CN116735389A - Method for obtaining elastoplastic fatigue crack growth rate based on low-cycle fatigue test - Google Patents

Method for obtaining elastoplastic fatigue crack growth rate based on low-cycle fatigue test Download PDF

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Publication number
CN116735389A
CN116735389A CN202210202428.9A CN202210202428A CN116735389A CN 116735389 A CN116735389 A CN 116735389A CN 202210202428 A CN202210202428 A CN 202210202428A CN 116735389 A CN116735389 A CN 116735389A
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crack
obtaining
elastoplastic
growth rate
fatigue
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吴海利
余潇
吕健
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Shanghai Electric Power Generation Equipment Co Ltd
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Shanghai Electric Power Generation Equipment Co Ltd
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N3/32—Investigating strength properties of solid materials by application of mechanical stress by applying repeated or pulsating forces
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N2203/0001—Type of application of the stress
    • G01N2203/0005—Repeated or cyclic
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N2203/0058—Kind of property studied
    • G01N2203/006—Crack, flaws, fracture or rupture
    • G01N2203/0062—Crack or flaws
    • G01N2203/0066—Propagation of crack
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N2203/0058—Kind of property studied
    • G01N2203/0069—Fatigue, creep, strain-stress relations or elastic constants
    • G01N2203/0073—Fatigue
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N2203/0058—Kind of property studied
    • G01N2203/0069—Fatigue, creep, strain-stress relations or elastic constants
    • G01N2203/0075—Strain-stress relations or elastic constants

Abstract

The application discloses a method for acquiring an elastoplastic fatigue crack growth rate based on a low-cycle fatigue test, which belongs to the technical field of fatigue crack growth rate acquisition and comprises the steps of acquiring a crack depth a i Ratio a to sample diameter D i Ratio of/D to modulus E ui /E u0 Is a first calibration relation of (a); obtaining crack propagation rate da/dN; obtaining stress intensity factor delta K i Depth of crack a i A third calibration relation of (2); obtaining elastoplastic fracture toughness value DeltaJ i Calculating a relational expression; obtaining crack propagation rate da/dN and elastoplastic fracture toughness value delta J i Is a fitting formula of (2). The application can obtain the fatigue crack growth rate of the metal material in the elastoplastic state through the low-cycle fatigue test, breaks the limit that the existing fatigue crack growth test is only suitable for the linear elastic stress state and the positive stress ratio, solves the problem that the fatigue crack growth rate can not be tested in the elastoplastic state, and can be applied to the service life assessment and damage tolerance assessment of the ductile material under the action of higher load.

Description

Method for obtaining elastoplastic fatigue crack growth rate based on low-cycle fatigue test
Technical Field
The application relates to the technical field of obtaining of fatigue crack growth rate, in particular to a method for obtaining elastoplastic fatigue crack growth rate based on a low-cycle fatigue test.
Background
The engineering component material inevitably has or generates defects such as holes, scratches or damages in the production and processing processes and long-term operation, and the fatigue crack growth rate of the material is a key index for judging whether the defective component is safely operated. According to the standard GBT 6398-2017 metal material fatigue crack growth rate test method, the test sample is recommended to be a rectangular section sample with initial cracks, a lower alternating load is applied to the test sample, the gap opening displacement of the test sample is measured by using a COD (chemical oxygen demand) gauge, and the crack depth is calculated, so that the relation between the fatigue crack growth rate and the linear elastic stress intensity factor delta K is obtained. The relation between the standard crack depth and the notch opening displacement is obtained based on the calibration of the linear elastic strain state, and is suitable for the plane strain crack expansion state under lower load. For the ductile material, the plastic area of the crack tip of the material is increased under the action of higher load exceeding the yield strength, the requirement of small-range yield of the line elastic fracture mechanics is not met, the plane strain stress intensity factor delta K is not suitable for description, and no perfect test method exists for the fatigue crack expansion rate in the elastoplastic state.
