CN109211685B - Processing method of high-temperature strain data of plastic material - Google Patents

Processing method of high-temperature strain data of plastic material Download PDF

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CN109211685B
CN109211685B CN201811097060.4A CN201811097060A CN109211685B CN 109211685 B CN109211685 B CN 109211685B CN 201811097060 A CN201811097060 A CN 201811097060A CN 109211685 B CN109211685 B CN 109211685B
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CN109211685A (en
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陈茉莉
汤剑飞
施则高
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Nanjing University of Aeronautics and Astronautics
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Abstract

The invention discloses a method for processing data of a high-temperature strain test of a plastic material, which mainly comprises the steps of obtaining an end point of a first section of test and a starting point of a second section of test according to control parameters when a extensometer is dismounted, and then carrying out interpolation data processing on curve gross defects caused by the dismounting of the extensometer by combining a threshold value. And calculating the strain value after the extensometer is detached according to the relationship between the displacement and the strain before the extensometer is detached, so that the strain data of the test is integrated. For materials with and without significant yield limits, the yield limit is obtained based on the intersection of the auxiliary curve and the test curve. A constitutive model of the material is obtained based on the data from the point after completion of the yield limit transition to the tensile strength. According to the invention, the automatic processing of test data defect removal, strain data completeness, yield limit calculation and constitutive model parameter fitting can be realized through programming, and the processing efficiency of the high-temperature strain test data of the plastic material can be effectively improved.

Description

Processing method of high-temperature strain data of plastic material
Technical Field
The invention relates to the field of high-temperature mechanical property testing, in particular to a method for processing high-temperature strain test data of a plastic material.
Background
The plastic material can not be broken even if the plastic material has larger deformation, has better shock resistance, is widely applied to the fields of aeroengine casings, nuclear power pipelines and the like, and is dedicated to research and development of novel processing technology of the plastic material by a plurality of domestic and foreign units. In order to know the influence of the novel processing technology on the mechanical property, a material test is needed, and a high-temperature strain test is one of basic mechanical tests of high-temperature resistant plastic materials.
In the high temperature strain test of plastic materials, commonly used sensors include displacement sensors, force sensors and high temperature extensometers for testing strain. The high-temperature extensometer matched with the domestic and foreign material testing machine is based on the working principle of a bridge circuit and structurally comprises a tool bit, a force arm, a circuit device, a lead wire and the like. The high-temperature tensile extensometer comprises 2 cutter heads, wherein the cutter heads are in contact with a test piece and are executive elements for the test piece strain test. The initial distance between 2 tool bits is called the standard square, and when the test piece takes place to warp, the distance between 2 tool bits changes along with the deformation of test piece, tests the distance of 2 tool bits through the bridge circuit, can obtain the average strain of test piece in the standard square.
For high temperature extensometers, the tool tip is typically made of ceramic or quartz materials because these two materials are resistant to high temperatures and have little deformation at high temperatures, which can more accurately respond to the deformation of the test piece. The defects that the ceramic and the quartz are both brittle materials, so that the measuring range of the high-temperature strain extensometer is limited, and large deformation cannot be tested, which causes the strain test of the large-deformation high-temperature plastic material to be difficult.
High temperature plastic materials have large deformation and obvious necking, and if the ratio of the test piece displacement to the test piece length is used for estimating strain, the error is often very large. In order to make the test result accurate and make the best use of the test result, the high-temperature strain test process of the plastic material is generally divided into two sections: the first stage of test, presetting an upper limit value of strain slightly smaller than the full range of the extensometer, testing the strain of the test section of the test piece by using the high-temperature extensometer until the strain reaches the preset value, stopping the movement of the testing machine and keeping the current test state, and removing the extensometer; in the second test, the loading was continued until the test piece broke, with the extensometer removed. Therefore, the first section of test can acquire accurate strain data, and the second section of test has no strain data, so that the requirement of the test on the strain test is met to the maximum extent under the existing test conditions.
