阅读说明：本技术 一种轴向疲劳试验机同轴度光学检测方法 (Optical detection method for coaxiality of axial fatigue testing machine ) 是由 李柏君 陈海龙 王军 金光宇 张康 于 2021-08-11 设计创作，主要内容包括：本发明公开了一种轴向疲劳试验机同轴度光学检测方法,在同轴度测试试样的平行段待测量区域喷涂油漆散斑,用光学应变测试系统拍摄并对比分析试样装载后的试样表面散斑照片,计算出试样加载前后试样表面垂直于参考零线的截线上的点的弹性变形；获得不同角度的拍摄照片；采用控制器分析前后照片的散斑变化,生成试验表面的应变分布,设置垂直于同轴度试样中轴线的参考零线,将测试所得照片按照参考零线设置应变值等于零,通过测量垂直于参考零线的截线上的点的主应变,获得试样测量区域内的主应变分布,观测不同角度截线上的点的主应变值计算同轴度；本发明采用油漆散斑作为应变参考点,测量过程操作简单,经济实用,避免了操作人员人为误差。(The invention discloses an optical detection method for coaxiality of an axial fatigue testing machine, which comprises the steps of spraying paint speckles in an area to be measured in a parallel section of a coaxiality test sample, shooting and comparing and analyzing a sample surface speckle picture after the sample is loaded by using an optical strain test system, and calculating elastic deformation of points on a section line of the sample surface perpendicular to a reference zero line before and after the sample is loaded; obtaining shot pictures at different angles; analyzing speckle changes of the front and rear photos by adopting a controller to generate strain distribution of a test surface, setting a reference zero line perpendicular to a central axis of a coaxiality sample, setting a strain value of the photo obtained by testing to be equal to zero according to the reference zero line, obtaining main strain distribution in a sample measurement area by measuring main strain of points on transversal lines perpendicular to the reference zero line, and observing main strain values of points on transversal lines with different angles to calculate coaxiality; the invention adopts the paint speckles as the strain reference points, has simple operation in the measuring process, is economical and practical, and avoids the human error of operators.)

1. An optical detection method for coaxiality of an axial fatigue testing machine is characterized by comprising the following steps:

1) spraying paint speckles in an area to be measured of a parallel section of a test sample;

2) after the paint speckles are dried, drawing a reference zero line vertical to the axis of the test sample on the upper part of a measurement area of the parallel section of the test sample by using a black marker pen;

3) clamping a test sample on a chuck of an axial fatigue testing machine, applying a tensile force of 1% of the maximum testing force of the testing machine as a preload, shooting a parallel section to-be-measured area of the test sample by using a dual-camera strain measurement system, applying the testing force to 4% of the maximum testing force of the testing machine by using a surface speckle picture as an initial reference picture for measuring and analyzing strain, and shooting a surface speckle picture of the test sample after the test sample is loaded;

4) translating the dual-camera strain measurement system around the testing machine, and collecting 8 photos before and after loading by the controller at 4 positions with the relative angles of 0 degrees, 90 degrees, 180 degrees and 270 degrees on the surface of the test sample;

5) analyzing speckle changes of the photos before and after loading, generating strain distribution on the surface of the test sample, and obtaining main strain of points on a transversal line perpendicular to the reference zero line;

6) because the loading process is in the elastic deformation range of the test sample, according to Hooke's law, the distance from the point on the transversal to the reference zero line is set to be L, and the distance from the point on the transversal to the reference zero line after loading is set to be L', and the distance is calculated according to a formula:

acquiring main strain of points on different section lines;

7) the main strain of the point on the section line corresponds to epsilon at 4 positions of 0 degrees, 180 degrees, 90 degrees and 270 degrees on the surface of the test sample₁、ε₂、ε₃、ε₄And calculating the coaxiality of the section strain according to a formula:

8) and obtaining the coaxiality of any point on the section line from the reference zero line L.

