A low-cycle multi-axial fatigue life prediction method based on powder high-temperature alloy damage mechanism

Abstract

The present application relates to the technical field of high-temperature structural component fatigue strength design and life assessment, and particularly relates to a low-cycle multi-axial fatigue life prediction method based on powder high-temperature alloy damage mechanism. The method comprises: for the dangerous point of the component under non-isothermal multi-axial cyclic loading, calculating pure fatigue damage, pure creep damage and fatigue-creep interaction damage caused by a single load cycle; accumulating the pure fatigue damage, the pure creep damage and the fatigue-creep interaction damage to obtain the total damage of the single load cycle; taking the inverse of the total damage to predict the total failure life of the component under non-isothermal multi-axial cyclic loading. The method of the present application realizes effective prediction of the low-cycle multi-axial fatigue life of the powder high-temperature alloy component by accurately decomposing the damage of the dangerous point under non-isothermal multi-axial cyclic loading, can more truly reflect the comprehensive prediction model of the failure physics of the powder high-temperature alloy under multi-axial thermal mechanical loading, and improves the accuracy and reliability of the life assessment.

Description

Technical Field

[0001] This invention relates to the field of fatigue strength design and life assessment technology for high-temperature structural components, specifically to a low-cycle multiaxial fatigue life prediction method based on the damage mechanism of powder superalloys. Background Technology

[0002] Powder metallurgical superalloys (such as FGH99 and FGH96) are widely used in critical hot-end components such as turbine disks in aero-engines due to their excellent high-temperature strength, creep resistance, and fatigue resistance. These components are subjected to the combined and coupled effects of high-temperature environments and complex multiaxial mechanical loads during service, i.e., multiaxial thermomechanical fatigue loads. Under such loads, material failure is the result of fatigue damage, creep damage, and the complex interaction between the two, making life prediction extremely challenging.

[0003] Currently, most life prediction methods used in engineering are based on the linear cumulative damage rule. These methods typically treat total damage as a linear superposition of fatigue damage and creep damage. However, this simplified framework has fundamental limitations: First, it fails to establish an independent, physically meaningful characterization term for "fatigue-creep interactive damage," instead implicitly allocating or ignoring its effects, resulting in the model's inability to depict the true physical picture of the competitive coupling of the two damage mechanisms. Second, even in some improved models that attempt to introduce interaction terms, these are mostly empirically based linear or symmetrical coupling forms, failing to characterize the nonlinear and asymmetric characteristics of the interaction as the damage state and load path change.

[0004] In particular, for powder metallurgy superalloys, under specific non-proportional multiaxial thermomechanical load paths (such as MOPTOP where both the mechanical and thermal phase angles are 90°), 90 The material exhibits anomalous damage behavior driven by dramatic changes in microscopic mechanisms, further amplifying the prediction error of the traditional linear cumulative framework. Although advanced multiaxial fatigue models, such as the critical surface method, can calculate pure fatigue damage more accurately, there is still a lack of systematic solutions on how to organically combine them with creep damage models and embed coupling mechanisms that can reflect the aforementioned complex interactions and non-proportional effects.

[0005] Therefore, there is an urgent need in this field for an innovative framework for life prediction. This framework should break through the constraints of traditional linear superposition and model fatigue-creep interaction damage as an independent, quantifiable, and mechanism-driven component. This would allow for the construction of a comprehensive prediction model that more realistically reflects the failure physics of powder superalloys under multiaxial thermomechanical loading, thereby fundamentally improving the accuracy and reliability of life assessment for critical components. Summary of the Invention

[0006] In view of this, the present invention proposes a low-cycle multiaxial fatigue life prediction method based on the damage mechanism of powder superalloys, which can at least solve the technical problems of low accuracy and poor reliability of existing low-cycle multiaxial fatigue life prediction methods.

[0007] This invention proposes a low-cycle multiaxial fatigue life prediction method based on the damage mechanism of powder superalloys, comprising the following steps: for the critical points of the component under non-isothermal multiaxial cyclic loading, determining the pure fatigue damage caused by a single load cycle. Pure creep damage and fatigue-creep interaction damage ; pure fatigue damage Pure creep damage and fatigue-creep interaction damage The total damage for this single load cycle is obtained by summing the results. ; for total damage Take the reciprocal to predict the total failure life of the component under non-isothermal multiaxial cyclic loading. N .

