Method and apparatus for calculating crack propagation life of engine structure in vibration fatigue

Abstract

The present invention relates to the technical field of mechanical property testing and characterization. Disclosed are a method and apparatus for calculating a crack propagation life of an engine structure in vibration fatigue, which method and apparatus aim to obtain reliable fracture mechanics parameters and a crack propagation rate curve and provide an accurately quantified crack propagation life, so as to provide methodological guidance for the life assessment of reusable engines. The calculation method comprises: acquiring a time-domain random stress spectrum of stress responses in an assessment section in a finite element model of an engine structure; on the basis of the time-domain random stress spectrum, performing finite element analysis processing on a crack model of the engine structure, so as to determine fracture mechanics parameters of a cracked structure; performing a vibration fatigue performance test on a crack propagation rate model, which is set up according to a preset crack propagation mode, and determining, by using parameter identification, a target parameter value corresponding to the crack propagation rate model; and in combination with the parameter value corresponding to the crack propagation rate model and a preset critical crack length value, performing crack propagation life calculation, so as to obtain a target crack propagation life.

Description

A method and apparatus for calculating the vibration fatigue crack propagation life of an engine structure.

[0001] This application claims priority to Chinese Patent Application No. 202410512958.2, filed on April 26, 2024, entitled "A method and apparatus for calculating the vibration fatigue crack propagation life of an engine structure", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This invention relates to the field of mechanical performance testing and characterization technology, and in particular to a method and apparatus for calculating the vibration fatigue crack propagation life of an engine structure. Background Technology

[0003] Reusable engines are one of the main development directions for aerospace launch vehicle propulsion systems. Under the requirement of reusability, the demands for engine fatigue strength design and life assessment are particularly prominent. Traditional fatigue analysis methods, based on stress / strain-life curves (SN curves), can provide life prediction results with a certain degree of reliability. However, when fatigue analysis methods are applied to reusable structures, the following problems exist: SN curve life models have limited parameters, failing to fully describe the fatigue damage process mechanism; furthermore, the load factors in fatigue analysis mainly consider the magnitude and number of cyclic stresses, making it difficult to account for the impact of load sequence on life. This leads to significant errors in life prediction results, which is detrimental to structural design and evaluation.

[0004] Damage tolerance methods and crack propagation techniques based on fracture mechanics have been widely applied in the aerospace field. Currently, linear elastic fracture mechanics methods are the primary approach, suitable for modeling macroscopic long cracks, material performance testing, and quasi-static fatigue life calculation. Vibration loads are a significant load characteristic of liquid rocket engines during their repeated use. Under vibration conditions, most of the fatigue life occurs in the crack initiation stage. To ensure normal engine operation, structural integrity must be maintained, and macroscopic cracks or cracks penetrating the wall thickness are generally not permitted. Therefore, when using fracture mechanics methods for engine fatigue design and life assessment, the structural response characteristics under vibration loads, the damage modes of non-penetrating wall thickness cracks, and effective performance data should be considered. Currently, linear elastic fracture mechanics has limitations such as parameter uncertainty when used for non-penetrating cracks in the crack initiation stage. Furthermore, the direct introduction of cracks into traditional modal vibration response calculations cannot account for elastoplastic and other nonlinear conditions, and the computational scale and efficiency of transient dynamics calculations for crack problems limit its widespread engineering application. Therefore, current fracture mechanics methods are insufficient to meet the needs of fatigue crack life assessment for engines under vibration conditions.

[0005] Therefore, it is necessary to develop a method for predicting fatigue crack propagation life under vibration loads on engine structures, so as to obtain reliable fracture mechanics parameters and crack propagation rate curves, give accurate quantitative crack propagation life, and provide methodological guidance for the life assessment of reusable engines. Summary of the Invention

[0006] The purpose of this invention is to provide a method and apparatus for calculating the vibration fatigue crack propagation life of engine structures, so as to obtain reliable fracture mechanics parameters and crack propagation rate curves, give an accurate quantified crack propagation life, and provide methodological guidance for the life assessment of reusable engines.

[0007] In a first aspect, the present invention provides a method for calculating the vibration fatigue crack propagation life of an engine structure, the calculation method comprising:

[0008] Obtain the time-domain stochastic stress spectrum of the stress response in the test section of the engine structure in the finite element model;

[0009] Based on the time-domain stochastic stress spectrum, a finite element analysis was performed on the crack model of the engine structure to determine the fracture mechanics parameters of the cracked structure.

