CN113295526B - Method for correcting displacement of testing machine by using resistance strain data - Google Patents
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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
- G01N3/08—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
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- 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
- G01N2203/0003—Steady
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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
- G01N2203/0058—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
- G01N2203/02—Details not specific for a particular testing method
- G01N2203/06—Indicating or recording means; Sensing means
- G01N2203/0617—Electrical or magnetic indicating, recording or sensing 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
- G01N2203/02—Details not specific for a particular testing method
- G01N2203/06—Indicating or recording means; Sensing means
- G01N2203/067—Parameter measured for estimating the property
- G01N2203/0676—Force, weight, load, energy, speed or acceleration
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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
- G01N2203/06—Indicating or recording means; Sensing means
- G01N2203/067—Parameter measured for estimating the property
- G01N2203/0682—Spatial dimension, e.g. length, area, angle
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Abstract
A method for correcting displacement of a testing machine by using resistance strain data comprises the following steps: step 1, processing a rock sample or a coal sample into a standard sample, sticking a strain gauge in the middle of the surface of the sample to measure the axial strain of the sample, performing a uniaxial compression test by a material testing machine, and importing experimental data into a computer after the test is finished; step 2, correcting axial strain data; step 3, correcting a displacement curve of the testing machine; and 4, step 4: and drawing a full stress-strain curve of the test piece. The invention adopts the resistance strain data to correct the displacement data of the testing machine, removes the influence of the deformation of the steel member and the deformation of the hydraulic rod, obtains more real displacement of the material testing machine, namely the deformation of the test piece, and provides guarantee for further researching the deformation and destruction characteristics of the test piece.
Description
Technical Field
The invention belongs to the technical field of rock mechanics, and particularly relates to a method for correcting displacement of a testing machine by using resistance strain data.
Background
At present, in the field of mechanics, in order to obtain accurate physical and mechanical characteristic information of a certain material, an electro-hydraulic servo testing machine is generally adopted to perform three physical and mechanical tests of compression resistance, tensile resistance and shear resistance, and relevant physical quantities are measured.
The measurement of part of physical quantities, such as material rigidity, impact energy index in impact tendency identification, elastic energy index and the like, requires accurate and real displacement data of the pressed test piece. For obtaining the displacement data of the test piece under pressure, three methods of measuring by using a displacement sensor data, a resistance strain data conversion and an extensometer of a material testing machine are generally adopted. The three data acquisition methods have certain disadvantages.
Data of a displacement sensor of a partial electro-hydraulic servo testing machine on the market are insufficient, the sensor for monitoring displacement change is arranged near an oil cylinder component of the testing machine, the overall displacement change condition of a test piece is determined by monitoring the ascending or descending displacement of the oil cylinder, the overall steel frame of the testing machine equipment can be pressed along with the test piece to generate certain deformation, and the deformation of the part can be monitored and recorded by the displacement sensor. Therefore, the measured displacement data not only include the displacement of the loaded compression of the test piece, but also include the displacement of the hydraulic column and the deformation of the steel frame of the testing machine, so that the data is larger than the actual data, and an error exists.
The specification of the resistance strain gauge used in the laboratory is 120 omega-20 AA or 15AA, namely the resistance value is 120 omega, the grid size is 3mm multiplied by 20mm or 3mm multiplied by 15mm, GB/T23561.8-2009. During the experiment, the test piece needs to be stuck on the surface of the test piece, and data acquisition is carried out through the collector. A large number of experiments show that the resistance strain gauge can be suddenly increased or reduced at local points in the experiment, the record data of the strain gauge are still continuous after the points are suddenly changed, which indicates that the strain gauge is not damaged, but the points have great influence on the drawing of data processing images, and in addition, at the end stage of the experiment, namely after the test piece reaches the peak value, the phenomena of sudden damage, local separation of the strain gauge, even integral falling failure and the like can occur. These phenomena are represented on the strain (displacement) -time curve as discontinuous jump points, which also results in the fact that the resistance strain gauge is not practical for measuring the strain and displacement after the test piece peak.
