Dynamic multi-physics field measurement experimental system based on embedded grating photoelastic model

Abstract

The present application provides a dynamic multi-physics field measurement experimental system based on an embedded grating photoelastic model. In the system, a photoelastic model that simultaneously satisfies the requirements of high-speed dynamic photoelastic stress measurement and moire deformation measurement is used to generate time series images through a circularly polarized dark field optical path; an axial load and a dynamic load are applied to the photoelastic model through a vertical loading device and a dynamic loading device in a loading unit, respectively; the vibration signal of the photoelastic model is collected through a vibration sensor in a synchronization unit, and the pulse light source and the image acquisition unit are simultaneously triggered by a synchronization trigger to collect the time series images generated by the circularly polarized dark field optical path. In this way, the time series images generated by the photoelastic model that simultaneously satisfies the requirements of high-speed dynamic photoelastic stress measurement and moire deformation measurement are used to eliminate the mutual interference in the photoelastic and moire measurements, realize the simultaneous measurement of stress field, displacement field, and strain field, and overcome the difficulties in multi-physics field measurement in the prior art.

Description

Technical Field

[0001] The present application relates to the field of rock mass disaster technology, and in particular to a dynamic multi-physics field measurement experimental system based on an embedded grating photoelastic model. Background Art

[0002] Quantitative characterization of the multi-physical field effects of rock mass disasters is the key to revealing the dynamic failure mechanism of rock masses and is of great significance to the scientific understanding of many disasters (such as earthquakes, rock bursts, etc.).

[0003] At present, the rock mass disaster process is mainly studied through laboratory models. In recent years, the combination of optical full-field measurement techniques such as photoelasticity, digital image correlation, and moiré method with high-speed photography technology has provided conditions for quantitatively characterizing the mechanical behavior of rock mass disasters. For example, high-speed photography technology combined with photoelasticity and digital image correlation methods has achieved the measurement of dynamic stress field and deformation field respectively.

[0004] However, current experiments are mostly aimed at measuring a single stress field or deformation field, and it is difficult to achieve simultaneous measurement of multiple physical fields. During rock mass disasters, physical fields such as stress, strain, vibration, energy, and velocity evolve simultaneously. Therefore, simultaneous measurement of multi-physical field information of rock mass disasters and intuitive quantitative characterization of the multi-physical field effects of rock mass disasters are key technical problems that need to be solved urgently. Summary of the invention

[0005] The purpose of the present application is to provide a dynamic multi-physics field measurement experimental system based on an embedded grating photoelastic model to solve or alleviate the problems existing in the above-mentioned prior art.

[0006] In order to achieve the above objectives, this application provides the following technical solutions:

[0007] The present application provides a dynamic multi-physics field measurement experimental system based on an embedded grating photoelastic model, comprising: an optical path unit, wherein the optical path unit comprises: a photoelastic model, a pulse light source, a first convex lens, a polarizer, a first quarter glass slide, a second quarter glass slide, an analyzer, and a second convex lens arranged along the same straight line direction; wherein the pulse light source and the second convex lens are respectively located on both sides of the photoelastic model, and the first convex lens, the polarizer, and the first quarter glass slide are arranged in sequence between the pulse light source and the photoelastic model; and the second quarter glass slide is arranged in sequence between the photoelastic model and the second convex lens. A glass slide, the analyzer; a loading unit, the loading unit comprising a vertical loading device and a dynamic loading device, the vertical loading device is used to apply an axial load to the photoelastic model; the dynamic loading device is used to apply a dynamic load to the photoelastic model; an image acquisition unit, the image acquisition unit is used to acquire time series images of the photoelastic model under the action of the dynamic load; a synchronization unit, the synchronization unit comprising a vibration sensor and a synchronization trigger, the vibration sensor is used to acquire the vibration signal of the photoelastic model and send it to the synchronization trigger, so that the synchronization trigger can simultaneously trigger the pulse light source and the image acquisition unit.

