CN111458243B - Experimental method for measuring mechanical properties of metal by using indentation instrument - Google Patents
Experimental method for measuring mechanical properties of metal by using indentation instrument Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/40—Investigating hardness or rebound hardness
- G01N3/42—Investigating hardness or rebound hardness by performing impressions under a steady load by indentors, e.g. sphere, pyramid
- G01N3/44—Investigating hardness or rebound hardness by performing impressions under a steady load by indentors, e.g. sphere, pyramid the indentors being put under a minor load and a subsequent major load, i.e. Rockwell system
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- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/08—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/62—Manufacturing, calibrating, or repairing devices used in investigations covered by the preceding subgroups
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/0001—Type of application of the stress
- G01N2203/0005—Repeated or cyclic
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/0014—Type of force applied
- G01N2203/0016—Tensile or compressive
- G01N2203/0019—Compressive
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/003—Generation of the force
- G01N2203/005—Electromagnetic means
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/0058—Kind of property studied
- G01N2203/0069—Fatigue, creep, strain-stress relations or elastic constants
- G01N2203/0075—Strain-stress relations or elastic constants
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/0058—Kind of property studied
- G01N2203/0076—Hardness, compressibility or resistance to crushing
- G01N2203/0078—Hardness, compressibility or resistance to crushing using indentation
- G01N2203/008—Residual indentation measurement
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/0058—Kind of property studied
- G01N2203/0092—Visco-elasticity, solidification, curing, cross-linking degree, vulcanisation or strength properties of semi-solid materials
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/02—Details not specific for a particular testing method
- G01N2203/0202—Control of the test
- G01N2203/0212—Theories, calculations
- G01N2203/0218—Calculations based on experimental data
Abstract
The invention provides an experimental method for determining metal mechanical properties by using an indenter, which is characterized in that a prepared sample is fixed after the mechanical error measurement of an indentation test is finished; performing an indentation test on the metal or alloy sample; converting the corresponding load-displacement value into a true stress-true plastic strain data point through a formula; and performing yield strength conversion and tensile strength estimation of the tested material: the invention utilizes the nano-indenter to measure the mechanical properties of the metal, and obtains the inertia, yield strength and engineering ultimate tensile strength of the true stress-true strain curve of the metal material. The method carries out automatic ball indentation test on the tested material by using an indenter method, carries out whole-course mapping on each loading and unloading cycle in the test process, avoids the occurrence of theoretical ideal values, has an error compensation link, and can accurately and directly measure the load-displacement data, the true stress-true strain curve, the yield strength and the engineering ultimate tensile strength of the tested material.
Description
Technical Field
The invention relates to an experimental method for measuring mechanical properties of metal by using an indenter, belonging to the technical field of nondestructive mechanical experiments.
Background
Socioeconomic and rapidly developing scientific technologies have led to increased attention being paid to the safety of industrial production and equipment service. Therefore, material quality inspection and life evaluation of industrial equipment have also become one of the focuses of attention. In order to accurately evaluate the residual life of industrial equipment and test the performance of in-service equipment, it is necessary to grasp the change of mechanical properties of materials. However, the conventional mechanical property test needs to damage the test sample in most cases, which means that the conventional mechanical property test method cannot perform online evaluation on the in-service equipment, so that the ball indentation test plays an extremely important role in online evaluation of the in-service equipment as a nondestructive test method.
As shown in fig. 1 and 2, a conventional indentation tester includes a gantry 1, a sensor 2, a test head 3, a spherical indenter 31, a fixture 4, an operating platform 5, a base 6, and the like,
chinese patent No. CN107860671A discloses a device and method for measuring yield strength and strain hardening index of metal material by indentation method, which loads load by servo motor, and repeats loading and unloading process, when the indentation depth reaches the set total indentation depth, stops loading, the obtained load-displacement curve is composed of a plurality of loading and unloading cycle curves, but each unloading process is partial unloading, the load applied in each cycle can not be completely unloaded, which obviously brings about no small error to the tested data. In addition, in the process of carrying out an indentation test, the indentation tester can generate measurement misdetection due to structural deformation and structural gaps, but the existing indentation test method does not contain a misdetection compensation link, and currently, no indentation test standard exists internationally, so that whether the methods can accurately reflect the authenticity of the tested material or not can not be accurately judged.