Because the test samples bear crack growth caused by alternating load in the test process of low cycle fatigue and crack growth rate of the metal material, students at home and abroad conduct many researches on the correlation between low cycle fatigue behavior and crack growth rate, the method mainly focuses on establishing a prediction formula of linear elastic fatigue crack growth rate based on a plurality of fitting parameters of low cycle fatigue, the construction of the existing prediction formula usually neglects the difference of alternating load stress ratio, and the reliability of the estimation result is low. Moreover, low cycle fatigue generally adopts high load higher than yield strength, and whether the crack tip is in a large-range yield state or not can be equivalent to fatigue crack growth failure criteria based on a small-range yield stress strain field is controversial, so that a method for accurately acquiring the fatigue crack growth rate of a metal material in an elastoplastic state is not available at present.
Disclosure of Invention
In view of the above, the present application aims to provide a method for obtaining an elastoplastic fatigue crack growth rate based on a low cycle fatigue test, so as to solve the technical problem that the elastoplastic fatigue crack growth rate of a metal material cannot be obtained.
The technical scheme adopted by the application is as follows: a method for obtaining an elastoplastic fatigue crack growth rate based on a low cycle fatigue test for obtaining a fatigue crack growth rate of a metal material in an elastoplastic state, the method comprising the steps of:
obtaining crack initiation unloading elastic modulus E of low-cycle fatigue test u0 And tensile unloading modulus of elasticity E after crack initiation ui ；
Obtaining crack depth a i Ratio a to sample diameter D i Ratio of/D to modulus E ui /E u0 Is a first calibration relation of (a);
obtaining crack propagation rate da/dN;
obtaining the crack surface area S ci And sample cross-sectional area S 0 Ratio S of (2) i /S 0 Ratio of modulus E ui /E u0 A second calibration relation of (2);
obtaining stress intensity factor delta K i Depth of crack a i A third calibration relation of (2);
obtaining elastoplastic fracture toughness value DeltaJ i And stress intensity factor DeltaK i Area S of crack surface ci Cross-sectional area S of sample 0 And plastic area U pi Is a calculated relation of (2);
obtaining crack propagation rate da/dN and elastoplastic fracture toughness value delta J i Is a fitting formula of (2).
Preferably, the first calibration relation is:
wherein ,p0 ～p n And D is the diameter of the sample and is the calibration coefficient of the first calibration relation.
Preferably, the second calibration relation is:
wherein ,q0 ～q n The calibration coefficient is the second calibration relation, S 0 Is the original cross-sectional area of the sample.
Preferably, the third calibration relation is:
wherein ,Δf is a fatigue load range value, Δf=f max –F min ；S 0 Is the original cross-sectional area of the sample, D is the sample diameter, ">k 0 ～k n And the calibration coefficient is the calibration coefficient of the third calibration relation.
Preferably, 4+.n+.6.
Preferably, the calculation relation is:
wherein ,△Jei Is an elastic component, deltaJ pi Is a plastic component.
Preferably, the fitting formula is:
wherein C is a fitting coefficient, and m is a fitting index.
Preferably, the sample is a round bar sample; wherein the crack surface area S ci The calculation formula of (2) is as follows:
wherein ,Sc The surface area of the crack is that theta is the angle value of the central angle corresponding to the chord length of the crack, a is the length of the deepest part of the crack, 2c is the chord length of the crack intersecting with the surface of the sample, D is the diameter of the sample,
preferably, the sample for the low cycle fatigue test is a round bar sample; after the low cycle fatigue test is completed, the crack front is marked by a heating coloring method.
Preferably, the obtaining the crack growth rate da/dN specifically includes: calculating crack depth a corresponding to unloading elastic modulus of the low cycle fatigue i Drawing crack depth a i And cycle number N i The crack growth rate da/dN is obtained using a secant method or a polynomial method.
The application has the beneficial effects that:
according to the method, the fatigue crack expansion rate of the metal material in the elastoplastic state can be obtained through a low-cycle fatigue test, so that the test process is simplified, and the test cost can be reduced; the method is suitable for testing environments such as any strain ratio, high temperature and the like, breaks through the limitation that the existing fatigue crack expansion test is only suitable for linear elastic stress state and positive stress ratio, solves the problem that the fatigue crack expansion rate can not be tested in an elastoplastic state, can be applied to service life assessment and damage tolerance assessment of ductile materials under the action of higher load, and is particularly suitable for fatigue crack expansion service life assessment of round-section components.
