CN118095019A - Method and device for calculating vibration fatigue crack extension life of engine structure - Google Patents
Method and device for calculating vibration fatigue crack extension life of engine structure Download PDFInfo
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Abstract
The invention discloses a calculation method and a calculation device for the vibration fatigue crack growth life of an engine structure, relates to the technical field of mechanical property test characterization, aims to obtain reliable fracture mechanical parameters and crack growth rate curves, provides accurate quantized crack growth life, and provides method guidance for repeated use engine life assessment. The calculation method comprises the following steps: acquiring a time domain random stress spectrum of stress response of an assessment section in a finite element model of an engine structure; based on the time domain random stress spectrum, carrying out finite element analysis processing on a crack model of the engine structure, and determining fracture mechanical parameters of the crack-containing structure; performing vibration fatigue performance test on a crack growth rate model established according to a preset crack growth mode, and determining a target parameter value corresponding to the crack growth rate model by utilizing parameter identification; and calculating the crack extension life by combining the parameter value corresponding to the crack extension rate model and a preset critical crack length value to obtain the target crack extension life.
Description
Technical Field
The invention relates to the technical field of mechanical property test characterization, in particular to a method and a device for calculating the expansion life of a vibration fatigue crack of an engine structure.
Background
The reuse of the engine is one of the main development directions of the spaceflight carrying power system, and under the reuse requirement, the fatigue strength design and service life assessment requirements of the engine are very outstanding. The conventional fatigue analysis method performs life prediction based on a stress/strain-life curve (S-N curve), and can give a life prediction result with a certain degree of reliability. However, when the fatigue analysis method is used for reusing a structure, the following exists: the S-N curve life model has fewer parameters, and a fatigue damage process mechanism cannot be completely described; in addition, the load factor in fatigue analysis mainly considers the magnitude and occurrence frequency of cyclic stress, and it is difficult to consider the influence of load sequence on life. This can lead to a large error in life prediction results, which is detrimental to structural design and evaluation.
The damage tolerance method and the crack propagation technology based on fracture mechanics are widely applied in the aviation field, and at present, the method mainly adopts a linear elastic fracture mechanics method, and is suitable for macroscopic long crack modeling, material performance test and quasi-static fatigue life calculation. The vibration load of the liquid rocket engine is a remarkable load characteristic in the repeated use process, and the fatigue life of the liquid rocket engine is mostly in a crack initiation stage under the vibration environment, so that the structural integrity is required to be maintained for ensuring the normal operation of the engine, and the occurrence of macro-cracks or cracks penetrating through the wall thickness is generally not allowed. Therefore, structural response characteristics under vibration load, damage modes of unperforated wall thickness cracks and effective performance data are important to consider when designing engine fatigue and evaluating service life based on fracture mechanics. At present, the linear elastic fracture mechanics have the limitations of uncertain parameters and the like when the linear elastic fracture mechanics are used for unperforated cracks in the crack initiation stage, in addition, the elastoplasticity and other nonlinear conditions cannot be considered by directly introducing the cracks in the traditional vibration response calculation based on a modal method, and the transient dynamics calculation scale and calculation efficiency of the crack problem limit the general application of the linear elastic fracture mechanics to engineering. Therefore, the current fracture mechanics method is difficult to adapt to the requirement of fatigue crack life assessment of an engine in a vibration environment.
Based on the above, it is necessary to develop a fatigue crack growth life prediction method for an engine structure under vibration load, so as to obtain reliable fracture mechanical parameters and crack growth rate curves, give accurate quantized crack growth life, and provide method guidance for repeated use of engine life assessment.
Disclosure of Invention
The invention aims to provide a method and a device for calculating the vibration fatigue crack growth life of an engine structure, so as to obtain reliable fracture mechanical parameters and crack growth rate curves, provide accurate quantized crack growth life and provide method guidance for repeated use of engine life assessment.
In a first aspect, the present invention provides a method for calculating the vibration fatigue crack growth life of an engine structure, the method comprising:
acquiring a time domain random stress spectrum of stress response of an assessment section in a finite element model of an engine structure;
based on the time domain random stress spectrum, carrying out finite element analysis processing on a crack model of the engine structure, and determining fracture mechanical parameters of the crack-containing structure;
Performing vibration fatigue performance test on a crack growth rate model established according to a preset crack growth mode, and determining a target parameter value corresponding to the crack growth rate model by utilizing parameter identification;
And calculating the crack extension life by combining the parameter value corresponding to the crack extension rate model and a preset critical crack length value to obtain the target crack extension life.
