is the probability function of the stress.

[0016] Further, the formula for the above difference calculation in step S2 is:

[0017]

[0018] Where D a is the cumulative fatigue damage after acceleration of the piecewise S-N curve, are the complete cumulative fatigue damages after acceleration of the two S-N curves respectively, is the assumed damage of the first segment of the S-N curve, is the assumed damage of the second segment of the S-N curve, P′(S) is the stress probability distribution function after acceleration, and k1, C1, k2, and C2 are the fatigue parameters of the two independent S-N curves, E P is the peak crossing number of the random vibration stress power spectral density function, S is the stress amplitude in the vibration fatigue process, and S0 is the stress at the segmentation point of the S-N curve.

[0019] Further, the formula for the above division calculation in step S3 is:

[0020]

[0021] Among them, D a is the cumulative fatigue damage after the acceleration of the piecewise S-N curve, and D o is the original fatigue damage. are the complete cumulative fatigue damages of two S-N curves respectively, P′(S) is the stress probability distribution function after acceleration, k1, C1, k2, and C2 are all fatigue parameters of two independent S-N curves, and k * is the acceleration ratio in the acceleration experiment, and E P is the peak crossing times of the random vibration stress power spectral density function, S is the stress amplitude in the vibration fatigue process. are all assumed cumulative fatigue damages, and S0 is the stress at the segmentation of the S-N curve.

[0022] Furthermore, the improved inverse power law formula characterized by calculating the stress probability function in step S4 is:

[0023]

[0024] Among them, D NBa is the cumulative fatigue damage after the acceleration of the piecewise S-N curve characterized by applying the Bendat method, and D NBo is the original cumulative fatigue damage characterized by applying the Bendat method. WBa is the cumulative fatigue damage after the acceleration of the piecewise S-N curve characterized by applying the Dirlik method, and D WBo is the original cumulative fatigue damage characterized by applying the Dirlik method. and are the complete cumulative fatigue damages of two S-N curves characterized by applying the Bendat method respectively. and are the complete cumulative fatigue damages of two S-N curves characterized by applying the Dirlik method respectively. k1 and k2 are the fatigue parameters of two independent S-N curves, and k * is the acceleration ratio of the acceleration test. and are the assumed cumulative fatigue damages before and after acceleration characterized by applying the Bendat method. and are the assumed cumulative fatigue damages before and after acceleration characterized by applying the Dirlik method.

[0025] Furthermore, the formula for correcting the relationship curve between the acceleration ratio and the accelerated fatigue life in step S5 is:

[0026]

[0027] Among them, T′a represents the accelerated fatigue life value calculated by the modified improved inverse power law formula, and T a represents the accelerated fatigue life, and T EXP represents the test value obtained from the accelerated vibration fatigue test, and T a (i) represents the predicted accelerated fatigue life by the improved inverse power law formula with the same load amplitude as the accelerated fatigue test, a represents the accelerated value, and i represents the corresponding value of the load amplitude of the accelerated fatigue test.

[0028] Compared with the prior art, the present invention has at least the following advantages or beneficial effects:

[0029] (1) The present invention provides a high-precision prediction method for vibration fatigue life based on accelerated fatigue test. By establishing an improved inverse power law formula considering the segmented S-N curve and correcting it with the accelerated fatigue test value, the vibration fatigue life under the original load spectrum is obtained, forming a high-precision life prediction method for accelerated vibration fatigue, which solves the problem of predicting the accelerated fatigue life of materials with segmented S-N curves. The principle is simple, easy to implement, and has certain engineering application value;

[0030] (2) The present invention overcomes the problem that the traditional inverse power law formula has a great error in predicting the original fatigue life of materials with segmented S-N curves in the accelerated fatigue test. Description of the Drawings

[0031] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required in the embodiments. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings.

[0032] Figure 1 It is a step diagram of a high-precision prediction method for vibration fatigue life based on accelerated fatigue test of the present invention. Detailed Embodiments

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some, but not all, of the embodiments of the present application. Usually, the components of the embodiments of the present application described and shown here can be arranged and designed in various different configurations.

[0034] Accordingly, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the claimed present application, but merely represents selected embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts fall within the scope of protection of the present application.

[0035] It should be noted that like reference numerals and letters denote like items in the following drawings, and thus, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0036] It should be noted that in this article, the term "comprising" or any other variant thereof is intended to cover a non-exclusive inclusion, such that a process, method, article, or device comprising a series of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or device. Without further limitation, elements defined by the statement "comprising..." do not preclude the presence of additional identical elements in the process, method, article, or device comprising the said elements.

[0037] In the description of the present application, it should also be noted that unless otherwise clearly defined and limited, the terms "arranged" and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to specific circumstances.

