An engineering damage evolution evaluation method based on EBSD semi-quantitative analysis

Abstract

The application discloses an engineering damage evolution evaluation method based on EBSD semi-quantitative analysis and relates to the technical field of multi-scale damage evaluation. The engineering damage evolution evaluation method based on EBSD semi-quantitative analysis comprises the following steps: through a dislocation accumulation mode and a crack nucleation mechanism of intracrystalline and grain boundaries under creep-fatigue, and in combination with a multi-scale state function, fatigue damage indicator of each cycle and creep damage indicator of each cycle are determined, so that the cycle period of mesoscopic crack nucleation of a material of a component to be measured, i.e. the creep-fatigue life of the material of the component to be measured, is predicted, and a relevant theoretical basis is provided for different stages from damage evolution to crack nucleation.

Description

Technical Field

[0001] This invention relates to the field of multi-scale damage assessment technology, and in particular to an engineering damage evolution evaluation method based on EBSD semi-quantitative analysis. Background Technology

[0002] Due to fluctuations in pressure, mechanical loads, and temperature, high-temperature rotating components inevitably endure harsher service environments and more complex loading conditions. Based on the loading characteristics of these components (takeoff-cruise-landing), creep-fatigue becomes the primary failure mode, initiating crack nucleation and propagation, thus posing a potential threat to structural integrity. Therefore, creep-fatigue research has attracted widespread attention in areas such as microstructure characterization, cyclic prediction of mesoscopic crack nucleation in component materials, and reliability assessment.

[0003] In continuous damage mechanics, creep-fatigue is generally classified into creep damage and fatigue damage. Creep damage manifests as grain boundary voids at high temperatures, while fatigue damage manifests as irreversible slip or plastic deformation under cyclic loading. Depending on the research scale, damage can take many forms, such as plastic deformation, voids, cracks, and stress / strain responses. It is generally considered that the mesoscopic scale at the grain level is the smallest scale associated with engineering requirements for component-level damage assessment and cyclic prediction of mesoscopic crack nucleation in component materials. In this context, in-situ experiments combined with electron backscattering diffraction (EBSD) have proven to be a powerful multi-scale technique for reflecting microstructure evolution, performance degradation, and damage accumulation.

[0004] EBSD has developed several typical orientation difference parameters for quantitatively describing mesoscopic plastic strain under external loading conditions, such as image quality (IQ), kernel averaged misorientation (KAM), and grain reference point misorientation (GROD). Since in-situ EBSD experiments have been proven to be a powerful multi-scale technique for reflecting microstructure evolution, performance degradation, and damage accumulation, predicting the cycle period of mesoscopic crack nucleation in the test component material using the kernel averaged misorientation parameter has become an important research direction for studying the cycle period of mesoscopic crack nucleation in component materials at high temperatures.

[0005] However, the precise correlation between mesoscale plastic strain and the cycle period of mesoscale crack nucleation in macroscale component materials remains controversial, especially in creep-fatigue conditions driven by multiple damage modes under multiphysics, which complicates the issue further. For example, in some heat-resistant steels with high initial dislocation densities, the changes in the center point orientation deviation parameter of the EBSD are non-monotonic with the cycle period of mesoscale crack nucleation in the tested component material due to the combined effects of dislocation multiplication and recovery. Therefore, it is impossible to determine whether the changes in the center point orientation deviation parameter of the EBSD can predict the cycle period of mesoscale crack nucleation in the tested component material. Summary of the Invention

[0006] The purpose of this invention is to provide an engineering damage evolution evaluation method based on EBSD semi-quantitative analysis, which can predict the cycle of mesoscopic crack nucleation in the material of the component under test by utilizing the change of the center point orientation deviation parameter of EBSD.

[0007] To achieve the above objectives, the present invention provides the following solution:

[0008] A method for evaluating engineering damage evolution based on EBSD semi-quantitative analysis includes:

[0009] Based on the physical meaning of the center point orientation deviation parameter of EBSD, the relationship between the average center point orientation deviation parameter of multiple grains and the average geometrically required dislocation density is determined; the physical meaning of the center point orientation deviation parameter is: the center point orientation deviation parameter is the lower limit of the sum of the densities of the six types of geometrically required dislocations.

[0010] Based on the energy dissipation criterion and combined with the relationship between the average center point orientation deviation parameter of the multiple grains and the average geometrically required dislocation density, a multi-scale state function with respect to the center point orientation deviation parameter is determined.

[0011] Based on the dislocation accumulation mode and crack nucleation mechanism within grains and grain boundaries under creep-fatigue conditions, and combined with the multi-scale state function, the fatigue damage indicator factor and the creep damage indicator factor for each cycle are determined.

[0012] Based on the linear damage accumulation criterion, and using the fatigue damage indicator factor and the creep damage indicator factor of each cycle, an energy-based crystallographic damage evolution equation is established.

[0013] Based on the crystallographic damage evolution equation, the cycle period of mesoscopic crack nucleation in the material of the component under test is determined.