Under the condition of adopting the technical scheme, after obtaining the time domain random stress spectrum of the stress response of the checking section in the finite element model of the engine structure, based on the time domain random stress spectrum, finite element analysis processing can be carried out on the crack model of the engine structure, so that fracture mechanical parameters of the crack-containing structure are determined, vibration fatigue performance tests are carried out on the crack expansion rate model established according to the preset crack expansion mode, the parameter identification is utilized to determine target parameter values corresponding to the crack expansion rate model, and finally, crack expansion life calculation can be carried out by combining the parameter values corresponding to the crack expansion rate model and the preset critical crack length values, so that the target crack expansion life is obtained. Based on the method, the method integrates the contents of structural random vibration response calculation, vibration stress response time domain simulation, crack modeling, fracture mechanical parameter calculation, crack expansion rate model parameter, initial crack length determination, crack expansion service life calculation and the like, can obtain structural random vibration steady-state response and time domain stress random spectrum, give accurate quantized fracture mechanical parameters, determine crack expansion rate model parameter and initial crack length based on fatigue performance test data, realize structural crack expansion service life calculation, and overcome the defects of large calculation result deviation caused by unclear mechanism, difficult parameter acquisition and unsuitable model when the traditional fatigue analysis method and the macroscopic crack analysis method of linear elastic fracture mechanics are used for calculating the service life of the non-penetrating thickness crack in a vibration environment.
Therefore, the calculation method of the vibration fatigue crack growth life of the engine structure can obtain reliable fracture mechanical parameters and crack growth rate curves, give accurate quantized crack growth life and provide method guidance for repeated use of engine life assessment.
In a second aspect, the present invention also provides a device for calculating the vibration fatigue crack growth life of an engine structure, for implementing the method for calculating the vibration fatigue crack growth life of an engine structure according to the first aspect, the computing device comprising:
The acquisition module is used for acquiring a time domain random stress spectrum of stress response of the examination section in the finite element model of the engine structure;
the first determining module is used for carrying out finite element analysis processing on a crack model of the engine structure based on the time domain random stress spectrum and determining fracture mechanical parameters of the crack-containing structure;
The second determining module is used for performing vibration fatigue performance test on the crack growth rate model established according to the preset crack growth mode, and determining a target parameter value corresponding to the crack growth rate model by utilizing parameter identification;
The obtaining module is used for carrying out crack extension service life calculation by combining the parameter value corresponding to the crack extension rate model and the preset critical crack length value to obtain the target crack extension service life.
Optionally, the acquiring module includes:
The first building unit is used for building a finite element model of the engine structure;
The first determining unit is used for applying random vibration load excitation to the finite element model of the engine structure and determining the power spectral density of stress response of the checking section;
The first obtaining unit is used for sampling the power spectrum density to obtain a time domain random stress spectrum of the stress response of the examination section.
Optionally, the first obtaining unit includes
The acquisition subunit is used for acquiring a stress amplitude probability density function corresponding to the power spectrum density;
The obtaining subunit is used for sampling the time stress response based on the stress amplitude probability density function and the peak probability density function to obtain a stress response sample;
And the determining subunit is used for carrying out randomization processing on the stress response sample and determining a time domain random stress spectrum of the stress response of the checking section.
Optionally, the first determining module includes:
The second building unit is used for building a crack model of the engine structure;
A second determining unit for determining an external load applied to the crack model based on the time domain random stress spectrum;
And the third determining unit is used for carrying out elastic-plastic finite element analysis processing on the crack model with the external load applied to determine fracture mechanical parameters corresponding to the lengths of the cracks.
Optionally, the fracture mechanics parameter comprises at least a stress intensity factor or a J-integral.
Optionally, the second determining module includes:
A third establishing unit, configured to establish a crack propagation rate model according to a preset crack propagation mode;
The acquisition unit is used for acquiring a vibration fatigue stress-life test curve or a vibration fatigue strain-life test curve of the engine structure;
A fourth determining unit for determining a test crack growth life based on the vibration fatigue stress-life test curve or the vibration fatigue strain-life test curve in combination with initial values of the initial crack length and crack growth rate parameters;
And the fifth determining unit is used for optimizing the initial value of the crack expansion rate parameter by using a parameter optimization method, and determining the parameter value with the smallest error as the parameter value corresponding to the crack expansion rate model.
