CN110763568B - Method for determining thickness anisotropy coefficient of pipe in any direction - Google Patents
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Abstract
A method for determining the anisotropy coefficient of a pipe in any direction belongs to the field of pipe performance testing. The method comprises the steps of firstly establishing a relational expression between the thickness anisotropy in any direction and a yield function, determining the undetermined coefficient of the yield function through a pipe bidirectional loading experimental method, and then substituting the established relational expression to determine the thickness anisotropy coefficient in any direction of the pipe. The method ensures the accuracy and reliability of the anisotropy coefficient from three aspects: 1) blanks of related experiments are original tube blanks, the shape of the tube is not required to be damaged, pre-deformation is not introduced, and the obtained experiment result can accurately reflect the plasticity of the tube; 2) an advanced yield function can be selected, and experimental data under different loading paths can be introduced simultaneously, so that the plastic flow characteristic of the pipe can be reflected more comprehensively; 3) designing characteristic experiments for obtaining the same deformation in different directions, and repeatedly iterating the finite element analysis and the characteristic experiments to ensure that the coefficients of the shearing components are accurate and reliable, thereby establishing an accurate and reliable yield function.
Description
Technical Field
The invention belongs to the field of pipe performance testing, and particularly relates to a method for determining the thickness anisotropy coefficient of a pipe in any direction.
Background
The hollow integral component manufactured by utilizing the metal pipe has the advantages of structure weight reduction and excellent mechanical property, and is widely applied in the fields of aerospace, automobiles and the like. Such members are generally manufactured by internal high pressure forming techniques in which a tube undergoes deformation under the combined action of internal pressure and axial force, and the tube undergoes a complex stress path from sealing, preforming to final forming. For complex components, even the process of loading-unloading-reloading can be carried out, and once the loading path is unreasonable, defects such as wrinkling, cracking and the like can occur. It is therefore important to determine reasonable process parameters (such as load paths, etc.) by accurate finite element analysis prior to forming. The premise of carrying out accurate finite element analysis is to construct an accurate plastic constitutive relation model, wherein the thickness anisotropy coefficients in different directions are important parameters for constructing the plastic constitutive relation model of the material. Common light alloy pipes can be generally divided into two types, one is seamless pipes manufactured by extrusion, such as aluminum alloy pipes, titanium alloy pipes, magnesium alloy pipes and the like; one type is a seamed pipe such as stainless steel, high strength steel pipe, etc. which is formed by rolling and then welding. The two types of pipes have obvious anisotropy, and the thickness anisotropy coefficients r of materials in different directions of the pipes are different, namely the materials in different directions of the pipes have different thinning resistance, and the pipe has different wall thickness distribution characteristics in different directions when the same deformation occurs. In addition, the stress principal axis is changed constantly when the complex section pipe member is formed, the stress principal axes of materials at different positions are different and are not coincident with the anisotropy principal axis of the materials, so that the construction of accurate pipe plastic constitutive relation not only needs the thickness anisotropy coefficients r of two principal axis directions in the pipe surfacezAnd rθThe thickness anisotropy coefficient of the tube in the non-principal axis direction is also required
(lower corner mark)
Representing the angle with the main axis z), e.g. the yield function r of Hill4845(ii) a Model parameter alpha of YLd2000-2d yield function7And alpha8By anisotropic parameters other than the principal axis, e.g. r45、r30、r60Determination and the like.
