Cylinder sample instantaneous displacement analysis method based on two-dimensional DIC

Abstract

The invention provides a two-dimensional DIC-based cylinder sample instantaneous displacement analysis method. The method comprises the following steps: firstly, placing a cylinder sample at a test position of mechanical test equipment; placing a high-speed camera at a shooting position, so that the cylindrical sample is positioned in a shooting area of the high-speed camera; in the process of carrying out a mechanical test on the cylindrical sample by using mechanical test equipment, shooting by using a high-speed camera to obtain a plurality of original speckle images; and finally, obtaining displacement data corresponding to each target mark according to the radius value of the cross section of the cylindrical sample and the positions of the target marks in all speckle original images. According to the method, the position of the target mark in the original speckle image is corrected, so that the instantaneous displacement of the cylindrical sample can be recorded and accurately calculated and analyzed by only one high-speed camera; the method for analyzing the instantaneous displacement of the cylindrical sample by using the two-dimensional DIC technology is simple to operate, small in occupied area, less in required equipment and low in price.

Description

Technical Field

[0001] The present application relates to the technical field of mechanical testing, and in particular to a method for analyzing the instantaneous displacement of a cylindrical specimen based on two-dimensional DIC. Background Art

[0002] Although the DIC (Digital Image Correlation) analysis method has been widely used in engineering construction, medical health and other fields, the two-dimensional DIC technology can only solve the deformation and displacement problems within the plane. Once the observed object rotates or undergoes other out-of-plane displacement, the results analyzed by this technology will produce large errors or even be impossible to analyze.

[0003] For example, the Hopkinson torsion bar device is a test device that can be used to study the changes in mechanical properties of a sample during instantaneous friction. During the experiment, it is necessary to accurately obtain the stress state and displacement at different positions. In the prior art, the Hopkinson torsion bar test mainly uses three-dimensional DIC technology to measure the rotational displacement of the sample. However, the software operation steps of the three-dimensional DIC technology are complicated and expensive. At the same time, since it requires the coordinated use of two cameras, it also has certain restrictions on the site. Therefore, there is an urgent need for a technology that is simple to operate, occupies a small area, requires less equipment, and is low-priced to achieve the measurement of the rotational displacement of the Hopkinson torsion bar test. Summary of the invention

[0004] In view of this, one of the technical problems solved by the embodiments of the present invention is to provide a cylindrical specimen instantaneous displacement analysis method based on two-dimensional DIC, so as to overcome the problems of complex software operation steps, high price and limited site in the prior art of measuring the rotational displacement in the Hopkinson torsion bar test using three-dimensional DIC technology.

[0005] The embodiment of the present application discloses a cylindrical specimen instantaneous displacement analysis method based on two-dimensional DIC, the method comprising:

[0006] Placing a cylindrical sample at a test position of a mechanical testing device; wherein a plurality of speckle marks are provided on a circumferential surface of the cylindrical sample;

[0007] placing a high-speed camera at a shooting position so that the cylindrical sample is located in a shooting area of ​​the high-speed camera;

[0008] In the process of the mechanical testing equipment performing a mechanical test on the cylindrical specimen, a plurality of original speckle images are obtained by photographing with the high-speed camera;

[0009] According to the cross-sectional radius value of the cylindrical specimen and the position of the target mark in all the speckle original images, displacement data corresponding to each target mark is obtained; wherein the target mark is one or more of all the speckle marks; and the displacement data is used to characterize the displacement change of the target mark during the mechanical test.

[0010] In an optional embodiment of the present invention, obtaining the displacement data corresponding to each target mark according to the cross-sectional radius value of the cylindrical sample and the position of the target mark in all the original speckle images includes:

[0011] Cutting the original speckle image into a plurality of local original images along the height direction;

[0012] According to a preset image stretching rule, all the local original images are stretched in the height direction to obtain a plurality of local corrected images;

[0013] Performing splicing processing on all the local correction images to obtain a speckle correction image;

[0014] The displacement data corresponding to each of the target marks is obtained according to the at least two speckle correction images.

[0015] In an optional embodiment of the present invention, when the axis of the cylindrical sample is parallel to the length direction of the speckle original image, the stretching process is performed on all the local original images in the height direction according to a preset image stretching rule to obtain a plurality of local corrected images, comprising:

[0016] Using the formula Performing stretching processing on all the local original images in the height direction respectively to obtain a plurality of the local corrected images;

[0017] Among them, r i is the stretching multiple of the i-th local original image in the height direction, and the first local original image is located at the top in the height direction; R is the cross-sectional radius value of the cylindrical specimen, and Δm is the width of the local original image.

