CN108731989B - Creep induction period prediction method containing residual stress under plastic transient creep condition - Google Patents

Creep induction period prediction method containing residual stress under plastic transient creep condition Download PDF

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CN108731989B
CN108731989B CN201710271738.5A CN201710271738A CN108731989B CN 108731989 B CN108731989 B CN 108731989B CN 201710271738 A CN201710271738 A CN 201710271738A CN 108731989 B CN108731989 B CN 108731989B
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徐连勇
邬栋权
荆洪阳
韩永典
赵雷
吕小青
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Tianjin University
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Abstract

The invention discloses a creep induction period prediction method containing residual stress under a plastic transient creep condition, which provides a creep induction period prediction model considering the residual stress, introduces an elastic following factor Z to calculate the creep induction period considering the residual stress by using a reference stress method, generates the residual stress by pre-compressing a compact tensile sample (CT), and applies a main load to perform a creep experiment, and has the beneficial effects that: the corrected creep induction period prediction model under the elastic transient creep condition is provided, so that a simplified creep induction period prediction method under the transient creep condition is provided, and the creep induction period under the elastic transient creep condition can be simply and effectively predicted in the structure.

Description

Creep induction period prediction method containing residual stress under plastic transient creep condition
Technical Field
The invention relates to a creep induction period engineering critical evaluation of a high-temperature structure containing residual stress under a plastic transient creep condition, which is to evaluate the creep crack initiation life of the high-temperature structure when a surface crack exists in the structure and the structure is under the plastic transient creep condition.
Background
The energy structure mainly based on coal burning is one of the main causes of haze weather in China, and coal burning power generation is the most main power generation mode in China at present, and the trend exists for a long time. Therefore, besides changing the energy structure, the development of a high-efficiency clean Ultra Supercritical (USC) unit is one of the important ways of energy conservation and emission reduction. However, the service environment of the key high-temperature pipeline of the unit is very severe due to the improvement of parameters such as steam temperature, steam pressure and the like, and particularly, various defects such as cracks, incomplete penetration, welding pores, slag inclusion and the like exist in the pipeline, so that the safe operation of the unit is seriously threatened, and scientific and accurate service life evaluation needs to be carried out on the unit.
For decades, various high temperature creep life assessment criteria and methods have been developed abroad for crack-containing components at high temperatures. The creep induction period is the longest period in the creep process, and the accurate prediction of the induction period has great significance for predicting the creep life of a high-temperature structure; an incubation period prediction model provided by Davies et al based on a toughness dissipation model considers the integrity of stress change in a creep process, but the influence of structural residual stress on the incubation period is not researched; residual stresses are widely present in process-manufactured high temperature components and have a significant impact on the service life of the component. A large number of studies have been widely conducted on the residual stress (residual stress) in the case of high-temperature creep. Therefore, a creep induction period prediction model considering the residual stress is established, and the creep induction period of the composite loading structure can be more accurately and completely evaluated.
Disclosure of Invention
On the basis of Davies work, the invention provides a creep induction period prediction model considering residual stress. By utilizing a reference stress method, an elastic following factor Z is introduced to calculate a creep induction period considering residual stress. Creep experiments were performed using compact tensile specimens (CT) to generate residual stress by precompression and applying a main load.