Therefore, the test data of each link is more real and reliable in the test process, and the prevention of ideal measurement is very important.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: the experimental method for measuring the mechanical property of the metal by using the indenter is more real and reliable in test data.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows: an experimental method for measuring metal mechanical properties by using an indenter comprises the following steps:
step 2, detaching the spherical test head of the indenter, mounting the flat-bottom test head, and detaching the indenter clamp from the operating table;
and 3, carrying out indentation test mechanical error measurement:
3.1 setting the rate at which the indenter test head is depressed to V in the indenter control system 0 ；
3.2 continuous loading and unloading are carried out at the same position in the measuring process, the process of one-time loading and complete unloading is a period, firstly, the number I, I of the loading and unloading periods is set in the indentation instrument control system>1 and setting the peak value of the applied load of the ith period as P i Wherein I =1, 2, 3 \8230I, unit: n;
3.3 control the start of mechanical error measurement in the indenter control system:
3.3.1 let i =1, first perform the first loading and unloading cycle; under the loading of motor drive, the flat-bottom test head presses the speed V according to settlement 0 And the flat-bottom test head is gradually pressed down, and the flat-bottom test head cannot be pressed into the operating table because the contact area between the flat-bottom test head and the operating table of the indentation instrument is large. After the flat-bottom test head contacts with an operation table of the indenter, the value of the load applied by the indenter is gradually increased from 0 until the flat-bottom test head is loaded to the set valueP 1 Value, at which point the indentor system records P 1 Corresponding sensor displacement value lambda under load 11 . The indenter then starts to unload the force and the load will go from P 1 Slowly unload to 0, at which time the indenter system will record the displacement value λ of the sensor under load of 0 21 ；
3.3.2 let i = i +1, the indenter will continue the ith loading and unloading cycle, and the loading value of the indenter gradually increases from 0 again until the set value P is loaded i Value, at which point the indentor system will record P i Corresponding sensor displacement value lambda under load 1i . The indenter then starts the unloading of the force and the load will be from P i Slowly unloading to 0 again, at which time the indenter system will record the displacement value lambda of the sensor under load of 0 2i
3.3.3 if I < I, jumping back to step 3.3.2, and if I ≧ I, continuing to execute step 3.3.4 downwards;
3.3.4 at this time, the displacement value recorded in the indenter system is the deformation of the whole mechanical structure of the indenter under the corresponding load; after the I cycle is finished, the measurement is finished, and the lambda is recorded in the indentation instrument system 1i (I =1, 2, 3 \ 8230; \8230; (I) and λ 2i (I =1, 2, 3 \8230; I) two sets of data;
and 5, performing an indentation test on the metal or alloy sample:
5.1 the pressing speed is kept constant, and the pressing speed of the indenter test head is still set to V in the indenter control system 0 ；
5.2 the number of load/unload cycles remains unchanged and is still set to I (I)>1) The peak value of the applied load of the i-th period is also kept unchanged and is still set as P i Wherein I =1, 2, 3 \8230I, unit: n;
5.3 controlling the indentation test to start in an indentation instrument control system;
5.3.1 let i =1, first the first loading and unloading cycle is performed: under the motor drive loading, the test head presses down the speed V according to the setting 0 Slowly pressing down, and vertically pressing a spherical pressure head at the tail end of the test head into the surface of the sample; when the spherical indenter contacts the metal sample, the indenter system starts to use the displacement value of the spherical indenter as the abscissa, and the displacement value unit is: mm, the value of the load applied by the indenter as ordinate, the unit of the load value: n, drawing a synchronous curve in a Cartesian coordinate system; the value of the applied load is gradually increased from 0 until the set value P is loaded 1 Value, at which point the indentor system will record P 1 Corresponding displacement value h of spherical pressure head under load t1 . The indenter then starts to unload the force and the load will go from P 1 Slowly unloading to 0, and recording the displacement value h of the spherical indenter under the load of 0 by the indenter system p1 ；
5.3.2 let i = i +1, the indenter will continue the ith loading and unloading cycle, and the loading value of the indenter gradually increases from 0 again until the set value P is loaded i Value, at which time the indentor system will record P i Corresponding displacement value h of spherical pressure head under load ti . The indenter then starts the unloading of the force and the load will be from P i Slowly unloading to 0 again, and recording the displacement value h of the spherical indenter under the load of 0 by the indenter system at the moment pi ；
5.3.3 if I < I, then jump back to step 5.3.2, if I ≧ I, then continue to execute step 5.3.4 downward;
5.3.4 at this time, a load-displacement curve of the indentation test process was generated in the indentor system and P was recorded i Wherein I =1, 2, 3 \8230 \ 8230:I, h ti Wherein I =1, 2, 3 \8230: \8230; I and h pi Wherein I =1, 2, 3 \8230, 8230, I three groups of data, P i I.e. the peak value of the applied load for the ith cycle, h ti I.e. the total penetration depth, h, of the ith period pi Namely the residual indentation depth of the ith period;