[0008] Preferably, the photoelastic model includes a single light-transmitting layer and a composite light-transmitting layer, the single light-transmitting layer and the composite light-transmitting layer are bonded together as a whole, and the composite light-transmitting layer is provided with a light-transmitting grating structure; wherein the single light-transmitting layer is opposite to the first quarter glass slide, the composite light-transmitting layer is opposite to the second quarter glass slide, and the single light-transmitting layer and the composite light-transmitting layer have the same elastic modulus and Poisson's ratio, as well as consistent photoelastic effect.

[0009] Preferably, the thickness range of the photoelastic model is [5, 10] mm, and the thickness range of the composite light-transmitting layer is [0.1, 0.5] mm.

[0010] Preferably, the image acquisition unit is located on the optical path of the convex lens and directly faces the convex lens.

[0011] Beneficial effects:

[0012] In the dynamic multi-physics field measurement experimental system based on the embedded grating photoelastic model provided in the embodiment of the present application, a pulse light source, a first convex lens, a polarizer, a first quarter glass slide, a photoelastic model, a second quarter glass slide, an analyzer and a second convex lens are arranged in sequence along the same straight line to form an optical path unit of a circularly polarized dark field optical path; an axial load is applied to the photoelastic model through a vertical loading device, and a dynamic load is applied to the photoelastic model through a dynamic loading device; a vibration signal of the photoelastic model is collected by a vibration sensor and sent to a synchronization trigger, which simultaneously triggers the pulse light source and the image acquisition unit, and the pulse light source emits a laser pulse, which passes through the prefabricated photoelastic model in the circularly polarized dark field optical path, and finally forms a time series image under the action of the dynamic load, and the time series image under the action of the dynamic load is collected by the image acquisition unit; further, the collected time series images are processed to realize simultaneous analysis of the stress field, displacement field and strain field.

[0013] Therefore, by utilizing a photoelastic model that can simultaneously measure stress using high-speed dynamic photoelastic method and deformation using moiré method, a time series image is generated through a circularly polarized dark-field optical path. Only one acquired photoelastic fringe image is needed to quantitatively extract the stress field, displacement field, and strain field inside the photoelastic model under dynamic loads, and obtain the full-field stress, displacement, and strain. This effectively overcomes the problem that previous test systems only measured a single physical field, and solves the difficult problem of simultaneous measurement of dynamic full-field stress and strain. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The drawings constituting part of the present application are used to provide a further understanding of the present application. The exemplary embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. Among them:

[0015] Figure 1 A schematic diagram of the principle of a dynamic multi-physics field measurement experimental system based on an embedded grating photoelastic model according to some embodiments of the present application;

[0016] Figure 2 A schematic diagram of the structure of a photoelastic model provided according to some embodiments of the present application;

[0017] Figure 3 To use Figure 1 The logic diagram of the dynamic multi-physics field measurement experimental system based on the embedded grating photoelastic model for high-speed dynamic multi-physics field synchronous measurement of the photoelastic model is shown.

[0018] Description of reference numerals:

[0019] 1. Pulse light source; 2. First convex lens; 3. Polarizer; 4. First quarter glass slide; 5. Photoelastic model; 6. Second quarter glass slide; 7. Analyzer; 8. Second convex lens; 9. Loading unit; 10. Synchronization unit; 11. Image acquisition unit. DETAILED DESCRIPTION

[0020] The present application will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments. Each example is provided by way of explanation of the present application and does not limit the present application. In fact, it will be clear to those skilled in the art that modifications and variations may be made in the present application without departing from the scope or spirit of the present application. For example, a feature shown or described as a part of an embodiment may be used in another embodiment to produce yet another embodiment. Therefore, it is desired that the present application includes such modifications and variations within the scope of the appended claims and their equivalents.

