A multi-degree-of-freedom photoelastic model adjusting device and a panoramic force chain network construction and analysis method based on image stitching

Abstract

The application discloses a multi-degree-of-freedom photoelastic model adjusting device and a panoramic force chain network construction analysis method based on image splicing, and the multi-degree-of-freedom photoelastic model adjusting device comprises a bearing platform, a transverse guide rail, a liftable longitudinal guide rail, a loading frame and an optical assembly, wherein the optical assembly comprises a camera, a polarizer, a polarizing mirror and an LED light source, and is all installed on the longitudinal guide rail which can be precisely moved, and the optical path height is consistent. The application realizes the horizontal and vertical multi-degree-of-freedom precise adjustment of the light source, the camera, the polarizing mirror and the polarizer through the movable guide rail, and overcomes the defects that the large-size polarizing mirror and the polarizer must be used in the analysis of the large-size model in the prior art. A plurality of photoelastic fringe images are shot, and a customized splicing algorithm is used to realize panoramic synthesis of the stress fringe images, so that the imaging quality is ensured, the equipment cost and the technical complexity are significantly reduced, and the high-resolution and full-field stress fringe collection of the large-size photoelastic model is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of granular material meso-analysis, in particular to a multi-degree-of-freedom photoelastic model adjusting device and a panoramic force chain network construction analysis method based on image stitching. BACKGROUND

[0002] Photoelastic experiment is a stress measurement method based on optical principles. By analyzing the interference fringes generated by transparent particles under stress conditions, the internal stress distribution of the material can be visualized. Traditional two-dimensional photoelastic experiment devices generally use fixed structures, and the spatial positions of the light source, polarizer, analyzer and camera are relatively fixed. When conducting large-size physical model experiments, in order to obtain complete stress fringe images, large polarizing components are often required, resulting in large equipment size, significant cost increase, and high experimental operation difficulty.

[0003] Image stitching technology is essentially a method of combining multiple images with overlapping areas into one wide-view, high-resolution image. Although it has been widely used in photogrammetry and remote sensing, its application in photoelastic experiments still faces challenges. Since photoelastic fringes are highly sensitive to light source conditions, polarizer angles and camera viewing angles, even slight equipment shifts or angle changes can cause differences in brightness, contrast and phase between images, severely interfering with the identification and matching of stitching features. In addition, there is currently a lack of a high-precision shooting platform that can achieve coordinated movement of optical components and ensure consistent optical paths. Therefore, constructing a panoramic force chain network (a panoramic force chain network refers to reconstructing a force chain structure image network in the full field range by registering and fusing local photoelastic images of a large-size photoelastic model sample collected in different positions through image stitching technology) not only depends on high-precision image processing algorithms, but also requires the cooperation of a supporting optical device and control system to achieve high-quality reconstruction of the global contact force distribution in large-size granular systems.

[0004] Therefore, there is an urgent need in the prior art for a special device and method that can achieve high-precision, high-resolution photoelastic image acquisition of large-size models and maintain lossless stitching of fringe phase information. SUMMARY

[0005] The main purpose of the present application is to provide a multi-degree-of-freedom photoelastic model adjusting device and a panoramic force chain network construction analysis method based on image stitching, aiming to solve the problem of the lack of a high-precision shooting platform that can achieve coordinated movement of optical components and ensure consistent optical paths in the prior art, thereby making it difficult to construct a high-quality panoramic force chain network.

[0006] To achieve the above-mentioned purpose, the present application provides a multi-degree-of-freedom photoelastic model adjusting device, which comprises:

[0007] The load platform, the transverse guide rail, the liftable longitudinal guide rail, the camera, the polarizer, the loading frame, the polarizer, the LED light source, the lens rotation control motor, the data collector, the power switch and the terminal;

[0008] The load platform, the transverse guide rail, the liftable longitudinal guide rail, the camera, the polarizer, the loading frame, the polarizer and the LED light source are arranged on the transverse guide rail, and the polarizer and the polarizer are connected with the lens rotation control motor, the loading frame is connected with the data collector, and the LED light source is connected with the power switch;

[0009] The transverse guide rail and the liftable longitudinal guide rail are used for adjusting the camera, the polarizer, the polarizer and the LED light source, and the loading frame is used for placing the photoelastic sample;

[0010] The camera is used for collecting multiple photoelastic fringe images after the LED light source is turned on, and sending the multiple photoelastic fringe images to the terminal;

[0011] The data collector is used for collecting the load value in the photoelastic test, and sending the load value to the terminal;

[0012] The terminal is used for receiving multiple photoelastic fringe images and load values, and calculating quantitative stress field results according to multiple photoelastic fringe images and load values. Optionally, the multi-degree-of-freedom photoelastic model adjusting device, wherein the surface of the load platform is provided with a regular array of threaded holes for fixing the transverse guide rail;

[0013] Optionally, the multi-degree-of-freedom photoelastic model adjusting device, wherein the surface of the load platform is provided with a regular array of threaded holes for fixing the transverse guide rail;

[0014] The transverse guide rail is distributed along the length direction of the load platform, and is equidistantly arranged in the width direction of the load platform.

