A system and method for measuring energy release rate of a moving crack under explosive loading

Abstract

This invention relates to a measurement system and method for the energy release rate of a moving crack under explosive loading, belonging to the field of explosion dynamics. The system includes: a cold light source, a speckle target surface, an electric translation stage, a specimen, a fixture, an explosive charge, a multi-channel timing delay controller, a pulse igniter, a high-speed camera, a camera bracket, and a computer. It employs a combination of digital gradient sensitive photometry and explosion dynamics testing techniques. A high-speed camera captures images of the speckle target surface behind the acrylic glass specimen under explosive loading. Digital gradient sensitive photometry measures the light deflection angle distribution near the tip of the moving crack in the acrylic glass specimen, thereby measuring the dynamic energy release rate of the moving crack. This method eliminates the tedious process of counting photoelastic fringes, simplifying the experimental steps, making the crack tip easier to identify, and providing reliable results. Compared to traditional methods, a crack propagation rate correction coefficient is added, making the experimental results more accurate.

Description

Technical Field

[0001] This invention relates to the field of explosion dynamics, and in particular to a system and method for measuring the energy release rate of a moving crack under explosive loading. Background Technology

[0002] With the significant increase in highly explosive special working conditions across various industries, the service environment of some critical load-bearing structures is becoming increasingly extreme and complex. The crack propagation characteristics and dynamic failure mechanisms within structures under explosive loads are crucial scientific foundations for predicting structural residual strength and assessing structural safety. Currently, the determination of crack tip fracture parameters under explosive loads mainly utilizes strain gauge measurement technology and optical measurement techniques such as photoelasticity, digital speckle correlation, and caustic line analysis. Strain gauge measurement requires attaching strain gauges for each measurement, making the testing process complex, and the results are affected by the accuracy of strain gauge attachment. Photoelasticity requires counting fringe levels for each measurement, making the process cumbersome. Optical measurement techniques such as digital speckle correlation and caustic line analysis have low accuracy in identifying crack tips, affecting the accuracy of crack propagation rate testing. Digital gradient sensing technology is a novel optical measurement technique based on the analysis of light deflection angles near stress singular fields to obtain information on the strain gradient field and fracture parameters at the crack tip. There is an urgent need to develop a system and method combining digital gradient sensing optical measurement technology and explosion dynamics testing technology to more conveniently detect the fracture parameters of moving cracks under explosive loads. Summary of the Invention

[0003] The purpose of this invention is to provide a measurement system and method for the energy release rate of moving cracks under explosive loading. By combining digital gradient sensitive optical measurement technology and explosion dynamics testing technology, it is possible to accurately measure the energy release rate of single or multiple explosive moving cracks at different times.

[0004] To achieve the above objectives, the present invention provides the following solution:

[0005] A measurement system for the energy release rate of a moving crack under explosive loading, the measurement system comprising:

[0006] 4. Speckle target surface;

[0007] Cold light source 2 is used to emit light and illuminate the speckle target surface 4;

[0008] Translation stage 6;

[0009] Specimen 9;

[0010] The clamp 7 is movably mounted on the translation stage 6, and the clamp 7 is used to fix the specimen 9;

[0011] The explosive charge 8 is fixed on the test piece 9;

[0012] The pulse igniter 11 is connected to the explosive charge 8;

[0013] High-speed camera 14 is used to photograph the speckle target surface 4;

[0014] A multi-channel timing delay controller 10 is connected to the pulse igniter 11 and the high-speed camera 14, and is used to send trigger signals to the pulse igniter 11 and the high-speed camera 14.

[0015] Computer 16, connected to the translation stage 6 and high-speed camera 14, is used to calculate the energy release rate of the moving crack under explosive load.

[0016] Optionally, the specimen 9 is an acrylic plate with a central borehole, and the explosive charge 8 is installed inside the central borehole of the acrylic plate specimen.

[0017] Optionally, the measurement system further includes:

[0018] Light source bracket 3, target surface support 5, and camera bracket 15;

[0019] The cold light source 2, the speckle target surface 4, and the high-speed camera 14 are sequentially fixed on the light source bracket 3, the target surface support 5, and the camera bracket 15.

[0020] Optionally, the translation stage 6 is an electric translation stage, and the clamp 7 moves up, down, left, and right within the electric translation stage 6.

