Fatigue Life Prediction Method for Nickel-Based Superalloys Considering the Hydrogen Influence Effect

Abstract

The present invention discloses a method for predicting the fatigue life of a nickel-based superalloy considering the hydrogen influence effect, which comprises the following steps: 1) low cycle fatigue tests of the nickel-based superalloy before and after hydrogen charging; 2) establishing a crystal plasticity constitutive model and a polycrystalline representative volume element model considering the microscopic deformation mechanism; 3) based on the cumulative damage theory and considering the fatigue life damage influenced by hydrogen, establishing a crack initiation life prediction model considering the hydrogen influence factor; 4) model verification, by conducting simulation analysis on the low cycle fatigue life before and after hydrogen charging and under different load conditions, and comparing with the test results. The present invention can predict the low cycle fatigue life of the nickel-based superalloy under different hydrogen charging effects and different load conditions, and the required parameters can be obtained according to the ordinary fatigue data of the material, without designing additional tests for parameter fitting, which has important engineering practical significance.

Description

Technical Field

[0001] The present invention relates to the technical field of low-cycle fatigue life prediction simulation of nickel-based superalloys, and particularly relates to a fatigue life prediction method for nickel-based superalloys considering the hydrogen influence effect. Background Art

[0002] When metal components work in a hydrogen environment, hydrogen will penetrate and accumulate inside the material, causing hydrogen embrittlement (HE) and hydrogen corrosion of the material. Generally, the macroscopic manifestations of hydrogen embrittlement include plastic loss caused by hydrogen, induced microcracks, delayed fracture caused, brittleness caused by hydrides, and irreversible damage caused by hydrogen gas, etc.

[0003] As the "heart" of an aircraft, an aeroengine is in a harsh working environment of high temperature, high pressure and high load for a long time. Components such as turbines and fans in the engine are extremely prone to damage, resulting in a decline in the performance of the engine and shortening the working life of the engine. Mechanical failures in many major flight accidents, nearly 60% involve problems with aeroengines. For aeroengines using hydrogen fuel, the damage under the influence of hydrogen embrittlement has a more serious impact on the life and reliability of key components such as the combustion chamber and turbine. This may pose a threat to flight safety. Therefore, it is necessary to deeply study the manufacturing metal materials of aeroengines and pay special attention to their tensile properties and fatigue resistance under the influence of hydrogen embrittlement to ensure the safe and reliable use of structural components. Summary of the Invention

[0004] The present invention provides a fatigue life prediction method for nickel-based superalloys considering the hydrogen influence effect. Its physical meaning in mathematical form is clear, and it can effectively predict the crack initiation life of nickel-based superalloys before and after hydrogen charging, which has important engineering practical significance.

[0005] An embodiment of the present invention provides a fatigue life prediction method for nickel-based superalloys considering the hydrogen influence effect, including the following steps:

[0006] For nickel-based superalloy test pieces, set different hydrogen charging states and different load conditions, and obtain the low-cycle fatigue life of the nickel-based superalloy test pieces;

[0007] Based on the crystal plasticity constitutive model and Voronoi polygons, establish a polycrystalline representative volume element model to characterize the microscopic deformation mechanism of nickel-based superalloys;

[0008] Based on the cumulative damage theory, considering the effect of local deformation on crack initiation of the material, establish a crack initiation life prediction model considering hydrogen influence factors;

[0009] The low-cycle fatigue life of a nickel-based superalloy test piece obtained under different hydrogen charging states and different load conditions is used to verify the crack initiation life prediction model considering hydrogen influence factors. After the model verification is passed, the final crack initiation life prediction model considering hydrogen influence factors is obtained.

