Vibration and conventional fatigue load coupled nonlinear damage accumulation prediction method

Abstract

The invention discloses a vibration and conventional fatigue load coupled nonlinear damage accumulation prediction method. The method comprises the following steps: analyzing and determining a peak stress at a dangerous point under the loading of a conventional fatigue load according to a finite element model of an engineering component; determining a stress amplitude probability density function at the dangerous point under random vibration loading according to structural dynamics analysis; searching a pre-generated material fatigue life curve; determining equivalent stress at the dangerous point under random vibration loading according to the fatigue life curve; calculating the ratio of the peak stress loaded by the conventional fatigue load at the dangerous point to the random vibration equivalent stress, and establishing a coupling damage parameter according to the vibration and conventional fatigue load coupling series; and establishing a nonlinear damage accumulation model of vibration and conventional fatigue load coupling. According to the nonlinear damage accumulation model provided by the invention, the influence of vibration, a conventional load sequence and a coupling series is considered, the parameter determination is simple, and high-precision prediction of structural damage evolution under complex load coupling can be realized.

Description

Technical Field

[0001] The present invention relates to fatigue damage accumulation technology under complex loads, and in particular to a nonlinear damage accumulation prediction method coupled with vibration and conventional fatigue loads. Background Art

[0002] Engineering structures are subjected to multiple, combined loads throughout their service life. The coupling of vibration and conventional fatigue loads has become a key driver 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 coupled effects of these two in the time and frequency domains significantly accelerate the initiation and propagation of microcracks. Under the combined effects of vibration and conventional loads, structures are more susceptible to damage accumulation and fatigue problems.

[0003] Existing research has established partial prediction frameworks for damage caused by the coupling of vibration and conventional loads based on the Miner criterion or the local stress-strain method. However, these theoretical systems are still based on the assumption of independent loads and fail to fully reveal the damage evolution path under the interaction of vibration and fatigue. Furthermore, traditional linear damage accumulation theories assume independent damage superposition and do not consider load sequence effects or the interaction between vibration and conventional loads. This results in the inability of linear damage accumulation theories to accurately simulate the coupled damage effects of vibration and conventional fatigue. Nonlinear damage accumulation theories that consider load sequence effects are mostly targeted at a single load type, such as conventional fatigue loads, and are still unable to quantify the contribution of vibration damage to the coupled effects of vibration and conventional fatigue. Therefore, there is currently no damage accumulation theory that can reveal the fatigue damage evolution process under the coupled effects of vibration and conventional fatigue loads. Summary of the Invention

[0004] Purpose of the invention: In response to the deficiencies in the prior art, the present invention proposes a nonlinear damage accumulation prediction method for coupling vibration and conventional fatigue loads to achieve high-precision prediction of structural damage evolution under complex load coupling.

[0005] Technical solution: The nonlinear damage accumulation prediction method for coupling vibration and conventional fatigue loads described in the present 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 dangerous point under random vibration loading based on structural dynamics analysis;

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

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

[0010] (5) Calculate the ratio of the peak stress of conventional fatigue load to the equivalent stress of random vibration at the dangerous point, and establish the coupling damage parameter according to the coupling series of vibration and conventional fatigue load;

[0011] (6) Establish a nonlinear damage accumulation model for the coupling of vibration and conventional fatigue loads to realize the prediction of nonlinear damage accumulation for the coupling of vibration and conventional fatigue loads.

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

[0013] Establish a 3D finite element model of the engineering structure: set material properties, select a hexahedral mesh for meshing, segment the circular notch area, and perform local mesh encryption.

[0014] Apply conventional fatigue loads to the finite element model and perform finite element analysis: a fully fixed boundary condition is applied on one side of the specimen to simulate the fixing effect of the fixture, and a static load is applied along the axial direction of the specimen on the other side;

[0015] Determine the structural fatigue danger point and obtain the peak stress S at the danger point n,max .

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

[0017] Apply random vibration loads to the finite element model and perform structural dynamics analysis to obtain the stress power spectrum density function G(f) at the structural danger point. Calculate the stress amplitude probability density function P(S) at the danger point based on the Dirlik model, as shown in the following formula:

[0018]

[0019] Where Z is the normalized stress amplitude, D i is the weight coefficient, Q and R are shape parameters, m0 is the 0th order spectral moment; m is the average frequency, γ is the irregularity factor, S is the stress amplitude, m i is the i-th order spectral moment, which is calculated by the following formula:

[0020]

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

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

[0023]

[0024] Where 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 dangerous point in step (4) is:

[0026]

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

[0028] Furthermore, the coupling damage parameter in step (5) is:

[0029]

[0030] Where m is the coupling series of vibration and conventional fatigue loads, S n,max is the peak stress at the dangerous point, S vib,eq is the equivalent stress at the dangerous point.

[0031] Furthermore, the nonlinear damage accumulation model of the coupling of vibration and conventional fatigue loads in step (6) is specifically as follows:

[0032]

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

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

[0035] a memory for storing computer programs capable of running on the processor;

[0036] The processor is configured to execute the steps of the above-mentioned method for predicting nonlinear damage accumulation under coupling of vibration and conventional fatigue loads when running the computer program.