[0014] Optionally, based on the linear damage accumulation criterion and utilizing the fatigue damage indicator and the creep damage indicator, an energy-based crystallographic damage evolution equation is established, which further includes:

[0015] Based on the crystallographic damage evolution equation and the in-situ creep-fatigue test characterized by EBSD, the center point orientation deviation parameter value and the EBSD orientation difference map of the material under test are determined.

[0016] Based on the center point orientation deviation parameter value of the material under test and the EBSD orientation difference map of the material under test, multiple stages of mesoscopic crack nucleation are divided, and the macroscopic strain energy density and mesoscopic orientation difference parameter increment of each stage are calculated; the multiple stages include: initial stage, void incubation stage, crack nucleation stage, macroscopic crack initiation stage and creep-fatigue failure stage.

[0017] Based on the macroscopic strain energy density and the mesoscopic orientation difference parameter increment at each stage, the fatigue damage rate, creep damage rate, and creep-fatigue damage rate at each stage are calculated.

[0018] Optionally, the relationship between the average orientation difference of the plurality of grains and the average geometrically required dislocation density is as follows:

[0019]

[0020] in, This is the average center point orientation deviation parameter for multiple grains. For the average geometry, the required dislocation density is ∝, which represents and They are in a direct proportional relationship.

[0021] Optionally, the multi-scale state function is:

[0022]

[0023] in, This is a multi-scale state function, where α is a scaling factor related to the scan step size, and β is a scaling factor related to the center point orientation deviation parameter analysis. This is the average center point orientation deviation parameter for multiple grains.

[0024] Optionally, the fatigue damage indicator factor for each cycle is:

[0025]

[0026] in, This represents the fatigue damage indicator for the i-th cycle at the mesoscale. Let be the fatigue strain energy density in the i-th cycle on a macroscopic scale. Let be the average orientation deviation parameter of the center point within the crystal during the i-th cycle. denoted as the net change in the average orientation deviation parameter of the intragranular and grain boundary centers during the i-th cycle, and l is a conversion coefficient independent of the cycle number.

[0027] Optionally, the creep damage indicator factor for each cycle is:

[0028]

[0029] in, This is the creep damage indicator for the i-th cycle at the mesoscale. Let be the creep strain energy density in the i-th cycle on a macroscopic scale. Let be the average orientation deviation parameter of the grain boundary center point in the i-th cycle. denoted as the net change in the average grain boundary center point orientation deviation parameter during the i-th cycle, and l is a conversion coefficient independent of the cycle number.

[0030] Optionally, the crystallographic damage evolution equation is:

[0031]

[0032]

[0033]

[0034] in, For the cumulative creep-fatigue damage up to the j-th cycle, For the fatigue damage in the i-th cycle, For the creep damage in the i-th cycle, Let be the fatigue strain energy density in the i-th cycle on a macroscopic scale. Let be the creep strain energy density in the i-th cycle on a macroscopic scale. This is the critical fatigue strain energy density up to the final damage state. This is the critical creep strain energy density up to the final damage state. This represents the critical net change in the average center point orientation deviation parameter within the crystal until the final damaged state. This represents the critical net change in the average center point orientation deviation parameter of the grain boundary up to the final damaged state. Let be the average orientation deviation parameter of the center point within the crystal during the i-th cycle. Let be the average orientation deviation parameter of the grain boundary center point in the i-th cycle.

[0035] Optionally, the cycle period for mesoscopic crack nucleation in the material of the component under test is:

[0036]

[0037] Where, N n The cycle period for mesoscopic crack nucleation in the material of the component under test. For the cumulative creep-fatigue damage up to the j-th cycle, This represents the creep-fatigue damage in the i-th cycle.

[0038] Optionally, the macroscopic strain energy density is:

[0039] Δw f =∫ N σ:dε p ;

[0040] Δw c =∫ N σ:dε c ;

[0041] Where, Δw f For macroscopic fatigue strain energy density, Δw c For macroscopic creep strain energy density, ε p For plastic strain, ε c σ represents creep strain, σ represents stress under external load, and N represents the number of cycles.

[0042] Optionally, the increment of the mesoscopic orientation difference parameter is:

[0043]

[0044]

[0045] in, Let be the net change in the average orientation deviation parameter of the crystal center point during the i-th cycle. Let be the net change in the average grain boundary center point orientation deviation parameter during the i-th cycle. Let be the average orientation deviation parameter of the center point within the crystal during the i-th cycle. Let be the average orientation deviation parameter of the grain boundary center point in the i-th cycle. This represents the average orientation deviation parameter of the center point within the grain and at the grain boundary in the undeformed state. This is the average orientation deviation parameter of the grain boundary center point in the undeformed state.

