CN118171523B - Fatigue life prediction method of nickel-based superalloy considering hydrogen influence effect - Google Patents
Fatigue life prediction method of nickel-based superalloy considering hydrogen influence effectInfo
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Abstract
本发明公开了一种考虑氢影响效应的镍基高温合金的疲劳寿命预测方法，包括如下步骤：1)镍基高温合金充氢前后的低周疲劳试验；2)建立了考虑微观变形机制的晶体塑性本构模型和多晶代表性体积单元模型；3)基于累积损伤理论，并考虑氢影响的疲劳寿命损伤，建立了考虑氢影响因素的裂纹萌生寿命预测模型；4)模型验证，通过对充氢前后以及不同载荷工况下的低周疲劳寿命进行仿真分析，并与试验结果对比。本发明能够对镍基高温合金不同充氢效果和不同载荷工况下的低周疲劳寿命进行预测，并且所需参数可根据材料普通疲劳数据得到，不用设计另外的试验进行参数拟合，具有重要工程实际意义。
The present invention discloses a fatigue life prediction method for nickel-based high-temperature alloys considering the effect of hydrogen, including the following steps: 1) low-cycle fatigue test of nickel-based high-temperature alloys before and after hydrogen charging; 2) establishing a crystal plastic constitutive model and a polycrystalline representative volume unit model considering the micro-deformation mechanism; 3) based on the cumulative damage theory, and considering the fatigue life damage affected by hydrogen, a crack initiation life prediction model considering hydrogen influence factors is established; 4) model verification, by simulating and analyzing 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 nickel-based high-temperature alloys under different hydrogen charging effects and different load conditions, and the required parameters can be obtained based on the common fatigue data of the material, without designing additional tests for parameter fitting, which has important engineering practical significance.
Description
Technical Field
The invention relates to the technical field of low cycle fatigue life prediction simulation of nickel-based superalloy, in particular to a fatigue life prediction method of nickel-based superalloy considering hydrogen influence effect.
Background
When a metal part is exposed to a hydrogen environment for operation, hydrogen can permeate and accumulate inside the material, causing hydrogen embrittlement (Hydrogen Embrittlement, HE) and hydrogen corrosion of the material, which are generally macroscopically manifested by hydrogen-induced plastic loss, induced microcracking, induced delayed fracture, hydride-induced brittleness, hydrogen-induced irreversible damage, and the like.
As the heart of an aircraft, the aeroengine is in a severe working environment with high temperature, high pressure and high load for a long time, and parts such as a turbine, a fan and the like in the engine are extremely easy to damage, so that the performance of the engine is reduced, and the working life of the engine is shortened. Mechanical failure of many major flight incidents, nearly 60% involve aeroengine problems. While aeroengines using hydrogen fuels, damage under the influence of hydrogen embrittlement has a more severe impact on the life and reliability of critical components such as combustors and turbines. This may pose a threat to the safety of the flight, and therefore the metallic materials of manufacture of aeroengines must be studied in depth, focusing on their tensile and fatigue resistance properties under the influence of hydrogen embrittlement, in order to ensure safe and reliable use of the structural components.
Disclosure of Invention
The invention provides a fatigue life prediction method of a nickel-based superalloy considering a hydrogen influence effect, which has definite physical meaning in a mathematical form, can effectively predict crack initiation life before and after hydrogen charging of the nickel-based superalloy, and has important engineering practical meaning.
The embodiment of the invention provides a fatigue life prediction method of a nickel-based superalloy considering a hydrogen influence effect, which comprises the following steps of:
setting different hydrogen charging states and different load working conditions for the nickel-based superalloy test piece to obtain the low cycle fatigue life of the nickel-based superalloy test piece;
Establishing a polycrystalline representative volume unit model based on the crystal plasticity constitutive model and the Voronoi polygon to represent a microscopic deformation mechanism of the nickel-based superalloy;
Based on the accumulated damage theory, taking the effect of the influence of local deformation on crack initiation of the material into consideration, and establishing a crack initiation life prediction model taking hydrogen influence factors into consideration;
And carrying out model verification on the crack initiation life prediction model considering the hydrogen influence factor by using the obtained low cycle fatigue life of the nickel-based superalloy test piece under different hydrogen charging states and different load working conditions, and obtaining a final crack initiation life prediction model considering the hydrogen influence factor after the model verification is passed.