[0018] In an optional embodiment of the present invention, before cutting one of the speckle original images into a plurality of local original images along the height direction, the method further includes:

[0019] Selecting a first corrected image and a second corrected image from all the speckle original images, and determining positions of a plurality of target marks in the first corrected image and the second corrected image; wherein the positions of the plurality of target marks in the first corrected image and the second corrected image are different;

[0020] Determining a displacement vector of the target mark according to a position of the target mark in the first corrected image and the second corrected image;

[0021] Determining an image rotation angle according to a displacement vector of the target marker;

[0022] According to the image rotation angle, all the original speckle images are rotated.

[0023] In an optional embodiment of the present invention, the widths of all the local original images are the same.

[0024] In an optional embodiment of the present invention, obtaining the displacement data corresponding to each target mark according to the cross-sectional radius value of the cylindrical sample and the position of the target mark in all the original speckle images includes:

[0025] According to the position of the target mark in all the original speckle images, calculating and obtaining the measurement data corresponding to the target mark;

[0026] According to the image distance and object distance of the high-speed camera during the mechanical test, and the radius of the cylindrical specimen, pseudo-displacement correction is performed on the measurement data corresponding to the target mark to obtain the displacement data corresponding to the target mark.

[0027] In an optional embodiment of the present invention, performing pseudo-displacement correction on the measurement data corresponding to the target mark according to the image distance and object distance of the high-speed camera during the mechanical test and the radius of the cylindrical specimen to obtain the displacement data corresponding to the target mark includes:

[0028] Using the formula Performing pseudo-displacement correction on the measurement data corresponding to the target mark to obtain the displacement data corresponding to the target mark;

[0029] Wherein, ΔD is the displacement value of the target mark; Z is the object distance of the high-speed camera during the mechanical test; L is the image distance of the high-speed camera during the mechanical test; R is the radius of the cylindrical specimen; D S0 D is the coordinate value corresponding to the length direction or height direction of the high-speed camera imaging plane in the original speckle image taken earlier; S1 It is the coordinate value corresponding to the target mark in the length direction or height direction of the imaging plane of the high-speed camera in the original speckle image with a later shooting time.

[0030] In an optional embodiment of the present invention, the method further includes:

[0031] According to the displacement data corresponding to the multiple target marks, the displacement field data and / or strain field data of the cylindrical specimen are calculated using the interpolation method; wherein the displacement field data is used to characterize the displacement change of the cylindrical specimen during the mechanical test; and the strain field data is used to characterize the strain change of the cylindrical specimen during the mechanical test.

[0032] In an optional embodiment of the present invention, in the height direction, the upper edge of the area where the cylindrical surface of the cylindrical sample is located is at least partially flush with the upper edge of the speckle original image, and the lower edge of the area where the cylindrical surface of the cylindrical sample is located is at least partially flush with the lower edge of the speckle original image; correspondingly, in the process of performing a mechanical test on the cylindrical sample by the mechanical testing equipment, obtaining a plurality of speckle original images by photographing with the high-speed camera includes:

[0033] In the process of the mechanical testing equipment performing a mechanical test on the cylindrical specimen, a plurality of original imaging images are obtained by taking pictures with the high-speed camera;

[0034] The multiple original imaging images obtained by the high-speed camera are cropped to obtain multiple original speckle images.

[0035] In an optional embodiment of the present invention, the mechanical testing equipment is a Hopkinson torsion bar equipment, and the length direction of the imaging original image is parallel to the axis of the cylindrical sample; the step of cropping the multiple imaging original images obtained by the high-speed camera to obtain the multiple speckle original images includes:

[0036] Selecting a first original image and a second original image from all the imaging original images, and determining positions of all the target marks in the first original image and the second original image; wherein at least a plurality of the target marks are located in different positions in the first original image and the second original image, and the shooting time of the first original image is earlier than the shooting time of the second original image;

[0037] Determine the theoretical projection position of the axis of the cylindrical sample in the first original image according to the positions of all the target marks in the first original image and the second original image;

[0038] According to the theoretical projection position of the axis of the cylindrical sample in the first original image, the radius value of the cylindrical sample, and the ratio value of the size of each pixel point in the imaging original image to the actual size of the cylindrical sample, all the imaging original images are cropped in the height direction to obtain a plurality of the speckle original images.