[0046] According to specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0047] This invention provides an engineering damage evolution evaluation method based on EBSD semi-quantitative analysis. By determining the dislocation accumulation mode and crack nucleation mechanism within grains and grain boundaries under creep-fatigue conditions, and combining it with multi-scale state functions, the fatigue damage indicator factor and creep damage indicator factor for each cycle are determined. This allows for the prediction of the cycle period of mesoscopic crack nucleation in the material under test, i.e., the creep-fatigue life of the material under test. It also provides a theoretical basis for different stages from damage evolution to crack nucleation. Attached Figure Description

[0048] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments 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 drawings can be obtained based on these drawings without creative effort.

[0049] Figure 1 The flowchart of the engineering damage evolution evaluation method based on EBSD semi-quantitative analysis provided by the present invention;

[0050] Figure 2 A typical partition diagram of the creep-fatigue hysteresis loop provided in an embodiment of the present invention;

[0051] Figure 3 A flowchart of a creep-fatigue damage grading method that considers the degradation of material mechanical properties over service time, provided in an embodiment of the present invention;

[0052] Figure 4 The image shows the creep-fatigue load waveform and in-situ EBSD characterization diagrams at different intervals under hybrid control, as provided in the embodiments of the present invention.

[0053] Figure 5 The evolution diagram of fatigue strain energy density under different creep-fatigue loads with normalized cycle number is provided in the embodiments of the present invention.

[0054] Figure 6 The evolution diagram of creep strain energy density under different creep-fatigue loads with normalized cycle number is provided in the embodiments of the present invention.

[0055] Figure 7 This is an evolution diagram of the net change in intragranular average KAM under different creep-fatigue loads as a function of normalized cycles, provided in an embodiment of the present invention.

[0056] Figure 8 This is an evolution diagram of the net change in average KAM of grain boundaries under different creep-fatigue loads as a function of normalized cycles, provided in an embodiment of the present invention.

[0057] Figure 9Multi-scale damage rate evolution curves for strain ranges of 1.6% and 2.0% and a load stress of 500 MPa are provided for embodiments of the present invention.

[0058] Figure 10 The prediction and verification diagrams of mesoscopic crack nucleation lifetime under different creep-fatigue loads are provided for the implementation of this invention. Detailed Implementation

[0059] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0060] The purpose of this invention is to provide a semi-quantitative engineering damage evolution evaluation method based on EBSD analysis. By analyzing the dislocation accumulation mode and crack nucleation mechanism within grains and at grain boundaries under creep-fatigue conditions, and combining this with multi-scale state functions, the method determines the fatigue damage indicator factor and the creep damage indicator factor for each cycle. This allows for the prediction of the cycle period for mesoscopic crack nucleation in the tested component material, i.e., the creep-fatigue life of the component material, and provides a theoretical basis for different stages from damage evolution to crack nucleation. Furthermore, this invention effectively reflects the crystallographic mechanism of crack nucleation and the multi-scale description of damage evolution. The creep-fatigue damage rate curve shows significant consistency with the dislocation dynamics differential equation, establishing the boundary between mesoscopic crack nucleation and macroscopic crack initiation, which is of great significance for exploring the frontiers of solid mechanics.

[0061] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0062] Example 1

[0063] like Figure 1 As shown, the engineering damage evolution evaluation method based on EBSD semi-quantitative analysis provided by this invention includes:

[0064] Step S101: Based on the physical meaning of the center point orientation deviation parameter of EBSD, determine the relationship between the average center point orientation deviation parameter of multiple grains and the average geometrically required dislocation density; the physical meaning of the center point orientation deviation parameter is: the center point orientation deviation parameter is the lower limit of the sum of the densities of the six types of geometrically required dislocations.

[0065] Step S102: Based on the energy dissipation criterion and combining the relationship between the average center point orientation deviation parameter of multiple grains and the average geometrically required dislocation density, a multi-scale state function for the center point orientation deviation parameter is determined. The energy dissipation criterion uses energy as a parameter, taking the sum of fatigue dissipation energy and creep dissipation energy as the total dissipation energy; material failure is determined when this total dissipation energy reaches a critical value.

[0066] Step S103: Based on the dislocation accumulation mode and crack nucleation mechanism within grains and at grain boundaries under creep-fatigue conditions, and combined with multi-scale state functions, determine the fatigue damage indicator factor and the creep damage indicator factor for each cycle. The crack nucleation mechanism is determined by judging the crack initiation and nucleation period based on the crack length.

[0067] Step S104: Based on the linear damage accumulation criterion and utilizing the fatigue damage indicator factor and creep damage indicator factor of each cycle, an energy-based crystallographic damage evolution equation is established. The linear damage accumulation criterion defines total damage as the linear superposition of creep damage and fatigue damage.

[0068] Step S105: Determine the cycle period of mesoscopic crack nucleation in the material of the component under test according to the crystallographic damage evolution equation.

[0069] Furthermore, based on the linear damage accumulation criterion and utilizing fatigue damage indicator and creep damage indicator, an energy-based crystallographic damage evolution equation is established, which also includes:

[0070] Based on the crystallographic damage evolution equation and in-situ creep-fatigue tests characterized by EBSD, the center point orientation deviation parameter value and the EBSD orientation difference map of the material under test are determined.

