Biaxial dynamic tearing performance testing device for a membrane material and usage method thereof

Abstract

The invention discloses a biaxial dynamic tearing performance testing device and a using method for a membrane material. The device comprises a cross-shaped frame composed of two crossbeams. Fixing devices are arranged at three ends of the cross-shaped frame for fixing a cross-shaped specimen, and a loading device is arranged at the other end to apply an instantaneous tensile force to the cross-shaped specimen. During the force application process, a high-speed camera is used to capture the crack propagation, and the crack propagation rate, size, etc. are calculated through the Opencv image recognition technology, solving the problem that the existing dynamic loading test method is not applicable to fabric building membrane materials.

Description

Technical Field

[0001] The present invention relates to the field of membrane structure performance testing, and particularly to a biaxial dynamic tearing performance testing device and a using method for a membrane material. Background Art

[0002] Membrane structures are new types of spatial structure systems that emerged in the mid- to late 20th century, and have the advantages of large span, light self-weight, convenient construction, and complex and variable building shapes. As a prestressed structure, the membrane surface is always in a state of biaxial tension. Due to the existence of initial defects or local stress concentration, it is extremely easy to cause local tearing of the membrane surface and rapid expansion, which will lead to the loss of membrane surface tension and even cause the overall collapse of the structure. In current domestic and foreign membrane structure design codes, the design strength of membrane materials is mostly obtained by considering the material resistance partial factor or safety factor on the basis of the uniaxial tensile strength of the membrane material, and the impact of tearing on structural safety is not clearly considered. Tearing failure is often the main failure form of membrane structures. Therefore, to ensure the safety, reliability and normal use of membrane structures during their service life, it is very necessary to ensure the tear resistance of the materials. Therefore, it is necessary to design a test device to understand the tear resistance of such building materials.

[0003] At present, there are many testing methods for the dynamic fracture performance of materials such as concrete and rock. Common dynamic testing devices include: drop hammers (pendulum hammers), drop weight testing machines, hydraulic servo testing machines, and Hopkinson bars, etc. However, due to the characteristics of fabric building membrane materials such as flexibility and small thickness, the commonly used specimen forms and testing methods are not suitable for membrane materials. There is an urgent need to propose a testing method and equipment suitable for the dynamic tearing performance of fabric building membrane materials to carry out research on the dynamic tearing performance of membrane materials. Summary of the Invention

[0004] Aiming at the above-mentioned existing technical deficiencies, the purpose of the present invention is to provide a biaxial dynamic tearing performance testing device and a using method for a membrane material, which solves the problem that the existing dynamic loading testing method is not applicable to fabric building membrane materials.

[0005] To solve the above technical problems, the present invention adopts the following technical solutions:

[0006] The present invention provides a biaxial dynamic tearing performance testing device for a membrane material, including a cross-shaped frame composed of two crossbeams. Sliders capable of sliding along the length direction thereof are respectively provided at both ends of the upper end surface of the crossbeam.

[0007] A clamp for clamping a cross-shaped specimen is slidably connected to the slider, and three of the clamps are connected to a fixing device, and the other clamp is connected to a loading device.

[0008] The fixing device includes a slide rail support plate fixed at the end of the cross-shaped frame.

[0009] A force-applying motor is fixed on the slide rail support plate and is slidably connected to the toothed plate, and the output end of the force-applying motor is meshed with the toothed plate to control its movement;

[0010] The end of the tooth plate away from the slide rail support plate is connected to the fixture through a tension sensor;

[0011] The loading device includes a hydraulic cylinder fixed to the end of the cross frame;

[0012] The hydraulic cylinder is provided with a force storage tank, and the extended end of the hydraulic cylinder is fixedly connected to the clamp on the same side.

[0013] Preferably, the clamp comprises a cross bar, which passes through the slider and is slidably connected thereto, one end of the cross bar is connected to the clamping plate, and the other end of the cross bar is connected to the tension sensor or the extended end of the hydraulic cylinder.