and 6, converting the corresponding load-displacement value into a true stress-true plastic strain data point through a formula:
6.1 in step 3 and step 5 λ has been obtained 2i 、h pi Value and P i Values according to the following formula:
the residual diameter d of the indentation in the ith loading and unloading period can be calculated pi The unit is: mm; in the above formula E 1 Elastic modulus of a spherical indenter, unit: mpa; e 2 Is the elastic modulus of the material to be tested, unit: mpa; d is the diameter of the spherical indenter in units: mm;
6.2 d has been calculated in step 6.1 pi By the following formula:
the true strain value epsilon of the ith loading and unloading period can be calculated pi D in the above formula is the diameter of the spherical pressure head;
6.3 the indentation residual diameter d for the ith load and unload cycle has been calculated in step 6.1 and step 6.2 pi And true strain value ε pi N sets of true stress-true strain sigma can be calculated and obtained by the following calculation procedure t —ε p A data point;
6.3.1 let i =0;
6.3.2 let i = i +1, calculate
Then checking
If the condition is satisfied, recording and storing sigma ti Then, step 6.3.5 is carried out, if the condition is not met, step 6.3.3 is carried out;
6.3.3 calculation
In the formula of alpha m Taking the value of the low strain rate sensitive material as 1 as a constraint factor index, and checking
If the condition is satisfied, recording and storing sigma ti Then, step 6.3.5 is carried out, if the condition is not met, step 6.3.4 is carried out;
6.3.4 calculation
In the formula alpha m The value of the constraint factor index is 1 for the sensitive material with low strain rate; e 2 The elastic modulus of the tested material is recorded and stored ti Then, a step 6.3.5 is carried out,
6.3.5 judging whether I = I is satisfied; if yes, performing step 6.4; if not, returning to the step 6.3.2;
6.4 in step 6.2N sets of true stress-true strain σ have been obtained t —ε p Data points, the indentor system plots the N data points on the abscissa as true plastic strain ε p The ordinate is the true stress sigma t In a cartesian coordinate system of (3), the true stress σ t Unit: mpa, and obtaining a true stress-true plastic strain curve measured by an indentation test through fitting;
and 7, converting the yield strength of the tested material:
7.1 already in step 3 and step 5, the i-th cycle λ is obtained 2i (I =1, 2, 3 \8230;. I), peak value P of applied load in the ith cycle i (I =1, 2, 3 \8230;. I) and total indentation depth h of the ith cycle ti (I =1, 2, 3 \8230;. I) by the formula:
d can be calculated ti (i＝1、2、3……I)，d ti (mm) is the total indentation diameter of the ith period;
7.2 treatment of P i (I =1, 2, 3 \ 8230; \8230; (I) and d ti (I =1, 2, 3 \8230; I) was transformed as follows to obtain I yield strength conversion data points:
(d ti /D；
)
in the above formula, beta m Is the yield coefficient of the material, B is the yield strength deviation parameter, in Mpa;
plot the I point at d ti The value/D is the abscissa of the bar,
in a Cartesian coordinate system of a vertical coordinate, a yield strength conversion curve can be obtained through fitting, and when d is ti The corresponding longitudinal coordinate value when/D =1 is the yield strength value alpha of the measured material y In Mpa;
and 8, estimating the tensile strength of the tested material:
8.1 in step 6, the true stress-true plastic strain curve of the material to be measured has been obtained by fitting, and the system is able to solve the equation of the power of this curve, in the form of y = Kx n So as to obtain a strength coefficient K and a strain hardening exponent n, the strength coefficient K unit: mpa;
8.2 substituting the strength coefficient K and the strain hardening index n value obtained in the step 8.1 into an engineering ultimate tensile strength value expression:
the ultimate tensile strength value sigma of the project can be calculated u The unit: mpa; sigma u The value is similar to the tensile strength value of the tested material, so the engineering ultimate tensile strength value sigma can be used u (Mpa) to estimate the tensile strength of the material under test;
step 9, controlling the indenter test head to ascend for a certain distance in the indenter control system so as to separate the indenter head from the tested material sample;
and step 10, loosening the clamp of the indentation instrument, adjusting the position of the tested material sample, then clamping and fixing again, repeating the steps 5 to 9, and starting to perform the next indentation test.
The invention has the beneficial effects that: the method utilizes the indenter to carry out automatic ball indentation test on the material to be tested, carries out whole-course mapping on each loading and unloading cycle in the test process, avoids the occurrence of theoretical ideal value, has error compensation link, and can accurately and directly measure the load-displacement data of the material to be tested, thereby further obtaining the true stress-true strain curve, the yield strength and the engineering ultimate tensile strength of the material to be tested.
Drawings
Fig. 1 is a schematic structural diagram of an indenter.
Fig. 2 is an enlarged view of the indenter test head mechanism.
FIG. 3 is a drawing showing the requirements of a sample of the metal Q345.
Fig. 4 is a schematic diagram of the load loading and unloading period of the indentation test.
Fig. 5 is a load-displacement graph of metal Q345 obtained by the indentation test.
Fig. 6 is an estimated curve of indentation parameters of the metal Q345 obtained by the indentation test.
Fig. 7 is a graph of the true stress-true plastic strain curve and engineering ultimate tensile strength estimate of the metal Q345 obtained by the indentation test.
In the figure: 1-an indentor portal frame; 2-force, displacement sensors; 3-an indentor test head; 4-a clamp body; 5-an indenter console; 6-an indentor base; 31-spherical indenter.
Detailed Description
Specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.
