Temperature field and deformation field synchronous measurement method and system

Abstract

The invention relates to a temperature field and deformation field synchronous measurement system and method based on laser speckle DIC and temperature field algorithm temperature measurement. The system comprises a 3CCD color camera, a lens, a three-band filter, a monochromatic light source, a mechanical support adjusting platform, a triangular support and a computer. A test piece is actively illuminated by blue laser, and a color image containing three channel sub-images of red, green and blue on the surface of a high-temperature sample before and after deformation is acquired by a 3CCD color camera. A temperature field algorithm is used for analyzing sub-images of the R channel and the G channel after deformation to calculate a temperature field of the surface of the test piece, and a digital image correlation method is used for analyzing sub-images of the B channel before and after deformation to obtain a strain field of the surface of the test piece, so that synchronous measurement of the temperature field and the deformation field of the surface of the test piece is realized. The principle is simple, the system structure is compact, temperature field measurement is not interfered by speckles, and non-contact, high-precision and synchronous measurement of a material deformation field and a temperature field under the action of force and thermal loads can be achieved.

Description

Technical Field

[0001] The present invention relates to a measurement method and a system thereof, and in particular to a temperature field deformation field synchronous measurement method and system based on laser speckle DIC and temperature field algorithm temperature measurement, belonging to the fields of optical measurement mechanics, high-temperature object surface deformation testing, and material high-temperature mechanical property testing technology. Background Art

[0002] Hypersonic vehicles have become a strategic development direction that major aerospace powers in the world are focusing on. With the substantial increase in the designed flight speed of hypersonic vehicles, their service environment has become increasingly harsh, which has brought new challenges to the safe service of hypersonic vehicles. Therefore, it is urgent to increase the investment in ground assessment and test capabilities of hypersonic vehicles and continue to promote the development of basic scientific research and technology in extreme environments. At present, the accurate characterization of the mechanical properties of high-temperature resistant materials and structures of hypersonic vehicles in extreme high-temperature environments is still a difficult problem in ground assessment and testing. Traditional contact deformation and temperature measurement methods, such as high-temperature strain gauges and thermocouples, can only measure the deformation and temperature of some points on the surface of the specimen. At the same time, the temperature and deformation sensors attached to the surface of the specimen will interfere with the actual temperature and deformation distribution of the surface of the specimen, resulting in the measurement value being unable to reflect the actual parameter distribution. In recent years, non-contact deformation and temperature measurement methods, such as three-dimensional digital correlation technology and infrared temperature measurement, have the problem of mutual interference. Therefore, in laboratory testing of hypersonic vehicle materials or structures, it is urgent to develop a high-precision non-contact measurement method that can simultaneously measure high-temperature deformation field and temperature field. This will enable the acquisition of richer and more comprehensive real experimental data for ground aerodynamic thermal environment simulation thermal tests.

[0003] When using digital image correlation method for deformation measurement, in order to ensure high-precision image matching, it is necessary to first obtain a stable and high-quality image sequence of the specimen surface during the experiment. However, in high-temperature deformation measurement, due to the significant increase in thermal radiation on the specimen surface, the image captured by the camera will gradually become saturated. When the temperature exceeds 600 degrees Celsius, the randomly distributed features in the captured image will weaken or even disappear, which will lead to de-correlation effect in digital image correlation matching.

[0004] In order to use the digital image correlation method to measure deformation at high temperatures over 600°C, Pan et al. invented a digital image correlation method combined with monochromatic blue light active imaging, which can isolate the influence of most thermal radiation on the specimen surface on imaging, thereby ensuring the acquisition of high-quality image sequences under high temperature conditions. Based on this method, Pan et al. achieved high-quality speckle image acquisition and deformation field measurement under high temperature conditions of 1200°C.