The technical scheme adopted for realizing the purpose of the invention is as follows:
the method for predicting the creep induction period containing residual stress under the plastic transient creep condition comprises the following steps:
s1: establishing a model: the model comprises a CT sample body, wherein a groove is formed in the front end of the middle of the CT sample body, a notch is formed in the rear part of the groove, an upper main load pin hole and a lower main load pin hole are further formed in the CT sample body, and the upper main load pin hole and the lower main load pin hole are arranged up and down correspondingly and are respectively arranged at the upper end and the lower end of the groove;
s2, firstly, the upper round pin and the lower round pin are used for carrying out compression loading with a preset size on the upper end and the lower end of the CT sample body, and then the upper round pin and the lower round pin are released, so that residual stress distribution can be generated near the notch of the CT sample body;
s3, inserting a prefabricated crack at the notch containing the residual stress to perform a creep test;
s4, applying main loads to the upper main load pin hole and the lower main load pin hole by using the pins, and performing a high-temperature creep test;
s5: the necessary parameters needed for calculating the induction period of the CT sample containing residual stress can be obtained through creep finite element simulation, under the condition of plastic transient creep, as shown in figure 4, the initial stress of a research point is in a plastic stress state, and the transition time t is reachedHRR-RRThen entering a transient creep stress state, and calculating the incubation period mainly comprises the following steps:
(1) firstly, calculating a stress intensity factor under composite loading, wherein the calculation formula is as follows:
Figure GDA0002230099720000021
in (I):
Figure GDA0002230099720000022
Figure GDA0002230099720000023
wherein:
Figure GDA0002230099720000024
is a stress intensity factor under the simulation calculation and only contains residual stress, and the unit is MPa (m)1/2)；
Figure GDA0002230099720000025
Is the main load stress intensity factorIn units of MPa (m)1/2) (ii) a P is the primary load in N; b is the thickness of the specimen in mm, BnIs the net thickness of the sample (B in this application)nB) in mm; a/W is the length ratio of the prefabricated crack, a is the length of the prefabricated crack, and the horizontal straight line distance from the center of the upper main load pin hole to the rear end of the prefabricated crack is adopted, and the unit is mm; w is the nominal sample width, and the horizontal linear distance from the circle center of the upper main load pin hole to the rear end of the CT sample body is adopted, and the unit is mm; f (a/W) is the geometric coefficient of the CT sample and is only related to a/W; v is a dimensionless plastic related term calculated as follows:
Figure GDA0002230099720000026
in (II) V0Is a non-dimensional parameter, and the parameter is,
Figure GDA0002230099720000027
Figure GDA0002230099720000028
is a plastic residual stress intensity factor with the unit of MPa (m)1/2)；
Figure GDA0002230099720000029
Is a stress intensity factor under the simulation calculation and only contains residual stress, and the unit is MPa (m)1/2)，
Figure GDA00022300997200000210
Using JSCalculation, JSIs the fracture parameter under the residual stress field, and the unit is MPa.m:
Figure GDA00022300997200000211
wherein: e' is the effective modulus of elasticity: e ═ E/(1-v)2) Where E is the modulus of elasticity, v is the poisson's ratio, and both E and v are described in the literature: (Zhao L, sting H, Xu L, Han Y, Xiu J. evaluation of related effects on crack growth by experimental instigation and numericalsimulation.Engng Fract Mech 2012；96:251–66.)，
Figure GDA00022300997200000212
And JSExtracting by using finite element simulation results;
in (II) LrIs a dimensionless parameter describing the main load amplitude:
Figure GDA00022300997200000213
wherein: sigmayIs the yield strength in MPa, see literature: (ZHao L, lacing H, Xu L, Han Y, XiuJ. evaluation of contract effects on crop grow growth by experiment simulation and numerical simulation. Engng frame Mech 2012; 96: 251-66.);
Figure GDA0002230099720000031
is the main load reference stress in MPa, calculated by the following formula:
Figure GDA0002230099720000032
wherein: n isLFor dimensionless crack aspect ratio parameters, the following is calculated:
Figure GDA0002230099720000033
constant number
Figure GDA0002230099720000034
(II):
Figure GDA0002230099720000035
wherein:
Figure GDA0002230099720000036
is the main load stress intensity factorIn units of MPa (m)1/2)，
Figure GDA0002230099720000037
Is a plastic main load stress intensity factor with the unit of MPa (m)1/2)；
Figure GDA0002230099720000038
Calculating by using a finite element simulation result:
β describes the amplitude of residual stress, which is a dimensionless parameter;
Figure GDA0002230099720000039
Figure GDA00022300997200000310
the unit is MPa, and finite element simulation calculation is utilized;
in the step (II), Z is a dimensionless elastic following factor, a stress-strain relation is extracted from a finite element simulation result, and an equivalent creep strain increment is taken
Figure GDA00022300997200000311
Equivalent elastic strain increment
Figure GDA00022300997200000312
The ratio of (A) to (B):
Figure GDA00022300997200000313
(2) and calculating the integral value of C under the steady-state creep composite stress field, wherein the calculation formula is as follows:
Figure GDA00022300997200000314
wherein A is creep hardening coefficient in MPa-n·h-1See, a: (Zhao L, sting H, Xu L, Han Y, Xiu J. evaluation of relationship effects on seed crack growth by yexperiment information and numberical simulation.Engng Fract Mech 2012；96:251–66.)，KIIs a composite stress intensity factor with the unit of MPa (m)1/2)。
Figure GDA00022300997200000315
Is the initial reference stress in MPa;
Figure GDA00022300997200000316
(3) then the conversion time tHRR-RRThe calculation formula is as follows:
Figure GDA0002230099720000041
in (III), σP0Is the normalized stress in units of MPa,. epsilonP0Is the normalized strain with the unit of 1, α is the strain hardening coefficient, N is the strain hardening index, σP0，εP0α and N are described in Zhao L, Xu L, Han Y, Jing H.two-parameter characterization of constrained effective by specific size one crack growth. Engng Fract Mech 2012; 96: 251-66.).
Figure GDA0002230099720000042
Is the creep strain rate of change in units of h-1In relation to the high temperature creep properties of the material, see literature: (ZHao L, lacing H, Xu L, Han Y, XiuJ. evaluation of contract effects on crop grow growth by experiment simulation and numerical simulation. Engng frame Mech 2012; 96: 251-66.); tau is redistribution time with unit h, extracted from finite element, n is dimensionless creep stress hardening index, In is dimensionless function related to n, specific values of n and In can be obtained by consulting literature: (Shih, C.F. 1983.Tables of Hutchinson-Rice-Rosengren Single Field Technical Report, MRL E-147),
Figure GDA0002230099720000043
is a dimensionless function related to theta and n,
Figure GDA0002230099720000044
is a dimensionless function related to theta and N,
Figure GDA0002230099720000045
and
Figure GDA0002230099720000046
the literature can be consulted to obtain: (Shih, C.F. 1983.Tables of Hutchinson-Rice-Rosenggren Single field Technical Report, MRL E-147.)
d is the extended distance of the creep damage before the crack tip reaches 1 when the creep initiation occurs, and the unit is mm, namely the critical distance of the creep initiation;
(4) finally, the incubation period time t under the condition of plastic transient creepi HRR-RRThe calculation formula is as follows:
Figure GDA0002230099720000047
(IV) in the following steps: epsiloncritIs uniaxial creep toughness, related to material properties, in units of 1, see literature: (ZHao L, string H, Xu L, Han Y, Xiu J. evaluation of relationship effects on crop blackgrowth by experimental initiation and numerical simulation. Engng FractMech 2012; 96: 251-66.), MSFRRThe multiaxial stress factor under transient creep conditions was calculated according to the relationship of Cocks and Ashby:
Figure GDA0002230099720000048
wherein: sinh is a hyperbolic sine function, hRRThree degrees for steady state creep stress, at steady state creep state:
Figure GDA0002230099720000049
theta is the crack tip angle in degrees and n is dimensionlessThe creep stress-hardening index of the steel,
Figure GDA00022300997200000410
and
Figure GDA00022300997200000411
is a dimensionless function related to θ and n, and specific values can be found in literature (Shih, C.F..1983.Tables of Hutchinson-Rice-Rosensgren Single Field quantities. Brown university technical Report, MRL E-147.);
(IV) in the following steps:
Figure GDA00022300997200000412
is the damage value accumulated in the bolerous stress phase:
Figure GDA0002230099720000051
wherein: c (t) is the integral value of the load loop in MPa mm (h) reflecting the transient creep process-1) And calculating by using a reference stress method:
Figure GDA0002230099720000052
(V) in: sigmarefIs the total reference stress in MPa, calculated using the following integral equation:
Figure GDA0002230099720000053
wherein:
Figure GDA0002230099720000054
is the total reference strain rate in units of h-1，
Figure GDA0002230099720000055
Is the primary load reference strain rate in units of h-1，
Figure GDA0002230099720000056
(V) in: epsilonrefIs the total reference strain, calculated using the formula:
Figure GDA0002230099720000057
wherein:
Figure GDA0002230099720000058
is the initial reference strain to which the strain is given,
Figure GDA0002230099720000059
and extracting through finite element simulation.