[0039] In the embodiment of the present invention, a cylindrical sample is first placed at a test position of a mechanical testing device; a high-speed camera is then placed at a shooting position so that the cylindrical sample is located in the shooting area of ​​the high-speed camera; a plurality of original speckle images are obtained by shooting with a high-speed camera during a mechanical test of the cylindrical sample by the mechanical testing device; finally, displacement data corresponding to each target mark is obtained according to the cross-sectional radius value of the cylindrical sample and the position of the target mark in all the original speckle images. In the embodiment of the present invention, the position of the target mark in the original speckle image is corrected, so that only one high-speed camera is required to realize the recording, relatively accurate calculation and analysis of the instantaneous displacement of the cylindrical sample. Compared with the prior art, the instantaneous displacement analysis method of cylindrical samples by two-dimensional DIC in the embodiment of the present invention is simple to operate, occupies a small area, requires less equipment, and is low in price. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0041] Figure 1 It is a schematic flow chart of a cylindrical specimen instantaneous displacement analysis method based on two-dimensional DIC disclosed in Example 1 of the present application;

[0042] Figure 2 It is a schematic diagram of the relative position relationship between the cylindrical sample and the shooting direction;

[0043] Figure 3 It is a schematic diagram of pseudo displacement in the height direction caused by the out-of-plane motion of the circumference of the cylindrical specimen;

[0044] Figure 4 It is a schematic flow chart of a cylindrical specimen instantaneous displacement analysis method based on two-dimensional DIC disclosed in Example 2 of the present application;

[0045] Figure 5 It is a schematic diagram of cutting the original speckle image into multiple local original images;

[0046] Figure 6 Schematic diagram of a speckle-corrected image obtained after stitching all local-corrected images. DETAILED DESCRIPTION

[0047] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0048] It should be noted that the terms "first", "second", "third" and "fourth" in the specification and claims of the present application are used to distinguish different objects rather than to describe a specific order. The terms "including" and "having" in the embodiments of the present application and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, device, product or equipment including a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or equipment.

[0049] Embodiment 1

[0050] like Figure 1 As shown, Figure 1 This is a schematic flow chart of a cylindrical sample instantaneous displacement analysis method based on two-dimensional DIC disclosed in Example 1 of the present application. The cylindrical sample instantaneous displacement analysis method based on two-dimensional DIC includes:

[0051] Step S101, placing a cylindrical specimen at a test position of a mechanical testing device.

[0052] In this embodiment, the mechanical testing equipment is a device that needs to load a cylindrical specimen according to the test requirements and measure the displacement or deformation, and the specific type of the equipment is not limited. For example, it can be a Hopkinson torsion bar device.

[0053] In this embodiment, see Figure 2 In order to measure and analyze the displacement and deformation of the cylindrical specimen during the test, it is necessary to set multiple speckle marks on the circumferential surface of the cylindrical specimen. The specific size and material of the cylindrical test are not limited and can be determined and processed according to the test requirements.

[0054] In addition, the number, shape, size, color and location of the speckle marks on the cylindrical specimen are not limited and can be reasonably selected according to actual application requirements.

[0055] For example, in order to facilitate tracking of the movement of the speckle markers during the test, the shapes or colors of the multiple speckle markers may be set to be different; in order to reduce the complexity of the test operation, the shapes or colors of the multiple speckle markers may be set to be the same.

[0056] For example, see Figure 2 In order to more comprehensively and accurately determine the displacement and deformation of the cylindrical specimen during the test, it is preferred that multiple speckle marks are evenly distributed on the circumferential surface of the cylindrical specimen.

[0057] Step S102: placing a high-speed camera at a shooting position so that the cylindrical sample is located in the shooting area of ​​the high-speed camera.

[0058] In this embodiment, a high-speed camera is used to photograph the circumferential surface of the cylindrical sample during the test to obtain multiple original speckle images. Figure 2 Before the test begins, the relative position of the cylindrical specimen and the high-speed camera needs to be adjusted to make the axis of the cylindrical specimen as close to the Figure 2 The y-axis of the coordinate system coincides with the Figure 2 The x-axis of the central coordinate system is parallel, so that the length direction of the original speckle image is parallel to the y-axis, and the height direction of the original speckle image is parallel to the z-axis.

[0059] In this embodiment, in order to reduce the test cost, the number of high-speed cameras in this embodiment is one, wherein the specific model of the high-speed camera and the relative distance to the cylindrical specimen are not limited and can be reasonably selected according to the actual application requirements. However, it is at least necessary to ensure that the entire cylindrical specimen is located in the shooting area of ​​the high-speed camera, so that the position of the target mark can be determined in all the images taken by the high-speed camera later.

[0060] In this embodiment, in order to ensure the accuracy of subsequent measurement results, when the circumferential surface of the cylindrical sample is photographed with a high-speed camera, it is necessary to make the imaging plane of the high-speed camera parallel to the axis of the cylindrical sample as much as possible.

[0061] Step S103, when the mechanical testing equipment performs a mechanical test on the cylindrical specimen, a high-speed camera is used to obtain a plurality of original speckle images.

[0062] In this embodiment, the original speckle image may be an image including only the area where the cylindrical sample's circumference is located, or may be an image including other areas in addition to the area where the cylindrical sample's circumference is located. The specific number of original speckle images is not limited and can be determined according to the test requirements and the shooting performance of the high-speed camera. In order to accurately measure the surface displacement of the cylindrical sample during the test, the number of original speckle images is at least three, one of which records the state of the cylindrical sample before displacement or deformation, one or more records the state of the cylindrical sample during displacement or deformation, and one records the state of the cylindrical sample no longer displaced or deformed.