[0015] Optionally, the multi-degree-of-freedom photoelastic model adjusting device, wherein the liftable longitudinal guide rail is arranged on the transverse guide rail in the vertical direction, and the liftable longitudinal guide rail can slide horizontally along the transverse guide rail;

[0016] The liftable longitudinal guide rail is divided into upper and lower layers, and the spacing between the upper and lower layers of the liftable longitudinal guide rail is adjusted by manual or electric mode to adapt to samples and optical path requirements of different heights;

[0017] The upper layer of the liftable longitudinal guide rail is provided with the camera and the analyzer, and the lower layer of the liftable longitudinal guide rail is provided with the polarizer and the LED light source.

[0018] Optionally, the multi-degree-of-freedom photoelastic model adjusting device, wherein the vertical scale and the horizontal scale are processed on the surface of the column of the liftable longitudinal guide rail.

[0019] The vertical scale is used for adjusting the installation height of the camera, the analyzer, the polarizer and the LED light source and the distance between the upper and lower layers of the liftable longitudinal guide rail.

[0020] The horizontal scale is used for controlling the horizontal moving distance of the camera, the analyzer, the polarizer and the LED light source.

[0021] Optionally, the multi-degree-of-freedom photoelastic model adjusting device, wherein the loading frame comprises a load sensor, a liftable support, a test model frame and a loading control lever.

[0022] The load sensor is arranged above the test model frame and connected with the data collector, and is used for monitoring and recording the load value in the experiment.

[0023] The liftable support is a movable structure, and is arranged below the test model frame and used for adjusting the position of the test model frame.

[0024] The test model frame is made of double-layer transparent acrylic plates and filled with photoelastic sensitive particle materials in the middle.

[0025] The loading control lever is arranged above the load sensor and used for applying load to the load sensor.

[0026] In addition, in order to achieve the above object, the application further provides a panoramic force chain network construction analysis method based on image stitching based on the multi-degree-of-freedom photoelastic model adjusting device.

[0027] The prepared photoelastic sample is placed in the test model frame, and the test model frame is adjusted to the center of the optical field of view through the liftable support.

[0028] The LED light source is turned on, the optical assembly is moved along the guide rail, and a plurality of overlapped photoelastic fringe images are shot in batches.

[0029] The plurality of photoelastic fringe images are preprocessed to obtain a plurality of preprocessed images, control points are arranged in the overlapping areas of the plurality of preprocessed images, the plurality of preprocessed images are positionally calibrated according to the control points, and a plurality of calibrated images are obtained.

[0030] Performing image transformation and fusion on the plurality of post-calibration images to generate a panoramic force chain network, performing fringe extraction and stress field calculation on the panoramic force chain network to obtain a quantitative stress field result.

[0031] Optionally, the panoramic force chain network construction analysis method based on image stitching, wherein the optical assembly is moved along the guide rail to take multiple photoelastic fringe images with overlapping areas, specifically comprising:

[0032] A plurality of shooting stations are preset, and the optical assembly is positioned at the plurality of shooting stations by adjusting the positions of the liftable longitudinal guide rail and the transverse guide rail;

[0033] The optical assembly includes a camera, an analyzer, a loading frame, a polarizer, and the LED light source, and all the optical components are fixed to the guide rail through rigid connectors;

[0034] At the plurality of shooting stations, the camera is used to take multiple overlapping photoelastic fringe images.

[0035] Optionally, the panoramic force chain network construction analysis method based on image stitching, wherein the optical assembly is positioned at the plurality of shooting stations by adjusting the positions of the liftable longitudinal guide rail and the transverse guide rail, specifically comprising:

[0036] The height of the camera, the analyzer, the polarizer, and the LED light source is adjusted through the vertical scale on the liftable longitudinal guide rail;

[0037] The horizontal movement distance of the camera, the analyzer, the polarizer, and the LED light source is adjusted through the horizontal scale on the transverse guide rail to complete the positioning of the optical assembly at the shooting station.

[0038] Optionally, the panoramic force chain network construction analysis method based on image stitching, wherein the multiple photoelastic fringe images are preprocessed to obtain multiple post-preprocessing images, specifically comprising:

[0039] The multiple photoelastic fringe images taken are imported into a terminal, and a preprocessing script is used to uniformly crop all the photoelastic fringe images to obtain multiple post-cropping images;

[0040] The multiple post-cropping images are subjected to gray scale normalization processing to obtain multiple post-preprocessing images.