[0021] Optionally, the measurement system further includes:

[0022] DC power supply 1 and the cold light source 2 are used to supply power to the cold light source 2;

[0023] Signal line 12 is connected to the pulse igniter 11;

[0024] The enameled wire 13 is connected at one end to the signal wire 11 and at the other end to the explosive charge 8.

[0025] Optionally, the cold light source 2 includes: a first cold light source and a second cold light source.

[0026] Optionally, the center of the speckle target 4, the center of the specimen 9, and the lens of the high-speed camera 14 are located on the same main optical axis.

[0027] Based on the system described above in this invention, this invention further provides a method for measuring the energy release rate of a moving crack under explosive loading. The method is applied to the aforementioned measurement system and includes:

[0028] Spray black and white paint spots onto the surface of speckle target 4;

[0029] The specimen 9 is fixed on the fixture 7 so that the surface of the specimen 9 is parallel to the speckle target surface 4;

[0030] The test specimen 9 was loaded with explosives and connected.

[0031] Turn on the DC power supply 1 and illuminate the surface of the speckle target 4 with the cold light source 2;

[0032] Adjust the optical path of the experimental system and aim the lens of the high-speed camera 14 at the speckle target surface behind the specimen 9;

[0033] Adjust the position and focal length of the lens of the high-speed camera 14 so that the paint spots on the speckle target surface 4 form a clear image in the center of the high-speed camera 14.

[0034] The multi-channel timing delay controller 10 sends a trigger signal, which transmits one of the signals to the pulse igniter 11 and the other trigger signal to the high-speed camera 14, thereby controlling the timing synchronization of the pulse igniter 11 and the high-speed camera 14.

[0035] After receiving an external trigger signal, the pulse igniter 11 generates an instantaneous high voltage to cause the explosive to detonate, and the high-speed camera 14 takes pictures continuously after receiving the external trigger signal.

[0036] After the explosive is detonated, one or more cracks are induced and propagated in the plexiglass plate specimen. The light deflection displacement field on the speckle target surface near the tip of the moving crack at different times is calculated by computer, and the light deflection angles in the X and Y directions are obtained by digital gradient sensitive photometry.

[0037] The energy release rate of the moving crack under explosive load is calculated based on the light deflection angle information of the test point located on the crack extension line.

[0038] Optionally, the formula for calculating the energy release rate of the moving crack under the explosive load is as follows:

[0039]

[0040] Among them, G T Let I be the energy release rate of the moving cracks under explosive loading, I be the total number of moving cracks caused by the explosive loading, E be the elastic modulus of the plexiglass specimen, and β be the energy release rate of the moving cracks under explosive loading. i Let φ be the angle between the extension line of the i-th moving crack and the X direction, M and N be the crack propagation velocity correction coefficients, and φ be the angle between the extension line of the i-th moving crack and the X direction. 0i and φ 90i These represent the light deflection angles in the X and Y directions at the test point on the speckle target surface, respectively.

[0041] Optionally, the expressions for the crack propagation rate correction coefficients M and N are as follows:

[0042]

[0043]

[0044] Where B and C are the thickness and elastic optical constants of the plexiglass specimen, respectively; ρ and ν are the density and Poisson's ratio of the plexiglass material, respectively; and V... i Let α be the propagation velocity of the i-th moving crack. d and α s To match the propagation speed V of the i-th crack i Relevant dynamic coefficients.

[0045] According to specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0046] The digital gradient sensing technology used in this invention is a novel non-contact optical measurement technology. Compared with traditional optical measurement technologies such as photoelasticity, digital speckle correlation, and caustic lines, the testing steps are more convenient and simpler, and the crack tip is easier to identify accurately. For the measurement of the energy release rate of moving cracks under explosive loads, this invention adds a crack propagation rate correction coefficient compared with traditional methods, making the experimental results more accurate. Attached Figure Description

[0047] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0048] Figure 1 This is a schematic diagram of the structure of the measurement system for the energy release rate of a moving crack under explosive loading according to the present invention.

[0049] Figure 2 This is a schematic diagram of the structure of the method for measuring the energy release rate of a moving crack under explosive loading according to the present invention.

[0050] Figure 3 This is a schematic diagram of light deflection in the region near the tip of the explosive motion crack of the present invention.