2. The optical detection method for the coaxiality of the axial fatigue testing machine according to claim 1, wherein the paint speckles sprayed in the step 1) are uniformly sprayed on the surfaces of the parallel sections of the test sample by using white matte paint, after the paint is dried in the air, the black matte paint is used for forming mist random black points to cover the surface of the test sample, and the black matte paint needs to be sufficiently atomized and uniformly distributed on the surface of the white paint.

3. The optical detection method for the coaxiality of the axial fatigue testing machine according to claim 1, wherein the line width bit of the reference zero line in the step 2) is 0.05 mm.

4. The optical detection method for the coaxiality of the axial fatigue testing machine according to claim 1, wherein 4% of the maximum testing force of the applied testing machine in the step 3) is required to meet the requirement that the maximum testing force used in the test should not cause plastic deformation of the test sample.

5. The optical detection method for the coaxiality of the axial fatigue testing machine according to claim 1, wherein when the double-camera strain measurement system in the step 4) shoots, the coaxiality test sample is ensured to be positioned in the depth of field measured by the double-camera strain measurement system.

Technical Field

The invention relates to the technical field of sample detection, in particular to an optical detection method for coaxiality of an axial fatigue testing machine.

Background

When the axial fatigue testing machine is used for detection, the coaxiality needs to be detected, a coaxiality tester adhered with a resistance strain gauge is used for detection at present, and a coaxiality calibration sample and a detected sample have similar geometric shapes. The coaxiality calibration sample is made of strengthened heat treatment steel or a material with the elasticity limit higher than 4% of the maximum test force of the tester.

The current detection method is to attach 3 groups of resistance strain gauges to a coaxiality calibration sample, collect 4 strain values with relative angles of 0 degrees, 90 degrees, 180 degrees and 270 degrees in one plane perpendicular to an axis on the surface of the sample, calculate the bending of two perpendicular directions of each plane and calculate the coaxiality of the bending plane, wherein 1 group of 4 strain gauges is used.

In the mode, in the actual test process, the measurement precision can be influenced due to the fact that the sticking positions of the resistance strain gauges are not uniformly distributed and the angles are unreasonable, and meanwhile, the mode is used for indirectly measuring the strain on the surfaces of the coaxiality calibration samples by measuring the electric signal change of the resistance strain gauges and can be influenced by null shift, temperature shift and the like. The resistance strain gauge is adhered to a tested piece by using an adhesive, the adhesive layer formed by the adhesive must accurately and rapidly transfer the strain of the tested piece to the sensitive grid, and the physical property of the adhesive layer can influence the testing precision. In addition, the strain gauge needs wire bonding and bridging, and the operation is relatively complicated.

The invention designs an optical test method for coaxiality of an axial fatigue testing machine, which can realize optical test of coaxiality. The measuring equipment and the testing machine and the test sample are not in contact, and strain gauges are not needed.

Disclosure of Invention

Aiming at the problems in the prior art, the invention aims to provide an optical detection method for the coaxiality of an axial fatigue testing machine.

The technical scheme adopted by the invention for solving the technical problems is as follows: an optical detection method for coaxiality of an axial fatigue testing machine comprises the following steps:

1) spraying paint speckles in an area to be measured of a parallel section of a test sample;

2) after the paint speckles are dried, drawing a reference zero line vertical to the axis of the test sample on the upper part of a measurement area of the parallel section of the test sample by using a black marker pen;

3) clamping a test sample on a chuck of an axial fatigue testing machine, applying a tensile force of 1% of the maximum testing force of the testing machine as a preload, shooting a parallel section to-be-measured area of the test sample by using a dual-camera strain measurement system, applying the testing force to 4% of the maximum testing force of the testing machine by using a surface speckle picture as an initial reference picture for measuring and analyzing strain, and shooting a surface speckle picture of the test sample after the test sample is loaded;

4) translating the dual-camera strain measurement system around the testing machine, and collecting 8 photos before and after loading by the controller at 4 positions with the relative angles of 0 degrees, 90 degrees, 180 degrees and 270 degrees on the surface of the test sample;

5) analyzing speckle changes of the photos before and after loading, generating strain distribution on the surface of the test sample, and obtaining main strain of points on a transversal line perpendicular to the reference zero line;