[0005] Based on the existing high-temperature full-field deformation and temperature measurement technology, a variety of high-temperature full-field temperature and deformation synchronous measurement methods have been developed in recent years. In 2014, R Montanini et al. proposed and discussed a new method for determining the thermal expansion coefficient of rigid solid materials. This method is called infrared image correlation (IIC), which is based on DIC between thermal images obtained by an infrared camera at different temperatures. In 2021, Guo et al. proposed a new calibration method to calibrate the internal and external parameters of infrared cameras and visible light cameras, and measured and reconstructed the temperature field and strain field on the surface of the sample. However, the above studies all require the production of randomly distributed high-temperature speckles on the surface of the sample. Due to the different emissivity of the high-temperature speckle material and the specimen material, there is a large error in the measured temperature. Summary of the invention

[0006] In order to solve the problem that the existing technology cannot meet the synchronous measurement of temperature field and deformation field of thermal-mechanical coupled deformation of materials under high temperature environment, the present invention proposes a synchronous measurement method of temperature field and deformation field based on laser speckle DIC and temperature field algorithm temperature measurement, which can realize non-contact, high-precision and synchronous measurement of deformation field and temperature field of materials under force and thermal loads. It has the advantages of wide application range, easy use of measurement system, high measurement accuracy, simple and compact system structure, etc.

[0007] The technical solution adopted by the present invention to solve the technical problem is: a temperature field and deformation field synchronous measurement system based on laser speckle D IC and temperature field algorithm temperature measurement includes a 3CCD color camera, a lens, a three-band filter, a monochromatic light source, a mechanical support adjustment platform, a tripod and a computer;

[0008] The 3CCD color camera is used to collect clear images of the surface of the test piece under high temperature conditions, and transmit the collected images to the computer in real time.

[0009] The three-band filter is used to filter the light into three narrow bands of R, G and B, which are collected by three channels of the 3CCD color camera respectively.

[0010] The monochromatic light source is a blue laser light source, and the laser is irradiated onto the surface of the object to be measured after being expanded and collimated.

[0011] The mechanical support platform is used to support the 3CCD color camera. By adjusting the mechanical support platform, six degrees of freedom can be adjusted in three directions and three angles in space, thereby adjusting the optical axis of the 3CCD color camera to be perpendicular to the area of ​​interest on the surface of the test piece and obtaining an image of the test piece.

[0012] The tripod support is used to support the 3CCD color camera and can also roughly adjust the height of the 3CCD color camera.

[0013] The computer is used to process the image data collected by the 3CCD color camera to obtain the strain and temperature data of the test piece surface.

[0014] The present invention also discloses a method for synchronously measuring temperature field and deformation field based on laser speckle DIC and temperature field algorithm temperature measurement;

[0015] 1) Place the test piece in front of the test system;

[0016] 2) Install a three-band filter in front of the lens, use a blue laser light source to actively illuminate the test piece, and adjust the 3CCD color camera to make the image clear;

[0017] 3) Using a 3CCD color camera to collect digital images containing three channel sub-images of R, G, and B on the surface of the test piece before and after deformation;

[0018] 4) The sub-images of the three channels R, G, and B are transferred to the computer. The temperature field of the surface of the test piece can be calculated by analyzing the sub-images of the R and G channels after deformation using the temperature field algorithm. The strain field of the sample surface can be obtained by analyzing the sub-images of the B channel before and after deformation using the digital image correlation method, thereby realizing the synchronous measurement of the temperature field and deformation field of the sample surface.

[0019] Beneficial Effects

[0020] 1. Use a three-band filter combined with a 3CCD color camera to collect sub-images of the R, G, and B channels of the test piece surface before and after deformation. The three-band filter only allows light of a specific band to enter the camera, and the camera RGB response spectrum has no overlap between the three channels, so it can effectively avoid crosstalk between the channels.

[0021] 2. The sub-images of the three channels of the 3CCD color camera are collected at the same time. The temperature field on the surface of the test piece can be calculated by analyzing the sub-images of the R channel and the G channel after deformation using the temperature field algorithm. The strain field on the surface of the sample can be obtained by analyzing the sub-images of the B channel before and after deformation using the digital image correlation method. Therefore, the temperature field and strain field data of the test piece at the same time can be measured using only one 3CCD color camera.