For the seamed pipe formed by coil welding after rolling, the measurement can also be carried out according to the FB/T5027-2016 standard by referring to the test method of the plate material. However, for the extruded seamless tube, because the tube has closed geometric characteristics, the value of the anisotropy coefficient r of the tube in any direction can not be obtained by directly referring to the measurement method of the plate. For determining the thickness coefficient of the extruded pipe, the following methods are available: (1) cutting an arc-shaped single-pull sample on the surface of the pipe along the axial direction, flattening the end part of the sample, and obtaining the axial thickness anisotropy coefficient r of the pipe through a unidirectional tensile testz. The method can only approximately obtain the axial thickness anisotropy coefficient of the pipe, and the middle measuring area of the sample is arc-shaped, so that the measurement error of the size in the width direction is easy to cause. (2) Intercepting a hoop tensile sample, and obtaining the hoop thickness anisotropy coefficient r of the pipe through a hoop tensile testθ(e.g. patent CN 104949884A). The method can only approximately obtain the circumferential direction anisotropy coefficient of the pipe, and the experimental result is inaccurate due to the fact that friction force exists between a sample and a used fixture during testing. Both the two methods can only obtain approximate axial and circumferential anisotropy coefficients of the extruded pipe, and can not accurately determine the anisotropy coefficients of the metal pipe in any direction.
In order to construct an accurate plastic constitutive relation of an extruded pipe, further perform accurate finite element analysis and determine reasonable process parameters, thereby reducing the research and development cost of a thin-wall hollow integral component and shortening the research and development time, a method capable of accurately determining the thickness anisotropy coefficient of the extruded pipe in any direction needs to be established.
Disclosure of Invention
The invention provides a method for determining the thickness direction anisotropy coefficient of a pipe in any direction, aiming at solving the problem that the thickness direction anisotropy coefficient of an extruded pipe in any direction cannot be obtained by the existing testing methods.
The core idea of the invention is as follows: establishing a relational expression between the thickness anisotropy in any direction and the yield function, determining the undetermined coefficient of the yield function by a pipe bidirectional loading experimental method, and then substituting the established relational expression to determine the thickness anisotropy coefficient of the pipe in any direction.
The technical scheme adopted by the invention for solving the problems is as follows:
a method for determining the anisotropy coefficient of a pipe in any direction is shown in figure 1, and comprises the following steps:
cutting a tube blank to be tested into a sample to be tested, and performing a bidirectional controllable loading bulging experiment on different tubes to obtain experimental data of stress and strain of the tubes in a bidirectional stress state under different fixed collar stress ratio loading paths;
selecting an equivalent strengthening state parameter to represent a strengthening state, and calculating stress and strain data of different loading paths under the same strengthening state by using the experimental data in the step one;
step three, selecting a proper yield function f,
determining a coefficient A to be determined in the yield function f by using the stress and strain data obtained in the step two; wherein sigmaz0For axial single tensile stress, σz、σθAnd σzθRespectively axial stress, hoop stress and shear stress of the pipe; a is an undetermined coefficient matrix of the main stress component, and U is an undetermined coefficient of the shear stress component; m is the power of the yield function;
reasonably setting undetermined coefficients U which cannot be determined by the experimental data in the first step and the second step in the yield function f, and giving initial values of the coefficients;
step five, performing characteristic experiments of plastic deformation of the pipe in different directions, and drawing experiments of the cylindrical part similar to the plate, so as to realize wall thickness distribution characteristics caused by anisotropy in different directions when the plastic deformation occurs, and extracting wall thickness experimental data in different directions;
step six, carrying out finite element analysis on the characteristic experiment in the step five by using the yield function f constructed in the step one to the step four, and extracting wall thickness simulation data in the same direction with the same deformation in the step five;
step seven, comparing and analyzing the wall thickness data in the corresponding direction under the condition of the corresponding deformation in the step five and the step six, and adjusting the value of the coefficient in the step four when the difference between the wall thickness data and the wall thickness data exceeds a set error range;
step eight, repeating the step four, the step six and the step seven until the wall thickness difference in the step six and the step five is within a set error range, and determining that the value of the coefficient in the step four is the optimal value meeting the requirement at the moment so as to determine a yield function f;
step nine, further calculating the thickness anisotropy coefficient of the pipe in any direction through the yield function f determined in the step eight
Further, in the first step, the two-way controllable loading bulging experiment of the pipe is to apply pressure in the pipe and apply axial tension or pressure on the end of the pipe at the same time, so that the pipe deforms under a set linear stress path, and flow stress and flow strain experiment data under the two-way stress state of the pipe are obtained, and the flow stress and flow strain experiment data specifically comprise axial strain epsilonzαStress component σzαHoop strain epsilonθαStress component σθαAnd alpha is the ratio of axial stress and hoop stress in the double-pull controllable loading bulging experiment, and the loading path is controlled to obtain experimental data under different alpha.