[0063] In this embodiment, in order to ensure the accuracy of test data recording and calculation and avoid errors, it is necessary to ensure that the position of the high-speed camera cannot change during the mechanical test.

[0064] Optionally, considering that the original imaging image directly obtained by the high-speed camera includes not only the area where the cylindrical sample is located, but also other areas, in order to more accurately calculate the displacement data corresponding to each target mark in the subsequent step, the original imaging image can be cropped to obtain the speckle original image, that is, step S103 can include the following sub-steps S103a and S103b:

[0065] Sub-step S103a, during the process of mechanical testing of the cylindrical specimen by the mechanical testing equipment, a high-speed camera is used to obtain a plurality of original imaging images.

[0066] Sub-step S103b, cropping the multiple original imaging images obtained by the high-speed camera to obtain multiple original speckle images.

[0067] Among them, in the height direction (corresponding to Figure 2 In the direction parallel to the z-axis in the middle), the upper edge of the area where the cylindrical surface of the sample is located is at least partially flush with the upper edge of the original speckle image, and the lower edge of the area where the cylindrical surface of the sample is located is at least partially flush with the lower edge of the original speckle image. In the length direction perpendicular to the height direction (corresponding to Figure 2 In the direction parallel to the y-axis, the edge of the circumferential surface of the cylindrical sample may be flush with the edge of the original speckle image, or may not be flush with the edge of the original speckle image, which is not limited in this embodiment.

[0068] In addition, the method for cropping the original image in sub-step S103b is not limited and can be reasonably selected according to actual application requirements. For example, one or more image recognition algorithms can be used to identify the edge of the cylindrical sample, and then the image area outside the edge of the cylindrical sample in the original image can be cropped to obtain the speckle original image; or after determining the center point of the imaging area of ​​the cylindrical sample, the image area outside the edge of the cylindrical sample can be cropped according to the length and radius of the cylindrical sample to obtain the speckle original image.

[0069] Furthermore, on the one hand, considering that the exposure, brightness and other parameters of the original image taken by the high-speed camera under different test environments may be different, and the color contrast between the cylindrical specimen and its background environment may also be different; on the other hand, considering that there are many types of image processing algorithms for edge recognition, it is relatively complicated to select a suitable image processing algorithm. Therefore, when the mechanical test equipment is a Hopkinson torsion bar equipment, and the length direction of the original image is parallel to the axis of the cylindrical specimen, under the premise of ensuring that the cropped speckle original image only includes the area where the cylindrical specimen is located, in order to simplify the complexity of image processing and improve the efficiency of the entire mechanical test result data processing, it is preferred that sub-step S103b also includes the following steps A-C:

[0070] Step A: Select a first original image and a second original image from all the original images, and determine the positions of a plurality of target marks in the first original image and the second original image.

[0071] The target mark may be all or part of all the speckle marks. However, considering that some speckle marks may be located on the side of the cylindrical specimen facing away from the high-speed camera during the test, or that the cylindrical specimen rotates during the test, causing it to appear in only one or a few original speckle images, in this embodiment, only the speckle marks recorded in multiple original speckle images during the loading process of the cylindrical specimen by the mechanical testing equipment are selected as target marks to analyze the displacement of the cylindrical specimen during the test.

[0072] Among them, at least a plurality of target marks are located at different positions in the first original image and the second original image, and the shooting time of the first original image is earlier than the shooting time of the second original image. That is, the second original image records the instantaneous state of displacement or deformation of the cylindrical sample; the first original image may record the instantaneous state of displacement or deformation of the cylindrical sample, or may record the instantaneous state of no displacement or deformation of the cylindrical sample.

[0073] In addition, there is no limitation on the specific method for selecting the first original image and the second original image, and there is no limitation on the method for determining the position of the target mark in the first original image and the second original image, and they can be flexibly selected according to actual application requirements.

[0074] Step B: determining the theoretical projection position of the axis of the cylindrical sample in the first original image according to the positions of all target marks in the first original image and the second original image.

[0075] Among them, considering that when the Hopkinson torsion bar device rotates the cylindrical sample, the displacement of the target mark obtained by directly measuring the position in the speckle image is the displacement after projection, which does not match the actual displacement of the target mark. However, if all the target marks are densely distributed along the axis of the cylindrical sample, the actual projection position of the target mark with the largest displacement in the first original image coincides with the theoretical projection position of the axis of the cylindrical sample in the first original image (because the axis of the cylindrical sample does not actually appear in the imaging original image, it is called the theoretical projection position here). Therefore, since the length direction of the imaging original image is parallel to the axis of the cylindrical sample, after determining the actual projection position of the target mark with the largest displacement in the first original image, the theoretical projection position of the axis of the cylindrical sample can be further determined in the first original image.