[0022] 3. Since there is no need to create artificial speckles on the sample surface, the interference of speckles on non-contact temperature measurement is avoided, and the accuracy of temperature measurement is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the system structure of the present invention;

[0024] Figure 2 The figure is a schematic diagram of the filtering rate of the three-band filter at different wavelengths. The three-band filter only allows light of a specific band to enter the camera, and the camera RGB response spectrum has no overlap between the three channels, so it can effectively avoid crosstalk between the channels;

[0025] Figure 3 The schematic diagram of the implementation process of the present invention is that the sample surface is irradiated with a blue laser to generate speckles to avoid the influence of artificial speckles. The sub-images of the three channels of the 3CCD color camera are collected at the same time. The temperature field of the surface of the test piece can be calculated by analyzing the sub-images of the R channel and the G channel after deformation using the temperature field algorithm. The strain field of the surface of the sample can be obtained by analyzing the sub-images of the B channel before and after deformation using the digital image correlation method. Therefore, the temperature field and strain field data of the test piece at the same time can be measured using only one 3CCD color camera;

[0026] In the figure: 1. 3CCD color camera; 2. lens; 3. three-band filter; 4. blue laser light source; 5. mechanical support adjustment platform; 6. tripod bracket; 7. computer. DETAILED DESCRIPTION

[0027] To make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be described in detail below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other implementation methods obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention.

[0028] like Figure 1As shown, the present invention performs synchronous measurement of temperature field and deformation field based on laser speckle DIC and temperature field algorithm, and the system comprises a 3CCD color camera (1); a lens (2); a three-band filter (3); a monochromatic light source (4); a mechanical support adjustment platform (5); a tripod (6) and a computer (7). The 3CCD color camera (1) is used to collect a clear image of the surface of the test piece under high temperature conditions, and transmit the collected image to the computer (7) in real time; the three-band filter (2) is used to filter light into three bands of light, which are collected by three channels of the 3CCD color camera (1) respectively; the monochromatic light source (4) is a blue laser light source; the mechanical support platform (5) is used to support the 3CCD color camera (1), and by adjusting the mechanical support platform (5), adjustment of six degrees of freedom in three directions and three angles in space can be achieved, thereby adjusting the optical axis of the 3CCD color camera (1) to be perpendicular to the area of ​​interest on the surface of the test piece, and obtaining an image of the test piece; the tripod bracket (6) is used to support the 3CCD color camera (1), and can also roughly adjust the height of the 3CCD color camera (1); the computer (7) is used to process the image data collected by the 3CCD color camera (1) to obtain real-time high-precision strain and temperature data of the test piece.

[0029] Embodiment 1

[0030] A temperature field and deformation field synchronous measurement system based on laser speckle DIC and temperature field algorithm temperature measurement, comprising a 3CCD color camera (1), a lens (2), a three-band filter (3), a monochromatic light source (4), a mechanical support adjustment platform (5), a tripod (6) and a computer (7);

[0031] The 3CCD color camera (1) is used to collect clear images of the surface of the test piece under high temperature conditions, and transmit the collected images to the computer (7) in real time.

[0032] The three-band filter (2) is used to filter light into three bands of light, which are respectively collected by three channels of the 3CCD color camera (1).

[0033] The monochromatic light source (4) is a blue laser light source.

[0034] The mechanical support platform (5) is used to support the 3CCD color camera (1). By adjusting the mechanical support platform (5), adjustment of a total of six degrees of freedom in three directions and three angles in space can be achieved, thereby adjusting the optical axis of the 3CCD color camera (1) to be perpendicular to the area of ​​interest on the surface of the test piece, and obtaining an image of the test piece.

[0035] The tripod support (6) is used to support the 3CCD color camera (1), and can also roughly adjust the height of the 3CCD color camera (1).

[0036] The computer (7) is used to process the image data collected by the 3CCD color camera (1) to obtain real-time high-precision strain and temperature data of the test piece.