[0010] Vibration fatigue performance tests were conducted on the crack propagation rate model established according to the preset crack propagation mode, and the target parameter values ​​corresponding to the crack propagation rate model were determined by parameter identification.

[0011] The crack propagation life is calculated by combining the parameter values ​​corresponding to the crack propagation rate model and the preset critical crack length value, and the target crack propagation life is obtained.

[0012] Using the above technical solution, after obtaining the time-domain random stress spectrum of the stress response of the test section in the finite element model of the engine structure, the crack model of the engine structure can be subjected to finite element analysis based on the time-domain random stress spectrum to determine the fracture mechanics parameters of the cracked structure. Vibration fatigue performance tests are then conducted on the crack propagation rate model established according to the preset crack propagation mode. The target parameter values ​​corresponding to the crack propagation rate model are determined by parameter identification. Finally, the crack propagation life can be calculated by combining the parameter values ​​corresponding to the crack propagation rate model and the preset critical crack length value to obtain the target crack propagation life. Based on this, the present invention integrates the calculation of random vibration response of structures, time-domain simulation of vibration stress response, crack modeling and fracture mechanics parameter calculation, determination of crack propagation rate model parameters and initial crack length, and crack propagation life calculation. It can obtain the steady-state response of random vibration of structures and the time-domain random stress spectrum, provide accurate quantified fracture mechanics parameters, determine crack propagation rate model parameters and initial crack length based on fatigue performance test data, and realize the calculation of structural crack propagation life. It overcomes the shortcomings of traditional fatigue analysis methods and macroscopic crack analysis methods of linear elastic fracture mechanics when used to calculate the life of non-penetrating thickness cracks under vibration environment, such as unclear mechanism, difficulty in obtaining parameters, and unsuitable model, which leads to large deviations in calculation results.

[0013] Therefore, the method for calculating the vibration fatigue crack propagation life of engine structures provided by this invention can obtain reliable fracture mechanics parameters and crack propagation rate curves, and give an accurate quantitative crack propagation life, providing methodological guidance for the life assessment of reusable engines.

[0014] In a second aspect, the present invention also provides a calculation device for the vibration fatigue crack propagation life of an engine structure, used to implement the calculation method for the vibration fatigue crack propagation life of an engine structure in the first aspect, the calculation device comprising:

[0015] The acquisition module is used to acquire the time-domain random stress spectrum of the stress response of the test section in the finite element model of the engine structure;

[0016] The first determination module is used to perform finite element analysis on the crack model of the engine structure based on the time-domain stochastic stress spectrum, and determine the fracture mechanics parameters of the cracked structure.

[0017] The second determining module is used to conduct vibration fatigue performance tests on the crack propagation rate model established according to the preset crack propagation mode, and to determine the target parameter values ​​corresponding to the crack propagation rate model by using parameter identification.

[0018] The acquisition module is used to calculate the crack propagation life by combining the parameter values ​​corresponding to the crack propagation rate model and the preset critical crack length value, and to obtain the target crack propagation life.

[0019] Optionally, the acquisition module includes:

[0020] The first building unit is used to build the finite element model of the engine structure;

[0021] The first determining unit is used to apply random vibration load excitation to the finite element model of the engine structure and determine the power spectral density of the stress response of the test section.

[0022] The first acquisition unit is used to sample the power spectral density to obtain the time-domain random stress spectrum of the stress response of the test section.

[0023] Optionally, the first obtaining unit includes:

[0024] Obtain sub-units to obtain the stress amplitude probability density function corresponding to the power spectral density;

[0025] Sub-units are obtained to sample the time-domain stress response based on the stress amplitude probability density function and the peak probability density function, thereby obtaining stress response samples.

[0026] The sub-unit is determined to randomize the stress response samples and determine the time-domain random stress spectrum of the stress response in the test section.

[0027] Optionally, the first determining module includes:

[0028] The second building unit is used to build a crack model of the engine structure;

[0029] The second determining unit is used to determine the external load applied to the crack model based on the time-domain random stress spectrum;

[0030] The third determining element is used to perform elastic-plastic finite element analysis on the crack model under external load to determine the fracture mechanics parameters corresponding to each crack length.

[0031] Optionally, the fracture mechanics parameters may include at least the stress intensity factor or the J integral.

[0032] Optionally, the second determining module includes:

[0033] The third establishment unit is used to establish a crack propagation rate model according to a preset crack propagation mode;

[0034] The acquisition unit is used to acquire the vibration fatigue stress-life test curve or vibration fatigue strain-life test curve of the engine structure.