Extensometers used in laboratories generally employ springs to fix the surface of a test piece for measuring axial and radial displacements of the test piece during loading. However, the accuracy of the data measured by the extensometer is uncertain because the sudden damage of the test piece often causes damage to the extensometer, and partial damage is irreversible.
Disclosure of Invention
On the basis of researching the loading rules of a test piece and a material testing machine, the invention aims to provide a method for correcting the displacement of the testing machine by using resistance strain data, and also provides a method for obtaining the real displacement of the test piece under pressure. The resistance strain data of the general measurement material strain in a laboratory is converted into displacement data through the relation between the strain and the displacement in material mechanics, and the data is taken as a measurement standard to correct the actually measured displacement data of the testing machine.
In order to achieve the purpose, the invention adopts the following technical scheme:
a method for correcting displacement of a testing machine by using resistance strain data comprises the following steps:
step 1, processing a rock sample or a coal sample into a standard sample, sticking a strain gauge in the middle of the surface of the sample to measure the axial strain of the sample, performing a uniaxial compression test by a material testing machine, and importing experimental data into a computer after the test is finished;
step 2, correcting axial strain data:
step 2.1, converting axial strain data into deformation data according to the length of a micro deformation/test piece in the mechanics of materials, and naming the data as axial strain deformation;
step 2.2, drawing a time-axial strain deformation curve; observing the curve, and correspondingly correcting, specifically: deleting sudden increase points or sudden decrease points; the curve segment which is still continuous after the deleted sudden increase point or sudden decrease point is adjusted downwards or upwards, is connected with the curve segment before the deleted sudden increase point or sudden decrease point to form a smooth curve, and is named as an axial strain deformation correction curve;
step 3, correcting the displacement curve of the testing machine:
step 3.1, drawing a test machine displacement-test force curve, and determining four stage points on the curve, namely an original point O, a straight-line segment starting point A, a test force maximum peak point B and a test end point C; selecting a straight line section on the curve, and performing linear fitting to find a first intersection point of the straight line section and the curve, namely a point A; the four stage points divide the curve into three sections, namely an OA section, an AB section and a BC section; finding time, test force, tester displacement and axial strain deformation correction value data corresponding to the point A and the point B in the updated original data after the axial strain data are corrected in the step 2; dividing the tester displacement data corresponding to the point A by the axial strain deformation correction value to obtain a numerical value, namely a multiple of the point A; dividing the tester displacement data corresponding to the point B by the axial strain deformation correction value to obtain a numerical value, namely a multiple of the point B;
step 3.2, correcting the displacement of the testing machine in a segmented manner:
step 3.2.1, section OA: dividing the displacement data of the testing machine in the interval by the multiple of the point A to obtain the corrected value of the displacement data of each point in the OB section;
step 3.2.2, AB: the corresponding displacement multiples of the point A and the point B are respectively used as the starting points a of the arithmetic progression0And end point anThe number of the displacement data in the period is the number n of terms of the arithmetic number sequence, and the tolerance d of the number sequence is calculated; calculating each equal differential term, and finally dividing the displacement data of the testing machine by the corresponding equal differential term to obtain the corrected value of each point of displacement data in the AB section;
step 3.2.3, segment BC: dividing the displacement data of the testing machine in the interval by the multiple of the point B to obtain the corrected value of the displacement data of each point behind the point B;
step 3.2.4, summarizing data of the OA section, the AB section and the BC section, and drawing a complete modified displacement curve of the testing machine;
and 4, step 4: drawing a full stress-strain curve of the test piece:
step 4.1, converting the corrected displacement data of the testing machine into strain data according to the strain in the mechanics of materials, namely the length of a micro deformation/test piece; according to the formula of stress calculation
Converting the test force data into stress data; wherein Rc is the stress of the test piece under uniaxial loading, and the unit is MPa; p is the test force of the test piece under uniaxial loading, and the unit is kN; f is the initial bearing area of the test piece in cm2；
And 4.2, drawing a tester-displacement and full stress-strain curve.
The segment correction method needs to be divided according to a specific test; the curves reflected by the test pieces made of different materials are not related to each other, and the correction is carried out according to specific conditions.