[0051] Symbol explanation:

[0052] 1-DC power supply; 2-Cold light source; 3-Light source bracket; 4-Speckle target surface; 5-Target surface support; 6-Translation stage; 7-Clamp; 8-Explosive charge; 9-Specimen; 10-Multi-channel timing delay controller; 11-Pulse igniter; 12-Signal line; 13-Enameled wire; 14-High-speed camera; 15-Camera bracket; 16-Computer. Detailed Implementation

[0053] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0054] The purpose of this invention is to provide a measurement system and method for the energy release rate of moving cracks under explosive loading. By combining digital gradient sensitive optical measurement technology and explosion dynamics testing technology, it is possible to accurately measure the energy release rate of single or multiple explosive moving cracks at different times.

[0055] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0056] Figure 1 This is a schematic diagram of the measurement system for the energy release rate of a moving crack under explosive loading according to the present invention. Figure 1 As shown, the system in this invention includes:

[0057] 1. DC power supply; 2. cold light source; 3. light source bracket; 4. speckle target surface; 5. target surface support; 6. translation stage; 7. fixture; 8. explosive charge; 9. test piece; 10. multi-channel timing delay controller; 11. pulse igniter; 12. signal line; 13. enameled wire; 14. high-speed camera; 15. camera bracket; and 16. computer.

[0058] Among them, specimen 9 is an organic glass plate specimen with a central borehole.

[0059] The cold light source 2 specifically includes two light sources: a first cold light source and a second cold light source.

[0060] Translation stage 6 is an electric translation stage.

[0061] DC power supply 1 is connected to cold light source 2 and is used to power cold light source 2;

[0062] The cold light source 2, the speckle target surface 4, and the high-speed camera 14 are respectively fixed on the light source bracket 3, the target surface support 5, and the camera bracket 15;

[0063] An acrylic plate specimen with a central borehole is fixed on a clamp 7. The clamp can move up, down, left, and right in an electric translation stage 6 to ensure that the center of the speckle target 4, the specimen 9, and the high-speed camera 14 are on the same main optical axis. An explosive charge 8 is installed in the central borehole of the acrylic plate specimen and is connected in sequence to an enameled wire 13 and a signal line 12. A multi-channel timing delay controller 10 is responsible for the timing control of the entire experimental setup and is connected to a pulse igniter 11 and a high-speed camera 14 through control lines. The electric translation stage 6 and the high-speed camera 14 are connected to a computer 16 through control lines.

[0064] Based on the measurement system described above in this invention, this invention further provides a method for measuring the energy release rate of a moving crack under explosive loading, such as... Figure 2 As shown, the measurement method includes:

[0065] Step 1: Spray black and white paint spots onto the surface of the speckle target.

[0066] Step 2: Fix the specimen on the fixture so that the surface of the specimen is parallel to the speckle target surface.

[0067] Step 3: Load the test specimen with the explosive and connect the wires.

[0068] Step 4: Turn on the DC power supply to illuminate the surface of the speckle target with the cold light source.

[0069] Step 5: Adjust the optical path of the experimental system and aim the high-speed camera lens at the speckle target surface behind the specimen.

[0070] Step 6: Adjust the position and focal length of the high-speed camera lens so that the paint spots on the speckle target surface form a clear image in the center of the high-speed camera. Mark how many pixels each millimeter corresponds to in the image and take a picture.

[0071] Step 7: The multi-channel timing delay controller sends a trigger signal, transmitting one of the signals to the pulse igniter and the other trigger signal to the high-speed camera, thereby controlling the timing synchronization of the pulse igniter and the high-speed camera.

[0072] Step 8: After receiving an external trigger signal, the pulse igniter generates a momentary high voltage to cause the explosive to detonate. After receiving the external trigger signal, the high-speed camera continuously takes pictures.

[0073] Step 9: After the explosive is detonated, one or more cracks will initiate and propagate within the plexiglass specimen. The light deflection displacement field on the speckle target surface near the tip of the moving crack at different times is calculated by computer, and the light deflection angles in the X and Y directions are obtained by digital gradient sensitive photometry.

