CN101975555B - A strain measurement method and device based on light transmission measurement technology - Google Patents

Abstract

The present invention proposes a strain measurement method and device based on light transmission measurement technology, the method is characterized in that: two rigid guide pins parallel to each other are fixed on both sides of the sample test section, the rigid guide pins are perpendicular to the central axis of the stretching direction of the sample test section, the length of the rigid guide pins is greater than the width of the sample test section, and a light transmission digital micrometer is used to measure the initial distance between the two rigid guide pins, the real-time distance during the stretching process, and the final distance after the stretching is completed, and the real-time strain and final strain of the sample test section are calculated, wherein the measurement position of the micrometer is located on both sides of the sample test section, and the distance from the central axis of the stretching direction of the sample test section is equal. The present invention measures the distance change of the rigid guide pins during the stretching process through the light transmission measurement technology, and realizes the rapid and convenient measurement of the strain of small test area materials, flexible materials and large deformation conditions. It overcomes the defects of the existing measurement methods and better makes up for the blind spots of the application of several methods.

Description

A strain measurement method and device based on light transmission measurement technology

technical field

The invention belongs to a strain measurement method and a measurement device in the mechanical field, in particular to a strain measurement method and a device based on light transmission measurement technology.

Background technique

At present, the strain measurement methods in the mechanical field mainly include the resistance strain method, the use of mechanical electronic extensometers, and the use of laser holographic interferometry and so on. However, due to the influence of the area of the strain gauge itself, the resistance strain method is often not suitable for measuring samples with a small surface area, and the strain gauge itself has strength limitations. When large deformation measurements are required, the resistance strain method is often not suitable. Not applicable; while using a mechanical electronic extensometer, it needs to be clamped on the sample. It is not applicable if the measured surface is too small or too large, and the stiffness of the material to be measured must be large enough, otherwise the material will be affected by the strain generated by the extensometer. The strain of the material itself; the equipment in laser holographic interferometry technology is relatively expensive, and it is greatly disturbed by mechanical vibration, acoustic vibration (such as environmental noise) and ambient light during detection, etc., so it needs to be detected in a quiet and clean dark room , has high requirements on the environment. These methods are not suitable for fast and convenient measurement of strain in small test area materials, flexible materials and large deformation conditions.

Contents of the invention

technical problem to be solved

In order to solve the technical problem that existing methods are not suitable for fast and convenient measurement of strain in small test area materials, flexible materials and large deformation conditions, the present invention proposes a strain measurement method and device based on light transmission measurement technology.

Technical solutions

The described strain measurement method based on light transmission measurement technology is characterized in that: comprising the following steps:

Step 1. Fix two rigid guide pins parallel to each other on both sides of the sample test section, the rigid guide pins are perpendicular to the central axis of the tensile direction of the sample test section, and the length of the rigid guide pins is greater than the width of the sample test section;

Step 2. Measure the distance S _l and S _r between two rigid guide pins with a light-transmitting digital micrometer, and take the average distance S = (S _l + S _r )/2 of S _l and S _r as the sample test The initial length S of the segment, where the measurement positions of S _l and S _r are located on both sides of the sample test section, and the distance from the central axis of the sample test section in the tensile direction is equal;

Step 3, stretching the sample, using a light-transmitting digital micrometer to measure the distance S′ _l and S′ _r between the two rigid guide pins in real time, the measurement position is the same as that in step 2, and the distance between S′ _l and S The average distance S' of ' _r = (S' _l + S' _r )/2 is taken as the length S' of the sample test section, and the strain ε' of the sample test section is obtained in real time by the formula ε'=(SS')/S ;

Step 4. When the set tensile force is reached, stop stretching the sample, and use a light-transmitting digital micrometer to measure the distance S″ _t and S″ _r between the two rigid guide pins. The measurement position is the same as that measured in step 2. The position is the same, the average distance S″=(S″ _l + S″ _r )/2 between S″ _l and S″ _r is used as the final length S″ of the sample test section, and the formula ε″=(SS″)/ S obtains the final strain ε" of the test section of the sample.

A preferred method of the strain measurement method based on light transmission measurement technology in the present invention is characterized in that: when the sample material is a metal material, use soldering to fix the rigid guide pin; when the sample material is a non-metallic material , secure the rigid pins with adhesive.

The preferred method of the strain measurement method based on light transmission measurement technology in the present invention is characterized in that: the rigid guide pin is a cylindrical guide pin with uniform thickness, and the hardness reaches at least 45HRC.

A device for implementing a strain measurement method based on light transmission measurement technology described in the present invention is characterized in that it includes a metal test bench and a light transmission digital micrometer, and the metal test bench is fixed on the testing machine through a clamping hole at the bottom On the platform, there are two micrometer placement grooves on the upper part of the metal test bench. There is a symmetrical mark between the two micrometer placement grooves. There is a centering groove above the symmetrical mark. The centering groove coincides with the longitudinal central axis of the symmetrical mark; The type digital micrometer is placed in the micrometer placement groove, and it is close to the symmetry mark; when the sample with a rigid guide pin is installed on the testing machine, the sample is centered through the centering groove.

