CN114647914A - Creep curve construction and parameter fitting method and computer equipment - Google Patents

Creep curve construction and parameter fitting method and computer equipment Download PDF

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CN114647914A
CN114647914A CN202011499863.XA CN202011499863A CN114647914A CN 114647914 A CN114647914 A CN 114647914A CN 202011499863 A CN202011499863 A CN 202011499863A CN 114647914 A CN114647914 A CN 114647914A
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creep
temperature
curve
stress
strain
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杨玫
吴德龙
窦英睿
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AECC Commercial Aircraft Engine Co Ltd
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    • G06—COMPUTING; CALCULATING OR COUNTING
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    • G06F2119/04—Ageing analysis or optimisation against ageing
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    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F2119/00—Details relating to the type or aim of the analysis or the optimisation
    • G06F2119/08—Thermal analysis or thermal optimisation
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    • G06—COMPUTING; CALCULATING OR COUNTING
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Abstract

The invention provides a creep curve construction and parameter fitting method and computer equipment, wherein the creep curve construction method comprises the steps of obtaining real creep curves under different temperature stresses; performing linear interpolation on the real creep curve, finding the time corresponding to the specified creep strain, and obtaining the temperature, the stress and the service life under the specified creep strain, wherein the linear interpolation adopts the nearby interpolation; fitting stress, temperature and service life to obtain a service life equation under different creep strains; and determining the temperature and the stress according to the original material test data, calculating the creep life corresponding to each creep strain at the specified temperature and stress by using the life equation, setting the abscissa as time and the ordinate as creep strain, and obtaining a calculated curve which is the constructed creep curve for analysis at different temperatures and stresses. And performing constitutive model parameter fitting by using the creep curve to obtain constitutive input of materials required by simulation analysis.