[0038] The following will describe in detail some embodiments of the present application in conjunction with the accompanying drawings. Without conflict, the following embodiments and the features in the embodiments can be combined with each other.

[0039] Embodiment

[0040] Please refer to Figure 1 , Figure 1 which shows a step diagram of a high-precision prediction method for vibration fatigue life based on an accelerated fatigue test provided by an embodiment of the present application.

[0041] A high-precision prediction method for vibration fatigue life based on an accelerated fatigue test provided by the present application includes the following steps:

[0042] S1. Split the piecewise S-N curve into two independent S-N curves, and obtain the complete fatigue damage of the two independent S-N curves based on the stress power spectral density function and vibration fatigue cumulative damage in the random vibration process;

[0043] S2. Calculate the difference between the complete fatigue damage based on two independent S-N curves and the damage value of the assumed S-N curve to obtain the actual cumulative fatigue damage of the piecewise S-N curve;

[0044] S3. Calculate the ratio of the actual cumulative fatigue damage of the piecewise S-N curve to the original fatigue damage to obtain the improved inverse power law formula;

[0045] S4. Calculate the stress probability function based on the improved inverse power law formula by the Bendat method or the Dirlik method to obtain the characterized improved inverse power law formula, and perform numerical analysis to obtain the relationship curve between the acceleration ratio and the accelerated fatigue life;

[0046] S5. Obtain the accelerated vibration fatigue test value and correct the relationship curve between the acceleration ratio and the accelerated fatigue life to obtain the original fatigue life under the original vibration load spectrum.

[0047] As a preferred implementation manner, the formula for the complete fatigue damage of the two independent S-N curves in step S1 is:

[0048]

[0049] Wherein, are the complete fatigue damages of the two independent S-N curves respectively, k1, C1, k2 and C2 are all fatigue parameters of the two independent S-N curves, E P is the peak crossing number of the random vibration stress power spectral density function, S is the stress amplitude in the vibration fatigue process, and P(S) is the probability function of the stress.

[0050] It should be noted that the calculation formula of E P is: m i represents the i-th spectral moment of the stress.

[0051] As a preferred implementation manner, the formula for the difference calculation in step S2 is:

[0052]

[0053] Wherein, D a is the cumulative fatigue damage after acceleration of the piecewise S-N curve, are the complete cumulative fatigue damages after acceleration of the two S-N curves respectively, is the assumed damage of the first-segment S-N curve, is the assumed damage of the second-segment S-N curve, P′(S) is the stress probability distribution function after acceleration, k1, C1, k2 and C2 are the fatigue parameters of the two independent S-N curves, E Pis the peak crossing number of the power spectral density function of the random vibration stress, S is the stress amplitude during the vibration fatigue process, and S0 is the stress at the segmentation of the S-N curve.

[0054] As a preferred implementation manner, the formula for the division calculation in step S3 is:

[0055]

[0056] where D a is the cumulative fatigue damage after acceleration of the segmented S-N curve, D o is the original fatigue damage, are the complete cumulative fatigue damages of the two S-N curves respectively, P′(S) is the stress probability distribution function after acceleration, k1, C1, k2, and C2 are all fatigue parameters of the two independent S-N curves, and k * is the acceleration ratio in the acceleration experiment, E P is the peak crossing number of the power spectral density function of the random vibration stress, S is the stress amplitude during the vibration fatigue process, are all assumed cumulative fatigue damages, and S0 is the stress at the segmentation of the S-N curve.

[0057] As a preferred implementation manner, the improved inverse power law formula obtained by calculating the stress probability function in step S4 is:

[0058]

[0059] where D NBa is the cumulative fatigue damage after acceleration of the segmented S-N curve characterized by the Bendat method, D NBo is the original cumulative fatigue damage characterized by the Bendat method, D WBa is the cumulative fatigue damage after acceleration of the segmented S-N curve characterized by the Dirlik method, D WBo is the original cumulative fatigue damage characterized by the Dirlik method, and are the complete cumulative fatigue damages of the two S-N curves characterized by the Bendat method respectively, and are the complete cumulative fatigue damages of the two S-N curves characterized by the Dirlik method respectively, k1 and k2 are the fatigue parameters of the two independent S-N curves, and k * is the acceleration ratio of the acceleration test, and are the assumed cumulative fatigue damages before and after acceleration characterized by the Bendat method, and are the assumed cumulative fatigue damages before and after acceleration characterized by the Dirlik method.