Preferably, d is the grain size of the material under investigation.
Preferably, Bn＝B。
Preferably, the finite element simulation is a computational simulation using ABAQUS6.14,
Figure GDA00022300997200000510
τ、ε0 refand the extraction process of Z comprises the following steps:
(5) firstly, establishing a finite element model of a pre-compressed loaded CT sample, setting elastic-plastic parameters in a material property module, setting compression load in a load module, and setting a constraint condition: including symmetric conditions and fixed conditions. The contact module is internally provided with a compression round pin which is in rigid contact with the upper surface and the lower surface of the sample, and the analysis step module is internally provided with output parameters: stress value, dividing grids in the grid module;
(6) the task calculation is submitted in the operation module to obtain the calculation result of the residual stress, and the secondary load reference stress sigma can be directly extracted from the field variable in the result fileref S；
(7) Establishing a sample model with the same size, carrying out a main load tensile test, setting elastic-plastic creep parameters at high temperature in a material property module, dividing grids in a grid module, setting rigid contact between a tensile pin and a pin hole in a contact module, inserting a prefabricated crack in the model, and setting output parameters in an analysis step module: stress strain value, stress intensity factor K value, rupture parameter J integral value set up tensile load in the load module to and restrain the condition: the method comprises the steps of (1) introducing the calculated residual stress into a preloading stress field under a symmetrical condition and a fixed condition;
(8) submitting task calculation in the operation module to obtain the calculation result of the creep-tensile experiment containing residual stress, and acquiring initial reference strain epsilon from field variables when tensile load is not applied after cracks are inserted in a result file0 refThe elastic residual stress intensity factor can be obtained from historical variables
Figure GDA0002230099720000061
And residual stress rupture parameter JSAt the initial moment of applying the tensile load, the plastic main load strength factor can be obtained
Figure GDA0002230099720000062
Extracting the change curve of C (t) along with time from the historical variables, taking the time of the stable moment as the redistribution time tau, obtaining the change curve of the equivalent stress along with the total strain increment from the historical variables, and obtaining the equivalent creep strain increment from the curve
Figure GDA0002230099720000063
Increment of equivalent elastic strain
Figure GDA0002230099720000064
Thereby obtaining the elastic tracking factor Z.
Compared with the prior art, the invention has the beneficial effects that:
compared with the existing model, the design method can expand the original prediction model into the model containing residual stress, so that the simplified prediction method of the creep induction period under the transient creep condition is provided, and the creep induction period under the elastic transient creep condition can be simply and effectively predicted in the structure.
Drawings
FIG. 1 is a schematic illustration of a compact tensile specimen (CT) precompression;
wherein: 1-upper round pin, 2-CT sample body, 3-upper main load pin hole, 4-groove, 5-notch, 6-prefabricated crack, 7-lower main load pin hole and 8-lower round pin.
FIG. 2 is a schematic representation of critical conditions for creep crack initiation.
Fig. 3 is a stress-strain relationship curve.
FIG. 4 initial stress to transient creep transition time.
Detailed Description
The invention is described in further detail below with reference to the figures and specific examples. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
In this example, a CT sample of P92 high temperature heat resistant steel, B20 mm, W40 mm, and a/W0.5, was selected as a study object, and a preload of 12000N and a main load P12000N were selected as study loads. The main material properties are given in the following table:
Figure GDA0002230099720000065
wherein E-16 is the power of-16 of 10.
