CN112926236A - High-temperature tensile test and high-temperature rheological damage model construction method for powder metallurgy material - Google Patents

High-temperature tensile test and high-temperature rheological damage model construction method for powder metallurgy material Download PDF

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CN112926236A
CN112926236A CN202110115316.5A CN202110115316A CN112926236A CN 112926236 A CN112926236 A CN 112926236A CN 202110115316 A CN202110115316 A CN 202110115316A CN 112926236 A CN112926236 A CN 112926236A
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郭彪
李强
张羽
李肖
简杰
敖进清
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Abstract

The invention discloses a high-temperature tensile test and high-temperature rheological damage model construction method of a powder metallurgy material, which combines finite element simulation with Gleeble high-temperature tensile test of the powder metallurgy material, measures tensile stress and strain data of a relatively uniform middle temperature section of a high-temperature tensile sample of the powder metallurgy material in the high-temperature tensile process, eliminates negative effects of temperature gradient generated when the Gleeble testing machine heats the tensile sample, determines critical fracture strain of the powder metallurgy material in the high-temperature tensile process, establishes a critical fracture strain model and a rheological stress constitutive model of the high-temperature tensile of the powder metallurgy material, further constructs a powder metallurgy material high-temperature rheological damage model coupling deformation temperature, strain rate, strain and stress, and performs appropriate correction to improve the accuracy of the damage model. The damage model is suitable for the optimization design of hot working processes and dies related to iron-based, aluminum-based, copper-based, titanium-based, magnesium-based and other powder metallurgy materials, can accurately predict damage cracking of the powder metallurgy materials in the hot working process, has good stability, and can be applied to the high-temperature plastic working processes and the computer aided design of the dies of the iron-based, aluminum-based, copper-based, titanium-based, magnesium-based and other powder metallurgy materials.

Description

High-temperature tensile test and high-temperature rheological damage model construction method for powder metallurgy material
Technical Field
The invention belongs to the field of high-temperature plastic processing engineering of powder metallurgy materials, and particularly relates to a powder metallurgy material high-temperature rheological damage model construction method suitable for hot processing technologies such as hot forging, hot rolling, hot extrusion, hot drawing and the like of iron-based, aluminum-based, copper-based, titanium-based, magnesium-based and other powder metallurgy materials and for optimal design of a die.
Background
The high-temperature rheological damage model of the powder metallurgy material is a mathematical model representing the dependency relationship between damage accumulation and stress, strain rate and temperature in the hot processing process of the powder metallurgy material, reflects the processability of the powder metallurgy material, and is a necessary basis for developing the computer aided design of hot processing processes (including forging, rolling, extruding, drawing and the like) of the powder metallurgy material and a die. However, the high-temperature rheological damage of the powder metallurgy material during the hot working process is closely related to the stress-temperature-speed-deformation state, and is difficult to directly measure in the actual hot working process with complex and dynamic state change. The ability of powder metallurgy Materials to resist fracture due to high temperature rheological damage has been reported in the literature using high temperature compression testing [ Guoai He, Feng Liu, Lan Huang, Liang jiang. analysis of forming cracks during hot compression of powder metallurgy Materials and advanced Engineering Materials, 2016; 18(10) 1823-32. R.Seetharam, S.Kanmani Subbu, M.J.Davidson.Hot work and discovery floor of found powder metals Al-B4C for compressing lubricating up. journal of Manufacturing Processes, 2017; 309-18. Qinyang ZHao, Fei Yang, Rob Torrens, Leando Bolzoni. company of the cracking boiler of powder metallurgy and ingot metallurgy Ti-5Al-5Mo-5V-3Cr alloys during the processing of materials, 2019; 12(3): 457-70. However, the high-temperature compression test can only qualitatively judge the high-temperature rheological damage cracking tendency of the powder metallurgy material in the high-temperature compression deformation process, but cannot quantitatively describe the high-temperature rheological damage behavior of the powder metallurgy material in the hot working process, and cannot accurately predict the high-temperature rheological damage cracking tendency of the powder metallurgy material in the hot working process. In fact, the occurrence of damage cracking in powder metallurgy materials during hot working is caused by tensile stress. Thus, the high temperature tensile test can be used to evaluate its ability to resist fracture from high temperature rheological damage. At present, high temperature tensile tests have been successfully applied to evaluate the ability of conventional fused cast metal materials to resist fracture by high temperature rheological damage. For example, the high temperature rheological damage fracture behavior of the conventional molten metal material at different temperatures and strain rates is measured by a material universal tester, and a high temperature rheological damage model is constructed to evaluate the high temperature rheological damage fracture resistance [ Y.C.Lin, Yan-Xing Liu, Ge Liu, Ming-Song Chen, you-Chun Huang. prediction of reaction fragment for 42CrMo steel at extruded temperature. Journal of Materials Engineering & Performance 2015,24:221-118.Beatrice variant, Stefania Brush, Andrea Ghiti, Rajv Shiv put. Johnson-Cook bed batch criterion evaluation of transformation crack defect and reaction fragment of reaction fragment, 8994. the high temperature rheological damage fracture model is obtained by measuring the fracture behavior of high temperature rheological damage fracture at different temperatures and strain rates and measuring crack damage of reaction fragment, and reaction fragment of reaction fragment, 2017,123. However, due to the limitation of the small tensile loading rate (the strain rate is usually less than 1/second) of the material universal tester, the difference between the measured high-temperature tensile rheological damage fracture data and the actual thermal processing conditions (the strain rate reaches several to dozens of seconds) is large, so that the application of the high-temperature rheological damage model constructed by the method in the actual production has obvious limitation. In order to obtain the high-temperature tensile rheological damage fracture data of the powder metallurgy material corresponding to the actual hot working condition (the strain rate can reach several to dozens of per second), a material thermal-mechanical simulation testing machine Gleeble can be adopted to carry out the high-temperature tensile test of the metal material. The Gleeble testing machine can provide a high tensile loading rate (the strain rate can reach dozens of per second), can accurately measure the high-temperature tensile load-displacement data of the powder metallurgy material, but cannot accurately measure the tensile strain of the tensile sample in the high-temperature tensile process without the assistance of an extensometer. Moreover, since the Gleeble tester heats the high temperature tensile sample by resistance heating, the joule heating effect will cause the tensile sample to have a significant temperature gradient along the axis or along the tensile direction, resulting in a high temperature at the center and a low temperature at the two ends of the tensile sample, which will eventually cause severe non-uniform deformation during the tensile process [ j.l.he, y.h.xiao, j.liu, z.s.cui, l.q.run.model for the compression of the reduced fraction SA508-3 step underscoring for the materials Science and technology.2014,30(10): 1239-. Therefore, when the Gleeble testing machine is used for measuring the high-temperature tensile rheological damage fracture of the powder metallurgy material, other auxiliary methods, such as finite element simulation auxiliary test, are needed to accurately measure the high-temperature tensile rheological damage fracture behavior of the powder metallurgy material, construct a high-precision high-temperature rheological damage model of the powder metallurgy material, and accurately evaluate the high-temperature rheological damage fracture resistance of the powder metallurgy material. However, at present, there is no Gleeble high-temperature tensile test method assisted by precise finite element simulation, which is used for accurately measuring the high-temperature tensile rheological damage fracture behavior of the powder metallurgy material, constructing a high-precision high-temperature rheological damage model of the powder metallurgy material and further accurately evaluating the capability of the powder metallurgy material for resisting the high-temperature rheological damage fracture under the hot working process condition. Therefore, a reasonable high-temperature tensile test experiment of the powder metallurgy material needs to be designed, a finite element simulation auxiliary test method is combined, the high-temperature tensile rheological damage fracture behavior of the powder metallurgy material under different temperatures and stress rates is systematically investigated, and a high-temperature tensile rheological stress constitutive model of the powder metallurgy material is established; meanwhile, the critical fracture strain of the powder metallurgy material when the powder metallurgy material is damaged and cracked in the high-temperature stretching process is measured, a high-temperature stretching critical fracture strain model of the powder metallurgy material is established, a high-precision powder metallurgy material high-temperature stretching rheological damage model is further established, the high-temperature rheological damage behavior of the powder metallurgy material is accurately represented, the damage and cracking tendency of the powder metallurgy material in the high-temperature plastic processing process is accurately predicted, and a basis is provided for the high-temperature plastic processing process and the optimal design of a die of the powder metallurgy material.
