CN109933820A - The creep incubation period prediction technique of the contained parameter unrelated with load is considered under elastic condition - Google Patents
The creep incubation period prediction technique of the contained parameter unrelated with load is considered under elastic condition Download PDFInfo
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Abstract
The invention discloses the creep incubation period prediction techniques that the contained parameter unrelated with load is considered under a kind of elastic condition to propose the creep incubation period prediction model for considering to restrain effect on the basis of Davies work.Using ductility exhaustion damage model, introduces contained parameter Q* unrelated with load and calculate the creep incubation period for considering to restrain effect.Apply main load using compact tensile specimen (CT) and carry out creep simulation experiment, beneficial effects of the present invention: succinctly can effectively predict under elastic condition creep incubation period in the structure.
Description
Technical field
The present invention relates to creep incubation period work of the thermal structure containing the contained parameter unrelated with load under elastic condition
Journey critical evaluation is exactly determined when, there are face crack and when being under the conditions of elastic stress, evaluating this thermal structure in structure
Creeping crack initiating life.
Background technique
Energy resource structure based on fire coal is one of the main reason of China's haze weather, and coal fired power generation be China at present most
Main generation mode, the trend is by long-term existence.Therefore, in addition to restructuring the use of energy, develop the ultra supercritical of high effect cleaning
(USC) unit is one of important channel of energy-saving and emission-reduction.However, the raising of vapor (steam) temperature and pressure and other parameters causes unit crucial
The Service Environment very severe of high-temperature pipe, it is various scarce that there are crackle, lack of penetration, weld blowhole and slag inclusions etc. especially in pipeline
It falls into, seriously threatens the safe operation of unit, need to carry out it accurate life appraisal of science.
In decades, for cracking member under high temperature, the development abroad review approach of a variety of high-temperature creep life-spans and
Method.Creep incubation period is the elapsed-time standards longest stage in creep process, and the Accurate Prediction of incubation period is for thermal structure
Creep life prediction is of great significance；The incubation period prediction model that Davies et al. is proposed based on toughness dissipation model considers
The integrality of creep process stress variation, but influence of the contained effect of structure to incubation period do not studied；It is close
Scientific research personnel has carried out a large amount of research for restraining influence of the effect to On Creep Crack Growth over year.Contained effect is widely deposited
It is in the high-temperature component fabricated, and significant impact is caused to the service life of component.It is compacted to be largely directed to high temperature
The research for restraining effect in the case of change is also unfolded extensively.Therefore the creep incubation period prediction model for considering to restrain effect is established, it can
With the more accurate creep incubation period for completely assessing Combined Loading structure.
Summary of the invention
The present invention proposes the creep incubation period prediction model for considering to restrain effect on the basis of Davies works.Benefit
With ductility exhaustion damage model, introduces the contained parameter Q* unrelated with load and calculate the creep incubation period for considering to restrain effect.
Apply main load using compact tensile specimen (CT) and carries out creep simulation experiment.
The technical solution adopted to achieve the purpose of the present invention is:
Containing the creep incubation period prediction technique of contained effect thermal structure, including following step under elastic condition of the invention
It is rapid:
S1: the creep incubation period prediction model under elastic condition containing contained effect thermal structure, including CT sample sheet are established
Body, the middle part front end of the CT sample ontology are equipped with slot, and the rear portion of slot is equipped with notch, slot, notch in the same plane, CT sample
It is additionally provided with main load pin hole, lower main load pin hole on ontology, upper main load pin hole, lower main load pin hole setting symmetrical above and below,
It is separately positioned on the upper and lower ends of slot；
S2: first indentation, there be inserted into precrack, precrack, slot, notch in the same plane, to carry out creep examination
It tests；
S3: apply main load in upper main load pin hole, lower main load pin hole using pin, carry out high-temerature creep test；
S4: calculating can be obtained by creep finite element modelling and joined containing necessity required for effect CT sample incubation period is restrained
Number, under elastic condition, calculating incubation period is mainly comprised the steps that
(2) the contained parameter Q under elastic condition is calculated first* K, its calculation formula is:
(I) in:It is the opening stress value at the crackle forward position obtained using FEM calculation, unit is Mpa, σ0It is
The yield strength of material, unit is MPa, referring to document: (Zhao L, Xu L, Han Y, Jing H.Two-parameter
characterization of constraint effect induced by specimen size on creep crack
growth.Engng Fract Mech 2012；96:251-66.), C* integral is the high temperature fracture obtained using FEM calculation
Parameter, unit are MPamm (h)-1, L is scalar distance, takes 1mm, InIt is dimensionless function related with n, occurrence can be with
Consulting literatures obtain: (Shih, C.F..1983.Tables of Hutchinson-Rice-Rosengren Singular
Field Quantities.Brown University Technical Report, MRL E-147.), n is nondimensional compacted
Varying stress hardenability value,It is creep strain change rate, unit h-1, related with material at high temperature creep attribute.N andReferring to text
It offers: (Zhao L, Jing H, Xu L, Han Y, Xiu J.Evaluation of constraint effects on creep
crack growth by experimental investigation and numerical simulation.Engng
Fract Mech 2012；96:251–66.)；
(I) in: σ22It is the opening stress value in the crackle forward position being calculated using elastic stress field, unit is MPa,
Wherein: r is spacing of the crackle rear portion tip to crackle forward position research point, and unit is mm, f22(θ) is related with θ
Dimensionless function, θ are crack tip angle, f22The occurrence of (θ) can be obtained with consulting literatures: Webster, G.A.,
1994.Fracture mechanics in the creep range.Journal of Strain Analysis for
Engineering Design 29,215–223.；
K is stress intensity factor, and unit is MPa (m)0.5, calculation formula:
Wherein: P is main load, unit N；B is sample thickness, unit mm；A/W is precrack length ratio, and a is
Precrack length, using the horizontal linear distance in the upper main load pin hole center of circle to precrack rear end, unit mm；W is name
Adopted specimen width, using the upper main load pin hole center of circle to the horizontal linear distance of CT sample ontology rear end, unit mm；f(a/W)
It is CT sample geometrical factor, it is only related with a/W；R is spacing of the crackle rear portion tip to crackle forward position research point, and unit is mm, θ
It is crack tip angle, f22(θ) is dimensionless function related with θ, and occurrence can be obtained with consulting literatures: Webster,
G.A.,1994.Fracture mechanics in the creep range.Journal of Strain Analysis
for Engineering Design 29,215–223.
(2) equivalent stress is calculatedUnit is MPa, its calculation formula is:
Wherein:It is dimensionless function related with θ, occurrence can be obtained with consulting literatures: Webster, G.A.,
1994.Fracture mechanics in the creep range.Journal of Strain Analysis for
Engineering Design 29,215–223.
(3) elastic stress time incubation period t off field is then calculatedi K, its calculation formula is:
(III) in: n is nondimensional creep stress hardenability value, εcritIt is uniaxial creep toughness, it is related with material properties,
Unit is 1,It is creep strain change rate, unit h-1, related with material at high temperature creep attribute.N, εcritWithReferring to text
It offers: (Zhao L, Jing H, Xu L, Han Y, Xiu J.Evaluation of constraint effects on creep
crack growth by experimental investigation and numerical simulation.Engng
Fract Mech 2012；96:251–66.)
(III) in: MSFKFor the Multiaxial stress factor under elastic condition, calculated according to Cocks and Ashby relational expression:
Wherein: n is nondimensional creep stress hardenability value, and sinh is hyperbolic sine function, hkFor three axis of elastic stress
Degree, under elastic stress state:
Wherein mean stressUnit is MPa, its calculation formula is:
Wherein: σ11,σ22And σ33It is the stress value in the crackle forward position obtained using K stress field calculation, unit is MPa,
Wherein: f11(θ), f22(θ), f33(θ) is dimensionless function related with θ, and θ is crack tip angle, f11(θ),
f22(θ), f33The occurrence of (θ) can be obtained with consulting literatures: Webster, G.A., 1994.Fracture mechanics in
the creep range.Journal of Strain Analysis for Engineering Design 29,215–223.
Preferably, the spacing r of crackle rear portion tip to crackle forward position research point, which takes d, d, is split when determining that creep germinating occurs
Creep impairment reaches 1 distance extended, the i.e. critical distance of creep germinating generation before point.
Preferably, d takes the crystallite dimension of research material.
Preferably, the finite element modelling carries out calculating simulation using ABAQUS6.14,The extraction of C* integrated value
Journey the following steps are included:
(3) finite element model for initially setting up the CT sample of main tensile load load, is arranged high in material properties module
The rigid of stretching pin and pin hole is arranged contact in mesh module grid division in the lower elastic creep parameters of temperature in module
Property contact, and be inserted into precrack in a model, set output parameter in analysis step module: stress value, fracture parameter C*
Tensile load and contained condition is arranged in integrated value in payload module: including symmetric condition and rigid condition,；
(4) task computation is submitted in operation module, obtains and contains creep stretching experiment calculated result, in destination file, from
The available stress value of field variableFracture parameter C* integrated value can be extracted from historical variable.