The method for predicting the creep induction period containing residual stress under the plastic transient creep condition comprises the following steps:
s1: a model as shown in fig. 1 was established: the model comprises a CT sample body 2, wherein a groove 4 is formed in the front end of the middle of the CT sample body 2, a notch 5 is formed in the rear portion of the groove 4, an upper main load pin hole 3 and a lower main load pin hole 7 are further formed in the CT sample body 1, and the upper main load pin hole 3 and the lower main load pin hole 7 are arranged in a vertically corresponding mode and are respectively arranged at the upper end and the lower end of the groove 4;
s2, firstly, the upper round pin 1 and the lower round pin 8 are used for carrying out compression loading on the CT sample body 2 with a preset size, and then the upper round pin 1 and the lower round pin 8 are released, so that a certain residual stress distribution is generated near the gap 5 of the CT sample body 2;
s3, inserting the prefabricated crack 6 at the notch containing the residual stress, wherein the groove 4, the notch 5 and the prefabricated crack 6 are on the same plane to perform a creep test;
s4, applying main loads to the upper main load pin hole 3 and the lower main load pin hole 7 by using the pins, and performing a high-temperature creep test;
s5: the necessary parameters needed for calculating the induction period of the CT sample containing residual stress can be obtained through creep finite element simulation, under the condition of plastic transient creep, as shown in figure 4, the initial stress of a research point is in a plastic stress state, and the transition time t is reachedHRR-RRAnd then entering a transient creep stress state.
The finite element simulation adopts ABAQUS6.14 to carry out calculation simulation, sigmaref S、
Figure GDA0002230099720000071
JS、
Figure GDA0002230099720000072
τ、ε0 refAnd the extraction process of Z comprises the following steps:
first, a finite element model of a pre-compressed loaded CT specimen as shown in fig. 1 is built, elasto-plastic parameters are set in a material property model, a compression load is set in a load model, and constraint conditions are set: including symmetric conditions and fixed conditions. The contact module is internally provided with a compression round pin which is in rigid contact with the upper surface and the lower surface of the sample, and the analysis step module is internally provided with output parameters: stress value, dividing grids in the grid module;
(ii) submitting task calculation in the operation module to obtain the calculation result of residual stress, and in the result file, directly extracting the secondary load reference stress from the field variable
Figure GDA0002230099720000073
(iii) establishing a sample model shown in FIG. 1, carrying out a main load tensile test, setting elastic-plastic creep parameters at high temperature in a material property module, dividing grids in a grid module, setting rigid contact between a tensile pin and a pin hole in a contact module, inserting a prefabricated crack in the model, and setting output parameters in an analysis step module: stress strain value, stress intensity factor K value, rupture parameter J integral value set up tensile load in the load module to and restrain the condition: the method comprises the steps of (1) introducing the calculated residual stress into a preloading stress field under a symmetrical condition and a fixed condition;
(iv) submitting task calculation to the operation module to obtain a calculation result of a creep-tensile experiment containing residual stress, wherein in a result file, when no tensile load is applied after the crack is inserted, and when no tensile load is applied after the crack is inserted, the initial reference strain epsilon can be obtained from the field variables0 refFrom the historical variables, 4.414386, the elastic residual stress intensity factor can be obtained
Figure GDA0002230099720000074
And residual stress rupture parameter JSThe plastic residual stress intensity factor can be calculated as 0.013MPa · m:
Figure GDA0002230099720000075
at the initial moment of applying the tensile load, the plastic main load strength factor can be obtained
Figure GDA0002230099720000076
Extracting the change curve of C (t) along with time from the historical variables, as shown in FIG. 4, taking the time of the stable moment in the curve as the redistribution time tau, obtaining the change curve of the equivalent stress along with the increment of the total strain from the historical variables, as shown in FIG. 3, and obtaining the increment of the equivalent creep strain from the curve
Figure GDA0002230099720000081
Increment of equivalent elastic strain
Figure GDA0002230099720000082
Further, the elastic tracking factor Z was obtained as 4.2.