[0035] The fourth determining unit is used to determine the test crack propagation life based on the vibration fatigue stress-life test curve or vibration fatigue strain-life test curve, combined with the initial values ​​of the initial crack length and crack propagation rate parameters.

[0036] The fifth determining unit is used to optimize the initial value of the crack propagation rate parameter using parameter optimization methods, and determine the parameter value with the smallest error corresponding to the parameter value of the crack propagation rate model.

[0037] Optional crack propagation rate models include:

[0038] Where a is the crack length, N is the number of cycles, C, n, p, q are undetermined model parameter values, f is the crack opening / closing function, R is the stress ratio, and ΔK is the stress intensity factor amplitude. th K is the crack propagation threshold value. max K represents the peak value of the stress intensity factor. C This refers to fracture toughness.

[0039] Optionally, the modules to be obtained include:

[0040] The second obtaining unit is used to combine the time-domain random stress spectrum, fracture mechanics parameters, target parameter values ​​corresponding to the crack propagation rate model, and preset critical crack length values ​​to calculate the crack propagation life using a cycle-by-cycle method or a block spectrum average life calculation method, and obtain the target crack propagation life.

[0041] The beneficial effects of the calculation device for engine structure vibration fatigue crack propagation life provided in the second aspect are the same as those of the calculation method for engine structure vibration fatigue crack propagation life described in the implementation method of the first aspect, and will not be repeated here. Attached Figure Description

[0042] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0043] Figure 1 is a flowchart of the steps of a method for calculating the vibration fatigue crack propagation life of an engine structure provided in an embodiment of the present invention;

[0044] Figure 2 is a flowchart of the steps of another method for calculating the vibration fatigue crack propagation life of an engine structure provided in an embodiment of the present invention;

[0045] Figure 3 shows the structural testing parts and their vibration stress response power spectral density curves in an embodiment of the present invention.

[0046] Figure 4(a) shows a typical narrowband distribution curve of stress response;

[0047] Figure 4(b) shows a typical broadband distribution curve of stress response;

[0048] Figure 5 is a schematic diagram of the time-domain stress random spectrum in an embodiment of the present invention;

[0049] Figure 6 is a schematic diagram of the crack model of the engine structure in an embodiment of the present invention;

[0050] Figure 7 is a schematic diagram of surface cracks in an embodiment of the present invention;

[0051] Figure 8 is a schematic diagram of the crack propagation rate model parameters and the determination of the initial crack length in an embodiment of the present invention.

[0052] Figure 9 is a schematic diagram of the calculation device for the vibration fatigue crack propagation life of the engine structure according to an embodiment of the present invention. Detailed Implementation

[0053] To facilitate a clear description of the technical solutions in the embodiments of the present invention, the terms "first" and "second" are used to distinguish identical or similar items with essentially the same function and effect. For example, the first threshold and the second threshold are merely used to distinguish different thresholds and do not limit their order. Those skilled in the art will understand that the terms "first" and "second" do not limit the quantity or execution order, and that the terms "first" and "second" are not necessarily different.

[0054] It should be noted that in this invention, the terms "exemplary" or "for example" are used to indicate examples, illustrations, or descriptions. Any embodiment or design described as "exemplary" or "for example" in this invention should not be construed as being more preferred or advantageous than other embodiments or designs. Specifically, the use of terms such as "exemplary" or "for example" is intended to present the relevant concepts in a concrete manner.

[0055] In this invention, "at least one" refers to one or more, and "more than one" refers to two or more. "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone, where A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, at least one of a, b, or c can represent: a, b, c, a combination of a and b, a combination of a and c, a combination of b and c, or a, b, and c, where a, b, and c can be single or multiple.

[0056] As shown in Figure 1, an embodiment of the present invention provides a method for calculating the vibration fatigue crack propagation life of an engine structure, including:

[0057] S101: Obtain the time-domain random stress spectrum of the stress response of the test section in the finite element model of the engine structure.

[0058] In this application, the finite element method is used to perform dynamic modeling of the structure, and random vibration load excitation is applied to obtain dynamic responses such as power spectral density (PSD) and root mean square (RMS) of the stress response of the test part.

[0059] Based on the obtained power spectral density of the vibration stress response, the probability density function of the amplitude and peak value of the time-domain stress response is analyzed and given. Then, random numbers of the stress response in the time domain are obtained by sampling, and a time-domain random stress spectrum is formed.

[0060] S102: Based on the time-domain stochastic stress spectrum, the crack model of the engine structure is subjected to finite element analysis to determine the fracture mechanics parameters of the cracked structure.