Optionally, the crack growth rate model includes:
，
Wherein a is crack length, N is cycle number, C, N, p, q are undetermined model parameter values, f is crack opening/closing function, R is stress ratio, ΔK is stress intensity factor amplitude, ΔK th is crack propagation threshold, K max is stress intensity factor peak value, and K C is fracture toughness.
Optionally, the obtaining module includes:
The second obtaining unit is used for calculating the crack extension life by using a cyclic joint cycle method or a block spectrum average life calculation method in combination with the time domain random stress spectrum, the fracture mechanical parameter, the target parameter value corresponding to the crack extension rate model and the preset critical crack length value to obtain the target crack extension life.
The beneficial effects of the device for calculating the vibration fatigue crack growth life of the engine structure provided in the second aspect are the same as those of the method for calculating the vibration fatigue crack growth life of the engine structure described in the implementation manner of the first aspect, and are not described here in detail.
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The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the invention and do not constitute a limitation on the invention. In the drawings:
FIG. 1 is a flow chart of steps of a method for calculating the life of vibration fatigue crack growth of an engine structure according to an embodiment of the present invention;
FIG. 2 is a flow chart of steps of a method for calculating vibration fatigue crack growth life of an engine structure according to another embodiment of the present invention;
FIG. 3 is a graph of the power spectral density of the vibration stress response of a structural assessment site according to an embodiment of the present invention;
FIG. 4 (a) is a typical narrow band distribution curve of stress response;
FIG. 4 (b) is a typical broadband profile of stress response;
FIG. 5 is a schematic diagram of a time domain stress random spectrum in an embodiment of the present invention;
FIG. 6 is a schematic diagram of a crack model of an engine structure in an embodiment of the present invention;
FIG. 7 is a schematic illustration of a surface crack in an embodiment of the present invention;
FIG. 8 is a schematic diagram of crack growth rate model parameters and initial crack length determination in an embodiment of the present invention;
FIG. 9 is a schematic diagram of a device for calculating the vibration fatigue crack growth life of an engine structure according to an embodiment of the present invention.
Detailed Description
In order to clearly describe the technical solution of the embodiments of the present invention, in the embodiments of the present invention, the words "first", "second", etc. are used to distinguish the same item or similar items having substantially the same function and effect. For example, the first threshold and the second threshold are merely for distinguishing between different thresholds, and are not limited in order. It will be appreciated by those of skill in the art that the words "first," "second," and the like do not limit the amount and order of execution, and that the words "first," "second," and the like do not necessarily differ.
In the present invention, the words "exemplary" or "such as" are used to mean serving as an example, instance, or illustration. Any embodiment or design described herein as "exemplary" or "for example" should not be construed as preferred or advantageous over other embodiments or designs. Rather, the use of words such as "exemplary" or "such as" is intended to present related concepts in a concrete fashion.
In the present invention, "at least one" means one or more, and "a plurality" means two or more. "and/or", describes an association relationship of an association object, and indicates that there may be three relationships, for example, a and/or B, and may indicate: a alone, a and B together, and B alone, wherein a, B may be singular or plural. The character "/" generally indicates that the context-dependent object is an "or" relationship. "at least one of" or the like means any combination of these items, including any combination of single item(s) or plural items(s). For example, at least one (one) of a, b or c may represent: a, b, c, a and b, a and c, b and c, or a, b and c, wherein a, b, c can be single or multiple.
As shown in fig. 1, an embodiment of the present invention provides a method for calculating an engine structural vibration fatigue crack growth life, including:
s101: and obtaining a time domain random stress spectrum of stress response of the checking section in the finite element model of the engine structure.
In the application, a finite element method is adopted to carry out dynamic modeling on a structure, and random vibration load excitation is applied to obtain dynamic responses such as power spectral density (Power Spectrum Density, PSD) and Root Mean Square (RMS) of stress response of an examination part.
And analyzing and giving a probability density function of a time domain stress response amplitude and a peak value according to the obtained power spectrum density of the vibration stress response, and then sampling to obtain a stress response time domain random number and form a time domain random stress spectrum.