[0008] In some embodiments, the calculation of pure fatigue damage includes: S11, obtaining the multiaxial stress-strain history of the critical point of the component; determining the critical damage surface of the critical point based on the critical plane method, and calculating the multiaxial equivalent damage parameters of the critical damage surface. S12, based on multiaxial equivalent damage parameters Calculate pure fatigue damage .

[0009] In some embodiments, in step S11, the multiaxial equivalent damage parameter The expression is:

[0010] In the formula, This represents the range of maximum shear strain on the damage critical surface. The range of normal strain between the maximum shear strain reversal points on the damage critical surface.

[0011] In some embodiments, in step S12, pure fatigue damage The expression is:

[0012]

[0013] In the formula, The fatigue strength coefficient is dimensionless. The fatigue strength index is dimensionless. The fatigue plasticity coefficient is dimensionless. The fatigue plasticity index is dimensionless. It is the elastic modulus, which is dimensionless; For reference fatigue life, weeks.

[0014] In some embodiments, pure creep damage The calculations include: S21, obtaining the axial stress-time history, shear stress-time history, and temperature-time history of the critical point within a load cycle; S22, discretizing the load cycle into multiple time intervals using a time-domain subdivision method; and S23, calculating the creep damage in each time interval based on the physical mechanism of creep damage. S24, summing creep damage across all time intervals. The pure creep damage of this load cycle is obtained. .

[0015] In some embodiments, in step S23, creep damage for each time interval is calculated. Includes: S231, which acquires the instantaneous temperature for each time interval. T i And calculate the equivalent creep stress for that time interval. S232, based on equivalent creep stress and instantaneous temperature T i The creep rupture time of the component in each time interval was determined using the creep rupture equation of the material. S233, based on creep rupture time and the duration of each time interval Calculate the creep damage caused during this time interval. .

[0016] In some embodiments, step S231, calculating the equivalent creep stress further includes: determining the axial stress for each time interval. Is it positive? If axial stress If positive, then the equivalent creep stress for that time interval is... ,in, If the stress is shear stress, then the equivalent creep stress for that time interval is defined; otherwise, the equivalent creep stress for that time interval is defined. It is zero.

[0017] In some embodiments, the calculation of fatigue-creep interaction damage includes: S31: obtaining the average temperature over a load cycle. S32: Identify the mechanical phase angle during load cycles. With thermal phase angle S33: Based on mechanical phase angle and thermal phase angle Determine rapid hardening parametersα S34: Based on average temperature and rapid hardening parameters α Calculate the interaction coefficient S35: Based on pure creep damage Determine the correction factor used to characterize the interaction asymmetry. S36: Based on pure fatigue damage Pure creep damage Interaction coefficient and correction factor Fatigue-creep interactive damage is calculated using nonlinear functions. .

[0018] In some embodiments, in step S31, the average temperature The acquisition includes: extracting a temperature-time history segment from a load cycle where the temperature is above a preset threshold; and obtaining the highest temperature of the segment. With the lowest temperature Based on the highest temperature With the lowest temperature Calculate the arithmetic mean of the segment. , which is the average temperature of this load cycle.

[0019] In some embodiments, the average temperature is expressed as: .

[0020] In some embodiments, the expression for the rapid hardening parameter in step S33 is: .

[0021] In some embodiments, in step S34, the interaction coefficient The expression is:

[0022] In the formula, m and n These are the material constants obtained by fitting experimental data.

[0023] In some embodiments, in step S35, the correction factor The expression is:

[0024] In the formula, g and h These are normal values ​​obtained through experimental calibration.

[0025] In some embodiments, in step S36, fatigue-creep alternating damage The expression is: .

[0026] Compared with the prior art, the present invention has the following advantages: 1. A damage analysis framework that better reflects physical reality has been established, achieving a refined decoupling of damage mechanisms. Traditional linear cumulative damage rules simply reduce total damage to the linear superposition of fatigue and creep damage. This framework theoretically ignores the complex competition and synergistic effects between fatigue and creep as two different physical mechanisms. This invention fundamentally overcomes this limitation, creatively proposing to decompose total damage into three components with clear physical orientations: pure fatigue damage, pure creep damage, and fatigue-creep interactive damage.