[0041] Optionally, the panoramic force chain network construction analysis method based on image stitching, wherein the image transformation and fusion of the plurality of calibrated images are performed to generate a panoramic force chain network, the fringe extraction and stress field calculation are performed on the panoramic force chain network to obtain quantitative stress field results, and specifically include:

[0042] The image transformation and fusion of the plurality of calibrated images are performed based on the control points to generate a panoramic force chain network;

[0043] The fringe numbering and extraction are performed on the panoramic force chain network to obtain fringe extraction results, and load data recorded by a load sensor is acquired;

[0044] According to the fringe extraction results and the load data, the stress distribution inside the photoelastic sample is calculated by using a photoelastic stress analysis algorithm, and quantitative stress field results are output according to the stress distribution.

[0045] In the present application, the multi-degree-of-freedom photoelastic model adjusting device comprises a bearing platform, a transverse guide rail, a liftable longitudinal guide rail, a loading frame and an optical assembly. The optical assembly comprises a camera, an analyzer, a polarizer and an LED light source, and is installed on the longitudinal guide rail which can be precisely moved to ensure the consistency of the optical path height. The present application realizes the horizontal and vertical multi-degree-of-freedom precise adjustment of the light source, the camera, the polarizer and the analyzer through the movable guide rail, and overcomes the defects in the prior art that large-size model analysis must be equipped with large polarizers and analyzers. By shooting multiple photoelastic fringe images and using a customized stitching algorithm to realize panoramic synthesis of the stress fringe images, the imaging quality is ensured while the equipment cost and technical complexity are significantly reduced, and high-resolution and full-field stress fringe collection of large-size photoelastic models is realized. BRIEF DESCRIPTION OF DRAWINGS

[0046] Figure 1 It is a whole structure schematic diagram of a multi-degree-of-freedom photoelastic model adjusting device provided by the embodiment of the present application;

[0047] Figure 2 It is a structure schematic diagram of a model frame and a loading frame of a multi-degree-of-freedom photoelastic model adjusting device provided by the embodiment of the present application;

[0048] Figure 3 It is a side view of a longitudinal liftable guide rail in a multi-degree-of-freedom photoelastic model adjusting device provided by the embodiment of the present application;

[0049] Figure 4 It is a front view of a longitudinal liftable guide rail of a multi-degree-of-freedom photoelastic model adjusting device provided by the embodiment of the present application;

[0050] Figure 5 It is a flowchart of a preferred embodiment of the panoramic force chain network construction analysis method based on image stitching of the present application;

[0051] Figure 6 is a picture instance graph taken at a first station in a panoramic force chain network construction analysis method based on image stitching provided by the embodiment of the application;

[0052] Figure 7 is a picture instance graph taken at a second station in a panoramic force chain network construction analysis method based on image stitching provided by the embodiment of the application;

[0053] Figure 8 is a picture instance graph taken at a third station in a panoramic force chain network construction analysis method based on image stitching provided by the embodiment of the application;

[0054] Figure 9 is a picture instance graph taken at a fourth station in a panoramic force chain network construction analysis method based on image stitching provided by the embodiment of the application;

[0055] Figure 10 is a position schematic diagram of a stitched picture in a whole sample in a panoramic force chain network construction analysis method based on image stitching provided by the embodiment of the application;

[0056] Figure 11 is a picture instance graph after four stitched pictures are stitched in a panoramic force chain network construction analysis method based on image stitching provided by the embodiment of the application.

[0057] The drawings show that: 1, bearing platform; 2, horizontal guide rail; 3, liftable vertical guide rail; 4, camera; 5, polarizer; 6, loading frame; 7, polarizer; 8, LED light source; 9, lens rotation control motor; 10, data collector; 11, power switch; 12, load sensor; 13, liftable support; 14, model frame; 15, loading control rod; 16, vertical direction scale; 17, horizontal direction scale. DETAILED DESCRIPTION

[0058] The present application provides a multi-degree-of-freedom photoelastic model adjusting device and method. To make the purpose, technical scheme and effect of the present application clearer and more explicit, the present application will be further described in detail below with reference to the drawings and examples. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application.

[0059] Those of skill in the art will understand that the herein-enunciated terms, including technical and scientific terms, are used in their ordinary meaning unless otherwise explicitly defined. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0060] In the description of the present application, it needs to be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like is based on the orientation or positional relationship shown in the drawings, and is only for the purpose of facilitating the description of the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application; in addition, if there is a description of "first", "second" and the like in the embodiments of the present application, the description of "first", "second" and the like is only for the purpose of description, and cannot be understood as indicating or implying the relative importance of the indicated technical features or implicitly indicating the number of the indicated technical features. Therefore, the features limited by "first", "second" can be explicitly or implicitly included at least one of the features. In addition, the technical solutions of various embodiments can be combined with each other, but it must be based on the realization of ordinary skilled in the art, when the combination of technical solutions appears contradictory or unachievable, it should be considered that the combination of technical solutions does not exist, nor within the scope of protection required by the present application.