Description

Creep curve construction and parameter fitting method and computer equipment
Technical Field
The invention relates to a high-temperature material creep deformation prediction method and system, in particular to a high-temperature material creep curve construction method and computer equipment.
Background
The creep phenomenon inevitably exists in the spare part of aeroengine long-term work in high temperature environment, need carry out creep analysis to high temperature part in the course of the work, and material creep curve is the essential factor of creep analysis. The material creep curve typically comprises a time-strain curve at different temperatures and different stresses. A group of model constitutive parameters can be fitted through a plurality of curves, the absolute temperature K, the stress and the time are variables during fitting, and when the square of a fitting correlation coefficient is greater than 80%, the creep parameters can be used with good fitting effect. When the square of the correlation coefficient is less than 80%, a temperature fitting curve is required, and each temperature corresponds to one group of creep parameters.
Because the parameters of the intermediate temperature are linearly interpolated in the finite element software, the creep strain amount of the intermediate temperature is larger than that of the high temperature, so that the analysis is not converged, and the temperature interval of the creep parameters of the material needs to be as small as possible to ensure that the calculated result is closer to the reality. Meanwhile, the temperature distribution gradient of some parts is large, high-temperature and low-temperature loads exist at the same time, the lowest temperature is lower than 40% of the melting point of the material, and creep calculation is carried out on the low-temperature area in the finite element software according to the input lowest temperature parameter, so that the creep amount can be calculated at the position where creep does not occur. The actual material test only has 3-4 groups of temperatures, the temperature interval can reach 100 ℃, and the analysis requirement cannot be met, so that a curve required by analysis needs to be constructed by using a creep curve obtained by the test and parameter fitting needs to be carried out.
Disclosure of Invention
The invention aims to provide a creep curve constructing method, which utilizes a creep curve obtained by testing to construct a curve required by analysis. A creep parameter fitting method is also provided, based on the aforementioned curve.
Another object of the invention is to provide a computer device which implements the method by means of a computer program.
To achieve the object, a creep curve constructing method includes the following steps:
acquiring real creep curves under different temperature stresses;
performing linear interpolation on the real creep curve, finding the time corresponding to the specified creep strain, and obtaining the temperature, the stress and the service life under the specified creep strain, wherein the linear interpolation adopts the nearby interpolation;
fitting stress, temperature and service life to obtain a service life equation under different creep strains; and
determining temperature and stress according to original material test data, calculating creep life corresponding to each creep strain under set temperature and stress by using the life equation, setting the abscissa as time and the ordinate as creep strain, and obtaining a calculated curve which is an analysis creep curve constructed under different temperatures and stresses.
In one embodiment, the creep life equation is a classical Larson-Miller life equation.
In one embodiment, the analytical creep curve is constructed with a temperature interval of no more than 5 ℃ and the temperature is extended toward cryogenic temperatures to 35% of the melting point temperature of the material, referenced to the material test curve temperature range.
In one embodiment, the relationship between the maximum stress S value and the temperature T at different temperatures is as follows:
Figure BDA0002843287240000021
wherein, TLFor the material test the minimum temperature, SLFor testing the highest stress at this temperature, THTest the maximum temperature, S, for the materialHThe highest stress was tested for this temperature.
In one embodiment, at least 3 stress levels are taken at the same temperature with a stress interval of no more than 20 MPa.
The creep parameter fitting method for achieving the purpose comprises the creep curve construction method and further comprises the step of obtaining creep constitutive model parameters by using the analysis creep curve fitting at different temperatures.
In one embodiment, the constitutive model required for computational analysis is adopted for the high-temperature material as
Figure BDA0002843287240000022
Respectively fitting according to temperature, wherein the independent variables are stress sigma and time t, and the dependent variable is creep strain epsiloncrAnd respectively taking natural logarithms at two sides of the equation of the constitutive model, performing linear regression on natural logarithm values according to the analysis creep curve, and converting the parameters after regression analysis to obtain constitutive parameters required by calculation at different temperatures.
In an embodiment, the creep curve construction method further comprises a step of verifying a creep law, wherein the step of verifying the constitutive parameters verifies the change relation of creep strain along with temperature under the same stress and time, the creep strain should be gradually increased along with the rise of the temperature, and if the change relation of the creep strain along with the temperature is incorrect, the creep curve is calculated according to a re-fitting life equation, and the analysis creep curve is carried out.
To achieve the above object, a computer device includes a memory, a processor, an input device, and a computer program stored in the memory and executable on the processor according to the input of the input device, wherein the processor implements the creep curve constructing method or the creep parameter fitting method when executing the program.
The stress life equation under different strains is obtained by processing the actual material test curve, the life of reaching the specified creep strain under different temperatures is obtained by calculation, and the creep deformation curve under certain temperature stress is obtained. Therefore, the creep curve meeting the requirements as much as possible is formed by utilizing the limited test curve and extending and constructing according to the stress life equation, the accuracy of the calculation result is ensured, and the material test requirements and the cost are reduced.
The material creep curve usually comprises time-strain curves at different temperatures and under different stresses, a group of model constitutive parameters are fitted through a plurality of curves, the fitting effect is poor, a temperature fitting curve is required to be divided, and each temperature corresponds to a group of creep constitutive parameters. The creep curve under multi-temperature and multi-stress meeting the analysis requirements is constructed by utilizing the actually measured finite creep curve of the material, and the step of verifying the creep rule is added in the optimized step, so that the creep strain is ensured to be increased along with the rise of the temperature, and the condition that the finite element analysis is not converged due to the error of the creep rule is avoided.
In addition, in a preferred embodiment, the structural curve is extended to low temperature, and the creep behavior is not calculated at the part of the structure below the limit of the melting point of the material through parameter setting, so that the error of the calculation result of the finite element is avoided.
And the real creep curve is input or the data of the real creep curve is constructed through a computer automatic processing operation system, so that parameters for direct calculation are obtained, and the working efficiency is improved.
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The above and other features, properties and advantages of the present invention will become more apparent from the following description of the embodiments with reference to the accompanying drawings, in which:
FIG. 1 is a flow chart of a creep curve construction method.
FIG. 2 is a flow chart of the operation of the creep curve configuration.
Detailed Description
As shown in FIG. 1, the creep parameter fitting method comprises a creep curve constructing method, the creep curve constructing method comprises steps 101 to 104, and the creep parameter fitting method further combines steps 105 and 106 to calculate constitutive parameters at different required temperatures on the basis of the constructed analysis creep curve.