Drawings
FIG. 1 is a schematic diagram of a semi-elliptical crack of a circular cross-section specimen of the present application;
FIG. 2 is a graph of tensile unloading modulus of elasticity versus cycle number for the present application;
FIG. 3 is a graph of crack depth versus cycle number for the present application;
FIG. 4 is a graph showing crack growth rate in an elastoplastic state of the present application.
Detailed Description
The following describes the embodiments of the present application in further detail with reference to the accompanying drawings. These embodiments are merely illustrative of the present application and are not intended to be limiting.
In the description of the present application, it should be noted that the terms "center", "longitudinal", "lateral", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, are merely for convenience in describing the present application and simplifying the description, and do not indicate or imply that the apparatus or elements referred to must have a specific orientation, be configured and operated in a specific orientation, and thus should not be construed as limiting the present application. Furthermore, the terms "first," "second," and the like, are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.
In the description of the present application, it should be noted that, unless explicitly specified and limited otherwise, the terms "mounted," "connected," and "connected" are to be construed broadly, and may be either fixedly connected, detachably connected, or integrally connected, for example; can be mechanically or electrically connected; can be directly connected or indirectly connected through an intermediate medium, and can be communication between two elements. The specific meaning of the above terms in the present application can be understood by those of ordinary skill in the art according to the specific circumstances.
Furthermore, in the description of the present application, unless otherwise indicated, the meaning of "a plurality" is two or more.
1-4, a method for obtaining an elastoplastic fatigue crack growth rate based on a low cycle fatigue test is used for obtaining the fatigue crack growth rate of a metal material in an elastoplastic state, and comprises the following steps:
obtaining crack initiation unloading elastic modulus E of low-cycle fatigue test u0 And tensile unloading modulus of elasticity E after crack initiation ui 。
Obtaining crack depth a i Ratio a to sample diameter D i Ratio of/D to modulus E ui /E u0 The first relation is:firstly, calculating crack depth a corresponding to each cycle in a low cycle fatigue test through a first calibration relation i By drawing the crack depth a i And cycle number N i To obtain a crack growth rate da/dN.
Obtaining the crack surface area S ci And sample cross-sectional area S 0 Ratio S of (2) i /S 0 Ratio of modulus E ui /E u0 The second calibration relation is:and calculating the crack surface area S corresponding to each cycle in the low cycle fatigue test through the second calibration relation ci 。
Obtaining stress intensity factor delta K i Depth of crack a i The third calibration relation of (2) is:and calculating the depth a of the crack in the low cycle fatigue test through the third calibration relation i Corresponding stress intensity factor DeltaK i 。
Obtaining elastoplastic fracture toughness value DeltaJ i And stress intensity factor DeltaK i Area S of crack surface ci Cross-sectional area S of sample 0 And plastic area U pi Is calculated by the following formula:and calculating the elastic-plastic fracture toughness value delta J corresponding to each cycle in the low-cycle fatigue test by a calculation relation i 。
Obtaining crack propagation rate da/dN and elastic moldingFracture toughness value DeltaJ i A power function fitting formula of (2), the power function fitting formula is:
according to the fatigue crack growth rate acquisition method, the fatigue crack growth rate of the metal material in the elastoplastic state can be acquired through a low-cycle fatigue test, so that the test process is simplified, and the test cost can be reduced; the fatigue crack growth rate acquisition method is suitable for testing environments such as any strain ratio, high temperature and the like, breaks through the limitation that the existing fatigue crack growth test is only suitable for linear elastic stress state and positive stress ratio, solves the problem that the fatigue crack growth rate can not be tested in an elastoplastic state, can be applied to service life assessment and damage tolerance assessment of a ductile material under the action of higher load, and is particularly suitable for fatigue crack growth service life assessment of a round-section component.
Example 1 as shown in fig. 1 to 4, a method for obtaining an elastoplastic fatigue crack growth rate based on a low cycle fatigue test for obtaining a fatigue crack growth rate of a metal material in an elastoplastic state, the method comprising the steps of:
s1: according to the low cycle fatigue test standard GBT 15248-2008 metal material axial constant amplitude low cycle fatigue test method, clamping extensometer on a round bar sample, clamping two ends of the sample on a fatigue testing machine, and controlling the strain amplitude to perform fatigue test until the preset load is reduced by a preset percentage or the sample breaks. During the whole test, the software records the corresponding maximum load F of each cycle max Minimum load F min Modulus of elasticity E for stretch releasing u And a hysteresis loop.