[0021] The complex structure inside natural rock mass leads to an extremely complex distribution of internal stress field. In order to analyze this complex stress field in detail, there are problems such as the coexistence of elastic-plastic stress field and the difficulty in deriving all stress components, which makes the demand for simultaneous characterization of stress field and strain field increasingly high. However, the current high-speed dynamic measurement of rock mass disasters is mainly aimed at a single stress field or deformation field, and the commonly used methods for measuring dynamic stress field or strain field are mainly photoelasticity, digital image correlation, and moiré method. The photoelasticity method intuitively reflects the distribution of full-field stress through the photoelastic stripes inside its loaded model, which is an intuitive and efficient full-field stress characterization method. The digital image correlation method tracks the changes in the spatial position of the speckle through the correlation function and calculates the displacement field and strain field. The moiré method reflects the full-field deformation information through the change of the regular grid phase.

[0022] Since the carriers required for photoelastic stress field measurement and digital image correlation method or moire method deformation measurement are inconsistent, the speckle in digital image correlation method and the grid structure in moire method will interfere with the photoelastic fringes, making it difficult to accurately measure the stress field; at the same time, the photoelastic fringes will also interfere with the speckle and grating, making it difficult to accurately measure the deformation field. Therefore, it is difficult to achieve simultaneous measurement of multiple physical fields.

[0023] Based on this, the present application designs and produces a test model that can simultaneously meet the requirements of high-speed dynamic photoelastic stress measurement and moiré deformation measurement. By combining high-speed photoelastic stress measurement, high-speed image acquisition and synchronous control, a photoelastic fringe image containing a grating structure is collected. Furthermore, the stress field, displacement field and strain field inside the test model under the action of dynamic loads can be quantitatively extracted through the photoelastic fringe processing containing the grating, thus overcoming the difficulty of simultaneous measurement of multiple physical fields in the prior art and realizing the simultaneous measurement of multiple physical fields of rock mass disasters under high-speed dynamic conditions, making the measurement results more accurate and efficient.

[0024] like Figures 1 to 3 As shown, the dynamic multi-physics field measurement experimental system based on the embedded grating photoelastic model includes: an optical path unit, a loading unit 9, an image acquisition unit 11 and a synchronization unit 10. Among them, the optical path unit uses the photoelastic model 5 that satisfies both the high-speed dynamic photoelastic stress measurement and the moiré deformation measurement, and generates time series images through the circular polarized dark field optical path; the axial load and the dynamic load are applied to the photoelastic model 5 through the vertical loading device and the dynamic loading device in the loading unit 9 respectively; the vibration signal of the photoelastic model 5 is collected through the vibration sensor in the synchronization unit 10, and the pulse light source 1 and the image acquisition unit 11 are triggered simultaneously by the synchronization trigger, and the image acquisition unit 11 collects the time series images generated by the circular polarized dark field optical path.

[0025] In the present application, the optical path unit includes: a pulse light source 1, a first convex lens 2, a polarizer 3, a first quarter glass slide, a photoelastic model 5, a second quarter glass slide, an analyzer 7 and a second convex lens 8 arranged in sequence along the same straight line direction; that is, the pulse light source 1 and the second convex lens 8 are respectively located on both sides of the photoelastic model 5, and the first convex lens 2, the polarizer 3 and the first quarter glass slide 4 are arranged in sequence between the pulse light source 1 and the photoelastic model 5; the second quarter glass slide 6 and the analyzer 7 are arranged in sequence between the photoelastic model 5 and the second convex lens 8.

[0026] The vertical loading device can be a uniaxial testing machine or a uniaxial press, and the photoelastic model 5 is placed on the loading platform of the vertical loading device. The downward pressing head of the vertical loading device directly loads the photoelastic model 5 to apply an axial load to the photoelastic model 5. The applied load is controlled by the servo motor of the vertical loading device to provide constant load and constant displacement boundary conditions for the photoelastic model 5. At the same time, the dynamic loading device can be an impact system such as a light gas gun, a Hopkinson bar or a heavy hammer to apply a dynamic load to the photoelastic model 5. Among them, the vertical loading device and the dynamic loading device apply an axial load and a dynamic load to the photoelastic model in the vertical direction and the horizontal direction respectively.