However, the high temperature plastic material segment test still has two problems to be solved: 1) estimating the strain data of the second section of test to ensure that the strain data is complete, thereby estimating the maximum engineering strain, engineering stress, true strain, true stress and the like; 2) the data processing of the gross defects caused by the removal of the extensometer is that although partial strain data are obtained in the subsection test, the loading is suspended due to the removal of the extensometer, so that an artificial gross defect (local discontinuity) appears on an original smooth test curve, the gross defect is caused by the sudden drop of local load caused by impact vibration, and the calculation accuracy of material constitutive model parameters is seriously influenced even a completely wrong result is caused by the existence of damping vibration in a short period of time after the test loading is continued.
For the problem 1), the common data processing method is to estimate the strain value after the extensometer is detached by using the elastic modulus and the loading force data, the method is simple, but the full range of the high-temperature extensometer is generally about 10%, most plastic materials enter a plastic section during the process of detaching the extensometer, and a great error is caused by estimating the plastic strain by adopting an elastic mode.
For the problem of 2), a common treatment is to treat the defect as a gross error, and then directly delete the defect data to make the curve look smooth. This approach does not fundamentally eliminate the discontinuity of the test data, and the existence of the discontinuity necessarily results in an error or error in the calculation of the constitutive model parameters of the plastic material.
Disclosure of Invention
The purpose of the invention is as follows: the invention provides a method for processing data of a high-temperature strain test of a plastic material, which solves the problems of incomplete strain test data and data processing of test results containing discontinuities caused by insufficient high-temperature strain extensometer measuring range of a ceramic or quartz cutter head during a high-temperature test of a large-deformation plastic material, and also solves the problem of parameter estimation of a constitutive model of the large-deformation plastic material. The method makes the processing process of the mechanical test data of the high-temperature large-deformation plastic material flow, facilitates the automatic processing of the test data through software programming, is suitable for the estimation of constitutive model parameters of various plastic materials, and can greatly improve the processing efficiency of the test data.
The technical scheme is as follows: in order to achieve the above object, the present invention may adopt the following technical solutions.
A processing method of high-temperature strain test data of a plastic material comprises a first section of test and a second section of test, wherein after the first section of test is finished, the testing machine stops moving and keeps the current state, an extensometer is dismounted, and the second section of test is started; setting extensometer control parameters as single parameters representing the pause motion of the testing machine, wherein in the testing process, when the response value of a sensor set by a program reaches the control parameters, a first section of test is finished, the testing machine pauses motion, a test data acquisition system acquires data of a plurality of sensors at equal time intervals from the beginning of the first section of test to the end of a second section of test, and the whole test data can be exported by the test system into a column format text file with a question header, and the processing method of the test data comprises the following steps:
(1) recording extensometer unloading parameters for controlling the end of the first section of test, and exporting all collected data as a text file, wherein each column in the file represents a sensor variable respectively; one of the columns represents displacement, one of the columns represents force, and one of the columns represents acceleration.