In step 101, the process begins by recording the material grade, the usage standard, and the melting point temperature range. The material generally refers to a high-temperature material, or a material which can bear certain stress under the temperature condition of more than 550 ℃ and has oxidation resistance and hot corrosion resistance, such as high-temperature alloy and ceramic material.
In step 102, the raw data of the material test is processed to obtain a real creep curve, for example, the total strain measured in the creep test is converted into creep strain, and the creep strain at a time is obtained by subtracting the strain value at 0 from the strain at a certain time. And performing linear interpolation on the real creep curves under different temperature stresses, finding the time corresponding to the specified creep strain, obtaining the temperature, the stress and the service life (time) under the specified creep strain, and adopting the nearby interpolation for the linear interpolation. One interpolation algorithm is:
Figure BDA0002843287240000041
wherein: ε is creep strain, t is time, i is an integer, ti，ti+1，εi，εi+1Creep strain and time, respectively, near ε, t. Creep strain equal spacing was selected, for example: 0.01%, 0.02%. 0.2%.
In step 103, a creep life equation is fitted. The time obtained by the linear interpolation in the step 102 is the creep life when the set temperature and stress are applied under the strain, and the life equation under different creep strains can be obtained by fitting the stress, the temperature and the life. In one embodiment, the creep life equation uses the classical Larson-Miller life equation: p ═ T (lg (T) + CC)/105And t is creep life;
Figure BDA0002843287240000042
theta is the temperature, CC is the material constant, and the value here is 20; p is Larson-Miller parameter, and is related to stress, and the relationship can be obtained by parameter fitting, and linear and polynomial can be used. Such as the relation P ═ C1+C2X+.....+CjXj-1Is a polynomial of degree (j-1), where X ═ lg (σ) and σ is the stress. And according to the fitting effect, selecting a proper integer j, wherein when j is 2, the linear fitting is carried out. If step 102 obtains m creep strains, then step 103 may obtain m life equations.
In step 104, a creep curve is constructed, the temperature and stress are determined according to the original material test data, and the creep life corresponding to each creep strain at a specified temperature and stress is calculated by using the life equation obtained in step 103, for example, the temperature is theta1Stress of σ1Substituting into the lifetime equation obtained in step 103, P can be obtained1And T1Then, the creep life corresponding to 0.01% strain can be calculated as t1Step 103 obtains m lifetime equations, and step 104 obtains m creep lifetimes, i.e., time. Setting the abscissa as time, the ordinate as creep strain, and the ordinate sorting from small to large according to strain to obtain a curveCreep curves at different temperatures and stresses. When the curve is constructed, the temperature interval is 5 ℃ or not higher than 5 ℃, the temperature range of the curve is tested by referring to the material, and the temperature is extended to 35% of the melting point temperature of the material towards low temperature; the relationship between the maximum stress values and the temperature at different temperatures is as follows:
Figure BDA0002843287240000051
wherein, TLFor the material test the minimum temperature, SLFor testing the highest stress at this temperature, THTest the maximum temperature, S, for the materialHThe highest stress was tested for this temperature.
At least 3 stress levels are taken at the same temperature, and the stress interval is 20MPa or not higher than 20 MPa.
In step 105, creep constitutive model parameters are fitted, and the creep curve fitting at different temperatures obtained in step 104 is used to obtain the creep constitutive model parameters. For example, corresponding to a class of high-temperature materials, the constitutive model required by computational analysis is adopted as follows:
Figure BDA0002843287240000052
when the respective fitting is performed according to the temperature, the independent variables are stress sigma and time t, and the dependent variable is creep strain epsiloncrAnd respectively taking natural logarithm to the constitutive model to obtain:
ln(εcr)＝ln(C1)+C2ln(σ)+(C3+1)ln(t)-C4/T-ln(C3+1)，
when fitting separately according to temperature, the coefficient of temperature term C in the formula4Is 0. The strain, stress and time data at the single temperature in step 104 is taken to be natural logarithms. Wherein the dependent variable is ln (epsilon)cr) The independent variables are ln (σ) and ln (t), according to the formula y ═ const + a1x1+a2x2Linear regression was performed. Then the relationship between the two sets of parameters is:
C3＝a2-1
C2＝a1，
C1＝exp(const+ln(a2))
fitting result a1、a2Const is converted according to the parameter relation to obtain parameter C1—C3Can be directly applied in the finite element model. The temperature distribution gradient of some parts is large, high-temperature and low-temperature loads exist at the same time, the lowest temperature is lower than 40% of the melting point of the material, and creep calculation is carried out on a low-temperature region in the finite element software according to the lowest temperature parameter, so that the creep amount can be calculated at the position where creep does not occur. Therefore, the creep behavior is not calculated when the curve is constructed by controlling the part 35% lower than the melting point of the material. By assigning a temperature of (35% T)meltWhen-1), C10 and the remaining parameters and temperature are 35% TmeltThe same is true.
In step 106, a creep law is verified, creep model parameters obtained in step 105 need to be verified, the relation of creep strain changing with temperature is verified under the same stress and time, and the creep strain should be gradually increased along with the increase of temperature. If the relation of creep strain changing along with temperature is incorrect, the step 103 is returned to select a proper relation of P and stress to re-fit the life equation. If the creep strain is correctly related to the temperature variation, the process proceeds to step 107.
In step 107, the process ends, and the parameters obtained in step 105 are input into the finite element analysis software for engineering analysis.
And constructing a multi-temperature multi-stress creep curve meeting the analysis requirement based on the actually measured limited creep curve of the material by utilizing the steps.
And based on the analysis creep curve or the creep parameters, the problem that the creep strain amount at the middle temperature is larger than that at the high temperature possibly existing in finite element analysis can be solved, and the creep strain amount is ensured to be increased along with the temperature rise.
The method also solves the problem that the creep calculation is carried out in a low-temperature area in the finite element according to the input lowest temperature parameter, a construction curve is extended to low temperature, and the creep behavior is not calculated at a position which is controlled to be 35 percent lower than the melting point of the material through the parameter.
The steps can design a computer automatic processing program by using a programming language, realize the input of the original creep curve of the material, and obtain the creep constitutive parameters for calculation.
A computer device comprises a memory, a processor, an input device and a computer program stored on the memory and capable of running on the processor according to the input of the input device, as shown in FIG. 2, the computer program 202 comprises 4 units of a material creep curve processing unit 301, a creep life equation fitting unit 302, a creep curve member unit 303, a creep model parameter fitting unit 304, etc., which respectively correspond to steps 102 and 106 in FIG. 1, wherein step 304 corresponds to steps 105 and 106 in FIG. 1 and the content thereof circulating to step 103. To obtain raw material data at input 201, the method includes: material grade, use standard, melting point temperature range, test stress range. The output 203 is a parameter output, mainly a constitutive parameter obtained based on the flow of fig. 1 and directly used for finite element calculation analysis.
Although the present invention has been disclosed in terms of the preferred embodiment, it is not intended to limit the invention, and variations and modifications may be made by one skilled in the art without departing from the spirit and scope of the invention. Therefore, any modifications, equivalent changes and modifications made to the above embodiments according to the technical essence of the present invention are within the scope of the present invention defined by the claims.

