CN108133082B - Method for determining stress measurement constant in indentation strain method based on finite element simulation - Google Patents
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- 238000000034 method Methods 0.000 title claims abstract description 42
- 238000007373 indentation Methods 0.000 title claims abstract description 36
- 238000004088 simulation Methods 0.000 title claims abstract description 36
- 238000005259 measurement Methods 0.000 title claims abstract description 35
- 239000000463 material Substances 0.000 claims abstract description 26
- 238000002474 experimental method Methods 0.000 claims abstract description 16
- 238000011088 calibration curve Methods 0.000 claims abstract description 13
- 239000007769 metal material Substances 0.000 claims abstract description 9
- 238000005516 engineering process Methods 0.000 claims description 5
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- 229910000851 Alloy steel Inorganic materials 0.000 description 2
- 235000003140 Panax quinquefolius Nutrition 0.000 description 2
- 240000005373 Panax quinquefolius Species 0.000 description 2
- 230000006835 compression Effects 0.000 description 2
- 238000007906 compression Methods 0.000 description 2
- 230000006698 induction Effects 0.000 description 2
- 230000003068 static effect Effects 0.000 description 2
- 230000005483 Hooke's law Effects 0.000 description 1
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Abstract
The invention discloses a method for determining a stress measurement constant of an indentation strain method based on finite element simulation, and belongs to the technical field of residual stress testing. The stress measurement constant is a relation coefficient between indentation strain increment and elastic strain, and is generally obtained by experimental calibration, and a calibration test plate is required to be in an unstressed state and has a large enough size, which brings great difficulty to a calibration experiment. Firstly, obtaining indentation strain increment in a stress-free material through an experiment; then establishing a finite element simulation calibration model, and determining the pressure head load of the corresponding material according to the strain increment under zero stress; finally, calculating the strain increment under each elastic strain; and then drawing a calibration curve by taking the elastic strain abscissa and the strain increment as the ordinate, and realizing non-experimental calibration of the stress measurement constant through the calibration curve. The method can obtain a calibration curve with higher accuracy and better regularity, and can be used as a non-experimental calibration method for most metal materials.
Description
Technical Field
The invention relates to the technical field of residual stress testing, in particular to a method for determining a stress measurement constant in an indentation strain method based on finite element simulation.
Background
The indentation strain method is a nearly lossless stress testing method which is used for solving the residual stress in a component by theoretical analysis and data induction according to strain variable information (called indentation superimposed strain increment, referred to as strain increment for short) obtained by indentation induction and finally utilizing Hooke's law. From the accuracy of the test, the strain change caused by the indentation is only a macroscopic change amount independent of the microstructure of the material and only related to the stress level in the component, so the accuracy is only related to the level of a tester and the calibration result of the stress measurement coefficient.
The determination of the stress measurement constant (i.e. the coefficient of relationship between the indentation strain increment and the elastic strain) is the key to determine the accuracy of the stress measurement. The stress measurement constants are determined by an experimental calibration method, and the rule is shown in figure 1. The used calibration test board needs to be in a stress-free state, namely, the test board needs to be subjected to stress relief treatment before calibration, and the stress state of the test board directly influences the accuracy and stability of a calibration result. Meanwhile, in order to meet loading conditions, the size of the test plate also has corresponding requirements, and a calibration test cannot be completed for a calibration test plate which cannot meet the conditions. This has a great limitation on whether some materials can measure residual stress by indentation strain.
By using a finite element numerical simulation technology, non-experimental calibration of the stress measurement constant can be realized.
In the prior art, a calibration result of a specific material has been studied by using a simulation calculation method [ document 1: analysis of indentation calibration experiments in residual stress measurements [ J ] machine fabrication, 2006: 44: 70-72 parts; document 2: influence of yield strength on indentation strain method measurement of residual stress [ D ]. sheng yang: institute of metals, china academy of sciences, 2006; document 3: menzuo. numerical simulation of indentation strain method in different stress fields [ D ]. shenyang: the institute of metals of the chinese academy of sciences, 2007; document 4: liu evolution. influence of material properties and directionality on indentation strain method measurement of residual stress [ D ]. sheng yang: the institute of metals, academy of sciences of china, 2013 ], and has achieved some results. However, in view of the limitations of the models, the conclusions cannot be drawn to other types of materials. Other determinations of stress measurement constants by indentation strain have not been reported, and there is currently no patent relating to the present invention. The invention aims to establish a general model capable of accurately obtaining a majority of metal material calibration curves, and solves the problems that some metal materials cannot be subjected to experimental calibration and the error in the experimental calibration is large, so that the accuracy of testing the residual stress by an indentation strain method is improved and the application range of the indentation strain method is expanded.