[0027] 2. This invention provides a scalable and in-depth core model architecture for high-precision life prediction, with strong inclusivity. The "computation-accumulation" framework provided by this invention is a highly structured, modular, and open system. The calculations of pure fatigue damage, pure creep damage, and interactive damage can be developed and optimized as three relatively independent modules. For example, the pure fatigue damage module can employ an advanced multiaxial fatigue model based on the critical surface method; the pure creep damage module can integrate the time-domain subdivision method with refined creep constitutive equations; and the interactive damage module provides a natural interface for introducing innovative models such as rapid hardening parameters and asymmetric correction factors.

[0028] 3. Significantly improves the systematicness and reliability of life prediction under complex loads, demonstrating outstanding engineering practical value. Addressing the challenge of life assessment for powder metallurgy components under non-isothermal, multiaxial cyclic loading, this method, through the aforementioned framework, for the first time systematically maps three key service characteristics—multiaxiality, temperature cycling, and phase coupling between the two—to different damage calculation modules for processing, and captures the coupling effect between them through interactive damage terms. This allows the prediction model to more comprehensively and realistically reflect the complexity of service conditions. Compared to traditional methods that suffer from large prediction biases and high dispersion under complex paths (especially non-proportional paths), applying this framework yields life prediction results with clearer logic, more stable results, and more explicit physical meaning, thus providing a more solid and reliable technical basis for the life determination, life extension, and reliability design of key components in major equipment such as aero-engines. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other embodiments can be obtained based on these drawings without creative effort.

[0030] Figure 1 The overall flowchart of a low-cycle multiaxial fatigue life prediction method based on the damage mechanism of powder superalloys provided in an embodiment of the present invention is shown below. Figure 2 A flowchart of a low-cycle multiaxial fatigue life prediction method based on the damage mechanism of powder superalloys provided in another embodiment of the present invention; Figure 3 This is a schematic diagram showing the specific shape and geometric dimensions of the thin-walled tube specimen used in the examples of this invention. Figure 4 This is a schematic diagram showing three load paths, loading waveforms, and strain paths for a uniaxial thermomechanical fatigue test according to an embodiment of the present invention. Figure 5 and Figure 6 A schematic diagram showing six load paths, loading waveforms, and strain paths for a multiaxial thermomechanical fatigue test provided in one embodiment of the present invention; Figure 7 This is a comparison chart of the predicted lifetime and the experimental lifetime obtained using the method of this invention. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to specific examples and the accompanying drawings.

[0032] It should be noted that all uses of "first" and "second" in the embodiments of the present invention are for the purpose of distinguishing two entities or parameters with the same name but different names. It is clear that "first" and "second" are only for the convenience of expression and should not be construed as limiting the embodiments of the present invention. Subsequent embodiments will not explain this in detail.

[0033] One embodiment of the present invention proposes a method for predicting low-cycle multiaxial fatigue life based on the damage mechanism of powder superalloys, such as... Figure 1 As shown, it includes the following steps: Based on the service conditions of the component, complete time-varying history data of the most critical points of geometric and stress concentration are obtained within a representative load cycle through numerical simulation (such as finite element analysis) or experimental measurement. These critical points are typically located at points of geometric abrupt change. For the critical points of the component under non-isothermal multiaxial cyclic loading, the pure fatigue damage caused by a single load cycle is calculated. Pure creep damage and fatigue-creep interaction damage ; pure fatigue damage Pure creep damage and fatigue-creep interaction damage The total damage for this single load cycle is obtained by summing the results. ,Right now ; for total damage Take the reciprocal to predict the total failure life of the component under non-isothermal multiaxial cyclic loading. N ,but .

[0034] This invention enables effective prediction of the low-cycle multiaxial fatigue life of powder metallurgy superalloy components by accurately decomposing the critical points under non-isothermal multiaxial cyclic loading. Specifically, by calculating and summing the damage components of pure fatigue, pure creep, and their interaction, this invention can more comprehensively reflect the comprehensive damage mechanism of materials under actual complex loads. Furthermore, this method improves the accuracy of life prediction, and is particularly suitable for harsh conditions such as high temperature and multiaxial stress states. Moreover, by taking the reciprocal of the total damage to obtain the failure life, it provides a reliable theoretical basis for engineering design, helping to optimize component design, improve safety performance, and extend service life.