Disclosure of Invention
In view of the above, the invention provides a powder metallurgy material high-temperature tensile test and high-temperature rheological damage model construction method assisted by finite element simulation, aiming at the problems that a Gleeble high-temperature tensile test method assisted by the finite element simulation is not available at present, the high-temperature tensile rheological damage fracture behavior of a powder metallurgy material is accurately measured, a high-precision high-temperature rheological damage model of the powder metallurgy material is constructed, and the high-temperature rheological damage resistance fracture capability of the powder metallurgy material under the thermal processing process condition is accurately evaluated.
In order to solve the technical problems, the invention discloses a high-temperature tensile test and high-temperature rheological damage model construction method of a powder metallurgy material, which comprises the following steps:
step 1: measuring high-temperature tensile load-displacement data of each tensile sample of the powder metallurgy material under different temperatures and strain rates by using a Gleeble heat-force simulation testing machine; meanwhile, measuring temperature distribution data of different positions of each tensile sample along the tensile direction in the tensile process, and determining the relative temperature equalization section of the middle part of each tensile sample;
step 2: establishing a finite element model with the same geometric shape, size and temperature distribution as those of each tensile sample in a finite element simulation program by adopting the temperature distribution data of each tensile sample measured in the step 1;
and step 3: adopting the high-temperature tensile load-displacement data of each tensile sample of the powder metallurgy material measured in the step 1, preliminarily calculating the high-temperature tensile rheological stress-strain data of the powder metallurgy material, then implanting a finite element simulation program, correcting, combining with the finite element model established in the step 2, and simulating and reproducing the high-temperature tensile process of each tensile sample in the step 1;
and 4, step 4: extracting the tensile load and the deformation of the relative temperature-equalizing section in the middle of each tensile sample determined in the step 1 from the finite element simulation result of the high-temperature stretching of each tensile sample in the step 3, and calculating the tensile rheological stress-strain data of the relative temperature-equalizing section in the middle of each tensile sample;
and 5: respectively establishing a high-temperature extensional rheological stress constitutive model and a critical fracture strain model of the powder metallurgy material by adopting extensional rheological stress-strain data of the relative temperature-equalizing section in the middle of each tensile sample calculated in the step 4:
σ＝f(T,ξ,ε)
εf＝f(T,ξ)
sigma and epsilonfRespectively representing the rheological stress and critical fracture strain of the powder metallurgy material under high-temperature stretching; t, xi and epsilon are temperature, strain rate and strain, respectively;
step 6: calculating the critical damage value D of the powder metallurgy material during high-temperature tensile fracture by adopting the powder metallurgy material high-temperature tensile rheological stress constitutive model and the critical fracture strain model established in the step 5f：
Figure BDA0002920395520000041
And 7: adopting the critical damage value D of the powder metallurgy material in high-temperature tensile fracture calculated in the step 6fEstablishing a normalized powder metallurgy material high-temperature extensional rheological damage model, and properly correcting by using an error correction function delta (T, xi), further eliminating the negative influence of the temperature gradient in the middle relative temperature-equalizing section of the tensile sample, so as to obtain the normalized and corrected powder metallurgy material high-temperature extensional rheological damage model:
Figure BDA0002920395520000042
(the cumulative damage value D is more than or equal to 1, cracking occurs; D is less than 1, cracking does not occur)
And 8: and (4) carrying out hot working experimental verification and necessary further correction on the powder metallurgy material high-temperature rheological damage model established in the step (7) to ensure the accuracy of the model.
Further, the step 1 specifically includes:
step 1.1: analyzing the actual hot working process of the powder metallurgy material, and determining the hot working process conditions such as the temperature and speed range of the powder metallurgy material in the hot working deformation process;
step 1.2: processing a high-temperature tensile sample with a specified shape and size according to a high-temperature tensile test standard of a metal material and the clamping requirement of a Gleeble thermal-force simulation testing machine;
step 1.3: in the range of the hot processing temperature and speed of the powder metallurgy material determined in the step 1.1, carrying out high-temperature tensile tests of the high-temperature tensile samples processed in the step 1.2 on a Gleeble testing machine under the combination conditions of different temperatures and stress speeds, and measuring high-temperature tensile load-displacement data of each tensile sample at the corresponding temperature and stress speed; meanwhile, a thermodetector is adopted to measure temperature distribution data of different positions of each tensile sample along the tensile direction in the tensile test, and the relative temperature equalization section of the middle part of each tensile sample is determined.
Further, the step 2 specifically includes:
step 2.1: establishing a finite element model with the same geometric shape and size as those of the high-temperature tensile sample in the step 1 in a finite element simulation program;
step 2.2: and (3) applying the temperature distribution data of each high-temperature tensile sample measured in the step (1) to each grid unit node of the finite element model established in the step (2.1), and establishing the finite element model with the same geometric shape, size and temperature distribution as those of each high-temperature tensile sample in the step (1).
Further, the step 3 specifically includes:
step 3.1: the high-temperature tensile load-displacement data of each tensile sample of the powder metallurgy material measured in the step 1 are adopted, the high-temperature tensile rheological stress-strain data of the powder metallurgy material are preliminarily calculated, and the stress and strain calculation formulas are respectively as follows:
σfirst stage＝4F(1+L/L0)/πd0 2
εFirst stage＝ln(1+L/L0)
σFirst stageAnd εFirst stageAnd the high-temperature tensile rheological stress and strain of the powder metallurgy material are preliminarily calculated; f and L are measured high-temperature tensile load and displacement of each tensile sample of the powder metallurgy material, and L is measured0And d0The length and the diameter of an initial gauge length section of the tensile sample;
step 3.2: implanting a finite element simulation program into the high-temperature tensile rheological stress-strain data of the powder metallurgy material preliminarily calculated in the step 3.1 in the form of a data set or a high-temperature rheological constitutive model constructed by the stress-strain data, combining with the finite element model established in the step 2, and establishing a finite element model which has the same geometric shape, size and temperature distribution as those of each high-temperature tensile sample in the step 1 and contains the high-temperature tensile rheological stress-strain data of the powder metallurgy material;
step 3.3: applying the same stretching rate and boundary conditions as those of the high-temperature stretching tests in the step 1 to the finite element models of the high-temperature stretching samples established in the step 3.2, simulating the high-temperature stretching test process of the stretching samples in the step 1, and obtaining finite element simulated stretching load-displacement data of the stretching samples under different high-temperature stretching test conditions;
step 3.4: and (3) comparing the high-temperature tensile load-displacement data and the tensile deformation profile of each tensile sample obtained by finite element simulation in the step (3.3) with the high-temperature tensile test result in the step (1), repeatedly regulating and controlling the high-temperature tensile rheological stress-strain data or the corresponding high-temperature rheological stress constitutive model of the powder metallurgy material implanted with the finite element program in the step (3.2) until the high-temperature tensile load-displacement data and the tensile deformation profile of each tensile sample obtained by simulation in the step (3.3) are the same as the high-temperature tensile test result in the step (1), and reproducing the high-temperature tensile test process of each tensile sample in the step (1).