Further, the second step comprises the following specific steps: the equivalent strengthening state parameter is plastic work WpFirst order increment of plastic work dWpOr second order increase of plastic work d2Wp；
When taking out the plastic work WpWhen the equivalent enhanced state parameter is obtained, the method passes
Wherein p represents that all experimental quantities are plastic components,
is the incremental component of the axial plastic strain of the pipe,
is the incremental component of hoop plastic strain of the pipe, sigmazIs the axial stress component, σ, of the pipeθIs the hoop stress component of the pipe.
When the first-order increment dW of the plastic work is takenpWhen the equivalent enhanced state parameter is obtained, the method passes
Wherein σijFor any of the components of the stress,
is any incremental component of plastic strain.
When taking the second-order increment d of plastic work2WpWhen the equivalent enhanced state parameter is obtained, the method passes
Further, in the third step, the yield function f is a Hill series yield function, a Barlat89 yield function or a YLd2000-2d yield function.
Further, in the fourth step, the initial value of the coefficient U is set reasonably in the following two ways:
(1) taking an empirical value 1 as an initial value of the coefficient U, taking a large step length of 0.2-0.4 as an initial adjustment step length in the adjustment of the coefficient U in the step seven, and taking a small step length of 0.01-0.05 as an adjustment step length after the range is locked until the error requirement is met;
(2) and (3) setting the value of the thickness anisotropy coefficient in a direction other than the main axis direction of the pipe as the thickness anisotropy coefficient in the axial direction of the pipe, and calculating the initial value of the coefficient U by using the thickness anisotropy coefficient in the direction.
Further, in the seventh step, the wall thickness difference criterion of the finite element analysis and the characteristic experiment may be selected as:
wherein the content of the first and second substances,
and
wall thickness data extracted by finite element analysis in the step six and wall thickness data extracted by characteristic experiments in the step five are respectively obtained, n is the number of data points, and psi is a set error range; when the wall thickness error is within the set error, stopping adjusting the coefficient U;
the set error range ψ is expressed as:
wherein, tz finite element analysisAnd tz characteristic experimentThe wall thickness is obtained through finite element analysis and characteristic experiments in the axial direction of the pipe respectively, m is the number of data points, eta is an amplification factor, and the value range is 1.5-2.
Furthermore, in the eighth step, the coefficient of anisotropy of the pipe in any direction is determined
The calculation process is as follows:
according to the definition of the thickness anisotropy coefficient and the condition of unchanged material volume, the thickness anisotropy coefficient and the material volume are axially formed with the pipe
Thickness anisotropy coefficient in angular direction
Expressed as:
wherein d εzAnd d εθPlastic strain increment, d epsilon, in axial and circumferential directions of the pipe respectivelyzθIs the shear strain increment.
Further obtaining the thickness anisotropy coefficient by Drucker flow criterion
Relation to yield function f:
the invention has the beneficial effects that:
firstly, the thickness anisotropy coefficient of the pipe in any direction can be accurately determined: the three aspects can ensure that the obtained thick anisotropy coefficient is accurate and reliable: (1) the blanks of the experiment are original tube blanks, the shape of the tube is not required to be damaged, pre-deformation is not introduced, and the obtained experiment result can accurately reflect the plasticity of the tube; (2) an advanced yield function f can be selected, and experimental data under different loading paths can be introduced simultaneously, so that the plastic flow characteristic of the pipe can be reflected more comprehensively; (3) and designing a characteristic experiment in which plastic deformation occurs in different directions, and repeatedly iterating the finite element analysis and the characteristic experiment to ensure that the coefficient of the shearing component is accurate and reliable, so that an accurate and reliable yield function f is established.
