A nonlinear damage accumulation prediction method coupling vibration and conventional fatigue load

Abstract

The application discloses a kind of nonlinear damage accumulation prediction methods of vibration and conventional fatigue load coupling, according to the finite element model analysis of engineering component, the peak stress at dangerous point under conventional fatigue load loading is determined;According to the stress amplitude probability density function at dangerous point under random vibration loading is determined according to structural dynamics analysis;Look up pre-generated material fatigue life curve;According to the equivalent stress at dangerous point under random vibration loading is determined according to fatigue life curve;The ratio of peak stress and random vibration equivalent stress of conventional fatigue load loading at dangerous point is calculated, and the coupling damage parameter is established according to vibration and conventional fatigue load coupling series;Establish nonlinear damage accumulation model of vibration and conventional fatigue load coupling.The nonlinear damage accumulation model proposed in the application considers the influence of vibration and conventional load sequence and coupling series, parameter determination is simple, and high-precision prediction of structure damage evolution under complex load coupling can be realized.

Description

Technical Field

[0001] This invention relates to fatigue damage accumulation technology under complex loads, and more particularly to a nonlinear damage accumulation prediction method that couples vibration and conventional fatigue loads. Background Technology

[0002] Engineering structures are subjected to multi-source composite loads during long-term service, among which the coupling effect of vibration loads and conventional fatigue loads has become a key cause of structural fatigue failure. Vibration loads induce local stress fluctuations through high-frequency dynamic excitation, while conventional fatigue loads lead to local plastic strain accumulation. The coupling effect of these two in the time and frequency domains significantly accelerates the initiation and propagation of microcracks. Under the combined action of vibration and conventional loads, structures are more prone to damage accumulation and fatigue problems.

[0003] Existing research has established partial prediction frameworks for coupled vibration and conventional load damage based on the Miner criterion or the local stress-strain method. However, these theoretical systems still rely on the assumption of independent load action and fail to deeply reveal the damage evolution path under the interaction of vibration and fatigue. Furthermore, traditional linear damage accumulation theories assume independent superposition of damage, neglecting the load order effect and the interaction between vibration and conventional loads. This results in linear damage accumulation theories being unable to accurately simulate the coupled damage effects of vibration and conventional fatigue. Nonlinear damage accumulation theories considering load order effects are mostly applied to single load types, such as conventional fatigue loads, and still cannot quantify the contribution of vibration damage under the coupled action of vibration and conventional fatigue. Therefore, there is currently no damage accumulation theory that can reveal the fatigue damage evolution process under the coupled action of vibration and conventional fatigue loads. Summary of the Invention

[0004] Purpose of the invention: To address the shortcomings of existing technologies, this invention proposes a nonlinear damage accumulation prediction method that couples vibration and conventional fatigue loads, enabling high-precision prediction of structural damage evolution under complex load coupling.

[0005] Technical solution: The nonlinear damage accumulation prediction method coupled with vibration and conventional fatigue loads described in this invention includes the following steps:

[0006] (1) Determine the peak stress at the critical point under conventional fatigue load based on the finite element model analysis of the engineering component;

[0007] (2) Determine the probability density function of stress amplitude at the critical point under random vibration loading based on structural dynamics analysis;

[0008] (3) Locate the pre-generated material fatigue life curve;

[0009] (4) Determine the equivalent stress at the critical point under random vibration loading based on the fatigue life curve;

[0010] (5) Calculate the ratio of peak stress under conventional fatigue load to equivalent stress under random vibration at the critical point, and establish coupling damage parameters based on the coupling level of vibration and conventional fatigue load;

[0011] (6) Establish a nonlinear damage accumulation model coupled with vibration and conventional fatigue load to predict the nonlinear damage accumulation coupled with vibration and conventional fatigue load.

[0012] Furthermore, the implementation process of step (1) is as follows:

[0013] Establish a three-dimensional finite element model of the engineering structure: set material properties, select a hexahedral structure mesh for mesh generation, and perform segmentation and local mesh refinement on the circular notch region;

[0014] Conventional fatigue loads were applied to the finite element model and finite element analysis was performed: a completely fixed boundary condition was applied on one side of the specimen to simulate the fixing effect of the fixture, and a static load was applied on the other side along the axial direction of the specimen.

[0015] Identify the structural fatigue hazard points and obtain the peak stress S at the hazard points. n,max .

[0016] Furthermore, the implementation process of step (2) is as follows:

[0017] Random vibration loads are applied to the finite element model, and structural dynamics analysis is performed to obtain the stress power spectral density function G(f) at the critical point of the structure. The stress amplitude probability density function P(S) at the critical point is calculated according to the Dirlik model, as shown in the following equation:

[0018]

[0019] Where Z is the normalized stress amplitude, and D i Here, Q and R are the weighting coefficients, Q and R are the shape parameters, and m0 is the 0th order spectral moment; x m The average frequency is given by γ, the irregularity factor is given by S, and the stress amplitude is given by m. i The i-th order spectral moment is calculated by the following formula:

[0020]

[0021] Where f is the frequency and G(f)d is the stress power spectral density function at the critical point.