As shown in fig. 1-6, an experimental method for measuring mechanical properties of metals by using an indenter comprises the following specific operation steps:
step 2, detaching the spherical test head of the indenter, mounting the flat-bottom test head, and detaching the indenter clamp from the operating table;
step 3, before the Q345 indentation test, the mechanical error measurement of the indentation test is carried out:
3.1 setting the rate of indenter test head depression to V in the indenter control System 0 ，V 0 ＝3mm/min；
3.2 in the measurement process, continuous loading and unloading of the load are required to be carried out at the same position, and the process of one-time loading and complete unloading is one period, so that firstly, the number of loading and unloading periods I =8 is required to be set in the indenter control system, and the peak value of the applied load of the ith period is set as P i (N)(i＝1、2、3、4、5、6、7、8)，P 1 ＝100N、P 2 ＝200N、P 3 ＝300N、P 4 ＝400N、P 5 ＝500N、P 6 ＝600N、P 7 ＝700N、P 8 ＝800N；
3.3 control the beginning of mechanical error measurement in the indentation instrument control system, under the motor drive loading, the force and displacement sensor 2 according to the set pressing speed V 0 And =3mm/min is slowly pressed down, the force and displacement sensor 2 is directly pressed on the surface of the indenter console 5 due to the removal of the test head 3, and the sensor 2 cannot be pressed into the indenter console 5 due to the large contact area between the force and displacement sensor 2 and the indenter console 5. At the moment when the force and displacement sensor 2 contacts the indenter console 5, the value of the load applied by the indenter gradually increases from 0 to P 1 =100N, at which time the indentor system will record P 1 Sensor displacement value λ corresponding to 100N 11 In this embodiment λ 11 =0.000055mm. The indenter then starts the unloading of the force and the load will be from P 1 Slowly unload to 0N, at which time the indentor system will record the displacement value λ of the sensor 2 under a load of 0N 21 In this embodiment λ 21 =0.51 μm. After the first loading and unloading period is finished, the indentation tester continues to perform the second loading and unloading period, and the load value is slowed down from 0N againSlowly grow until it is loaded to the set P 2 =200N, at which time the indentor system will record P 2 Sensor 2 displacement value λ corresponding to 200N 12 In this embodiment λ 12 =0.61 μm, then the indenter starts the unloading of the force, the load will be from P 2 =200N is again slowly unloaded to 0N, at which point the indentor system will register a displacement value λ of the sensor 2 under a load of 0N 22 In this embodiment λ 22 And (3) 823000, wherein the load value gradually increases from 0N again until the load value is loaded to the set P when the load value is sequentially increased to the I (8) th loading and unloading period 8 =800N, at which time the indentor system will record P 8 Sensor 2 displacement value λ corresponding to =800N 18 In this embodiment λ 18 =4.1 μm. The indenter then starts the unloading of the force and the load will be from P 8 =800N, slowly unloaded again to 0N, at which time the indenter system will record the displacement value λ of the sensor 2 under a load of 0N 28 In this embodiment λ 28 =3.4 μm. Since the sensor 2 is not pressed into the indenter console 5, the displacement value recorded in the indenter system is the deformation of the entire mechanical structure of the indenter under the corresponding load. And the measurement is finished after the I (i.e. 8) th period is finished. At this time, lambda has been recorded in the indentor system 1i (i =1, 2, 3, 4, 5, 6, 7, 8) and λ 2i (i =1, 2, 3, 4, 5, 6, 7, 8) two sets of data, in this example, λ 11 ＝0.000055μm、λ 12 ＝0.61μm、λ 13 ＝0.69μm、λ 14 ＝0.79μm、λ 15 ＝0.94μm、λ 16 ＝1.6μm、λ 17 ＝2.7μm、λ 18 ＝4.1μm；λ 21 ＝0.51μm、λ 22 ＝0.56μm、λ 23 ＝0.63μm、λ 24 ＝0.72μm、λ 25 ＝0.86μm、λ 26 ＝1.2μm、λ 27 ＝2.3μm、λ 28 ＝3.4μm。
and 5, carrying out an indentation test on the Q345 sample:
5.1 the pressing speed is kept constant, and the pressing speed of the indenter test head 3 is still set to V in the indenter control system 0 ，V 0 ＝3mm/min；
5.2 continuous loading and unloading at the same point are required in the measurement process, as shown in fig. 4, the process of one loading and complete unloading is a period, the number of loading and unloading periods remains unchanged, I (I = 8) is still set, the peak value of the applied load in the ith period remains unchanged, and P is still set i (N)(i＝1、2、3、4、5、6、7、8)，P 1 ＝100N、P 2 ＝200N、P 3 ＝300N、P 4 ＝400N、P 5 ＝500N、P 6 ＝600N、P 7 ＝700N、P 8 ＝800N；