[0010] Optionally, in an embodiment of the present invention, establishing a polycrystalline representative volume element model based on a crystal plasticity constitutive model and a Voronoi polygon includes:

[0011] In the crystal plasticity constitutive model, when a polycrystalline material is subjected to an external load, the total deformation gradient F of each individual crystal material is expressed as:

[0012] F = F e *F p

[0013] In the formula, F e represents the deformation gradient of the crystal, and F p represents the plastic shear deformation that occurs in the material;

[0014] The deformed velocity gradient tensor L is the sum of L e and L p :

[0015]

[0016] L p is expressed as an equation related to the plastic slip rate γ:

[0017]

[0018] In the formula, γ α , s α and m α are respectively the plastic slip rate, slip direction vector, and slip plane normal vector of the α-th slip system. In the classical phenomenological constitutive model, the critical shear stress is usually used as the state variable of the slip system, is an equation about the shear stress τ α , and:

[0019]

[0020] The resolved shear stress of the α-th slip system:

[0021] τ α = σ: μ α

[0022]

[0023] Introduce the back stress X αBased on the original crystal plasticity kinematic theory to describe the hardening response of materials under cyclic loading, in the slip system of the crystal, τ α and The relationship between them is:

[0024]

[0025] In the formula, is the reference strain rate, n is the rate sensitivity coefficient related to the material properties, X α is the back stress, which is used to describe the cyclic deformation behavior of materials under fatigue loading; g α is the current strength parameter of the α slip system; sgn() is the sign function, and the non-linear evolution equation of the back stress parameter is:

[0026]

[0027] In the formula, C is the direct hardening modulus; D is the dynamic recovery modulus, which is related to the material response during loading;

[0028]

[0029] In the formula, h αβ is the slip hardening modulus caused by latent hardening. When α = β, the reason for the hardening of the slip system is the reason of the slip system itself. At this time, h αβ = h αα represents the self-hardening modulus. When α ≠ β, h αβ represents the latent hardening modulus, indicating that the hardening generated by the slip system α is affected by the slip system β. γ β is the plastic shear deformation rate of the slip system β, h represents the hardening modulus, indicating the hardening effect of the slip system β on the slip system α;

[0030] h αβ (γ) = h(γ)[q + (1 - q)δ αβ

[0031]

[0032] In the formula, q is a constant, which is used to describe the relationship between the latent hardening and self-hardening behaviors of the material; h0 represents the initial hardening modulus, γ is the cumulative shear strain of all slip systems, τ0 and τ s Saturation hardening modulus and saturation shear stress; The expression of γ is:

[0033]

[0034] Optionally, in an embodiment of the present invention, a crack initiation life prediction model considering the influence of hydrogen is established, including:

[0035] ​According to the cumulative damage theory, when the damage accumulation coefficient is equal to 1, the material will fail. When the material experiences multiple different stress cycles, the damage contribution of each cycle is represented by the D value of the damage accumulation coefficient. Suppose the expected life of a material under a stress level S is N. If the material undergoes m stress cycles under the stress level S, each cycle corresponds to a loading with a stress amplitude of S, and the damage contribution of each cycle is expressed as 1 / N. After m cycles, the total damage accumulation coefficient D is:

[0036]

[0037] The stabilized cumulative plastic shear strain increment ΔP is adopted cyc as the fatigue indicator factor FIP. When the cumulative plastic shear strain P cri reaches a certain critical value, the material fails. Suppose P cri is a material constant that does not change with the change of the external load and is determined by the fatigue life measured through a single fatigue test:

[0038] FIP = ΔP cyc = P cyc | N - P cyc | N-1

[0039] In order to reflect the relationship between hydrogen and the fatigue life, a function f(σ) that considers the damage caused by hydrogen is established. In the fatigue damage accumulation life prediction model, the damage caused is expressed as:

[0040] FIP H = f(σ) * FIP

[0041] At this time, the fatigue index factor FIP'(ΔP cyc-H ) of the material during a single-cycle loading process is the sum of the original FIP and FIP H :

[0042] FIP' = FIP + FIP H

[0043] When the hydrogen concentration in the material is 0, f(σ) = 0, and at this time FIP' = FIP;

[0044] The expression for predicting the life of the test using the fatigue index factor FIP'(ΔP cyc-H ) considering the influence of hydrogen charging is:

[0045] FIP' = ΔP cyc + f(σ)ΔP cyc

[0046] = (1 + f(σ))ΔP cyc

[0047] Assume that the cumulative plastic shear strain value P when the material fails after hydrogen charging cri-H is still a constant. When P cri-H reaches the critical value, the material fails and cracks initiate. The critical value P cri-H is determined by the primary fatigue test value of the hydrogen-charged specimen. Therefore, the fatigue life prediction model of the hydrogen-charged specimen is:

[0048]

[0049] The embodiment of the present invention proposes a fatigue life prediction method for nickel-based superalloys considering the hydrogen influence effect, establishes an elastoplastic constitutive model and a polycrystalline representative volume element. This model considers the microscopic deformation mechanism of polycrystalline materials to simulate the damage evolution of the microstructure of materials under different cyclic stress loading environments, uses the cumulative plastic shear strain as the damage indicator factor to predict the fatigue life of nickel-based superalloys, and on this basis, introduces the damage of hydrogen to the material life for correction to achieve the prediction of the fatigue life of nickel-based superalloys affected by hydrogen.

[0050] Additional aspects and advantages of the present invention will be given in part in the following description, become apparent in part from the following description, or be understood through the practice of the present invention. Description of the Drawings

[0051] The above-mentioned and / or additional aspects and advantages of the present invention will become apparent and easy to understand from the following description of the embodiments in conjunction with the drawings, where:

[0052] Figure 1 is a flowchart of a fatigue life prediction method for nickel-based superalloys considering the hydrogen influence effect provided according to an embodiment of the present invention;

[0053] Figure 2 is a comparison error band diagram of the predicted life of the microscopic model and the test results;

[0054] Figure 3 is a comparison error band diagram of the hydrogen-induced fatigue life prediction and the test results. Detailed Embodiments

[0055] The embodiments of the present invention will be described in detail below. The examples of the embodiments are shown in the drawings, where the same or similar reference numerals denote the same or similar elements or elements with the same or similar functions throughout. The embodiments described below by referring to the drawings are exemplary and are intended to explain the present invention and should not be construed as limiting the present invention.

[0056] Figure 1Flow chart of a method for predicting the fatigue life of a nickel-based superalloy considering the hydrogen influence effect according to an embodiment of the present invention.

[0057] As Figure 1 shown, the method for predicting the fatigue life of the nickel-based superalloy considering the hydrogen influence effect includes the following steps:

[0058] Step 1, for the nickel-based superalloy test piece, set different hydrogen charging states and different load conditions, and obtain the low-cycle fatigue life of the nickel-based superalloy test piece.

[0059] First, conduct low-cycle fatigue tests before and after hydrogen charging of the nickel-based superalloy, and obtain the low-cycle fatigue life of the nickel-based superalloy test piece under different hydrogen charging states and different load conditions.

[0060] Step 2, establish a polycrystalline representative volume element model based on the crystal plasticity constitutive model and Voronoi polygons to characterize the micro-deformation mechanism of the nickel-based superalloy.

[0061] It can be understood that the embodiments of the present invention establish a crystal plasticity constitutive model and a polycrystalline representative volume element model considering the micro-deformation mechanism.

[0062] Specifically, the establishment of the crystal plasticity constitutive model:

[0063] In this model, when a polycrystalline material is subjected to an external load, the total deformation gradient F of each individual crystal material can be expressed as:

[0064] F = F e *F p

[0065] The deformed velocity gradient tensor L is the sum of the elastic deformation L e and the plastic deformation L p :

[0066]

[0067] The plastic velocity gradient L p can be expressed as an equation related to the plastic slip rate γ:

[0068]

[0069] In the formula, γ α , s α and m α are respectively the plastic slip rate, slip direction vector, and slip plane normal vector of the α-th slip system. In the classical phenomenological constitutive model, the critical shear stress is usually used as the state variable of the slip system, is about the shear stress τ α , Equation of

[0070]

[0071] Resolved shear stress of the α slip system:

[0072] τ α = σ: μ α

[0073]

[0074] Introduce back stress X α Based on the original crystal plasticity theory of motion to describe the hardening response of materials under cyclic loading. In the slip system of the crystal, τ α and The relationship between them is as follows:

[0075]

[0076] In the formula, is the reference strain rate, n is the rate sensitivity coefficient related to the material properties, X α is the back stress, used to describe the cyclic deformation behavior of materials under fatigue loads; g α is the current strength parameter of the α slip system; sgn() is the sign function, and the non-linear evolution equation of the back stress parameter is:

[0077]

[0078] In the formula, C is the direct hardening modulus; D is the dynamic recovery modulus, related to the material response during loading.