[0035] In some embodiments, the calculation of pure fatigue damage specifically includes the following steps.

[0036] S11: Obtain the multiaxial stress-strain history of the critical point of the component; based on the critical plane method, determine the damage critical surface of the critical point and calculate the multiaxial equivalent damage parameters of the damage critical surface. Among them, the damage critical surface is the plane with the largest normal strain amplitude in the plane of maximum shear strain amplitude. This represents the equivalent strain range on the damage critical surface. Multiaxial equivalent damage parameters. The expression is:

[0037] In the formula, This represents the range of maximum shear strain on the damage critical surface. The range of normal strain between the maximum shear strain reversal points on the damage critical surface is given by known input values.

[0038] S12, based on multiaxial equivalent damage parameters Calculate pure fatigue damage .

[0039] Specifically, the multiaxial equivalent damage parameters calculated in step S11 As input, the reference fatigue life of the component material under the current strain amplitude is calculated by solving the Manson-Coffin equation of the material. Among them, the strain amplitude and reference fatigue life established by the Manson-Coffin equation are... The relationship is as follows:

[0040] In the formula, The fatigue strength coefficient is dimensionless. The fatigue strength index is dimensionless. The fatigue plasticity coefficient is dimensionless. The fatigue plasticity index is dimensionless. It is the elastic modulus, which is dimensionless.

[0041] Pure fatigue damage caused by a single load cycle Defined as the reference fatigue life The reciprocal:

[0042] This formula indicates that, under the current load conditions, each load cycle consumes 1 / 3 of the material's reference fatigue life. .

[0043] In some embodiments, pure creep damage The calculation specifically includes the following steps: S21, Obtain the axial stress-time history of a critical point within a load cycle. Shear stress-time history and temperature-time history ; S22 uses a time-domain subdivision method to discretize the load cycle into n consecutive time intervals on the time axis. The duration of the i-th interval is denoted as Δt. i The axial stress, shear stress, and temperature state within this range can be represented by representative values. i , i and T i To characterize.

[0044] S23, based on the physical mechanism of creep damage, calculates creep damage for each time interval. ; S24, summing creep damage across all time intervals. The pure creep damage of this load cycle is obtained. ,Right now .

[0045] Specifically, in some embodiments, in step S23, creep damage for each time interval is calculated. include: S231, Obtain the instantaneous temperature for each time interval. T i And calculate the equivalent creep stress for that time interval. Specifically, before calculating the equivalent creep stress, the axial stress in each time interval is first determined. Is it positive? If axial stress If positive, then the equivalent creep stress for that time interval is... Otherwise, define the equivalent creep stress for that time interval. =0, and skip subsequent steps S232 and S233.

[0046] S232, based on equivalent creep stress and instantaneous temperature T i By using the creep rupture equation of the material, the creep fracture time of the component in each time interval is determined. Specifically, the creep rupture equation is, for example, the Larson-Miller equation. This equation allows us to calculate or look up the time required for a material to undergo creep rupture under constant stress-temperature conditions, i.e., the creep rupture time of the material. .

[0047] S233, based on creep rupture time Duration of the time interval Calculate the creep damage caused during this time interval. . The expression is:

[0048] Then the pure creep damage of this load cycle The expression is:

[0049] In some embodiments, the calculation of fatigue-creep interaction damage includes: S31: Obtain the average temperature over a load cycle ; S32: Identify the mechanical phase angle during load cycles (Phase difference between axial mechanical strain cycle and shear mechanical strain cycle) and thermal phase angle (Phase difference between axial mechanical strain cycle and temperature cycle); S33: Based on mechanical phase angle and thermal phase angle Determine rapid hardening parameters α ; S34: Based on average temperature and rapid hardening parameters α Calculate the interaction coefficient ; S35: Based on pure creep damage Determine the correction factor used to characterize the interaction asymmetry. ; S36: Based on pure fatigue damage Pure creep damage Interaction coefficient and correction factor Fatigue-creep interactive damage is calculated using nonlinear functions. .