(2) Removing the question header of the test data file in the step (1) to enable the test data file to be in a pure numerical format;
(3) according to a control parameter c during the removal of the extensometer0Retrieving a data file, the control parameter c0Setting a small quantity epsilon corresponding to a specific value of a certain sensor in the test program1In the data file, at c0In the corresponding column of the sensor, test data c are sequentially searched and recorded from the 1 st line to the last line of the fileiLet | ci-c0|<ε1Obtaining a two-dimensional set { (l)i,ci)|i＝1,2,…m，liIs ciCorresponding row number, m is the set length }, let N1＝l1Its physical meaning is the row number at the end of the first trial; let N2＝lmIts physical meaning is the line number at the beginning of the second test; setting a small threshold epsilon2And 15 ε1>ε2>5ε1Finding out the line number N after the loading force exceeds the local extreme value in the second test starting period3；
(4) Setting a natural number N4Let N stand for5＝N3-N2+N4Are respectively paired with [ N1+1，N3]The displacement and the force in the range are interpolated, the number of interpolation points is N5；
(5) From Nth2The line start search force is first reduced to a line number N less than or equal to 0kNe；NeReflecting the real end time of the test, reading NeThe displacement of the row obtains the maximum displacement data of the test;
(6) to [1, N ] in the data file1]Line-wide displacement data, N by interpolation5Displacement data, data file [ N3，Ne]The displacement data in the line range are connected to obtainDisplacement data after defect removal, N in totald＝Ne-N3+N1+N5+1 data;
(7) to [1, N ] in the data file1]Line-wide force data, interpolated N5Individual force data, data file [ N3，Ne]Connecting the force data in the line range to obtain the force data after the hair defect is removed, wherein the data volume and the displacement are the same and are NdA piece of data; dividing the force data by the cross-sectional area of the test piece to obtain engineering stress data;
(8) setting a natural number N7And N8，N7<N8And make the Nth1-N8Row data in plastic phase, pair [ N1-N8,N1-N7]Performing polynomial fitting on the displacement and strain curves in the line range to obtain the displacement-strain relation before detaching the extensometer, and according to the relation and [ N1+1,Nd]Displacement data in the range, and the strain after the first stage of test is calculated to be [ N ]1+1,Nd]Data within a range;
(9) 1, N in the data file1]Line-wide strain data, [ N ] calculated in step 8)1+1,Nd]Connecting the strain data in the range to obtain complete strain data, and obtaining the Nth engineering straindIndividual strain values;
(10) obtaining the maximum force through a search algorithm; according to the maximum force and the cross section area of the test section of the test piece, the tensile strength of the material can be obtained;
(11) obtaining the true strain and the true stress of the material according to the calculation formulas of the engineering strain and the true strain and the engineering stress and the true stress;
(12) selecting an elastic section on an engineering strain-engineering stress curve, and calculating the elastic modulus E of the material through linear fitting;
(13) calculating the yield limit of the material;
for materials with significant yield limits, the method of calculating the yield limit of the material is as follows:
13a) multiplying all the strain data by E to obtain an auxiliary curve sigmae＝Eεe，σeFor engineering stress,. epsiloneIs engineering strain;
13b) for domain [1, N1]Sequentially calculating the difference value between the engineering stress data and the auxiliary curve according to the engineering strain of the line, and performing differential calculation on the difference value sequence;
13c) setting a differential small quantity epsilon3And is epsilon3<-50Mpa, finding the difference smaller than epsilon using a search algorithm3Line number N of the first data of (2)9In the definition domain [1, N9]Searching the maximum engineering stress in the line range as the yield limit sigma of the materialp；
For materials without a significant yield limit, the method of calculating the yield limit of the material is as follows:
13d) searching the strain data for the line number N at which the strain value closest to the 0.2% absolute difference is located10；
13e) Setting a natural number N11And N is11>Nd[ 4 ] strain [ N10,N10+N11]Definition domain of line composition, calculating auxiliary curve function sigmae＝E(εe-0.002)；
13f) To strain [ N ]10,N10+N11]Calculating the difference between the auxiliary curve and the engineering stress in the definition domain, searching for the difference with the minimum absolute value by using a search algorithm, and recording the engineering stress corresponding to the difference as the yield limit sigma of the materialp；
(14) Record σpLine number N in engineering stress data12；
(15) Searching the line number N where the maximum true stress is located by utilizing a search algorithm13Setting a natural number N14Make N be12+N14<N13Will [ N ]12+N14,N13]And substituting the true strain and true stress data in the line range into a constitutive model of the material, and estimating a hardening coefficient a and a hardening index n in the constitutive model through polynomial fitting.
Preferably,. epsilon.in step (3)1＝c0/5000，ε2＝100ε1。
Preferably, N in step 4)4The interpolation mode is linear interpolation 20.
Preferably, N in step 8)7＝int[Ne/240],N8＝5N7，N1-N8>200, displacement and strain curves are in a linear fitting mode.
Preferably, the search algorithm in all steps is a bubble algorithm.
Preferably,. epsilon.in step (13)3＝-65Mpa。
Further, the calculation formula of the engineering strain and the true strain is as follows:
εt＝log(1+εe)σt＝σe(1+εe)
wherein epsilontIs true strain, σtIs true stress.