[0076] Step C, according to the theoretical projection position of the axis of the cylindrical sample in the first original image, the radius value of the cylindrical sample, and the ratio value of the size of each pixel point in the imaging original image to the actual size of the cylindrical sample, all the imaging original images are cropped in the height direction to obtain multiple speckle original images.

[0077] Among them, since the axis of the cylindrical sample usually does not move during the test of the Hopkinson torsion bar device, after the theoretical projection position of the axis of the cylindrical sample is determined in an original imaging image, the original imaging image can be further cropped in the height direction according to the radius value of the cylindrical sample and the ratio value of the size of each pixel point in the original imaging image to the actual size of the cylindrical sample, so that in the height direction, the upper edge of the area where the circular surface of the cylindrical sample is located is at least partially flush with the upper edge of the original speckle image, and the lower edge of the area where the circular surface of the cylindrical sample is located is at least partially flush with the lower edge of the original speckle image.

[0078] Step S104, obtaining displacement data corresponding to each target mark according to the cross-sectional radius value of the cylindrical sample and the position of the target mark in all the original speckle images.

[0079] In this embodiment, the displacement data is used to characterize the displacement change of the target marker during the mechanical test. The specific characterization method of the displacement data is not limited and can be reasonably selected according to actual application requirements.

[0080] In this embodiment, since only one high-speed camera is used and the imaging plane of the high-speed camera is parallel to the axis of the cylindrical sample, if the target mark is found to be displaced in the height direction by analyzing the original speckle image, it indicates that the target mark is likely to be rotated relative to the axis of the cylindrical sample during the test. If the displacement of the target mark in the height direction in the original speckle image is directly used as the rotational displacement of the target mark, it will be inconsistent with the actual rotational displacement of the target mark. Therefore, in step S104, it is necessary to further process and calculate the displacement data of each target mark according to the cross-sectional radius value of the cylindrical sample and the position of the target mark in all the original speckle images.

[0081] Optionally, considering that the imaging principle of the high-speed camera is pinhole imaging, it is usually required during the test that the plane object being measured cannot move out of the plane or the deformation caused by the out-of-plane movement is very small. However, in the actual test process, out-of-plane movement is inevitable due to factors such as the Poisson effect. If the plane specimen being measured undergoes deformation due to out-of-plane movement, it will be reflected in the digital image, and the digital image of the plane specimen being measured will be enlarged or reduced. When the digital image is analyzed by software, the software cannot distinguish whether the cylindrical specimen of the plane being measured is actually enlarged or reduced or caused by the out-of-plane movement of the cylindrical specimen. The displacement data obtained by analysis may be greatly different from the actual result. Therefore, in order to determine the displacement data actually corresponding to the target mark, step S104 may include the following sub-steps S104a and S104b:

[0082] Sub-step S104a, calculating and obtaining the measurement data corresponding to the target mark according to the position of the target mark in all the original speckle images.

[0083] The measurement data corresponding to the target mark is obtained by directly measuring the position of the target mark in multiple original speckle images.

[0084] For example, see Figure 2 , if the actual position of the target mark when the i-th speckle original image is taken is p i , the actual position when the i+1th speckle original image is taken is p i+1 If , then the coordinate value of the target mark in the height direction in the i-th speckle original image is z i , the coordinate value in the height direction of the i+1th original speckle image is z i+1 , then the displacement of the target mark in the height direction is directly measured using the i-th speckle original image and the i+1-th speckle original image as z i and z i+1 The difference.

[0085] Sub-step S104b, according to the image distance and object distance of the high-speed camera during the mechanical test, and the radius of the cylindrical specimen, pseudo-displacement correction is performed on the measurement data corresponding to the target mark to obtain displacement data corresponding to the target mark.

[0086] The specific method for performing pseudo-displacement correction on the measurement data corresponding to the target mark is not limited and can be reasonably selected according to actual application requirements. For example, correction can be performed according to a preset data comparison table or formula.

[0087] Furthermore, in order to more accurately and simply determine the displacement data corresponding to the target mark, sub-step S104b may include:

[0088] Using the formula The pseudo-displacement correction is performed on the measurement data corresponding to the target mark to obtain the displacement data corresponding to the target mark.

[0089] Among them, ΔD is the displacement value of the target mark, that is, the actual displacement value of the target mark within the shooting time interval of two original speckle images, for example Figure 3 Middle D 1 and D 0 The distance between them; Z is the object distance of the high-speed camera during the mechanical test; see Figure 3 , L is the image distance of the high-speed camera during the mechanical test; R is the radius of the cylindrical specimen; D S0 D is the coordinate value of the target mark in the length direction or height direction of the high-speed camera imaging plane in the original speckle image taken earlier; S1 It is the coordinate value corresponding to the length direction or height direction of the target mark in the imaging plane of the high-speed camera in an original speckle image with an earlier shooting time.