Further, the step 4 specifically includes:
step 4.1: extracting the displacements of the finite element grid nodes at two ends of the relative temperature-equalizing section in the middle of each tensile sample determined in the step 1 from the finite element simulation result of the high-temperature stretching of each tensile sample in the step 3, subtracting the displacements to obtain the tensile deformation of the relative temperature-equalizing section in the middle of each tensile sample, and then calculating the tensile strain data of the relative temperature-equalizing section in the middle of each tensile sample, wherein the strain calculation formula is as follows:
ε＝ln(1+L'/L0')
L0'L' and epsilon are respectively the initial length, the tensile deformation and the strain of the middle relative temperature equalizing section of each tensile sample of the powder metallurgy material;
step 4.2: extracting tensile load corresponding to the tensile strain of the relative temperature-equalizing section in the middle of each tensile sample in the step 4.1 from the finite element simulation result of the high-temperature stretching of each tensile sample in the step 3, and calculating the tensile rheological stress data of the relative temperature-equalizing section in the middle of each tensile sample, wherein the rheological stress calculation formula is as follows:
σ＝4F(1+L'/L0')/πd0 2
F、d0and sigma is the load, initial diameter and rheological stress of the relative temperature-equalizing section in the middle of each tensile sample of the powder metallurgy material.
Further, the step 5 specifically includes:
step 5.1: and (4) establishing a high-temperature extensional rheological stress constitutive model of the powder metallurgy material by adopting the extensional rheological stress-strain data of the relative temperature-equalizing section in the middle of each tensile sample calculated in the step 4:
Figure BDA0002920395520000061
a0,a1,a2,a3,a4,a5,a6,a7,a8is a material constant;
step 5.2: establishing a high-temperature tensile critical fracture strain model of the powder metallurgy material by adopting the tensile strain data of the relative temperature-equalizing section in the middle of each tensile sample calculated in the step 4:
Figure BDA0002920395520000062
q isThermal deformation activation energy of the powder metallurgy material; r is an ideal gas constant; t ispThe temperature corresponding to the maximum strain at break; b0,b1,b2,b3,b4,b5Is a material constant.
Further, the step 6 specifically includes:
step 6.1: establishing a critical damage value model of the powder metallurgy material high-temperature tensile fracture based on the powder metallurgy material high-temperature tensile rheological stress constitutive model and the critical fracture strain model established in the step 5:
Figure BDA0002920395520000063
step 6.2: calculating the rheological stress of the powder metallurgy material in the high-temperature stretching at 0-epsilon according to the critical damage value model of the powder metallurgy material in the high-temperature stretching fracture established in the step 6.1fThe definite integral of the tensile strain in the range is used to obtain the critical damage value D of the powder metallurgy material at the high-temperature tensile fracturef。
Further, the step 7 specifically includes:
step 7.1: adopting the critical damage value D of the powder metallurgy material in high-temperature tensile fracture calculated in the step 6fEstablishing a normalized powder metallurgy material high-temperature extensional rheological damage model:
Figure BDA0002920395520000071
(the cumulative damage value D is more than or equal to 1, cracking occurs; D is less than 1, cracking does not occur)
Step 7.2: implanting a finite element simulation program into the normalized powder metallurgy material high-temperature tensile rheological damage model established in the step 7.1, combining with the finite element simulation for reproducing the high-temperature tensile test process of each tensile sample in the step 3, predicting load-displacement data of each tensile sample subjected to high-temperature tensile fracture, comparing the load-displacement data with the high-temperature tensile test result of each tensile sample in the step 1, and properly correcting by using an error correction function delta (T, xi) to further eliminate the negative influence of the temperature gradient in the relative temperature equalization section in the middle of each tensile sample, thereby establishing the normalized and corrected powder metallurgy material high-temperature rheological damage model:
Figure BDA0002920395520000072
δ(T,ξ)＝c0+c1T+c2T2+c3T3+c4 lnξ
(the cumulative damage value D is more than or equal to 1, cracking occurs; D is less than 1, cracking does not occur)
c0,c1,c2,c3,c4Is a material constant.
Further, the step 8 specifically includes:
step 8.1: carrying out a hot working experiment of the powder metallurgy material under different temperature and strain rate conditions, and measuring the critical deformation of the powder metallurgy material which is damaged and cracked in the hot working;
step 8.2: embedding the normalized and corrected high-temperature rheological damage model established in the step 7 into a finite element program, setting finite element simulation conditions the same as those of the hot working experiment in the step 8.1, predicting critical deformation of the powder metallurgy material subjected to damage and cracking in the hot working process, comparing the critical deformation with the actual measurement result in the step 8.1, verifying the prediction precision and stability of the normalized and corrected high-temperature rheological damage model established in the step 7, and performing necessary further correction to obtain the high-temperature rheological damage model of the powder metallurgy material with high precision and high stability.
Further, the high-temperature tensile test and high-temperature rheological damage model construction method of the powder metallurgy material can be used for high-temperature tensile test and high-temperature rheological damage model construction of iron-based, aluminum-based, copper-based, titanium-based, magnesium-based and other powder metallurgy materials, and the constructed high-temperature rheological damage model can be applied to hot working processes of hot forging, hot rolling, hot extrusion, hot drawing and the like of the powder metallurgy material and the optimal design of a die.
Compared with the prior art, the invention can obtain the following technical effects:
(1) the method adopts a Gleeble thermal-mechanical simulation testing machine to carry out high-temperature tensile test on the powder metallurgy material corresponding to the actual thermal processing temperature and speed range, and assists in testing the stress-strain data of the relative temperature-equalizing section in the middle of a tensile sample by means of finite element simulation, and establishes a rheological stress constitutive model of the high-temperature tensile of the powder metallurgy material; meanwhile, determining the critical fracture strain amount of the tensile sample when the tensile fracture occurs, and establishing a critical fracture strain model of the powder metallurgy material under high-temperature tension; therefore, a powder metallurgy material high-temperature rheological damage model coupling thermal processing technological parameters such as deformation temperature, strain rate and the like is constructed, verification and necessary correction are carried out, and finally, a high-precision powder metallurgy material high-temperature rheological damage model is obtained. The damage model represents the quantitative influence of temperature, speed, deformation and stress state on the high-temperature rheological damage of the powder metallurgy material in the hot processing process, can intuitively and accurately describe the high-temperature rheological damage behavior of the powder metallurgy material in the hot processing process, and reveals the high-temperature rheological damage mechanism of the powder metallurgy material; the damage model can accurately calculate the accumulated damage of the powder metallurgy material in the hot working process, accurately predict the damage cracking and damage fracture resistance of the powder metallurgy material in the hot working process, and the prediction precision meets the engineering application requirements.