5.3 controlling the indentation test to start in the indentation instrument control system, and under the drive loading of the motor, the test head 3 controls the indentation test to start according to the set indentation speed V 0 And slowly pressing down by 3mm/min, and vertically pressing a spherical pressing head 31 at the tail end of the testing head 3 into the surface of the Q345 sample. At the moment when the spherical indenter 31 comes into contact with the Q345 sample, the indenter system starts to perform synchronous curve plotting in a cartesian coordinate system with the displacement value (mm) of the spherical indenter 31 as the abscissa and the load value (N) applied by the indenter as the ordinate. The value of the applied load is gradually increased from 0N until the set value P is loaded 1 When =100N, the indentor system will record P 1 Spherical indenter 31 displacement value h corresponding to 100N t1 In this embodiment, h t1 =0.01734mm, and the indentor then starts to unload the force, the load will be from P 1 =100N slow unload to 0N, at which time the indentor system will record the displacement value h of the spherical indenter 31 at 0N p1 In this embodiment, h p1 =0.01625mm. After the first loading and unloading period is finished, the indenter continues to perform the second loading and unloading period, and the load value gradually increases from 0N again until the preset P is loaded 2 =200N, indentation instrument system at this timeWill record P 2 Spherical indenter 31 displacement value h corresponding to 200N t2 In this embodiment, h t2 =0.03011mm. The indenter then starts the unloading of the force and the load will be from P 2 =200N is again slowly unloaded to 0N, at which point the indenter system will record the displacement value h of the spherical indenter 31 at 0 load p2 In this embodiment, h p2 =0.02634mm 8230that the load value gradually increases from 0N again until the set P is loaded 8 =800N, at which time the indentor system will record P 8 Spherical indenter displacement value h corresponding to 800N t8 In this embodiment, h t8 =0.13258mm, then the indenter starts the unloading of the force, the load will be from P 8 =800N is again slowly unloaded to 0N, at which point the indenter system will record the displacement value h of the spherical indenter 31 under a load of 0N p8 In this embodiment, h p8 =0.120812mm. And the measurement is finished after the 8 th period is finished. As shown in FIG. 5, a load-displacement curve of the indentation test process is generated in the indenter system, and P is recorded in the indenter system i (i＝1、2、3、4、5、6、7、8)、h ti (i =1, 2, 3, 4, 5, 6, 7, 8) and h pi (i =1, 2, 3, 4, 5, 6, 7, 8) three sets of data, P i I.e., the peak of the applied load for the ith cycle, P in this embodiment 1 ＝100N、P 2 ＝200N、P 3 ＝300N、P 4 ＝400N、P 5 ＝500N、P 6 ＝600N、P 7 ＝700N、P 8 ＝800N；h ti I.e. the total penetration depth of the ith cycle, in this example, h t1 ＝0.01734mm、h t2 ＝0.03011mm、h t3 ＝0.04667mm、h t4 ＝0.06321mm、h t5 ＝0.08001mm、h t6 ＝0.09592mm、h t7 ＝0.11321mm、h t8 ＝0.13258mm；h pi I.e. the residual indentation depth of the ith period, in this embodiment, h p1 ＝0.01625mm、h p2 ＝0.02634mm、h p3 ＝0.04435mm、h p4 ＝0.06023mm、h p5 ＝0.07382mm、h p6 ＝0.09156mm、h p7 ＝0.10867mm、h p8 ＝0.120812mm；
And 6, converting the corresponding load-displacement value into a true stress-true plastic strain data point through a formula:
6.1 in step 3 and step 5 λ has been obtained 2i 、h pi Value and P i Values according to the following formula:
the residual diameter d of the indentation in the ith loading and unloading period can be calculated pi (mm). In the above formula E 1 (Mpa) is the modulus of elasticity of the spherical indenter, E 1 ＝510000Mpa；E 2 (Mpa) is the modulus of elasticity of the material to be tested, E 2 =206000Mpa; d (mm) is the diameter of the spherical indenter, D =1mm. By substituting the values, d in this embodiment can be obtained p1 ＝0.25287mm，d p2 ＝0.32029mm，d p3 ＝0.41174mm，d p4 ＝0.47582mm，d p5 ＝0.52296mm，d p6 ＝0.57681mm，d p7 ＝0.62245mm，d p8 ＝0.65182mm。
6.2 in step 6.1 the indentation residual diameter d for the ith load and unload cycle has been calculated pi By the following formula:
the true strain value epsilon of the ith loading and unloading period can be calculated pi (i =1, 2, 3, 4, 5, 6, 7, 8) where D is the diameter of the spherical indenter and D =1mm, and pi substituting the values to obtain the true strain value of the ith load and unload cycle, in this embodiment, ε p1 ＝0.05162，ε p2 ＝0.07103，ε p3 ＝0.08712，ε p4 ＝0.10013，ε p5 ＝0.11012，ε p6 ＝0.12157，ε p7 ＝0.13312，ε p8 ＝0.14311。
6.3 the indentation residual diameter d for the ith load and unload cycle has been calculated in step 6.1 and step 6.2 pi And true strain value ε pi By the following calculation procedure:
6.3.1 let i =0;
6.3.2 let i = i +1, calculate
Then checking
If the condition is satisfied, recording and storing sigma ti Then, step 6.3.5 is carried out, if the condition is not met, step 6.3.3 is carried out;
6.3.3 calculation
In the formula alpha m Taking the value of the low strain rate sensitive material as 1 as a constraint factor index, and checking
If the condition is satisfied, recording and storing sigma ti Then, step 6.3.5 is carried out, if the condition is not met, step 6.3.4 is carried out;
6.3.4 calculation
In the formula alpha m The value of the constraint factor index for the low strain rate sensitive material is 1; e 2 The elastic modulus of the tested material is recorded and stored ti Then, a step 6.3.5 is carried out,
6.3.5 determining whether I = I is satisfied; if yes, performing step 6.4; if not, returning to the step 6.3.2;
the true stress value sigma of the ith loading and unloading period can be calculated ti (Mpa), in this example,. Sigma. t1 ＝645.91241Mpa，σ t2 ＝689.89564Mpa，σ t3 ＝702.67565Mpa，σ t4 ＝706.85345Mpa，σ t5 ＝710.01274Mpa，σ t6 ＝715.47847Mpa，σ t7 ＝719.02374Mpa，σ t8 ＝720.10637Mpa。
Thus 8 groups of sigma can be obtained ti —ε pi (true stress-true strain) data points, (0.05162, 645.91241), (0.07103, 689.89564), (0.08712, 702.67565), (0.10013, 706.85345), (0.11012, 710.01274), (0.12157, 715.47847), (0.13312, 719.02374), (0.14311, 720.10637)
6.3 at step 6.2 already 8 groups of σ have been obtained t —ε p (true stress-true strain) data points, as shown in FIG. 7, the indentor system plots these 8 data points on the abscissa for true plastic strain ε p The ordinate is the true stress sigma t In a Cartesian coordinate system of (Mpa), a true stress-true plastic strain curve measured by an indentation test can be obtained through fitting;
and 7, conversion of yield strength of Q345:
7.1 already in step 3 and step 5, the i-th cycle λ is obtained 2i (i =1, 2, 3, 4, 5, 6, 7, 8), peak value P of the i-th cycle applied load i (i =1, 2, 3, 4, 5, 6, 7, 8) and total indentation depth h for the ith cycle ti (i =1, 2, 3, 4, 5, 6, 7, 8) by the following formula:
d can be calculated ti (i＝1、2、3、4、5、6、7、8)，d ti (mm) is the total indentation diameter of the ith period. D =1mm, λ 2i Value and h ti Substituting the value to obtain d t1 ＝0.25343mm、d t2 ＝0.34823mm、d t3 ＝0.42112mm、d t4 ＝0.48341mm、d t5 ＝0.54572mm、d t6 ＝0.59019mm、d t7 ＝0.63087mm、d t8 ＝0.68831mm。
7.2 treatment of P i (i =1, 2, 3, 4, 5, 6, 7, 8) and d ti (i =1, 2, 3, 4, 5, 6, 7, 8) are transformed as follows to obtain 8 yield strength transformsData points are calculated:
(d ti /D；
)
in the above formula,. Beta. m For the yield coefficient of the material, B (Mpa) is the yield strength offset parameter, in this example, β m ＝0.22，B＝0。
These 8 points are plotted at d as shown in FIG. 6 ti The value/D is the abscissa of the bar,
in a Cartesian coordinate system of a vertical coordinate, a yield strength conversion curve can be obtained through fitting, and when d is ti The corresponding longitudinal coordinate value when/D =1 is the yield strength value alpha of the measured material y (Mpa), yield strength value alpha of Q345 sample in this example y ＝400.41Mpa。
Step 8, estimating the tensile strength of Q345:
8.1 in step 6, the true stress-true plastic strain curve of the material to be measured has been obtained by fitting, and the system is able to solve the equation of the power of this curve, in the form of y = Kx n Thereby obtaining the strength coefficient K (Mpa) and the strain hardening index n. As shown in fig. 7, the system can have solved the power relation equation for this curve, which is:
y＝883.17x 0.0997
as shown in fig. 7, the strength factor K =883,17mpa and the strain hardening index n =0.0997 were obtained
8.2 substituting the strength factor K =883,17mpa, the strain hardening index n =0.0997 and e =2.71828 obtained in step 8.1 into an engineering ultimate tensile strength value expression:
the ultimate tensile strength value sigma of the project can be calculated u (Mpa)。σ u The value of (Mpa) is similar to the tensile strength value of the material to be tested, thereforeUsing engineering ultimate tensile strength values sigma u (Mpa) to estimate the tensile strength of the material under test. As shown in FIG. 7, in this embodiment, σ u ＝635.2067213Mpa
Step 9, controlling the indenter test head 3 to ascend for a certain distance in the indenter control system to separate the indenter pressure head from the Q345 test sample;
and 10, loosening the indenter clamp 4, adjusting the position of the Q345 sample, then clamping and fixing again, repeating the steps 5 to 9, and starting to perform the next indentation test.