[0071] Based on the center point orientation deviation parameter value and the EBSD orientation difference map of the material under test, multiple stages of mesoscopic crack nucleation are divided, and the macroscopic strain energy density and mesoscopic KAM increment of each stage are calculated. The multiple stages include: initial stage, void incubation stage, crack nucleation stage, macroscopic crack initiation stage and creep-fatigue failure stage.

[0072] Based on the macroscopic strain energy density and mesoscopic orientation difference parameter increments at each stage, the fatigue damage rate, creep damage rate, and creep-fatigue damage rate at each stage are calculated to provide a quantitative description of multi-scale damage evolution.

[0073] The following provides a detailed description of each step in the engineering damage evolution evaluation method based on EBSD semi-quantitative analysis provided by this invention.

[0074] Step S101 specifically includes:

[0075] In the theory of continuous dislocations, it is assumed that the lattice curvature is related to the crystallographic structure (Burdenshall vector b and line vector l) of geometrically required dislocations (GNDs) in the lattice. Based on the orientation relationship between b and l, and the 2D-EBSD orientation difference mapping of face-centered cubic (FCC) materials, the relationship between lattice curvature and GND density can be expressed as:

[0076]

[0077] In the formula, Let θ be the relative rotation component of the j-th local lattice axis. j (j = 1, 2, 3) the i-th global axial relative distance component x i The gradient within (i = 1, 2) and For the Burgers vector and line vector of the nth dislocation type, The GND density refers to the density of the six dislocation types, usually indicating the highest density under 2D-EBSD.

[0078] Based on the L1 matrix regularity, the inequalities related to the directions x1 and x2 can be expressed as:

[0079]

[0080]

[0081] Since the L1 positive matrix is ​​approximately equal to the effective size of the Burgh's vector b, the above inequality can be expressed as:

[0082]

[0083]

[0084] In orientation difference analysis with a scan step size of h, the above inequality can be further expressed as:

[0085]

[0086] Based on the two-dimensional (2D) EBSD orientation difference mapping, the physical meaning of KAM is that it is the lower bound of the sum of the densities of the six dislocation types. The above inequality can be expressed as follows:

[0087]

[0088] In the formula, The density of geometrically required dislocations (GNDs) for the six dislocation types is usually referred to as the highest density under 2D-EBSD, where b is the Burgers vector and h is the scan step size of EBSD.

[0089] Assuming each grain subjected to external inelastic strain is approximately spherical, then the average KAM within a given grain... ave The equation is as follows:

[0090]

[0091] In the formula, S g Let D be the area and diameter of a given grain. Is with polar angle Related local KAM, ρ G Given the GND density of edge dislocations within a given grain.

[0092] Multiple grains The equation is as follows:

[0093]

[0094] In the formula, Let n be the grain area of ​​the nth grain within the observation region. S represents the average KAM of the nth grain within the observation region, where m is the total number of grains. t The total grain area, The average GND density of multiple grains.

[0095] Equation (3) can be simplified to the relationship between the average orientation difference of multiple grains and the average geometrically required dislocation density, as follows:

[0096]

[0097] In the formula, This is the average center point orientation deviation parameter for multiple grains. For the average geometry, the required dislocation density is ∝, which represents and They are in a direct proportional relationship.

[0098] Step S102 specifically includes:

[0099] In thermodynamic systems, such as creep-fatigue tests at high temperatures, the equation for the energy conservation principle in transient analysis is as follows:

[0100]

[0101] In the formula, ρ is the material density. Let be the law of conservation of internal energy per unit mass, and σ be the stress under external load. Let be the strain rate tensor under external load, q be the heat flux vector per unit area of ​​the normal, and ψ be the heat provided per unit mass.

[0102] The second term represents the strain energy density rate caused by external mechanical work.

[0103] The discretized equation of equation (5) in the increment time is as follows:

[0104] ρ·Δe=Δw+ΔQ (6)

[0105] Δw and ΔQ are correlated; for example, under conventional cyclic loading, the stored energy density accounts for approximately 5% of the heat transfer, which can be represented by the proportionality coefficient ξ. The term ρ·Δe, which is related to internal energy, can be expressed as a state function depending on the specific mass system. Therefore, equation (6) can be written as:

[0106]

[0107] In the formula, It is a form of state parameter represented by a single variable or combination of variables (x1, x2, ...). It is the corresponding state function.

[0108] Storage energy density of polycrystalline metallic materials across multiple grains The equation is as follows:

[0109]

[0110] In the formula, ε represents the average statistical storage dislocation (SSD) density across multiple grains. p This is plastic strain.

[0111] By comparing the common features between equations (7) and (8), we can obtain:

[0112]

[0113]

[0114] Assuming a fixed proportional relationship exists between GND and SSD generated by cyclic deformation through stretching and compression, the state function of equation (10) can be expressed as:

[0115]

[0116] In the formula, α is a proportionality coefficient related to the scanning step size.