Claims (9)

1. A creep curve constructing method, comprising:
acquiring real creep curves under different temperature stresses;
performing linear interpolation on the real creep curve, finding the time corresponding to the specified creep strain, and obtaining the temperature, the stress and the service life under the specified creep strain, wherein the linear interpolation adopts the nearby interpolation;
fitting the stress, the temperature and the service life to obtain a service life equation under different creep strains; and
determining temperature and stress according to original material test data, calculating creep life corresponding to each creep strain under set temperature and stress by using the life equation, setting the abscissa as time and the ordinate as creep strain, and obtaining a calculated curve which is an analysis creep curve constructed under different temperatures and stresses.
2. The method of claim 1 wherein the creep age equation is a classical Larson-Miller age equation.
3. The method of claim 1 wherein said analytical creep curve formation is conducted at a temperature interval of no more than 5 ℃ and the temperature is extended toward cryogenic temperatures to 35% of the melting point temperature of the material, with reference to the material test curve temperature range.
4. A method of constructing a creep curve according to claim 3, wherein the maximum stress S at different temperatures is related to the temperature T by the equation:
Figure FDA0002843287230000011
wherein, TLFor the material test the minimum temperature, SLFor testing the highest stress at this temperature, THTest the maximum temperature, S, for the materialHThe highest stress was tested for this temperature.
5. The creep curve construction method of claim 1, wherein at least 3 stress levels are taken at the same temperature and the stress interval is not higher than 20 MPa.
6. A creep parameter fitting method comprising the creep curve construction method according to any one of claims 1 to 5, further comprising obtaining creep constitutive model parameters using the analytical creep curve fitting at different temperatures.
7. Creep according to claim 6The parameter fitting method is characterized in that the constitutive model required by calculation and analysis is adopted for the high-temperature material
Figure FDA0002843287230000021
When the respective fitting is performed according to the temperature, the independent variables are stress sigma and time t, and the dependent variable is creep strain epsiloncrAnd respectively taking natural logarithms on two sides of the equation of the constitutive model, performing linear regression on natural logarithm values according to the analysis creep curve, and converting parameters after regression analysis to obtain constitutive parameters required by calculation at different temperatures.
8. The creep parameter fitting method according to claim 6, further comprising a step of verifying a creep rule, which is to verify the constitutive parameters, verify a change relationship of creep strain with temperature under the same stress and time, and gradually increase creep strain with the increase of temperature, and if the change relationship of creep strain with temperature is incorrect, perform the creep curve construction method by re-fitting a life equation and calculating the analysis creep curve.
9. A computer apparatus comprising a memory, a processor, an input device and a computer program according to the input of the input device and stored on the memory and executable on the processor, wherein the processor when executing the program implements a creep curve construction method according to any one of claims 1 to 5 or a creep parameter fitting method according to claim 6 or 7 or 8.
CN202011499863.XA 2020-12-17 2020-12-17 Creep curve construction and parameter fitting method and computer equipment Pending CN114647914A (en)

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