Preferably, N in step (15)14＝int[Ne/30]
Has the advantages that:
the invention has the following positive effects on the plastic material high-temperature large-strain sectional test due to the insufficient measuring range of the extensometer:
1. the method is convenient for automatic programming realization, and ensures that no break point exists in the transition between the first section of test data and the second section of test data, which is closer to a true value, and the parameter estimation of a subsequent constitutive model is more accurate.
2. Based on the function relation between displacement and strain of the plastic deformation section before the extensometer is detached, the method for estimating the strain data after the extensometer is detached is provided, so that the strain data is integrated.
3. The method is suitable for calculating the high-temperature yield limit of the plastic material and also suitable for calculating the yield limits of any other materials at high temperature, normal temperature, low temperature and the like.
4. And the identification of parameters in the material constitutive model is realized by retrieving data rows of yield limit and tensile strength. The method is convenient for automatic programming to realize the constitutive model building of the material, and is suitable for building constitutive models of high-temperature plastic materials and other metal or intermetallic compound materials.
5. Through the proposed high-temperature test data processing method, parameters such as maximum displacement, maximum load, engineering strain, engineering stress, true strain, true stress, yield strength, tensile strength, flow stress, elastic modulus, hardening coefficient, hardening index and the like of the material can be obtained through automatic programming.
Drawings
FIG. 1 test data processing flow;
FIG. 2 test data file format;
FIG. 3 is a graph showing displacement-force curves obtained by the test;
FIG. 4 is a graph showing the strain curves obtained by the test;
FIG. 5 shows the displacement curves obtained in the test, a) being a whole graph and b) being a partial enlarged graph;
FIG. 6 is a graph showing displacement-strain curves obtained by the test;
FIG. 7 is a schematic illustration of gross defects at the transition between the first and second test data;
FIG. 8 is a schematic view of displacement-force curves after treatment of a hair defect;
FIG. 9 is a complete engineering strain curve;
FIG. 10 is a schematic diagram of engineering strain-engineering stress curves after treatment of a hair defect;
FIG. 11 is a schematic diagram of true strain-true stress curves;
FIG. 12 is a schematic view of a calculation of the yield limit of a material with a clear yield limit, a) in its entirety, b) in a partially enlarged view;
FIG. 13 is a schematic illustration of a material yield limit calculation without a significant yield limit;
FIG. 14 is a graph comparing the parameter identification result of the constitutive model with the test result, wherein σ is0Is a rheological stress,. epsilon0＝σ0E; e is the modulus of elasticity.
Detailed Description
The processing method of the plastic material high temperature strain test data provided by the invention is explained with reference to the attached drawings.
The high temperature strain test divides the test into two sections by setting extensometer removal control parameters in a test program, the test comprises a first section of test and a second section of test, wherein the first section of test can acquire effective strain data, after the first section of test is finished, the testing machine stops moving and keeps the current state, the extensometer is dismounted, the second section of test has no effective strain data, the control parameter of the extensometer is a single parameter representing the pause movement of the testing machine, in the test process, when the response value of the sensor set by the program reaches the control parameter, the first section of test is finished, the testing machine stops moving, the test data acquisition system acquires data of a plurality of sensors (the sensors corresponding to the extensometer unloading control parameter must be included) at equal time intervals from the beginning of the first section of test to the end of the second section of test, and the whole test data can be exported into a column format text file with a question header by the test system.
The method for processing the high-temperature strain test data of the plastic material comprises the following steps:
1) a data file with the sensor variables as column formats is obtained, as shown in fig. 2, the 1 st column represents displacement measured data, the 3 rd column represents strain measured data, the 4 th column represents force measured data, and the rest columns represent auxiliary data, such as displacement control signals, running time and the like.
2) The test data file is subject to the question header removal to be in a pure numerical format, and if the test data volume is too large, the test data can be properly compressed, so that the data processing efficiency is accelerated.