[0061] In the description of the present application, it needs to be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like is based on the orientation or positional relationship shown in the drawings, and is only for the purpose of facilitating the description of the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application; in addition, if there is a description of "first", "second" and the like in the embodiments of the present application, the description of "first", "second" and the like is only for the purpose of description, and cannot be understood as indicating or implying the relative importance of the indicated technical features or implicitly indicating the number of the indicated technical features. Therefore, the features limited by "first", "second" can be explicitly or implicitly included at least one of the features. In addition, the technical solutions of various embodiments can be combined with each other, but it must be based on the realization of ordinary skilled in the art, when the combination of technical solutions appears contradictory or unachievable, it should be considered that the combination of technical solutions does not exist, nor within the scope of protection required by the present application.

[0062] A multi-degree-of-freedom photoelastic model adjusting device provided by the present application, as shown in Figure 1 The multi-degree-of-freedom photoelastic model adjusting device comprises:

[0063] The bearing platform 1, the transverse guide rail 2, the liftable longitudinal guide rail 3, the camera 4, the polarizer 5, the loading frame 6, the polarizer 7, the LED light source 8, the lens rotation control motor 9, the data collector 10 and the power switch 11;

[0064] The horizontal guide rail 2 is laid on the load-bearing platform 1. The liftable vertical guide rail 3 and the loading frame 6 are connected above the horizontal guide rail 2. The camera 4, the analyzer 5, the polarizer 7 and the LED light source 8 are respectively installed on the liftable vertical guide rail 3. The analyzer 5 and the polarizer 7 are connected to the lens rotation control motor 9. The loading frame 6 is connected to the data acquisition device 10. The LED light source 8 is connected to the power switch 11.

[0065] The transverse guide rail 2 and the liftable longitudinal guide rail 3 are used to adjust the camera 4, the analyzer 5, the polarizer 7, and the LED light source 8. The loading frame 6 is used to place the photoelastic sample. The camera 4 is used to acquire multiple photoelastic fringe images after the LED light source 8 is turned on, and send the multiple photoelastic fringe images to the terminal. The data acquisition device is used to acquire the load value in the photoelastic test and send the load value to the terminal. The terminal is used to receive the multiple photoelastic fringe images and the load value, and calculate the quantitative stress field result based on the multiple photoelastic fringe images and the load value.

[0066] In this embodiment, the load-bearing platform 1 is a rigid metal platform with a regularly arrayed array of threaded holes on its surface for mounting and fixing the transverse guide rails 2. Four transverse guide rails 2 are arranged along the entire length of the platform and maintain equal spacing in the width direction to provide a stable horizontal movement reference. The liftable longitudinal guide rail 3 is connected to the transverse guide rails 2 via a slider and can move horizontally along the transverse guide rails. This longitudinal guide rail is divided into upper and lower layers, and the distance between the two layers can be adjusted manually or electrically to accommodate samples of different heights and optical path requirements. The upper layer houses the camera 4 and the analyzer 5, while the lower layer houses the polarizer 7 and the LED light source 8. All optical components are fixed to the guide rails via rigid connectors to ensure that the same optical axis height is maintained throughout the movement.

[0067] Among them, camera 4 is used to capture images (photoelastic fringe images); the analyzer 5 has the same structure as polarizer 7, and its core function is to detect the two polarized beams output by the photoelastic model and convert their optical path difference into visible fringes through interference effect, thereby realizing the visualization of stress distribution; polarizer 7 is the key device for realizing the polarization of light, and its core function is to convert the natural light emitted by the light source into linearly polarized light, that is, light whose electric field vibration direction is fixed in a certain plane, providing excitation conditions for the birefringence effect of the photoelastic model; LED light source 8 is the energy source of the entire photoelastic observation system, and its core function is to provide light radiation with specific optical characteristics, providing the basis for subsequent polarization processing and interference effect.

[0068] Furthermore, the surface of the load-bearing platform 1 is provided with a regular array of threaded holes for fixing the transverse guide rails 2; the transverse guide rails 2 are distributed along the length direction of the load-bearing platform 1 and are equidistantly arranged in the width direction of the load-bearing platform 1 to provide a stable horizontal movement reference.

[0069] The liftable longitudinal guide rail 3 is arranged vertically on the transverse guide rail 2, and the liftable longitudinal guide rail 3 can slide horizontally along the transverse guide rail 2; the liftable longitudinal guide rail 3 is divided into upper and lower layers, and the distance between the upper and lower layers of the liftable longitudinal guide rail 3 can be adjusted manually or electrically to adapt to the requirements of samples of different heights and optical paths; the upper layer of the liftable longitudinal guide rail 3 is equipped with the camera 4 and the analyzer 5, and the lower layer of the liftable longitudinal guide rail 3 is equipped with the polarizer 7 and the LED light source 8.