[0061] Specifically, firstly, a crack propagation mode is assumed, the crack form is given, and the crack propagation path is defined. Then, a crack model is performed on the engine structure. The structural crack model mainly considers two points: firstly, it should be able to encompass the propagation range from the initial crack to the critical crack length; secondly, it should include the main structural features that affect the fracture mechanics parameters of cracks that do not penetrate the thickness, such as fillets, openings, and varying thicknesses. Finally, load points in the time-domain stochastic stress spectrum are selected as external loads and applied to the crack model for linear elastic or elastic-plastic finite element calculations to obtain the fracture mechanics parameters Ki (stress intensity factor) or Ji (J integral) corresponding to each crack length ai.

[0062] S103: Conduct vibration fatigue performance tests on the crack propagation rate model established according to the preset crack propagation mode, and use parameter identification to determine the target parameter values ​​corresponding to the crack propagation rate model.

[0063] Specifically, firstly, vibration fatigue performance test data such as fatigue stress-life curves or strain-life curves of materials or structural components under vibration loads are obtained, a crack propagation rate model is given, and the initial crack form is assumed; then, fracture mechanics calculations are performed on the vibration fatigue performance test specimens to obtain fracture mechanics parameters such as stress intensity factor Ktest; finally, for each stress level of the vibration fatigue performance test data (curve), initial values ​​of crack propagation rate model parameters and initial crack length are preset, the test crack propagation life at each stress level is calculated, and the parameter optimization result with the smallest error to the test life result is obtained as the final parameter identification value through parameter optimization method.

[0064] Based on this, this application transforms the material fatigue damage model characterized by a single mechanical parameter S (stress or strain) and life N into a material fatigue damage model characterized by initial crack size and fracture mechanics performance parameters, and obtains the crack propagation rate model parameter values.

[0065] S104: Calculate the crack propagation life by combining the parameter values ​​corresponding to the crack propagation rate model and the preset critical crack length value, and obtain the target crack propagation life.

[0066] Specifically, the time-domain stochastic stress spectrum and fracture mechanics parameters are substituted into the crack propagation rate model. By specifying the critical crack length *af* and the initial crack length *a0*, the crack propagation life is calculated using either a cyclic-by-cyclic method or a block spectrum average life calculation method, thus obtaining the final crack propagation life. It should be understood that a set of stochastic stress spectra corresponds to a set of crack propagation life values.

[0067] Compared with the prior art, the method for calculating the vibration fatigue crack propagation life of an engine structure provided in this embodiment of the invention, after obtaining the time-domain random stress spectrum of the stress response of the test section in the finite element model of the engine structure, can perform finite element analysis on the crack model of the engine structure based on the time-domain random stress spectrum, thereby determining the fracture mechanics parameters of the cracked structure, and conduct vibration fatigue performance tests on the crack propagation rate model established according to the preset crack propagation mode, use parameter identification to determine the target parameter value corresponding to the crack propagation rate model, and finally combine the parameter value corresponding to the crack propagation rate model and the preset critical crack length value to calculate the crack propagation life and obtain the target crack propagation life. Based on this, the embodiments of the present invention integrate the calculation of random vibration response of structures, time-domain simulation of vibration stress response, crack modeling and fracture mechanics parameter calculation, determination of crack propagation rate model parameters and initial crack length, and crack propagation life calculation. It can obtain the steady-state response of random vibration of structures and the time-domain stress random spectrum, provide accurate quantified fracture mechanics parameters, determine crack propagation rate model parameters and initial crack length based on fatigue performance test data, and realize the calculation of structural crack propagation life. It overcomes the shortcomings of traditional fatigue analysis methods and macroscopic crack analysis methods of linear elastic fracture mechanics when used to calculate the life of non-penetrating thickness cracks under vibration environment, such as unclear mechanism, difficulty in obtaining parameters, and unsuitable model, which leads to large deviations in calculation results.

[0068] Therefore, the method for calculating the vibration fatigue crack propagation life of engine structures provided in this embodiment of the invention can obtain reliable fracture mechanics parameters and crack propagation rate curves, and provide accurate quantitative crack propagation life, thus providing methodological guidance for the life assessment of reusable engines.

[0069] As shown in Figure 2, this embodiment of the invention also provides another method for calculating the vibration fatigue crack propagation life of an engine structure. The specific steps of the method for calculating the vibration fatigue crack propagation life of an engine structure provided by this embodiment of the invention will be described in detail below with reference to Figures 2 to 8.