[0050] In some embodiments, in step S31, the average temperature The acquisition includes: Extract the temperature-time history segment of the high-temperature bearing stage that significantly contributes to creep damage in a load cycle; in a specific embodiment, the high-temperature bearing stage is defined as the period when the temperature is higher than a preset threshold (e.g., 500°C); Get the highest temperature of the segment With the lowest temperature ; Based on the highest temperature With the lowest temperature Calculate the arithmetic mean of the segment. The average temperature is taken as the average temperature of this load cycle. The expression for the average temperature is: .

[0051] In some embodiments, in step S33, the rapid hardening parameter α Used to quantify the accelerating effect of a specific thermo-mechanical non-proportional path on damage evolution, it is the mechanical phase angle. With thermal phase angle function, and when =90° and The maximum value is achieved at 90°. In one embodiment, the rapid hardening parameter... α The expression is: .

[0052] In some embodiments, in step S34, the interaction coefficient This study comprehensively characterizes the combined effects of temperature and load path on the fatigue-creep interaction strength. The interaction coefficient... The expression is:

[0053] In the formula, m and n These are the material constants obtained by fitting experimental data. This formula reflects the interaction strength with temperature. It exhibits exponential variation and is rapidly hardened by parameters. α Linear modulation.

[0054] In some embodiments, in step S35, the correction factor This is used to characterize the asymmetry of the interaction between fatigue and creep damage, that is, the characteristic that the interaction intensity varies non-linearly with the level of creep damage. It is a pure creep damage... The function. Correction factor. The expression is:

[0055] In the formula, g h and h are the material normal numbers obtained through experimental calibration, which include fatigue tests with different holding times.

[0056] In some embodiments, in step S36, fatigue-creep alternating damage The expression is: .

[0057] The following section further illustrates the invention based on the life prediction process of FGH99 powder superalloy under uniaxial and multiaxial thermomechanical fatigue loads under different conditions.

[0058] FGH99 is a nickel-based superalloy prepared by powder metallurgy. Due to its excellent high-temperature strength, creep resistance, and fatigue performance, it is widely used in key hot-end components such as turbine disks in aero-engines. Its main chemical composition is shown in Table 1.

[0059] Table 1 Chemical composition (wt.%) of FGH99 powder superalloy

[0060] For fatigue testing, all tests were conducted on a shaft-torsion hydraulic servo testing system. Temperature loads were applied using a radio frequency induction coil, and cooling was achieved using air-cooled pipes. Strain during the test was measured using a tension-torsion high-temperature extensometer. Temperature measurements during the test were performed using an infrared thermometer. Furthermore, all tests were conducted in air. Figure 3 The shape and geometry of the thin-walled tube specimen used in this embodiment are shown.

[0061] Both uniaxial and multiaxial thermomechanical fatigue tests employ strain control methods. For uniaxial thermomechanical fatigue tests, it is necessary to control the thermal phase angle between the axial mechanical strain waveform and the temperature waveform. Thermal phase angle These are 0°, 90°, and 180°, respectively. For multiaxial thermomechanical fatigue testing, it is necessary to control not only the thermal phase angle... It is also necessary to control the mechanical phase angle between the axial mechanical strain waveform and the shear strain waveform. Mechanical phase angle These are 0° and 90° respectively. Therefore, uniaxial thermomechanical fatigue testing includes TIP (thermally in phase) and TOP. 90 (Heat 90° non-isophase) and TOP 180 (Thermal 180° non-in-phase) Three load paths (e.g.) Figure 4 As shown), multiaxial thermomechanical fatigue testing includes MIPTIP (mechanically in phase and thermomechanically in phase) and MIPTOP. 90 (Mechanical in-phase, thermally non-in-phase 90°), MIPTOP 180 (Mechanical in-phase, thermally non-in-phase 180°), MOPTIP (Mechanical 90° non-in-phase, thermally in-phase), MOPTOP 90 (Mechanical 90° non-isophase, thermal 90° non-isophase) and MOPTOP 180 (Mechanical 90° non-phase, thermal 180° non-phase) Six load paths (e.g.) Figure 5 and Figure 6 (As shown).

