A Spectral Load Life Prediction Method Based on Load Action Order

Abstract

This paper discloses a spectral load life prediction method based on load order. By applying the damage equivalence principle, the creep-fatigue damage evolution equation based on continuum damage mechanics, and load factors, this method is generalized to multiple levels to develop a nonlinear cumulative life prediction model under spectral loads based on KAM, which considers the load order. This model then predicts the life under a specific acceleration spectrum. This method focuses on the microstructure of grain boundary misorientation within the material, considers the load order, and employs a nonlinear cumulative principle. It can be applied to calculate component life under spectral loads in actual engines.

Description

Technical Field

[0001] The present invention relates to the technical field of high-temperature structural strength, and in particular to a spectral load life prediction method based on load action order. Background Art

[0002] Turbine disks, a key hot-end component in aircraft engines, are subject to complex cyclic loading during service. Under high-temperature conditions, turbine disks experience both creep damage caused by the continuous loads of steady-state operation and fatigue damage caused by variable loads resulting from equipment startups and shutdowns, temperature fluctuations, and other factors. These two types of damage act simultaneously on the disks. This situation reflects the typical characteristics of high-temperature random creep-fatigue loading.

[0003] The reasons for the poor accuracy of existing spectral load prediction methods are as follows: First, creep loads and fatigue loads are extracted separately to calculate damage, and then linear accumulation is used to calculate the total damage. However, in the creep-fatigue process, creep and fatigue promote each other, resulting in more serious damage than the sum of the two; second, the influence of the order of load action is not considered. Studies have shown that the high load that acts first will promote the low load that acts later, while the low load that acts first will inhibit the high load that acts later. The above two reasons lead to the insufficient prediction accuracy of existing models. In addition, most models for calculating single-stage creep-fatigue loads are based on macroscopic aspects and do not pay enough attention to microscopic aspects.

[0004] Therefore, it is necessary to develop a nonlinear cumulative life prediction model under spectral loads based on microstructural changes and load effects, which can provide strong support for the life calculation of hot end components of aero-engines subjected to complex loads. Summary of the Invention

[0005] In order to make up for the lack of life prediction methods for hot end components under complex loads in engineering, the present invention proposes a spectral load life prediction method that takes into account the orientation difference between the lattices inside the material and the order of load action.

[0006] In order to achieve the above object, the present invention is implemented through the following technical solutions:

[0007] The present invention is a spectral load life prediction method based on load action order, comprising the following steps: first, using the energy parameter E p Obtain the influence of holding time, stress, and loading waveform on the creep-fatigue life of the material; obtain the average strain failure ε at different life fractions under different stresses and holding times based on uniaxial creep-fatigue tests N and the average strain at fracture ε c-f ;

[0008] The average strain in the material damage process is selected as the damage variable, and based on continuum damage mechanics, the creep-fatigue damage evolution equation at constant temperature is derived.

[0009] Based on failure life N c-f The relationship between the KAM and the material intracrystalline misorientation is extended to multiple levels according to the damage equivalence principle to obtain a nonlinear accumulation model based on KAM.

[0010] The load action factor (E) is introduced into the nonlinear accumulation model based on KAM. pi / E pi+1 ) 2 Finally, the nonlinear cumulative life prediction model under spectral load based on KAM considering the order of load action is obtained, and the life under a certain acceleration spectrum is predicted using the nonlinear cumulative life prediction model under spectral load based on KAM considering the order of load action. The expression of the nonlinear cumulative life prediction model under spectral load based on KAM considering the order of load action is:

[0011]

[0012] in, is the remaining life fraction of the i-th load level, n i is the number of cycles of the i-th level load, N c-fi is the failure life under the action of the i-th level load alone, f(KAM i-1 ) is the failure life under the action of the i-1th level load alone, D is the total creep-fatigue damage, b is a parameter related to temperature, E Pi is the energy parameter of the i-th level load.

[0013] A further improvement of the present invention is that the energy parameter E p is the area formed by the loading waveform and the zero stress line under stress control, and its expression is:

[0014]

[0015] Among them, t h is the holding time at maximum stress, σ max is the maximum stress, t1 is the loading time, t2 is the unloading time, σ min is the minimum stress, Δσ is the difference between the maximum stress and the minimum stress, and t0 is the total time of one cycle.

[0016] A further improvement of the present invention is that the average strain in the material damage process is selected as the damage variable, and based on continuum damage mechanics, the creep-fatigue damage evolution equation at constant temperature is derived. The expression of the creep-fatigue damage evolution equation is:

[0017]

[0018] Where D is the total creep-fatigue damage, D is 0 at the initial moment and 1 at failure, N is the number of cycles currently performed, N c-f is the number of cycles to failure, i.e., failure life, a and b are parameters related to temperature;

[0019] The average strain in the material damage process is selected as the damage variable and is defined as follows:

[0020]

[0021] Among them, ε N is the average axial strain of the material after N cycles, ε c-f is the average axial strain at material failure.