[0060] To further give the expression form of the assumed damage, the incomplete gamma function is introduced and applied to the improved inverse power law formulas of the Bendat method and the Dirlik method:

[0061]

[0062]

[0063]

[0064]

[0065]

[0066]

[0067]

[0068]

[0069] Among them, and are the assumed cumulative fatigue damages after acceleration characterized by the Bendat method, and are respectively the assumed cumulative fatigue damages before acceleration characterized by the Bendat method, and are the assumed cumulative fatigue damages after acceleration characterized by the Dirlik method, and are the assumed cumulative fatigue damages before acceleration characterized by the Dirlik method. k1, C1 and k2, C2 are the fatigue parameters of two independent S-N curves. k * is the acceleration ratio in the acceleration experiment. Γ and γ are incomplete gamma functions. E P is the peak crossing times of the random vibration stress power spectral density function. S0 is the stress at the segmentation of the S-N curve. m0 is the 0th order spectral moment. Q, Q1, D1, D2, D3 and R are all parameters defined by spectral moments in the Dirlik method.

[0070] According to the fatigue cumulative damage theory, when the damage D reaches 1, fatigue failure is considered to occur. Therefore, the relationship between fatigue life and damage can be expressed as:

[0071] T = 1 / D,

[0072] where T represents the fatigue life and D represents the damage;

[0073] Therefore, the fatigue damages before and after acceleration in the improved inverse power law formula can be further rewritten by the fatigue life T:

[0074]

[0075] Among them, k1 and k2 represent the fatigue parameters of the independent S-N curve, and k * represents the acceleration ratio in the accelerated experiment, and respectively represent the complete cumulative fatigue damage of two S-N curves, are both assumed cumulative fatigue damages, and T a represents the accelerated fatigue life.

[0076] Thus, by applying the Bendat and Dirlik methods, the acceleration ratio k * and the accelerated fatigue life T a can be numerically analyzed to establish a relationship curve.

[0077] As a preferred implementation, the formula for correcting the relationship curve between the acceleration ratio and the accelerated fatigue life in step S5 is:

[0078]

[0079] Among them, T′ a represents the value of the accelerated fatigue life calculated by the corrected improved inverse power law formula, T a represents the accelerated fatigue life, T EXP represents the test value obtained from the accelerated vibration fatigue test, and T a (i) represents the prediction of the accelerated fatigue life by the improved inverse power law formula with the same load amplitude as the accelerated fatigue test, a represents the accelerated value, and i represents the corresponding value of the load amplitude of the accelerated fatigue test.

[0080] Therefore, the original fatigue life T′ under the original vibration load spectrum can be found on the corrected relationship curve of the accelerated fatigue life and the acceleration ratio o .

[0081] It can be understood that the structure shown in the figure is only schematic. A high-precision prediction method for vibration fatigue life based on accelerated fatigue tests may also include more or fewer components than those shown in the figure, or have a different configuration from that shown in the figure. Each component shown in the figure can be implemented by hardware, software, or a combination thereof.

[0082] In the embodiments provided in the present application, it should be understood that the disclosed system or method can also be implemented in other ways. The embodiments described above are merely illustrative. For example, the flowcharts and block diagrams in the accompanying drawings show the possible architectures, functions, and operations of systems, methods, and computer program products according to multiple embodiments of the present application. In this regard, each block in the flowchart or block diagram may represent a module, a program segment, or a part of code, and the module, program segment, or part of code contains one or more executable instructions for implementing the specified logical function. It should also be noted that in some alternative implementations, the functions marked in the blocks may occur in a different order than that marked in the accompanying drawings. For example, two consecutive blocks may actually be executed substantially in parallel, and they may sometimes be executed in the reverse order, depending on the functions involved. It should also be noted that each block in the block diagram and / or flowchart, as well as the combination of blocks in the block diagram and / or flowchart, can be implemented by a dedicated hardware-based system for performing the specified functions or actions, or can be implemented by a combination of dedicated hardware and computer instructions.

[0083] In addition, in each embodiment of the present application, the various functional modules may be integrated together to form an independent part, or each module may exist separately, or two or more modules may be integrated to form an independent part.

[0084] If the function is implemented in the form of a software functional module and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present application, in essence, or the part that contributes to the prior art, or a part of this technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions for causing a computer device (which may be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods described in various embodiments of the present application. The aforementioned storage medium includes: various media such as USB flash drives, mobile hard disks, read-only memories (ROMs), random access memories (RAMs), magnetic disks, or optical discs that can store program codes.

[0085] In summary, the high-precision vibration fatigue life prediction method based on the accelerated fatigue test provided by the embodiments of the present application establishes an improved inverse power law formula considering the piecewise S-N curve, and corrects it through the accelerated fatigue test values to obtain the vibration fatigue life under the original load spectrum, forming a high-precision life prediction method for accelerated vibration fatigue. It overcomes the problem that the traditional inverse power law formula has a great prediction error for the original fatigue life of materials with piecewise S-N curves in the accelerated fatigue test, solves the problem of predicting the accelerated fatigue life of materials with piecewise S-N curves, has a simple principle, is easy to implement, and has certain engineering application value.