[0037] The present invention provides a storage medium having a computer program stored thereon, which, when executed by at least one processor, implements the steps of the above-mentioned method for predicting nonlinear damage accumulation due to coupling of vibration and conventional fatigue loads.

[0038] Beneficial effects: Compared with the prior art, the present invention has the following beneficial effects: the present invention calculates the ratio of the conventional load peak stress at the structural dangerous point to the equivalent stress of random vibration, and introduces the coupling load series to establish the coupling damage parameter to quantify the contribution of vibration damage; the parameter determination is simple, and high-precision prediction of the evolution of structural damage under complex load coupling can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a flow chart of the nonlinear damage accumulation prediction method for coupling vibration and conventional fatigue loads;

[0040] Figure 2 It is a schematic diagram of mesh division in finite element modeling;

[0041] Figure 3 It is a schematic diagram of the probability density function of stress amplitude at the dangerous point under random vibration loading. DETAILED DESCRIPTION

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

[0043] like Figure 1 As shown, the present invention provides a nonlinear damage accumulation prediction method for coupling 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 established in ABAQUS. The material properties were set, and hexahedral structure mesh was selected for mesh division. The circular notch area was segmented and the local mesh was encrypted. The global mesh size was set to 0.5 mm and the local mesh size was set to 0.1 mm. A total of 315,774 units were generated in the final model.

[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 along the axial direction of the specimen on the other side.

[0047] Through the stress cloud diagram of the finite element analysis results, the structural fatigue danger point is determined and the peak stress S at the danger point is obtained. n,max .

[0048] Step 2: Determine the probability density function of the stress amplitude at the dangerous 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, a modal analysis was performed to obtain the first three natural frequencies of the specimen and the corresponding mode shape characteristics. Then, a fully fixed boundary condition was applied to one side of the specimen to simulate the fixture's fixing effect, while an acceleration excitation along the specimen's thickness was applied to the other side.

[0050] Finite element analysis results are used to identify structural fatigue risk points and obtain the stress power spectrum density function G(f) at these risk points. The stress cloud diagram of the analysis results determines the location of the structural fatigue risk point, and the stress power spectrum density function data of the structural fatigue risk point is output through ODB field variables.

[0051] The probability density function P(S) of the stress amplitude at the dangerous point is calculated according to the Dirlik model, as follows:

[0052]

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

[0054]

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

[0056]

[0057] Where f is the frequency and G(f) is the power spectral density function at the dangerous point.

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

[0059]

[0060] Where 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 dangerous point of the structure under random vibration loading is:

[0063]

[0064] Step 5: Calculate the ratio of the peak stress of conventional fatigue load to the equivalent stress of random vibration at the critical point, and establish the coupling damage parameter based on the coupling series of vibration and conventional fatigue load, including:

[0065] The coupling damage parameter expression is:

[0066]

[0067] Where m is the coupling order of vibration and conventional fatigue loads.

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

[0069] The theoretical model expression of nonlinear damage accumulation under vibration and conventional fatigue coupling load is:

[0070]

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

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

[0073] The present invention also provides a storage medium having a computer program stored thereon, which, when executed by at least one processor, implements the steps of the above-mentioned method for predicting nonlinear damage accumulation due to coupling of vibration and conventional fatigue loads.

[0074] The material used in this embodiment is 2A12 aluminum alloy, and a coupling test of vibration and conventional fatigue loads was carried out. First, a finite element analysis was performed on the test piece to determine the dangerous point and obtain the peak stress at the dangerous point when the fatigue load was applied; then a dynamic analysis was performed on the test piece to obtain the stress amplitude probability density function P(S) at the dangerous point, and then the vibration equivalent stress at the dangerous point was calculated based on the material fatigue life curve. Then, the coupling damage parameter was established based on the ratio of the conventional load peak stress to the vibration equivalent stress at the dangerous point and the coupled load spectrum series. Finally, a nonlinear damage accumulation model for the coupling of 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 Sushi DC-200. The coupled test spectrum consisted of a combination of random vibration and conventional fatigue loading. The test loads were as follows: The coupled test scheme is listed in Table 1.

[0076] (a) Vibration load parameters: Broadband flat spectrum random vibration excitation is applied with a frequency range of 5-100 Hz and a power spectral density (PSD) of 0.037 g. 2 / Hz, total root mean square 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 N 50 =78512Cycles.

[0078] Table 1 Vibration and conventional load coupling test plan

[0079]

[0080] Establish the finite element model of the test piece and divide the mesh into Figure 2 The peak stress S at the dangerous point under conventional load is obtained by static analysis. n,max =415.6MPa, apply random vibration load to the structure for dynamic analysis, obtain the power spectrum density function at the dangerous point, and calculate the stress amplitude probability density function P(S) at the dangerous point according to the Dirlik model as follows: Figure 3 As shown. The fatigue life curve of the material is:

[0081] S 5.96 N=10 18.87

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

[0083]

[0084] Modeling nonlinear damage accumulation for vibration and conventional loads:

[0085]

[0086] The cumulative damage of vibration and conventional load coupling calculated according to the model is listed in Table 2. miner represents the cumulative damage calculated based on the linear criterion, D sumrepresents the cumulative damage calculated by the nonlinear damage accumulation theory proposed in this invention, and “*” represents an abnormal data point. In order to facilitate the comparison of the accuracy of the test results, the error factor of the cumulative damage calculated by the damage accumulation theory relative to the critical damage is defined as follows:

[0087] error=(DD CR )×100%

[0088] Where D represents the cumulative damage calculated based on Miner's linear criterion or the cumulative damage calculated based on the proposed nonlinear damage accumulation theory, and D CR The critical damage defined by the nonlinear damage accumulation model has a value of 1.