[0027] In a specific example, the dynamic loading device uses a horizontal light gas gun for impact loading, in which a high pressure chamber, a gun barrel connected to the high pressure chamber, and a projectile detachably arranged at the free end of the gun barrel are provided. The high pressure gas chamber provides power, so that the projectile indirectly impacts the photoelastic model 5 through the loading platform at a preset impact speed, thereby realizing dynamic loading of the photoelastic model 5.

[0028] The image acquisition unit 11 is located on the circularly polarized dark field optical path, that is, directly facing the convex lens on the optical path of the convex lens, so as to acquire time series images of the photoelastic model 5 under the action of dynamic load. Specifically, a high-speed camera can be used, and the camera is set on the straight line from the pulse light source 1 to the convex lens, and the high-speed camera is located near the focus of the convex lens to ensure that the image focused by the convex lens can be clearly imaged on the high-speed camera.

[0029] The synchronization unit 10 includes a vibration sensor and a synchronization trigger. The vibration sensor is electrically connected to the synchronization trigger, and the vibration sensor is located on the photoelastic model 5. Based on the on-off principle of the vibration sensor, the vibration signal of the photoelastic model 5 is collected. Specifically, the vibration sensor is arranged close to the impact loading point to ensure that the vibration signal can be captured in the first time when the impact loading is performed, and the on-off signal is generated to realize the generation of the trigger electrical signal and send it to the synchronization trigger. The synchronization trigger simultaneously triggers the pulse light source 1 and the image acquisition unit 11, so that the pulse light source 1 emits a laser pulse and the image acquisition unit 11 is started, thereby realizing high-speed image acquisition of the photoelastic model 5 under dynamic load.

[0030] In the present application, the pulse light source 1 can adopt a laser pulse light source 1, a monochromatic light pulse light source 1 or a white light pulse light source 1, and the divergent light emitted by the pulse light source 1 is adjusted to collimated light through the first convex lens 2; a projection photoelastic light path is formed by a polarizer 3, a first quarter glass slide 4, a photoelastic model 5, a second quarter glass slide, and an analyzer 7, and the photoelastic light path is adjusted to a circularly polarized dark field or a bright field, so that under this light path, the photoelastic fringe order directly corresponds to the principal stress difference (that is, the difference between the first principal stress and the second principal stress in material mechanics); the collimated light is focused by the second convex lens 8 so that it can be collected by a high-speed camera.

[0031] In the present application, the photoelastic model 5 includes a single light-transmitting layer (base layer) and a composite light-transmitting layer (grating layer), the single light-transmitting layer and the composite light-transmitting layer are bonded together as a whole, and the composite light-transmitting layer is provided with a light-transmitting grating structure. Specifically, the single light-transmitting layer and the composite light-transmitting layer have the same elastic modulus and Poisson's ratio, as well as consistent photoelastic effect, so as to simultaneously meet the requirements of high-speed dynamic photoelastic stress measurement and moiré deformation measurement, that is, through a collected photoelastic fringe image, the stress field, displacement field, and strain field inside the photoelastic model 5 can be simultaneously measured.

[0032] In the present application, the single light-transmitting layer and the composite light-transmitting layer of the photoelastic model 5 can be prepared by 3D printing technology, or a light-transmitting grating structure can be directly processed on the surface of the photoelastic model 5. The single light-transmitting layer adopts a material, and the composite light-transmitting layer adopts a translucent material to ensure that the grating of the composite light-transmitting layer can be clearly identified by a high-speed camera. The overall thickness range of the photoelastic model 5 is [5,10] mm, and the thickness range of the composite light-transmitting layer is [0.1,0.5] mm. Preferably, the thickness range of the composite light-transmitting layer is [0.3,0.5] mm, so that the light emitted by the pulse light source 1 can pass through the photoelastic model 5, and the grating layer can be clearly distinguished from the base layer, effectively ensuring that the grating structure can be clearly captured during image acquisition, while meeting the requirements of high-speed dynamic photoelastic stress measurement and moiré deformation measurement.