[0074] Step 10: Calculate the energy release rate of the moving crack under explosive load based on the light deflection angle information of the test point located on the crack extension line. The specific calculation process is as follows:

[0075] Figure 3 This is a schematic diagram of light deflection near the tip of a burst-induced crack. x and y are local rectangular coordinate systems with the origin fixed at the crack tip, where the x-direction is the direction of the crack extension line and the y-direction is perpendicular to the crack extension line. r and θ are local polar coordinate systems with the origin fixed at the crack tip. According to dynamic fracture mechanics theory, when a burst load causes single or multiple cracks to propagate in an acrylic glass specimen, the local dynamic singular stress field at the tip of the i-th moving crack is:

[0076]

[0077] in, Let i be the stress component near the tip of the i-th moving crack. and These are the Type I and Type II dynamic stress intensity factors at the crack tip, respectively. and The angular distribution function related to the crack propagation rate has the following component expressions:

[0078]

[0079] in, and To match the propagation speed V of the i-th crack i The relevant dynamic coefficients, ρ, E, and ν, are the density, elastic modulus, and Poisson's ratio of the plexiglass specimen, respectively.

[0080] Based on the principle of digital gradient-sensitive photometry, the relationship between the light deflection angle near the tip of the i-th crack and the local dynamic singular stress field is as follows:

[0081]

[0082] in, and , respectively, are the components of the light deflection angle along the x and y directions of the local coordinate system, and B and C are the thickness and elastic optical constant of the plexiglass specimen, respectively.

[0083] Substituting formulas ① and ② into formula ③, the components of the ray deflection angle along the x and y directions in the local coordinate system at the point to be measured on the i-th extension line of the moving crack (i.e., y = 0), at a distance from the crack tip equal to the thickness B of the plexiglass specimen, are:

[0084]

[0085] It should be noted that there are two reasons for choosing the point to be tested as the distance from the crack tip equal to the thickness B of the plexiglass specimen: first, to ensure that the point to be tested is located within the dominant region of the crack tip K, thus guaranteeing the accuracy of the experimental test; and second, to make the expression for the light deflection angle more concise and simplify the data processing flow.

[0086] According to the coordinate transformation relationship, the relationship between the components of the ray deflection angle along the x and y directions in the local coordinate system and its components along the x and y directions in the global coordinate system is as follows:

[0087]

[0088] Where, φ 0i =δ 0i / Δ and φ 90i =δ 90i / Δ represent the components of the light deflection angle along the X and Y directions, respectively, Δ is the distance between the plexiglass plate specimen and the speckle target surface, and δ 0i and δ 90i These represent the components of the light deflection displacement along the global coordinates (X and Y directions) on the speckle target surface, respectively, calculated using digital speckle correlation software during the test. β i Let be the angle between the extension line of the i-th moving crack and the X direction.

[0089] Combining formulas ④ and ⑤, the Type I and Type II dynamic stress intensity factors at the tip of the i-th moving crack are:

[0090]

[0091] Based on the relationship between energy release rate and stress intensity factor, and considering the superposition of energy release rates of different moving cracks caused by explosive loading, the total energy release rate G of moving cracks under explosive loading is then calculated. T for:

[0092]

[0093] Where I is the total number of kinematic cracks caused by the explosive load, and M and N are crack propagation rate correction coefficients, the expressions of which are:

[0094]

[0095]

[0096] The system and method described above in this invention have the following beneficial effects:

[0097] This invention employs a method combining digital gradient-sensitive photometry and explosion dynamics testing techniques. A high-speed camera captures images of the speckle target surface behind a polyacrylic glass (PAG) specimen under explosive loading. Digital gradient-sensitive technology measures the light deflection angle distribution near the tip of a moving crack in the PAG, thereby measuring the dynamic energy release rate of the moving crack. The digital gradient-sensitive technology used in this invention is a novel photometry technique. Compared to traditional photoelastic methods, it eliminates the tedious process of counting photoelastic fringe orders, simplifying the experimental procedure. Compared to other photometry techniques such as digital speckle correlation and caustic line methods, it makes crack tips easier to identify and provides more reliable experimental results. For measuring the energy release rate of a moving crack under explosive loading, this invention adds a crack propagation velocity correction coefficient compared to traditional methods, making the experimental results more accurate.

[0098] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the systems disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the descriptions are relatively simple; relevant parts can be referred to the method section.