[0090] Optionally, after obtaining the displacement data corresponding to the target mark, the displacement and strain variation law of the cylindrical specimen during the test can be further fitted, that is, step S104 can also include step S105: according to the displacement data corresponding to multiple target marks, the displacement field data and / or strain field data of the cylindrical specimen are calculated by interpolation method.

[0091] Among them, the displacement field data is used to characterize the displacement change of the cylindrical specimen during the mechanical test; the strain field data is used to characterize the strain change of the cylindrical specimen during the mechanical test.

[0092] As can be seen from the above embodiments of the present invention, the embodiments of the present invention first place the cylindrical sample at the test position of the mechanical testing equipment; then place a high-speed camera at the shooting position so that the cylindrical sample is located in the shooting area of ​​the high-speed camera; and then use the high-speed camera to shoot and obtain multiple speckle original images during the mechanical testing of the cylindrical sample by the mechanical testing equipment; finally, according to the cross-sectional radius value of the cylindrical sample and the position of the target mark in all the speckle original images, the displacement data corresponding to each target mark is obtained. The embodiments of the present invention correct the position of the target mark in the speckle original image, so that only one high-speed camera is needed to realize the recording and relatively accurate calculation and analysis of the instantaneous displacement of the cylindrical sample. Compared with the prior art, the instantaneous displacement analysis method of the cylindrical sample of the two-dimensional DIC of the embodiment of the present invention is simple to operate, occupies a small area, requires less equipment, and is low in price.

[0093] Embodiment 2

[0094] like Figure 4 As shown, Figure 4 This is a schematic flow chart of a cylindrical sample instantaneous displacement analysis method based on two-dimensional DIC disclosed in Example 2 of the present application. The cylindrical sample instantaneous displacement analysis method based on two-dimensional DIC includes:

[0095] Step S201, placing a cylindrical specimen at a test position of a mechanical testing device.

[0096] In this embodiment, step S201 is substantially the same as or similar to step S101 in the aforementioned first embodiment, and will not be described in detail herein.

[0097] Step S202: placing a high-speed camera at a shooting position so that the cylindrical sample is located in the shooting area of ​​the high-speed camera.

[0098] In this embodiment, step S202 is substantially the same as or similar to step S102 in the aforementioned first embodiment, and will not be described in detail herein.

[0099] Step S203: During the process of mechanical testing of the cylindrical specimen by the mechanical testing equipment, a high-speed camera is used to obtain a plurality of original speckle images.

[0100] In this embodiment, step S203 is substantially the same as or similar to step S103 in the first embodiment, and will not be described in detail herein.

[0101] Step S205 , cutting a speckle original image into a plurality of local original images along the height direction.

[0102] In this embodiment, in order to ensure the image processing effect, it is preferred that the number of pixels in the height direction of the local original image is an integer. In addition, the heights of all local original images may be the same or different, which is not limited in this embodiment.

[0103] Optionally, considering that it is difficult to ensure that the shooting direction of the high-speed camera is completely perpendicular to the axis of the cylindrical sample when the high-speed camera is set up before the test, in order to reduce the impact of the angle error when the high-speed camera is set on the final calculation result, the image can be rotated for control. Specifically, between step S203 and step S205, the following sub-steps S204a to S204d can also be included:

[0104] Sub-step S204a, selecting a first corrected image and a second corrected image from all the original speckle images, and determining the position of the target mark in the first corrected image and the second corrected image.

[0105] The position of the target mark in the first correction image and the second correction image is different, that is, the target mark is displaced within the shooting time interval of the first correction image and the second correction image. In order to simplify the complexity of data processing, only one speckle mark can be selected as the target mark in sub-step S204a.

[0106] Sub-step S204b: determining a displacement vector of the target mark according to the position of the target mark in the first corrected image and the second corrected image.

[0107] Sub-step S204c, determining the image rotation angle according to the displacement vector of the target mark.

[0108] After obtaining the displacement vector V of the target marker, it can be first decomposed in the image height direction and length direction to obtain the displacement V in the length direction L and the displacement in the height direction V H ; Then use the formula Calculate the image rotation angle α.

[0109] Sub-step S204d: performing rotation processing on all original speckle images according to the image rotation angle.

[0110] Step S206 , stretching all local original images in the height direction according to a preset image stretching rule to obtain a plurality of local corrected images.