[0022] A further improvement of the present invention is that the failure life N c-f The expression of the relationship with the material intracrystalline orientation difference KAM is:

[0023]

[0024] The relationship between the material intracrystalline orientation difference KAM and stress and holding time is as follows:

[0025]

[0026] A further improvement of the present invention is that the expression of the nonlinear accumulation model based on KAM is:

[0027]

[0028] The present invention has the following beneficial effects: its method considers the misorientation between the material's internal lattices and incorporates microscopic failure mechanisms as parameters into the life prediction model. It also considers the effect of the load sequence on material life, employing a nonlinear accumulation method that is more accurate than linear accumulation. This method effectively assesses the effects of microstructural changes and load sequence on damage, achieving a prediction error of 10.6%, and is applicable to component life calculations under actual engine load profiles. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is an implementation flow chart of the present invention;

[0030] Figures 2a to 2i is a fitting curve of parameter p in the damage evolution equation of GH4169 at 650°C in an embodiment of the present invention;

[0031] in, Figure 2a The stress and holding time are fitted with p values ​​of 750 MPa-5 s;

[0032] Figure 2b The stress and holding time are p values ​​of the 750MPa-10s fitting;

[0033] Figure 2c The stress and holding time are p values ​​of the 750MPa-15s fitting;

[0034] Figure 2d The p value of the stress and holding time is 800 MPa-5s;

[0035] Figure 2e The p value of the stress and holding time is 800 MPa-10s;

[0036] Figure 2f The p value of the stress and holding time is 800 MPa-15s;

[0037] Figure 2g The stress and holding time are fitted with p-values ​​of 850 MPa-5 s;

[0038] Figure 2h The stress and holding time are fitted with the p value of 850 MPa-10 s;

[0039] Figure 2i The p value of the stress and holding time is 750MPa-5s850MPa-15s;

[0040] Figure 3 is the fitting curve of parameters a and b in the damage evolution equation of GH4169 at 650°C in the embodiment of the present invention;

[0041] Figure 4 It is a diagram of the predicted load spectrum in an embodiment of the present invention. DETAILED DESCRIPTION

[0042] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only intended to illustrate the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0043] The present invention is a spectral load life prediction method based on the order of load action. Through the damage equivalence law, the creep-fatigue damage evolution equation based on continuous damage mechanics and the load action factor are applied, and the nonlinear cumulative life prediction model under spectral load considering the order of load action is obtained based on KAM and extended to multiple levels. Its expression is:

[0044]

[0045] in, is the remaining life fraction of the i-th load level, n i is the number of cycles of the i-th level load, N c-fi is the failure life under the action of the i-th level load alone, f(KAM i-1 ) is the failure life of the i-1th level load alone, that is, the i-1th level creep-fatigue failure life, D is the total creep-fatigue damage, b is a parameter related to temperature, E p Characterizes a single trapezoidal wave as a load-related quantity, namely the energy parameter, E Pi is the energy parameter of the i-th level load.

[0046] like Figure 1 As shown, this embodiment is a spectral load life prediction method for nickel-based high-temperature alloy materials based on load action order, comprising the following steps:

[0047] Step 1, by applying the energy parameter E p To reflect the influence of holding time, stress, and loading waveform on the creep-fatigue life of the material, the energy parameter E p is the area formed by the loading waveform and the zero stress line under stress control, and its expression is:

[0048]

[0049] Among them, t h is the holding time at maximum stress, σ max is the maximum stress, t1 is the loading time, t2 is the unloading time, σ min is the minimum stress, Δσ is the difference between the maximum stress and the minimum stress, and t0 is the total time of one cycle.

[0050] Step 2: Obtain the average strain failure ε at different life fractions under different stresses and holding times according to the uniaxial creep-fatigue test N and the average strain at fracture ε c-f ;

[0051] Step 3: Perform creep-fatigue damage evolution based on continuum damage mechanics on the material at a constant temperature. The creep-fatigue damage evolution equation based on continuum damage mechanics at a constant temperature is as follows:

[0052]

[0053] Where D is the total creep-fatigue damage, D is 0 at the initial moment and 1 at failure. N is the number of cycles currently performed, N c-f is the number of failure cycles, i.e., failure life, a and b are parameters related to temperature and can be obtained by fitting.

[0054] In the process of fitting a and b, first a(E p ) b The data of fitting p as a constant p are shown in Table 1:

[0055] Table 1 Fitting data of different holding time and stress p value

[0056]

[0057]

[0058] The p-value fitting curve is as follows Figures 2a to 2i The fitting parameters a=16.68,b=-0.67 are shown in Figure 2. Figure 3 shown.

[0059] The average strain in the material damage process is selected as the damage variable and is defined as follows:

[0060]

[0061] Among them, ε N is the average axial strain of the material after N cycles, ε c-f is the average axial strain at material failure.