Optionally, in one embodiment of the invention, building the polycrystalline representative volume cell model based on the crystalline plastic constitutive model and the Voronoi polygon comprises:
In the crystalline plastic constitutive model, when the polycrystalline material is subjected to an applied load, the total deformation gradient F of each individual crystalline material is expressed as:
F=Fe*Fp
wherein F e represents a deformation gradient of the crystal, and F p represents plastic shear deformation of the material;
The deformed velocity gradient tensor L is the sum of L e and L p:
l p is expressed as an equation related to the plastic slip rate γ:
Wherein gamma α、sα and m α are the plastic slip ratio, slip direction vector and slip plane normal vector of the alpha-th slip system, respectively, in a classical model of the constellation, critical shear stress is usually used as a state variable of the slip system, Relates to the shear stress tau α,Equation of:
Decomposition shear stress of the alpha slip system:
τα＝σ：μα
Introducing back stress X α to describe hardening reaction of material under cyclic loading based on original crystal plastic motion theory, and in crystal sliding system, tau α and The relation between the two is:
In the formula, For reference strain rate, n is a rate sensitivity coefficient related to material properties, X α is back stress for describing cyclic deformation behavior under material fatigue load, g α is a current strength parameter of an alpha slip system, sgn () is a sign function, and a nonlinear evolution equation of the back stress parameter is:
Wherein, C is the direct hardening modulus, D is the dynamic recovery modulus, which is related to the material response when loaded;
Wherein h αβ is a slip hardening modulus due to latent hardening, when α=β, the cause of hardening by the slip system is the cause of the slip system itself, at this time h αβ＝hαα is a self hardening modulus, when α+noteβ, h αβ is a latent hardening modulus, indicates that hardening by the slip system α is affected by the slip system β, γ β is a plastic shear deformation rate of the slip system β, h is a hardening modulus, and indicates a hardening effect of the slip system β on the slip system α;
hαβ(γ)＝h(γ)[q+(1-q)δαβ]
Where q is a constant used to describe the material's latent and self-hardening behavior relationship, h 0 represents the initial hardening modulus, γ is the cumulative shear strain for all slip systems, τ 0 and τ s saturated hardening modulus and saturated shear stress, where γ is expressed as:
optionally, in one embodiment of the present invention, establishing the crack initiation life prediction model taking into account the hydrogen influencing factor includes:
According to the cumulative damage theory, when the damage accumulation coefficient is equal to 1, the damage contribution of each cycle is expressed by the damage accumulation coefficient D value when the material undergoes a plurality of different stress cycles, assuming that the expected lifetime of a material at stress level S is N, if the material undergoes m stress cycles at stress level S, each cycle corresponds to a loading of stress amplitude S, the damage contribution of each cycle is expressed as 1/N, and after m cycles the total damage accumulation coefficient D is:
The stable accumulated plastic shear strain increment DeltaP cyc is adopted as a fatigue indication factor FIP, when the accumulated plastic shear strain P cri reaches a certain critical value, the material is destroyed, and the fatigue life measured by a fatigue test is determined by assuming that P cri is a material constant which does not change with the change of external load:
FIP=ΔPcyc＝Pcyc|N-Pcyc|N-1
in order to reflect the relationship of the influence of hydrogen on the fatigue life, a function f (sigma) is established which considers the damage to the material caused by the influence of hydrogen, and in a life prediction model of fatigue damage accumulation, the damage is expressed as:
FIPH=f(σ)*FIP
The fatigue index factor FIP' (delta P cyc-H) of the material in the single cyclic loading process is the sum of the original FIP and the FIP H:
FIP'=FIP+FIPH
When the hydrogen concentration in the material is 0, f (σ) =0, where FIP' =fip;
the expression for predicting the life of the test by using the fatigue index factor FIP' (Δp cyc-H) considering the effect of hydrogen charging is:
FIP'=ΔPcyc+f(σ)ΔPcyc
=(1+f(σ))ΔPcyc
assuming that the cumulative plastic shear strain value P cri-H at material failure after charging is still a constant, when P cri-H reaches a critical value, the material fails and cracks initiate, and the critical value P cri-H is determined by a fatigue test value of the charged sample, so the fatigue life prediction model of the charged sample is:
The embodiment of the invention provides a fatigue life prediction method of a nickel-based superalloy taking the hydrogen effect into consideration, an elastoplastic constitutive model and a polycrystalline representative volume unit are established, the model takes a microscopic deformation mechanism of a polycrystalline material into consideration, so as to simulate the damage evolution of a microstructure of the material under different cyclic stress loading environments, the fatigue life of the nickel-based superalloy is predicted by using accumulated plastic shear strain as a damage indication factor, and hydrogen is introduced to correct the damage of the material life on the basis, thereby realizing the prediction of the fatigue life of the nickel-based superalloy affected by the hydrogen.
Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Drawings
The foregoing and/or additional aspects and advantages of the invention will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings, in which:
FIG. 1 is a flow chart of a method for predicting fatigue life of a nickel-base superalloy that accounts for hydrogen effects, according to an embodiment of the present invention;
FIG. 2 is a graph of error bands of microscopic model predicted lifetime versus test results;
FIG. 3 is a graph of error bands of hydrogen fatigue life predictions versus test results.
Detailed Description
Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to like or similar elements or elements having like or similar functions throughout. The embodiments described below by referring to the drawings are illustrative and intended to explain the present invention and should not be construed as limiting the invention.
Fig. 1 is a flowchart of a fatigue life prediction method for a nickel-base superalloy considering a hydrogen influence effect according to an embodiment of the present invention.
As shown in fig. 1, the fatigue life prediction method of the nickel-base superalloy considering the hydrogen influence effect includes the steps of:
step 1, setting different hydrogen charging states and different load working conditions for a nickel-based superalloy test piece to obtain the low cycle fatigue life of the nickel-based superalloy test piece.
Firstly, performing low cycle fatigue tests before and after hydrogen charging of the nickel-based superalloy to obtain the low cycle fatigue life of the nickel-based superalloy test piece under different hydrogen charging states and different load working conditions.
And 2, establishing a polycrystalline representative volume unit model based on the crystal plasticity constitutive model and the Voronoi polygon to characterize a microscopic deformation mechanism of the nickel-based superalloy.
It is appreciated that embodiments of the present invention create crystalline plastic constitutive models and polycrystalline representative volumetric unit models that take into account microscopic deformation mechanisms.
Specifically, building a crystal plasticity constitutive model:
In this model, the total deformation gradient F of each individual crystalline material when the polycrystalline material is subjected to an applied load can be expressed as:
F=Fe*Fp
the velocity gradient tensor after deformation L is the sum of the elastic deformation L e and the plastic deformation L p:
the plastic velocity gradient L p can be expressed as an equation relating the plastic slip rate γ:
wherein γ α、sα and m α are the plastic slip ratio, slip direction vector, and slip plane normal vector of the alpha-th slip system, respectively. In classical conformational models, critical shear stress is typically used as a state variable for the slip system, Relates to the shear stress tau α,Equation of:
Decomposition shear stress of the alpha slip system:
τα＝σ：μα
Introducing back stress X α to describe hardening reaction of material under cyclic loading based on original crystal plastic motion theory, and in crystal sliding system, tau α and The relationship between them is as follows:
In the formula, For reference strain rate, n is a rate sensitivity coefficient related to material properties, X α is back stress for describing cyclic deformation behavior under material fatigue load, g α is a current strength parameter of an alpha slip system, sgn () is a sign function, and a nonlinear evolution equation of the back stress parameter is:
Wherein C is the direct hardening modulus, D is the dynamic recovery modulus, and is related to the material response upon loading.