Disclosure of Invention
The invention aims to provide a method for determining a stress measurement constant in an indentation strain method based on finite element simulation.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
a method for determining a stress measurement constant of an indentation strain method based on finite element simulation is to realize non-experimental calibration of the stress measurement constant of a metal material by adopting a numerical simulation technology, and specifically comprises the following steps:
(1) obtaining indentation strain increment in the stress-free material through experiments;
(2) establishing a finite element simulation calibration model, and determining the pressure head load of the corresponding material according to the finite element simulation calibration model on the basis of the strain increment under zero stress obtained in the experiment of the step (1);
(3) calculating the strain increment under each elastic strain based on the tensile curve of the material; then with elastic strain epsiloneAnd drawing a calibration curve by using the abscissa and the strain increment delta epsilon as the ordinate, and realizing non-experimental calibration of the stress measurement constant through the calibration curve.
In the step (3), the initial yield strength sigma is obtained through the tensile curve of the materialyAnd yield strain εyAnd further calculating the strain increment under each elastic strain.
In the step (3), the non-experimental calibration process of the stress measurement constant is as follows: in the calibration curve, each point applying the direction of the uniaxial tension or compressive strain is fitted according to the power of 3, each point of the transverse strain output deviating from the power of 3 fitting curve is fitted according to a straight line under the condition of high-value uniaxial tension stress, and the equation coefficient calculated by two equations obtained after fitting is the stress measurement constant of the indentation strain method.
In the step (2), the size of the established finite element simulation calibration model is 48mm multiplied by 4mm, and the minimum unit size is 0.04mm multiplied by 0.03mm multiplied by 0.004 mm.
The invention has the following advantages and beneficial effects:
1. the method can accurately determine the non-experimental calibration method of the stress measurement constants of most metal materials, and solves various difficulties and possible errors (including experimental errors, calibration test plate preparation, test plate zero-stress treatment, calibration device reliability and the like) in experimental calibration.
2. The method is characterized in that a finite element numerical simulation technology is introduced, the characteristic analysis of the dynamic indentation material is carried out, the reasonable indentation load is dynamically determined for different materials on the basis of the strain increment experimental data under the stress-free condition and on the basis of the traditional tensile curve, and a calibration model capable of accurately determining the stress measurement constant is established. The simulation calibration result and the experiment calibration result are compared and verified, and the method has better regularity and higher accuracy, can be used as a non-experiment calibration method for most metal materials, and can obtain a calibration curve with higher accuracy and better regularity.
Drawings
FIG. 1 is a schematic diagram of an experimental calibration curve.
FIG. 2 is a simulated calibration model.
FIG. 3 is a comparison of simulation and calibration results for aluminum alloy 7N 01.
FIG. 4 is a comparison of simulation and calibration results for low alloy steel Q345.
Detailed Description
The present invention will be described in detail below with reference to examples and drawings, wherein the experimental calibration section is performed according to GB/T24179-2009 indentation Strain test for residual stress of Metal materials.
The invention relates to a method for determining a stress measurement constant of an indentation strain method based on finite element simulation, which adopts a numerical simulation technology to realize non-experimental calibration of the stress measurement constant of a metal material, and comprises the following specific processes: firstly, obtaining the strain increment of a material under zero stress through experiments; then, determining the pressure head load of the corresponding material by adopting a numerical simulation calibration model shown in FIG. 2 and taking experimental data under zero stress as a basis; and finally, calculating the strain increment under each elastic strain to obtain a calibration curve, and realizing non-experimental determination of the stress measurement constant.
In the method, the calculation precision can be ensured only when the model size and the unit size are proper, and the calculation cost is reduced. The model adopts 48 multiplied by 4mm, and the minimum unit size is 0.04 multiplied by 0.03 multiplied by 0.004 mm.
Example 1:
firstly, obtaining a tensile property curve of the aluminum alloy 7N01 material to obtain initial yield strength sigmayAnd yield strain εy. The increase in indentation strain in the unstressed material was obtained experimentally. Establishing a finite element simulation calibration model, wherein the diameter of a pressure head is phi 1.588 mm. And determining the magnitude of the static load pressed-in load of the pressure head according to the strain increment under the stress-free condition obtained by experiments. Accordingly, an average molecular weight of-0.9. epsilon. is obtainedy～0.9εyAny elastic strain and strain increment under the condition of interval uniaxial tension or compression. Fitting the result of the direction of applying the uniaxial tension or compressive strain according to the power of 3, and fitting the result of the direction perpendicular to the result according to a straight line if the result deviates from the power of 3 and the curve, wherein the obtained equation coefficient is the stress measurement constant of the indentation strain method.