(2) The damage model can accurately calculate and predict the accumulated damage and cracking of the powder metallurgy material under different hot working conditions of forging, rolling, extruding, drawing and the like, can be used for the optimal design of hot working processes and dies of the powder metallurgy material such as hot forging, hot rolling, hot extruding, hot drawing and the like, improves the equipment model selection and the process and die design efficiency, and has good engineering applicability.
Of course, it is not necessary for any one product in which the invention is practiced to achieve all of the above-described technical effects simultaneously.
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The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the invention and not to limit the invention. In the drawings:
FIG. 1 is an example of the temperature distribution of a high temperature tensile specimen of FC0205 powder metallurgy steel in the example of the invention when subjected to high temperature tensile.
FIG. 2 is an example of the load-displacement results of a high temperature tensile finite element simulation of a high temperature tensile test specimen of FC0205 powder metallurgy steel in an embodiment of the invention compared with the actual measurement results.
FIG. 3 is an example of the comparison of the stress-strain results predicted by the FC0205 powder metallurgy steel high temperature tensile rheological stress constitutive model and the measured results in the embodiment of the invention.
FIG. 4 is a comparison of the critical fracture strain value predicted by the FC0205 powder metallurgy steel high-temperature tensile critical fracture strain model in the embodiment of the invention and the measured value.
FIG. 5 is a comparison of the damage cracking results predicted by the FC0205 powder metallurgy steel high-temperature extensional rheological damage model and the actual measurement results in the embodiment of the invention.
FIG. 6 is a predicted stability analysis of the FC0205 powder metallurgy steel high temperature rheological damage model in an embodiment of the invention.
FIG. 7 is an example of the temperature distribution in the high temperature drawing of the high temperature tensile specimen of F0005 powder metallurgy steel in the example of the present invention.
FIG. 8 is an example of the comparison of the load-displacement results of the high temperature tensile finite element simulation of the F0005 powder metallurgy steel high temperature tensile specimen with the actual measurement results in the example of the present invention.
FIG. 9 is an example of the comparison of the stress-strain results predicted by the high temperature tensile rheological stress constitutive model of F0005 powder metallurgy steel with the measured results in the example of the present invention.
FIG. 10 is a comparison of the critical fracture strain value predicted by the high-temperature tensile critical fracture strain model of F0005 powder metallurgy steel in the example of the present invention with the measured value.
FIG. 11 is a comparison of the damage cracking results predicted by the high temperature tensile rheological damage model of F0005 powder metallurgy steel in accordance with the present invention and the actual measurement results.
FIG. 12 is a predicted stability analysis of the high temperature rheological damage model of F0005 powder metallurgy steel in an example of the invention.
Detailed Description
The following embodiments are described in detail with reference to the accompanying drawings, so that the implementation process of the present invention for solving the technical problems and achieving the technical effects by applying technical means can be fully understood and implemented.
The invention relates to a high-temperature tensile test and high-temperature rheological damage model construction method of a powder metallurgy material, which specifically comprises the following steps:
step 1: measuring high-temperature tensile load-displacement data of each tensile sample of the powder metallurgy material under different temperatures and strain rates by using a Gleeble heat-force simulation testing machine; meanwhile, measuring temperature distribution data of different positions of each tensile sample along the tensile direction in the tensile process, and determining the relative temperature equalization section of the middle part of each tensile sample;
step 1.1: analyzing the actual hot working process of the powder metallurgy material, and determining the hot working process conditions such as the temperature and speed range of the powder metallurgy material in the hot working deformation process;
step 1.2: processing a high-temperature tensile sample with a specified shape and size according to a high-temperature tensile test standard of a metal material and the clamping requirement of a Gleeble thermal-force simulation testing machine;
step 1.3: in the range of the hot processing temperature and speed of the powder metallurgy material determined in the step 1.1, carrying out high-temperature tensile tests of the high-temperature tensile samples processed in the step 1.2 on a Gleeble testing machine under the combination conditions of different temperatures and stress speeds, and measuring high-temperature tensile load-displacement data of each tensile sample at the corresponding temperature and stress speed; meanwhile, measuring temperature distribution data of different positions of each tensile sample along the tensile direction in a tensile test by using a temperature measuring instrument, and determining a relative temperature equalizing section in the middle of each tensile sample;
step 2: establishing a finite element model with the same geometric shape, size and temperature distribution as those of each tensile sample in a finite element simulation program by adopting the temperature distribution data of each tensile sample measured in the step 1;
step 2.1: establishing a finite element model with the same geometric shape and size as those of the high-temperature tensile sample in the step 1 in a finite element simulation program;
step 2.2: applying the temperature distribution data of each high-temperature tensile sample measured in the step 1 to each grid element node of the finite element model established in the step 2.1, and establishing a finite element model with the same geometric shape, size and temperature distribution as those of each high-temperature tensile sample in the step 1;
and step 3: adopting the high-temperature tensile load-displacement data of each tensile sample of the powder metallurgy material measured in the step 1, preliminarily calculating the high-temperature tensile rheological stress-strain data of the powder metallurgy material, then implanting a finite element simulation program, correcting, combining with the finite element model established in the step 2, and simulating and reproducing the high-temperature tensile process of each tensile sample in the step 1;
step 3.1: the high-temperature tensile load-displacement data of each tensile sample of the powder metallurgy material measured in the step 1 are adopted, the high-temperature tensile rheological stress-strain data of the powder metallurgy material are preliminarily calculated, and the stress and strain calculation formulas are respectively as follows:
σfirst stage＝4F(1+L/L0)/πd0 2
εFirst stage＝ln(1+L/L0)
σFirst stageAnd εFirst stageThe high-temperature tensile rheological stress and strain of the powder metallurgy material are preliminarily calculated; f and L are measured high-temperature tensile load and displacement of each tensile sample of the powder metallurgy material, and L is measured0And d0The length and the diameter of an initial gauge length section of the tensile sample;
step 3.2: implanting a finite element simulation program into the high-temperature tensile rheological stress-strain data of the powder metallurgy material preliminarily calculated in the step 3.1 in the form of a data set or a high-temperature rheological constitutive model constructed by the stress-strain data, combining with the finite element model established in the step 2, and establishing a finite element model which has the same geometric shape, size and temperature distribution as those of each high-temperature tensile sample in the step 1 and contains the high-temperature tensile rheological stress-strain data of the powder metallurgy material;
step 3.3: applying the same stretching rate and boundary conditions as those of the high-temperature stretching tests in the step 1 to the finite element models of the high-temperature stretching samples established in the step 3.2, simulating the high-temperature stretching test process of the stretching samples in the step 1, and obtaining finite element simulated stretching load-displacement data of the stretching samples under different high-temperature stretching test conditions;
step 3.4: comparing the high-temperature tensile load-displacement data and the tensile deformation profile of each tensile sample obtained by finite element simulation in the step 3.3 with the high-temperature tensile test result in the step 1, repeatedly regulating and controlling the high-temperature tensile rheological stress-strain data or the corresponding high-temperature rheological stress constitutive model of the powder metallurgy material implanted with the finite element program in the step 3.2 until the high-temperature tensile load-displacement data and the tensile deformation profile of each tensile sample obtained by simulation in the step 3.3 are the same as the high-temperature tensile test result in the step 1, and reproducing the high-temperature tensile test process of each tensile sample in the step 1;
and 4, step 4: extracting the tensile load and the deformation of the relative temperature-equalizing section in the middle of each tensile sample determined in the step 1 from the finite element simulation result of the high-temperature stretching of each tensile sample in the step 3, and calculating the tensile rheological stress-strain data of the relative temperature-equalizing section in the middle of each tensile sample;
step 4.1: extracting the displacements of the finite element grid nodes at two ends of the relative temperature-equalizing section in the middle of each tensile sample determined in the step 1 from the finite element simulation result of the high-temperature stretching of each tensile sample in the step 3, subtracting the displacements to obtain the tensile deformation of the relative temperature-equalizing section in the middle of each tensile sample, and then calculating the tensile strain data of the relative temperature-equalizing section in the middle of each tensile sample, wherein the strain calculation formula is as follows:
ε＝ln(1+L'/L0')
L0'L' and epsilon are respectively the initial length, the tensile deformation and the strain of the middle relative temperature equalizing section of each tensile sample of the powder metallurgy material;
step 4.2: extracting tensile load corresponding to the tensile strain of the relative temperature-equalizing section in the middle of each tensile sample in the step 4.1 from the finite element simulation result of the high-temperature stretching of each tensile sample in the step 3, and calculating the tensile rheological stress data of the relative temperature-equalizing section in the middle of each tensile sample, wherein the rheological stress calculation formula is as follows:
σ＝4F(1+L'/L0')/πd0 2
F、d0and sigma is the load, initial diameter and rheological stress of the relative temperature-equalizing section in the middle of each tensile sample of the powder metallurgy material.
