阅读说明：本技术 一种获得材料多应变率下高精度硬化模型参数的方法 (Method for obtaining high-precision hardening model parameters of material under multiple strain rates ) 是由 姜子涵 梁宾 赵岩 姜发同 袁超 王扬卫 范吉富 王腾腾 张伟 王宝川 计遥遥 于 2021-09-06 设计创作，主要内容包括：本发明公开了一种获得材料多应变率下高精度硬化模型参数的方法,包括以下步骤：S1、进行高速拉伸试验,获得工程应力-工程应变曲线；S2、计算真应力塑性应变曲线；S3、进行拟合外延得到外延应力应变曲线；S4、将外延应力应变曲线组合成应力应变曲线表；S5、调整应力应变曲线表形状；S6、建立数值模型,对比试验及仿真结果中的力-变形曲线；S7、返回S5,优化多应变率应力应变曲线表形状,直到S6中对标结果满足要求即得。本发明将多应变率下的材料试样进行同时对标,优化迭代得到高精度的多应变率本构模型参数,解决了现有多应变率本构模型参数建立过程中不能同时进行不同应变率下材料性能优化的问题,克服现有方法所存在的不足。(The invention discloses a method for obtaining high-precision hardening model parameters of a material under multiple strain rates, which comprises the following steps: s1, carrying out a high-speed tensile test to obtain an engineering stress-engineering strain curve; s2, calculating a true stress plastic strain curve; s3, performing fitting epitaxy to obtain an epitaxy stress strain curve; s4, combining the epitaxial stress-strain curves into a stress-strain curve table; s5, adjusting the shape of the stress-strain curve table; s6, establishing a numerical model, and comparing force-deformation curves in the test and simulation results; and S7, returning to S5, and optimizing the shape of the multi-strain-rate stress-strain curve table until the standard result in S6 meets the requirement. According to the method, the material samples under multiple strain rates are subjected to simultaneous calibration and optimization iteration to obtain high-precision multiple strain rate constitutive model parameters, so that the problem that the material performance optimization under different strain rates cannot be simultaneously carried out in the existing multiple strain rate constitutive model parameter establishing process is solved, and the defects of the existing method are overcome.)

1. A method for obtaining high-precision hardening model parameters of a material under multiple strain rates is characterized by comprising the following steps:

s1, performing a high-speed tensile test on the material to obtain an engineering stress-engineering strain curve of the material under multi-strain-rate unidirectional stretching;

s2, calculating a true stress plastic strain curve of the material sample under multiple strain rates;

s3, fitting epitaxy is carried out on the true stress plastic strain curve under multiple strain rates, and an epitaxy stress strain curve corresponding to each strain rate is obtained;

s4, combining the epitaxial stress-strain curves corresponding to the strain rates into an epitaxial stress-strain table curve table, wherein the corresponding values of the curves are the strain rates corresponding to the curves;

s5, adjusting the shape of the curve table of the epitaxial stress-strain table by giving different values of the weighting coefficients alpha of the epitaxial stress-strain curves under various strain rates, wherein the value range of alpha is 0-1;

s6, establishing a numerical model for the material sample with each strain rate, calling the epitaxial stress-strain curve table obtained in S5 uniformly, carrying out simulation calculation in finite element software, and comparing force-deformation curves in a test and a simulation result;

and S7, returning to S5, and optimizing the value of the weighting coefficient alpha until the standard result of the numerical models of all the material samples in S6 meets the requirement that the error is within 5%, so as to finally obtain the multi-strain-rate high-precision hardening model parameters.

2. The method for obtaining high precision hardening model parameters of materials at multiple strain rates as claimed in claim 1, wherein the multiple strain rates are described by strain rates of parallel sections of the test specimen, wherein the strain rates of the parallel sections of the test specimen during the test range from 0.1/s to 1000/s.

3. The method for obtaining high-precision hardening model parameters under multiple strain rates of materials according to claim 2, wherein in S5, the stress-strain curve after the epitaxy is obtained by fitting Voce + + and Hockett-Sherby constitutive equations, and the equation after the combination of the Voce + + and Hockett-Sherby constitutive equations is as follows:

in the formula: sigma is true stress, alpha is a weighting coefficient, the value range is 0-1, and a₅、a₆、b₅、b₆、c₅、c₆、d₅、d₆For unknown parameters, e, is obtained by fitting_plIs a plastic strain.

4. The method for obtaining high precision hardening model parameters at multiple strain rates of material as claimed in claim 1, wherein the finite element software is LS-DYNA simulation analysis software.