[0117] Combining equation (4), the improved state function that matches the EBSD analysis can be expressed as:

[0118]

[0119] in, This is a multi-scale state function, where α is a scaling factor related to the scan step size, and β is a scaling factor related to the center point orientation deviation parameter analysis. This is the average center point orientation deviation parameter for multiple grains.

[0120] Step S103 specifically includes:

[0121] Based on the energy dissipation theory, the macroscopic fatigue damage driving force Δw f and creep damage driving force Δw c It can be represented as:

[0122] Δw f =∫ N σ:dε p (13)

[0123] Δw c =∫ N σ:dε c (14)

[0124] In the formula, the symbol "Δ" represents the given variable of the fully closed hysteresis loop. For example... Figure 2 As shown, according to the creep-fatigue hysteresis loop, Δw f Δw represents the strain energy density associated with plastic deformation. c This represents the strain energy density associated with creep deformation.

[0125] Based on the dislocation accumulation modes characterized by EBSD, it was found that the GND density increases exponentially from the grain interior to the grain boundaries, manifesting as intragranular fatigue damage, leading to dislocation accumulation at the grain boundaries and promoting the initiation of grain boundary cracks. The GND density increases linearly from the grain boundaries to the triplet grain boundaries, manifesting as grain boundary creep damage and weakening the grain boundary strength. Therefore, the different GND accumulation modes and crack nucleation mechanisms within and at the grain boundaries under creep-fatigue conditions determine the derivation strategy for the damage factor.

[0126] In equation (8) Write it as ΔG with the cycle number as the smallest unit. f , representing the fatigue energy storage density at the mesoscopic scale (per cycle, per area), combined with equations (8), (13), and (14) to obtain ΔG f The expression is as follows:

[0127]

[0128] In the formula, It is the intragranular average KAM on multiple grains in a grain boundary-free neighborhood.

[0129] Similarly, the equation for creep storage density (per cycle, per area) at the mesoscale is as follows:

[0130]

[0131] In the formula, It is the average KAM of multiple grain boundaries. Therefore, ΔG f The influence of grain boundaries can be eliminated, ΔG c It can eliminate the effects of irreversible slippage.

[0132] Equations (15) and (16) can be rewritten as fatigue damage indicator factors for each cycle related to the cycle number, where g is the value of g. f and creep damage indicator g c The equation is as follows:

[0133]

[0134]

[0135] in, This represents the fatigue damage indicator for the i-th cycle at the mesoscale. Let be the fatigue strain energy density in the i-th cycle on a macroscopic scale. Let be the average orientation deviation parameter of the center point within the crystal during the i-th cycle. Let be the net change in the average orientation deviation parameter of the intragranular and grain boundary centers during the i-th cycle, and l be a conversion coefficient independent of the cycle number. This is the creep damage indicator for the i-th cycle at the mesoscale. Let be the creep strain energy density in the i-th cycle on a macroscopic scale. Let be the average orientation deviation parameter of the grain boundary center point in the i-th cycle. denoted as the net change in the average grain boundary center point orientation deviation parameter during the i-th cycle, and l is a conversion coefficient independent of the cycle number.

[0136] in,

[0137]

[0138]

[0139]

[0140] In the formula, the symbol “Λ” represents the change in absolute value, taking into account both cyclic softening and hardening. and These are the fatigue energy storage density and creep energy storage density of the i-th cycle at the mesoscale, respectively. and These are the fatigue strain energy density and creep strain energy density of the i-th cycle on a macroscopic scale, respectively. and These are the intragranular and grain boundary average KAM values ​​in the undeformed state. and These are the intragranular and grain boundary averages (KAM) for the i-th cycle, respectively. and , respectively, are the net changes in the intragranular and grain boundary average KAM during the i-th cycle, and l is a conversion coefficient independent of the cycle number.

[0141] Step S104 is as follows:

[0142] Based on equations (17) and (18), the storage energy density is used as a state parameter to define the fatigue damage in the i-th cycle. and creep damage The equation is as follows:

[0143]

[0144]

[0145] In the formula, and It refers to the critical fatigue energy storage density and critical creep energy storage density up to the final damage state.

[0146] Based on the Linear Cumulative Damage Criterion (LDS), the cumulative creep-fatigue damage evolution equation is as follows:

[0147]

[0148]

[0149]

[0150] in, For the cumulative creep-fatigue damage up to the j-th cycle, For the fatigue damage in the i-th cycle, For the creep damage in the i-th cycle, Let be the fatigue strain energy density in the i-th cycle on a macroscopic scale. Let be the creep strain energy density in the i-th cycle on a macroscopic scale. This is the critical fatigue strain energy density up to the final damage state. This is the critical creep strain energy density up to the final damage state. This represents the critical net change in the average center point orientation deviation parameter within the crystal until the final damaged state. This represents the critical net change in the average center point orientation deviation parameter of the grain boundary up to the final damaged state. Let be the average orientation deviation parameter of the center point within the crystal during the i-th cycle. Let be the average orientation deviation parameter of the grain boundary center point in the i-th cycle.