S102: based on the time domain random stress spectrum, finite element analysis processing is carried out on the crack model of the engine structure, and fracture mechanical parameters of the crack-containing structure are determined.
Specifically, a crack propagation mode is first assumed, a crack form is given, and a crack propagation path is set. Then, crack modeling is carried out on the engine structure, and two points are mainly considered in the structural crack model: firstly, the expansion range from the initial crack to the critical crack length can be enveloped; secondly, the steel comprises main structural characteristics such as fillets, holes, variable thickness and the like which have influence on fracture mechanical parameters of cracks with no penetration thickness. And finally, selecting load points in the time domain random stress spectrum as external load to be applied to the crack model for linear elasticity or elastic-plastic finite element calculation, and obtaining fracture mechanical parameters Ki (stress intensity factors) or Ji (J integral) corresponding to each crack length ai.
S103: and carrying out vibration fatigue performance test on the crack growth rate model established according to the preset crack growth mode, and determining a target parameter value corresponding to the crack growth rate model by utilizing parameter identification.
Specifically, firstly, vibration fatigue performance test data such as a fatigue stress-life curve or a strain-life curve of a material or a structural member under vibration load are obtained, a crack expansion rate model is given, and an initial crack form is assumed; then, fracture mechanics calculation is carried out on the vibration fatigue performance test piece, and fracture mechanics parameters such as stress intensity factors Ktest are obtained; finally, presetting a crack growth rate model parameter initial value and an initial crack length initial value for each stress level of vibration fatigue performance test data (curve), calculating the test crack growth life of each stress level, and obtaining a parameter optimization result with the smallest error with the test life result as a final parameter identification value by a parameter optimization method.
Based on the method, a material fatigue damage model represented by a single mechanical parameter S (stress or strain) and a service life N is converted into a material fatigue damage model represented by an initial crack size and a fracture mechanical property parameter, and a crack propagation rate model parameter value is obtained.
S104: and calculating the crack extension life by combining the parameter value corresponding to the crack extension rate model and a preset critical crack length value to obtain the target crack extension life.
Specifically, substituting a time domain random stress spectrum and fracture mechanics parameters into a crack expansion rate model, and calculating crack expansion life by specifying critical crack length af and initial crack length a0 and adopting a cyclic joint-cyclic method or a block spectrum average life calculation method to obtain final crack expansion life. It should be appreciated that a set of stress random spectra corresponds to a set of crack growth life values.
Compared with the prior art, the method for calculating the vibration fatigue crack extension life of the engine structure provided by the embodiment of the invention can be used for carrying out finite element analysis processing on the crack model of the engine structure based on the time domain random stress spectrum after obtaining the time domain random stress spectrum of the stress response of the checking section in the finite element model of the engine structure, so as to determine the fracture mechanical parameters of the crack-containing structure, carrying out vibration fatigue performance test on the crack extension rate model established according to the preset crack extension mode, determining the target parameter value corresponding to the crack extension rate model by utilizing parameter identification, and finally carrying out crack extension life calculation by combining the parameter value corresponding to the crack extension rate model and the preset critical crack length value to obtain the target crack extension life. Based on the above, the embodiment of the invention integrates the contents of structural random vibration response calculation, vibration stress response time domain simulation, crack modeling, fracture mechanical parameter calculation, crack expansion rate model parameter, initial crack length determination, crack expansion service life calculation and the like, can obtain structural random vibration steady-state response and time domain stress random spectrum, give accurate quantitative fracture mechanical parameter, determine crack expansion rate model parameter and initial crack length based on fatigue performance test data, realize structural crack expansion service life calculation, and overcome the defects of large calculation result deviation caused by unclear mechanism, difficult parameter acquisition and inapplicability of the model when the traditional fatigue analysis method and the macroscopic crack analysis method of linear elastic fracture mechanics are used for service life calculation of the non-penetrated thickness crack in a vibration environment.
Therefore, the calculation method of the vibration fatigue crack growth life of the engine structure provided by the embodiment of the invention can obtain reliable fracture mechanical parameters and crack growth rate curves, give accurate quantized crack growth life and provide method guidance for repeated use engine life assessment.