Secondly, the thickness anisotropy coefficients in any direction of the pipe determined by the method can be used for constructing an accurate pipe plasticity constitutive relation, such as the thickness anisotropy coefficients in the axial direction, the circumferential direction, the direction of 45 degrees with the axial direction and other directions required for constructing the accurate pipe plasticity constitutive relation are provided.
And thirdly, the thickness anisotropy coefficient of the pipe in any direction determined by the method can be used for accurately and comprehensively describing the plastic flow characteristic of the anisotropic pipe.
The thickness anisotropy coefficient of the pipe in any direction determined by the method can be used for carrying out precise finite element analysis on the forming of the integral complex section component of the pipe, and further determining reasonable process parameters (such as a loading path and the like).
Fifthly, the method can be used for determining the thickness anisotropy coefficients of various anisotropic pipes in any direction, such as aluminum alloy, titanium alloy, magnesium alloy, high-strength steel and the like, and has wide application range.
And sixthly, initial samples of the experiment related to the invention are all original tube blanks with certain lengths, and the samples are easy to process.
And seventhly, the thickness anisotropy coefficient of the pipe in any direction determined by the method can provide an effective means for evaluating the performance of the pipe.
Drawings
FIG. 1 is a schematic diagram of a method for determining the anisotropy coefficient of a pipe in any direction according to the present invention.
FIG. 2 shows the definition of any direction of a pipe according to the present invention
Schematic representation of (a).
FIG. 3 is a schematic diagram of the experimental principle of controllable bidirectional loading of the pipe according to the present invention.
FIG. 4 is a finite element simulation model of the bulging forming three-way pipe.
FIG. 5 is an experimental schematic diagram (forming initial state) of the bulging forming T-shaped three-way pipe of the invention; wherein, (a) is a front view, and (b) is a left view.
FIG. 6 is an experimental schematic diagram (forming intermediate state) of the bulging forming T-shaped three-way pipe of the invention; wherein, (a) is a front view, and (b) is a left view.
FIG. 7 shows the T-shaped three-way pipe after the bulging forming of the invention.
FIG. 8 is a cross three-way pipe after bulging forming according to the present invention.
FIG. 9 is a sample after the two-way controllable loading experiment of the pipe according to the embodiment.
FIG. 10 shows the T-shaped tee after expansion forming according to the embodiment.
FIG. 11 shows the wall thickness distribution of the tee obtained by the experiment and simulation in the embodiment in the axial direction and the 45-degree direction.
FIG. 12 is a tee after finite element simulation deformation as described in the examples.
FIG. 13 shows the results of the thickness anisotropy coefficients in any direction of the pipe measured in the examples.
In the figure, 1 tube blank; 2, forming a lower die by bulging the three-way pipe; 3, forming an upper die by bulging the three-way pipe; 4, forming a right punch by bulging the three-way pipe; and 5, forming a left punch by bulging the three-way pipe.
Detailed Description
The technical solution of the present invention will be further described with reference to specific examples.
The implementation process of the invention is described by taking a 6061O-state aluminum alloy extruded pipe with the outer diameter of 60mm and the wall thickness of 1.8mm as an example and combining figures 1-13:
step one, cutting the tube blank to be tested into samples with the length of 390mm, and performing 2 groups of tube bidirectional controllable loading bulging experiments, as shown in fig. 9, to obtain experimental data of stress and strain of the tube in a bidirectional stress state under the stress ratio loading path of the 2 fixed collars.
The pipe bidirectional loading experiment is carried out on a special pipe bidirectional loading experiment testing device (refer to a patent CN105300802B), tensile load is applied to the end part of a pipe, pressure medium is applied to the interior of the pipe to enable the pipe to deform under a set stress path, experimental data (axial and circumferential stress and strain data of the pipe) under the bidirectional stress state of the pipe are obtained, and multiple groups of experimental data are obtained by changing the set stress path;
step two, calculating the increment W for reaching the same plastic workpThe experimental data points for the two-way loading of the tubing obtained are shown in table 1.