[0037] Embodiment 2

[0038] A method for synchronously measuring temperature field and deformation field based on laser speckle DIC and temperature field algorithm temperature measurement, the method is based on the synchronous measurement system for temperature field and deformation field described in embodiment 1, and comprises the following steps:

[0039] 1) Place the high temperature test piece to be tested right in front of the test system;

[0040] 2) Install a three-band filter (3) in front of the lens (2), actively illuminate the test piece with a monochromatic light source (4), and adjust the 3CCD color camera (1) to make the image clear;

[0041] 3) using a 3CCD color camera (1) to collect sub-images of three channels, R, G, and B, of the surface of the test piece before and after deformation;

[0042] 4) The sub-images of the three channels R, G, and B are transferred to the computer. The temperature field of the surface of the test piece can be calculated by analyzing the sub-images of the R and G channels after deformation using the temperature field algorithm. The strain field of the surface of the specimen can be obtained by analyzing the sub-images of the B channel before and after deformation using the digital image correlation method.

[0043] The temperature field algorithm includes the following contents: the temperature field algorithm determines the temperature of the object to be measured by measuring the spectral radiation ratio at wavelengths corresponding to the two channels R and G of the 3CCD color camera (1);

[0044] According to the relationship between the spectral radiation emittance M0 of the object and the wavelength λ and temperature T, the formula is:

[0045]

[0046] Where C1=3.742×10 -16 W·m 2 is the first radiation constant; C2=1.4388×10 -2 m·K is the second radiation constant, and e is a natural constant with a value of approximately 2.718281828459045.

[0047] The spectral radiation emittance M of a gray body with an emissivity of ε(λ) on the photosensitive element of a 3CCD camera ccd for:

[0048]

[0049] where τ a (λ) and τ0(λ) are the spectral transmittances of the atmosphere and the optical system respectively, D is the aperture of the optical system, and f' is the focal length of the optical system.

[0050] The relationship between the grayscale U measured by the camera and the received spectral radiation emittance is as follows:

[0051] U=R(λ)AM ccd (λ)

[0052] Where R(λ) is the grayscale response coefficient of the camera's photosensitive element, and A is the area of ​​the camera's photosensitive element.

[0053] Then, the grayscale ratio K(T) of the wavelength corresponding to the R and G channels of the 3CCD color camera (1) can be obtained as:

[0054]

[0055] Assume that the experimental object is a gray body, that is, ε(λ) is a constant. In addition, because the light path is short during the temperature measurement experiment, the atmospheric spectral transmittance τ a (λ) can be approximately considered to be 1.

[0056] After simplification, the ratio K(T) of the dual-wavelength signal is:

[0057]

[0058] in, It is only related to 3CCD color cameras and can be obtained through black body furnace calibration. After the system is calibrated, the grayscale ratio of the R and G channels of the 3CCD color camera (1) can be measured to obtain the temperature of the object to be measured.

[0059] The principle of the digital image correlation method is as follows: after acquiring the digital image of the sample surface before and after deformation of the B channel of the 3CCD color camera, in order to obtain the image displacement of a certain calculation point, it is first necessary to select a square reference image sub-area centered at the calculation point in the reference image, and search for the deformed image sub-area with the greatest similarity to its grayscale distribution in the deformed image.

[0060] In order to quantitatively calculate the similarity between the reference image sub-region and the corresponding deformed image sub-region, a suitable objective function is defined; the objective function used is the zero-mean normalized sum of squared difference (ZNSSD) function; for the reference image sub-region centered at point (x0, y0) in the reference image, its objective function can be written as:

[0061]

[0062] Where: f(x,y) represents the gray value at the midpoint (x,y) of the reference image sub-region, g(x',y') represents the gray value at the midpoint (x',y') of the deformed image sub-region, and is the average grayscale value of the reference and deformed image sub-regions; p = (u, u x ,u y ,v,v x ,v y ) T is the deformation parameter vector of the point to be calculated. Assuming that the coordinates (x, y) in the reference image sub-region and the position (x', y') in the deformed image sub-region are described by a first-order shape function, then:

[0063]

[0064] Here: u, v are the displacements of the center of the image sub-region in the x and y directions, Δx, Δy are the distances from point (x, y) to the center point (x0, y0) of the image sub-region, and u x ,u y ,v x ,v y is the first-order displacement gradient.