S2: as shown in FIG. 2, the tensile unloading elastic modulus E is plotted u And number of cycles N i E of (2) u -N i A curve; at E u -N i On the curve, the modulus of elasticity E of the low cycle fatigue test in the middle and late stage of stretching and unloading u Descending, selecting the cycle number at the beginning of descending as the crack initiation cycle number, and recording as N u0 Number of crack initiation cycles N u0 The corresponding tensile unloading elastic modulus was taken as the crack initiation elastic modulus, denoted E u0 The method comprises the steps of carrying out a first treatment on the surface of the Number of crack initiation cycles N u0 The tensile unloading elastic modulus corresponding to the previous cycle number is the tensile unloading elastic modulus before crack initiation and the crack initiation cycle number N u0 The tensile unloading elastic modulus corresponding to the number of the subsequent cycles is the tensile unloading elastic modulus after crack initiation and is marked as E ui 。
S3: calculation of tensile unloading elastic modulus E after crack initiation ui Modulus of elasticity E at crack initiation u0 Ratio E of (2) ui /E u0 。
S4: the test sample after the low cycle fatigue test is subjected to a heating coloring method for printing, and after the test sample is broken, the crack depth is measured; as shown in fig. 1, the crack surface shape of the low stress fatigue is generally a semi-oval shape, the length of the deepest crack is denoted as a, and the chord length at which the crack intersects the surface of the sample is denoted as 2c.
S5: obtaining crack depth a i Ratio a to sample diameter D i Ratio of/D to modulus E ui /E u0 The first relation is:for calculating crack depth a corresponding to each cycle in low cycle fatigue test i . Wherein, for round bar samples which are calibrated and have the same material and the same radial dimension, the calibration coefficient (p 0 ～p n ) For the fixed value, known calibration coefficients can be directly used; for the round bar sample calibrated for the first time, the specific calibration process is as follows:
the first calibration method comprises the following steps: taking n=5, referring to S1-S3, performing a low cycle fatigue test on a plurality of round bar samples with the same specification, and obtaining crack depth a corresponding to the last cycle of 5 round bar samples i And tensile unloading modulus of elasticity E after crack initiation ui Calculating to obtain a calibration coefficient p in the first calibration relation 0 ～p 5 。
The second calibration method comprises the following steps: taking n=5, referring to S1-S3, performing low cycle fatigue test on the round bar sample, and communicatingObtaining crack depth a corresponding to 5 cycles of the same round bar sample through finite element analysis i And tensile unloading modulus of elasticity E after crack initiation ui Calculating to obtain a calibration coefficient p in the first calibration relation 0 ～p 5 。
S6: calculating crack depth a corresponding to each cycle of the low cycle fatigue test according to the first calibration relation i The method comprises the steps of carrying out a first treatment on the surface of the As shown in fig. 3, for crack depth a i And cycle number N i An a-N relationship is plotted and a secant method or a polynomial method is used to obtain the crack growth rate da/dN.
S7: obtaining the crack surface area S ci And sample cross-sectional area S 0 Ratio S of (2) i /S 0 Ratio of modulus E ui /E u0 The second calibration relation is:for calculating the crack surface area S corresponding to each cycle in the low cycle fatigue test ci 。
Wherein, for round bar samples of the same material and the same radial dimension which have been calibrated, the calibration coefficient (q 0 ～q n 4.ltoreq.n.ltoreq.6) is a constant value, and known calibration coefficients can be used directly.
Wherein the calibration coefficient q 0 ～q n The calibration mode of (2) refers to the first calibration relation to calibrate the coefficient p 0 ～p n Is used for the calibration mode of the device.
In determining the calibration coefficient in the second relation, the crack surface area S ci The calculation formula of (2) is as follows:cross-sectional area S of sample 0 The calculation formula of (2) is as follows: />
wherein ,Sc The crack surface area, theta is the central angle corresponding to the crack chord length, D is the diameter of the sample,
s8: obtaining stress intensity factor delta K i Depth of crack a i The third relation is:for calculating the depth a of the crack in the low cycle fatigue test i Corresponding stress intensity factor DeltaK i 。
wherein ,Δf is a fatigue load range value, Δf=f max –F min ；S 0 Is the original cross-sectional area of the sample, D is the sample diameter, ">k 0 ～k n And the calibration coefficient is the calibration coefficient of the third calibration relation.