[0079]

[0080] In the formula, h αβ is the slip hardening modulus caused by latent hardening. When α = β, the reason for the hardening of the slip system is the reason of the slip system itself. At this time, h αβ = h αα represents the self-hardening modulus. When α ≠ β, h αβ represents the latent hardening modulus, indicating that the hardening of the slip system α is affected by the slip system β, γ β is the plastic shear deformation rate of the slip system β, h represents the hardening modulus, indicating the hardening effect of the slip system β on the slip system α.

[0081] h αβ (γ) = h(γ)[q + (1 - q)δ αβ

[0082] ​

[0083] In the formula, q is a constant used to describe the relationship between the latent hardening and self-hardening behaviors of the material; h0 represents the initial hardening modulus, γ is the cumulative shear strain of all slip systems, τ0 and τ s Saturated hardening modulus and saturated shear stress; the expression of γ is:

[0084]

[0085] Step 3: Based on the cumulative damage theory, considering the effect of local deformation on the crack initiation of the material, a crack initiation life prediction model considering the influence of hydrogen is established.

[0086] The embodiment of the present invention establishes a crack initiation life prediction model considering the influence of hydrogen based on the cumulative damage theory.

[0087] Specifically, the establishment of the crack initiation life prediction model considering the influence of hydrogen:

[0088] According to the cumulative damage theory, when the damage accumulation coefficient (usually denoted by D) is equal to 1, the material will fail. When the material undergoes multiple different stress cycles, the damage contribution of each cycle can be represented by the D value. Assume that the expected life of a material under a stress level S is N. Now, if the material undergoes m stress cycles at this stress level (each cycle corresponds to a loading with a stress amplitude of S), then the damage contribution of each cycle can be expressed as 1 / N. Therefore, after m cycles, the total damage accumulation coefficient D is:

[0089]

[0090] The plastic deformation of the material plays a very important role in the crack initiation process of the material. In the fatigue damage accumulation theory, the initiation of fatigue cracks is regarded as the result of the accumulation of plastic deformation. The accumulation of plastic deformation of the material is closely related to the shear strain in the crystal. Therefore, when studying the plastic deformation of the crystal, the accumulated plastic shear strain suffered by the material should be mainly considered. Therefore, in this chapter, the stabilized incremental accumulated plastic shear strain ΔP cyc is used as the fatigue indicator parameter (FIP). When the accumulated plastic shear strain P cri reaches a certain critical value, the material fails. Assume that P cri is a material constant that does not change with the change of the external load. Its value can be determined by the fatigue life measured in a single fatigue test.

[0091] FIP = ΔP cyc = P cyc | N - P cyc | N-1

[0092] To reflect the relationship of the influence of hydrogen on fatigue life, a function f(σ) considering the damage caused by hydrogen is established in this paper. In the fatigue damage accumulation life prediction model, the damage caused by this part is expressed as:

[0093] FIP H = f(σ) * FIP

[0094] At this time, the fatigue index factor FIP'(ΔP cyc-H ) of the material during a single cyclic loading is the sum of the original FIP and FIP H :

[0095] FIP' = FIP + FIP H

[0096] When the hydrogen concentration in the material is 0, f(σ) = 0, and at this time FIP' = FIP.

[0097] The expression for predicting the life of the test using the fatigue index factor FIP'(ΔP cyc-H ) considering the influence of hydrogen charging is:

[0098] FIP' = ΔP cyc + f(σ)ΔP cyc

[0099] = (1 + f(σ))ΔP cyc

[0100] Assume that the cumulative plastic shear strain value P cri-H when the material fails after hydrogen charging is still a constant. When P cri-H reaches the critical value, the material fails and cracks initiate. The critical value P cri-H is determined by the primary fatigue test value of the hydrogen-charged specimen. Therefore, the fatigue life prediction model for the hydrogen-charged specimen is:

[0101]

[0102] Step 4: Use the low-cycle fatigue lives of the nickel-based superalloy test pieces obtained under different hydrogen charging states and different load conditions to verify the crack initiation life prediction model considering the influence of hydrogen. After the model verification passes, the final crack initiation life prediction model considering the influence of hydrogen is obtained.