[0065] Using the algorithm to calculate C ZNSSD (p) The minimum value of p is the actual displacement of the calculation point. After obtaining the full-field displacement, the full-field strain can be obtained by differential. In the present invention, a blue laser light source is used to irradiate the surface to produce speckles, thereby avoiding the influence of artificial speckles on the sample. The three-band filter used in the present invention only allows light of a specific band to enter the camera, and the camera RGB response spectrum has no overlap between the three channels, so it can effectively avoid crosstalk between the channels and improve the accuracy of temperature measurement. In the present invention, the sub-images of the three channels of the 3CCD color camera are collected at the same time. The temperature field of the surface of the test piece can be calculated by analyzing the sub-images of the R channel and the G channel after deformation using the temperature field algorithm. The strain field of the surface of the sample can be obtained by analyzing the sub-images of the B channel before and after deformation using the digital image correlation method. Therefore, only one 3CCD color camera can be used to measure the temperature field and strain field data of the test piece at the same time, reducing the experimental cost and avoiding the problem of synchronous matching of temperature and displacement fields during multi-camera measurement.

[0066] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions only describe the principles of the present invention. The present invention may be subject to various changes and improvements without departing from the spirit and scope of the present invention. These changes and improvements fall within the scope of the present invention. The scope of protection claimed by the present invention is defined by the attached claims and their equivalents.

Claims

1. A temperature field and deformation field synchronous measurement system is a temperature field and deformation field synchronous measurement system based on laser speckle DIC and temperature field algorithm temperature measurement, characterized by: It comprises a 3CCD color camera (1), a lens (2), a three-band filter (3), a monochromatic light source (4), a mechanical support adjustment platform (5), a tripod (6) and a computer (7); The 3CCD color camera (1) is used to collect clear images of the surface of the test piece under high temperature conditions, and transmit the collected images to the computer (7) in real time; The three-band filter (3) is used to filter the light into three narrow bands of R, G and B, which are respectively collected by three channels of the 3CCD color camera (1); The monochromatic light source (4) is a blue laser light source, and the laser is irradiated onto the surface of the object to be measured after beam expansion and collimation, so as to generate laser speckles that can be collected by the B channel of the 3CCD color camera (1); The mechanical support platform (5) is used to support the 3CCD color camera (1). By adjusting the mechanical support platform (5), adjustment of six degrees of freedom in three directions and three angles in space can be achieved, thereby adjusting the optical axis of the 3CCD color camera (1) to be perpendicular to the area of ​​interest on the surface of the test piece, and obtaining an image of the test piece; The tripod support (6) is used to support the 3CCD color camera (1), and can also roughly adjust the height of the 3CCD color camera (1); The computer (7) is used to process the image data collected by the 3CCD color camera (1) to obtain the strain and temperature data of the test piece surface.

2. A method for synchronously measuring temperature field and deformation field based on laser speckle DIC and temperature field algorithm temperature measurement, the method is based on the synchronous measurement system for temperature field and deformation field according to claim 1, and is characterized by: The following steps are involved: 1) Place the test piece in front of the test system; 2) Install a three-band filter (3) in front of the lens (2), actively illuminate the test piece with a blue laser light source (4), and adjust the 3CCD color camera (1) to make the image clear; 3) using a 3CCD color camera (1) to collect digital images containing three channel sub-images of R, G, and B on the surface of the test piece before and after deformation; 4) The sub-images of the three channels R, G, and B are transferred to the computer. The temperature field of the surface of the test piece can be calculated by analyzing the sub-images of the R and G channels after deformation using the temperature field algorithm. The strain field of the sample surface can be obtained by analyzing the sub-images of the B channel before and after deformation using the digital image correlation method, thereby realizing the synchronous measurement of the temperature field and deformation field of the sample surface.