5. The method for obtaining the high-precision hardening model parameters under the multiple strain rates of the material as claimed in claim 3, wherein in S1, the engineering stress of the material sample is obtained by dividing the force by the cross-sectional area of the parallel section of the sample, and the engineering strain of the material sample is obtained by dividing the deformation by the gauge length.

6. The method for obtaining high-precision hardening model parameters under multiple strain rates of materials according to claim 5, wherein in S1, according to the room temperature test method of part 1 of the national standard GB/T228.1-2010 metal material tensile test, the engineering stress-strain middle elastic section part obtained by the test is found out, and the yield strength, tensile strength and elastic modulus data of the material sample are obtained.

7. The method for obtaining high-precision hardening model parameters under multiple strain rates of material according to claim 6, wherein in S2, the elastic section data are deleted, and the data after the necking point are removed, so as to obtain effective data in the plastic deformation of the material.

8. The method for obtaining the high-precision hardening model parameters of the material under the multiple strain rates as claimed in claim 7, wherein in S2, the true stress and the true strain of the material are calculated according to the conversion formula, the plastic strain-true stress curve of the material is calculated through the plastic strain calculation formula, and the first point X axis of the curve is zeroed to obtain the true stress plastic strain curve.

Technical Field

The invention relates to the technical field of material mechanics tests, in particular to a method for obtaining high-precision hardening model parameters of a material under multiple strain rates.

Background

At present, the mechanical properties of materials under multiple strain rates are mostly obtained by means of a high-speed tensile test, and a true stress plastic strain curve obtained by the high-speed tensile test is only effective before a necking point. However, the plastic strain due to the necking point tends to be small, often within 0.1. Therefore, this curve alone cannot be used to characterize the deformation behavior of a material under large deformations. Therefore, in research, a hardening curve (true stress plastic strain curve) of the material containing large deformation after the yield point is obtained by adopting a hardening model fitting epitaxial combined simulation target-aiming mode, and each strain rate curve after the target-aiming is combined into a multi-strain-rate true stress-plastic strain table for calling. However, this method has the following disadvantages: (1) processing and fitting an epitaxial true stress plastic strain curve only aiming at experimental data under a certain single strain rate, and neglecting the phenomenon that the strain rate of a local area is rapidly increased after necking of a sample; (2) the simulation benchmarking of the sample is carried out by only adopting a certain strain rate curve in the fitting benchmarking, and the problem that the called curves are different due to different strain rates of different positions of the sample is ignored; (3) the finally applied data of the multi-strain-rate true stress-plastic strain table is formed by combining single calibration results, and the effect is poor in practical application.

Disclosure of Invention

The invention aims to: aiming at the problems existing in the process of establishing the multi-strain-rate constitutive model hardening curve of the existing material, the method for obtaining the high-precision hardening model parameters of the material under the multi-strain rate is provided, the problems that the material performance and the final application effect are poor under the multi-strain rate cannot be considered simultaneously in the process of establishing the curve are mainly solved, and the material hardening model curve establishment is carried out on the material sample under the multi-strain rate by adopting a multi-objective multi-parameter optimization method so as to overcome the defects existing in the prior art.

The technical scheme adopted by the invention is as follows: a method for obtaining high-precision hardening model parameters of a material under multiple strain rates comprises the following steps:

s1, performing a high-speed tensile test on the material to obtain an engineering stress-engineering strain curve of the material under multi-strain-rate unidirectional stretching;

s2, calculating a true stress plastic strain curve of the material sample under multiple strain rates;

s3, fitting epitaxy is carried out on the true stress plastic strain curve under multiple strain rates, and an epitaxy stress strain curve corresponding to each strain rate is obtained;

s4, combining the epitaxial stress-strain curves corresponding to the strain rates into an epitaxial stress-strain table curve table, wherein the corresponding values of the curves are the strain rates corresponding to the curves;

s5, adjusting the shape of the curve table of the epitaxial stress-strain table by giving different values of the weighting coefficients alpha of the epitaxial stress-strain curves under various strain rates, wherein the value range of alpha is 0-1;

s6, establishing a numerical model for the material sample with each strain rate, calling the curve table of the epitaxial stress strain table obtained in S5 uniformly, carrying out simulation calculation in finite element software, and comparing force-deformation curves in a test and a simulation result;

and S7, returning to S5, and optimizing the value of the weighting coefficient alpha until the standard result of the numerical models of all the material samples in S6 meets the requirement that the error is within 5%, so as to finally obtain the multi-strain-rate high-precision hardening model parameters.

In the method, the engineering stress of the material sample is obtained by dividing the force by the sectional area of the parallel section of the sample, and the engineering strain of the material sample is obtained by dividing the deformation by the gauge length. Further, in S1, according to the room temperature test method of part 1 of the national standard GB/T228.1-2010 metal material tensile test, finding out the engineering stress-strain middle elastic section part obtained by the test, and obtaining the yield strength, tensile strength and elastic modulus data of the material sample.