As shown in fig. 2, the embodiment of the invention further provides another method for calculating the vibration fatigue crack growth life of the engine structure, and the specific steps of the method for calculating the vibration fatigue crack growth life of the engine structure provided by the embodiment of the invention will be described in detail with reference to fig. 2 to 8.
S201: and establishing a finite element model of the engine structure.
S202: and (3) applying random vibration load excitation to the finite element model of the engine structure, and determining the power spectral density of stress response of the examination section.
In the application, a finite element method is adopted to carry out dynamic simulation modeling on a structure, and random vibration load excitation is applied to obtain power spectral density (Power Spectrum Density, PSD) and Root Mean Square (RMS) of stress response of an examined part, as shown in figure 3. FIG. 3 schematically shows a stress power spectral density curve of a severe vibration stress response part of an engine structure, namely an examination section, wherein the abscissa represents frequency in Hz, and the ordinate represents stress power spectral density in MPa 2/Hz.
S203: and sampling the power spectrum density to obtain a time domain random stress spectrum of stress response of the examination section.
Specifically, the probability density function giving the time domain stress response is analyzed for the power spectrum density of the obtained vibration stress response, then the time domain random number of the stress response is obtained by sampling, and the time domain random stress spectrum is formed.
The step S203 includes the following sub-steps:
substep A1: obtaining a stress amplitude probability density function corresponding to the power spectrum density;
substep A2: sampling the time stress response based on the stress amplitude probability density function and the peak probability density function to obtain a stress response sample;
substep A3: and carrying out randomization treatment on the stress response sample, and determining a time domain random stress spectrum of stress response of the checking section.
Analyzing the PSD spectrum of the vibration stress response, FIG. 4 (a) is a typical narrow band distribution curve of the stress response; fig. 4 (b) is a typical broadband profile of stress response. As shown in fig. 4 (b), if the broadband is randomly distributed, a Dirlik model is adopted to obtain a stress amplitude probability density function of the broadband distribution; as shown in fig. 4 (a), if the Narrow-band distribution is adopted, a Narrow-band model is adopted to obtain a stress amplitude probability density function of the Narrow-band distribution; and simultaneously, combining with a hypothesized peak probability density function obeying Gaussian distribution, sampling the time stress response to obtain a group of stress response samples with a sufficient number, and finally obtaining a time domain random stress spectrum by a randomization method, wherein in fig. 5, the abscissa represents time, the ordinate represents stress and the ordinate represents Mpa, and the abscissa represents time.
S204: based on the time domain random stress spectrum, finite element analysis processing is carried out on the crack model of the engine structure, and fracture mechanical parameters of the crack-containing structure are determined.
Wherein the fracture mechanics parameter comprises at least a stress intensity factor or a J integral.
The step S204 includes the following sub-steps:
substep B1: establishing a crack model of the engine structure, as shown in fig. 6;
substep B2: determining an external load applied to the crack model based on the time domain random stress spectrum;
Substep B3: and carrying out elastic-plastic finite element analysis treatment on the crack model with the external load, and determining fracture mechanical parameters corresponding to the lengths of the cracks.
The specific test method comprises the following steps: first, assuming a Crack propagation mode, a Crack form, such as edge angle Crack (EDGE CRACK), surface Crack (Surface Crack), is given as shown in fig. 7. Or deep Crack (Embedded Crack), etc., to set a Crack propagation path. Then, finite element modeling is carried out on a crack model of the engine structure, and two points are mainly considered in the structural crack model: firstly, the expansion range from the initial crack to the critical crack length can be enveloped; secondly, the steel comprises main structural characteristics such as fillets, holes, variable thickness and the like which have influence on fracture mechanical parameters of cracks with no penetration thickness. And finally, applying the time domain random stress spectrum of the stress response of the examination section as an external load to a crack model for carrying out elastic-plastic finite element calculation to obtain fracture mechanical parameters Ki (stress intensity factors) or Ji (J integral) corresponding to each crack length ai.
Based on the method, the three-dimensional crack modeling of the actual complex structure is simplified into the problem of proper-scale crack modeling reflecting the main characteristics and stress response characteristics of the structural crack, meanwhile, the structural dynamic response is used as load input to carry out fracture mechanics calculation, the dynamic problem is converted into static problem, and then the elastoplastic fracture mechanics parameter solution can be obtained, so that the problem that elastoplastic analysis and nonlinear factor simulation cannot be carried out in steady-state vibration response calculation based on a modal method is solved.