[0151] Step 105, specifically:

[0152] Based on equations (24), (25), and (26), the prediction equation for the cycle period of mesoscopic crack nucleation in the material of the component under test is as follows:

[0153]

[0154] Where, N n The cycle period for mesoscopic crack nucleation in the material of the component under test. For the cumulative creep-fatigue damage up to the j-th cycle, This represents the creep-fatigue damage in the i-th cycle.

[0155] The following section details the process of dividing the initial stage, the void incubation stage, the crack nucleation stage, the macroscopic crack initiation stage, and the creep-fatigue failure stage, as well as the specific procedures for calculating the macroscopic strain energy density and mesoscopic KAM increment for each stage.

[0156] By conducting at least two sets of continuous creep-fatigue tests under target load conditions, the shortest life is taken as the reference life N for creep-fatigue failure. f According to N f Determine the interrupted lifetime fraction under in-situ creep-fatigue testing to cover as much of the different stages of crack nucleation as possible. During the interruption interval, unload the load on the specimen to zero and perform EBSD characterization at a fixed viewpoint to obtain the orientation difference parameter KAM value and the corresponding orientation difference map.

[0157] Specifically, based on the EBSD orientation difference map of the material under test, the following stages are qualitatively divided: initial stage (I), void incubation stage (II), crack nucleation stage (i.e., mesoscopic crack nucleation stage) (III), macroscopic crack initiation stage (IV), and creep-fatigue failure stage (V). The stage between (I) and (II) is defined as the defect-free stage, which ends when the first void / defect appears; the stage between (II) and (III) is defined as the void coalescence process, which ends when an intergranular crack of approximately 20 μm appears; the stage between (III) and (IV) is defined as the short crack propagation process, which ends when a main crack of 295 μm appears; and the stage between (IV) and (V) is the final fracture stage, accounting for approximately 10% of the creep-fatigue life.

[0158] Based on the hysteresis loop from the in-situ creep-fatigue test, calculate the values ​​in equations (25) and (26). and Based on the KAM value, calculate the values ​​in equations (25) and (26). and

[0159] Based on the hysteresis loop from the in-situ creep-fatigue test, calculate the values ​​in equations (25) and (26). and The formula is as follows:

[0160] Δw f =∫ N σ:dε p ;

[0161] Δw c =∫ N σ:dε c ;

[0162] In the formula, the symbol "Δ" represents the given variable of the fully closed hysteresis loop, Δw f For macroscopic fatigue strain energy density, Δw c For macroscopic creep strain energy density, ε p For plastic strain, ε c Let σ be the creep strain, σ be the stress under external load, and N be the number of cycles. σ and dε p The colon ":" between the tensors represents the double dot product of the tensors.

[0163]

[0164]

[0165] In the formula, N f It is the baseline lifespan of the material of the component under test.

[0166] Calculate based on KAM value and The specific formula is as follows:

[0167]

[0168]

[0169] In the formula, the symbol "Λ" represents the change in absolute value (considering both cyclic softening and hardening). Let be the net change in the average orientation deviation parameter of the crystal center point during the i-th cycle. Let be the net change in the average grain boundary center point orientation deviation parameter during the i-th cycle. Let be the average orientation deviation parameter of the center point within the crystal during the i-th cycle. Let be the average orientation deviation parameter of the grain boundary center point in the i-th cycle. This represents the average orientation deviation parameter of the center point within the grain and at the grain boundary in the undeformed state. This is the average orientation deviation parameter of the grain boundary center point in the undeformed state.

[0170]

[0171]

[0172] In the formula, N f The baseline lifespan of the material of the component under test. This represents the critical net change in the average center point orientation deviation parameter within the crystal until the final damaged state. This represents the critical net change in the average center point orientation deviation parameter of the grain boundary up to the final damaged state.

[0173] Example 2

[0174] like Figure 3 As shown, the creep-fatigue damage grading method considering the degradation of material mechanical properties over service time in the engineering damage evolution evaluation method based on EBSD semi-quantitative analysis provided by this invention is as follows:

[0175] S301 calculates creep damage and fatigue damage of the material of the component under test through multiple sets of experiments, and obtains the traditional creep-fatigue damage interaction criterion.

[0176] S302, calculate the tensile plastic strain energy under each interrupted life, establish the material mechanical property degradation parameters related to the tensile plastic strain energy, and define the relationship between the material mechanical property degradation parameters and the damage level.

[0177] S303, fits the functional relationship between the degradation parameters of material mechanical properties and the critical damage value, and establishes a creep-fatigue damage interaction criterion related to the degradation of material mechanical properties.

[0178] S304, plot a three-dimensional creep-fatigue damage grading diagram of the degradation of material mechanical properties over service time.

[0179] S305 calculates the state points of the material under test during service, places them in a three-dimensional damage grading map, and determines the damage level and safety of the material under test.