In the method, the engineering stress and the engineering strain of the material are calculated, the data before the yield strength and after the necking point are removed, and the true stress plastic strain curve of the material sample is obtained through formula conversion. The calculation of the true stress, the true strain and the plastic strain of the material adopts the following formula:

and (3) calculating the true stress:

σ_Tsigma (1+ epsilon) formula (1)

And (3) true strain calculation:

ε_Tlnn (1+ epsilon) formula (2)

Calculating the plastic strain:

ε_pl＝ln(1+ε_T-sigma/E) formula (3)

In the formula (1) and the formula (2), sigma and epsilon are engineering stress strain and strain, respectively. In the formula (3), ε_plIs plastically strained,. epsilon_TTrue strain, E is the modulus of elasticity.

In the present invention, the true stress plastic strain curves obtained and processed for the experiments are only pre-necking data. For the data after necking, the measured stress is distorted due to the fact that the actual section is reduced, and therefore a hardening model is adopted to carry out fitting extrapolation on the processed true stress plastic strain curve data. Commonly used hardening models are classified into a saturated hardening model and a non-saturated hardening model, and the specific formula is shown below. In order to ensure that the curve has a larger adjustment range, a mixed hardening model obtained by mixing a saturated hardening model and a non-saturated hardening model by adopting a weighting coefficient is selected, so that a larger adjustment space is obtained.

Unsaturated hardening model:

hollmon constitutive equation:

simplifying the J-C constitutive equation:

swift constitutive equation:

ghosh constitutive equation:

voce + + constitutive equation:

saturated hardening model:

Hockett-Sherby constitutive equation:

voce constitutive equation:

in the above formula, a, b, c and d are unknown parameters and need to be obtained by fitting.

In the invention, a stress-strain curve after epitaxy is obtained by fitting a Voce + + and Hockett-Sherby constitutive equation (certainly, other equation combinations can be selected, different equations can be freely combined, and the two equations are taken as examples here) and an equation obtained by combining the Voce + + and Hockett-Sherby constitutive equations is shown in formula (11):

voce + + -Hockett-Sherby constitutive equation:

in the formula: sigma is true stress, alpha is a weighting coefficient, and the value is (0-1), a₅、a₆、b₅、b₆、c₅、c₅、d₅、d₆For unknown parameters, e, is obtained by fitting_plIs a plastic strain.

Further, the multiple strain rate is described by the strain rate of the parallel section of the sample, wherein the range of the multiple strain rate is 0.1/s-1000/s, and the sample corresponding to the multiple strain rate is a high-speed tensile sample.

Preferably, the finite element software is LS-DYNA simulation analysis software.

In summary, due to the adoption of the technical scheme, the invention has the beneficial effects that:

1. the method comprises the steps of firstly obtaining a true stress plastic strain curve of a material in front of a necking point under multiple strain rates through a material high-speed tensile test and data processing, fitting by adopting a hardening model formula based on the curve to obtain an initial hardening model parameter table, then establishing a finite element model under corresponding loading conditions based on the material high-speed tensile test under different strain rates, calibrating a force-deformation curve in each strain rate test, optimizing hardening model parameters, and continuously adjusting the hardening model parameters in the optimization process until the calibration results of samples under all conditions meet requirements, thereby obtaining high-precision multiple strain rate material hardening model parameters;

2. according to the method, the material samples under different strain rates are subjected to simultaneous benchmarking, the optimization iteration is carried out to obtain the high-precision multi-strain-rate hardening model parameters, the problem that the material performance characterization under different strain rates cannot be considered simultaneously in the existing hardening model parameter establishing process is solved, the application effect in the actual benchmarking of the samples is good, the error is within 5%, and the defects of the existing method are overcome.

Drawings

FIG. 1 is a unidirectional tensile force-deformation curve at a strain rate of 100/s to 1000/s for a test example of the present invention;

FIG. 2 is a stress-strain curve of uniaxial tension engineering at a strain rate of 100/s-1000/s for a test example of the present invention;

FIG. 3 is a true stress plastic strain curve at a strain rate of 100/s-1000/s for a test example of the present invention;

FIGS. 4 to 7 are a true stress plastic strain curve and an epitaxial curve at a strain rate of 100/s, a strain rate of 200/s, a strain rate of 500/s, and a strain rate of 1000/s, respectively, according to the test examples of the present invention;

FIGS. 8-11 are graphs of simulation and test versus standard force-deformation at strain rates of 100/s, 200/s, 500/s, and 1000/s, respectively, for a test example of the present invention;

FIG. 12 is a schematic view showing the structure of a high-speed tensile specimen according to a test example of the present invention.

