CN109086529B - Method for determining stress calculation function in indentation strain method based on strain increment under zero pressure - Google Patents
Method for determining stress calculation function in indentation strain method based on strain increment under zero pressure Download PDFInfo
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Abstract
The invention discloses a method for determining a stress calculation function of an indentation strain method based on a strain increment under zero stress, and belongs to the technical field of residual stress testing. The method takes alloy steel materials as research objects, combines experimental calibration and simulated calibration, and firstly obtains the strain increment delta epsilon of the stress-free material through indentation experiments 0 The method comprises the steps of carrying out a first treatment on the surface of the Obtaining mechanical property parameters of the alloy steel material to be tested through a tensile experiment, and obtaining yield strength sigma y Tensile strength sigma b Yield ratio sigma y /σ b Yield strain ε y The method comprises the steps of carrying out a first treatment on the surface of the And finally substituting the mechanical performance parameters into a unified expression of the material stress calculation function, calculating to obtain strain increment values corresponding to different elastic strains, and fitting the relationship of the strain increment values and the material stress calculation function according to a third power. The method can quickly and accurately obtain the stress calculation function for the indentation strain method of the new alloy steel material, and meets the requirement of testing residual stress by adopting the indentation strain method under the condition that the material is not calibrated.
Description
Technical Field
The invention relates to the technical field of residual stress testing, in particular to a method for determining a stress calculation function in an indentation strain method based on a strain increment under zero stress.
Background
The indentation strain method is a nearly lossless stress test method for obtaining the relation between elastic strain and strain increment, namely a stress calculation function, through experiments or analog calculation according to strain variable information (called indentation superposition strain increment, abbreviated as strain increment) obtained by indentation induction, and then solving the residual stress in the component by utilizing Hooke's law. From the accuracy of the test, the strain change caused by indentation is only macroscopic and is independent of the change amount of the microstructure of the material, and is only related to the material performance and stress level, so that the accuracy is only related to the operation level of a tester and the determination result of a stress calculation function.
The determination of the stress calculation function is the key to determine whether the stress measurement is accurate or not. At present, the determination of the stress calculation function is obtained by adopting an experimental calibration method, and the rule is shown in fig. 1. When the experiment is calibrated, the stress state of the calibration test plate and the size of the test plate are required correspondingly, and the calibration experiment can not be completed when the calibration test plate meeting the conditions can not be provided; at the same time, the loading implementation of elastic strain is difficult to achieve in an ideal state. Although non-experimental calibration of the stress calculation function can be realized by referring to the finite element numerical simulation technology, the difficulty for ordinary technicians is great by grasping the finite element simulation technology and obtaining accurate results. If the stress calculation function of the material to be measured cannot be accurately obtained, the application of the indentation strain method in measuring the stress is hindered.
In the prior art, research on calibration results of specific materials by using experimental and analog calculation methods has been carried out [ e.g. document 1: sun Yuan, wang Qingming, xia Fengfang, et al analysis of indentation calibration experiments in residual stress measurement [ J ]. Machine fabrication, 2006:44:70-72 parts; document 2: effect of yield strength on indentation strain measurement residual stress [ D ]. Sunk positive: metal institute, academy of sciences, 2006; document 3: chen Jing and Jiang Yunlu Chen Huaining, a method for determining indentation strain method stress measurement constants based on finite element simulation, application number 201711277423.8, but no research and application of any non-calibrated acquisition method of the relevant material stress calculation function have been found.
The invention aims to establish an indentation strain method stress calculation function which can rapidly and accurately obtain alloy steel materials under the non-calibration condition so as to facilitate the application of the indentation strain method in testing residual stress.
Disclosure of Invention
The invention aims to provide a method for determining a stress calculation function in an indentation strain method based on strain increment under zero stress, and the calculation method provided by the invention can be proved to be capable of rapidly and accurately obtaining the stress calculation function of an alloy steel material through numerical simulation and experimental verification.