[0033] After the time series images of the photoelastic model are collected by the dynamic multi-physics field measurement experiment system based on the embedded grating photoelastic model through any of the above-mentioned embodiments, first, the collected time series images containing the grating under the circularly polarized dark field light path are Fourier transformed to obtain the spectrum diagram corresponding to the time series image; then, the positive and negative first-order spectra in the spectrum diagram corresponding to the time series image are deleted; and the spectrum diagram without the positive and negative first-order spectra is inverse Fourier transformed to obtain the time series image without the grating.

[0034] Next, according to the cosine function relationship between the evolution curve of a single pixel in the time series and the fringe order in the time series image without grating, the fringe order corresponding to the photoelastic fringe is calculated, and based on the law of stress optics, the stress field corresponding to the photoelastic fringe order is calculated.

[0035] Specifically, based on the multiple full-field stress fringe grayscale images that change continuously, the grayscale value change series of the pixel points at each position in the image is obtained, and the grayscale values ​​of the pixels at the same position on the multiple full-field stress fringe grayscale images that change continuously are extracted to form the grayscale value change series of the pixel points. The grayscale value change series of the pixel points at each position is converted into a change curve, and the average value of the peaks and troughs in the change curve is calculated; according to the number of troughs below the average value, the integer part of the fringe level of the pixel point at the corresponding position is obtained. According to the cosine function relationship between the change curve y and the decimal part x of the fringe level:

[0036] y=I b +I a (1-cosδ),

[0037] The decimal part of the fringe level of each pixel is calculated. b is the background light intensity, I a is the light intensity of the light source, and δ is the optical path difference.

[0038] The relationship between the optical path difference δ and the fringe order n is:

[0039]

[0040] Then, based on the law of stress optics, the full-field fringe order is multiplied by the optical fringe constant to calculate the stress field corresponding to the photoelastic fringe order.

[0041] At the same time, the grating image of the superimposed photoelastic stripes is filtered using windows of [1, p / 2] and [p / 2, 1] respectively to obtain unidirectional gratings distributed horizontally (x direction) and vertically (y direction). The unidirectional gratings are sampled using a sampling interval equal to the grating intercept p, and the sampled data are interpolated using the spline interpolation method to generate sampled moiré. Then, according to the formula:

[0042]

[0043] Calculate the wrapped phase of the time series image corresponding to the photoelastic model 5. Among them, is the wrapping phase in the y direction of the mth time series image corresponding to the photoelastic model 5, I m is the light intensity of the circularly polarized dark field light path corresponding to the mth time series image, p is the grating pitch in the photoelastic model 5; m is the image sequence number of the time series image, i is the moiré image sequence number of the sampled moiré formed by interpolation, and both m and i are positive integers.

[0044] Then, the wrapped phase of the time series image is unwrapped to determine the phase change of the time series image corresponding to the photoelastic model 5. Specifically, the calculated wrapped phase of the time series image corresponding to the photoelastic model 5 is a discontinuous phase of [0, 2π]. By unwrapping the wrapped phase, the continuous phase of the time series image corresponding to the photoelastic model 5 is obtained. At the same time, the image before deformation is processed in the same way (i.e., the grid structure before deformation is sampled and analyzed to obtain the phase before deformation), and the phase after deformation is subtracted from the phase before deformation to obtain the phase corresponding to the displacement field of the time series image of the photoelastic model 5, i.e., the phase change.