TABLE 1 strain data points for the same plastic work
And step three, selecting Barlat89 for the yield function f. The yield function f-plane stress state of Barlat89 is defined as follows:
in the formula: f is the yield function; m is a constant related to the crystal structure of the material, and is 6 when the material is in a body-centered cubic structure, and is 8 when the material is in a face-centered cubic structure; a, c undetermined constants related to the anisotropy of the pipe; sigmaeFor the equivalent stress, the initial yield stress corresponding to the axial uniaxial tensile test in this example was 34 MPa. k is a radical of1And k2The expressions are respectively:
wherein the undetermined constants a, c satisfy the relation
a＝2-c (7)
Therefore, the equation has 3 undetermined coefficients which are a, h and p respectively, wherein [ a and h ] are undetermined coefficient matrixes of the main stress component, and p can be determined only by the shearing stress component.
According to Drucker flow criteria:
it is possible to obtain:
in the formula (9), after the derivatives are obtained by the two formulas, only sigma is contained11,σ22A, h, if further
Given a set of σ11,σ22And
an expression about a, h can be obtained; further specifies another set of σ11,σ22And
another expression for a, h can be derived. Two equations and two unknowns are calculated by Matlab programming to obtain undetermined coefficient matrix [ a, h ] of the main stress component]A is 1.3151, h is 0.9201, and c is 0.6849. Further, the thickness anisotropy coefficient r in the two principal axis directions is calculated by the formula (4)0＝0.46，r90＝0.59。
Step four, through hypothesis r45＝r0And (3) calculating an initial value of the undetermined coefficient p which cannot be determined by the experimental data in the first step and the second step in the yield function f, wherein the initial value of p is 0.9357.
And step five, cutting the pipe blank to be measured into a tubular sample with the length of 300mm, performing a three-way pipe bulging experiment by using the three-way pipe die shown in figures 4-6, wherein plastic deformation with similar deformation is generated in all directions of a branch pipe of the three-way pipe, the obtained three-way pipe is shown in figure 10, the wall thickness of the branch pipe in the axial direction and the 45-degree direction is extracted, and the wall thickness distribution is shown in figure 11.
And step six, establishing a three-way pipe bulging finite element simulation model as shown in fig. 4, performing three-way pipe bulging finite element simulation by using the yield function determined in the step one to the step four and dynaform finite element simulation software, and extracting wall thickness simulation data in the same direction with the deformation in the step five as shown in fig. 11 according to the simulation result as shown in fig. 12.
Step seven, comparing and analyzing the wall thickness data in the corresponding directions under the conditions of the corresponding deformation amounts in the step five and the step six, finding that the difference between the axial directions shown by MN is 0.0075, and the difference between the EF direction experiment and the finite element simulation is 0.046833, which is larger than the set error psi of 1.5 × 0.0075 of 0.01125. Adjusting r45The initial adjustment step length is 0.2, and the range is lockedAnd adjusting the step length after the step is enclosed, and taking a small step length of 0.02 until the error requirement is met.
And step eight, repeating the step four, the step six and the step seven until the wall thickness difference between the step six and the step five is within a set error range, and determining that the value of the coefficient in the step four at the moment is the optimal value meeting the requirement, so as to determine a yield function f, wherein the parameters of the determined yield function f are shown in the table 2.
TABLE 2 coefficients of the Barlat89 yield function
Step nine, further calculating the thickness anisotropy coefficient of the pipe in any direction through the yield function f determined in the step eight
For the thickness anisotropy coefficient of the direction to be solved, only the angle value of the direction to be solved is given
The thickness anisotropy coefficient in the angular direction can be calculated from equation (2) by the yield function f, and the calculation result is shown in fig. 13.
The present invention is not limited to the above embodiments, and any person skilled in the art can make many modifications and equivalent variations by using the above-described structures and technical contents without departing from the scope of the present invention.