The above-mentioned embodiments are merely illustrative of the principles and effects of the present invention, and some embodiments may be used, not restrictive; it should be noted that, for those skilled in the art, various changes and modifications can be made without departing from the inventive concept of the present invention, and these changes and modifications belong to the protection scope of the present invention.
Claims (1)
1. An experimental method for measuring metal mechanical properties by using an indenter comprises the following steps:
step 1, after sampling of a blank is completed, grinding and polishing the surface of the blank to enable the blank to meet the requirements of the size and the surface roughness of a sample, and then completing preparation of a metal or alloy material sample;
step 2, detaching the spherical test head of the indenter, mounting the flat-bottom test head, and detaching the indenter clamp from the operating table;
step 3, measuring the mechanical error of the indentation test:
3.1 setting the rate at which the indenter test head is depressed to V in the indenter control system 0 ；
3.2 continuous loading and unloading are carried out at the same position in the measuring process, the process of one-time loading and complete unloading is a period, firstly, the number I, I of the loading and unloading periods is set in the indentation instrument control system>1 and setting the peak value of the applied load of the ith period as P i Wherein I =1, 2, 3 \ 8230i, unit: n;
3.3 control the start of mechanical error measurement in the indenter control system:
3.3.1 let i =1, first performing a first loading and unloading cycle; under the loading of motor drive, the flat-bottom test head presses the speed V according to the settlement 0 Gradually pressing down, wherein the flat bottom test head cannot be pressed into the operation table because the contact area of the flat bottom test head and the operation table of the indenter is large, and after the flat bottom test head is contacted with the operation table of the indenter, the load value applied by the indenter is gradually increased from 0 until the flat bottom test head is loaded to the set P 1 Value, at which point the indentor system records P 1 Corresponding sensor displacement value lambda under load 11 Then the indenter starts to unload the force, the load will be from P 1 Slowly unload to 0, at which time the indentor system will record the displacement value λ of the sensor under load of 0 21 ；
3.3.2 let i = i +1, the indenter will continue the ith loading and unloading cycle, and the loading value of the indenter gradually increases from 0 again until the set value P is loaded i Value, at which point the indentor system will record P i Corresponding sensor displacement value lambda under load 1i Then the indenter starts to unload the force, the load will be from P i Again slowly unload to 0, at which time the indentor system will record the displacement value λ of the sensor under load of 0 2i
3.3.3 if I < I, jumping back to step 3.3.2, and if I ≧ I, continuing to execute step 3.3.4 downwards;
3.3.4 at this time, the displacement value recorded in the indenter system is the deformation of the whole mechanical structure of the indenter under the corresponding load; after the I cycle is finished, the measurement is finished, and the lambda is recorded in the indentation instrument system 1i (I =1, 2, 3 \8230;. I) and λ 2i (I =1, 2, 3 \8230; I) two sets of data;
step 4, after the mechanical error measurement of the indentation test is completed, controlling a force sensor and a displacement sensor to rise in an indentation instrument system, dismantling a flat-bottom testing head, installing the indentation instrument testing head, installing a clamp on an indentation instrument operation table, and fixing the sample prepared in the step 1 through the clamp;
and 5, performing an indentation test on the metal or alloy sample:
5.1 pressing downThe speed is kept constant, and the pressing speed of the indenter test head is still set to V in the indenter control system 0 ；
5.2 the number of load/unload cycles remains unchanged and is still set to I (I)>1) The peak value of the applied load of the i-th period is also kept unchanged and is still set as P i Wherein I =1, 2, 3 \ 8230i, unit: n;
5.3, controlling the beginning of the indentation test in an indentation instrument control system;
5.3.1 let i =1, first the first loading and unloading cycle is performed: under the loading of motor drive, the test head presses down the speed V according to the settlement 0 Slowly pressing down, and vertically pressing a spherical pressure head at the tail end of the test head into the surface of the sample; when the spherical indenter contacts the metal sample, the indenter system begins to use the displacement value of the spherical indenter as the abscissa, and the displacement value unit: mm, the value of the load applied by the indenter as ordinate, the unit of the load value: n, drawing a synchronous curve in a Cartesian coordinate system; the value of the applied load is gradually increased from 0 until the set value P is loaded 1 Value, at which point the indentor system will record P 1 Corresponding displacement value h of spherical pressure head under load t1 The indenter then starts to unload the force, the load will be from P 1 Slowly unloading to 0, and recording the displacement value h of the spherical indenter under the load of 0 by the indenter system p1 ；