Beneficial effect

The invention measures the distance change of the rigid guide pin in the stretching process through the light transmission measurement technology, and realizes the rapid and convenient measurement of the strain and stress of materials with a small test area and large deformation conditions. It overcomes the defects of the existing measurement methods and better makes up for the blind spots in the application of several methods.

Description of drawings

Fig. 1: structural representation of the present invention;

Figure 2: Schematic diagram of the structure of the metal test bench;

Figure 3: Schematic diagram of the testing machine platform;

Figure 4: Schematic diagram of light transmission digital micrometer measurement;

Figure 5: Schematic diagram of a dog-bone-shaped specimen;

Among them: 1. Metal test bench; 2. Light-transmitting digital micrometer; 3. Sample; 4. Rigid guide pin; 5. Testing machine platform; 6. Micrometer placement groove; 7. Symmetrical mark; 8. Centering groove; 9. Relief hole; 10. Clamping hole; 11. Testing machine platform base; 12. Testing machine platform installation protrusion; micrometer receiver.

Detailed ways

The present invention is specifically described below in conjunction with embodiment:

With reference to accompanying drawing 1, accompanying drawing 2 and accompanying drawing 3, the strain measuring device based on light transmission measurement technology of the present invention comprises metal test stand 1 and light-transmitting digital micrometer 2, and metal test stand 1 passes through the stuck hole at the bottom 10 is fixed on the platform 5 of the testing machine; there are two micrometer placement grooves 6 on the upper part of the metal test bench 1, a symmetrical mark 7 is located between the two micrometer placement grooves 6, and a centering groove 8 is arranged above the symmetrical mark 7. The middle groove 8 coincides with the longitudinal central axis of the symmetry mark 7; the light-transmitting digital micrometer 2 is placed in the micrometer placement groove 6, and is closely attached to the symmetry mark 7, and the light-transmitting digital micrometer 2 The micrometer 2 is fixed to the metal test bench 1; the sample 3 with the rigid guide pin 4 is installed on the testing machine, and the central axis of the sample test section is aligned with the centering groove 8 to ensure that the two light-transmitting digital micrometers The distance between the measuring position of gauge 2 and the central axis of the sample test section is equal.

In the present embodiment, the above-mentioned strain measuring device is used to measure the strain of the rectangular pure copper sample and the dog-bone-shaped pure copper sample (the shape diagram of the dog-bone-shaped sample is provided in the accompanying drawing 5). The type of digital micrometer 2 is LS-7010 produced by KEYENCE Company, the size of the rectangular pure copper sample is 16×1×9 (mm), and the size of the middle test section of the dog-bone pure copper sample is 6×1×6 (mm).

First, fix two parallel rigid guide pins 4 on both sides of the test section of the rectangular pure copper sample and the dog-bone-shaped pure copper sample by soldering method, the rigid guide pins and the central axis of the tensile direction of the test section of the sample Vertical, and the length of the rigid guide pin 4 is greater than the width of the sample test section; the rigid guide pin 4 used is a cylindrical guide pin with uniform thickness, and the hardness reaches 45HRC.

Secondly, the pattern 3 fixed with the rigid guide pin 4 is installed on the testing machine, and the central axis of the sample test section is aligned with the centering groove 8, so as to ensure that the measurement position of the two light-transmitting digital micrometers 2 is far from the test sample. The distance from the central axis of the segment is equal. Measure the distances S _t and S _r between the two rigid guide pins with a light-transmitting digital micrometer 2, S _l is the distance measured at the left side of the sample test section, and S _r is the distance measured at the right side of the sample test section For the distance measured at the position, take the average distance S=(S _l +S _r )/2 between S _l and S _r as the initial length S of the test section of the sample.

Next, start the testing machine, stretch the sample, and measure the distance S′ _l and S′ _r between the two rigid guide pins 4 in real time by using the light-transmitting digital micrometer 2, and take the average of S′ _l and S′ _r The distance S' = (S' _l + S' _r )/2 is taken as the length S' of the sample test section, and the strain ε' of the sample test section is obtained in real time by the formula ε'=(SS')/S. The stress-strain curve is drawn by combining the sample strain value obtained in real time with the stress value provided by the stretching machine.

Finally, when the testing machine reaches the set tensile force, the tensile sample is stopped, and the distances S″ _l and S″ _r between the two rigid guide pins 4 are measured by using the light-transmitting digital micrometer 2, with S″ The average distance between _l and S″ _r S″=(S″ _l +S″ _r )/2 is used as the final length S″ of the sample test section, and the sample test section is obtained by the formula ε″=(SS″)/S The final strain ε″.