Compared with prior art, the beneficial effects of the present invention are:
The invention proposes creep incubation period prediction models under modified elastic condition, compared with existing model, the design
Method can expand to original prediction model in the model containing contained effect, thus under proposing the elastic condition of simplification a kind of
Creep incubation period prediction technique, therefore brief introduction effectively can be predicted under elastic condition creep incubation period in the structure.
Detailed description of the invention
Fig. 1 compact tensile specimen (CT) stretches schematic diagram；
Wherein: 1-CT sample ontology, the upper main load pin hole of 2-, 3- slot, 4- notch, 5- precrack, main load pin under 6-
Hole.
Fig. 2 creeping crack germinates critical condition schematic diagram；
Specific embodiment
The present invention is described in further detail below in conjunction with the drawings and specific embodiments.It should be appreciated that described herein
Specific embodiment be only used to explain the present invention, be not intended to limit the present invention.
Containing the creep incubation period prediction model of contained effect thermal structure under elastic condition of the invention, CT sample ontology 1,
The middle part front end of the CT sample ontology 1 is equipped with slot 3, and the rear portion of slot 3 is equipped with notch 4, is additionally provided with main load on CT sample ontology 1
Lotus pin hole 2, lower main load pin hole 6, upper main load pin hole 2, lower main about 6 load pin hole are correspondingly arranged, and are separately positioned on slot 3
Upper and lower ends；
P92 high-temperature refractory steel is chosen, with B=10mm, the CT sample of W=20mm, a/W=0.5 are as research object, with master
Load p=1200N is as research load.Its main material attribute see the table below:
Containing the creep incubation period prediction technique of contained effect thermal structure, including following step under elastic condition of the invention
It is rapid:
S1: first indentation, there be inserted into precrack, precrack, slot, notch in the same plane, to carry out creep examination
It tests；
S2: apply master in upper main load pin hole, lower main load pin hole using pin on the CT sample containing precrack
Load carries out high-temerature creep test；
S3: call parameter required for calculating CT sample incubation period can be obtained by crossing creep finite element modelling.In elastic strip
Under part, calculating incubation period is mainly comprised the steps that
(1) each parameter is calculated first:
(a) the contained parameter Q* under elastic conditionK:
(b) the main density of load factor of elasticity:
Following data are extracted by finite element result:
I. the finite element model for initially setting up the CT sample of main tensile load load, is arranged high temperature in material properties module
Under elastic creep parameters, in mesh module grid division, in the rigidity for contacting setting in module and stretching pin and pin hole
Contact, and it is inserted into precrack in a model, output parameter is set in analysis step module: stress value, fracture parameter C*.?
Tensile load and contained condition are set in payload module: including symmetric condition and rigid condition；
Ii. task computation is submitted in operation module, obtains and contains creep stretching experiment calculated result, in destination file, from
The available stress value of field variableFracture parameter C*=0.000666564MPa can be extracted from historical variable
mm h‐1.
(a) it tables look-up: f22The material parameter ε of (θ)=1, P92 steelcrit=0.2；N=11, calculate elastic stress and
When restraining, we take the distance r=d=0.05mm before splitting point.
The opening stress in crackle forward position:
(2) it tables look-up:
Equivalent stress:
(3) germinating occurred under elastic stress field is then calculated:
It tables look-up: f11(θ)=1, f33(θ)=0
Mean stress:
Three axis degree of stress:
The Multiaxial stress factor:
D (mm) is that creep impairment reaches 1 distance extended, i.e. creep germinating hair before determining to split point when creep germinating occurs
Raw critical distance generally takes the crystallite dimension of research material, as shown in Figure 2.
Elastic condition lower incubation period:
The above is only a preferred embodiment of the present invention, it is noted that for the common skill of the art
For art personnel, various improvements and modifications may be made without departing from the principle of the present invention, these improvements and modifications
Also it should be regarded as protection scope of the present invention.