[0111] In this embodiment, the specific content of the image stretching rule is not limited and can be reasonably selected according to actual application requirements. For example, after determining the center line of the original speckle image in the height direction, the multiple local original images located above the center line can be stretched from bottom to top in sequence according to the stretching multiple sequence from small to large, and the multiple local original images located below the center line can be stretched from top to bottom in sequence.

[0112] Optionally, in order to simplify the complexity of cutting the speckle original image and avoid the image processing software from automatically stretching or compressing the local original image and the local corrected image, it is preferred that the widths of all the local original images are the same, and the numbers of pixels in the height direction of all the local original images and the local corrected images are integers.

[0113] For example, see Figure 5 The length of the original speckle image corresponds to 320 pixels, and the height corresponds to 256 pixels. The original speckle image can be cut into 64 local original images along the height direction, and the height of each local original image corresponds to 4 pixels.

[0114] Optionally, in order to obtain the displacement data corresponding to the target mark more accurately later, when the widths of all the local original images are the same and the axis of the cylindrical sample is parallel to the length direction of the speckle original image, step S206 may include:

[0115] Using the formula All local original images are stretched in the height direction to obtain multiple local corrected images.

[0116] Among them, r i is the stretching multiple of the i-th local original image in the height direction, see Figure 5 , the first local original image is located at the top in the height direction; R is the cross-sectional radius of the cylindrical specimen, and Δm is the width of the local original image.

[0117] Step S207: stitching all the local corrected images to obtain a speckle corrected image.

[0118] In this embodiment, the obtained speckle correction image can be seen in Figure 6 , the height of the image is greater than the height of the cylindrical sample in the original speckle image. Through steps S205 to S207, multiple original speckle images can be processed and multiple corresponding speckle correction images can be obtained.

[0119] Step S208: obtaining displacement data corresponding to each target mark according to at least two speckle correction images.

[0120] In this embodiment, similar to the above-mentioned embodiment 1, the displacement data is used to characterize the displacement change of the target mark during the mechanical test. Since the speckle correction image is equivalent to unfolding the circumference of the cylindrical specimen into a plane and photographing it with a high-speed camera, after determining the position of the target mark on the two speckle correction images, the displacement corresponding to the target mark can be directly measured from the image.

[0121] As can be seen from the above embodiments of the present invention, this embodiment cuts a speckle original image into multiple local original images along the height direction; then stretches all the local original images in the height direction according to the preset image stretching rule to obtain multiple local corrected images; then splices all the local corrected images to obtain a speckle corrected image; thus, the displacement data corresponding to each target mark can be directly obtained based on at least two speckle corrected images. Compared with the above embodiments, the real displacement corresponding to the target mark can be determined more simply and accurately.

[0122] So far, specific embodiments of the present application have been described. Other embodiments are within the scope of the appended claims. In some cases, the actions recorded in the claims can be performed in a different order and still achieve the desired results. In addition, the processes depicted in the accompanying drawings do not necessarily require the specific order or sequential order shown to achieve the desired results. In some embodiments, multitasking and parallel processing can be advantageous.

[0123] The present application is described with reference to the flowcharts and / or block diagrams of the methods according to the embodiments of the present application. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of the processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0124] It should also be noted that the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, commodity or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, commodity or device. In the absence of more restrictions, the elements defined by the sentence "comprises a ..." do not exclude the existence of other identical elements in the process, method, commodity or device including the elements.

[0125] Those skilled in the art should understand that the present application may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present application may take the form of a computer program product implemented on one or more computer storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program codes.

[0126] The various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referenced to each other, and each embodiment focuses on the differences from other embodiments.

[0127] The above are only embodiments of the present application and are not intended to limit the present application. For those skilled in the art, the present application may have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included within the scope of the claims of the present application.

Claims

1. A method for analyzing the instantaneous displacement of cylindrical specimens based on two-dimensional DIC, characterized in that: The method comprises: Placing a cylindrical sample at a test position of a mechanical testing device; wherein a plurality of speckle marks are provided on a circumferential surface of the cylindrical sample; placing a high-speed camera at a shooting position so that the cylindrical sample is located in a shooting area of ​​the high-speed camera; In the process of the mechanical testing equipment performing a mechanical test on the cylindrical specimen, a plurality of original speckle images are obtained by photographing with the high-speed camera; According to the cross-sectional radius value of the cylindrical specimen and the position of the target mark in all the speckle original images, displacement data corresponding to each target mark is obtained; wherein the target mark is one or more of all the speckle marks; and the displacement data is used to characterize the displacement change of the target mark during the mechanical test.

2. The method according to claim 1, characterized in that The step of obtaining displacement data corresponding to each target mark according to the cross-sectional radius value of the cylindrical sample and the position of the target mark in all the original speckle images comprises: Cutting the original speckle image into a plurality of local original images along the height direction; According to a preset image stretching rule, all the local original images are stretched in the height direction to obtain a plurality of local corrected images; Performing splicing processing on all the local correction images to obtain a speckle correction image; The displacement data corresponding to each of the target marks is obtained according to the at least two speckle correction images.