6) because the loading process is in the elastic deformation range of the test sample, according to Hooke's law, the distance from the point on the transversal to the reference zero line is set to be L, and the distance from the point on the transversal to the reference zero line after loading is set to be L', and the distance is calculated according to a formula:

acquiring main strain of points on different section lines;

7) the main strain of the point on the section line corresponds to epsilon at 4 positions of 0 degrees, 180 degrees, 90 degrees and 270 degrees on the surface of the test sample₁、ε₂、ε₃、ε₄And calculating the coaxiality of the section strain according to a formula:

coaxiality

8) And obtaining the coaxiality of any point on the section line from the reference zero line L.

Specifically, the paint speckles sprayed in the step 1) are uniformly sprayed on the surfaces of the parallel sections of the test sample by using white matte paint, after the paint is dried in the air, the black matte paint is adopted to form mist random black points to cover the surfaces of the test sample, and the black matte paint needs to be sufficiently atomized and uniformly distributed on the surfaces of the white paint.

Specifically, the line width bit of the reference zero line in the step 2) is 0.05 mm.

Specifically, 4% of the maximum test force of the application tester in the step 3) needs to satisfy the maximum force used in the test that should not cause plastic deformation of the test specimen.

Specifically, when the dual-camera strain measurement system in the step 4) shoots, the coaxiality test sample is ensured to be positioned in the depth of field measured by the dual-camera strain measurement system.

The invention has the following beneficial effects:

the invention designs an optical detection method for coaxiality of an axial fatigue testing machine

1) The method comprises the steps of obtaining the strain distribution of the whole surface of a measuring area of a parallel section of a sample in a non-contact manner by adopting an optical measuring mode, obtaining the strain change of the vertical distance of the sample before and after loading on different sections, quickly and accurately calculating the coaxiality according to a formula, and greatly reducing the dependence on experimental preparation operation experience of an operator such as a strain foil and the like;

2) paint speckles are used as strain reference points, the measurement process is simple to operate, economical and practical, and human errors of operators are avoided;

3) the method is suitable for checking the coaxiality of the laboratory equipment during the period, and automatically checking the state of the equipment before the fatigue test is carried out, and is convenient and quick;

4) by combining the strain distribution chart analysis and the coaxiality calculation, the coaxiality of any point on a section line in a region to be measured on the surface of the sample can be visually observed.

Drawings

FIG. 1 is a schematic diagram of speckle sprayed on the surface of an optical test sample for coaxiality and the drawing of a reference neutral line.

Fig. 2 is a schematic view of the measurement principle.

Fig. 3 is a schematic view of different observation angles.

Fig. 4 is a schematic diagram of principal strains at points on different stubs.

FIG. 5 is a schematic view of the coaxiality of points on the sectional line.

In the figure: 1-dual camera strain measurement system; 2-a controller; 3-testing the sample; 4-paint speckling; 5-section line; a-reference zero line.

Detailed Description

The technical solutions in the embodiments of the present invention will be described in further detail in the following clearly and completely with reference to the accompanying drawings in the embodiments of the present invention. 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.

The working principle of the optical detection method for the coaxiality of the axial fatigue testing machine is as follows:

(1) paint speckles 4 are sprayed on the parallel section to be measured area of the coaxiality test sample 3, the test sample 3 is clamped on a chuck of an axial fatigue testing machine, a picture of the paint speckles 4 on the surface of the sample after the sample is loaded is shot and contrastively analyzed by a double-camera strain measurement system 1, and elastic deformation of points on a section line 5, perpendicular to a reference zero line A-A, of the surface of the sample before and after the sample is loaded is calculated.

(2) The dual camera strain measurement system 1 is translated around the tester to obtain photographs taken at different angles. During shooting, the coaxiality test sample 3 is ensured to be positioned in the depth of field measured by the dual-camera strain measurement system 1.