Where h αβ is the slip hardening modulus due to latent hardening, when α=β, the cause of hardening by the slip system is the cause of the slip system itself, where h αβ＝hαα is the self hardening modulus, when α+noteβ, h αβ is the latent hardening modulus, indicates that hardening 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, and h is the hardening modulus, and indicates the hardening effect of the slip system β on the slip system α.
hαβ(γ)＝h(γ)[q+(1-q)δαβ]
Where q is a constant used to describe the material's latent and self-hardening behavior relationship, h 0 represents the initial hardening modulus, γ is the cumulative shear strain for all slip systems, τ 0 and τ s saturated hardening modulus and saturated shear stress, where γ is expressed as:
And 3, based on the accumulated damage theory, taking the effect of the influence of local deformation on crack initiation of the material into consideration, and establishing a crack initiation life prediction model taking hydrogen influence factors into consideration.
The embodiment of the invention establishes a crack initiation life prediction model considering hydrogen influence factors based on the accumulated damage theory.
Specifically, the establishment of a crack initiation life prediction model taking into consideration hydrogen influence factors:
According to the cumulative damage theory, when the damage accumulation coefficient (generally denoted by D) is equal to 1, the material is damaged. When the material is subjected to a plurality of different stress cycles, the damage contribution for each cycle can be represented by a D value. Let N be the expected lifetime of a material at stress level S. Now, if the material has undergone m stress cycles at this stress level (each cycle corresponding to a loading of stress amplitude S), the damage contribution per cycle can be expressed as 1/N. Thus, after m cycles, the total damage accumulation coefficient D is:
The plastic deformation of the material plays a very important role in the crack initiation process of the material, the initiation of fatigue cracks is regarded as the result of plastic deformation accumulation in the fatigue damage accumulation theory, and the plastic deformation accumulation of the material is closely related to the shear strain in crystals, so the accumulated plastic shear strain suffered by the material should be mainly considered in researching the plastic deformation of crystals, therefore, the accumulated plastic shear strain increment DeltaP cyc after stabilization is adopted as a Fatigue Indicator (FIP) in the chapter, the material is destroyed when the accumulated plastic shear strain P cri reaches a certain critical value, and the P cri is assumed to be a material constant which does not change with the change of external load. The value can be determined by the fatigue life measured by one fatigue test.
FIP=ΔPcyc＝Pcyc|N-Pcyc|N-1
To reflect the relationship of hydrogen to the effect of fatigue life, a function f (σ) was established herein that considers the effect of hydrogen on the damage to the material, and in the life prediction model of fatigue damage accumulation, the damage caused by this portion is expressed as:
FIPH=f(σ)*FIP
The fatigue index factor FIP' (delta P cyc-H) of the material in the single cyclic loading process is the sum of the original FIP and the FIP H:
FIP'=FIP+FIPH
when the hydrogen concentration in the material is 0, f (σ) =0, where FIP' =fip,
The expression for predicting the life of the test by using the fatigue index factor FIP' (Δp cyc-H) considering the effect of hydrogen charging is:
FIP'=ΔPcyc+f(σ)ΔPcyc
=(1+f(σ))ΔPcyc
assuming that the cumulative plastic shear strain value P cri-H at material failure after charging is still a constant, when P cri-H reaches a critical value, the material fails and cracks initiate, and the critical value P cri-H is determined by a fatigue test value of the charged sample, so the fatigue life prediction model of the charged sample is:
and 4, carrying out model verification on the crack initiation life prediction model considering the hydrogen influence factors by using the obtained low cycle fatigue life of the nickel-based superalloy test piece under different hydrogen charging states and different load working conditions, and obtaining a final crack initiation life prediction model considering the hydrogen influence factors after the model verification is passed.