[0103] By performing simulation analysis on the low-cycle fatigue lives before and after hydrogen charging and under different load conditions, and comparing with the test results, the accuracy and reliability of the crack initiation life prediction model considering the influence of hydrogen are verified. When the accuracy is greater than the set threshold, the fatigue life prediction model of the nickel-based superalloy considering the hydrogen influence effect can be obtained.

[0104] The fatigue life prediction method of the nickel-based superalloy considering the hydrogen influence effect of the present invention will be described in detail below through a specific embodiment.

[0105] (1) For nickel-based superalloy test pieces, different hydrogen charging states and different load conditions are set, and their low-cycle fatigue lives are obtained.

[0106] (2) Using Fortran language, based on the UMAT user subroutine, a crystal plasticity constitutive model is written. Based on the Voronoi polygon method, a representative volume element of the polycrystal model is established to realize the characterization of the local micro-deformation mechanism of the polycrystal.

[0107] In this model, when the polycrystalline material is subjected to an external load, the total deformation gradient F of each individual crystal material can be expressed as:

[0108] F = F e *F p (1)

[0109] In the formula, F e represents the deformation gradient of the crystal, which is the deformation caused by lattice distortion and rigid body rotation. According to the theoretical assumption, this part is called elastic deformation. F p represents the plastic shear deformation that occurs in the material, and this part is called plastic deformation.

[0110] The velocity gradient tensor L after deformation is the sum of the elastic deformation L e and the plastic deformation L p :

[0111]

[0112] When the lattice does not deform, is set as the unit vector of the slip direction of the α-th slip system, and is the unit normal vector of the slip plane, then there is:

[0113]

[0114] In the formula, is the plastic slip rate of the α-th slip system, which is an equation about the shear stress τ α 、 and. And and both satisfy the orthogonality relationship:

[0115]

[0116] s α ·m α = 0 (5)

[0117] In the deformed material structure, the vector of the slip direction is s α and the vector of the normal direction of the slip plane is m α , and the relationship between the unit vectors of the slip direction and the normal direction of the slip plane in the initial structure is:

[0118]

[0119]

[0120] Therefore, we have:

[0121]

[0122] In the decomposition of the velocity gradient tensor L, the symmetric part and the anti-symmetric part are extracted, and the expression is as follows:

[0123] L = D + W (9)

[0124] where D represents the symmetric part, also known as the Deformation Rate Tensor, which is used to describe the deformation rate of each point in the medium; W represents the anti-symmetric part, also known as the Spin Tensor, which describes the rotation rate of each point in the medium.

[0125]

[0126] From the above equation (9), the expressions of the deformation rate tensor D and the spin tensor W can be obtained as follows:

[0127]

[0128]

[0129] Similar to the velocity gradient tensor L, the deformation rate tensor D and the spin tensor W are further decomposed into the elastic deformation parts D e 、D p and the plastic deformation parts W e 、W p :

[0130]

[0131] The deformation rate tensor D can be expressed as:

[0132]

[0133]

[0134] where:

[0135]

[0136] The rotation deformation rate tensor W can be expressed as:

[0137]

[0138]

[0139]

[0140] These equations constitute the basic description of crystal kinematics, which effectively relate the slip shear rate inside the crystal to the external macroscopic deformation rate.

[0141] According to crystal plasticity theory, the slip deformation of a crystal cannot affect the elastic deformation stage of the crystal lattice. Therefore, the constitutive equation in the elastic stage can be expressed as:

[0142]

[0143] where the definition of L is the transient elastic modulus tensor, is the Jaumann rate of the Kirchhoff stress tensor based on the intermediate structure.