[0062] Subsequently, the low-cycle multiaxial fatigue life prediction method based on the damage mechanism of powder superalloys described in this invention was applied to evaluate the failure life of FGH99 powder superalloy under the aforementioned fatigue loads. Taking the MOPTIP test as an example, as follows... Figure 2 As shown, the steps are as follows: Step 1): Multiaxial fatigue damage parameters based on critical surfaces calculate; Obtain the multiaxial stress-strain history of the critical point of the component; based on the critical plane method, find the plane with the largest normal strain amplitude in the plane of maximum shear strain amplitude as the damage critical plane; calculate the multiaxial equivalent damage parameters of this damage critical plane. , The equivalent strain range on the critical surface, multiaxial equivalent damage parameter The expression is:

[0063] In the formula, This represents the range of maximum shear strain on the damage critical surface. The range of normal strain between the maximum shear strain reversal points on the damage critical surface is given; these are all known input values. In this embodiment, the obtained damage critical surface... , .

[0064] Step 2): Pure fatigue damage Calculation; Based on the damage parameters obtained in step 1) The reference fatigue life for pure fatigue failure of the component material under the current strain amplitude is obtained by back-calculation using the Manson-Coffin equation. Based on reference fatigue life Calculate the pure fatigue damage caused by each load cycle. Among them, the strain amplitude and reference fatigue life established by the Manson-Coffin equation are... The relationship is as follows:

[0065] but,

[0066] In the formula, The fatigue strength coefficient is dimensionless. The fatigue strength index is dimensionless. The fatigue plasticity coefficient is dimensionless. The fatigue plasticity index is dimensionless. It is the elastic modulus, dimensionless; it can be obtained from material handbooks or basic fatigue tests.

[0067] Low-cycle fatigue data of FGH99 alloy were processed to obtain hysteresis loops under different strain amplitudes, and the elastic strain amplitude and plastic strain amplitude corresponding to its half-life were obtained. Origin software was used to perform fitting analysis on the low-cycle fatigue life corresponding to different half-life elastic strain amplitudes and plastic strain amplitudes.

[0068] At 25℃, E = 219.3 GPa, we can obtain... =5307.2MPa, b=-0.23, =2.43, c=-0.853, therefore the Manson-Coffin formula for strain control is as follows:

[0069] Derived from the damage critical surface and And then find If it lasts for 524 weeks, then its fatigue damage... =0.0019.

[0070] Step 3): Pure creep damage Calculation; Obtain the axial stress-time history at the critical point within a load cycle. Shear stress-time history Temperature-Time History The time-domain subdivision method is used to discretize the load cycle into n consecutive time intervals on the time axis, and the duration of the i-th interval is denoted as Δt. i The axial stress, shear stress, and temperature state within this range can be represented by representative values. i , i and T i To characterize it. For each time interval i (i=1,2,...,n), determine the axial stress in that interval. Is it positive? If so... If the stress is greater than 0 (tensile stress), then calculate the equivalent creep stress for that time interval. , ;when When ≤0, the equivalent creep stress in this time interval The creep damage in this interval is directly defined as zero, and subsequent calculations are skipped; for intervals where the equivalent creep stress is greater than zero, the creep damage is determined based on the equivalent creep stress. and instantaneous temperature T i By using the creep rupture equation of the material, the creep fracture time of the component in each time interval is determined. The creep damage in each time interval is then... The pure creep damage for a given cycle is obtained by summing the creep damage across all intervals within that cycle. :

[0071] To achieve accurate calculations, the creep rupture equation for the material needs to be determined. In the embodiments of the present invention targeting the FGH99 alloy, the Manson-Sokop equation is selected as the constitutive model describing its creep fracture behavior. This equation establishes the equivalent stress. Temperature T and creep rupture time The quantitative relationship between them can be expressed by the general formula:

[0072] In the formula, T represents creep rupture time, in hours (h); T represents temperature, in degrees Celsius (°C). Equivalent stress, unit: megapascals (MPa). The correlation coefficient is specific to the material.

[0073] A systematic isothermal and isostatic creep test was conducted on FGH99 alloy to obtain fracture time data under various stress-temperature combinations. Multiple nonlinear regression fitting was performed on the experimental data using Origin software to obtain a specific parameter set for the MS equation applicable to FGH99 alloy, as shown in the table below:

[0074] Taking the typical load path MOPTIP (Mechanical In-Phase-Thermal In-Phase) as an example, the above method is applied to calculate pure creep damage, accumulating the creep damage of all intervals within one cycle. Find .