(3) And analyzing the paint speckle 4 change of the pictures before and after by adopting the controller 2 to generate the strain distribution on the surface of the test sample 3. Setting 1 reference zero line A-A vertical to the central axis of the coaxiality sample, and setting a strain value equal to zero in a photo obtained by testing according to the reference zero line in the post-processing. The distribution of the principal strain in the measurement area of the sample is obtained by measuring the principal strain of the points on the section line 5 perpendicular to the reference zero line, and the coaxiality is calculated by observing the principal strain values of the points on the section lines 5 at different angles according to fig. 3.

The working process of the optical detection method for the coaxiality of the axial fatigue testing machine comprises the following steps:

the working process of the invention is as follows:

(1) paint speckles 4 are sprayed on the area to be measured of the parallel section of the test sample 3, white matte paint is uniformly sprayed on the surface of the parallel section of the test sample, and after the paint is dried in the air, black matte paint is adopted to form mist random black points to cover the surface of the test sample. The black matte paint needs to be sufficiently atomized and uniformly distributed on the white paint surface.

(2) After the paint speckles 4 are dried in the air, a reference zero line perpendicular to the axis of the sample is drawn on the upper part of the measurement area of the parallel section of the sample by using a black marker pen, and the line width is 0.05mm, as shown in A-A in figure 2.

(3) The test specimen 3 is clamped on the chuck of the axial fatigue testing machine. A tensile force of 1% of the maximum test force of the tester was applied as a preload. By using the dual-camera strain measuring system 1, the area to be measured of the parallel section of the test sample 3 is shot, and the surface speckle picture is taken as an initial reference picture for measuring and analyzing strain. The test force is applied to 4% of the maximum test force of the tester (the maximum force used in the test should not cause plastic deformation of the test specimen), and a speckle picture of the surface of the test specimen 3 after the specimen is loaded is taken.

(4) The dual-camera strain measurement system 1 is translated around the testing machine, and 8 photos before and after loading are acquired at 4 positions with the relative angles of 0 degrees, 90 degrees, 180 degrees and 270 degrees on the surface of the test sample 3 by the controller 2. During shooting, the coaxiality test sample is ensured to be positioned in the depth of field measured by the double-camera strain measurement system 1.

(5) The speckle variation of the photographs before and after loading is analyzed to generate the strain distribution of the test surface, and the principal strain of a point on the transversal 5 perpendicular to the reference zero line is obtained.

(6) Because the loading process is in the range of experimental elastic deformation, according to hooke's law, the distance from the point on the transversal 5 to the reference zero line is set to be L, and the distance from the point on the transversal 5 after loading to the reference zero line A-A is set to be L'. Calculating according to the formula:

and obtaining the main strain of points on different section lines 5, wherein the section line 1 is at an observation angle of 0 degree, and the section line 2 is at an observation angle of 180 degrees. FIG. 4: principal strain diagrams for points on different section lines.

(7) The main strains of the points on the section lines 5 at 4 positions of 0 degrees, 180 degrees, 90 degrees and 270 degrees on the surface of the test sample 3 respectively correspond to epsilon₁、ε₂、ε₃、ε₄The coaxiality of the strain of the section 5 is calculated. Calculating according to the formula:

coaxiality

(8) The coaxiality of any point on the section from the reference zero line L can be obtained as shown in fig. 5. FIG. 5: the coaxiality of each point on the sectional line is schematically shown.

The invention adopts an optical measurement mode to obtain the strain change before and after the sample is loaded, and calculates the coaxiality by adopting a formula. The mode of translating the dual-camera strain measurement system 1 around the testing machine is adopted to realize the measurement of the surface strain of the test sample 3 and the strain analysis of the acquisition coaxiality sample without contact. By combining the strain distribution chart analysis and the coaxiality calculation, the coaxiality of any point on a section line in a region to be measured on the surface of the sample can be visually observed, and the method is not limited to a certain specific plane.

The present invention is not limited to the above embodiments, and any structural changes made under the teaching of the present invention shall fall within the scope of the present invention, which is similar or similar to the technical solutions of the present invention.

The techniques, shapes, and configurations not described in detail in the present invention are all known techniques.