[0144]

[0145] where, is the Jaumann rate of the Cauchy stress based on the initial structure:

[0146]

[0147] So,

[0148]

[0149] From formulas (12), (14), (20) and (22), it can be obtained that

[0150]

[0151] The above equation relates the rate of change of stress, the rate of change of strain and the slip shear strain rate. Usually, the orientation factor P α is used as the bridge between the resolved shear stress, shear strain of each slip system and the macroscopic stress and strain.

[0152] Therefore, the resolved shear stress on the α-th slip can be calculated by the following formula:

[0153] τ α =σ:μ α (25)

[0154] The shear strain on each slip is synthesized into the strain components in the material system, which can be calculated by the following formula:

[0155]

[0156] Introduce the back stress X α Based on the original crystal plasticity theory of motion to describe the hardening response of materials under cyclic loading. In the slip system of the crystal, τ α and The relationship between them is as follows:

[0157]

[0158] In the formula, is the reference strain rate, n is the rate sensitivity coefficient related to the material properties, X α is the back stress, which is used to describe the cyclic deformation behavior of materials under fatigue loads; g α is the current strength parameter of the α slip system; sgn() is the sign function, and the nonlinear evolution equation of the back stress parameter is:

[0159]

[0160] In the formula, C is the direct hardening modulus; D is the dynamic recovery modulus, which is related to the material response during loading.

[0161]

[0162] In the formula, h αβ is the slip hardening modulus caused by latent hardening. When α = β, the reason for the hardening of the slip system is the reason of the slip system itself. At this time, h αβ = h αα represents the self-hardening modulus. When α ≠ β, h αβ represents the latent hardening modulus, indicating that the hardening generated by the slip system α is affected by the slip system β. γ β is the plastic shear deformation rate of the slip system β. h represents the hardening modulus, indicating the hardening effect of the slip system β on the slip system α:

[0163] h αβ (γ) = h(γ)[q + (1 - q)δ αβ (30)

[0164]

[0165] In the formula, q is a constant, which is used to describe the relationship between the latent hardening and self-hardening behaviors of materials; h0 represents the initial hardening modulus, γ is the cumulative shear strain of all slip systems, τ0 and τ s are the saturated hardening modulus and saturated shear stress; the expression of γ is:

[0166]

[0167] (3) According to the cumulative damage theory, when the damage accumulation coefficient (usually denoted by D) equals 1, the material will fail. When the material undergoes multiple different stress cycles, the damage contribution of each cycle can be represented by the D value. Assume that the expected life of a material under a stress level S is N. Now, if the material undergoes m stress cycles under this stress level (each cycle corresponding to a loading with a stress amplitude of S), then the damage contribution of each cycle can be expressed as 1 / N. Therefore, after m cycles, the total damage accumulation coefficient D is:

[0168]

[0169] Calculate the plastic shear strain increment ΔP of each single cycle of each slip system in the model under the external load according to the established finite element calculation model cyc , whose value will tend to be stable after experiencing a period of change. Regarding it as a constant increment, as the fatigue indicator factor FIP, extract the plastic shear strain increment ΔP of each single cycle after stabilization under different external loads cyc for subsequent calculations.

[0170] FIP = ΔP cyc = P cyc | N - P cyc | N-1 (34)

[0171] (4) During the finite element calculation process, only need to focus on the unit positions with the most significant plastic deformation during the simulation process, and regard them as the possible positions of crack initiation. When the cumulative plastic shear strain at this position exceeds the critical plastic strain of the material, it is considered that the material has experienced fatigue failure. Extract the plastic shear strain increment ΔP of each single cycle of the unit position with the most significant plastic deformation under a certain external load condition cyc and the experimental fatigue crack initiation life N f Calculate the critical cumulative plastic shear strain P at crack initiation of this material cri-fat , and consider this value as a material constant that does not change with the change of external load.

[0172]

[0173] (5) Substitute the plastic shear strain increment ΔP of each single cycle under different loads calculated in step (3) cyc and the critical cumulative plastic shear strain P at crack initiation cri-fat into Equation (36) to calculate the predicted fatigue crack initiation life under the remaining loads.