Wherein the calibration coefficient k 0 ～k n The calibration mode of (2) refers to the first calibration relation to calibrate the coefficient p 0 ～p n Is used for the calibration mode of the device.
S9: acquiring plastic area U surrounded by hysteresis loop corresponding to each cycle pi 。
S10: obtaining the elastic-plastic fracture toughness value delta J corresponding to each cycle i The calculation formula is as follows:
for calculating the elastic-plastic fracture toughness value DeltaJ corresponding to each cycle in the low-cycle fatigue test i 。
wherein ,△Jei Is an elastic component, deltaJ pi Is a plastic component.
S11: as shown in fig. 4, the crack depth propagation rate da i dN and elastoplastic fracture toughness value DeltaJ i Performing power function simulationAnd obtaining fitting parameters of crack growth rate and elastoplastic fracture toughness value:
wherein C is a fitting coefficient, and m is a fitting index.
1-4, a method for obtaining an elastoplastic fatigue crack growth rate based on a low cycle fatigue test, the method comprising the steps of:
s1: round bar sample processing was performed on the test material, with a sample diameter d=8 mm. Clamping an extensometer on the round bar sample for controlling and measuring the strain quantity; and (3) mounting the round bar sample holding the extensometer on a fatigue testing machine, performing triangular wave waveform fatigue test on the sample by using strain control, wherein the strain ratio is-1, the strain amplitude is +/-0.4%, and running the fatigue test until failure and fracture occur. In the present embodiment, the failure number N f Sample material was 30Cr2Ni4MoV alloy with elastic modulus e=202 GPa and yield strength R at room temperature =6424 times p0.2 =810 MPa, tensile strength R m ＝910Mpa。
S2: during the low cycle fatigue test, software is used to record the corresponding maximum load F of each cycle max Minimum load F min Modulus of elasticity E for stretch unloading u And a hysteresis loop.
S3: as shown in FIG. 2, the tensile unloading elastic modulus E is plotted u And number of cycles N i E of (2) u -N i A curve. At E u -N i On the curve, the modulus of elasticity E of the fatigue test in the middle and late stage of stretching and unloading u Descending, selecting the cycle number at the beginning of descending as the crack initiation cycle number and recording as N u0 In the present embodiment, N u0 =4860 times; number of crack initiation cycles N u0 The corresponding tensile unloading elastic modulus is the crack initiation elastic modulus and is marked as E u0 In the present embodiment, E u0 ＝186900MPa。
S4: counting the number of crack initiation cycles N u0 After crack initiation and pull-upModulus of elasticity E under load and unload ui Modulus of elasticity E at crack initiation u0 Ratio E of (2) ui /E u0 。
S5: according to the crack depth a i Ratio a to sample diameter D i Ratio of/D to modulus E ui /E u0 Is a first calibration relation of (2)Calculating crack depth a corresponding to each cycle in low cycle fatigue test i 。
S6: as shown in FIG. 3, the crack depth a is plotted i And cycle number N i And obtaining the crack growth rate da/dN by using a secant method or a polynomial method.
S7: according to the crack surface area S ci And sample cross-sectional area S 0 Ratio S of (2) i /S 0 Ratio of modulus E ui /E u0 Is a second calibration relation of (2)Calculating crack surface area S corresponding to each cycle in low cycle fatigue test ci 。
S8: according to stress intensity factor DeltaK i Depth of crack a i Third calibration relation of (2)Calculating the depth a of the crack in the low cycle fatigue test i Corresponding stress intensity factor DeltaK i 。
S9: calculation of the plastic region area U using a test software program pi And is directly obtained from the test data list.
S10: according to the elastoplastic fracture toughness value DeltaJ i Calculation formulaCalculating the elastic-plastic fracture toughness value delta J corresponding to each cycle i 。
S11: as shown in fig. 4, the crack depth propagation rate da i dN and elastoplastic fracture toughness value DeltaJ i Performing power function fitting to obtain fitting parameters of crack propagation rate and elastoplastic fracture toughness value:
wherein c= 9.178 ×10 -20 KJ/m 2 M=8.091, effective range da/dN e (5×10) -4 ～5×10 -3 )。
The foregoing is merely a preferred embodiment of the present application, and it should be noted that modifications and substitutions can be made by those skilled in the art without departing from the technical principles of the present application, and these modifications and substitutions should also be considered as being within the scope of the present application.