[0070] It is understandable that all the aforementioned optical components (camera 4, analyzer 5, loading frame 6, polarizer 7, and the LED light source 8) are fixed to the guide rail by rigid connectors in order to ensure that they maintain the same optical axis height during movement.

[0071] Furthermore, the loading frame 6 includes a load sensor 12, a height-adjustable support 13, a test model frame 14, and a loading control lever 15; the load sensor 12 is positioned above the test model frame 14 and connected to the data acquisition unit 10, used to monitor and record the load value during the experiment; the height-adjustable support 13 is a vertically movable structure, positioned below the test model frame 14, used to adjust the position of the test model frame 14; the test model frame 14 is made of double-layer transparent acrylic sheet, with photoelastic sensitive particle material filled in the middle; the loading control lever 15 is positioned above the load sensor 12, used to apply a load to the load sensor 12.

[0072] like Figure 2 As shown, the loading frame 6 is fixed to the central area of ​​the load-bearing platform 1, and has an internal liftable bracket 13 for fixing the test model frame 14. The test model frame 14 is made of double-layer transparent acrylic sheet, with photoelastic sensitive particle material filling the middle. The load sensor 12 is installed on the upper part of the loading frame and connected to the data acquisition unit 10 for real-time monitoring and recording of the load value during the experiment. A loading control lever 15 is also provided above the load sensor 12.

[0073] Furthermore, the surface of the column of the liftable longitudinal guide rail 3 is machined with a vertical scale 16 (e.g., Figure 3 (as shown) and the horizontal scale 17 (as shown) Figure 4(As shown). The vertical scale 16 is used to adjust the installation height of the camera 4, the analyzer 5, the polarizer 7, and the LED light source 8, as well as the distance between the upper and lower rails of the liftable longitudinal guide rail 3; the horizontal scale 17 is used to control the horizontal movement distance of the camera 4, the analyzer 5, the polarizer 7, and the LED light source 8.

[0074] In this embodiment, the column surface of the liftable longitudinal guide rail 3 is precision-machined with horizontal and vertical scales for accurately positioning the height and horizontal position of the optical components. The horizontal scale is used to control the horizontal movement distance of the camera 4, analyzer 5, polarizer 7, and LED light source 8, while the vertical scale is used to precisely adjust the installation height of each optical component and the distance between the two guide rails.

[0075] Furthermore, the lens rotation control motor 9 is connected to the analyzer 5 and the polarizer 7 respectively, and is used to precisely control the angle of the polarizer in the experiment in order to obtain fringe images under different polarization states.

[0076] Furthermore, such as Figure 5 As shown, based on the aforementioned multi-degree-of-freedom photoelastic model adjustment device, this invention also provides a panoramic force chain network construction and analysis method based on image stitching, wherein the panoramic force chain network construction and analysis method based on image stitching includes:

[0077] S10. Place the prepared photoelastic sample into the test model frame, and adjust the test model frame to the center of the optical field of view using the liftable bracket.

[0078] Specifically, the prepared photoelastic sample (made of a material with stress birefringence properties, it is a model used to analyze stress distribution in photoelasticity experiments) is placed in the test model frame of the loading frame, and the height of the test model frame is adjusted by a height-adjustable bracket so that the photoelastic sample in the test model frame is at the center of the optical field of view. This helps to ensure that light can pass through the sample uniformly and that the light path will not be changed due to the offset of the sample. This ensures that the propagation and interference of light during the experiment can proceed in the expected manner, making the experimental results repeatable and comparable.

[0079] S20. Turn on the LED light source, move the optical components along the guide rail, and capture multiple overlapping photoelastic stripe images in segments.

[0080] Understandably, before moving the optical components along the guide rail, the process includes adjusting the angles of the polarizer 7 and the analyzer 5 to initially observe the fringe formation. The purpose is to establish a stable polarization interference optical path, confirm that the fringes can form normally and are clearly distinguishable, and provide a reliable observational basis for subsequent quantitative analysis steps such as measuring the fringe order and calculating stress values.

[0081] After confirming that the stripes can be formed normally and are clearly distinguishable, press the power switch 11 to turn on the LED light source 8 and provide incident light.

[0082] Furthermore, the optical component moving along the guide rail captures multiple photoelastic fringe images with overlapping areas in segments, specifically including:

[0083] Multiple shooting positions are pre-set, and the optical components are positioned at the multiple shooting positions by adjusting the positions of the liftable longitudinal guide rail 3 and the transverse guide rail 2.

[0084] The optical components include: camera 4, analyzer 5, loading frame 6, polarizer 7 and LED light source 8. All optical components are fixed to the guide rail by rigid connectors.

[0085] Multiple overlapping photoelastic stripe images are captured in segments by the cameras at various shooting positions.