And 5: respectively establishing a high-temperature extensional rheological stress constitutive model and a critical fracture strain model of the powder metallurgy material by adopting extensional rheological stress-strain data of the relative temperature-equalizing section in the middle of each tensile sample calculated in the step 4:
σ＝f(T,ξ,ε)
εf＝f(T,ξ)
sigma and epsilonfRespectively representing the rheological stress and critical fracture strain of the powder metallurgy material under high-temperature stretching; t, xi and epsilon are temperature, strain rate and strain, respectively;
step 5.1: and (4) establishing a high-temperature extensional rheological stress constitutive model of the powder metallurgy material by adopting the extensional rheological stress-strain data of the relative temperature-equalizing section in the middle of each tensile sample calculated in the step 4:
Figure BDA0002920395520000121
a0,a1,a2,a3,a4,a5,a6,a7,a8is a material constant;
step 5.2: establishing a high-temperature tensile critical fracture strain model of the powder metallurgy material by adopting the tensile strain data of the relative temperature-equalizing section in the middle of each tensile sample calculated in the step 4:
Figure BDA0002920395520000122
q is the thermal deformation activation energy of the powder metallurgy material; r is an ideal gas constant; t ispThe temperature corresponding to the maximum strain at break; b0,b1,b2,b3,b4,b5Is a material constant.
Step 6: calculating the critical damage value D of the powder metallurgy material during high-temperature tensile fracture by adopting the powder metallurgy material high-temperature tensile rheological stress constitutive model and the critical fracture strain model established in the step 5f；
Figure BDA0002920395520000123
Step 6.1: establishing a critical damage value model of the powder metallurgy material high-temperature tensile fracture based on the powder metallurgy material high-temperature tensile rheological stress constitutive model and the critical fracture strain model established in the step 5:
Figure BDA0002920395520000124
step 6.2: calculating the rheological stress of the powder metallurgy material in the high-temperature stretching at 0-epsilon according to the critical damage value model of the powder metallurgy material in the high-temperature stretching fracture established in the step 6.1fThe definite integral of the tensile strain in the range is used to obtain the critical damage value D of the powder metallurgy material at the high-temperature tensile fracturef；
And 7: adopting the critical damage value D of the powder metallurgy material in high-temperature tensile fracture calculated in the step 6fEstablishing a normalized powder metallurgy material high-temperature tensile rheological damage model, and carrying out appropriate correction by using an error correction function delta (T, xi), wherein the expression of the normalized and corrected powder metallurgy material high-temperature rheological damage model is as follows:
Figure BDA0002920395520000131
(the cumulative damage value D is more than or equal to 1, cracking occurs; D is less than 1, cracking does not occur)
Step 7.1: adopting the critical damage value D of the powder metallurgy material in high-temperature tensile fracture calculated in the step 6fEstablishing a normalized powder metallurgy material high-temperature extensional rheological damage model:
Figure BDA0002920395520000132
(the cumulative damage value D is more than or equal to 1, cracking occurs; D is less than 1, cracking does not occur)
Step 7.2: implanting a finite element simulation program into the normalized powder metallurgy material high-temperature tensile rheological damage model established in the step 7.1, combining with the finite element simulation for reproducing the high-temperature tensile test process of each tensile sample in the step 3, predicting load-displacement data of each tensile sample subjected to high-temperature tensile fracture, comparing the load-displacement data with the high-temperature tensile test result of each tensile sample in the step 1, and properly correcting by using an error correction function delta (T, xi) to further eliminate the negative influence of the temperature gradient in the relative temperature equalization section in the middle of each tensile sample, thereby establishing the normalized and corrected powder metallurgy material high-temperature rheological damage model:
Figure BDA0002920395520000133
δ(T,ξ)＝c0+c1T+c2T2+c3T3+c4 lnξ
(the cumulative damage value D is more than or equal to 1, cracking occurs; D is less than 1, cracking does not occur)
c0,c1,c2,c3,c4Is a material constant.
And 8: carrying out hot working experimental verification and necessary further correction on the powder metallurgy material high-temperature rheological damage model established in the step 7 to ensure the accuracy of the model;
step 8.1: carrying out a hot working experiment of the powder metallurgy material under the conditions of different temperatures and strain rates, and measuring the critical deformation of the powder metallurgy material which is damaged and cracked in the hot working process;
step 8.2: embedding the normalized and corrected high-temperature rheological damage model established in the step 7 into a finite element program, setting finite element simulation conditions the same as those of the hot working experiment in the step 8.1, predicting critical deformation of the powder metallurgy material subjected to damage and cracking in the hot working process, comparing the critical deformation with the actual measurement result in the step 8.1, verifying the prediction precision and stability of the normalized and corrected high-temperature rheological damage model established in the step 7, and performing necessary further correction to obtain the high-temperature rheological damage model of the powder metallurgy material with high precision and high stability.
And (3) analyzing the prediction precision of the high-temperature rheological damage model: FIG. 5 shows the use of this model for predicting the strain rate of FC0205 powder metallurgy steel in hot forging process (deformation temperature 850--1) And (4) comparing the damage cracking result with the actual measurement result, wherein the prediction precision of the hot forging deformation amount of the cracking is controlled to be less than 5% in error, and the prediction precision meets the engineering application requirement. FIG. 11 is a graph showing the use of this model for predicting the strain rate of F0005 powder metallurgy steel in the hot forging process (deformation temperature 830--1) And (4) comparing the damage cracking result with the actual measurement result, wherein the prediction precision of the forging deformation amount of the cracking is controlled to be less than 5% in error, and the prediction precision meets the engineering application requirement.