[0174]

[0175] (6) To reflect the relationship between hydrogen and fatigue life, a function f(σ) that takes into account the damage caused by hydrogen to the material is established, and its expression is obtained by fitting the life damage caused by hydrogen under the corresponding load conditions.

[0176] (7) In the life prediction model of fatigue damage accumulation considering the influence of hydrogen, the damage caused by hydrogen is expressed as:

[0177] FIP H = f(σ) * FIP (37)

[0178] At this time, the fatigue index factor FIP'(ΔP cyc-H ) of the material during a single-cycle loading process is the sum of the original FIP and FIP H :

[0179] FIP' = FIP + FIP H (38)

[0180] When the hydrogen concentration in the material is 0, f(σ) = 0, and at this time FIP' = FIP.

[0181] The expression for predicting the life of the test using the fatigue index factor FIP'(ΔP cyc-H ) considering the influence of hydrogen charging is:

[0182]

[0183] Assume that the cumulative plastic shear strain value P cri-H when the material fails after hydrogen charging is still a constant. When P cri-H reaches the critical value, the material fails and cracks initiate. The critical value P cri-H is also determined by the value of a single fatigue test of the hydrogen-charged specimen. Therefore, the fatigue life prediction model for the hydrogen-charged specimen is:

[0184]

[0185] (8) Model verification: Predict the fatigue crack initiation life of GH4169 superalloy at room temperature before and after hydrogen charging under different load conditions, and compare it with the test results. It can be clearly seen from the error band distribution diagrams of Figure 2 and Figure 3 that when using the cumulative damage theory to select plastic deformation as the fatigue indicator factor and introducing the function f(σ) of the damage affected by the stress magnitude of the hydrogen-charged specimen to correct the life damage for crack initiation life prediction, the errors are all within twice the error band, verifying the accuracy of the model.

[0186] A fatigue life prediction method for nickel-based superalloys considering the hydrogen influence effect according to an embodiment of the present invention establishes an elastoplastic constitutive model and a polycrystalline representative volume element. This model takes into account the micro-deformation mechanism of polycrystalline materials and is used to simulate the damage evolution of the microstructure of the material under different cyclic stress loading environments. The cumulative plastic shear strain is used as a damage indicator factor to predict the fatigue life of nickel-based superalloys, and on this basis, the damage of hydrogen to the material life is introduced for correction to achieve the prediction of the fatigue life of nickel-based superalloys affected by hydrogen.

[0187] In the description of this specification, the description referring to terms such as "an embodiment", "some embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or N embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0188] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one of these features. In the description of the present invention, the meaning of "N" is at least two, such as two, three, etc., unless otherwise specifically defined.

[0189] Any process or method description shown in the flowchart or described in other ways herein can be understood as representing a module, segment, or part of code including one or N executable instructions for implementing a customized logical function or process. The scope of the preferred embodiments of the present invention includes additional implementations, where the functions can be executed in a manner that is not shown or discussed, including in a substantially simultaneous manner according to the functions involved or in the reverse order, which should be understood by those skilled in the art of the embodiments of the present invention.

