CN113987752A - A kind of testing method, equipment and computer readable storage medium of Poisson's ratio - Google Patents
A kind of testing method, equipment and computer readable storage medium of Poisson's ratio Download PDFInfo
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Abstract
本发明涉及材料测试技术领域，具体公开了一种泊松比的测试方法、设备及计算机可读存储介质，通过对待测量样本进行形变测试，并测量在形变测试过程中待测量样本随测试时间变化而变化的多个应变力数据；根据多个应变力数据，计算获得待测量样本的纵向应变‑应力值曲线，根据曲线斜率变化区分弹性形变阶段，并计算弹性模量值；依据多个应变力数据以及弹性模量值，计算出纵向塑性应变值，计算并输出弹性泊松比值、弹塑性泊松比值‑纵向应变关系曲线和塑性泊松比值‑纵向塑性应变曲线。本发明通过结合理论与实际测试，建立了弹性泊松比、弹塑性泊松比、塑性泊松比的直接测试方法，提高了测试效率与准确性，易于实现自动化测试与运算。
The invention relates to the technical field of material testing, and specifically discloses a Poisson's ratio testing method, equipment and computer-readable storage medium. By performing a deformation test on a sample to be measured, and measuring the change of the sample to be measured with test time during the deformation test process and multiple strain force data that change; according to the multiple strain force data, calculate the longitudinal strain-stress value curve of the sample to be measured, distinguish the elastic deformation stage according to the curve slope change, and calculate the elastic modulus value; Data and elastic modulus values, calculate the longitudinal plastic strain value, calculate and output the elastic Poisson's ratio, the elastic-plastic Poisson's ratio-longitudinal strain relationship curve, and the plastic Poisson's ratio-longitudinal plastic strain curve. The present invention establishes direct testing methods of elastic Poisson's ratio, elastic-plastic Poisson's ratio and plastic Poisson's ratio by combining theory and practical testing, improves testing efficiency and accuracy, and is easy to realize automatic testing and calculation.
Description
Technical Field
The invention relates to the technical field of material testing, in particular to a method and equipment for testing Poisson's ratio and a computer readable storage medium.
Background
The Poisson ratio is a material parameter which must be related in industrial design, and refers to the ratio of the absolute value of transverse positive strain and axial positive strain when the material is unidirectionally pulled or pressed, also called transverse deformation coefficient, and is an elastic Poisson ratio which is commonly used in production and life and is an elastic constant for reflecting the transverse deformation of the material; at present, the measurement of the elastic Poisson's ratio of a material has been developed by measuring the longitudinal and transverse strain of the material under tension and then calculating the ratio.
However, after the material enters the plastic deformation stage from the elastic deformation, the poisson ratio is no longer constant, but becomes a function relation curve of strain, and after the material enters the plastic deformation, a phenomenon of necking can occur along with severe deformation, so that the edge of the detected material is not flat, especially for high polymer materials, after the material enters the plastic deformation stage, the necking shown by some materials can be very severe and obvious; leading to the calculation of the elastoplastic poisson's ratio and the shaped poisson's ratio becoming a difficult problem.
The existing Poisson ratio measuring method or device only generally measures the elastic Poisson ratio in the Poisson ratio measurement carried out by various industries according to the existing measuring technology, and rarely relates to the elastic-plastic Poisson ratio measurement or the plastic Poisson ratio measurement after entering a plastic deformation stage. The elastic-plastic poisson ratio and the shaping poisson ratio can be indirectly obtained in a theoretical derivation or simulation mode, but the change of each parameter of a necking stage in the process of the material from elastic deformation to plastic deformation cannot be accurately predicted, and the actual deformation condition of the measured material is difficult to simulate or derive. Therefore, a direct test method for the elastoplastic poisson's ratio and the plastic poisson's ratio of a material is needed.
Disclosure of Invention
Embodiments of the present invention provide a method and an apparatus for testing a poisson's ratio, and a computer-readable storage medium, which overcome the problem that it is difficult to directly measure an elastic-plastic poisson's ratio and a plastic poisson's ratio and calculate a result.