[0075] Step 4): Obtain the average temperature during a multiaxial thermomechanical fatigue load cycle; For a given load cycle, extract the temperature-time history segment of the high-temperature sustained-load phase that significantly contributes to creep damage within that load cycle; obtain the highest temperature of the segment. With the lowest temperature Based on the highest temperature With the lowest temperature Calculate the arithmetic mean of the segment. The average temperature is taken as the average temperature of this load cycle. The expression for the average temperature is:

[0076] In the MOPTIP trial, ℃.

[0077] Step 5): Introduce rapid hardening parameters Characterizing the moderating effect of thermo-mechanical phase angle interaction on damage mechanisms, especially in MOPTOP 90 Under special pathways, the continuous rapid hardening and sudden drop in lifespan are caused by the synergistic propagation of micropores and secondary cracks.

[0078]

[0079] In the formula This is the mechanical phase angle; This is the thermal phase angle; obviously, in the MOPTIP test, The value is 1.

[0080] Step 6): Calculate the interaction coefficients based on steps 4) and 5). ;

[0081] Where -0.0098 and 8.4242 are material constants obtained by fitting experimental data. In the MOPTIP test, The value is 193.53.

[0082] Step 7): Pure creep damage obtained from Step 3). The correction coefficient λ is obtained; By fitting multiple uniaxial fatigue test data and calculating the life formula, the coefficient λ was varied until the predicted life from the test equaled the experimental life. This process was then used to fit the correction coefficient λ for pure creep damage. The function expression:

[0083] Among them, 4466.83 and 0.55 are material constants obtained through experimental calibration, including fatigue tests with different holding times. In the MOPTIP test, .

[0084] Step 8): Calculate creep-fatigue interactive damage based on steps 2), 3), 6), and 7). ; Based on the pure fatigue damage obtained in step 2) The creep damage obtained in step 3) The interaction coefficients obtained in step 6) And the correction factor obtained in step 7). The fatigue-creep interaction damage of this cycle is calculated using the following formula. :

[0085] For the MOPTIP experiment, its interactive impairment .

[0086] Step 9): Calculation of total damage; Accumulated pure fatigue damage in step 2) Creep damage in step 4) And fatigue-creep interaction damage in step 8) The total damage for each load cycle is obtained. :

[0087] For the MOPTIP test, the total damage was 0.00667.

[0088] Step 10): Based on step 9), predict the failure life under multiaxial thermomechanical fatigue load; The total damage obtained in step 9) Take the reciprocal to predict the total failure life of the component under multiaxial thermomechanical fatigue loading:

[0089] For the MOPTIP test, the predicted lifetime N was 149.9 weeks, while the actual test lifetime was 135 weeks, with a ratio of 1.11, which shows that the present invention is accurate and reliable.

[0090] In this embodiment, based on the low-cycle fatigue test life results at different temperatures (400℃, 500℃, 600℃), a temperature-related fatigue parameter equation can be fitted to determine the fatigue parameters at room temperature (25℃).

[0091] To fully verify the accuracy and reliability of the method proposed in this invention, the life prediction results of this invention are compared with the actual failure life obtained by the FGH99 alloy thin-walled tube specimen in multiaxial thermomechanical fatigue tests. The comparison results are as follows: Figure 7 As shown. By analyzing... Figure 7 Analysis shows that the prediction results proposed in this invention are in good agreement with the experimental results, and the vast majority of data points fall within the 2x error dispersion band, which indicates that the proposed lifetime prediction method is feasible.

[0092] This invention discloses a low-cycle multiaxial fatigue life prediction method based on the damage mechanism of powder superalloys. To address the problem of insufficient prediction accuracy of traditional models due to continuous rapid hardening and complex damage competition caused by specific thermo-mechanical phase coupling in powder superalloys under multiaxial thermomechanical loading, this invention proposes a rapid hardening parameter. To characterize this rapid hardening behavior, an asymmetric fatigue-creep interactive damage model was constructed. To verify the effectiveness of the proposed method, a systematic multiaxial thermomechanical fatigue test covering various load paths was conducted. The results showed that the proposed method can accurately estimate the fatigue life of FGH99 alloy under complex force-thermal coupling conditions. The error between the predicted life and the experimental results was within two bands, indicating that the method is reliable and engineering feasible. Therefore, the proposed method has significant engineering implications for the life assessment, reliability design, and safe maintenance of hot-end components in equipment such as aero-engines.