[0089] Table 2 Vibration and conventional load coupling damage test results and cumulative damage calculation results

[0090]

[0091] Using this method to calculate the cumulative damage of coupled vibration and conventional loads, the proposed nonlinear cumulative theory, compared to the Miner criterion, calculated cumulative damage closer to the critical damage under two-level coupled spectrum loading conditions. Under four- and ten-level coupled spectrum loading conditions, the cumulative damage calculation results of the two models were similar. Of the 17 valid data points in the coupled test, 82% had cumulative damage values ​​within ±20% of the critical damage value, demonstrating excellent prediction results for the cumulative damage of coupled vibration and conventional loads.

[0092] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art could make various modifications and improvements without departing from the spirit of the present application, all of which fall within the scope of protection of the present application. Therefore, the scope of protection of the present patent application shall be determined by the appended claims.

Claims

1. A nonlinear damage accumulation prediction method for coupling vibration and conventional fatigue loads, characterized in that: The following steps are involved: (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 dangerous point under random vibration loading based on structural dynamics analysis; (3) Find the pre-generated material fatigue life curve; (4) Determine the equivalent stress at the dangerous point under random vibration loading based on the fatigue life curve; (5) Calculate the ratio of the peak stress of conventional fatigue load to the equivalent stress of random vibration at the dangerous point, and establish the coupling damage parameter according to the coupling series of vibration and conventional fatigue load; (6) Establish a nonlinear damage accumulation model for the coupling of vibration and conventional fatigue loads to realize the prediction of nonlinear damage accumulation for the coupling of vibration and conventional fatigue loads.

2. The nonlinear damage accumulation prediction method for coupling vibration and conventional fatigue loads according to claim 1 is characterized in that: The implementation process of step (1) is as follows: Establish a 3D finite element model of the engineering structure: set material properties, select a hexahedral mesh for meshing, segment the circular notch area, and perform local mesh encryption. Apply conventional fatigue loads to the finite element model and perform finite element analysis: a fully fixed boundary condition is applied on one side of the specimen to simulate the fixing effect of the fixture, and a static load is applied along the axial direction of the specimen on the other side; Determine the structural fatigue danger point and obtain the peak stress S at the danger point n,max .

3. The nonlinear damage accumulation prediction method for coupling vibration and conventional fatigue loads according to claim 1 is characterized in that: The implementation process of step (2) is as follows: Apply random vibration loads to the finite element model and perform structural dynamics analysis to obtain the stress power spectrum density function G(f) at the structural danger point; and calculate the stress amplitude probability density function P(S) at the danger point according to the Dirlik model, as shown in the following formula: Where Z is the normalized stress amplitude, D i is the weight coefficient, Q and R are shape parameters, m0 is the 0th order spectral moment; m is the average frequency, γ is the irregularity factor, S is the stress amplitude, m i is the i-th order spectral moment, which is calculated by the following formula: Where f is the frequency and G(f)d is the stress power spectrum density function at the dangerous point.

4. The nonlinear damage accumulation prediction method for coupling vibration and conventional fatigue loads according to claim 1 is characterized in that: The step (3) is achieved by the following formula: Where 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 for coupling vibration and conventional fatigue loads according to claim 1 is characterized in that: The equivalent stress at the dangerous point in step (4) is: Where S represents the stress amplitude and dS represents the integral of S.

6. The nonlinear damage accumulation prediction method for coupling vibration and conventional fatigue loads according to claim 1 is characterized in that: The coupling damage parameter in step (5) is: Where m is the coupling series of vibration and conventional fatigue loads, S n,max is the peak stress at the dangerous point, S vib,eq is the equivalent stress at the dangerous point.

7. The nonlinear damage accumulation prediction method for coupling vibration and conventional fatigue loads according to claim 1 is characterized in that: The nonlinear damage accumulation model of the coupling of vibration and conventional fatigue loads in step (6) is as follows: Among them, D i is the damage caused by the i-th level load, D CR is the critical damage value, m is the coupling level of vibration and conventional fatigue load, k i is the coupling damage parameter, n i is the number of loading cycles for level i, N fi is the fatigue life under the i-th load level.

8. A device, characterized in that: comprising a memory and a processor, wherein: a memory for storing computer programs capable of running on the processor; A processor is configured to execute the steps of the nonlinear damage accumulation prediction method for coupling vibration and conventional fatigue loads as claimed in any one of claims 1 to 7 when running the computer program.

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

Images