The invention provides a method for testing Poisson's ratio, which comprises the following steps:
carrying out deformation test on a sample to be measured, and measuring a plurality of strain force data of the sample to be measured, which change along with the change of test time in the deformation test process; wherein the plurality of strain force data comprises stress values, transverse strain values, and longitudinal strain values;
according to the multiple strain force data, calculating to obtain a longitudinal strain value-stress value curve of the sample to be measured, calculating an elastic modulus value, and according to the multiple strain force data and the elastic modulus value, calculating a longitudinal plastic strain value;
obtaining an elastic Poisson ratio according to a transverse strain value-longitudinal strain value curve;
and obtaining a Poisson ratio measurement result of the sample to be measured according to the elastic Poisson ratio value and the longitudinal plastic strain value.
Preferably, the method for performing the deformation test on the sample to be measured includes:
mounting the sample to be measured on a testing device, and inputting testing parameters in the testing device; the testing device is used for enabling a sample to be measured to deform and recording a real-time stress value;
starting the testing device and the deformation recognition device at the same time, and carrying out deformation testing on the sample to be measured; the deformation identification device is used for measuring the transverse strain and the longitudinal strain of the sample to be measured in real time.
Preferably, before the sample to be measured is mounted on the testing device, the method further comprises:
preparing a sample to be measured into a standard sample;
the speckles with randomly changed gray levels are arranged on the surface of the standard sample and used for the deformation identification device to acquire the transverse strain value and the longitudinal strain value data of the standard sample through image identification.
Preferably, according to the transverse strain value-longitudinal strain value curve, the method for obtaining the elastic poisson ratio is as follows:
and combining the transverse strain value and the longitudinal strain value to obtain a relation curve of the transverse strain value and the longitudinal strain value, and performing regression linear fitting on the elastic section of the initial line to obtain a linear slope, namely the elastic Poisson ratio.
Preferably, the method for obtaining a poisson's ratio measurement of the sample to be measured from the elastic poisson's ratio value and the longitudinal plastic strain value is:
according to the multiple strain force data, calculating an elastic Poisson ratio and an elastic modulus value, and further calculating a longitudinal true strain;
acquiring a relation curve of a transverse strain value and a longitudinal true strain value, establishing a first fitting equation according to the exponential relation, and deriving a fitting curve of the first fitting equation to obtain a curve slope, namely an elastic-plastic Poisson's ratio value-longitudinal strain value curve;
obtaining a relation curve of the longitudinal plastic strain value and the transverse strain value by calculating the longitudinal plastic strain value and the longitudinal strain value, and calculating the slope of the curve to obtain a plastic Poisson ratio-longitudinal strain value curve;
calculating a longitudinal true strain value according to the elastic Poisson ratio, acquiring a relation curve of the transverse strain value and the longitudinal true plastic strain value, establishing a second fitting equation according to the exponential relation, and deriving a fitting curve of the second fitting equation to obtain a curve slope, namely a plastic Poisson ratio-longitudinal true plastic strain value curve;
and further calculating to obtain a plastic Poisson's ratio-longitudinal plastic strain value curve.
The invention provides a test device of Poisson's ratio, comprising: the system comprises a deformation testing module, a first calculating module, a second calculating module and a Poisson ratio calculating module;
the deformation testing module is used for carrying out deformation testing on a sample to be tested and measuring a plurality of strain force data of the sample to be tested, which change along with the change of testing time, in the deformation testing process;
the first calculation module is used for calculating an elastic modulus value and a longitudinal plastic strain value of the sample to be measured according to the strain force data;
the second calculation module is used for obtaining an elastic Poisson ratio according to a transverse strain value-longitudinal strain value curve;
the Poisson ratio calculating module is used for obtaining a Poisson ratio measuring result of the sample to be measured according to the elastic Poisson ratio value and the longitudinal plastic strain value.
The invention provides a terminal device, which comprises a processor and a storage device, wherein the storage device is used for storing one or more programs; when the one or more programs are executed by the processor, the processor implements the poisson's ratio testing method described above.