[0070] S201: Establish a finite element model of the engine structure.

[0071] S202: Apply random vibration load excitation to the finite element model of the engine structure to determine the power spectral density of the stress response of the test section.

[0072] In this application, the finite element method is used to perform dynamic simulation modeling of the structure. Random vibration load excitation is applied to obtain the power spectral density (PSD) and root mean square (RMS) values ​​of the stress response at the test location, as shown in Figure 3. Figure 3 illustrates the stress power spectral density curves of the severely affected part of the engine structure's vibration stress response, i.e., the test section. The horizontal axis represents frequency in Hz, and the vertical axis represents stress power spectral density in MPa. 2 / Hz.

[0073] S203: The power spectral density is sampled to obtain the time-domain random stress spectrum of the stress response of the test section.

[0074] Specifically, for the obtained power spectral density of the vibration stress response, the probability density function of the time-domain stress response is analyzed and given. Then, random numbers in the time domain of the stress response are obtained by sampling and a time-domain random stress spectrum is formed.

[0075] Step S203 above includes the following sub-steps:

[0076] Sub-step A1: Obtain the stress amplitude probability density function corresponding to the power spectral density;

[0077] Sub-step A2: Based on the stress amplitude probability density function and the peak probability density function, the time-domain stress response is sampled to obtain stress response samples;

[0078] Sub-step A3: Randomize the stress response samples to determine the time-domain random stress spectrum of the stress response in the test section.

[0079] The PSD spectrum of the vibration stress response was analyzed. Figure 4(a) shows a typical narrow-band distribution curve of the stress response; Figure 4(b) shows a typical wide-band distribution curve of the stress response. As shown in Figure 4(b), if it is a wide-band random distribution, the Dirlik model is used to obtain the stress amplitude probability density function of the wide-band distribution; as shown in Figure 4(a), if it is a narrow-band distribution, the Narrow-band model is used to obtain the stress amplitude probability density function of the narrow-band distribution. At the same time, combined with the assumed peak probability density function following a Gaussian distribution, the time-domain stress response is sampled to obtain a sufficient number of stress response samples. Finally, the time-domain random stress spectrum is obtained through randomization, as shown in Figure 5. In Figure 5, the horizontal axis represents time in seconds, and the vertical axis represents stress in MPa.

[0080] S204: Based on the time-domain stochastic stress spectrum, finite element analysis is performed on the crack model of the engine structure to determine the fracture mechanics parameters of the cracked structure.

[0081] Among them, the fracture mechanics parameters include at least the stress intensity factor or the J integral.

[0082] Step S204 above includes the following sub-steps:

[0083] Sub-step B1: Establish a crack model of the engine structure, as shown in Figure 6;

[0084] Sub-step B2: Determine the external load applied to the crack model based on the time-domain stochastic stress spectrum;

[0085] Sub-step B3: Perform elastic-plastic finite element analysis on the crack model with applied external load to determine the fracture mechanics parameters corresponding to each crack length.

[0086] The specific experimental method is as follows: First, assume the crack propagation mode and give the crack form, such as edge crack, surface crack, or embedded crack, as shown in Figure 7, and set the crack propagation path. Then, perform finite element modeling on the crack model of the engine structure. The structural crack model mainly considers two points: one is that it can encompass the propagation range from the initial crack to the critical crack length; the other is that it includes the main structural features that affect the fracture mechanical parameters of the non-penetrating thickness crack, such as fillets, openings, and variable thickness. Finally, apply the time-domain random stress spectrum of the stress response of the above test section as an external load to the crack model for elastic-plastic finite element calculation to obtain the fracture mechanical parameters Ki (stress intensity factor) or Ji (J integral) corresponding to each crack length ai.

[0087] Based on this, this application simplifies the three-dimensional crack modeling of actual complex structures into a crack modeling problem of appropriate scale that reflects the main characteristics of structural cracks and stress response features. At the same time, it uses the structural dynamic response as a load input for fracture mechanics calculation, transforming the dynamic problem into a static problem, thereby obtaining the elastoplastic fracture mechanics parameter solution. This solves the problem that steady-state vibration response calculation based on the modal method cannot perform elastoplastic analysis and nonlinear factor simulation.

[0088] S205: Establish a crack propagation rate model according to the preset crack propagation mode.