3) As shown in FIG. 5, the control parameter when the extensometer is removed is that when the cylinder displacement reaches 5mm, c0However, the data collected by the experiment has errors, it is difficult to find a row with a displacement equal to 5mm from the first column in fig. 2, or the data with a displacement of 5mm contains a plurality of rows, so that the error threshold is set to be a small amount epsilon10.001mm, in the displacement column data, from line 1 to the last line of the file, test data c is searched and recorded in sequenceiLet | ci-c0|<ε1Obtaining a two-dimensional set { (l)i,ci)|i＝1,2,…m，liIs ciCorresponding row number, m is the set length }.
4) Let N1＝l1Let N stand for2＝lm。
5) From the displacement-force curves in FIG. 3 and the enlarged views in FIG. 7, it can be seen that N is2The row is located at the bottom of the defect, so that a threshold value epsilon is set2Can order epsilon2Finding out the line number N after the loading force exceeds the local extreme value in the beginning period of the second period of test3The displacement data of this row is the first occurrence c0Data 0.1mm larger.
6) Setting a natural number N 420, let N5＝N3-N2+N4Are respectively paired with [ N1+1，N3]The displacement and the force in the range are interpolated, the number of interpolation points is N5. With this method, not only can the hair defects be removed, but also a smoother displacement and force curve can be obtained, as shown in fig. 8.
7) As shown in fig. 2 and 7, it can be seen from the data at the end of the curve that the test data acquisition is not stopped after the test piece is snapped, but data after the load is reduced to 0kN or less is acquired along with the impact at the time of breaking, but the data after 0kN is redundant data and affects the calculation of the maximum displacement, the maximum engineering strain and the like, so that an effective breaking position needs to be found, namely, the line number of the load is reduced to 0kN or less. From the Nth2Line number N with line start search loading force reduced to below 0kNe。NeReflecting the real end time of the test, reading NeThe displacement of the row, the maximum displacement of the test can be obtained.
8) For [1, N ] in data file1]Line-wide displacement data, N by interpolation5Displacement data, data file [ N3，Ne]The displacement data in the line range is connected with the 3 segments of data to obtain the displacement data after the defect is removed, and N is totald＝Ne-N3+N1+N5+1 data.
9) For [1, N ] in data file1]Line-wide force dataN obtained by interpolation5Individual force data, data file [ N3，Ne]Connecting the 3 segments of data to obtain the force data after removing the flaw, wherein the data volume and the displacement are the same and are NdAnd (4) data. And dividing the force data by the cross-sectional area of the test piece to obtain engineering stress data.
10) As shown in fig. 4 to 6, although the displacement-force curve in fig. 7 is a non-linear curve, the relationship between displacement and strain is close to linear in the first stage of the test, and the test can obtain complete displacement data, so that the data of strain in the second stage of the test can be fitted through the relationship between displacement and strain, and the strain data can be completed.
11) Considering the nonlinear influence in fig. 7, the strain data of the second test is fitted only with the displacement-strain relationship before the removal of the extensometer, and the strain data of the second test is obtained by using the displacement data of the second test as an independent variable. The specific method comprises the following steps:
11a) setting a natural number N7And N8，N7<N8And make the Nth1-N8Row data in plastic phase, pair [ N1-N8,N1-N7]Performing polynomial fitting on the displacement and strain curves in the line range for the first time to obtain the displacement-strain relation before detaching the extensometer, and according to the relation and [ N ]1+1,Nd]Displacement data in the range, and the strain after the first stage of test is calculated to be [ N ]1+1,Nd]Data within the range.
11b) Will [1, N ] in the data file1]Line-wide strain data, [ N ] calculated in step 8)1+1,Nd]Connecting the strain data in the range to obtain complete strain data, and obtaining the Nth engineering straindIndividual strain values.
12) The maximum force is obtained by the search algorithm. And obtaining the tensile strength of the material according to the maximum force and the cross section area of the test section of the test piece.