Claims (4)
1. considering the creep incubation period prediction technique of the contained parameter unrelated with load under a kind of elastic condition, which is characterized in that
The following steps are included:
S1: the creep incubation period prediction model under elastic condition containing contained effect thermal structure, including CT sample ontology, institute are established
The middle part front end for stating CT sample ontology is equipped with slot, and the rear portion of slot is equipped with notch, slot, notch in the same plane, CT sample ontology
On be additionally provided with main load pin hole, lower main load pin hole, upper main load pin hole, lower main load pin hole setting symmetrical above and below, respectively
The upper and lower ends of slot are set；
S2: first indentation, there be inserted into precrack, precrack, slot, notch in the same plane, to carry out creep test；
S3: apply main load in upper main load pin hole, lower main load pin hole using pin, carry out high-temerature creep test；
S4: can obtain calculating by creep finite element modelling and contain call parameter required for restraining effect CT sample incubation period,
Under elastic condition, calculating incubation period is mainly comprised the steps that
(1) the contained parameter Q under elastic condition is calculated first* K, its calculation formula is:
(I) in:It is the opening stress value at the crackle forward position obtained using FEM calculation, unit is Mpa, σ0It is material
Yield strength, unit is MPa, and C* integral is the high temperature fracture parameter obtained using FEM calculation, unit MPamm
(h)-1, L is scalar distance, takes 1mm, InIt is dimensionless function related with n, n is nondimensional creep stress hardenability value,
It is creep strain change rate, unit h-1, related with material at high temperature creep attribute；
(I) in: σ22It is the opening stress value in the crackle forward position being calculated using elastic stress field, unit is MPa,
Wherein: r is spacing of the crackle rear portion tip to crackle forward position research point, and unit is mm, f22(θ) is related with θ immeasurable
Guiding principle function, θ are crack tip angles；
K is stress intensity factor, and unit is MPa (m)0.5, calculation formula:
Wherein: P is main load, unit N；B is sample thickness, unit mm；A/W is precrack length ratio, and a is prefabricated
Crack length, using the horizontal linear distance in the upper main load pin hole center of circle to precrack rear end, unit mm；W is nominal examination
Sample width, using the upper main load pin hole center of circle to the horizontal linear distance of CT sample ontology rear end, unit mm；F (a/W) is CT
Sample geometrical factor, it is only related with a/W；R is spacing of the crackle rear portion tip to crackle forward position research point, and unit is mm, and θ is to split
Line tip angle, f22(θ) is dimensionless function related with θ,
(2) equivalent stress is calculatedUnit is MPa, its calculation formula is:
Wherein:It is dimensionless function related with θ,
(3) elastic stress time incubation period t off field is then calculatedi K, its calculation formula is:
(III) in: n is nondimensional creep stress hardenability value, εcritIt is uniaxial creep toughness, unit related with material properties
It is 1,It is creep strain change rate, unit h-1, it is related with material at high temperature creep attribute,
(III) in: MSFKFor the Multiaxial stress factor under elastic condition, calculated according to Cocks and Ashby relational expression:
Wherein: n is nondimensional creep stress hardenability value, and sinh is hyperbolic sine function, hkFor three axis degree of elastic stress,
Under elastic stress state:
Wherein mean stressUnit is MPa, its calculation formula is:
Wherein: σ11,σ22And σ33It is the stress value in the crackle forward position obtained using K stress field calculation, unit is MPa,
Wherein: f11(θ), f22(θ), f33(θ) is dimensionless function related with θ, and θ is crack tip angle.
2. considering the creep incubation period prediction of the contained parameter unrelated with load under a kind of elastic condition as described in claim 1
Method, it is characterised in that: it is when determining that creep germinating occurs that the spacing r of crackle rear portion tip to crackle forward position research point, which takes d, d,
Creep impairment reaches 1 distance extended, the i.e. critical distance of creep germinating generation before splitting point.
3. considering the creep incubation period prediction of the contained parameter unrelated with load under a kind of elastic condition as claimed in claim 2
Method, it is characterised in that: d takes the crystallite dimension of research material.
4. considering the creep incubation period prediction of the contained parameter unrelated with load under a kind of elastic condition as described in claim 1
Method, it is characterised in that: the finite element modelling carries out calculating simulation using ABAQUS6.14,The extraction of C* integrated value
Process the following steps are included:
(1) finite element model for initially setting up the CT sample of main tensile load load, is arranged under high temperature in material properties module
Elastic creep parameters connect contacting the rigidity that setting stretches pin and pin hole in module in mesh module grid division
Touching, and it is inserted into precrack in a model, output parameter is set in analysis step module: stress value, fracture parameter C* integral
Value, is arranged tensile load and contained condition: including symmetric condition and rigid condition in payload module；
(2) task computation is submitted in operation module, obtains and contains creep stretching experiment calculated result, in destination file, become from field
Measure available stress valueFracture parameter C* integrated value can be extracted from historical variable.
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| CN111539144A (en) * | 2020-04-20 | 2020-08-14 | 中车青岛四方机车车辆股份有限公司 | Fracture toughness calculation method and system for crack-containing structural part |
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| CN111539144A (en) * | 2020-04-20 | 2020-08-14 | 中车青岛四方机车车辆股份有限公司 | Fracture toughness calculation method and system for crack-containing structural part |
| CN111539144B (en) * | 2020-04-20 | 2023-09-22 | 中车青岛四方机车车辆股份有限公司 | Fracture toughness calculation method and system for structural member containing cracks |
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