[0022] Furthermore, step (3) is achieved through the following formula:

[0023]

[0024] In the formula, S represents the stress amplitude, N represents the fatigue life, c0 is the SN curve parameter, and C is the material parameter.

[0025] Furthermore, the equivalent stress at the danger point mentioned in step (4) is:

[0026]

[0027] Where S represents the stress amplitude, and dS represents the integral over S.

[0028] Further, the coupling damage parameters in step (5) are:

[0029]

[0030] Where m is the coupling level of vibration and conventional fatigue load, S n,max S represents the peak stress at the critical point. vib,eq This represents the equivalent stress at the danger point.

[0031] Furthermore, the nonlinear damage accumulation model coupled with vibration and conventional fatigue load described in step (6) is as follows:

[0032]

[0033] Among them, D i For the damage caused by the i-th level load, D CR The critical damage value is given by m, where m is the coupling level of vibration and conventional fatigue load, and k is the value of k. i Let n be the coupling damage parameter. i Let N be the number of loading cycles for the i-th level load. fi Let be the fatigue life under the i-th level load.

[0034] The device according to the present invention includes a memory and a processor, wherein:

[0035] Memory is used to store computer programs that can run on a processor;

[0036] A processor, configured to, while running the computer program, perform the steps of the nonlinear damage accumulation prediction method coupled with vibration and conventional fatigue loads as described above.

[0037] The present invention provides a storage medium storing a computer program, which, when executed by at least one processor, implements the steps of the nonlinear damage accumulation prediction method coupled with vibration and conventional fatigue load as described above.

[0038] Beneficial effects: Compared with the prior art, the beneficial effects of the present invention are: The present invention quantifies the contribution of vibration damage by using the ratio of the peak stress of conventional loads to the equivalent stress of random vibration at the critical point of the structure, and by introducing the coupling load series to establish coupling damage parameters; the parameters are simple to determine and can achieve high-precision prediction of structural damage evolution under complex load coupling. Attached Figure Description

[0039] Figure 1 This is a flowchart of a nonlinear damage accumulation prediction method that couples vibration and conventional fatigue loads.

[0040] Figure 2 This is a schematic diagram of mesh generation for finite element modeling;

[0041] Figure 3 This is a schematic diagram of the probability density function of stress amplitude at a critical point under random vibration loading. Detailed Implementation

[0042] The present invention will now be described in further detail with reference to the accompanying drawings.

[0043] like Figure 1 As shown, this invention provides a nonlinear damage accumulation prediction method coupled with vibration and conventional fatigue loads, the main steps of which are as follows:

[0044] Step 1: Determine the peak stress at the critical point under conventional fatigue load based on the finite element model analysis of the engineering component.

[0045] A three-dimensional finite element model of the engineering structure was created in ABAQUS. Material properties were set, and a hexahedral structure mesh was selected for mesh generation. The circular notch region was segmented and the local mesh was refined. The global mesh size was set to 0.5 mm, and the local mesh size was 0.1 mm. The final model generated a total of 315,774 elements.

[0046] Conventional fatigue loads were applied to the finite element model and finite element analysis was performed. A completely fixed boundary condition was applied on one side of the specimen to simulate the fixing effect of the fixture, and a static load F was applied on the other side along the axial direction of the specimen.

[0047] By using the stress cloud diagram from the finite element analysis results, the fatigue hazard points of the structure were identified, and the peak stress S at the hazard points was obtained. n,max .

[0048] Step 2: Determine the probability density function of stress amplitude at the critical point under random vibration loading based on structural dynamics analysis.

[0049] Based on the three-dimensional finite element model of the engineering structure, random vibration loads were applied to the finite element model and structural dynamics analysis was performed. First, modal analysis was performed to obtain the first three natural frequencies of the specimen and the corresponding mode shapes. Then, a completely fixed boundary condition was applied to one side of the specimen to simulate the fixing effect of the clamp, while an acceleration excitation along the thickness direction of the specimen was applied to the other side.

[0050] The fatigue hazard points of the structure were determined by finite element analysis, and the stress power spectral density function G(f) at the hazard points was obtained. The stress contour plot of the analysis results determined the location of the fatigue hazard points, and the stress power spectral density function data of the fatigue hazard points was output through the ODB field variables.