[0180] Example 3

[0181] This embodiment uses a nickel-based IN718 superalloy as the research object to study its damage evolution trend during creep-fatigue and predict the mesoscopic crack nucleation life. To approximate the actual creep-fatigue interaction in engineering, creep-fatigue tests were conducted on IN718 at 650℃ under a hybrid control mode. The loading waveform is shown below. Figure 4As shown. The total strain range Δε t , load stress σ h and holding time t h The changes of the three parameters are shown in Table 1, which is a summary table of load condition parameters.

[0182] Table 1

[0183]

[0184] The first step is to conduct at least two sets of continuous creep-fatigue tests under each load condition, and use the shortest life as the reference life N for creep-fatigue failure. f As shown in Table 1. Based on N f Determine the interrupted lifetime fraction under in-situ creep-fatigue testing to cover as much of the different stages of crack nucleation as possible, such as... Figure 4 As shown. During the interruption interval, the load on the specimen was unloaded to zero for EBSD characterization at a fixed viewpoint, obtaining the orientation difference parameter KAM value and the corresponding orientation difference map.

[0185] The second step involves qualitatively dividing the material into four stages based on the EBSD orientation difference map of the target material: the initial stage (I), the void incubation stage (II), the crack nucleation stage (III), the macroscopic crack initiation stage (IV), and the material-level creep-fatigue failure stage (V). Stages (I) to (II) are defined as the defect-free stage, ending with the appearance of the first void / defect; stages (II) to (III) are defined as the void aggregation process, ending with the appearance of an intergranular crack of approximately 20 μm; stages (III) to (IV) are defined as the short crack propagation process, ending with the appearance of a 295 μm main crack; and stages (IV) to (V) constitute the final fracture stage, accounting for approximately 10% of the creep-fatigue life.

[0186] The third step is to calculate the hysteresis loop based on the in-situ creep-fatigue test. and like Figure 5-6 As shown; based on the EBSD orientation difference parameter KAM value, calculate and like Figure 7-8 As shown. and The growth is largely synchronous and, essentially, throughout the cycle. All Above. This indicates that creep-dominated grain boundary damage causes dislocations to accumulate near the grain boundaries, forming GNDs, making the lattice more prone to twisting near the grain boundaries, resulting in a larger orientation difference. Furthermore, as... Figure 7-8 As shown, during the corresponding stage (III) There will be a slight decrease because mesoscopic crack nucleation leads to local stress relaxation, causing stress and strain to redistribute around the small crack tip.

[0187] The fourth step is to calculate the fatigue damage rate. creep damage rate and creep-fatigue damage rate To perform a quantitative description of multi-scale damage evolution, such as Figure 9 As shown, the multi-scale damage exhibits strong nonlinearity throughout the cycle, demonstrating significant consistency with the dislocation dynamics differential equation. This indicates that the multi-scale damage equation of this invention successfully describes the fluctuations influenced by microstructural features.

[0188] The fifth step is to predict the creep-fatigue mesoscopic crack nucleation lifetime N based on the cumulative damage rate. n The prediction results are as follows Figure 10 As shown, the predicted points all fall within the corresponding experimental observation intervals, which provides empirical evidence for the accuracy of the multi-scale damage evaluation method of this invention.

[0189] This invention integrates orientation difference mapping information at the mesoscale into the macroscopic mechanical response, establishing a multiscale damage mechanics description of crystallographic structure evolution. This provides a theoretical basis for multiscale damage evaluation and, in identifying the damage evolution and crack nucleation mechanism of component materials used in high-temperature environments at the grain-level mesoscale, provides a theoretical basis for multiscale damage evaluation and life prediction in the field of solid mechanics.

[0190] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0191] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for evaluating the evolution of engineering damage based on EBSD semi-quantitative analysis, characterized in that, include: Based on the physical meaning of the center point orientation deviation parameter of EBSD, the relationship between the average center point orientation deviation parameter of multiple grains and the average geometrically required dislocation density is determined. The physical meaning of the center point orientation deviation parameter is: the center point orientation deviation parameter is the lower limit of the sum of the densities of the six types of geometrically necessary dislocations; Based on the energy dissipation criterion and combined with the relationship between the average center point orientation deviation parameter of the multiple grains and the average geometrically required dislocation density, a multi-scale state function with respect to the center point orientation deviation parameter is determined. Based on the dislocation accumulation mode and crack nucleation mechanism within grains and grain boundaries under creep-fatigue conditions, and combined with the multi-scale state function, the fatigue damage indicator factor and the creep damage indicator factor for each cycle are determined. Based on the linear damage accumulation criterion, and using the fatigue damage indicator factor and the creep damage indicator factor of each cycle, an energy-based crystallographic damage evolution equation is established. Based on the crystallographic damage evolution equation, the cycle period of mesoscopic crack nucleation in the material of the component under test is determined.