Claims (10)

1. A method for obtaining an elastoplastic fatigue crack growth rate based on a low cycle fatigue test for obtaining a fatigue crack growth rate of a metal material in an elastoplastic state, the method comprising the steps of:
obtaining crack initiation unloading elastic modulus E of low-cycle fatigue test u0 And tensile unloading modulus of elasticity E after crack initiation ui ；
Obtaining crack depth a i Ratio a to sample diameter D i Ratio of/D to modulus E ui /E u0 Is a first calibration relation of (a);
obtaining crack propagation rate da/dN;
obtaining the crack surface area S ci And sample cross-sectional area S 0 Ratio S of (2) i /S 0 Ratio of modulus E ui /E u0 A second calibration relation of (2);
obtaining stress intensity factor delta K i Depth of crack a i A third calibration relation of (2);
obtaining elastoplastic fracture toughness value DeltaJ i And stress intensity factor DeltaK i Area S of crack surface ci Cross-sectional area S of sample 0 And plastic areaU pi Is a calculated relation of (2);
obtaining crack propagation rate da/dN and elastoplastic fracture toughness value delta J i Is a fitting formula of (2).
2. The method for obtaining an elastoplastic fatigue crack growth rate based on a low cycle fatigue test according to claim 1, wherein the first calibration relation is:
wherein ,p0 ～p n And the calibration coefficient is the calibration coefficient of the first calibration relation.
3. The method for obtaining an elastoplastic fatigue crack growth rate based on a low cycle fatigue test according to claim 1, wherein the second calibration relation is:
wherein ,q0 ～q n And the calibration coefficient is the calibration coefficient of the second calibration relation.
4. The method for obtaining an elastoplastic fatigue crack growth rate based on a low cycle fatigue test according to claim 1, wherein the third calibration relation is:
wherein ,Δf is a fatigue load range value, Δf=f max –F min ；k 0 ～k n And the calibration coefficient is the calibration coefficient of the third calibration relation.
5. The method for obtaining an elastoplastic fatigue crack growth rate based on a low cycle fatigue test according to any of claims 2-4, wherein 4+.n+.6.
6. The method for obtaining an elastoplastic fatigue crack growth rate based on a low cycle fatigue test according to claim 1, wherein the calculated relationship is:
wherein ,△Jei Is an elastic component, deltaJ pi Is a plastic component.
7. The method for obtaining an elastoplastic fatigue crack growth rate based on a low cycle fatigue test according to claim 1, wherein the fitting formula is:
wherein C is a fitting coefficient, and m is a fitting index.
8. The method for obtaining an elastoplastic fatigue crack growth rate based on a low cycle fatigue test according to claim 1, wherein the specimen is a round bar specimen; wherein the crack surface area S ci The calculation formula of (2) is as follows:
wherein ,Sc The crack surface area, θ is the angle value of the central angle corresponding to the chord length of the crack, a is the length of the deepest part of the crack, and 2c is the crack and the angle value of the central angleThe chord length of the intersection of the sample surfaces, D is the sample diameter,
9. the method for obtaining an elastoplastic fatigue crack growth rate based on a low cycle fatigue test according to claim 1, wherein the sample of the low cycle fatigue test is a round bar sample; after the low cycle fatigue test is completed, the crack front is marked by a heating coloring method.
10. The method for obtaining an elastoplastic fatigue crack growth rate based on a low cycle fatigue test according to claim 1, wherein the obtaining the crack growth rate da/dN specifically comprises: calculating crack depth a corresponding to unloading elastic modulus of each cycle of the low cycle fatigue test i Drawing crack depth a i And cycle number N i The crack growth rate da/dN is obtained using a secant method or a polynomial method.
CN202210202428.9A 2022-03-03 2022-03-03 Method for obtaining elastoplastic fatigue crack growth rate based on low-cycle fatigue test Pending CN116735389A (en)

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