By performing simulation analysis on the low cycle fatigue life before and after hydrogen charging and under different load working conditions, and comparing the simulation analysis with test results, the accuracy and reliability of the crack initiation life prediction model considering hydrogen influence factors are verified. And when the accuracy is larger than a set threshold value, obtaining a model for predicting the fatigue life of the nickel-based superalloy considering the hydrogen influence effect.
The fatigue life prediction method of the nickel-base superalloy of the present invention, which takes into consideration the hydrogen influence effect, is described in detail below by way of one embodiment.
(1) Setting different hydrogen charging states and different load working conditions for the nickel-based superalloy test piece to obtain the low cycle fatigue life of the nickel-based superalloy test piece;
(2) And writing a crystal plastic constitutive model based on UMAT user subroutines by using the Fortran language, and establishing a representative volume unit of the polycrystalline model based on a Voronoi polygon method to realize characterization of a local microscopic deformation mechanism of the polycrystalline.
In this model, the total deformation gradient F of each individual crystalline material when the polycrystalline material is subjected to an applied load can be expressed as:
F=Fe*Fp (1)
in the formula, F e represents a deformation gradient of the crystal, which is deformation caused by lattice distortion and rigid rotation, and this portion is called elastic deformation according to theoretical assumption. F p denotes plastic shear deformation of the material, which is referred to as plastic deformation.
The velocity gradient tensor after deformation L is the sum of the elastic deformation L e and the plastic deformation L p:
when the crystal lattice is not deformed, the crystal lattice is Is set as a unit vector in the slip direction of the alpha slip system,The unit normal vector for the slip plane is:
In the formula, The plastic slip ratio of the alpha slip system is about the shear stress τ α,And equation of the sum. And is also provided withAndThe two satisfy the orthogonal relationship:
sα·mα=0 (5)
In the deformed material structure, the vector of the slip direction is s α, the vector of the slip plane normal direction is m α, and the relation between the unit vector of the slip direction and the unit vector of the slip plane normal direction of the initial structure is as follows:
Thus, there are:
The symmetrical part and the antisymmetric part are extracted in the decomposition of the velocity gradient tensor L, and the expression mode is as follows:
L=D+W (9)
Wherein D represents a symmetrical portion, also called a deformation rate Tensor (Deformation Rate Tensor), describing the deformation rate of each point in the medium, and W represents an antisymmetric portion, also called a rotational deformation rate Tensor (Spin Tensor), describing the rotation rate of each point in the medium.
The expression of the deformation ratio tensor D and the rotational deformation ratio tensor W can be obtained from the above expression (9) as follows:
Similar to the velocity gradient tensor L, the deformation ratio tensor D and the rotational deformation ratio tensor W are further split into an elastic deformation portion D e、Dp and a plastic deformation portion W e、Wp:
the deformation tensor D can be expressed as:
wherein:
the rotational deformation tensor W can be expressed as:
these equations constitute the basic description of crystal kinematics, which effectively relates the slip shear rate inside the crystal to the external macroscopic deformation rate.
From crystal plastic theory, slip deformation of crystals cannot affect the elastic deformation phase of crystal lattice, and thus constitutive equation of the elastic phase can be expressed as:
where L is defined as the modulus of elasticity tensor of the transient, Is Jaumann rate based on Kirchhoff stress tensor of the intermediate structure.
Wherein, the Jaumann rate of Cauchy stress based on initial structure:
So that the number of the parts to be processed,
From equations (12), (14), (20) and (22),
The above equation relates the rate of change of stress, the rate of change of strain, and the slip shear strain rate. Generally, an orientation factor P α is used as a bridge between the shear stress and shear strain and the macroscopic stress and strain of each sliding system.