The method for calculating the induction period mainly comprises the following steps:
(1) first, each parameter is calculated:
(a) elastic main load strength factor:
Figure GDA0002230099720000083
Figure GDA0002230099720000084
(b) main load reference stress:
Figure GDA0002230099720000085
Figure GDA0002230099720000086
(c) amplitude of main load:
Figure GDA0002230099720000087
Figure GDA0002230099720000088
(d) residual stress reference stress:
Figure GDA0002230099720000089
magnitude of residual stress:
Figure GDA00022300997200000810
(e) elastic following factor:
Figure GDA00022300997200000811
Figure GDA00022300997200000812
Figure GDA00022300997200000813
(f) plastic related terms:
Figure GDA00022300997200000814
Figure GDA00022300997200000815
(2) therefore, the stress intensity factor under composite loading
Figure GDA0002230099720000091
Initial reference stress:
Figure GDA0002230099720000092
the integral value of C under the steady-state creep composite stress field is as follows:
Figure GDA0002230099720000093
j integral value under composite loading:
Figure GDA0002230099720000094
(3) the conversion time t is then calculatedK-RR：
(a) And (6) looking up a table to obtain:
Figure GDA0002230099720000095
In＝4.99，
Figure GDA0002230099720000096
the material parameter n of P92 steel is 5.23,
Figure GDA0002230099720000097
εcrit＝0.2；N＝11,
Figure GDA0002230099720000098
IN＝4.49。
the redistribution time τ is 27.9047h.
Figure GDA0002230099720000099
Stress triaxial degree:
Figure GDA00022300997200000910
multiaxial stress factor:
Figure GDA00022300997200000911
Figure GDA00022300997200000912
damage value accumulated during plastic stress phase:
Figure GDA00022300997200000913
(4) the incubation period time under the plastic transient creep condition is as follows:
Figure GDA00022300997200000914
the foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.

Claims (3)

1. The prediction method of creep induction period containing residual stress under the condition of plastic transient creep is characterized by comprising the following steps: the method comprises the following steps:
s1: establishing a model: the model comprises a CT sample body, wherein a groove is formed in the front end of the middle of the CT sample body, a notch is formed in the rear part of the groove, an upper main load pin hole and a lower main load pin hole are further formed in the CT sample body, and the upper main load pin hole and the lower main load pin hole are arranged up and down correspondingly and are respectively arranged at the upper end and the lower end of the groove;
s2, firstly, the upper round pin and the lower round pin are used for carrying out compression loading with a preset size on the upper end and the lower end of the CT sample body, and then the upper round pin and the lower round pin are released, so that residual stress distribution can be generated near the notch of the CT sample body;
s3, inserting a prefabricated crack at the notch containing the residual stress to perform a creep test;
s4, applying main loads to the upper main load pin hole and the lower main load pin hole by using the pins, and performing a high-temperature creep test;
s5: necessary parameters required for calculating the induction period of the CT sample containing residual stress can be obtained through creep finite element simulation, under the condition of plastic transient creep, the initial stress of a research point is in a plastic stress state, and the transition time t is reachedHRR-RRThen entering a transient creep stress state, and calculating the incubation period mainly comprises the following steps:
(1) firstly, calculating a stress intensity factor under composite loading, wherein the calculation formula is as follows:
Figure FDA0002422106570000011
in (I):
Figure FDA0002422106570000012
Figure FDA0002422106570000013
wherein:
Figure FDA0002422106570000014
is a stress intensity factor under the simulation calculation and only contains residual stress, and the unit is MPa (m)1/2)；
Figure FDA0002422106570000015