S205: and establishing a crack growth rate model according to a preset crack growth mode.
Specifically, given a crack growth rate model, the model considers factors such as stress intensity factor amplitude, stress intensity factor maximum, stress intensity factor threshold, crack closure and the like, for example, a NASGRO crack growth rate formula is adopted:
，
Where a is the crack length, N is the number of cycles, C, N, p, q are the values of the model parameters to be determined, f is the crack opening/closing function, R is the stress ratio, ΔK is the stress intensity factor amplitude, ΔK th is the crack propagation threshold, K max is the stress intensity factor peak, and K C is the fracture toughness.
S206: and obtaining a vibration fatigue stress-life test curve or a vibration fatigue strain-life test curve of the engine structure.
S207: based on the vibration fatigue stress-life test curve or the vibration fatigue strain-life test curve, the initial crack length and the initial value of the crack growth rate parameter are combined to determine the test crack growth life.
S208: and optimizing the initial value of the crack expansion rate parameter by using a parameter optimization method, and determining the parameter value with the minimum error as the parameter value corresponding to the crack expansion rate model.
In the present application, vibration fatigue stress-life or strain-life test data (curve) of a material or a structural member is obtained, an initial value (a 0 ini,Cini,nini,pini,qini) of an initial crack length a0 and a crack growth rate parameter is assumed for each stress/strain level of a test, and a test crack growth life is calculated, and a parameter optimization result having the smallest error with a test life result is obtained as a final target parameter value by a parameter optimization method, as shown in fig. 8.
Based on the method, the material fatigue damage model represented by the single mechanical parameter S (stress or strain) and the service life N is converted into the material fatigue damage model represented by the crack size and the fracture mechanical property parameter thereof, and the crack expansion rate model parameter value is obtained.
S209: and calculating the crack extension life by combining the parameter value corresponding to the crack extension rate model and a preset critical crack length value to obtain the target crack extension life.
In the application, a target crack propagation life is calculated by combining a time domain random stress spectrum, a fracture mechanical parameter, a target parameter value corresponding to a crack propagation rate model and a preset critical crack length value and by using a cyclic joint cyclic method or a block spectrum average life calculation method, so as to obtain the target crack propagation life.
It should be appreciated that a set of stress random spectra corresponds to a set of crack growth life values.
The embodiment of the invention has the beneficial effects that:
(1) Through steady-state vibration response calculation and stress response time domain simulation, not only the frequency domain characteristics of structural stress response are considered, but also the time domain statistical characteristics of stress response are considered, the stress characteristics under vibration load are completely reserved, and the service life calculation is more complete and fine;
(2) The time domain stress response is used as an external load to carry out crack modeling, so that a load basis is provided for converting the integral crack modeling of the structure into the crack modeling of the local structure, the model scale is reduced, and the calculation efficiency is greatly improved. On the other hand, the dynamic calculation is converted into the static calculation, so that more real elastoplasticity and nonlinear solution can be obtained, and the accuracy of fracture mechanical parameters is obviously improved;
(3) The fatigue performance test data are fully utilized to identify the crack propagation rate model parameters and the initial crack length distribution, so that the source reliability of key performance parameters for calculating the crack propagation life is ensured, the modeling mechanism is clearer, the uncertainty of the traditional extrapolation method through a macroscopic long crack model is avoided, and the reasonable and reliable calculation model and calculation result are ensured.
As shown in fig. 9, an embodiment of the present invention further provides a device 300 for calculating the propagation life of a vibration fatigue crack of an engine structure, which is configured to implement the method for calculating the propagation life of a vibration fatigue crack of an engine structure in the above embodiment, where the computing device includes:
The acquisition module 301 is configured to acquire a time domain random stress spectrum of an assessment segment stress response in a finite element model of an engine structure;
the first determining module 302 is configured to perform finite element analysis on a crack model of the engine structure based on the time domain random stress spectrum, and determine fracture mechanical parameters of the crack-containing structure;
a second determining module 303, configured to perform a vibration fatigue performance test on a crack growth rate model established according to a preset crack growth mode, and determine a target parameter value corresponding to the crack growth rate model by using parameter identification;
and the obtaining module 304 is configured to calculate a crack growth lifetime by combining a parameter value corresponding to the crack growth rate model and a preset critical crack length value, so as to obtain a target crack growth lifetime.