Thus, the shear stress on the α -slip can be calculated by:
τα＝σ:μα (25)
The shear strain on each slip is synthesized to each strain component under the material system can be calculated by the following formula:
Introducing back stress X α to describe hardening reaction of material under cyclic loading based on original crystal plastic motion theory, and in crystal sliding system, tau α and The relationship between them is as follows:
In the formula, For reference strain rate, n is a rate sensitivity coefficient related to material properties, X α is back stress for describing cyclic deformation behavior under material fatigue load, g α is a current strength parameter of an alpha slip system, sgn () is a sign function, and a nonlinear evolution equation of the back stress parameter is:
Wherein C is the direct hardening modulus, D is the dynamic recovery modulus, and is related to the material response upon loading.
Where h αβ is the slip hardening modulus due to latent hardening, when α=β, the cause of hardening by the slip system is the cause of the slip system itself, where h αβ＝hαα is the self hardening modulus, when α+noteβ, h αβ is the latent hardening modulus, indicates that hardening 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 is the hardening modulus, and indicates the hardening effect of the slip system β on the slip system α:
hαβ(γ)＝h(γ)[q+(1-q)δαβ] (30)
Where q is a constant used to describe the material's latent and self-hardening behavior relationship, h 0 represents the initial hardening modulus, γ is the cumulative shear strain for all slip systems, τ 0 and τ s saturated hardening modulus and saturated shear stress, where γ is expressed as:
(3) According to the cumulative damage theory, when the damage accumulation coefficient (generally denoted by D) is equal to 1, the material is damaged. When the material is subjected to a plurality of different stress cycles, the damage contribution for each cycle can be represented by a D value. Let N be the expected lifetime of a material at stress level S. Now, if the material has undergone m stress cycles at this stress level (each cycle corresponding to a loading of stress amplitude S), the damage contribution per cycle can be expressed as 1/N. Thus, after m cycles, the total damage accumulation coefficient D is:
According to the established finite element calculation model, calculating a plastic shear strain increment delta P cyc of a single cycle of each sliding system in the model under the action of external load, wherein the value of the plastic shear strain increment delta P cyc tends to be stable after a period of change, taking the plastic shear strain increment delta P cyc of the single cycle after each stabilization under the action of different external loads as a fatigue indication factor FIP, and participating in subsequent calculation.
FIP=ΔPcyc＝Pcyc|N-Pcyc|N-1 (34)
(4) In the finite element calculation process, only the cell position where plastic deformation is most remarkable in the simulation process needs to be focused, and the cell position is regarded as a possible position for crack initiation. When the plastic shear strain at this location builds up beyond the critical plastic strain of the material, the material is considered to have undergone fatigue failure. The critical cumulative plastic shear strain P cri-fat at the time of crack initiation of the material was calculated from the single cycle plastic shear strain increase Δp cyc and the test fatigue crack initiation life N f for a cell location where plastic deformation was most pronounced under external load conditions, and the value was considered to be a material constant that did not change with changes in external load.
(5) Substituting the single-cycle plastic shear strain increment delta P cyc under different load actions calculated in the step (3) and the critical accumulated plastic shear strain P cri-fat during crack initiation into the formula (36) to calculate the fatigue crack initiation prediction life under the rest load actions.
(6) In order to reflect the relationship of the influence of hydrogen on the fatigue life, a function f (sigma) which considers the damage to the material caused by the influence of hydrogen is established, and the expression is obtained by using life damage fitting caused by hydrogen under the corresponding load working condition.
(7) In the life prediction model of fatigue damage accumulation considering the influence of hydrogen, the damage caused by hydrogen is expressed as:
FIPH=f(σ)*FIP (37)
The fatigue index factor FIP' (delta P cyc-H) of the material in the single cyclic loading process is the sum of the original FIP and the FIP H:
FIP'=FIP+FIPH (38)
when the hydrogen concentration in the material is 0, f (σ) =0, and FIP' =fip.