[0086] The foregoing is only a preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, various changes and modifications can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

[0087] For those skilled in the art, it is obvious that the present application is not limited to the details of the above exemplary embodiments, and can be implemented in other specific forms without departing from the spirit or basic characteristics of the present application. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present application is defined by the appended claims rather than the above description. Therefore, it is intended to include all changes falling within the meaning and scope of the equivalent elements of the claims in the present application. Any reference signs in the claims should not be regarded as limiting the claimed claims.

Claims

1. A high-precision prediction method for vibration fatigue life based on an accelerated fatigue test, characterized in that It includes the following steps: S1. Split the piecewise S-N curve into two independent S-N curves, and obtain the complete fatigue damage of the two independent S-N curves based on the stress power spectral density function and vibration fatigue cumulative damage during the random vibration process; S2. Calculate the difference between the complete fatigue damage of the two independent S-N curves and the damage value of the assumed S-N curve to obtain the accelerated cumulative fatigue damage of the piecewise S-N curve; S3. Calculate the division of the accelerated cumulative fatigue damage of the piecewise S-N curve by the original fatigue damage to obtain the improved inverse power law formula; S4. Calculate the stress probability function based on the improved inverse power law formula by the Bendat method or Dirlik method to obtain the characterized improved inverse power law formula, and perform numerical analysis to obtain the relationship curve between the acceleration ratio and the accelerated fatigue life; S5. Obtain the accelerated vibration fatigue test value and correct the relationship curve between the acceleration ratio and the accelerated fatigue life to obtain the original fatigue life under the original vibration load spectrum; The calculation formula for the complete fatigue damage of the two independent S-N curves described in step S1 is: Among them, are the complete fatigue damages of two independent S-N curves, and k1, C1, k2, and C2 are all fatigue parameters of the two independent S-N curves, E p is the peak crossing number of the random vibration stress power spectral density function, S is the stress amplitude during the dynamic fatigue process, and P(S) is the probability function of the stress; The formula for the difference calculation described in step S2 is: Among them, D a is the cumulative fatigue damage after the acceleration of the segmented S-N curve, are the complete cumulative fatigue damages after the acceleration of the two S-N curves respectively, is the assumed damage of the first-segment S-N curve, is the assumed damage of the second-segment S-N curve, P′(S) is the stress probability distribution function after acceleration, k1, C1, k2 and C2 are the fatigue parameters of the two independent S-N curves, E p is the peak crossing number of the random vibration stress power spectral density function, S is the stress amplitude during the vibration fatigue process, and S0 is the stress at the segmentation point of the S-N curve; The formula for correcting the relationship curve between the acceleration ratio and the accelerated fatigue life described in step S5 is: Among them, T' a represents the accelerated fatigue life value calculated by the modified inverse power law formula after correction, T a represents the accelerated fatigue life, T EXP represents the test value obtained from the accelerated vibration fatigue test, T a (i) represents the prediction of the accelerated fatigue life by the modified inverse power law formula with the same load amplitude as the accelerated fatigue test, a represents the accelerated value, and i represents the corresponding value of the load amplitude of the accelerated fatigue test.

2. The high-precision vibration fatigue life prediction method based on an accelerated fatigue test according to claim 1, wherein The formula for the division calculation described in step S3 is: Among them, D a is the cumulative fatigue damage after the acceleration of the segmented S-N curve, and D o is the original fatigue damage. are the complete cumulative fatigue damages of the two S-N curves respectively. P′(S) is the stress probability distribution function after acceleration. k1, C1, k2, and C2 are all fatigue parameters of the two independent S-N curves. k * is the acceleration ratio in the acceleration experiment. E P is the peak crossing number of the random vibration stress power spectral density function. S is the stress amplitude during the vibration fatigue process. are all assumed cumulative fatigue damages. S0 is the stress at the segmentation point of the S-N curve.

3. The high-precision vibration fatigue life prediction method based on an accelerated fatigue test according to claim 1, wherein The characterized improved inverse power law formula obtained by calculating the stress probability function in step S4 is: Among them, D NBa is the cumulative fatigue damage after acceleration of the piecewise S-N curve characterized by the Bendat method, D NBo is the original cumulative fatigue damage characterized by the Bendat method, D WBa is the cumulative fatigue damage after acceleration of the piecewise S-N curve characterized by the Dirlik method, D WBo is the original cumulative fatigue damage characterized by the Dirlik method, and are the complete cumulative fatigue damages of two S-N curves characterized by the Bendat method, and are the complete cumulative fatigue damages of two S-N curves characterized by the Dirlik method, k1 and k2 are the fatigue parameters of two independent S-N curves, k * is the acceleration ratio in the acceleration test, and are the assumed cumulative fatigue damages before and after acceleration characterized by the Bendat method, and are the assumed cumulative fatigue damages before and after acceleration characterized by the Dirlik method.

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