[0086] It is understood that the optical components are precisely positioned sequentially at multiple preset shooting positions via the horizontal guide rail 2 and the liftable vertical guide rail 3 (the number of preset positions is set by the user; in this embodiment, it is four). For example... Figure 6-9 As shown, in this embodiment, four partially overlapping photoelastic stripe images were captured from the photoelastic sample in the loading frame 6 using the camera. Each image ensured an overlap area of ​​30% to 40%, and all optical elements maintained their height aligned with the optical path throughout the imaging process.

[0087] The loading frame 6 is fixed to the central area of ​​the load-bearing platform 1, and has a liftable bracket 13 inside for fixing the test model frame 14. The load sensor 12 is used to monitor and record the load value in real time during the experiment. A loading control lever 15 is also provided above the load sensor 12 for applying load to the load sensor 12.

[0088] Furthermore, the step of adjusting the positions of the liftable longitudinal guide rail 3 and the transverse guide rail 2 to fix the optical components at multiple shooting positions specifically includes:

[0089] The heights of the camera 4, the analyzer 5, the polarizer 7, and the LED light source 8 can be adjusted using the vertical scale 16 on the liftable longitudinal guide rail 3.

[0090] The horizontal movement distance of the camera 4, the analyzer 5, the polarizer 7, and the LED light source 8 is adjusted by using the horizontal scale 17 on the horizontal guide rail 2 to complete the positioning of the optical components at the shooting station.

[0091] In this embodiment, after turning on the LED light source 8 and adjusting the angles of the polarizer 7 and analyzer 5 to initially observe the formation of the stripes, the camera 4, analyzer 5, polarizer 7 and LED light source 8 are precisely adjusted to the same preset height according to the vertical scale of the liftable longitudinal guide rail 3 to ensure the optical path is collimated; and the movement distance of the transverse guide rail 2 is controlled by the horizontal scale 17 to achieve precise positioning of the optical components.

[0092] S30. Preprocess the multiple photoelastic stripe images to obtain multiple preprocessed images. Set control points in the overlapping area of ​​the multiple preprocessed images. Perform position calibration on the multiple preprocessed images according to the control points to obtain multiple calibrated images.

[0093] The step of preprocessing multiple photoelastic stripe images to obtain multiple preprocessed images specifically includes:

[0094] The captured multiple photoelastic stripe images are imported into the terminal, and a preprocessing script is used to uniformly crop all the photoelastic stripe images to obtain multiple cropped images.

[0095] Multiple cropped images are subjected to grayscale normalization to obtain multiple preprocessed images.

[0096] In this embodiment, multiple photosynthetic stripe images are imported into a terminal (computer). A preprocessing script written in Python is used to uniformly crop all the photosynthetic stripe images, remove irrelevant backgrounds, and obtain multiple cropped images. The images are then aligned and grayscale normalized to reduce brightness differences caused by uneven lighting, resulting in multiple preprocessed images.

[0097] Furthermore, control points are set within the overlapping area of ​​multiple preprocessed images. Since multiple preprocessed images often have positional deviations due to factors such as shooting angle and device displacement, it is necessary to first find the overlapping area they all cover. Within this area, control points with clear features and corresponding positions in each image are selected. By calculating the coordinate differences of these points, the transformation relationship between the images is determined, thereby correcting the image positions and completing precise calibration. Taking four images as an example, control point pairs are manually set within the overlapping area of ​​the four images. This manual or automatic setting of control point pairs within the overlapping area completes the positional calibration between the images.

[0098] S40. Perform image transformation and fusion on multiple calibrated images to generate a panoramic force chain network. Perform stripe extraction and stress field calculation on the panoramic force chain network to obtain quantitative stress field results.

[0099] Specifically, an image registration and fusion algorithm is performed on multiple calibrated images to ultimately generate a schematic diagram of the position of the stitched image within the overall sample. Figure 10It can be seen that the method of the present invention successfully synthesizes four partial images (a, b, c, and d) into a complete panoramic image. For example... Figure 11 As shown, an example image of the graphic after stitching four images is presented. This seamless, high-resolution full-field stress fringe pattern effectively avoids stitching misalignment and phase information distortion. The fringes are continuous and natural, providing a high-quality data foundation for subsequent stress analysis.

[0100] Furthermore, the step of performing image transformation and fusion on multiple calibrated images to generate a panoramic force chain network, and then performing fringe extraction and stress field calculation on the panoramic force chain network to obtain quantitative stress field results, specifically includes:

[0101] Based on the control points, image transformation and fusion are performed on multiple calibrated images to generate a panoramic force chain network.

[0102] The panoramic force chain network is numbered and extracted to obtain the stripe extraction results, and the load data recorded by the load sensor is obtained.

[0103] Based on the stripe extraction results and the load data, the stress distribution inside the photoelastic sample is calculated using a photoelastic stress analysis algorithm, and a quantitative stress field result is output based on the stress distribution.