Claims (8)
1. A method for determining the anisotropy coefficient of a pipe in any direction is characterized by comprising the following steps:
cutting a tube blank to be tested into a sample to be tested, and performing a bidirectional controllable loading bulging experiment on different tubes to obtain experimental data of stress and strain of the tubes in a bidirectional stress state under different fixed collar stress ratio loading paths;
selecting an equivalent strengthening state parameter to represent a strengthening state, and calculating stress and strain data of different loading paths under the same strengthening state by using the experimental data in the step one;
step three, selecting a proper yield function f,
determining undetermined coefficients capable of being determined in the yield function f by using the stress and strain data obtained in the step two; wherein sigmaz0For axial single tensile stress, σz、σθAnd σzθRespectively axial stress, hoop stress and shear stress of the pipe; a is an undetermined coefficient matrix of the main stress component, U is an undetermined coefficient of the shear stress component, and m is the power of the yield function;
reasonably setting undetermined coefficients which cannot be determined by the experimental data in the first step and the second step in the yield function f, and giving initial values of the coefficients;
step five, performing characteristic experiments of similar plastic deformation of the pipe in different directions to realize wall thickness distribution characteristics caused by anisotropy in different directions, and extracting wall thickness experimental data in different directions of the same deformation area;
step six, carrying out finite element analysis on the characteristic experiment in the step five by using the yield function f constructed in the step one to the step four, and extracting wall thickness simulation data in the same direction with the same deformation in the step five;
step seven, comparing and analyzing the wall thickness data in the corresponding direction under the condition of the corresponding deformation in the step five and the step six, and adjusting the value of the coefficient in the step four when the difference between the wall thickness data and the wall thickness data exceeds a set error range;
step eight, repeating the step four, the step six and the step seven until the wall thickness difference in the step six and the step five is within a set error range, and determining that the value of the coefficient in the step four is the optimal value meeting the requirement at the moment so as to determine a yield function f;
step nine, further calculating the thickness anisotropy coefficient of the pipe in any direction through the yield function f determined in the step eight
Coefficient of anisotropy in any direction of pipe
The calculation process is as follows:
according to the definition of the thickness anisotropy coefficient and the condition of unchanged material volume, the thickness anisotropy coefficient and the material volume are axially formed with the pipe
Thickness anisotropy coefficient in angular direction
Expressed as:
wherein d εzAnd d εθRespectively, the plastic strain increment in the axial direction and the circumferential direction of the pipe, d epsilonzθIs the shear strain increment;
further obtaining the thickness anisotropy coefficient by Drucker flow criterion
Relation to yield function f:
2. the method for determining the anisotropy coefficient of the pipe material in any direction as claimed in claim 1, wherein in the first step, the bidirectional controllable loading bulging experiment of the pipe material is performed on the pipe materialApplying axial tension or pressure on the end part of the pipe while applying pressure inside the pipe to deform the pipe under a set linear stress path to obtain experimental data of flow stress and flow strain of the pipe under a bidirectional stress state, wherein the experimental data specifically comprises axial strain epsilonzαStress component σzαHoop strain epsilonθαStress component σθαAnd alpha is the ratio of axial stress and hoop stress in the double-pull controllable loading bulging experiment, and the loading path is controlled to obtain experimental data under different alpha.
3. The method for determining the anisotropy coefficient of the pipe material in any direction as claimed in claim 1 or 2, wherein in the second step, the equivalent strengthening state parameter is plastic work WpFirst order increment of plastic work dWpOr second order increase of plastic work d2Wp；
When taking out the plastic work WpWhen the equivalent enhanced state parameter is obtained, the method passes
Calculating stress and strain data under different loading paths under the same strengthening state; wherein p represents that all experimental quantities are plastic components,
is the incremental component of the axial plastic strain of the pipe,
is the incremental component of hoop plastic strain of the pipe, sigmazIs the axial stress component, σ, of the pipeθIs the pipe circumferential stress component;
when the first-order increment dW of the plastic work is takenpWhen the equivalent enhanced state parameter is obtained, the method passes
Calculating stress and strain data under different loading paths under the same strengthening state; wherein σijIs any one ofThe component of the stress is a component of the stress,
is any plastic strain increment component;
when taking the second-order increment d of plastic work2WpWhen the equivalent enhanced state parameter is obtained, the method passes
And calculating stress and strain data under different loading paths under the same strengthening state.