[0089] Specifically, given a crack propagation rate model, the model considers factors such as the stress intensity factor amplitude, the maximum stress intensity factor, the stress intensity factor threshold, and crack closure, such as using the NASGRO crack propagation rate formula:

[0090] Where a is the crack length, N is the number of cycles, C, n, p, and q are undetermined model parameter values, f is the crack opening / closing function, R is the stress ratio, and ΔK is the stress intensity factor amplitude. th K is the crack propagation threshold value. max K represents the peak value of the stress intensity factor. C This refers to fracture toughness.

[0091] S206: Obtain the vibration fatigue stress-life test curve or vibration fatigue strain-life test curve of the engine structure.

[0092] S207: Determine the test crack propagation life based on the vibration fatigue stress-life test curve or vibration fatigue strain-life test curve, combined with the initial values ​​of the initial crack length and crack propagation rate parameters.

[0093] S208: Using parameter optimization methods, the initial values ​​of the crack propagation rate parameters are optimized, and the parameter values ​​with the smallest errors are determined to be the parameter values ​​corresponding to the crack propagation rate model.

[0094] In this application, vibration fatigue stress-life or strain-life test data (curves) of materials or structural components are obtained. For each stress / strain level of the test, initial values ​​(a0) of the initial crack length a0 and crack propagation rate parameters are assumed. ini C ini n ini p ini q ini The test crack propagation life was calculated, and the parameter optimization result with the smallest error from the test life result was obtained as the final target parameter value through parameter optimization method, as shown in Figure 8.

[0095] Based on this, this application transforms the material fatigue damage model characterized by a single mechanical parameter S (stress or strain) and life N into a material fatigue damage model characterized by crack size and its fracture mechanical properties, and obtains the crack propagation rate model parameter values.

[0096] S209: Calculate the crack propagation life by combining the parameter values ​​corresponding to the crack propagation rate model and the preset critical crack length value, and obtain the target crack propagation life.

[0097] In this application, the crack propagation life is calculated by combining the time-domain stochastic stress spectrum, fracture mechanics parameters, target parameter values ​​corresponding to the crack propagation rate model, and preset critical crack length values, using a cycle-by-cycle method or a block spectrum average life calculation method, to obtain the target crack propagation life.

[0098] It should be understood that a set of random stress spectra corresponds to a set of crack propagation life values.

[0099] The beneficial effects of the embodiments of the present invention are:

[0100] (1) By calculating the steady-state vibration response and simulating the stress response in the time domain, both the frequency domain characteristics of the structural stress response and the time domain statistical characteristics of the stress response are considered. The stress characteristics under vibration load are fully preserved, making the life calculation more comprehensive and precise.

[0101] (2) Using time-domain stress response as an external load for crack modeling provides a load basis for transforming overall structural crack modeling into local structural crack modeling, reducing the model size and significantly improving computational efficiency. On the other hand, it transforms dynamic calculations into static calculations, enabling the acquisition of more realistic elastoplastic and nonlinear solutions, and significantly improving the accuracy of fracture mechanics parameters.

[0102] (3) By making full use of fatigue performance test data to identify crack propagation rate model parameters and initial crack length distribution, the source of key performance parameters for crack propagation life calculation is reliable, the modeling mechanism is clearer, and the uncertainty of traditional extrapolation method through macroscopic long crack model is avoided, ensuring that the calculation model and calculation results are reasonable and reliable.

[0103] As shown in Figure 9, this embodiment of the invention also provides a calculation device 300 for the vibration fatigue crack propagation life of an engine structure, used to implement the calculation method for the vibration fatigue crack propagation life of an engine structure in the above embodiment. The calculation device includes:

[0104] The acquisition module 301 is used to acquire the time-domain random stress spectrum of the stress response of the test section in the finite element model of the engine structure;

[0105] The first determining module 302 is used to perform finite element analysis on the crack model of the engine structure based on the time-domain stochastic stress spectrum, and determine the fracture mechanics parameters of the cracked structure.

[0106] The second determining module 303 is used to conduct vibration fatigue performance tests on the crack propagation rate model established according to the preset crack propagation mode, and to determine the target parameter values ​​corresponding to the crack propagation rate model by using parameter identification.

[0107] The module 304 is used to calculate the crack propagation life by combining the parameter values ​​corresponding to the crack propagation rate model and the preset critical crack length value, so as to obtain the target crack propagation life.

[0108] Optionally, the acquisition module 301 includes:

[0109] The first building unit is used to build the finite element model of the engine structure;

[0110] The first determining unit is used to apply random vibration load excitation to the finite element model of the engine structure and determine the power spectral density of the stress response of the test section.

[0111] The first acquisition unit is used to sample the power spectral density to obtain the time-domain random stress spectrum of the stress response of the test section.