[0104] In this embodiment, a spatial transformation model is constructed based on control points, and multiple calibrated images are uniformly mapped to the same coordinate system to achieve accurate registration. Subsequently, a multi-resolution fusion algorithm is used to integrate the stress information of the registered images, eliminate stitching gaps and grayscale differences, and finally generate a complete and continuous panoramic force chain network, clearly presenting the stress transmission path and distribution characteristics across the entire domain.

[0105] In the quantitative analysis phase of the photoelastic experiment, the previously generated panoramic force chain network first needs to be refined. Using digital image processing technology, fringe center extraction algorithms (such as grayscale centroid method and skeleton extraction method) are employed to identify and number the interference fringes in the panoramic force chain network one by one. Taking the zero-order fringe (where the stress difference is zero) as a benchmark, the fringe numbers of each order are sequentially labeled according to the density and distribution pattern of the fringe. Simultaneously, the pixel coordinates, direction, and grayscale characteristics of each fringe are recorded, forming a complete fringe extraction result, providing intuitive optical feature basis for subsequent stress calculations.

[0106] Simultaneously, load data recorded in real-time by the load sensor during the experiment is retrieved. This data must precisely correspond to the acquisition time of the fringe image and cover key parameters such as load peak value, stable value, and loading rate at different stages of the loading process, ensuring that the load conditions for stress analysis are clear and traceable. Based on the above fringe extraction results and load data, the core algorithm for photoelastic stress analysis is used for calculation: according to the stress-light law, the optical path difference corresponding to the fringe number is converted into the principal stress difference at each point of the sample; the boundary stress conditions are determined by combining the load data, and the magnitude and direction of the principal stress are solved by the stress balance equation and geometric equation. After correcting the calculation error through iterative optimization algorithm, a quantitative stress field result containing the stress value of each pixel and the principal stress direction angle is finally generated, which can be output in the form of color cloud map, contour map, etc., clearly quantifying the stress distribution characteristics inside the photoelastic sample.

[0107] In summary, this invention provides a multi-degree-of-freedom photoelastic model adjustment device and a panoramic force chain network construction and analysis method based on image stitching. The multi-degree-of-freedom photoelastic model adjustment device comprises a load-bearing platform, a transverse guide rail, a liftable longitudinal guide rail, a loading frame, and optical components. The optical components include a camera, an analyzer, a polarizer, and an LED light source, all mounted on a precisely movable longitudinal guide rail to ensure consistent optical path height. This invention achieves precise horizontal and vertical multi-degree-of-freedom adjustment of the light source, camera, polarizer, and analyzer through a movable guide rail, overcoming the shortcomings of existing technologies that require large polarizers and analyzers for large-size model analysis. By capturing multiple photoelastic fringe images and employing a customized stitching algorithm to achieve panoramic synthesis of stress fringe images, the invention significantly reduces equipment costs and technical complexity while ensuring imaging quality. It achieves high-resolution, full-field stress fringe acquisition for large-size photoelastic models, effectively avoiding image distortion and phase distortion. It offers advantages such as high flexibility, convenient operation, and high data processing accuracy, making it suitable for the study of the micromechanical behavior of granular materials in the field of geotechnical mechanics.

[0108] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or terminal that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or terminal. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or terminal that includes that element.

[0109] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A multi-degree-of-freedom photoelastic model adjustment device, characterized in that, The multi-degree-of-freedom photoelastic model adjustment device includes: a load-bearing platform, a transverse guide rail, a liftable longitudinal guide rail, a camera, a polarizer, a loading frame, a polarizer, an LED light source, a lens rotation control motor, a data acquisition unit, a power switch, and a terminal. The horizontal guide rail is laid on the load-bearing platform. The liftable vertical guide rail and the loading frame are connected above the horizontal guide rail. The camera, the analyzer, the polarizer and the LED light source are respectively installed on the liftable vertical guide rail. The analyzer and the polarizer are connected to the lens rotation control motor. The loading frame is connected to the data acquisition unit. The LED light source is connected to the power switch. The horizontal guide rail and the adjustable vertical guide rail are used to adjust the camera, the analyzer, the polarizer, and the LED light source; the loading frame is used to place the photoelastic sample. The camera is used to capture multiple photoelastic stripe images after the LED light source is turned on, and to send the multiple photoelastic stripe images to the terminal; The data acquisition device is used to collect the load values ​​in the photoelastic test and send the load values ​​to the terminal; The terminal is used to receive multiple photoelastic fringe images and the load value, and calculate a quantitative stress field result based on the multiple photoelastic fringe images and the load value; The liftable longitudinal guide rail is arranged vertically on the transverse guide rail, and the liftable longitudinal guide rail can slide horizontally along the transverse guide rail. The liftable longitudinal guide rail is divided into upper and lower layers. The distance between the upper and lower layers of the liftable longitudinal guide rail can be adjusted manually or electrically to adapt to the requirements of samples of different heights and optical paths. The camera and the analyzer are mounted on the upper layer of the liftable longitudinal guide rail, and the polarizer and the LED light source are mounted on the lower layer of the liftable longitudinal guide rail. The vertical column surface of the liftable longitudinal guide rail is machined with a vertical scale and a horizontal scale. The vertical scale is used to adjust the installation height of the camera, the analyzer, the polarizer, and the LED light source, as well as the distance between the upper and lower rails of the liftable longitudinal guide rail. The horizontal scale is used to control the horizontal movement distance of the camera, the analyzer, the polarizer, and the LED light source.