The beneficial technical effects of the invention are as follows:
the invention adopts the resistance strain data to correct the displacement data of the testing machine, removes the influence of the deformation of the steel member and the deformation of the hydraulic rod, obtains more real displacement of the material testing machine, namely the deformation of the test piece, and provides guarantee for further researching the deformation and destruction characteristics of the test piece.
Drawings
FIG. 1 is a schematic view of the axial strain deformation correction of the present invention;
FIG. 2 is a schematic diagram of the displacement-test force curve of the testing machine of the present invention;
FIG. 3 is a schematic diagram of the displacement sectional correction OA section of the testing machine of the present invention;
FIG. 4 is a schematic diagram of the displacement sectional correction AB section of the testing machine of the present invention;
FIG. 5 is a schematic view of the displacement sectional correction BC of the testing machine of the present invention;
FIG. 6 is a schematic view of the displacement correction of the testing machine according to the present invention;
FIG. 7 is a graph of tester displacement versus test force before and after correction according to the present invention;
fig. 8 is a modified stress-strain curve of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and examples.
As shown in fig. 1 to 8, a method for correcting tester displacement by using resistance strain data includes the following steps:
step 1, processing a coal sample into a standard test piece, wherein the real size of the coal test piece used in the test is as follows: 49.88mm in diameter, 99.73mm in height and 1954mm in cross-sectional area2The sampling frequency of a testing machine is 10Hz, a strain gage is pasted on the middle part of the surface of a test piece to measure the axial strain of the test piece, a uniaxial compression test is carried out through a material testing machine, and after the test is finished, experimental data, namely time, testing force, testing machine displacement and axial strain data in the loading process are led into Excel of a computer, the peak load is 44.72kN, the compressive strength is 22.88MPa, and the elastic modulus is 2110 MPa;
step 2, correcting axial strain data:
step 2.1, converting axial strain data into deformation data according to the length of a micro deformation/test piece in the mechanics of materials, and naming the data as axial strain deformation;
step 2.2, drawing a time-axial strain deformation curve; observing the curve, and correspondingly correcting, specifically: deleting sudden increase points or sudden decrease points; descending or ascending the curve segment which is still continuous after the deleted sudden increase point or sudden decrease point, connecting the curve segment with the curve segment before the deleted sudden increase point or sudden decrease point to form a smooth curve, and naming the smooth curve as an axial strain deformation correction curve, as shown in figure 1;
step 3, correcting the displacement curve of the testing machine:
step 3.1, drawing a curve of the displacement of the testing machine and the testing force, determining four stage points on the curve as shown in fig. 2, wherein the four stage points are an original point O, a straight-line segment starting point A, a testing force maximum peak point B and a testing end point C respectively; selecting a straight line section on the curve, and performing linear fitting to find a first intersection point of the straight line section and the curve, namely a point A; the four stage points divide the curve into three sections, namely an OA section, an AB section and a BC section; finding time, test force, tester displacement and axial strain deformation correction value data corresponding to the point A and the point B in the updated original data table after the axial strain data are corrected in the step 2; dividing the tester displacement data corresponding to the point A by the axial strain deformation correction value to obtain a numerical value, namely a multiple of the point A; dividing the tester displacement data corresponding to the point B by the axial strain deformation correction value to obtain a numerical value, namely a multiple of the point B;
step 3.2, correcting the displacement of the testing machine in a segmented manner:
step 3.2.1, section OA: dividing the displacement data of the testing machine in the interval by the multiple of the point A to obtain the corrected value of the displacement data of each point in the OB section, as shown in FIG. 3;
step 3.2.2, AB: the corresponding displacement multiples of the point A and the point B are respectively used as the starting points a of the arithmetic progression0And end point anThe number of the displacement data in the period is the number n of terms of the arithmetic number sequence, and the tolerance d of the number sequence is calculated; calculating each equal differential term, and finally dividing the corresponding equal differential term by the displacement data of the testing machine to obtain each point in the AB sectionThe correction values of the displacement data, as shown in fig. 4;
step 3.2.3, segment BC: dividing the displacement data of the testing machine in the interval by the multiple of the point B to obtain the corrected value of the displacement data of each point behind the point B, as shown in FIG. 5;
step 3.2.4, summarizing data of the OA section, the AB section and the BC section, and drawing a complete modified displacement curve of the testing machine, as shown in FIG. 6;
and 4, step 4: drawing a full stress-strain curve of the test piece:
step 4.1, converting the corrected displacement data of the testing machine into strain data according to the strain in the mechanics of materials, namely the length of a micro deformation/test piece; according to the formula of stress calculation
Converting the test force data into stress data; wherein Rc is the stress of the test piece under uniaxial loading, and the unit is MPa; p is the test force of the test piece under uniaxial loading, and the unit is kN; f is the initial bearing area of the test piece in cm2；
Step 4.2: tester-displacement and full stress-strain curves were plotted as shown in fig. 7 and 8.