Claims

1. A method for predicting the fatigue life of a nickel-based superalloy considering the hydrogen influence effect, characterized in that Including the following steps: For the nickel-based superalloy test piece, different hydrogen charging states and different load conditions are set, and the low-cycle fatigue life of the nickel-based superalloy test piece is obtained; Based on the crystal plasticity constitutive model and Voronoi polygons, a polycrystalline representative volume element model is established to characterize the microscopic deformation mechanism of nickel-based superalloys; Based on the cumulative damage theory, considering the effect of local deformation on the crack initiation of materials, a crack initiation life prediction model considering the influence of hydrogen is established; Using different hydrogen charging states and different load conditions, the low-cycle fatigue life of the nickel-based superalloy test piece obtained is used to verify the crack initiation life prediction model considering the influence of hydrogen. After the model verification passes, the final crack initiation life prediction model considering the influence of hydrogen is obtained; Establishing a crack initiation life prediction model considering the influence of hydrogen includes: According to the cumulative damage theory, when the damage accumulation coefficient is equal to 1, the material will fail. When the material experiences multiple different stress cycles, the damage contribution of each cycle is represented by the damage accumulation coefficient D value. Assuming that the expected life of a material under a stress level S is N, if the material experiences m stress cycles under the stress level S, each cycle corresponds to a loading with a stress amplitude of S, and the damage contribution of each cycle is expressed as 1 / N. After m cycles, the total damage accumulation coefficient D is: Adopt the increment of accumulated plastic shear strain ΔP after stabilization cyc as the fatigue indicator factor FIP. When the accumulated plastic shear strain P cri reaches a certain critical value, the material fails. Assume that P cri is a material constant that does not change with the change of external load and is determined by the fatigue life measured through a single fatigue test: FIP = ΔP cyc = P cyc | N - P cyc | N-1 In order to reflect the relationship between the influence of hydrogen on fatigue life, a function f(σ) that considers the damage caused by the influence of hydrogen on the material is established. In the fatigue damage accumulation life prediction model, the damage caused is expressed as: FIP H = f(σ) * FIP At this time, the fatigue index factor FIP'(ΔP cyc-H ) during a single-cycle loading process of the material is the sum of the original FIP and FIP H : FIP' = FIP + FIP H When the hydrogen concentration in the material is 0, f(σ) = 0, and at this time, FIP' = FIP; Using the fatigue index factor FIP'(ΔP cyc-H ) considering the influence of hydrogen charging, the expression for predicting the life of the test is as follows: FIP' = ΔP cyc + f(σ)ΔP cyc = (1 + f(σ))ΔP cyc Assume that the cumulative plastic shear strain value P at the time of material failure after hydrogen charging cri-H remains a constant. When P cri-H reaches the critical value, the material fails and cracks initiate. The critical value P cri-H is determined by the primary fatigue test value of the hydrogen-charged specimen. Therefore, the fatigue life prediction model for the hydrogen-charged specimen is as follows:

2. The method according to claim 1, wherein Establishing a polycrystalline representative volume element model based on the crystal plasticity constitutive model and Voronoi polygons includes: In the crystal plasticity constitutive model, when a polycrystalline material is subjected to an external load, the total deformation gradient F of each individual crystal material is expressed as: F = F e *F p where F e represents the deformation gradient of the crystal, and F p represents the plastic shear deformation that occurs in the material; The deformed velocity gradient tensor L is L e and L p The sum of: L p expressed as an equation related to the plastic slip rate γ: where γ α , s α and m α are respectively the plastic slip rate, the slip direction vector and the slip plane normal vector of the α-th slip system. In the classical phenomenological constitutive model, the critical shear stress is usually used as the state variable of the slip system. is an equation about the shear stress τ α , τ c α and: The resolved shear stress of the α slip system: Introduce the back stress X α Based on the original crystal plasticity kinematic theory to describe the hardening response of materials under cyclic loading. In the slip system of the crystal, τ α and γ α The relationship between them is: In the formula, is the reference strain rate, n is the rate sensitivity coefficient related to material properties, X α is the back stress, which is used to describe the cyclic deformation behavior of the material under fatigue load; g α is the current strength parameter of the α slip system; sgn() is the sign function, and the non-linear evolution equation of the back stress parameter is: In the formula, C is the direct hardening modulus; D is the dynamic recovery modulus, which is related to the material response during loading; where h αβ is the slip hardening modulus caused by latent hardening. When α = β, the reason for the hardening of the slip system is due to the slip system itself. At this time, h αβ = h αα represents the self-hardening modulus. When α ≠ β, h αβ represents the latent hardening modulus, indicating that the hardening generated by the slip system α is affected by the slip system β. γ β is the plastic shear deformation rate of the slip system β. h represents the hardening modulus, indicating the hardening effect of the slip system β on the slip system α; h αβ (γ) = h(γ)[q+(1 - q)δ αβ ​ where q is a constant used to describe the relationship between latent hardening and self-hardening behavior of the material; h0 represents the initial hardening modulus, γ is the cumulative shear strain of all slip systems, τ0 and τ s the saturated hardening modulus and the saturated shear stress; the expression of γ is as follows:

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