[0093] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0094] 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 for predicting low-cycle multiaxial fatigue life based on the damage mechanism of powder superalloys, characterized in that, Includes the following steps: For critical points of components under non-isothermal multiaxial cyclic loading, the pure fatigue damage caused by a single load cycle is determined. Pure creep damage and fatigue-creep interaction damage ; The pure fatigue damage Pure creep damage and fatigue-creep interaction damage The total damage for this single load cycle is obtained by summing the results. ; Regarding the total damage Take the reciprocal to predict the total failure life of the component under the non-isothermal multiaxial cyclic loading. N .

2. The method according to claim 1, characterized in that, The calculation of pure fatigue damage includes: S11, Obtain the multiaxial stress-strain history of the critical point of the component; Based on the critical plane method, determine the damage critical surface of the critical point, and calculate the multiaxial equivalent damage parameters of the damage critical surface. ; S12, based on the multiaxial equivalent damage parameters Calculate the pure fatigue damage .

3. The method according to claim 2, characterized in that, In step S11, the multiaxial equivalent damage parameter The expression is: In the formula, This represents the range of maximum shear strain on the damage critical surface. The range of normal strain between the maximum shear strain reversal points on the damage critical surface.

4. The method according to claim 2, characterized in that, In step S12, the pure fatigue damage The expression is: In the formula, The fatigue strength coefficient is dimensionless. The fatigue strength index is dimensionless. The fatigue plasticity coefficient is dimensionless. The fatigue plasticity index is dimensionless. It is the elastic modulus, which is dimensionless; For reference fatigue life, weeks.

5. The method according to claim 1, characterized in that, The pure creep damage The calculations include: S21, obtain the axial stress-time history, shear stress-time history, and temperature-time history of the critical point within a load cycle; S22, the load is cyclically discretized into multiple time intervals using the time-domain subdivision method; S23, based on the physical mechanism of creep damage, calculates creep damage for each time interval. ; S24, summing creep damage across all time intervals. The pure creep damage of this load cycle is obtained. .

6. The method according to claim 5, characterized in that, In step S23, the creep damage for each time interval is calculated. include: S231, Obtain the instantaneous temperature for each time interval. T i And calculate the equivalent creep stress for that time interval. ; S232, based on the equivalent creep stress and instantaneous temperature T i The creep rupture time of the component in each time interval was determined using the creep rupture equation of the material. ; S233, based on the creep rupture time and the duration of each time interval Calculate the creep damage caused during this time interval. .

7. The method according to claim 6, characterized in that, In step S231, calculating the equivalent creep stress includes: Determine the axial stress in each time interval Is it positive? If axial stress If positive, then the equivalent creep stress for that time interval is... ,in, Shear stress; Otherwise, define the equivalent creep stress for that time interval. It is zero.

8. The method according to claim 1, characterized in that, The calculation of the fatigue-creep interaction damage includes: S31: Obtain the average temperature over a load cycle ; S32: Identify the mechanical phase angle during load cycles With thermal phase angle ; S33: Based on the mechanical phase angle and thermal phase angle Determine rapid hardening parameters α ; S34: Based on the average temperature and rapid hardening parameters α Calculate the interaction coefficient ; S35: Based on the pure creep damage Determine the correction factor used to characterize the interaction asymmetry. ; S36: Based on the aforementioned pure fatigue damage Pure creep damage Interaction coefficient and correction factor The fatigue-creep interaction damage is calculated using a nonlinear function. .

9. The method according to claim 8, characterized in that, In step S31, the average temperature The acquisition includes: Extract a temperature-time history segment from a load cycle where the temperature is above a preset threshold. Obtain the highest temperature of the segment. With the lowest temperature ; Based on the highest temperature With the lowest temperature Calculate the arithmetic mean of the segment. , which is the average temperature of this load cycle.

10. The method according to claim 8, characterized in that, In step S36, the fatigue-creep interactive damage The expression is: 。

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