In order to achieve the above purpose, the technical scheme adopted by the invention is as follows:
a method for determining stress calculation function of indentation strain method based on strain increment under zero stress adopts non-calibration method, and brings strain increment and mechanical property obtained under zero stress of alloy steel material to be measured into unified expression of strain increment calculation function of the material, so as to obtain stress calculation function of the material. The method comprises the following steps:
(1) The indentation strain increment delta epsilon of the material to be tested under zero stress is obtained through an indentation test 0 ；
(2) Obtaining mechanical property parameters of a material to be tested through a stretching experiment, wherein the mechanical property parameters are yield ratio sigma y /σ b Yield strain ε y The method comprises the steps of carrying out a first treatment on the surface of the The yield ratio is the yield strength sigma of the material y And tensile strength sigma b Is a ratio of (2);
(3) Increasing the indentation strain delta epsilon obtained in the step (1) and the step (2) 0 Yield ratio sigma y /σ b And yield strain ε y Carrying out calculation to obtain corresponding strain increment values of the material to be measured under different elastic strains in a unified expression of a material stress calculation function, namely a formula (1); and obtaining a stress calculation function of the material by adopting a non-calibration method;
in formula (1), z=Δ∈/Δ∈ 0 ，Δε 0 The indentation strain increment of the material to be measured under zero stress is shown, and delta epsilon is the indentation strain increment of the material to be measured under other stresses; x is elastic strain epsilon and yield strain epsilon y The ratio epsilon/epsilon y Y is the yield ratio sigma y /σ b P1-p12 are equation coefficients obtained using some known alloy steel material calibration results, where: the values of p1- [12 are shown in Table 1.
TABLE 1
In the step (1), before an indentation test is carried out, stress-free treatment is carried out on the material to be tested, and the mechanical properties of the material cannot be changed in the treatment process; strain delta epsilon for zero stress of material 0 The strain increment value is obtained by adopting an indentation strain method on the surface of the material after annealing or other stress relief methods on the premise of not changing the original performance of the material.
In the step (3), the non-calibration process of the stress calculation function is as follows: according to the strain increment under each elastic strain calculated in the step (3), taking the elastic strain as an abscissa and the corresponding strain increment as an ordinate, performing data fitting on the obtained data points [ elastic strain epsilon, strain increment delta epsilon ] according to a 3-time function, and obtaining a stress calculation function of an indentation strain method, wherein the stress calculation function is shown as a formula (2);
Δε＝B 0 +B 1 ε+B 2 ε 2 +B 3 ε 3 (2)；
in the formula (2), B 0 、B 1 、B 2 、B 3 Is the stress calculation coefficient determined by equation (1).
The invention has the following advantages and beneficial effects:
1. the method of the invention brings related parameters into the known unified expression of the strain increment based on the strain increment and mechanical property of the alloy steel material to be measured under zero stress, can rapidly and accurately obtain the stress calculation function of the material, and completely realizes the requirement of testing residual stress by adopting an indentation strain method under the condition of non-calibration of the material.
2. The strain increment calculation function unified expression of the alloy steel material is convenient for users to expand the application range of the indentation strain method, and solves the problem that the indentation strain method cannot be adopted because the stress calculation function cannot be obtained in certain test occasions.
Drawings
FIG. 1 is a schematic diagram of a method for determining a stress calculation function by indentation strain method.
FIG. 2 is a comparison of non-calibrated and simulated calibration results for material # 1 using equation 1.
FIG. 3 is a comparison of non-calibrated and simulated calibration results for material # 2 using equation 1.
Detailed Description
The present invention is described in detail below with reference to examples and drawings, wherein an experimental calibration section is performed according to GB/T24179-2009 "method for measuring indentation strain of residual stress of metallic materials", and a simulation calibration section is performed with reference to document 3 (Chen Jing to Jiang Yunlu Chen Huaining, a method for determining stress measurement constant of indentation strain based on finite element simulation, application No. 201711277423.8).
The invention relates to a method for determining an indentation strain method stress calculation function based on strain increment under zero stress, which is a non-calibration method for realizing a material to be measured by adopting a unified expression of the alloy steel material indentation strain method strain increment calculation function, and comprises the following specific processes: firstly, obtaining a strain increment of a stress-free material through an indentation experiment; secondly, obtaining the yield strength, the tensile strength and the yield strain of the material through a tensile test; then, the obtained parameters are brought into a unified expression (formula 1) of a strain increment calculation function, and strain increments under different elastic strains are calculated; finally, the above results are used to determine the coefficients in equation 2, thereby achieving a non-calibrated determination of the stress calculation function (i.e., equation 2).
Example 1:
firstly, thoroughly eliminating residual stress in the No. 1 alloy steel material by means of heat treatment and the like, and obtaining the strain increment delta epsilon of the stress-free material by adopting an indentation method 0 The method comprises the steps of carrying out a first treatment on the surface of the Then obtaining the tensile property curve of the No. 1 material to obtain the yield strength sigma y Tensile strength sigma b And yield strain ε y . By substituting the obtained parameters into the strain increment unified expression (i.e., equation 1), a strain of-0.9ε can be obtained y ～0.9ε y Any relation between elastic strain and strain increment in the interval; fitting the obtained result according to the 3 rd power, wherein the obtained equation is the stress calculation function (namely formula 2) obtained by a non-calibration method.