The labels in the figure are: in FIGS. 8 to 11, 1 is a curve of a conventional method (comparative example), 2 is a curve of a method of the present invention (test example), 3 in FIG. 8 is a 100/s strain rate test curve, 3 in FIG. 9 is a 200/s strain rate test curve, 3 in FIG. 10 is a 500/s strain rate test curve, and 3 in FIG. 11 is a 1000/s strain rate test curve; in fig. 12, the dimensions indicated are all the dimensions of the sample specified in the national standard test in mm.

Detailed Description

The present invention will be described in detail below with reference to the accompanying drawings.

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

The material sample is shown in fig. 12:

high-speed tensile sample: the high speed tensile test specimen has a definite national standard specified specimen size, size and structure as shown in fig. 12.

Comparative example: obtaining an engineering stress-strain curve of the material under multiple strain rates by adopting a traditional high-speed tensile test method, and processing to obtain a real stress-plastic strain curve before necking under each strain rate; and then, adopting a hardening model to fit epitaxy and tabulation, and combining a simulation benchmarking mode to obtain a true stress and true strain curve of the material after a contraction point under multiple strain rates, wherein the true stress and true strain curve is used as a comparative example.

Test example: still taking the material as a sample, the method for confirming the multi-strain-rate high-precision hardening model parameters of the material sample comprises the following steps:

s1, obtaining a mechanical property curve of the material under various strain rates through a high-speed tensile test, namely a force-deformation curve, as shown in figure 1; according to the actually measured width and thickness of the high-speed tensile sample, on the basis of a force-deformation curve obtained by a testing machine, the force is divided by the sectional area of the parallel section of the sample to obtain the engineering stress of the material, and the deformation is divided by the gauge length to obtain the engineering strain of the material under various strain rates, namely the material engineering stress-engineering strain curve (the stress unit is MPa) is shown in figure 2; according to part 1 of the national standard GB/T228.1-2010 metal material tensile test: a room temperature test method and ISO 26203-2-2011Metallic materials-Tensile testing at high strain rates-Servo and other test systems find out the elastic section part in the engineering stress-strain obtained by the test, and obtain the yield strength, Tensile strength and elastic modulus (the unit of the elastic modulus is MPa) data of the material;

s2, deleting elastic segment data, eliminating data after necking points (corresponding to the highest points of engineering stress-strain curves), calculating true stress and plastic strain curves of the material under various strain rates through a formula (1), a formula (2) and a formula (3), and zeroing the abscissa of the first point of the curve, as shown in FIG. 3, of the true stress and the plastic strain curves under various strain rates;

s3, fitting Voce + + and Hockett-Sherby constitutive equations to obtain a true stress plastic strain epitaxial curve at each strain rate, as shown in FIGS. 4-7;

s4, combining the epitaxial stress-strain curves corresponding to the strain rates into an epitaxial stress-strain curve table, wherein the corresponding values of the curves are the strain rates corresponding to the curves;

s5, giving different values through a weighting coefficient alpha in a formula (11), wherein the value range of alpha is between 0 and 1, and adjusting the linear shape of an epitaxial stress strain curve table;

s6, establishing numerical models for material samples with different strain rates such as 100/S, 200/S, 500/S and 1000/S (the tests are all carried out according to ISO 26203-2-2011Metallic materials-Tensile at high strain rates-service-hydraulic and other test systems), adopting a true stress plastic strain epitaxial curve (alpha gives an initial value between 0 and 1) obtained in S6, carrying out simulation calculation in finite element software LS-DYNA, and comparing the force-deformation curves in the test and simulation results;

and S7, returning to S5, optimizing the value of the weighting coefficient alpha until the standard result of the simulation result under all strain rates in S6 meets the requirement that the error is within 5%, and finally obtaining the high-precision material hardening model parameters of the material under multiple strain rates, wherein FIGS. 8-11 are the final optimization results of the embodiment.

As shown in FIGS. 8-11, the maximum error of the simulation calibration results of the conventional method at strain rates of 100/s, 200/s, 500/s and 1000/s is (calculated by simulation software) 14.83%, 16.25%, 6.24% and 6.65%, while the maximum error of the simulation calibration results of the method of the present invention at the strain rates is (calculated by simulation software) 2.4%, 4.57%, 3.61% and 1.74%. Compared with the prior art, the calibration result errors of the parameters of the material multi-strain-rate hardening model obtained by the method are obviously lower than those of the prior art, and the problem that the material performance characterization under various strain rates cannot be considered simultaneously in the process of establishing the parameters of the material multi-strain-rate hardening model is solved.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.