Stability analysis of high temperature rheological Damage model: FIG. 6 shows the error of applying this model to the prediction of the damage cracking in hot forging of FC0205 powder metallurgy steel, and it can be seen that the damage model has good and stable prediction capability even if the hot forging temperature of FC0205 powder metallurgy steel is decreased from the start forging temperature (1000 ℃) to the finish forging temperature (850 ℃). FIG. 12 shows the error of the use of this model for the prediction of the hot forging damage cracking of F0005 powder metallurgy steel, and it can be seen that the damage model has a good and stable prediction ability even if the hot forging temperature of F0005 powder metallurgy steel is decreased from the start forging temperature (980 ℃ C.) to the finish forging temperature (830 ℃ C.).
And carrying out application verification on the obtained metal material high-temperature rheological damage model. The method comprises the following specific steps:
example 1 was carried out:
predicting the cracking of the FC0205 powder metallurgy steel at high temperature tensile damage, and analyzing the prediction precision and stability. Combining with the common hot working process conditions of FC0205 powder metallurgy steel, the hot working parameter range is obtained: the processing temperature is 850 ℃ and 1000 ℃; the processing strain rate is 0.01-10s-1The following Gleeble high temperature tensileTensile test experiment:
deformation temperature (. degree. C.): 850, 900, 950, 1000; rate of strain(s)-1)：0.01，0.1，1.0，10。
According to the method for constructing the high-temperature tensile test and the high-temperature rheological damage model, firstly, based on a Gleeble thermal tensile test result, a finite element model which has the same shape, size and actual temperature distribution as those of each tensile sample of the FC0205 powder metallurgy steel is established, for example, the finite element model of the tensile sample at the set temperature of 950 ℃ is shown in a figure 1; subsequently, a high-temperature tensile test procedure was simulated which reproduced the respective tensile specimens, for example, the tensile specimens were set at a set temperature of 950 ℃ and a strain rate of 1s-1The comparison of the load-displacement finite element simulation results and the actual measurement results under the conditions is shown in FIG. 2; then, determining tensile rheological stress-strain data of relative temperature-equalizing sections in the middle of each tensile sample, and establishing a rheological stress constitutive model of high-temperature tensile of the FC0205 powder metallurgy steel, for example, setting the temperature and the strain rate at 950 ℃ for 1s-1The comparison of the stress-strain results predicted by the constitutive model under the condition with the actual measurement results is shown in FIG. 3; meanwhile, determining the nonlinear relation between the critical fracture strain of each tensile sample subjected to damage fracture and the corresponding temperature and strain rate, establishing a corresponding critical fracture strain model, and comparing the critical fracture strain predicted by the model with the actual measurement result as shown in FIG. 4; then, establishing a normalized FC0205 powder metallurgy steel high-temperature tensile damage model based on the established constitutive model and a critical damage value calculated by a critical fracture strain model; finally, the established normalized FC0205 powder metallurgy steel high temperature extensional rheological damage model is modified as necessary to obtain high prediction accuracy. The normalized and corrected high-temperature tensile rheological damage model of the FC0205 powder metallurgy steel is as follows:
Figure BDA0002920395520000151
(the cumulative damage value D is more than or equal to 1, cracking occurs; D is less than 1, cracking does not occur)
T, xi and epsilon are temperature, strain rate and strain, respectively; σ is tensile stress; a is0,a1,a2,a3,a4,a5,a6,a7,a8,b0,b1,b2,b3,b4,b5,c0,c1,c2,c3,c4See table 1 for material parameters.
TABLE 1FC0205 powder metallurgy steel high temperature rheological Damage model Material parameters
Figure BDA0002920395520000152
The high-temperature rheological damage model predicts the hot forging process of the FC0205 powder metallurgy steel (the deformation temperature is 850--1) The comparison of the forging deformation amount of the damaged crack and the actual measurement result is shown in figure 5, the prediction relative error is less than +/-5 percent, and the application requirement of the actual hot working engineering is met. The high-temperature rheological damage model predicts the thermal processing process of the FC0205 powder metallurgy steel (the deformation temperature is 850--1) The stability analysis of the damage cracking is shown in figure 6, and it can be seen from the figure that the high-temperature rheological damage model is suitable for the FC0205 powder metallurgy steel, and the damage cracking prediction relative errors in the whole range from the initial forging temperature (1000 ℃) to the final forging temperature (850 ℃) are less than +/-5%, so that the high-temperature rheological damage model has good and stable prediction capability.
Example 2 was carried out:
predicting the high-temperature tensile damage cracking of the F0005 powder metallurgy steel and analyzing the prediction precision and stability. Combining the common hot working process conditions of the F0005 powder metallurgy steel, the hot working parameter range is obtained: the processing temperature is 830-980 ℃; the processing strain rate is 0.01-10s-1The following Gleeble high temperature tensile test experiment was designed:
deformation temperature (. degree. C.): 830, 880, 930, 980; rate of strain(s)-1)：0.01，0.1，1.0，10。
According to the method for constructing the high-temperature tensile test and the high-temperature rheological damage model, firstly, based on the Gleeble thermal tensile test result, a finite element model with the same shape, size and actual temperature distribution as those of each tensile sample of the F0005 powder metallurgy steel is established, for example, the set temperature of the tensile sample at 930 DEG CThe finite element model of the degree is shown in figure 7; subsequently, the high temperature tensile test procedure of each tensile specimen was simulated and reproduced, for example, the tensile specimen was set at 930 ℃ for a set temperature and a strain rate of 1s-1The comparison of the load-displacement finite element simulation results and the actual measurement results under the conditions is shown in FIG. 8; then, the tensile rheological stress-strain data of the relative temperature-equalizing section in the middle of each tensile sample is determined, and a rheological stress constitutive model of the high-temperature tensile of the F0005 powder metallurgy steel is established, for example, the temperature and the strain rate are set at 930 ℃ for 1s-1The comparison of the stress-strain results predicted by the constitutive model under the condition with the actual measurement results is shown in FIG. 9; meanwhile, determining the nonlinear relation between the critical fracture strain of each tensile sample subjected to damage fracture and the corresponding temperature and strain rate, and establishing a corresponding critical fracture strain model, wherein the comparison between the critical fracture strain predicted by the model and the actual measurement result is shown in FIG. 10; then, establishing a normalized F0005 powder metallurgy steel high-temperature tensile damage model based on the established constitutive model and a critical damage value calculated by a critical fracture strain model; finally, the established normalized F0005 powder metallurgy steel high-temperature tensile rheological damage model is subjected to necessary correction so as to obtain high prediction accuracy. The normalized and corrected high temperature tensile rheological damage model of F0005 powder metallurgy steel is:
Figure BDA0002920395520000161
(the cumulative damage value D is more than or equal to 1, cracking occurs; D is less than 1, cracking does not occur)
T, xi and epsilon are temperature, strain rate and strain, respectively; σ is tensile stress; a is0,a1,a2,a3,a4,a5,a6,a7,a8,b0,b1,b2,b3,b4,b5,c0,c1,c2,c3,c4See table 2 for material parameters.