The invention provides a computer-readable storage medium, which comprises a stored computer program, wherein when the computer program runs, a device where the computer-readable storage medium is located is controlled to execute the poisson's ratio testing method.
The embodiment of the invention has the following beneficial effects:
the invention provides a method and equipment for testing Poisson's ratio and a computer readable storage medium, wherein a sample to be tested is subjected to deformation testing, a plurality of strain force data of the sample to be tested, which changes along with the change of testing time, are measured in the deformation testing process, an elastic modulus value and a longitudinal plastic strain value are calculated, and finally a Poisson's ratio measuring result of the sample to be tested is obtained; by combining theory and actual test, a direct test method and a data processing method of the elastic Poisson ratio, the elastic-plastic Poisson ratio and the plastic Poisson ratio are established, the test efficiency and accuracy are improved, the method is easy to apply to automatic test and operation, and the universality is high.
Drawings
FIG. 1 is a schematic flow chart diagram of one embodiment of a method for testing Poisson's ratio provided by the present invention;
FIG. 2 is a schematic structural diagram of an embodiment of a test apparatus provided in the present invention;
FIG. 3 is a schematic structural diagram of one embodiment of a standard sample provided by the present invention;
FIG. 4 shows the lateral strain ε according to one embodiment of the present inventionyAnd longitudinal strain εxA graph of the relationship;
FIG. 5 is a graph of engineering stress strain for one embodiment of the present invention;
FIG. 6 is a graph of a linear fit of elastic Poisson's ratio values for one embodiment of the present invention;
FIG. 7 is a plot of the elasto-plastic Poisson's ratio for a direct calculation of one embodiment of the present invention;
FIG. 8 is a graph comparing the elasto-plastic Poisson's ratio curves of the direct calculation method and the reduced data volume method according to one embodiment of the present invention;
FIG. 9 is a plot of a linear fit of the elastoplastic Poisson's ratio at large deformation (. gtoreq.30%) for one embodiment of the present invention;
FIG. 10 is a graph showing the transverse strain ε at a lower deflection (< 30%) of one embodiment of the present inventionyCorresponding to longitudinal strain epsilonxFitting a curve graph in an exponential manner;
FIG. 11 is a plot of the elastoplastic Poisson's ratio for a curve fitting method according to one embodiment of the present invention;
FIG. 12 shows the lateral strain ε according to one embodiment of the present inventionyAnd longitudinal plastic strain epsilonpA graph of the relationship;
FIG. 13 is a graph comparing plastic Poisson ratio curves for direct calculation and reduced data volume methods according to one embodiment of the present invention;
FIG. 14 is a plot of a linear fit of the plastic Poisson's ratio for large deformation (. gtoreq.30%) for one embodiment of the present invention;
FIG. 15 shows the transverse strain ε at a lower deflection (< 30%) of one embodiment of the present inventionyFor plastic strain epsilonpFitting a curve graph in an exponential manner;
FIG. 16 is a plot of the plastic Poisson's ratio for a curve fitting method according to one embodiment of the present invention.
In the figure: 1. a tensile testing machine; 2. stretching the clamp; 3. a standard sample; 4. a force value sensor; 5. a computer; 6. a CCD camera.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Referring to fig. 1, a schematic flow chart of a poisson's ratio testing method according to an embodiment of the present invention includes the following steps:
s1, carrying out deformation test on the sample to be measured through test equipment, and measuring a plurality of strain force data of the sample to be measured changing along with the change of test time in the deformation test process; wherein the plurality of strain force data comprises stress values, transverse strain values and longitudinal strain values;
s2, according to the multiple strain force data, calculating to obtain a longitudinal strain value-stress value curve of the sample to be measured, and calculating an elastic modulus value; calculating a longitudinal plastic strain value according to the strain force data and the elastic modulus value;
s3, calculating and outputting an elastic Poisson ratio according to the transverse strain value-longitudinal strain value curve;
and S4, obtaining the elastic-plastic Poisson ' S ratio and the plastic Poisson ' S ratio of the sample to be measured according to the elastic Poisson ' S ratio and the longitudinal plastic strain value.