Is the main load stress intensity factor with the unit of MPa (m)1/2) (ii) a P is the primary load in N; b is the thickness of the specimen in mm, BnIs the net thickness of the sample, BnB in mm; a/W is the length ratio of the prefabricated crack, a is the length of the prefabricated crack, and the horizontal straight line distance from the center of the upper main load pin hole to the rear end of the prefabricated crack is adopted, and the unit is mm; w is the nominal sample width, and the horizontal linear distance from the circle center of the upper main load pin hole to the rear end of the CT sample body is adopted, and the unit is mm; f (a/W) is the geometric coefficient of the CT sample and is only related to a/W; v is a dimensionless plastic related term calculated as follows:
Figure FDA0002422106570000016
in (II) V0Is a non-dimensional parameter, and the parameter is,
Figure FDA0002422106570000017
Figure FDA0002422106570000018
is a plastic residual stress intensity factor with the unit of MPa (m)1/2)；
Figure FDA0002422106570000019
Is a stress intensity factor under the simulation calculation and only contains residual stress, and the unit is MPa (m)1/2)，
Figure FDA00024221065700000110
Using JSCalculation, JSIs the fracture parameter under the residual stress field, and the unit is MPa.m:
Figure FDA0002422106570000021
wherein: e' is the effective modulus of elasticity: e ═ E/(1-v)2) E is the modulus of elasticity, v is the Poisson's ratio,
Figure FDA0002422106570000022
and JSExtracting by using finite element simulation results;
in (II) LrIs a dimensionless parameter describing the main load amplitude:
Figure FDA0002422106570000023
wherein: sigmayIs the yield strength in MPa;
Figure FDA0002422106570000024
is the main load reference stress in MPa, calculated by the following formula:
Figure FDA0002422106570000025
wherein: n isLFor dimensionless crack aspect ratio parameters, the following is calculated:
Figure FDA0002422106570000026
constant number
Figure FDA0002422106570000027
(II):
Figure FDA0002422106570000028
wherein:
Figure FDA0002422106570000029
is the main load stress intensity factor with the unit of MPa (m)1/2)，
Figure FDA00024221065700000210
Is a plastic main load stress intensity factorIn the order of MPa (m)1/2)；
Figure FDA00024221065700000211
Calculating by using a finite element simulation result:
β describes the amplitude of residual stress, which is a dimensionless parameter;
Figure FDA00024221065700000212
Figure FDA00024221065700000213
the unit is MPa, and finite element simulation calculation is utilized;
in the step (II), Z is a dimensionless elastic following factor, a stress-strain relation is extracted from a finite element simulation result, and an equivalent creep strain increment is taken
Figure FDA00024221065700000214
Equivalent elastic strain increment
Figure FDA00024221065700000215
The ratio of (A) to (B):
Figure FDA00024221065700000216
(2) and calculating the integral value of C under the steady-state creep composite stress field, wherein the calculation formula is as follows:
Figure FDA00024221065700000217
wherein A is creep hardening coefficient in MPa-n·h-1，KIIs a composite stress intensity factor with the unit of MPa (m)1 /2)，
Figure FDA00024221065700000218
Is the initial reference stress in MPa;
Figure FDA0002422106570000031
(3) then the conversion time tHRR-RRThe calculation formula is as follows:
Figure FDA0002422106570000032
in (III), σP0Is the normalized stress in units of MPa,. epsilonP0Is the normalized strain in units of 1, α is the strain hardening coefficient, N is the strain hardening exponent,
Figure FDA0002422106570000033
is the creep strain rate of change in units of h-1Tau is redistribution time in units of h extracted from finite elements, n is dimensionless creep stress hardening index, InIs a non-dimensional function related to n,
Figure FDA0002422106570000034
is a dimensionless function related to theta and n,
Figure FDA0002422106570000035
d is the extended distance of the creep damage before the crack tip reaches 1 when the creep initiation occurs, and the unit is mm, namely the critical distance of the creep initiation;
(4) finally, the incubation period time t under the condition of plastic transient creepi HRR-RRThe calculation formula is as follows:
Figure FDA0002422106570000036
(IV) in the following steps: epsiloncritIs uniaxial creep toughness, related to material properties, and has a unit of 1, MSFRRMultiaxial stress factor for transient creep conditions, according to Cocks and AshbyCalculating the equation:
Figure FDA0002422106570000037
wherein: sinh is a hyperbolic sine function, hRRThree degrees for steady state creep stress, at steady state creep state:
Figure FDA0002422106570000038