Wherein, when obtaining the initial length S of the sample test section and the final length S" of the sample test section, the following processing method is adopted: under static force, use the light-transmitting digital micrometer 2 at 2400 times/second Collect data frequently, and collect data continuously for 10 seconds, so as to obtain enough data. Taking the measurement of S _l as an example, assuming that 24,000 data of S _l are obtained in 10 seconds of collection, they are χ ₁ ~χ ₂₄₀₀₀ , and the average value obtained is:

$\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; \&chi;</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 24000</span>}}\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; 24000</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; \&chi;</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}$

The standard deviation is:

$\mathrm{<span\; class="notranslate">\; \&sigma;</span>}<span\; class="notranslate">\; =</span>\sqrt{\frac{\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; 24000</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&chi;</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; -</span>\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; \&chi;</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 23999</span>}}}$

之外的值，用剩余数据再求一次得到均值

取

其余S_r、S″_l和S″_r以同样方法得到。Use the Raida criterion to eliminate gross errors, that is, exclude the

For values other than , use the remaining data to find the mean again

Pick

The rest of S _r , S″ _l and S″ _r are obtained in the same way.

The comparison results between the strain measurement results of this method and the resistance strain method, the overall strain measured by the stretching machine and the theoretical calculation value are given below under the tensile force of 700N and 1400N. Among them, since the strain gauge is broken under the tensile force of 1400N, there is no result of the resistance strain method under this condition, and there is no theoretical model when it enters the plastic deformation stage under the tensile force of 1400N. In addition, the global strain measured by the tensile machine is mainly used for comparison of the rectangular specimens, because the global strain should be the same as the local strain for the rectangular specimens, which is not the case for the dog-bone specimens. In addition, in the theoretical calculation, due to the irregular shape of the dog-bone pattern, the theoretical value cannot be calculated.

It can be seen from the results in the table that for small test areas and large deformation samples, the traditional resistance strain method not only has limitations in the measurement range, but also has large errors in the measurement results within the tolerance range; The results obtained by the strain are relatively close to the theoretical value and the overall strain measured by the stretching machine, and the measurement range is large, which can be used in practice.

Claims (4)

1. strain measurement method based on the light transmission measuring technique is characterized in that: may further comprise the steps:

Step 1, fixing two rigidity that are parallel to each other are drawn pin in specimen test section both sides, and it is vertical with the central axis of specimen test section draw direction that rigidity is drawn pin, and rigidity is drawn the width of pin length greater than the specimen test section;

Step 2, adopt light pass through the formula digital micrometer measure two rigidity draw between pin apart from S _lAnd S _r, S _lBe the distance that measure measuring position, specimen test section left side, S _rThe distance of measuring for measuring position, specimen test section right side is with S _lAnd S _rMean distance S=(S _l+ S _r)/2 are as the initial length S of specimen test section, wherein S _lAnd S _rThe measuring position be positioned at specimen test section both sides, and equate with the distance of specimen test section draw direction central axis;

Step 3, tensile sample, adopt light pass through the formula digital micrometer measure in real time two rigidity draw between pin apart from S ' _lAnd S ' _r, the measuring position is identical in measuring position and the step 2, with S ' _lAnd S ' _rMean distance S '=(S ' _l+ S ' _r)/2 are as the length S ' of specimen test section, through formula ε '=(S-S ')/S obtain in real time the strain stress of specimen test section ';

Step 4, when reaching the tensile force of setting, stop tensile sample, adopt light pass through the formula digital micrometer measure two rigidity draw between pin apart from S " _lAnd S " _r, the measuring position is identical in measuring position and the step 2, with S " _lAnd S " _rMean distance S "=(S " _l+ S " _r)/2 are as the final lengths S of specimen test section ", and through formula ε "=(S-S ")/S obtain the final strain stress of specimen test section ".

2. a kind of strain measurement method based on the light transmission measuring technique according to claim 1 is characterized in that:

When sample material was metal material, pin was drawn in use soldering fixedly rigidity; When sample material was nonmetallic materials, use viscose glue fixedly rigidity drew pin.

3. a kind of strain measurement method based on the light transmission measuring technique according to claim 1 is characterized in that: it is that the cylinder of even thickness draws pin that rigidity is drawn pin, and hardness reaches 45HRC at least.

4. device of realizing the said strain measurement method based on the light transmission measuring technique of claim 1; It is characterized in that: comprise that metallographictest platform and two light pass through the formula digital micrometer; The metallographictest platform is fixed on the testing machine platform through the hole clipping of bottom, and two micrometer mounting grooves are arranged at metallographictest platform top, is symmetrical mark between two micrometer mounting grooves; There is the centering groove symmetry mark top, and the centering groove overlaps with symmetrical mark longitudinal center axis; Light passes through the formula digital micrometer and is placed in the micrometer mounting groove, and is close on the symmetrical mark; When having rigidity and draw the sample of pin and be installed on the testing machine, through the centering groove with sample centering.

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