The method for testing the Poisson's ratio provided by the embodiment of the invention establishes a direct test method and a data processing method for the elastic Poisson's ratio, the elastic-plastic Poisson's ratio and the plastic Poisson's ratio by combining theory and actual test, improves the test efficiency and accuracy, is easy to apply to automatic test and operation, and has high universality.
Referring to fig. 2 and fig. 3, a schematic diagram of a poisson ratio testing apparatus and a standard sample 3 according to an embodiment of the present invention is provided, including: standard specimen 3 adopts dumbbell type spline, and the testing arrangement who adopts includes tensile testing machine 1, tensile anchor clamps 2 and force value sensor 4, and tensile testing machine 1 and tensile anchor clamps 2 junction are located to force value sensor 4, and deformation recognition device includes CCD camera 6 and computer 5, and computer 5 links to each other respectively with force value sensor 4 and CCD camera 6 through the data line, and the operation has the software that is used for data acquisition and image analysis in the computer 5. The method comprises the steps that scattered spots are sprayed on a standard sample 3 before testing so that a CCD camera 6 can collect image information, the standard sample 3 is arranged in a tensile clamp 2, a computer 5 controls a tensile testing machine 1 to conduct tensile testing, a force value sensor 4 obtains stress value information, the CCD camera 6 identifies and obtains real-time image information of the standard sample 3, and a transverse strain value and a longitudinal strain value are obtained through image identification.
Preferably, the size of the speckle corresponds to 3 to 5 pixels in the captured image of the deformation recognition device.
Preferably, the CCD camera 6 of the deformation recognition device is specifically a three-dimensional strain measurement system, the standard sample strip is photographed by the CCD camera 6 of at least 2 different angles, the speckle images before and after the deformation of the surface of the standard sample strip are analyzed by using the computer binocular vision theory and the material mechanics theory to dynamically track the movement of the speckles on the surface of the standard sample strip and obtain a three-dimensional displacement field, and the three-dimensional strain field of the standard sample strip is calculated on the basis.
It will be appreciated by those skilled in the art that the schematic diagram is merely an example of a test device and does not constitute a limitation of a test device, and may include more or fewer components than shown, or some components in combination, or different components, e.g., the test device may also include input output devices, network access devices, buses, etc.
The Poisson ratio testing equipment provided by the embodiment of the invention can calculate the elastic Poisson ratio, the elastic-plastic Poisson ratio and the plastic Poisson ratio according to the test data through a one-time deformation test, so that the testing efficiency is greatly improved, and the operation is convenient and efficient.
As one embodiment of the present invention, a poisson ratio testing method is provided, and the following calculation method for implementing the poisson ratio testing method is combined with theoretical derivation and actual testing as follows:
(1) the elastic Poisson ratio calculation method comprises the following steps:
let the measured stress value be σyTransverse strain εyLongitudinal strain of epsilonx；
By stress value σyWith longitudinal strain epsilonxObtaining an engineering stress-strain curve according to the data, and calculating an elastic modulus value:
incorporating transverse strain εy(Y-axis) and longitudinal strain εx(X-axis) data, obtaining a relation strain curve;
elastic Poisson's ratio mueIs in the transverse directionyCorresponding to longitudinal strain epsilonxThe amount of stretching deformation Deltaε of one of the two coordinate axes (transverse direction) perpendicular to the stretching direction in the initial linear portion of the relationship curveyAmount of deformation from the stretching direction (longitudinal direction) Δ εxThe negative value of the ratio; in the initial linear elastic section (standard ISO527-1:2019 specifies strain ε in the longitudinal directionxLinear region between 0.3% and yield strain) is subjected to regression linear fitting, and the linear slope is the elastic poisson ratio
(2) The calculation method of the elastic-plastic Poisson ratio is as follows:
incorporating longitudinal strain epsilonxAnd transverse strain εyCalculating the slope of the relation curve, namely the elastic-plastic Poisson's ratio mu-longitudinal strain epsilonxA curve;
the total elastic-plastic strain is equal to the elastic straineWith plastic strain epsilonpSum, i.e. epsilon ═ epsilone+εpThe corresponding elastic-plastic Poisson's ratio is mu, the elastic modulus value of the material is E, and the stress sigma is a function sigma (epsilon) of the elastic-plastic total strain epsilon; the elastic Poisson's ratio is still mueObtaining the elastic strain epsiloneσ/E; therefore, the strain in the longitudinal direction (X-axis) of the tensile standard specimen 3 is εx＝ε＝εe+εpThe ratio of ∈ in the width (Y-axis) and thickness (Z-axis) directionsy＝εz＝-με；
Setting the initial volume of the test area of the research object tensile standard sample 3 as V0Length width thickness, due to the effect of elastic deformation on initial stretching, the volume change (plastic deformation volume is constant), derived from the formula:
usually σ/E is much less than 1, total elastoplastic strain εx＝ε＝εe+εpCorresponding elasto-plastic poisson ratio mu ═ epsilony/εx＝-εyEpsilon, general true strain epsilon*Ln (1+ epsilon), we simplify:
thus transverse strain εyWith true strain in the longitudinal direction epsilon*Presenting an exponential relationship; according to the test data and formula conversion making transverse strain epsilonyAnd longitudinal strain εxRelationship of data by true strain ε*Converting longitudinal true strain epsilon into an ln (1+ epsilon) formulax *Obtaining transverse strain epsilonyWith true strain in the longitudinal direction epsilonx *A relation curve, establishing a fitting equation according to the exponential relation, and deriving the fitting curve to obtain the slope of the curve, namely the elastic-plastic Poisson ratio mu-longitudinal true strain epsilonx *The curve can further obtain the elastoplasticity Poisson ratio mu-longitudinal strain epsilonxCurve line.
(3) The calculation method of the plastic Poisson ratio is as follows:
longitudinal strain data epsilonxConverting longitudinal plastic strain epsilon according to a formulapIncorporating longitudinal plastic strain epsilonpAnd transverse strain εyCalculating the slope of the relation curve to obtain the plastic Poisson ratio mupLongitudinal strain εxA curve;
total elastic-plastic strain equal to longitudinal elastic straineWith longitudinal plastic strain epsilonpSum, i.e. epsilon ═ epsilone+εpIn the width (transverse Y-axis) and thickness (Z-axis) directions should be ∈y＝εz＝-(μeεe+μpεp)；
Setting the initial volume of the test area of the research object tensile standard sample 3 as V0Length width thickness, the plastic poisson ratio is derived according to the formula:
longitudinal strain epsilonx＝ε＝εe+εpLongitudinal elastic strain epsiloneCorresponding elastic Poisson's ratio mue＝-εy/εeLongitudinal plastic strain epsilonpCorresponding plastic Poisson's ratio mup＝-εy/εpTrue strain in the longitudinal direction epsilon*＝(εe *+εp *)＝ln(1+ε)＝ln(1+εe+εp) Elastic properties mu of the material after plastic deformation has taken placeeAnd εeThe influence on the plastic strain is very little and ignored, so the method is simplified into the method：
Thus transverse strain εyTrue plastic strain epsilon with longitudinal directionp *Presenting an exponential relationship; according to the test data and formula conversion making transverse strain epsilonyAnd longitudinal strain εxData dependence through true strain epsilon*Converting longitudinal true strain epsilon into an ln (1+ epsilon) formulax *According to the equatione+εp＝σ/E+εpObtaining transverse strain epsilonyTrue plastic strain epsilon with longitudinal directionp *Establishing a fitting equation according to the exponential relationship, and deriving the fitting curve to obtain a curve slope which is the plastic Poisson ratio mupTrue plastic strain epsilon with longitudinal directionp *Curve according to longitudinal plastic strain epsilonpTrue plastic strain epsilon with longitudinal directionp *To obtain the plastic Poisson's ratio mupLongitudinal plastic strain εpCurve, finally the plastic Poisson's ratio mu can be obtainedpLongitudinal strain εxCurve line.
Referring to fig. 2 to fig. 16, a specific test data graph and a graph obtained by operation of the poisson's ratio test method according to one embodiment of the present invention are shown, and the following describes the calculation steps of the poisson's ratio test method according to this embodiment in detail with reference to the drawings.