2. The multi-degree-of-freedom photoelastic model adjustment device according to claim 1, characterized in that, The surface of the load-bearing platform is provided with a regularly arranged array of threaded holes for fixing the transverse guide rail; The transverse guide rails are distributed along the entire length of the load-bearing platform and are equidistantly arranged along the width of the load-bearing platform.

3. The multi-degree-of-freedom photoelastic model adjustment device according to claim 1, characterized in that, The loading frame includes a load sensor, a liftable support, a test model frame, and a loading control lever; The load sensor is positioned above the test model frame and connected to the data acquisition unit to monitor and record the load values ​​during the experiment. The liftable support is a structure that can move up and down. The liftable support is located below the test model frame and is used to adjust the position of the test model frame. The test model frame is made of double-layer transparent acrylic sheet, with photoelastic sensitive particle material filling the middle. The loading lever is positioned above the load sensor and is used to apply a load to the load sensor.

4. A panoramic force chain network construction and analysis method based on image stitching for a multi-degree-of-freedom photoelastic model adjustment device according to any one of claims 1-3, characterized in that, The panoramic force chain network construction and analysis method based on image stitching includes: The prepared photoelastic sample is placed in the test model frame, and the test model frame is adjusted to the center of the optical field of view using a liftable bracket; Turn on the LED light source, move the optical components along the guide rail, and capture multiple overlapping photoelastic stripe images in segments. Multiple photoelastic stripe images are preprocessed to obtain multiple preprocessed images. Control points are set in the overlapping area of ​​the multiple preprocessed images. The positions of the multiple preprocessed images are calibrated according to the control points to obtain multiple calibrated images. Multiple calibrated images are transformed and fused to generate a panoramic force chain network. Stripe extraction and stress field calculation are performed on the panoramic force chain network to obtain quantitative stress field results.

5. The panoramic force chain network construction and analysis method based on image stitching according to claim 4, characterized in that, The optical component that moves along the guide rail captures multiple photoelastic stripe images with overlapping areas in segments, specifically including: Multiple shooting positions are pre-set, and the optical components are positioned at each of the multiple shooting positions by adjusting the positions of the liftable longitudinal guide rail and the transverse guide rail. The optical components include: a camera, an analyzer, a loading frame, a polarizer, and the LED light source. All optical components are fixed to the guide rail by rigid connectors. Multiple overlapping photoelastic stripe images are captured in segments by the cameras at various shooting positions.

6. The panoramic force chain network construction and analysis method based on image stitching according to claim 5, characterized in that, The step of adjusting the positions of the liftable longitudinal and transverse guide rails to fix the optical components at the multiple shooting positions specifically includes: The height of the camera, the analyzer, the polarizer, and the LED light source can be adjusted using a vertical scale on the adjustable longitudinal guide rail; The horizontal movement distance of the camera, analyzer, polarizer, and LED light source is adjusted by using a horizontal scale on the transverse guide rail to complete the positioning of the optical components at the shooting station.

7. The panoramic force chain network construction and analysis method based on image stitching according to claim 4, characterized in that, The step of preprocessing multiple photoelastic stripe images to obtain multiple preprocessed images specifically includes: The captured multiple photoelastic stripe images are imported into the terminal, and a preprocessing script is used to uniformly crop all the photoelastic stripe images to obtain multiple cropped images. Multiple cropped images are subjected to grayscale normalization to obtain multiple preprocessed images.

8. The panoramic force chain network construction and analysis method based on image stitching according to claim 4, characterized in that, The process of transforming and fusing multiple calibrated images to generate a panoramic force chain network, and then performing stripe extraction and stress field calculation on the panoramic force chain network to obtain quantitative stress field results, specifically includes: Based on the control points, image transformation and fusion are performed on multiple calibrated images to generate a panoramic force chain network. The panoramic force chain network is numbered and extracted to obtain the stripe extraction results, and the load data recorded by the load sensor is obtained. Based on the stripe extraction results and the load data, the stress distribution inside the photoelastic sample is calculated using a photoelastic stress analysis algorithm, and a quantitative stress field result is output based on the stress distribution.

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