[0045] Specifically, the operation in step S103 is performed on the stripes after horizontal (x direction) and vertical (y direction) filtering, respectively, to obtain the horizontal (x direction) and vertical (y direction) phase changes, respectively. Then, the horizontal (x direction) and vertical (y direction) phase changes are divided by 2π and multiplied by the grating pitch p of the photoelastic model 5, respectively, to obtain the horizontal (x direction) and vertical (y direction) displacement fields and strain fields, respectively.

[0046] Finally, based on the least squares method, a fixed window is selected, assuming that the window contains (2n+1) 2 displacement point data, (2n+1)2 The displacement data points are fitted into a plane, and the coefficients of the fitted plane equation are solved. Some coefficients directly correspond to the normal strain and shear strain in the plane problem, and then the full-field strain of the time series image corresponding to the photoelastic model 5 is calculated.

[0047] It should be noted that the calculations of the stress field and the displacement field corresponding to the time series images of the photoelastic model 5 do not have a sequential order relationship and can be performed synchronously.

[0048] Thus, by using the photoelastic model 5 that meets the requirements of high-speed dynamic photoelastic stress measurement and moire deformation measurement, a collected photoelastic fringe image containing a grating is used to eliminate the mutual interference in the photoelastic and moire measurements, and to achieve simultaneous measurement of the stress field, displacement field, and strain field inside the photoelastic model 5, thus overcoming the difficulty of multi-physics field measurement in the prior art. Moreover, the dynamic multi-physics field measurement experimental system based on the embedded grating photoelastic model proposed in this application can be used for simultaneous measurement of dynamic stress field and deformation field of complex models.

[0049] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A dynamic multi-physics field measurement experimental system based on an embedded grating photoelastic model, characterized in that: include: An optical path unit, the optical path unit comprising: a photoelastic model, a pulse light source, a first convex lens, a polarizer, a first quarter glass slide, a second quarter glass slide, an analyzer and a second convex lens arranged along the same straight line direction; wherein the pulse light source and the second convex lens are respectively located on both sides of the photoelastic model, and the first convex lens, the polarizer and the first quarter glass slide are arranged in sequence between the pulse light source and the photoelastic model; the second quarter glass slide and the analyzer are arranged in sequence between the photoelastic model and the second convex lens; wherein the photoelastic model comprises a single light-transmitting layer and a composite light-transmitting layer, the single light-transmitting layer and the composite light-transmitting layer are bonded as a whole, and the composite light-transmitting layer is provided with a light-transmitting grating structure; the single light-transmitting layer is opposite to the first quarter glass slide, the composite light-transmitting layer is opposite to the second quarter glass slide, the single light-transmitting layer and the composite light-transmitting layer have the same elastic modulus and Poisson's ratio, and consistent photoelastic effect; the thickness range of the photoelastic model is , and the thickness range of the composite light-transmitting layer is ; A loading unit, the loading unit comprising a vertical loading device and a dynamic loading device, the vertical loading device is used to apply an axial load to the photoelastic model; the dynamic loading device is used to apply a dynamic load to the photoelastic model; An image acquisition unit, the image acquisition unit is used to acquire time series images generated by the photoelastic model under a dynamic load to simultaneously meet stress measurement and strain measurement; A synchronization unit, wherein the synchronization unit includes a vibration sensor and a synchronization trigger. The vibration sensor is located on the photoelastic model and is arranged close to the impact loading point. The vibration sensor is used to collect the vibration signal of the photoelastic model and send it to the synchronization trigger, so that the synchronization trigger can simultaneously trigger the pulse light source and the image acquisition unit.

2. The dynamic multi-physics field measurement experimental system based on the embedded grating photoelastic model according to claim 1 is characterized in that: The vibration sensor collects the vibration of the photoelastic model to generate an on-off signal, and sends the on-off signal to the synchronization trigger.

3. The dynamic multi-physics field measurement experimental system based on the embedded grating photoelastic model according to claim 1 is characterized in that: The image acquisition unit is located on the optical path of the convex lens and faces the convex lens.

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