Referring to fig. 2 and 3, a material to be measured is injection-molded or machined into a standard sample 3, and is adjusted for a set time under a standard environment;
the standard sample 3 was pretreated: speckle preparation, namely forming a speckle pattern with randomly changing gray scale on the surface of the standard sample 3 for identifying and acquiring image information by using a CCD camera 6 and an image analysis system of Digital Image Correlation (DIC).
Installing a standard sample 3 on a tensile clamp 2 of a tensile testing machine 1, and setting parameters of the standard sample 3, such as spacing, testing rate, acquisition frequency and the like;
adjusting a CCD camera 6 and a light source to obtain a clear image of the standard sample 3 on the tensile testing machine 1, wherein the exposure frequency of the camera is adjusted to be the same as that of the tensile testing machine 1;
simultaneously starting a tensile test program of the tensile tester 1 and monitoring image information of the CCD camera 6;
after the test is finished, stopping image acquisition of the CCD camera 6, and deriving stress value data of the tensile testing machine 1 and image data of the CCD camera 6;
image data is led into a computer 5 to be calibrated through an image analysis system, a virtual extensometer is established, and transverse strain epsilon is calculated, merged and drawny(Y-axis) and longitudinal strain εx(X-axis) relationship curve.
Referring to fig. 4, the combined stress values σyWith longitudinal strain epsilonxAnd (3) obtaining an engineering stress-strain curve according to the data, and calculating an elastic modulus value:
referring to FIG. 5, the elastic Poisson's ratio μe: in transverse direction of strain epsilonyCorresponding to longitudinal strain epsilonxThe amount of stretching deformation Deltaε of one of the two coordinate axes (transverse direction) perpendicular to the stretching direction in the initial linear portion of the relationship curveyAmount of deformation from the stretching direction (longitudinal direction) Δ εxThe negative value of the ratio. Elastic section of the starting thread (Standard ISO527-1:2019 specifies a strain ε in the longitudinal directionxLinear region between 0.3% and 4.3% of yield strain) to obtain an elastic poisson ratio by performing regression linear fitting on the relation curve and taking 0.7% to 2.3% of linear regression fitting:
referring to fig. 6, the elastoplastic poisson ratio μ: incorporating longitudinal strain epsilonx(X-axis) and transverse strain εy(Y-axis) relation curve.
Referring to FIG. 7, the slope of the curve is calculated directly, and the curve appears smooth overall but locally due to the large number of data points (2800 data points)There are fluctuations, which are caused by test accuracy and systematic errors, and the obtained elasto-plastic poisson's ratio mu and longitudinal strain epsilonxThe relation curve has large data fluctuation and strong interference, the whole trend is that the data is gradually stable after increasing and then decreasing, but the target result cannot be obtained.
Referring to FIGS. 8 and 9, the longitudinal strain ε is achieved by decreasing the data volumex(X-axis) and transverse strain εyThe (Y-axis) relation curve is smooth as a whole, so that the data volume can be reduced, the fluctuation interference is reduced, and the obtained elastoplasticity Poisson ratio mu and the longitudinal strain epsilonxAnd the data fluctuation can be obviously improved by reducing the data quantity, and the curve trend is more obvious. When longitudinal strain epsilonxAt a higher time, longitudinal strain εx(X-axis) and transverse strain εyThe relation curve (Y axis) is in a linear trend, and the elastic-plastic Poisson ratio can be represented by a linear regression fitting coefficient; when longitudinal strain epsilonxExpressed as the elastic poisson ratio at the initial elastic stage. However, the information of the curve turning part cannot be effectively retained and embodied by the method for reducing the data points, because the data point interval is increased, the slope is the average value of the slopes of the secants of adjacent data points, and the elastic-plastic poisson ratio of the material in the curve turning process cannot be accurately embodied.