The high-temperature rheological damage model predicts the hot forging process of the F0005 powder metallurgy steel (the deformation temperature is 830-980 ℃, and the strain rate is 0-7 s)-1) Forging with damage crackingThe comparison of the deformation and the actual measurement result is shown in figure 11, the prediction relative error is less than +/-5 percent, and the application requirement of the actual hot working engineering is met. The high-temperature rheological damage model predicts the hot working process of the F0005 powder metallurgy steel (the deformation temperature is 830--1) The stability analysis of the damage cracking is shown in figure 12, and it can be seen from the figure that the high-temperature rheological damage model is suitable for the damage cracking prediction relative errors of F0005 powder metallurgy steel within the whole range from the initial forging temperature (980 ℃) to the final forging temperature (830 ℃) which are less than +/-5%, and has good and stable prediction capability.
TABLE 2F0005 powder metallurgy steel high temperature rheological Damage model Material parameters
Figure BDA0002920395520000171
In conclusion, the high-temperature tensile test and high-temperature rheological damage model construction method for the powder metallurgy material provided by the invention can meet the simulation prediction requirements of high-temperature rheological damage cracking of the powder metallurgy material required in hot forging, hot rolling, hot extrusion, hot drawing and other hot processing processes of iron-based, aluminum-based, copper-based, titanium-based, magnesium-based and other powder metallurgy materials and the optimized design process of a die.
While the foregoing description shows and describes several preferred embodiments of the invention, it is to be understood, as noted above, that the invention is not limited to the forms disclosed herein, but is not to be construed as excluding other embodiments and is capable of use in various other combinations, modifications, and environments and is capable of changes within the scope of the inventive concept as expressed herein, commensurate with the above teachings, or the skill or knowledge of the relevant art. And that modifications and variations may be effected by those skilled in the art without departing from the spirit and scope of the invention as defined by the appended claims.

Claims (10)

1. A high-temperature tensile test and high-temperature rheological damage model building method for a powder metallurgy material is characterized by comprising the following steps:
step 1: measuring high-temperature tensile load-displacement data of each tensile sample of the powder metallurgy material under different temperatures and strain rates by using a Gleeble heat-force simulation testing machine; meanwhile, measuring temperature distribution data of different positions of each tensile sample along the tensile direction in the tensile process, and determining the relative temperature equalization section of the middle part of each tensile sample;
step 2: establishing a finite element model with the same geometric shape, size and temperature distribution as those of each tensile sample in a finite element simulation program by adopting the temperature distribution data of each tensile sample measured in the step 1;
and step 3: adopting the high-temperature tensile load-displacement data of each tensile sample of the powder metallurgy material measured in the step 1, preliminarily calculating the high-temperature tensile rheological stress-strain data of the powder metallurgy material, then implanting a finite element simulation program, correcting, combining with the finite element model established in the step 2, and simulating and reproducing the high-temperature tensile process of each tensile sample in the step 1;
and 4, step 4: extracting the tensile load and the deformation of the relative temperature-equalizing section in the middle of each tensile sample determined in the step 1 from the finite element simulation result of the high-temperature stretching of each tensile sample in the step 3, and calculating the tensile rheological stress-strain data of the relative temperature-equalizing section in the middle of each tensile sample;
and 5: respectively establishing a high-temperature extensional rheological stress constitutive model and a critical fracture strain model of the powder metallurgy material by adopting extensional rheological stress-strain data of the relative temperature-equalizing section in the middle of each tensile sample calculated in the step 4:
σ＝f(T,ξ,ε)
εf＝f(T,ξ)
sigma and epsilonfRespectively representing the rheological stress and critical fracture strain of the powder metallurgy material under high-temperature stretching; t, xi and epsilon are temperature, strain rate and strain, respectively;
step 6: calculating the critical damage value D of the powder metallurgy material during high-temperature tensile fracture by adopting the powder metallurgy material high-temperature tensile rheological stress constitutive model and the critical fracture strain model established in the step 5f：
Figure FDA0002920395510000011
And 7: adopting the critical damage value D of the powder metallurgy material in high-temperature tensile fracture calculated in the step 6fEstablishing a normalized powder metallurgy material high-temperature extensional rheological damage model, and properly correcting by using an error correction function delta (T, xi), further eliminating the negative influence of the temperature gradient in the middle relative temperature-equalizing section of the tensile sample, so as to obtain the normalized and corrected powder metallurgy material high-temperature extensional rheological damage model:
Figure FDA0002920395510000021
(the cumulative damage value D is more than or equal to 1, cracking occurs; D is less than 1, cracking does not occur)
And 8: and (4) carrying out hot working experimental verification and necessary further correction on the powder metallurgy material high-temperature rheological damage model established in the step (7) to ensure the accuracy of the model.
2. The method for high-temperature tensile test and high-temperature rheological damage model building of powder metallurgy material according to claim 1, wherein the step 1 specifically comprises:
step 1.1: analyzing the actual hot working process of the powder metallurgy material, and determining the hot working process conditions such as the temperature and speed range of the powder metallurgy material in the hot working deformation process;
step 1.2: processing a high-temperature tensile sample with a specified shape and size according to a high-temperature tensile test standard of a metal material and the clamping requirement of a Gleeble thermal-force simulation testing machine;
step 1.3: in the range of the hot processing temperature and speed of the powder metallurgy material determined in the step 1.1, carrying out high-temperature tensile tests of the high-temperature tensile samples processed in the step 1.2 on a Gleeble testing machine under the combination conditions of different temperatures and stress speeds, and measuring high-temperature tensile load-displacement data of each tensile sample at the corresponding temperature and stress speed; meanwhile, a thermodetector is adopted to measure temperature distribution data of different positions of each tensile sample along the tensile direction in the tensile test, and the relative temperature equalization section of the middle part of each tensile sample is determined.
3. The method for high-temperature tensile test and high-temperature rheological damage model building of powder metallurgy material according to claim 1, wherein the step 2 specifically comprises:
step 2.1: establishing a finite element model with the same geometric shape and size as those of the high-temperature tensile sample in the step 1 in a finite element simulation program;
step 2.2: and (3) applying the temperature distribution data of each high-temperature tensile sample measured in the step (1) to each grid unit node of the finite element model established in the step (2.1), and establishing the finite element model with the same geometric shape, size and temperature distribution as those of each high-temperature tensile sample in the step (1).