[0099] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A system for measuring the energy release rate of a moving crack under explosive loading, characterized in that, The measurement system includes: speckle target surface (4); A cold light source (2) is used to emit light and irradiate the speckle target surface (4); Translation stage (6); Specimen (9); The clamp (7) is movably mounted on the translation stage (6) and is used to fix the specimen (9). An explosive charge (8) is fixed on the test piece (9); A pulse igniter (11) is connected to the explosive charge (8); A high-speed camera (14) is used to photograph the speckle target surface (4). A multi-channel timing delay controller (10) is connected to the pulse igniter (11) and the high-speed camera (14) and is used to send trigger signals to the pulse igniter (11) and the high-speed camera (14); A computer (16), connected to the translation stage (6) and the high-speed camera (14), is used to calculate the energy release rate of the moving crack under explosive load; The formula for calculating the energy release rate of the moving crack under explosive loading is as follows: ； in, The energy release rate of a moving crack under explosive loading. This represents the total number of kinematic cracks caused by the explosive load. The elastic modulus of the plexiglass specimen. For the first The extension line of the moving crack and The angle between directions, and This is a correction factor for crack propagation rate. and The test points are located on the speckle target surface. direction and directional light deflection angle; The crack propagation rate correction factor and The expression is as follows: ， ； ， ； in, and The values ​​represent the thickness and elastic optical constants of the plexiglass specimen, respectively. and The density and Poisson's ratio of the acrylic sheet material. For the first The propagation rate of a moving crack, and In order to be with the first Crack propagation rate Relevant dynamic coefficients.

2. The measurement system for the energy release rate of a moving crack under explosive loading according to claim 1, characterized in that, The specimen (9) is an organic glass plate with a central borehole, and the explosive charge (8) is installed inside the central borehole of the organic glass plate specimen.

3. The measurement system for the energy release rate of a moving crack under explosive loading according to claim 1, characterized in that, The measurement system also includes: Light source bracket (3), target support (5) and camera bracket (15); The cold light source (2), speckle target surface (4) and high-speed camera (14) are fixed sequentially on the light source bracket (3), target surface support (5) and camera bracket (15).

4. The measurement system for the energy release rate of a moving crack under explosive loading according to claim 1, characterized in that, The translation stage (6) is an electric translation stage, and the clamp (7) moves up, down, left, and right in the electric translation stage (6).

5. The measurement system for the energy release rate of a moving crack under explosive loading according to claim 1, characterized in that, The measurement system also includes: A DC power supply (1) and the cold light source (2) are used to power the cold light source (2); The signal line (12) is connected to the pulse igniter (11); The enameled wire (13) is connected at one end to the signal wire (12) and at the other end to the explosive charge (8).

6. The measurement system for the energy release rate of a moving crack under explosive loading according to claim 1, characterized in that, The cold light source (2) includes: a first cold light source and a second cold light source.

7. The measurement system for the energy release rate of a moving crack under explosive loading according to claim 1, characterized in that, The center of the speckle target (4), the center of the specimen (9), and the lens of the high-speed camera (14) are located on the same main optical axis.

8. A method for measuring the energy release rate of a moving crack under explosive loading, characterized in that, The measurement method is applied to the measurement system as described in any one of claims 1-7, and the measurement method includes: Spray black and white paint spots onto the surface of the speckle target (4); The specimen (9) is fixed on the fixture (7) so that the surface of the specimen (9) is parallel to the speckle target surface (4); The test specimen (9) is loaded with explosives and connected to wires. Turn on the DC power supply (1) and illuminate the surface of the speckle target (4) with the cold light source (2); Adjust the optical path of the experimental system and aim the lens of the high-speed camera (14) at the speckle target surface behind the specimen (9); Adjust the position and focal length of the lens of the high-speed camera (14) so ​​that the paint spots on the speckle target surface (4) form a clear image in the center of the high-speed camera (14); The multi-channel timing delay controller (10) sends a trigger signal, which transmits one of the signals to the pulse igniter (11) and the other trigger signal to the high-speed camera (14) to control the timing synchronization of the pulse igniter (11) and the high-speed camera (14); The pulse igniter (11) generates a momentary high voltage after receiving an external trigger signal, causing the explosive to detonate. The high-speed camera (14) takes continuous photos after receiving an external trigger signal. After the explosive detonates, single or multiple cracks initiate and propagate within the plexiglass specimen. The displacement field of light deflection on the speckle target surface near the crack tip at different times is calculated by computer, and then obtained using digital gradient-sensitive photometry. X direction and Y The angle of deflection of light rays from a given direction; The energy release rate of the moving crack under explosive load is calculated based on the light deflection angle information of the test point located on the crack extension line.

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