[0112] Optionally, the first obtaining unit includes:

[0113] Obtain sub-units to obtain the stress amplitude probability density function corresponding to the power spectral density;

[0114] Sub-units are obtained to sample the time-domain stress response based on the stress amplitude probability density function and the peak probability density function, thereby obtaining stress response samples.

[0115] The sub-unit is determined to randomize the stress response samples and determine the time-domain random stress spectrum of the stress response in the test section.

[0116] Optionally, the first determining module 302 includes:

[0117] The second building unit is used to build a crack model of the engine structure;

[0118] The second determining unit is used to determine the external load applied to the crack model based on the time-domain random stress spectrum;

[0119] The third determining element is used to perform elastic-plastic finite element analysis on the crack model under external load to determine the fracture mechanics parameters corresponding to each crack length.

[0120] Optionally, the fracture mechanics parameters may include at least the stress intensity factor or the J integral.

[0121] Optionally, the second determining module 303 includes:

[0122] The third establishment unit is used to establish a crack propagation rate model according to a preset crack propagation mode;

[0123] The acquisition unit is used to acquire the vibration fatigue stress-life test curve or vibration fatigue strain-life test curve of the engine structure.

[0124] The fourth determining unit is used to determine the test crack propagation life based on the vibration fatigue stress-life test curve or vibration fatigue strain-life test curve, combined with the initial values ​​of the initial crack length and crack propagation rate parameters.

[0125] The fifth determining unit is used to optimize the initial value of the crack propagation rate parameter using parameter optimization methods, and determine the parameter value with the smallest error corresponding to the parameter value of the crack propagation rate model.

[0126] Optional crack propagation rate models include:

[0127] Where a is the crack length, N is the number of cycles, C, n, p, q are undetermined model parameter values, f is the crack opening / closing function, R is the stress ratio, and ΔK is the stress intensity factor amplitude. th K is the crack propagation threshold value. max K represents the peak value of the stress intensity factor. C This refers to fracture toughness.

[0128] Optionally, obtaining module 304 includes:

[0129] The second obtaining unit is used to combine the time-domain random stress spectrum, fracture mechanics parameters, target parameter values ​​corresponding to the crack propagation rate model, and preset critical crack length values ​​to calculate the crack propagation life using a cycle-by-cycle method or a block spectrum average life calculation method, and obtain the target crack propagation life.

[0130] The beneficial effects of the engine structure vibration fatigue crack propagation life calculation device provided in this embodiment of the invention are the same as the beneficial effects of the engine structure vibration fatigue crack propagation life calculation method described in the above embodiments, and will not be repeated here.

[0131] Although the invention has been described herein in conjunction with various embodiments, those skilled in the art will understand and implement other variations of the disclosed embodiments by reviewing the accompanying drawings, the disclosure, and the appended claims in carrying out the claimed invention. In the claims, the word "comprising" does not exclude other components or steps, and "a" or "an" does not exclude a plurality. A single processor or other unit can implement several functions listed in the claims. While different dependent claims may recite certain measures, this does not mean that these measures cannot be combined to produce good results.

[0132] Although the invention has been described in conjunction with specific features and embodiments, it is obvious that various modifications and combinations can be made therein without departing from the spirit and scope of the invention. Accordingly, this specification and drawings are merely exemplary descriptions of the invention as defined by the appended claims, and are considered to cover any and all modifications, variations, combinations, or equivalents within the scope of the invention. Clearly, those skilled in the art can make various alterations and modifications to the invention without departing from its spirit and scope. Thus, if such modifications and modifications of the invention fall within the scope of the claims and their equivalents, the invention is also intended to include such modifications and modifications.

Claims

1. A method for calculating the vibration fatigue crack propagation life of an engine structure, characterized in that, The methods include: Obtain the time-domain stochastic stress spectrum of the stress response in the test section of the engine structure in the finite element model; Based on the time-domain stochastic stress spectrum, the crack model of the engine structure is subjected to finite element analysis to determine the fracture mechanics parameters of the cracked structure. Vibration fatigue performance tests were conducted on the crack propagation rate model established according to the preset crack propagation mode, and the target parameter values ​​corresponding to the crack propagation rate model were determined by parameter identification. The crack propagation life is calculated by combining the parameter values ​​corresponding to the crack propagation rate model and the preset critical crack length value, and the target crack propagation life is obtained.