Claims (1)
1. A method for correcting displacement of a testing machine by using resistance strain data comprises the following steps:
step 1, processing a rock sample or a coal sample into a standard sample, sticking a strain gauge in the middle of the surface of the sample to measure the axial strain of the sample, performing a uniaxial compression test by a material testing machine, and importing experimental data into a computer after the test is finished;
step 2, correcting axial strain data:
step 2.1, converting axial strain data into deformation data according to the length of a micro deformation/test piece in the mechanics of materials, and naming the data as axial strain deformation;
step 2.2, drawing a time-axial strain deformation curve; observing the curve, and correspondingly correcting, specifically: deleting sudden increase points or sudden decrease points; the curve segment which is still continuous after the deleted sudden increase point or sudden decrease point is adjusted downwards or upwards, is connected with the curve segment before the deleted sudden increase point or sudden decrease point to form a smooth curve, and is named as an axial strain deformation correction curve;
step 3, correcting the displacement curve of the testing machine:
step 3.1, drawing a test machine displacement-test force curve, and determining four stage points on the curve, namely an original point O, a straight-line segment starting point A, a test force maximum peak point B and a test end point C; selecting a straight line section on the curve, and performing linear fitting to find a first intersection point of the straight line section and the curve, namely a point A; the four stage points divide the curve into three sections, namely an OA section, an AB section and a BC section; finding time, test force, tester displacement and axial strain deformation correction value data corresponding to the point A and the point B in the updated original data after the axial strain data are corrected in the step 2; dividing the tester displacement data corresponding to the point A by the axial strain deformation correction value to obtain a numerical value, namely a multiple of the point A; dividing the tester displacement data corresponding to the point B by the axial strain deformation correction value to obtain a numerical value, namely a multiple of the point B;
step 3.2, correcting the displacement of the testing machine in a segmented manner:
step 3.2.1, section OA: dividing the displacement data of the testing machine in the interval by the multiple of the point A to obtain the corrected value of the displacement data of each point in the OB section;
step 3.2.2, AB: the corresponding displacement multiples of the point A and the point B are respectively used as the starting points a of the arithmetic progression0And end point anThe number of the displacement data in the period is the number n of terms of the arithmetic number sequence, and the tolerance d of the number sequence is calculated; calculating each equal differential term, and finally dividing the displacement data of the testing machine by the corresponding equal differential term to obtain the corrected value of each point of displacement data in the AB section;
step 3.2.3, segment BC: dividing the displacement data of the testing machine in the interval by the multiple of the point B to obtain the corrected value of the displacement data of each point behind the point B;
step 3.2.4, summarizing data of the OA section, the AB section and the BC section, and drawing a complete modified displacement curve of the testing machine;
and 4, step 4: drawing a full stress-strain curve of the test piece:
step 4.1, rootingAccording to the strain in the mechanics of materials, converting the corrected displacement data of the testing machine into strain data as micro deformation/length of the test piece; according to the formula of stress calculation
Converting the test force data into stress data; wherein Rc is the stress of the test piece under uniaxial loading, and the unit is MPa; p is the test force of the test piece under uniaxial loading, and the unit is kN; f is the initial bearing area of the test piece in cm2；
And 4.2, drawing a full stress-strain curve of the test piece.
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