[0051] The probability density function P(S) of the stress amplitude at the critical point is calculated based on the Dirlik model, as shown in the following formula:

[0052]

[0053] In the formula, Z is the normalized stress amplitude, and D... i Here, is the weighting coefficient, Q and R are shape parameters, and m0 is the 0th-order spectral moment. The expressions for each parameter are as follows:

[0054]

[0055] In the formula, x m The average frequency is given by γ, the irregularity factor is given by S, and the stress amplitude is given by m. i Let be the i-th order spectral moment. The spectral moment is calculated by the following formula:

[0056]

[0057] In the formula, f is the frequency, and G(f) is the power spectral density function at the danger point.

[0058] Step 3: Locate the pre-generated material fatigue life curve. The expression for the material fatigue life curve is:

[0059]

[0060] In the formula, S represents the stress amplitude, N represents the fatigue life, c0 is the SN curve parameter, and C is the material parameter.

[0061] Step 4: Determine the equivalent stress at the critical point under random vibration loading based on the fatigue life curve.

[0062] The equivalent stress expression at the critical point of the structure under random vibration loading is:

[0063]

[0064] Step 5: Calculate the ratio of the peak stress under conventional fatigue load to the equivalent stress under random vibration at the critical point. Establish coupled damage parameters based on the coupling level of vibration and conventional fatigue load, specifically including:

[0065] The expression for the coupling damage parameter is:

[0066]

[0067] In the formula, m is the coupling level of vibration and conventional fatigue load.

[0068] Step 6: Establish a nonlinear damage accumulation model coupling vibration and conventional fatigue loads, specifically including:

[0069] The theoretical model expression for the nonlinear damage accumulation of coupled vibration and conventional fatigue loads is as follows:

[0070]

[0071] In the formula, D i For the damage caused by the i-th level load, D CR The critical damage value is given by m, where m is the coupling level of vibration and conventional fatigue load, and k is the value of k. i Let n be the coupling damage parameter. i Let N be the number of loading cycles for the i-th level load. fi Let be the fatigue life under the i-th level load.

[0072] The present invention also provides an apparatus comprising a memory and a processor, wherein: the memory is configured to store a computer program capable of running on the processor; and the processor is configured to, when running the computer program, execute the steps of the nonlinear damage accumulation prediction method coupled with vibration and conventional fatigue loads as described above.

[0073] The present invention also provides a storage medium storing a computer program that, when executed by at least one processor, implements the steps of the nonlinear damage accumulation prediction method coupled with vibration and conventional fatigue load as described above.

[0074] In this embodiment, 2A12 aluminum alloy was used as the material, and coupled tests of vibration and conventional fatigue loads were conducted. First, finite element analysis was performed on the test specimen to determine the critical point and obtain the peak stress at the critical point under fatigue load. Then, dynamic analysis was performed on the test specimen to obtain the stress amplitude probability density function P(S) at the critical point. Next, the vibration equivalent stress at the critical point was calculated based on the material fatigue life curve. Then, coupled damage parameters were established based on the ratio of the peak stress under conventional load to the vibration equivalent stress at the critical point and the coupled load spectrum order. Finally, a nonlinear damage accumulation model of the coupled vibration and conventional loads was established. The detailed process is as follows:

[0075] Fatigue loading was performed using an MTS809 fatigue testing machine, and random vibration loading was performed using a Suzhou Testing DC-200 machine. The coupled test spectrum consisted of a combination of random vibration and conventional fatigue loads, and the test loads are as follows: The coupled test schemes are listed in Table 1.

[0076] (a) Vibration load parameters: A broadband flat-spectrum random vibration excitation was applied, with a frequency range of 5-100Hz and a power spectral density (PSD) of 0.037g. 2 / Hz, total mean square root g RMS = 1.87g. Vibration failure time T 50 =76.3min.

[0077] (b) Conventional fatigue load: A constant amplitude fatigue load is applied, with a nominal peak stress of 189.8 MPa, a stress ratio of 0.1, and a loading frequency of 5 Hz, corresponding to a median fatigue life of N. 50 = 78512 Cycles.

[0078] Table 1. Vibration and Conventional Load Coupling Test Scheme

[0079]

[0080] Establish a finite element model of the test specimen, and mesh it as follows: Figure 2 As shown. Static analysis yields the peak stress S at the critical point under conventional load. n,max =415.6MPa. A dynamic analysis was performed on the structure under random vibration load to obtain the power spectral density function at the critical point. The stress amplitude probability density function P(S) at the critical point was calculated using the Dirlik model. Figure 3 As shown. The fatigue life curve of the material is:

[0081] S 5.96 N = 10 18.87

[0082] The integral yields the equivalent stress of random vibration at the danger point as S. vib,eq =153.86MPa. Therefore, the expression for the coupling damage parameter k is obtained:

[0083]

[0084] Establish a nonlinear damage accumulation model for vibration and conventional loads:

[0085]

[0086] The cumulative damage calculated based on the model and the coupling of vibration and conventional load is listed in Table 2, where D... miner D represents the cumulative damage calculated based on the linear criterion. sumThe cumulative damage calculated using the nonlinear damage accumulation theory proposed in this invention is represented by "*", indicating outlier data points. To facilitate comparison of the accuracy of experimental results, the error factor *error*, calculated by the damage accumulation theory relative to the critical damage, is defined as follows:

[0087] error = (DD CR )×100%

[0088] In the formula, D represents the cumulative damage calculated based on the miner linear criterion or the cumulative damage calculated based on the proposed nonlinear damage accumulation theory. CR The critical damage is defined for the nonlinear damage accumulation model, with a value of 1.