[0062] Step 4, based on failure life N c-f The relationship between the material intracrystalline orientation difference KAM is extended to multiple levels according to the damage equivalence principle to obtain a nonlinear accumulation model based on KAM. c-f The expression of the relationship with the material intracrystalline orientation difference KAM is:

[0063]

[0064] The relationship between the material intracrystalline orientation difference KAM and stress and holding time is as follows:

[0065]

[0066] According to the damage principle, taking two-stage loading as an example, the damage caused by the first-stage waveform acting n1 times can be equivalent to the damage caused by the second-stage waveform acting n'2 times. The damage accumulation process of the two-stage loading can be equivalent to the damage accumulation process of the second-stage waveform acting n2+n'2 times, and the expression is:

[0067]

[0068] Among them, E P1 is the energy parameter of the first-level load, and f(KAM1) is the first-level creep-fatigue failure life. Since the single-level life is calculated using the life prediction model based on the intracrystalline orientation difference KAM, the life is expressed as f(KAM).

[0069] The expressions of the two-level residual creep-fatigue life fraction and the two-level damage accumulation are as follows:

[0070]

[0071] Extending to multiple levels, we get a nonlinear cumulative model based on KAM, which is expressed as:

[0072]

[0073] Step 5: Introduce the load factor (E pi / E pi+1 ) 2 Finally, the nonlinear cumulative life prediction model under spectral load considering the load action order based on KAM is obtained, and the expression is:

[0074]

[0075] The life prediction is performed using the nonlinear cumulative life prediction model under spectral loads based on KAM considering the order of load action. The predicted spectrum is as follows: Figure 4 As shown, the calculated data of the predicted spectrum are shown in Table 2:

[0076] Table 2 Prediction spectrum calculation data

[0077]

[0078] Finally, the damage accumulation value ΣD under this load spectrum is calculated c-f It is 0.01086455.

[0079] The life calculation method is:

[0080]

[0081] In the formula: ΣD c-f The cumulative damage of a spectrum.

[0082] The predicted lifespan under this spectrum is 92 cycles.

[0083] The results of the spectrum test are shown in Table 3:

[0084] Table 3 Acceleration spectrum test data

[0085]

[0086] The average number of cycles to fracture of the five specimens is 103 cycles, and the prediction error is 10.6%.

[0087] It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by those skilled in the art in the art to which the present invention belongs. It should also be understood that terms such as those defined in common dictionaries should be understood to have meanings consistent with their meanings in the context of the prior art and, unless defined similarly as herein, will not be interpreted in an idealized or overly formal sense.

[0088] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A spectral load life prediction method based on load action order, characterized by: The following steps are involved: Using the energy parameter E p Obtain the influence of holding time, stress, and loading waveform on the creep-fatigue life of the material; obtain the average strain failure ε at different life fractions under different stresses and holding times based on uniaxial creep-fatigue tests N and the average strain at fracture ε c-f ; The average strain in the material damage process is selected as the damage variable, and based on continuum damage mechanics, the creep-fatigue damage evolution equation at constant temperature is derived. Based on failure life N c-f The relationship between the KAM and the material intracrystalline misorientation is extended to multiple levels according to the damage equivalence principle to obtain a nonlinear accumulation model based on KAM. The load action factor (E) is introduced into the nonlinear accumulation model based on KAM. pi / E pi+1 ) 2 Finally, the nonlinear cumulative life prediction model under spectral load based on KAM considering the order of load action is obtained, and the life under a certain acceleration spectrum is predicted using the nonlinear cumulative life prediction model under spectral load based on KAM considering the order of load action. The expression of the nonlinear cumulative life prediction model under spectral load based on KAM considering the order of load action is: in, is the remaining life fraction of the i-th load level, n i is the number of cycles of the i-th level load, N c-fi is the failure life under the action of the i-th level load alone, f(KAM i-1 ) is the failure life under the action of the i-1th level load alone, D is the total creep-fatigue damage, b is a parameter related to temperature, E Pi is the energy parameter of the i-th level load.

2. The method for predicting lifespan of a load spectrum based on the order of load action according to claim 1, characterized in that: Energy parameter E p is the area formed by the loading waveform and the zero stress line under stress control, and its expression is: Among them, t h is the holding time at maximum stress, σ max is the maximum stress, t1 is the loading time, t2 is the unloading time, σ min is the minimum stress, Δσ is the difference between the maximum stress and the minimum stress, and t0 is the total time of one cycle.

3. The method for predicting lifespan of a load spectrum based on load action order according to claim 1, characterized in that: The average strain in the material damage process is selected as the damage variable. Based on the continuum damage mechanics, the creep-fatigue damage evolution equation at constant temperature is derived. The expression of the creep-fatigue damage evolution equation is: Where D is the total creep-fatigue damage, D is 0 at the initial moment and 1 at failure, N is the number of cycles currently performed, N c-f is the number of cycles to failure, i.e., failure life, a and b are parameters related to temperature; The average strain in the material damage process is selected as the damage variable and is defined as follows: Among them, ε N is the average axial strain of the material after N cycles, ε c-f is the average axial strain at material failure.

4. The method for predicting lifespan of a load spectrum based on load action order according to claim 1, characterized in that: The failure life N c-f The expression of the relationship with the material intracrystalline orientation difference KAM is: The relationship between the material intracrystalline orientation difference KAM and stress and holding time is as follows:

5. The method for predicting lifespan of a load spectrum based on load action order according to claim 1, characterized in that: The expression of the nonlinear accumulation model based on KAM is:

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