The expression for predicting the life of the test by using the fatigue index factor FIP' (Δp cyc-H) considering the effect of hydrogen charging is:
assuming that the cumulative plastic shear strain value P cri-H at material failure after charging is still a constant, when P cri-H reaches a critical value, the material fails and cracks initiate, and the critical value P cri-H is also determined by a fatigue test value of the charged sample, so the fatigue life prediction model of the charged sample is:
(8) Model verification, namely carrying out fatigue life prediction on a GH4169 high-temperature alloy under different load working conditions before and after room temperature hydrogen charging, comparing the fatigue crack initiation life prediction with test results, and verifying the accuracy of the model by using a cumulative damage theory to select plastic deformation as a fatigue indication factor and introducing a crack initiation life prediction model for correcting the damage of the hydrogen charging sample under the function f (sigma) of damage influenced by the stress magnitude, wherein the error is within a double error band, as can be seen from error band distribution diagrams of fig. 2 and 3.
According to the fatigue life prediction method of the nickel-based superalloy considering the hydrogen effect, which is provided by the embodiment of the invention, an elastoplastic constitutive model and a polycrystalline representative volume unit are established, the model considers a microscopic deformation mechanism of a polycrystalline material, so as to simulate the damage evolution of a microstructure of the material under different cyclic stress loading environments, the fatigue life of the nickel-based superalloy is predicted by using accumulated plastic shear strain as a damage indication factor, and hydrogen is introduced to correct the damage of the material life on the basis, so that the fatigue life of the nickel-based superalloy influenced by the hydrogen is predicted.
In the description of the present specification, a description referring to terms "one embodiment," "some embodiments," "examples," "specific examples," or "some examples," etc., means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present invention. In this specification, schematic representations of the above terms are not necessarily directed to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or N embodiments or examples. Furthermore, the different embodiments or examples described in this specification and the features of the different embodiments or examples may be combined and combined by those skilled in the art without contradiction.
Furthermore, the terms "first," "second," and the like, are used for descriptive purposes only and are not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "N" means at least two, for example, two, three, etc., unless specifically defined otherwise.
Any process or method descriptions in flow charts or otherwise described herein may be understood as representing modules, segments, or portions of code which include one or more executable instructions for implementing specific logical functions or steps of the process, and additional implementations are included within the scope of the preferred embodiment of the present invention in which functions may be executed out of order from that shown or discussed, including substantially concurrently or in reverse order from that shown or discussed, depending on the functionality involved, as would be understood by those reasonably skilled in the art of the embodiments of the present invention.
Claims (2)
1. A fatigue life prediction method of a nickel-base superalloy considering a hydrogen influence effect, comprising the steps of:
setting different hydrogen charging states and different load working conditions for the nickel-based superalloy test piece to obtain the low cycle fatigue life of the nickel-based superalloy test piece;
Establishing a polycrystalline representative volume unit model based on the crystal plasticity constitutive model and the Voronoi polygon to represent a microscopic deformation mechanism of the nickel-based superalloy;
Based on the accumulated damage theory, taking the effect of the influence of local deformation on crack initiation of the material into consideration, and establishing a crack initiation life prediction model taking hydrogen influence factors into consideration;
the low cycle fatigue life of the obtained nickel-base superalloy test piece is utilized to carry out model verification on the crack initiation life prediction model considering the hydrogen influence factors by utilizing different hydrogen charging states and different load working conditions, and after the model verification is passed, the final crack initiation life prediction model considering the hydrogen influence factors is obtained;