theta is the crack tip angle in degrees, n is the dimensionless creep stress hardening exponent,
Figure FDA0002422106570000039
and
Figure FDA00024221065700000310
is a dimensionless function related to θ and n;
(IV) in the following steps:
Figure FDA00024221065700000311
is the damage value accumulated in the bolerous stress phase:
Figure FDA00024221065700000312
wherein: c (t) is the integral value of the load loop in MPa mm (h) reflecting the transient creep process-1) And calculating by using a reference stress method:
(V) in: sigmarefIs the total reference stress in MPa, calculated using the following integral equation:
Figure FDA0002422106570000041
wherein:
Figure FDA0002422106570000042
is the total reference strain rate in units of h-1，
Figure FDA0002422106570000043
Figure FDA0002422106570000044
Is the primary load reference strain rate in units of h-1，
Figure FDA0002422106570000045
(V) in: epsilonrefIs the total reference strain, calculated using the formula:
εref＝ε0 ref+A∫σn refdt
wherein: epsilon0 refIs the initial reference strain, ε0 refAnd extracting through finite element simulation.
2. The method of claim 1, wherein the method comprises the step of predicting creep induction period with residual stress under plastic transient creep conditions, wherein the creep induction period is as follows: d takes the grain size of the material under study.
3. The method of claim 1, wherein the method comprises the step of predicting creep induction period with residual stress under plastic transient creep conditions, wherein the creep induction period is as follows: the finite element simulation was computationally simulated using ABAQUS6.14,
Figure FDA0002422106570000046
JS、
Figure FDA0002422106570000047
τ、ε0 refand the extraction process of Z comprises the following steps:
(1) firstly, establishing a finite element model of a pre-compressed loaded CT sample, setting elastic-plastic parameters in a material property module, setting compression load in a load module, and setting a constraint condition: including symmetry condition and fixed condition, set up the rigid contact of compression round pin and sample upper and lower surface in the contact module, set up output parameter in the analysis step module: stress value, dividing grids in the grid module;
(2) the task calculation is submitted in the operation module to obtain the calculation result of the residual stress, and the secondary load reference stress can be directly extracted from the field variables in the result file
Figure FDA0002422106570000048
(3) Establishing a sample model with the same size, carrying out a main load tensile test, setting elastic-plastic creep parameters at high temperature in a material property module, dividing grids in a grid module, setting rigid contact between a tensile pin and a pin hole in a contact module, inserting a prefabricated crack in the model, and setting output parameters in an analysis step module: stress strain value, stress intensity factor K value, rupture parameter J integral value set up tensile load in the load module to and restrain the condition: the method comprises the steps of (1) introducing the calculated residual stress into a preloading stress field under a symmetrical condition and a fixed condition;
(4) submitting task calculation in the operation module to obtain the calculation result of the creep-tensile experiment containing residual stress, and acquiring initial reference strain epsilon from field variables when tensile load is not applied after cracks are inserted in a result file0 refThe stress intensity factor under only residual stress of the simulation calculation can be obtained from the historical variables
Figure FDA0002422106570000049
And residual stress rupture parameter JSAt the initial moment of applying the tensile load, the stress intensity factor of the plastic main load can be obtained
Figure FDA00024221065700000410
From historical variablesExtracting the change curve of C (t) along with time, taking the time of stable time as redistribution time tau, obtaining the change curve of equivalent stress along with total strain increment from historical variables, and obtaining the equivalent creep strain increment from the curve
Figure FDA00024221065700000411
Increment of equivalent elastic strain
Figure FDA00024221065700000412
Thereby obtaining the elastic tracking factor Z.
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