5.3.2 let i = i +1, the indenter will continue the ith loading and unloading cycle, and the loading value of the indenter gradually increases from 0 again until the set value P is loaded i Value, at which time the indentor system will record P i Corresponding displacement value h of spherical pressure head under load ti Then the indenter starts to unload the force, the load will be from P i Slowly unloading to 0 again, and recording the displacement value h of the spherical indenter under the load of 0 by the indenter system at the moment pi ；
5.3.3 if I < I, then jump back to step 5.3.2, if I ≧ I, then continue to execute step 5.3.4 downward;
5.3.4 at this point in the indenter system, a load-displacement graph of the indentation test procedure was generated and P was recorded i Therein is disclosedWherein I =1, 2, 3 \8230, 8230I, h ti Wherein I =1, 2, 3 \ 8230; \8230I and h pi Wherein I =1, 2, 3 \8230 \ 8230, three groups I of data, P i I.e. the peak value of the applied load for the ith cycle, h ti I.e. the total penetration depth, h, of the ith cycle pi Namely the residual indentation depth of the ith period;
and 6, converting the corresponding load-displacement value into a true stress-true plastic strain data point through a formula:
6.1 in step 3 and step 5 λ has been obtained 2i 、h pi Value and P i Values according to the following formula:
the residual diameter d of the indentation in the ith loading and unloading period can be calculated pi The unit: mm; in the above formula E 1 Is the elastic modulus of a spherical indenter, unit: mpa; e 2 Is the elastic modulus of the material to be tested, unit: mpa; d is the diameter of the spherical indenter, in units: mm;
6.2 d has been calculated in step 6.1 pi By the following formula:
the true strain value epsilon of the ith loading and unloading period can be calculated pi D in the above formula is the diameter of the spherical pressure head;
6.3 the indentation residual diameter d for the ith load and unload cycle has been calculated in step 6.1 and step 6.2 pi And true strain value ε pi N sets of true stress-true strain sigma can be calculated and obtained by the following calculation procedure t —ε p A data point;
6.3.1 let i =0;
6.3.2 let i = i +1, calculate
Then checking
If the condition is satisfied, recording and storing sigma ti Then, step 6.3.5 is carried out, if the condition is not met, step 6.3.3 is carried out;
6.3.3 calculation
In the formula of alpha m Taking the value of the low strain rate sensitive material as 1 for a constraint factor index, and checking
If the condition is satisfied, recording and storing sigma ti Then, step 6.3.5 is carried out, if the condition is not met, step 6.3.4 is carried out;
6.3.4 calculation
In the formula alpha m The value of the constraint factor index for the low strain rate sensitive material is 1; e 2 The elastic modulus of the tested material is recorded and stored ti Then, a step 6.3.5 is carried out,
6.3.5 judging whether I = I is satisfied; if yes, performing step 6.4; if not, returning to the step 6.3.2;
6.4 in step 6.2N sets of true stress-true strain σ have been obtained t —ε p Data points, the indentor system plots the N data points on the abscissa as true plastic strain ε p The ordinate is the true stress sigma t In a cartesian coordinate system of (3), the true stress σ t Unit: mpa, and obtaining a true stress-true plastic strain curve measured by an indentation test through fitting;
and 7, converting the yield strength of the tested material:
7.1 in step 3 and step 5 already the i-th cycle λ is obtained 2i (I =1, 2, 3 \8230;. I) and the peak value P of the I-th cycle applied load i (I =1, 2, 3 \8230;. I) and total indentation depth h of the ith cycle ti (I =1, 2, 3 \8230;. I) by the following formula:
d can be calculated ti (i＝1、2、3……I)，d ti (mm) is the total indentation diameter of the ith period;
7.2 treatment of P i (I =1, 2, 3 \8230;. I) and d ti (I =1, 2, 3 \8230;. I) was transformed as follows to obtain I yield strength conversion data points:
in the above formula, beta m Is the yield coefficient of the material, B is the yield strength deviation parameter, in Mpa;
plot the I point at d ti the/D is the abscissa, and the D is the abscissa,
in a Cartesian coordinate system of a vertical coordinate, a yield strength conversion curve can be obtained through fitting, and when d is ti The corresponding longitudinal coordinate value when/D =1 is the yield strength value alpha of the measured material y In Mpa;
step 8, estimating the tensile strength of the tested material:
8.1 in step 6, the true stress-true plastic strain curve of the material to be measured has been obtained by fitting, and the system is able to solve the equation of the power of this curve, in the form of y = Kx n So as to obtain a strength coefficient K and a strain hardening index n, the strength coefficient K unit: mpa;
8.2 substituting the strength coefficient K and the strain hardening index n value obtained in the step 8.1 into an engineering ultimate tensile strength value expression:
the ultimate tensile strength value sigma of the project can be calculated u The unit: mpa;
step 9, controlling the indenter test head to ascend for a certain distance in the indenter control system so as to separate the indenter head from the tested material sample;
and step 10, loosening the clamp of the indentation instrument, adjusting the position of the tested material sample, then clamping and fixing again, repeating the steps 5 to 9, and starting to perform the next indentation test.
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