2. The engineering damage evolution evaluation method based on EBSD semi-quantitative analysis according to claim 1, characterized in that, Based on the linear damage accumulation criterion, and utilizing the fatigue damage indicator and the creep damage indicator, an energy-based crystallographic damage evolution equation is established, which then includes: Based on the crystallographic damage evolution equation and the in-situ creep-fatigue test characterized by EBSD, the center point orientation deviation parameter value and the EBSD orientation difference map of the material under test are determined. Based on the center point orientation deviation parameter value of the material under test and the EBSD orientation difference map of the material under test, multiple stages of mesoscopic crack nucleation are divided, and the macroscopic strain energy density and mesoscopic orientation difference parameter increment of each stage are calculated; the multiple stages include: initial stage, void incubation stage, crack nucleation stage, macroscopic crack initiation stage and creep-fatigue failure stage. Based on the macroscopic strain energy density and the mesoscopic orientation difference parameter increment at each stage, the fatigue damage rate, creep damage rate, and creep-fatigue damage rate at each stage are calculated.

3. The engineering damage evolution evaluation method based on EBSD semi-quantitative analysis according to claim 1, characterized in that, The relationship between the average orientation difference of the plurality of grains and the average geometrically required dislocation density is as follows: in, This is the average center point orientation deviation parameter for multiple grains. For the average geometry, the required dislocation density is ∝, which represents and They are in a direct proportional relationship.

4. The engineering damage evolution evaluation method based on EBSD semi-quantitative analysis according to claim 1, characterized in that, The multi-scale state function is: in, This is a multi-scale state function, where α is a scaling factor related to the scan step size, and β is a scaling factor related to the center point orientation deviation parameter analysis. This is the average center point orientation deviation parameter for multiple grains.

5. The engineering damage evolution evaluation method based on EBSD semi-quantitative analysis according to claim 1, characterized in that, The fatigue damage indicator factors for each cycle are: in, This represents the fatigue damage indicator for the i-th cycle at the mesoscale. Let be the fatigue strain energy density in the i-th cycle on a macroscopic scale. Let be the average orientation deviation parameter of the center point within the crystal during the i-th cycle. denoted as the net change in the average orientation deviation parameter of the intragranular and grain boundary centers during the i-th cycle, and l is a conversion coefficient independent of the cycle number.

6. The engineering damage evolution evaluation method based on EBSD semi-quantitative analysis according to claim 1, characterized in that, The creep damage indicator factors for each cycle are: in, This is the creep damage indicator for the i-th cycle at the mesoscale. Let be the creep strain energy density in the i-th cycle on a macroscopic scale. Let be the average orientation deviation parameter of the grain boundary center point in the i-th cycle. denoted as the net change in the average grain boundary center point orientation deviation parameter during the i-th cycle, and l is a conversion coefficient independent of the cycle number.

7. The engineering damage evolution evaluation method based on EBSD semi-quantitative analysis according to claim 1, characterized in that, The crystallographic damage evolution equation is as follows: in, For the cumulative creep-fatigue damage up to the j-th cycle, For the fatigue damage in the i-th cycle, For the creep damage in the i-th cycle, Let be the fatigue strain energy density in the i-th cycle on a macroscopic scale. Let be the creep strain energy density in the i-th cycle on a macroscopic scale. This is the critical fatigue strain energy density up to the final damage state. This is the critical creep strain energy density up to the final damage state. This represents the critical net change in the average center point orientation deviation parameter within the crystal until the final damaged state. This represents the critical net change in the average center point orientation deviation parameter of the grain boundary up to the final damaged state. Let be the average orientation deviation parameter of the center point within the crystal during the i-th cycle. Let be the average orientation deviation parameter of the grain boundary center point in the i-th cycle.

8. The engineering damage evolution evaluation method based on EBSD semi-quantitative analysis according to claim 1, characterized in that, The cycle period for mesoscopic crack nucleation in the material of the component under test is: Where, N n The cycle period for mesoscopic crack nucleation in the material of the component under test. For the cumulative creep-fatigue damage up to the j-th cycle, This represents the creep-fatigue damage in the i-th cycle.

9. The engineering damage evolution evaluation method based on EBSD semi-quantitative analysis according to claim 2, characterized in that, The macroscopic strain energy density is: Δw f =∫ N p:d p ; Δw c =∫ N p:d c ; Where, Δw f For macroscopic fatigue strain energy density, Δw c For macroscopic creep strain energy density, ε p For plastic strain, ε c σ represents creep strain, σ represents stress under external load, and N represents the number of cycles.

10. The engineering damage evolution evaluation method based on EBSD semi-quantitative analysis according to claim 2, characterized in that, The increment of the mesoscopic orientation difference parameter is: in, Let be the net change in the average orientation deviation parameter of the crystal center point during the i-th cycle. Let be the net change in the average grain boundary center point orientation deviation parameter during the i-th cycle. Let be the average orientation deviation parameter of the center point within the crystal during the i-th cycle. Let be the average orientation deviation parameter of the grain boundary center point in the i-th cycle. This represents the average orientation deviation parameter of the center point within the grain and at the grain boundary in the undeformed state. This is the average orientation deviation parameter of the grain boundary center point in the undeformed state.

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