2. The method for calculating the vibration fatigue crack propagation life of an engine structure according to claim 1, characterized in that, The acquisition of the time-domain stochastic stress spectrum of the stress response of the test section in the finite element model of the engine structure includes: Establish a finite element model of the engine structure; Random vibration load excitation was applied to the finite element model of the engine structure to determine the power spectral density of the stress response in the test section; The power spectral density is sampled to obtain the time-domain random stress spectrum of the stress response of the test section.

3. The method for calculating the vibration fatigue crack propagation life of an engine structure according to claim 2, characterized in that, The step of sampling the power spectral density to obtain the time-domain random stress spectrum of the stress response of the test section includes: Obtain the stress amplitude probability density function corresponding to the power spectral density; Based on the stress amplitude probability density function and the peak probability density function, the time-domain stress response is sampled to obtain stress response samples. The stress response samples are randomized to determine the time-domain random stress spectrum of the stress response of the test section.

4. The method for calculating the vibration fatigue crack propagation life of an engine structure according to claim 1, characterized in that, The step of performing finite element analysis on the crack model of the engine structure based on the time-domain stochastic stress spectrum to determine the fracture mechanics parameters of the cracked structure includes: Establish a crack model of the engine structure; Based on the time-domain random stress spectrum, the external load applied to the crack model is determined; The crack model subjected to the external load was subjected to elastic-plastic finite element analysis to determine the fracture mechanics parameters corresponding to each crack length.

5. The method for calculating the vibration fatigue crack propagation life of an engine structure according to claim 4, characterized in that, The fracture mechanics parameters include at least the stress intensity factor or the J integral.

6. The method for calculating the vibration fatigue crack propagation life of an engine structure according to claim 1, characterized in that, The vibration fatigue performance test is conducted on a crack propagation rate model established according to a preset crack propagation mode, and the target parameter values ​​corresponding to the crack propagation rate model are determined by parameter identification, including: Establish the crack propagation rate model according to the preset crack propagation mode; Obtain the vibration fatigue stress-life test curve or vibration fatigue strain-life test curve of the engine structure; Based on the vibration fatigue stress-life test curve or the vibration fatigue strain-life test curve, and combined with the initial values ​​of the initial crack length and crack propagation rate parameters, the test crack propagation life is determined. The initial value of the crack propagation rate parameter is optimized using a parameter optimization method, and the parameter value with the smallest error is determined to be the parameter value corresponding to the crack propagation rate model.

7. The method for calculating the vibration fatigue crack propagation life of an engine structure according to claim 6, characterized in that, The crack propagation rate model includes: Where a is the crack length, N is the number of cycles, C, n, p, and q are undetermined model parameter values, f is the crack opening / closing function, R is the stress ratio, and ΔK is the stress intensity factor amplitude. th K is the crack propagation threshold value. max K represents the peak value of the stress intensity factor. C This refers to fracture toughness.

8. The method for calculating the vibration fatigue crack propagation life of an engine structure according to claim 1, characterized in that, The step of calculating the crack propagation life by combining the parameter values ​​corresponding to the crack propagation rate model and the preset critical crack length value to obtain the target crack propagation life includes: By combining the time-domain random stress spectrum, the fracture mechanics parameters, the target parameter values ​​corresponding to the crack propagation rate model, and the preset critical crack length value, the crack propagation life is calculated using a cyclic-to-cyclic method or a block spectrum average life calculation method to obtain the target crack propagation life.

9. A calculation device for the vibration fatigue crack propagation life of an engine structure, characterized in that, The computing device includes: The acquisition module is used to acquire the time-domain random stress spectrum of the stress response of the test section in the finite element model of the engine structure; The first determining module is used to perform finite element analysis on the crack model of the engine structure based on the time-domain random stress spectrum to determine the fracture mechanics parameters of the cracked structure. The second determining module is used to conduct vibration fatigue performance tests on the crack propagation rate model established according to the preset crack propagation mode, and to determine the target parameter values ​​corresponding to the crack propagation rate model by using parameter identification. The acquisition module is used to calculate the crack propagation life by combining the parameter values ​​corresponding to the crack propagation rate model and the preset critical crack length value, and to obtain the target crack propagation life.

10. The calculation device for vibration fatigue crack propagation life of engine structure according to claim 9, characterized in that, The acquisition module includes: The first establishment unit is used to establish the finite element model of the engine structure; The first determining unit is used to apply random vibration load excitation to the finite element model of the engine structure and determine the power spectral density of the stress response of the test section. The first obtaining unit is used to sample the power spectral density to obtain the time-domain random stress spectrum of the stress response of the test section.

Images