Referring to FIGS. 10 and 11, the true longitudinal strain ε is formulated*When longitudinal strain is equal to ln (1+ epsilon)xBelow 30%, the approximation can be seen as the true strain ε in the longitudinal direction*With longitudinal strain epsilonxIn a linear relationship, the transverse strain ε can be obtainedyWith longitudinal strain epsilonxAlso in exponential relation to longitudinal strain epsilonxPerforming exponential fitting on a relation curve within 30% to obtain a fitting curve, deriving the fitting curve to obtain an elastic-plastic Poisson's ratio curve, combining the elastic-plastic Poisson's ratio curve with a linear trend of more than 30%, and obtaining the elastic-plastic Poisson's ratio-longitudinal strain epsilonxAnd the curve is smooth and stable.
Referring to FIG. 12, the plastic Poisson's ratio μp: according to the formula ∈ ═ epsilone+εp＝σ/E+εpConversion of plastic strain epsilonpIncorporating longitudinal plastic strain epsilonp(X axis) and transverseTo strain epsilony(Y-axis) relation; the slope of the curve is directly calculated, and the curve is smooth as a whole due to more data points (more than 2800 data), but has fluctuation on part, which is influenced by test precision and system error, and the obtained plastic Poisson ratio mu is obtainedpLongitudinal plastic strain εpThe relation curve graph has large data fluctuation and strong interference, the overall trend is that the data is increased firstly and then is reduced to be gradually stable, but the target result cannot be obtained.
Referring to FIGS. 13 and 14, the longitudinal plastic strain εp(X-axis) and transverse strain εyThe (Y-axis) relation curve is smooth as a whole, so that the data volume can be reduced, the fluctuation interference is reduced, and the obtained plastic Poisson ratio mupWith longitudinal plastic strain epsilonpThe relation curve graph can obviously improve the data fluctuation by reducing the data quantity, and the curve trend is more obvious. When longitudinal plastic strain epsilonpAt a higher longitudinal plastic strain εp(X-axis) and transverse strain εyThe (Y-axis) relationship curve is linear in trend, and the plastic Poisson's ratio can be expressed by linear regression fitting coefficient. However, the information of the curve turning part cannot be effectively retained and embodied by the method for reducing the data points, because the data point interval is increased, the slope is the average value of the slopes of the secants of adjacent data points, and the plastic poisson ratio of the material in the curve turning cannot be accurately embodied.
Referring to FIGS. 15 and 16, the true longitudinal strain ε is formulated*When plastic strain in longitudinal direction is ∈ ln (1+ epsilon)pBelow 30%, the approximation can be seen as the true longitudinal plastic strain εp *With longitudinal plastic strain epsilonpIn a linear relationship, the transverse strain ε can be obtainedyWith longitudinal plastic strain epsilonpAlso in an exponential relationship to longitudinal plastic strain epsilonpPerforming exponential fitting on a relation curve within 30% to obtain a fitting curve, deriving the fitting curve, combining the derived fitting curve with the linear trend of more than 30% to obtain the plastic Poisson ratio-longitudinal plastic strain epsilonpAnd the curve is smooth and stable.
The invention also discloses a test device of Poisson's ratio, comprising: the device comprises a deformation testing module, a first calculating module, a second calculating module and a Poisson ratio calculating module.
The deformation testing module is used for carrying out deformation testing on a sample to be tested and measuring a plurality of strain force data of the sample to be tested, which change along with the change of testing time, in the deformation testing process; wherein the plurality of strain force data comprises stress values, transverse strain values, and longitudinal strain values.
The first calculation module is used for calculating and obtaining a longitudinal strain value-stress value curve of the sample to be measured according to the plurality of strain force data, calculating an elastic modulus value, and calculating a longitudinal plastic strain value according to the plurality of strain force data and the elastic modulus value.
The second calculation module is used for obtaining a relation curve of the transverse strain value and the longitudinal strain value by combining the transverse strain value and the longitudinal strain value, and performing regression linear fitting on an initial line elastic section of the relation curve, wherein the obtained linear slope is the elastic Poisson ratio.
The Poisson ratio calculating module is used for obtaining a Poisson ratio measuring result of the sample to be measured according to the elastic Poisson ratio value and the longitudinal plastic strain value.