[0089] Table 2. Results of vibration and conventional load coupled damage tests and cumulative damage calculations.

[0090]

[0091] Using this invention to calculate the cumulative damage of vibration and conventional load coupling, compared with the miner criterion, the cumulative damage calculated by the proposed nonlinear cumulative theory is closer to the critical damage under two-level coupled spectrum loading conditions. Under four-level and ten-level coupled spectrum loading conditions, the cumulative damage calculation results of the two models are similar. Among the 17 valid data points in the coupled test, 82% of the data points have cumulative damage values ​​within ±20% of the critical damage value, demonstrating good prediction results for the cumulative damage of vibration and conventional load coupling.

[0092] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method of predicting non-linear damage accumulation coupling vibration and conventional fatigue loading, characterized by, Includes the following steps: (1) Determine the peak stress at the critical point under conventional fatigue load based on the finite element model analysis of the engineering component; (2) Determine the probability density function of stress amplitude at the critical point under random vibration loading based on structural dynamics analysis; (3) Locate the pre-generated material fatigue life curve; (4) Determine the equivalent stress at the critical point under random vibration loading based on the fatigue life curve; (5) Calculate the ratio of peak stress under conventional fatigue load to equivalent stress under random vibration at the critical point, and establish coupled damage parameters based on the coupling level of vibration and conventional fatigue load; (6) Establish a nonlinear damage accumulation model coupled with vibration and conventional fatigue load to predict the nonlinear damage accumulation coupled with vibration and conventional fatigue load; The coupling damage parameters mentioned in step (5) are: where m is the coupling order of the vibration and the conventional fatigue load, S n,max is the peak stress at the critical point, is the equivalent stress at the critical point; The nonlinear damage accumulation model coupled with vibration and conventional fatigue load in step (6) is as follows: wherein, is the damage caused by the nth level load, D CR is the critical damage value, m is the coupling order of the vibration and the conventional fatigue load, is the coupling damage parameter, is the damage caused by the nth level load loading cycle number, is the fatigue life under the nth level load.

2. The method of claim 1, wherein, The implementation process of step (1) is as follows: Establish a three-dimensional finite element model of the engineering structure: set material properties, select a hexahedral structure mesh for mesh generation, and perform segmentation and local mesh refinement on the circular notch region; Conventional fatigue loads were applied to the finite element model and finite element analysis was performed: a completely fixed boundary condition was applied on one side of the specimen to simulate the fixing effect of the fixture, and a static load was applied on the other side along the axial direction of the specimen. determining structural fatigue critical points and obtaining peak stresses S at the critical points n,max .

3. The method of claim 1, wherein, The implementation process of step (2) is as follows: The stress power spectral density function at the dangerous point of the structure is obtained by applying random vibration load to the finite element model and conducting structural dynamics analysis The stress amplitude probability density function P(S) at the dangerous point is calculated according to the Dirlik model, specifically as follows: where Z is the normalized stress amplitude, D i are weight coefficients, Q and R are shape parameters, m0 is the 0th order spectral moment; x m is the mean frequency, γ is the irregularity factor, S is the stress amplitude, m i is the i-th order spectral moment, calculated by where f is the frequency, is the stress power spectral density function at the critical point.

4. The nonlinear damage accumulation prediction method coupled with vibration and conventional fatigue loads according to claim 1, characterized in that, Step (3) is achieved through the following formula: In the formula, S represents the stress amplitude, N represents the fatigue life, c0 is the SN curve parameter, and C is the material parameter.

5. The nonlinear damage accumulation prediction method coupled with vibration and conventional fatigue loads according to claim 1, characterized in that, The equivalent stress at the danger point mentioned in step (4) is: Where S represents the stress amplitude, dS represents the integral over S, and c0 is the parameter of the SN curve.

6. A device, characterized in that, Includes memory and processor, wherein: Memory is used to store computer programs that can run on a processor; A processor, configured to, while running the computer program, perform the steps of the nonlinear damage accumulation prediction method coupled with vibration and conventional fatigue loads as described in any one of claims 1 to 5.

7. A storage medium, characterized in that, The storage medium stores a computer program that, when executed by at least one processor, implements the steps of the nonlinear damage accumulation prediction method for the coupling of vibration and conventional fatigue loads as described in any one of claims 1 to 5.

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