3. The method for synchronously measuring temperature field and deformation field based on laser speckle DIC and temperature field algorithm temperature measurement according to claim 2, characterized in that: The temperature field algorithm includes the following contents: determining the temperature of the object to be measured by measuring the spectral radiation ratio at wavelengths corresponding to the two channels R and G of the 3CCD color camera (1); According to the relationship between the spectral radiation emittance M0 of the object and the wavelength λ and temperature T, the formula is: Where C1=3.742×10 -16 W·m 2 is the first radiation constant; C2=1.4388×10 -2 m·K is the second radiation constant, e is the natural constant, and its value is about 2.718281828459045; The spectral radiation emittance M of a gray body with an emissivity of ε(λ) on the photosensitive element of a 3CCD camera ccd for: where τ a (λ) and τ0(λ) are the spectral transmittances of the atmosphere and the optical system, respectively, D is the aperture of the optical system, and f′ is the focal length of the optical system; The relationship between the grayscale U measured by the camera and the received spectral radiation emittance is as follows: U=R(λ)AM ccd (l) Where R(λ) is the grayscale response coefficient of the camera's photosensitive element, and A is the area of ​​the camera's photosensitive element; The grayscale ratio K(T) of the wavelength corresponding to the R and G channels of the 3CCD color camera (1) is obtained as follows: Assume that the experimental object is a gray body, that is, ε(λ) is a constant. In addition, because the light path is short during the temperature measurement experiment, the atmospheric spectral transmittance τ a (λ) can be approximately considered to be 1; After simplification, the ratio K(T) of the dual-wavelength signal is: in, It is only related to the 3CCD color camera and is obtained through blackbody furnace calibration. After the system is calibrated, the grayscale ratio of the R and G channels of the 3CCD color camera (1) can be measured to obtain the temperature of the object to be measured.

4. The method for synchronously measuring temperature field and deformation field based on laser speckle DIC and temperature field algorithm temperature measurement according to claim 2, characterized in that: The digital image correlation method is as follows: after acquiring the digital images of the sample surface before and after deformation of the B channel of the 3CCD color camera, in order to obtain the image displacement of a certain calculation point, firstly, a square reference image sub-area centered at the calculation point is selected in the reference image, and the deformed image sub-area with the greatest similarity to its grayscale distribution in the deformed image is searched; In order to quantitatively calculate the similarity between the reference image sub-region and the corresponding deformed image sub-region, a suitable objective function is defined; the objective function used is the zero-mean normalized sum of squared difference (ZNSSD) function; for the reference image sub-region centered at point (x0, y0) in the reference image, its objective function is written as: Where: f(x, y) represents the gray value at the midpoint (x, y) of the reference image sub-region, g(x', y') represents the gray value at the midpoint (x', y') of the deformed image sub-region, and is the average grayscale value of the reference and deformed image sub-areas; p = (u, u x ,u y ,v,v x , v y ) T is the deformation parameter vector of the point to be calculated. Assuming that the coordinates (x, y) in the reference image sub-region and the position (x′, y′) in the deformed image sub-region are described by a first-order shape function, then: Here: u, v are the displacements of the center of the image sub-region in the x and y directions, Δx, Δy are the distances from point (x, y) to the center point (x0, y0) of the image sub-region, and u x ,u y , v x , v y is the first-order displacement gradient; Using the algorithm to calculate C ZNSSD (p) The minimum value of p is the actual displacement of the calculation point. After obtaining the full-field displacement, the full-field strain can be obtained by differential calculation.

5. A non-volatile storage medium, characterized in that: The non-volatile storage medium includes a stored program, wherein when the program is executed, the device where the non-volatile storage medium is located is controlled to execute the method according to any one of claims 2 to 4.

6. An electronic device, characterized in that: It comprises a processor and a memory; the memory stores computer-readable instructions, and the processor is used to execute the computer-readable instructions, wherein the computer-readable instructions execute any method described in claims 2-4 when executed.

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