13) The true strain and the true stress of the material can be obtained according to the calculation formulas of the engineering strain and the true strain, the engineering stress and the true stress, the engineering strain-engineering stress curve is shown in fig. 11, and the true strain-true stress curve is shown in fig. 12.
14) And selecting an elastic section on an engineering strain-engineering stress curve, and calculating the elastic modulus E of the material through linear fitting.
15) Referring to fig. 7, the test piece has no material with obvious yield limit, and the method for calculating the yield limit of the material is as follows:
15a) searching the strain data for the line number N at which the strain value closest to the 0.2% absolute difference is located10；
15b) Setting a natural number N11And N is11>Nd[ 4 ] strain [ N10,N10+N11]Definition domain of line composition, calculating auxiliary curve function sigmae＝E(εe-0.002) as shown in fig. 13.
15c) To strain [ N ]10,N10+N11]Calculating the difference between the auxiliary curve and the engineering stress in the definition domain, searching for the difference with the minimum absolute value by using the search algorithm, and recording the engineering stress corresponding to the difference, which is the yield limit sigma of the materialpAs shown in fig. 13.
16) Record σpLine number N in engineering stress data12Searching for the line number N where the maximum true stress is13Setting a natural number N14Make N be12+N14<N13Will [ N ]12+N14,N13]The true strain and true stress data in the line range are substituted into the constitutive model of the material, the hardening coefficient a, the hardening index n, and the like in the constitutive model are estimated by polynomial fitting, and the results of fitting the curve and the test curve are shown in fig. 14.
17) The final high temperature plastic material test data processing results are shown schematically in table 1.
TABLE 1 test data processing results
Figure GDA0002819967400000071

Claims (5)

1. A processing method of high-temperature strain test data of a plastic material is characterized in that the test comprises a first section of test and a second section of test, wherein after the first section of test is finished, the test machine stops moving and keeps the current state, an extensometer is dismounted, and the second section of test is started; setting extensometer control parameters as single parameters representing the pause motion of the testing machine, wherein in the testing process, when the response value of a sensor set by a program reaches the control parameters, a first section of test is finished, the testing machine pauses motion, a test data acquisition system acquires data of a plurality of sensors at equal time intervals from the beginning of the first section of test to the end of a second section of test, and the whole test data is exported by the testing system into a column format text file with a question head, and the processing method of the test data comprises the following steps:
(1) recording extensometer unloading parameters for controlling the end of the first section of test, and exporting all collected data as a text file, wherein each column in the file represents a sensor variable respectively; one column representing displacement, one column representing force, and one column representing acceleration;
(2) removing the question header of the test data file in the step (1) to enable the test data file to be in a pure numerical format;
(3) according to the control parameters when the extensometer is detachedc 0Retrieving a data file, the control parameterc 0Setting small quantities corresponding to specific values of a certain sensor in a test programε 1In the data file, inc 0In the corresponding column of the sensor, test data are sequentially searched and recorded from the 1 st line to the last line of the filec i To enable gradient of oxygenc i -c 0|<ε 1Obtaining a two-dimensional set { (l i ,c i )|i=1,2,…m，l i Is composed ofc i The number of the corresponding line is set to,mset length, letN 1=l 1Its physical meaning is the row number at the end of the first trial; order toN 2= l m Its physical meaning is the second stageThe row number at the start of the test; setting a small thresholdε 2And 15 areε 1>ε 2>5ε 1，ε 1=c 0(5000); finding out the line number after the loading force exceeds the local extreme value in the second period of test starting periodN 3；
(4) Setting natural numberN 4，N 4= 20; order toN 5=N 3- N 2+N 4Respectively for [ 2 ], [N 1+1，N 3]The displacement and the force in the range are interpolated, the number of interpolation points isN 5；
(5) From the firstN 2The line start search force is first reduced to a line number of less than or equal to 0kNN e ；N e Reflecting the true end time of the test, readingN e The displacement of the row obtains the maximum displacement data of the test;