4. The method for determining the anisotropy coefficient of the pipe in any direction as claimed in claim 1 or 2, wherein in the fourth step, the initial value of the coefficient U is set reasonably as follows:
(1) taking an empirical value 1 as an initial value of the coefficient U, taking a large step length of 0.2-0.4 as an initial adjustment step length in the adjustment of the coefficient U in the step seven, and taking a small step length of 0.01-0.05 as an adjustment step length after the range is locked until the error requirement is met;
(2) and (3) setting the value of the thickness anisotropy coefficient in a direction other than the main axis direction of the pipe as the thickness anisotropy coefficient in the axial direction of the pipe, and calculating the initial value of the coefficient U by using the thickness anisotropy coefficient in the direction.
5. The method for determining the anisotropy coefficient of the pipe in any direction as claimed in claim 3, wherein in the fourth step, the initial value of the coefficient U is set reasonably as follows:
(1) taking an empirical value 1 as an initial value of the coefficient U, taking a large step length of 0.2-0.4 as an initial adjustment step length in the adjustment of the coefficient U in the step seven, and taking a small step length of 0.01-0.05 as an adjustment step length after the range is locked until the error requirement is met;
(2) and (3) setting the value of the thickness anisotropy coefficient in a direction other than the main axis direction of the pipe as the thickness anisotropy coefficient in the axial direction of the pipe, and calculating the initial value of the coefficient U by using the thickness anisotropy coefficient in the direction.
6. The method for determining the thickness anisotropy coefficient of any direction of a pipe material according to claim 1, 2 or 5, wherein in the seventh step, the wall thickness difference criterion of the finite element analysis and the characteristic experiment can be selected as follows:
wherein the content of the first and second substances,
and
wall thickness data extracted by finite element analysis in the step six and wall thickness data extracted by characteristic experiments in the step five are respectively obtained, n is the number of data points, and psi is a set error range; when the wall thickness error is within the set error, stopping adjusting the coefficient U;
the set error range ψ is expressed as:
wherein, tz finite element analysisAnd tz characteristic experimentThe wall thickness is obtained through finite element analysis and characteristic experiments in the axial direction of the pipe respectively, m is the number of data points, eta is an amplification factor, and the value range is 1.5-2.
7. The method for determining the thickness anisotropy coefficient of any direction of a pipe material according to claim 3, wherein in the seventh step, the wall thickness difference criterion of the finite element analysis and the characteristic experiment is selected as follows:
wherein the content of the first and second substances,
and
wall thickness data extracted by finite element analysis in the step six and wall thickness data extracted by characteristic experiments in the step five are respectively obtained, n is the number of data points, and psi is a set error range; when the wall thickness error is within the set error, stopping adjusting the coefficient U;
the set error range ψ is expressed as:
wherein, tz finite element analysisAnd tz characteristic experimentThe wall thickness is obtained through finite element analysis and characteristic experiments in the axial direction of the pipe respectively, m is the number of data points, eta is an amplification factor, and the value range is 1.5-2.
8. The method for determining the thickness anisotropy coefficient of any direction of a pipe material as claimed in claim 4, wherein in the seventh step, the wall thickness difference criterion of the finite element analysis and the characteristic experiment is selected as follows:
wherein the content of the first and second substances,
and
wall thickness data extracted by finite element analysis in the step six and wall thickness data extracted by characteristic experiments in the step five are respectively obtained, n is the number of data points, and psi is a set error range; stopping the adjustment of the coefficient when the wall thickness error is within the set errorU；
The set error range ψ is expressed as:
wherein, tz finite element analysisAnd tz characteristic experimentThe wall thickness is obtained through finite element analysis and characteristic experiments in the axial direction of the pipe respectively, m is the number of data points, eta is an amplification factor, and the value range is 1.5-2.
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