Optionally, the acquiring module 301 includes:
The first building unit is used for building a finite element model of the engine structure;
The first determining unit is used for applying random vibration load excitation to the finite element model of the engine structure and determining the power spectral density of stress response of the checking section;
The first obtaining unit is used for sampling the power spectrum density to obtain a time domain random stress spectrum of the stress response of the examination section.
Optionally, the first obtaining unit includes
The acquisition subunit is used for acquiring a stress amplitude probability density function corresponding to the power spectrum density;
The obtaining subunit is used for sampling the time stress response based on the stress amplitude probability density function and the peak probability density function to obtain a stress response sample;
And the determining subunit is used for carrying out randomization processing on the stress response sample and determining a time domain random stress spectrum of the stress response of the checking section.
Optionally, the first determining module 302 includes:
The second building unit is used for building a crack model of the engine structure;
A second determining unit for determining an external load applied to the crack model based on the time domain random stress spectrum;
And the third determining unit is used for carrying out elastic-plastic finite element analysis processing on the crack model with the external load applied to determine fracture mechanical parameters corresponding to the lengths of the cracks.
Optionally, the fracture mechanics parameter comprises at least a stress intensity factor or a J-integral.
Optionally, the second determining module 303 includes:
A third establishing unit, configured to establish a crack propagation rate model according to a preset crack propagation mode;
The acquisition unit is used for acquiring a vibration fatigue stress-life test curve or a vibration fatigue strain-life test curve of the engine structure;
A fourth determining unit for determining a test crack growth life based on the vibration fatigue stress-life test curve or the vibration fatigue strain-life test curve in combination with initial values of the initial crack length and crack growth rate parameters;
And the fifth determining unit is used for optimizing the initial value of the crack expansion rate parameter by using a parameter optimization method, and determining the parameter value with the smallest error as the parameter value corresponding to the crack expansion rate model.
Optionally, the crack growth rate model includes:
，
Wherein a is crack length, N is cycle number, C, N, p, q are undetermined model parameter values, f is crack opening/closing function, R is stress ratio, ΔK is stress intensity factor amplitude, ΔK th is crack propagation threshold, K max is stress intensity factor peak value, and K C is fracture toughness.
Optionally, the obtaining module 304 includes:
The second obtaining unit is used for calculating the crack extension life by using a cyclic joint cycle method or a block spectrum average life calculation method in combination with the time domain random stress spectrum, the fracture mechanical parameter, the target parameter value corresponding to the crack extension rate model and the preset critical crack length value to obtain the target crack extension life.
The beneficial effects of the device for calculating the vibration fatigue crack extension life of the engine structure provided by the embodiment of the invention are the same as those of the method for calculating the vibration fatigue crack extension life of the engine structure described in the above embodiment, and are not repeated here.
Although the invention is described herein in connection with various embodiments, other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the "a" or "an" does not exclude a plurality. A single processor or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.
Although the invention has been described in connection with specific features and embodiments thereof, it will be apparent that various modifications and combinations can be made without departing from the spirit and scope of the invention. Accordingly, the specification and drawings are merely exemplary illustrations of the present invention as defined in the appended claims and are considered to cover any and all modifications, variations, combinations, or equivalents that fall within the scope of the invention. It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention also include such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.
Claims (10)
1. A method for calculating the propagation life of a vibration fatigue crack of an engine structure, the method comprising:
acquiring a time domain random stress spectrum of stress response of an assessment section in a finite element model of an engine structure;
based on the time domain random stress spectrum, performing finite element analysis processing on a crack model of the engine structure, and determining fracture mechanical parameters of the crack-containing structure;
performing vibration fatigue performance test on a crack growth rate model established according to a preset crack growth mode, and determining a target parameter value corresponding to the crack growth rate model by utilizing parameter identification;
And calculating the crack extension life by combining the parameter value corresponding to the crack extension rate model and a preset critical crack length value to obtain the target crack extension life.