FIG. 2 is a graph comparing non-calibrated and simulated calibration results for material # 1 using equation 1. The comparison result shows that the non-calibration method is well matched with the simulation calibration result.
Example 2:
firstThe indentation strain increment delta epsilon of the alloy steel material 2# material under no stress is obtained through experiments 0 The method comprises the steps of carrying out a first treatment on the surface of the Obtaining a tensile property curve to obtain yield strength sigma y Tensile strength sigma b And yield strain ε y . By substituting the obtained parameters into the strain increment unified expression (i.e., equation 1), a strain of-0.9ε can be obtained y ～0.9ε y Any relation between elastic strain and strain increment in the interval; fitting the obtained result according to the 3 rd power, wherein the obtained equation is the stress calculation function (namely formula 2) obtained by a non-calibration method.
FIG. 3 is a graph comparing the non-calibrated and simulated calibration results of material # 2 using equation 2. The comparison result shows that the non-calibration method is well matched with the simulation calibration result.
Claims (1)
1. A method for determining an indentation strain method stress calculation function based on a strain increment under zero stress is characterized by comprising the following steps: the method adopts a non-calibration method, and brings the strain increment and mechanical property of the alloy steel material to be measured under the condition of no stress into a unified expression of a strain increment calculation function of the same material, so as to obtain the stress calculation function of the material; the method comprises the following steps:
(1) The indentation strain increment delta epsilon of the material to be tested under zero stress is obtained through an indentation test 0 The method comprises the steps of carrying out a first treatment on the surface of the Wherein the strain increment delta epsilon of the material under zero stress 0 The strain increment value is obtained by adopting an indentation strain method on the surface of the material after annealing or other stress relief methods on the premise of not changing the original performance of the material;
(2) Obtaining mechanical property parameters of a material to be tested through a stretching experiment, wherein the mechanical property parameters are yield ratio sigma y /σ b Yield strain ε y The method comprises the steps of carrying out a first treatment on the surface of the The yield ratio is the yield strength sigma of the material y And tensile strength sigma b Is a ratio of (2);
(3) Increasing the indentation strain delta epsilon obtained in the step (1) and the step (2) 0 Yield ratio sigma y /σ b And yield strain ε y The material to be measured is obtained by calculation in a unified expression of a material stress calculation function, namely formula (1)Corresponding strain increment values at different elastic strains; and obtaining a stress calculation function of the material by adopting a non-calibration method;
in formula (1), z=Δ∈/Δ∈ 0 ，Δε 0 The indentation strain increment of the material to be measured under zero stress is shown, and delta epsilon is the indentation strain increment of the material to be measured under other stresses; x is elastic strain epsilon and yield strain epsilon y The ratio epsilon/epsilon y Y is the yield ratio sigma y /σ b P1-p12 are equation coefficients obtained using some known alloy steel material calibration results, where: p1=1.026, p2=0.695, p3= -1.229, p4=0.973, p5= -0.900, p6= -0.513, p7= -1.309, p8=0.544, p9= -1.210, p10= -1.904, p11= -1.281, p12=1.149;
the non-calibration process of the stress calculation function is as follows: according to the strain increment under each elastic strain calculated in the step (3), taking the elastic strain epsilon as an abscissa and the corresponding strain increment delta epsilon as an ordinate, and performing data fitting on the obtained data points according to a 3-time function to obtain a stress calculation function of an indentation strain method, wherein the stress calculation function is shown as a formula (2);
in the formula (2), B 0 、B 1 、B 2 、B 3 Is the stress calculation coefficient determined by equation (1).
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| CN101975693A (en) * | 2010-10-11 | 2011-02-16 | 肖锋 | Data measuring and calculating method for uniaxial tensile test |
| JP2012238168A (en) * | 2011-05-11 | 2012-12-06 | Sumitomo Rubber Ind Ltd | Rubber material simulation method |
| CN107024401A (en) * | 2017-04-20 | 2017-08-08 | 西北工业大学 | Obtain the method and system of metal material anisotropy and tension and compression asymmetry |
| CN108133082A (en) * | 2017-12-06 | 2018-06-08 | 中国科学院金属研究所 | A kind of method that stress measurement constant in Indentation strain method is determined based on finite element modelling |
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