establishing a crack initiation life prediction model considering hydrogen influence factors, including:
According to the cumulative damage theory, when the damage accumulation coefficient is equal to 1, the damage contribution of each cycle is expressed by the damage accumulation coefficient D value when the material undergoes a plurality of different stress cycles, assuming that the expected lifetime of a material at stress level S is N, if the material undergoes m stress cycles at stress level S, each cycle corresponds to a loading of stress amplitude S, the damage contribution of each cycle is expressed as 1/N, and after m cycles the total damage accumulation coefficient D is:
The stable accumulated plastic shear strain increment DeltaP cyc is adopted as a fatigue indication factor FIP, when the accumulated plastic shear strain P cri reaches a certain critical value, the material is destroyed, and the fatigue life measured by a fatigue test is determined by assuming that P cri is a material constant which does not change with the change of external load:
FIP=ΔPcyc＝Pcyc|N-Pcyc|N-1
in order to reflect the relationship of the influence of hydrogen on the fatigue life, a function f (sigma) is established which considers the damage to the material caused by the influence of hydrogen, and in a life prediction model of fatigue damage accumulation, the damage is expressed as:
FIPH=f(σ)*FIP
The fatigue index factor FIP' (delta P cyc-H) of the material in the single cyclic loading process is the sum of the original FIP and the FIP H:
FIP'=FIP+FIPH
when the hydrogen concentration in the material is 0, f (σ) =0, where FIP' =fip,
The expression for predicting the life of the test by using the fatigue index factor FIP' (Δp cyc-H) considering the effect of hydrogen charging is:
FIP'=ΔPcyc+f(σ)ΔPcyc
=(1+f(σ))ΔPcyc
assuming that the cumulative plastic shear strain value P cri-H at material failure after charging is still a constant, when P cri-H reaches a critical value, the material fails and cracks initiate, and the critical value P cri-H is determined by a fatigue test value of the charged sample, so the fatigue life prediction model of the charged sample is:
2. the method of claim 1, wherein building a polycrystalline representative volumetric cell model based on the crystalline plastic constitutive model and the Voronoi polygon comprises:
In the crystalline plastic constitutive model, when the polycrystalline material is subjected to an applied load, the total deformation gradient F of each individual crystalline material is expressed as:
F=Fe*Fp
wherein F e represents a deformation gradient of the crystal, and F p represents plastic shear deformation of the material;
The deformed velocity gradient tensor L is the sum of L e and L p:
l p is expressed as an equation related to the plastic slip rate γ:
Wherein gamma α、sα and m α are the plastic slip ratio, slip direction vector and slip plane normal vector of the alpha-th slip system, respectively, in a classical model of the constellation, critical shear stress is usually used as a state variable of the slip system, The equation for shear stress τ α、τc α and:
Decomposition shear stress of the alpha slip system:
The introduction of back stress X α describes the hardening reaction of materials under cyclic loading based on the original crystal plastic motion theory, and in the slip system of crystals, the relation between tau α and gamma α is as follows:
In the formula, For reference strain rate, n is a rate sensitivity coefficient related to material properties, X α is back stress for describing cyclic deformation behavior under material fatigue load, g α is a current strength parameter of an alpha slip system, sgn () is a sign function, and a nonlinear evolution equation of the back stress parameter is:
Wherein, C is the direct hardening modulus, D is the dynamic recovery modulus, which is related to the material response when loaded;
Wherein h αβ is a slip hardening modulus due to latent hardening, when α=β, the cause of hardening by the slip system is the cause of the slip system itself, at this time h αβ＝hαα is a self hardening modulus, when α+noteβ, h αβ is a latent hardening modulus, indicates that hardening by the slip system α is affected by the slip system β, γ β is a plastic shear deformation rate of the slip system β, h is a hardening modulus, and indicates a hardening effect of the slip system β on the slip system α;
hαβ(γ)＝h(γ)[q+(1-q)δαβ]
Where q is a constant used to describe the material's latent and self-hardening behavior relationship, h 0 represents the initial hardening modulus, γ is the cumulative shear strain for all slip systems, τ 0 and τ s saturated hardening modulus and saturated shear stress, where γ is expressed as:
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