2. The method for calculating the vibration fatigue crack growth life of the engine structure according to claim 1, wherein the obtaining the time-domain stochastic stress spectrum of the stress response of the examination section in the finite element model of the engine structure comprises:
Establishing a finite element model of the engine structure;
applying random vibration load excitation to the finite element model of the engine structure, and determining the power spectral density of stress response of the assessment section;
and sampling the power spectrum density to obtain a time domain random stress spectrum of the stress response of the examination section.
3. The method for calculating the vibration fatigue crack growth life of the engine structure according to claim 2, wherein the sampling the power spectrum density to obtain the time domain random stress spectrum of the stress response of the test section comprises:
acquiring a stress amplitude probability density function corresponding to the power spectrum density;
Sampling the time stress response based on the stress amplitude probability density function and the peak probability density function to obtain a stress response sample;
and carrying out randomization treatment on the stress response sample, and determining a time domain random stress spectrum of the stress response of the examination section.
4. The method for calculating the vibration fatigue crack growth life of an engine structure according to claim 1, wherein the performing finite element analysis processing on the crack model of the engine structure based on the time domain random stress spectrum to determine fracture mechanics parameters of the crack-containing structure comprises:
Establishing a crack model of the engine structure;
Determining an external load applied to the crack model based on the time domain random stress spectrum;
And carrying out elastic-plastic finite element analysis treatment on the crack model applied with the external load, and determining fracture mechanical parameters corresponding to the lengths of the cracks.
5. The method of claim 4, wherein the fracture mechanics parameter comprises at least a stress intensity factor or a J-integral.
6. The method for calculating the vibration fatigue crack growth life of an engine structure according to claim 1, wherein the performing the vibration fatigue performance test on the crack growth rate model established according to the preset crack growth mode, determining the target parameter value corresponding to the crack growth rate model by using parameter identification, comprises:
Establishing the crack growth rate model according to the preset crack growth mode;
acquiring a vibration fatigue stress-life test curve or a vibration fatigue strain-life test curve of the engine structure;
determining a test crack growth life based on the vibration fatigue stress-life test curve or the vibration fatigue strain-life test curve in combination with initial values of initial crack length and crack growth rate parameters;
And optimizing the initial value of the crack expansion rate parameter by using a parameter optimization method, and determining the parameter value with the minimum error as the parameter value corresponding to the crack expansion rate model.
7. The method of calculating a vibratory fatigue crack growth life for an engine structure of claim 6, wherein the crack growth rate model comprises:
，
Where a is the crack length, N is the number of cycles, C, N, p, q are the values of the model parameters to be determined, f is the crack opening/closing function, R is the stress ratio, ΔK is the stress intensity factor amplitude, ΔK th is the crack propagation threshold, K max is the stress intensity factor peak, and K C is the fracture toughness.
8. The method for calculating the crack growth life of the vibration fatigue of the engine structure according to claim 1, wherein the calculating the crack growth life by combining the parameter value corresponding to the crack growth rate model and the preset critical crack length value to obtain the target crack growth life comprises:
And carrying out crack extension life calculation by using a cyclic joint circulation method or a block spectrum average life calculation method in combination with the time domain random stress spectrum, the fracture mechanical parameter, a target parameter value corresponding to the crack extension rate model and a preset critical crack length value to obtain a target crack extension life.
9. A computing device for engine structural vibration fatigue crack growth life, the computing device comprising:
The acquisition module is used for acquiring a time domain random stress spectrum of stress response of the examination section in the finite element model of the engine structure;
the first determining module is used for carrying out finite element analysis processing on the crack model of the engine structure based on the time domain random stress spectrum to determine fracture mechanical parameters of the crack-containing structure;
the second determining module is used for performing vibration fatigue performance test on a crack expansion rate model established according to a preset crack expansion mode, and determining a target parameter value corresponding to the crack expansion rate model by utilizing parameter identification;
The obtaining module is used for carrying out crack extension service life calculation by combining the parameter value corresponding to the crack extension rate model and a preset critical crack length value to obtain a target crack extension service life.
10. The engine structural vibration fatigue crack growth life calculation device of claim 9, wherein the acquisition module comprises:
A first building unit for building a finite element model of the engine structure;
the first determining unit is used for applying random vibration load excitation to the finite element model of the engine structure and determining the power spectral density of stress response of the checking section;
The first obtaining unit is used for sampling the power spectrum density to obtain a time domain random stress spectrum of the stress response of the examination section.
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