4. The method for high-temperature tensile test and high-temperature rheological damage model building of powder metallurgy material according to claim 1, wherein the step 3 specifically comprises:
step 3.1: the high-temperature tensile load-displacement data of each tensile sample of the powder metallurgy material measured in the step 1 are adopted, the high-temperature tensile rheological stress-strain data of the powder metallurgy material are preliminarily calculated, and the stress and strain calculation formulas are respectively as follows:
σfirst stage＝4F(1+L/L0)/πd0 2
εFirst stage＝ln(1+L/L0)
σFirst stageAnd εFirst stageThe high-temperature tensile rheological stress and strain of the powder metallurgy material are preliminarily calculated; f and L are measured high-temperature tensile load and displacement of each tensile sample of the powder metallurgy material, and L is measured0And d0The length and the diameter of an initial gauge length section of the tensile sample;
step 3.2: implanting a finite element simulation program into the high-temperature tensile rheological stress-strain data of the powder metallurgy material preliminarily calculated in the step 3.1 in the form of a data set or a high-temperature rheological constitutive model constructed by the stress-strain data, combining with the finite element model established in the step 2, and establishing a finite element model which has the same geometric shape, size and temperature distribution as those of each high-temperature tensile sample in the step 1 and contains the high-temperature tensile rheological stress-strain data of the powder metallurgy material;
step 3.3: applying the same stretching rate and boundary conditions as those of the high-temperature stretching tests in the step 1 to the finite element models of the high-temperature stretching samples established in the step 3.2, simulating the high-temperature stretching test process of the stretching samples in the step 1, and obtaining finite element simulated stretching load-displacement data of the stretching samples under different high-temperature stretching test conditions;
step 3.4: and (3) comparing the high-temperature tensile load-displacement data and the tensile deformation profile of each tensile sample obtained by finite element simulation in the step (3.3) with the high-temperature tensile test result in the step (1), repeatedly regulating and controlling the high-temperature tensile rheological stress-strain data or the corresponding high-temperature rheological stress constitutive model of the powder metallurgy material implanted with the finite element program in the step (3.2) until the high-temperature tensile load-displacement data and the tensile deformation profile of each tensile sample obtained by simulation in the step (3.3) are the same as the high-temperature tensile test result in the step (1), and reproducing the high-temperature tensile test process of each tensile sample in the step (1).
5. The method for high-temperature tensile test and high-temperature rheological damage model building of powder metallurgy material according to claim 1, wherein the step 4 specifically comprises:
step 4.1: extracting the displacements of the finite element grid nodes at two ends of the relative temperature-equalizing section in the middle of each tensile sample determined in the step 1 from the finite element simulation result of the high-temperature stretching of each tensile sample in the step 3, subtracting the displacements to obtain the tensile deformation of the relative temperature-equalizing section in the middle of each tensile sample, and then calculating the tensile strain data of the relative temperature-equalizing section in the middle of each tensile sample, wherein the strain calculation formula is as follows:
ε＝ln(1+L'/L0')
L0'L' and epsilon are respectively the initial length, the tensile deformation and the strain of the middle relative temperature equalizing section of each tensile sample of the powder metallurgy material;
step 4.2: extracting tensile load corresponding to the tensile strain of the relative temperature-equalizing section in the middle of each tensile sample in the step 4.1 from the finite element simulation result of the high-temperature stretching of each tensile sample in the step 3, and calculating the tensile rheological stress data of the relative temperature-equalizing section in the middle of each tensile sample, wherein the rheological stress calculation formula is as follows:
σ＝4F(1+L'/L0')/πd0 2
F、d0and sigma is the load, initial diameter and rheological stress of the relative temperature-equalizing section in the middle of each tensile sample of the powder metallurgy material.
6. The method for high-temperature tensile test and high-temperature rheological damage model building of powder metallurgy material according to claim 1, wherein the step 5 specifically comprises:
step 5.1: and (4) establishing a high-temperature extensional rheological stress constitutive model of the powder metallurgy material by adopting the extensional rheological stress-strain data of the relative temperature-equalizing section in the middle of each tensile sample calculated in the step 4:
Figure FDA0002920395510000041
a0,a1,a2,a3,a4,a5,a6,a7,a8is a material constant;
step 5.2: establishing a high-temperature tensile critical fracture strain model of the powder metallurgy material by adopting the tensile strain data of the relative temperature-equalizing section in the middle of each tensile sample calculated in the step 4:
Figure FDA0002920395510000042
q is the thermal deformation activation energy of the powder metallurgy material; r is an ideal gas constant; t ispThe temperature corresponding to the maximum strain at break; b0,b1,b2,b3,b4,b5Is a material constant.
7. The method for high-temperature tensile test and high-temperature rheological damage model building of powder metallurgy material according to claim 1, wherein the step 6 specifically comprises:
step 6.1: establishing a critical damage value model of the powder metallurgy material high-temperature tensile fracture based on the powder metallurgy material high-temperature tensile rheological stress constitutive model and the critical fracture strain model established in the step 5:
Figure FDA0002920395510000043
step 6.2: calculating the rheological stress of the powder metallurgy material in the high-temperature stretching at 0-epsilon according to the critical damage value model of the powder metallurgy material in the high-temperature stretching fracture established in the step 6.1fThe definite integral of the tensile strain in the range is used to obtain the critical damage value D of the powder metallurgy material at the high-temperature tensile fracturef。
8. The method for high-temperature tensile test and high-temperature rheological damage model building of powder metallurgy material according to claim 1, wherein the step 7 specifically comprises:
step 7.1: adopting the critical damage value D of the powder metallurgy material in high-temperature tensile fracture calculated in the step 6fEstablishing a normalized powder metallurgy material high-temperature extensional rheological damage model:
Figure FDA0002920395510000044
(the cumulative damage value D is more than or equal to 1, cracking occurs; D is less than 1, cracking does not occur)
Step 7.2: implanting a finite element simulation program into the normalized powder metallurgy material high-temperature tensile rheological damage model established in the step 7.1, combining with the finite element simulation for reproducing the high-temperature tensile test process of each tensile sample in the step 3, predicting load-displacement data of each tensile sample subjected to high-temperature tensile fracture, comparing the load-displacement data with the high-temperature tensile test result of each tensile sample in the step 1, and properly correcting by using an error correction function delta (T, xi) to further eliminate the negative influence of the temperature gradient in the relative temperature equalization section in the middle of each tensile sample, thereby establishing the normalized and corrected powder metallurgy material high-temperature rheological damage model:
Figure FDA0002920395510000051
δ(T,ξ)＝c0+c1T+c2T2+c3T3+c4lnξ
(the cumulative damage value D is more than or equal to 1, cracking occurs; D is less than 1, cracking does not occur)
c0,c1,c2,c3,c4Is a material constant.
9. The method for high-temperature tensile test and high-temperature rheological damage model building of powder metallurgy material according to claim 1, wherein the step 8 specifically comprises:
step 8.1: carrying out a hot working experiment of the powder metallurgy material under the conditions of different temperatures and strain rates, and measuring the critical deformation of the powder metallurgy material which is damaged and cracked in the hot working process;
step 8.2: embedding the normalized and corrected high-temperature rheological damage model established in the step 7 into a finite element program, setting finite element simulation conditions the same as those of the hot working experiment in the step 8.1, predicting critical deformation of the powder metallurgy material subjected to damage and cracking in the hot working process, comparing the critical deformation with the actual measurement result in the step 8.1, verifying the prediction precision and stability of the normalized and corrected high-temperature rheological damage model established in the step 7, and performing necessary further correction to obtain the high-temperature rheological damage model of the powder metallurgy material with high precision and high stability.
10. The method for constructing the high-temperature tensile test and high-temperature rheological damage model of the powder metallurgy material according to claim 1, is characterized in that the method for constructing the high-temperature tensile test and the high-temperature rheological damage model is suitable for constructing the high-temperature tensile test and the high-temperature rheological damage model of the powder metallurgy materials such as iron-based, aluminum-based, copper-based, titanium-based and magnesium-based materials, and the constructed high-temperature rheological damage model can be applied to the optimized design of hot working processes such as hot forging, hot rolling, hot extrusion and hot drawing of the powder metallurgy materials and dies.
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