(6) and the data file is stored for the data file [1,N 1]displacement data in line range, obtained by interpolationN 5The displacement data and the data fileN 3，N e ]Connecting the displacement data in the line range to obtain the displacement data after removing the flaw, andN d =N e -N 3+N 1+N 5+1 data;
(7) and the data file is stored for the data file [1, N 1]line-wide force data, interpolatedN 5Personal data, data fileN 3，N e ]Connecting the force data in the line range to obtain the force data after removing the flaw, wherein the data volume and the displacement are the same and are allN d A piece of data; dividing the force data by the cross-sectional area of the test piece to obtain engineering stress data; (8) setting natural numberN 7AndN 8，N 7<N 8and make it firstN 1-N 8The row data is in the plasticity stage, para [, ]N 1-N 8, N 1-N 7]Polynomial fitting is carried out on the displacement and strain curves in the line range to obtain the relation of displacement and strain before the removal of the extensometer, and the relation is obtained according toN 1+1,N d ]Displacement data in the range, and calculating the strain after the first stage of test is finishedN 1+1,N d ]Data within a range;N 7=int[N e /240],N 8=5N 7，N 1-N 8>200；
(9) and the step of storing the value of [1,N 1]data on strain in the line range, calculated in step 8 [ ], ] [, ]N 1+1,N d ]Connecting the strain data within the range to obtain complete strain data, and obtaining the maximum engineering strainN d Individual strain values;
(10) obtaining the maximum force through a search algorithm; according to the maximum force and the cross section area of the test section of the test piece, the tensile strength of the material can be obtained;
(11) obtaining the true strain and the true stress of the material according to the calculation formulas of the engineering strain and the true strain and the engineering stress and the true stress;
(12) selecting an elastic section on an engineering strain-engineering stress curve, and calculating the elastic modulus of the material through linear fittingE；
(13) Calculating the yield limit of the material;
for materials with significant yield limits, the method of calculating the yield limit of the material is as follows:
13a) multiplying the entire strain data byETo obtain an auxiliary curveσ e =Eε e ，σ e In order to achieve the engineering stress,ε e is engineering strain;
13b) for the definition of the domain [1,N 1]sequentially calculating the difference value between the engineering stress data and the auxiliary curve according to the engineering strain of the line, and performing differential calculation on the difference value sequence;
13c) setting a differential quantumε 3And is andε 3<-50Mpa, finding the difference smaller thanε 3Line number of the first data ofN 9The method is performed in the domain of definition [1,N 9]searching the maximum engineering stress in the line range as the yield limit of the materialσ p ；
For materials without a significant yield limit, the method of calculating the yield limit of the material is as follows:
13d) search for the line number in the strain data where the strain value closest to 0.2% absolute difference is locatedN 10；
13e) Setting natural numberN 11And is andN 11>N d [ 4 ] corresponding to the variation [ 2 ]N 10,N 10+N 11]Definition domain of line composition, calculating auxiliary curve functionσ e =E(ε e -0.002)；
13f) For strainN 10,N 10+N 11]Calculating the difference between the auxiliary curve and the engineering stress in the definition domain, searching for the difference with the minimum absolute value by using a search algorithm, and recording the engineering stress corresponding to the difference as the yield limit of the materialσ p ；
(14) Recordingσ p Line number in engineering stress dataN 12；
(15) Searching for line number of maximum true stress by using search algorithmN 13Setting natural numberN 14，N 14=int[N e /30](ii) a Make itN 12+N 14<N 132 ofN 12+N 14,N 13]The true strain and true stress data in the line range are substituted into the constitutive model of the material, and the hardening coefficient in the constitutive model is estimated through polynomial fittingaHardening indexn。
2. The processing method according to claim 1, characterized in that: the interpolation mode in the step 4) is linear interpolation.
3. The processing method according to claim 1, characterized in that: the search algorithm in all steps is a bubble algorithm.
4. The processing method according to claim 1, characterized in that: in the step (13)ε 3=-65Mpa。
5. The process of claim 1, wherein the engineering strain and the true strain are calculated by the formula:
ε t =log(1+ε e ) σ t =σ e (1+ε e )
whereinε t In order to be a true strain,σ t is true stress.
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