The Poisson ratio calculating module comprises an elastic-plastic Poisson ratio calculating unit and a plastic Poisson ratio calculating unit.
The elastic-plastic Poisson ratio calculation unit is used for calculating an elastic Poisson ratio value and an elastic modulus value according to the multiple strain force data and further calculating longitudinal true strain; and obtaining a relation curve of the transverse strain value and the longitudinal true strain value, establishing a first fitting equation according to the exponential relation, and deriving the fitting curve of the first fitting equation to obtain a curve slope so as to obtain an elastic-plastic Poisson ratio value-longitudinal strain value curve.
The plastic Poisson ratio calculating unit is used for calculating a longitudinal strain value and a longitudinal plastic strain value to obtain a longitudinal plastic strain value-transverse strain value relation curve, and calculating the slope of the curve to obtain a plastic Poisson ratio-longitudinal strain value curve; calculating a longitudinal true strain value according to the elastic Poisson ratio, acquiring a relation curve of the transverse strain value and the longitudinal true plastic strain value, establishing a second fitting equation according to the exponential relation, and deriving a fitting curve of the second fitting equation to obtain a curve slope, namely a plastic Poisson ratio-longitudinal true plastic strain value curve; and further calculating to obtain a plastic Poisson's ratio-longitudinal plastic strain value curve.
The invention also discloses a terminal device, which comprises a processor and a storage device, wherein the storage device is used for storing one or more programs; when the one or more programs are executed by the processor, the processor implements the poisson's ratio testing method described above. The Processor may be a Central Processing Unit (CPU), other general purpose Processor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), an off-the-shelf Programmable Gate Array (FPGA) or other Programmable logic device, discrete Gate or transistor logic, discrete hardware components, etc. The general purpose processor may be a microprocessor or the processor may be any conventional processor or the like, which is the control center for the test equipment and connects the various parts of the overall test equipment using various interfaces and lines.
The storage means may be adapted to store computer programs and/or modules, and the processor may be adapted to implement various functions of the terminal device by running or executing the computer programs and/or modules stored in the storage means and by invoking data stored in the storage means. The storage device may mainly include a storage program area and a storage data area, wherein the storage program area may store an operating system, an application program required for at least one function, and the like; the storage data area may store data created according to the use of the terminal device, and the like. In addition, the storage device may include high speed random access memory, and may also include non-volatile memory, such as a hard disk, a memory, a plug-in hard disk, a Smart Media Card (SMC), a Secure Digital (SD) Card, a Flash memory Card (Flash Card), at least one magnetic disk storage device, a Flash memory device, or other volatile solid state storage device.
Wherein the poisson's ratio testing apparatus integrated module/unit, if implemented in the form of a software functional unit and sold or used as a stand-alone product, may be stored in a computer readable storage medium. Based on such understanding, all or part of the flow in the method according to the embodiments of the present invention may also be implemented by a computer program, which may be stored in at least one computer-readable storage medium and used for instructing related hardware to implement the steps of the above-described embodiments of the method when executed by a processor. Wherein the computer program comprises computer program code, which may be in the form of source code, object code, an executable file or some intermediate form, etc. The computer readable medium may include: any entity or device capable of carrying computer program code, recording medium, U.S. disk, removable hard disk, magnetic disk, optical disk, computer Memory, Read-Only Memory (ROM), Random Access Memory (RAM), electrical carrier wave signals, telecommunications signals, software distribution media, and the like.
It should be noted that the above-described embodiments of the apparatus and device are merely schematic, where units illustrated as separate components may or may not be physically separate, and components illustrated as units may or may not be physical units, may be located in one place, or may be distributed on multiple network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the solution of the present embodiment. In addition, in the drawings of the device embodiments provided by the present invention, the connection relationship between the modules indicates that there is a communication connection between them, and may be specifically implemented as one or more communication buses or signal lines. One of ordinary skill in the art can understand and implement it without inventive effort.
The foregoing is a preferred embodiment of the present invention, and it should be noted that it would be apparent to those skilled in the art that various modifications and enhancements can be made without departing from the principles of the invention, and such modifications and enhancements are also considered to be within the scope of the invention.
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