3. The method according to claim 2, characterized in that When the axis of the cylindrical sample is parallel to the length direction of the speckle original image, the stretching process is performed on all the local original images in the height direction according to the preset image stretching rule to obtain a plurality of local corrected images, including: Using the formula Performing stretching processing on all the local original images in the height direction respectively to obtain a plurality of the local corrected images; Among them, r i is the stretching multiple of the i-th local original image in the height direction, and the first local original image is located at the top in the height direction; R is the cross-sectional radius value of the cylindrical specimen, and Δm is the width of the local original image.

4. The method according to claim 2, characterized in that: Before cutting the speckle original image into a plurality of local original images along the height direction, the method further includes: Selecting a first corrected image and a second corrected image from all the speckle original images, and determining positions of a plurality of target marks in the first corrected image and the second corrected image; wherein the positions of the plurality of target marks in the first corrected image and the second corrected image are different; Determining a displacement vector of the target mark according to a position of the target mark in the first corrected image and the second corrected image; Determining an image rotation angle according to a displacement vector of the target marker; According to the image rotation angle, all the original speckle images are rotated.

5. The method according to claim 2, characterized in that: All of the partial original images have the same width.

6. The method according to claim 1, characterized in that The step of obtaining displacement data corresponding to each target mark according to the cross-sectional radius value of the cylindrical sample and the position of the target mark in all the original speckle images comprises: According to the position of the target mark in all the original speckle images, calculating and obtaining the measurement data corresponding to the target mark; According to the image distance and object distance of the high-speed camera during the mechanical test, and the radius of the cylindrical specimen, pseudo-displacement correction is performed on the measurement data corresponding to the target mark to obtain the displacement data corresponding to the target mark.

7. The method according to claim 6, characterized in that The method of performing pseudo-displacement correction on the measurement data corresponding to the target mark according to the image distance and object distance of the high-speed camera during the mechanical test and the radius of the cylindrical specimen to obtain the displacement data corresponding to the target mark includes: Using the formula Performing pseudo-displacement correction on the measurement data corresponding to the target mark to obtain the displacement data corresponding to the target mark; Wherein, ΔD is the displacement value of the target mark; Z is the object distance of the high-speed camera during the mechanical test; L is the image distance of the high-speed camera during the mechanical test; R is the radius of the cylindrical specimen; D S0 D is the coordinate value corresponding to the length direction or height direction of the high-speed camera imaging plane in the original speckle image taken earlier; S1 It is the coordinate value corresponding to the target mark in the length direction or height direction of the imaging plane of the high-speed camera in the original speckle image with a later shooting time.

8. The method according to claim 1, characterized in that The method further comprises: According to the displacement data corresponding to the multiple target marks, the displacement field data and / or strain field data of the cylindrical specimen are calculated using the interpolation method; wherein the displacement field data is used to characterize the displacement change of the cylindrical specimen during the mechanical test; and the strain field data is used to characterize the strain change of the cylindrical specimen during the mechanical test.

9. The method according to claim 1, characterized in that: In the height direction, the upper edge of the area where the cylindrical surface of the cylindrical sample is located is at least partially flush with the upper edge of the speckle original image, and the lower edge of the area where the cylindrical surface of the cylindrical sample is located is at least partially flush with the lower edge of the speckle original image; correspondingly, in the process of performing a mechanical test on the cylindrical sample by the mechanical testing equipment, obtaining a plurality of speckle original images by photographing with the high-speed camera includes: In the process of the mechanical testing equipment performing a mechanical test on the cylindrical specimen, a plurality of original imaging images are obtained by taking pictures with the high-speed camera; The multiple original imaging images obtained by the high-speed camera are cropped to obtain multiple original speckle images.

10. The method according to claim 9, characterized in that The mechanical testing equipment is a Hopkinson torsion bar equipment, and the length direction of the imaging original image is parallel to the axis of the cylindrical sample; the multiple imaging original images obtained by the high-speed camera are cropped to obtain multiple speckle original images, including: Selecting a first original image and a second original image from all the imaging original images, and determining positions of all the target marks in the first original image and the second original image; wherein at least a plurality of the target marks are located in different positions in the first original image and the second original image, and the shooting time of the first original image is earlier than the shooting time of the second original image; Determine the theoretical projection position of the axis of the cylindrical sample in the first original image according to the positions of all the target marks in the first original image and the second original image; According to the theoretical projection position of the axis of the cylindrical sample in the first original image, the radius value of the cylindrical sample, and the ratio value of the size of each pixel point in the imaging original image to the actual size of the cylindrical sample, all the imaging original images are cropped in the height direction to obtain a plurality of the speckle original images.

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