Fig. 3 is a graph comparing the results of finite element simulation and experimental results for the aluminum alloy 7N01 material (simulation curves and experimental data in the loading direction only). The comparison result shows that the simulation calibration result and the experiment calibration result show good consistency. Because of the influence of the state of the calibration test board during the experiment and inevitable errors during operation, the experimental calibration data are dispersed, and the simulated calibration data show better regularity.
Example 2:
first, Q345 low is obtainedObtaining the initial yield strength sigma of the tensile property curve of the alloy steel materialyAnd yield strain εy. The increase in indentation strain in the unstressed material was obtained experimentally. And establishing a finite element simulation calibration model, wherein the diameter of a pressure head is 1.588 mm. And determining the magnitude of the static load pressed-in load of the pressure head according to the strain increment under the stress-free condition obtained by experiments. Accordingly, an average molecular weight of-0.9. epsilon. is obtainedy～0.9εyAny elastic strain and strain increment under the condition of interval uniaxial tension or compression. Fitting the result of the direction of applying the uniaxial tension or compressive strain according to the power of 3, and fitting the result of the direction perpendicular to the result according to a straight line if the result deviates from the power of 3 and the curve, wherein the obtained equation coefficient is the stress measurement constant of the indentation strain method.
Fig. 4 is a graph comparing finite element simulation results and experimental results for Q345 material (simulation curves and experimental data for the loading direction only). The comparison result shows that the simulation calibration result and the experiment calibration result show good consistency. Because of the influence of the state of the calibration test board during the experiment and inevitable errors during operation, the experimental calibration data are dispersed, and the simulated calibration data show better regularity.
Claims (3)
1. A method for determining a stress measurement constant of an indentation strain method based on finite element simulation is characterized in that: the method adopts a numerical simulation technology to realize non-experimental calibration of the stress measurement constant of the metal material, and specifically comprises the following steps:
(1) obtaining indentation strain increment in the stress-free material through experiments;
(2) establishing a finite element simulation calibration model under the zero stress obtained in the experiment of the step (1)
Determining the pressure head load of the corresponding material according to the strain increment of the material and a finite element simulation calibration model;
(3) calculating the strain increment under each elastic strain based on the tensile curve of the material; then drawing a calibration curve by taking the elastic strain abscissa and the strain increment as the ordinate, and realizing non-experimental calibration of the stress measurement constant through the calibration curve; the non-experimental calibration process of the stress measurement constant is as follows: in a calibration curve, fitting each point in the direction of applying the uniaxial tension or compressive strain according to the power of 3; under the condition of high-value unidirectional tensile stress, each point of the transverse strain output deviating from a 3-order square fitting curve is fitted according to a straight line, and an equation coefficient calculated by two equations obtained after fitting is a stress measurement constant of the indentation strain method.
2. The method for determining indentation strain stress measurement constants based on finite element simulation of claim 1, wherein: in the step (3), the initial yield strength and the yield strain are obtained through the tensile curve of the material, and the strain increment under each elastic strain is further calculated.
3. The method for determining indentation strain stress measurement constants based on finite element simulation of claim 1, wherein: in the step (2), the size of the established finite element simulation calibration model is 48mm multiplied by 4mm, and the size of the minimum unit is 0.04mm multiplied by 0.03mm multiplied by 0.004 mm.
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| CN109086529B (en) * | 2018-08-07 | 2023-05-30 | 中国科学院金属研究所 | Method for determining stress calculation function in indentation strain method based on strain increment under zero pressure |
| CN109145417B (en) * | 2018-08-07 | 2023-01-17 | 中国科学院金属研究所 | Method for directly determining indentation strain method stress calculation function based on mechanical properties of material |
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| CN111366283A (en) * | 2020-03-30 | 2020-07-03 | 中国科学院金属研究所 | Method for detecting residual stress of welded structural part by auxiliary indentation strain method |
| CN111735728B (en) * | 2020-05-22 | 2023-03-31 | 扬州市舜意机械有限公司 | Method and device for identifying mechanical property of vibration damping coating |
| CN113297772B (en) * | 2021-06-07 | 2022-04-01 | 南昌航空大学 | Method for simulating residual stress distribution of composite material by using finite element software |
| CN116577190B (en) * | 2023-07-13 | 2023-11-28 | 南京华建检测技术有限公司 | Intelligent detection method for T-shaped experimental test block |
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