[0014] Preferably, pillars supporting the cross frame are fixed to the four ends and the middle portion thereof, and connecting rods are connected between the pillar in the middle and the other pillars.

[0015] Preferably, a slide rail for the sliding block to slide is provided on the crossbeam.

[0016] The present invention also provides a method for using a biaxial dynamic tearing performance testing device for a film material, comprising the following steps:

[0017] Step 1: Use a fixture to clamp the four ends of the cross-shaped specimen respectively, arrange a high-speed camera facing the cross-shaped specimen to record the entire dynamic tearing process of the specimen, and connect the tension sensor to the computer to record the dynamic tearing load;

[0018] Step 2: The force motor is connected to a computer, and the computer controls the rotation of the force motor to control the lateral movement of the tooth plate until the value of the tension sensor reaches the preload value;

[0019] Step 3: The loading device starts working at this time. When the energy stored in the accumulator reaches the designed value, the solenoid valve is used to control its opening, and the energy is instantly released into the hydraulic cylinder to realize the tensile test under high strain rate conditions.

[0020] Step 4: The computer reads the value of the tension sensor in real time and draws the load-time curve to extract the test data;

[0021] Step 5: After the test, use a computer to read the content captured by the high-speed camera, read each frame of the video through the frame extraction tool, identify the cracks in the image based on Opencv image processing technology, and calculate the lateral size of the crack, the crack opening size, and the crack propagation rate.

[0022] Preferably, in step one, a high-speed camera with 250 frames per second is used. To ensure that each frame of the image corresponds to a load value, the acquisition frequencies of the high-speed camera and the tensile sensor should be consistent.

[0023] Preferably, the specific method of step five is as follows:

[0024] S1. Using Opencv image processing technology, first define a ratio to measure the number of pixels per given measurement unit. Then, balance the illumination of the acquired image by the Mask equalization method. Next, use the rectangle detection method to frame the crack and perform perspective transformation for correction, so that the crack in the image can be automatically extracted.

[0025] S2. Perform grayscale processing on the extracted crack region image by the weighted average method to reduce image information. Then, use Gaussian filtering to eliminate the influence of noise. Finally, use the K-means clustering algorithm to enhance the contrast of this region to complete the image preprocessing work.

[0026] S3. For the preprocessed image, first use the Canny edge extraction algorithm to extract the crack edge. Use dilation and erosion operations to eliminate any gaps between the edges, find the contour line corresponding to the crack in the figure, and draw the rectangular border circumscribing the contour.

[0027] S4. Calculate the transverse size and crack opening size of the crack in the picture from the coordinates of the four corner points of the border and the initially set ratio.

[0028] S5. Calculate the crack propagation rate through the size change of the pictures in the front and back frames.

[0029] The beneficial effects of the present invention are as follows:

[0030] The present invention makes up for the deficiency that the existing dynamic loading device is not applicable to membrane materials. By applying dynamic loads to the membrane material with initial defects through a hydraulic cylinder to explore the dynamic tearing performance of the membrane material, since the loading process is very short and it is difficult to observe the test phenomena with the naked eye, a high-speed camera and a high-frequency and high-sensitivity tensile sensor are used to capture the characteristics of the dynamic tearing process. In addition, image recognition technology is used to process crack propagation to obtain the crack propagation rate and the change of crack size, which is convenient for the experimenter to understand the crack propagation mechanism. The entire test method has simple operation steps, combines high-precision instruments to measure data to reduce test errors, and uses computer technology to analyze the tearing mechanism to improve the reliability of the conclusion. Description of the Drawings

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0032] Figure 1 Schematic structural diagram of a biaxial dynamic tearing performance testing device for a membrane material provided by an embodiment of the present invention;

[0033] Figure 2 Schematic structural diagram (side view) of a biaxial dynamic tearing performance testing device for a membrane material provided by an embodiment of the present invention;

[0034] Figure 3 Schematic structural diagram (top view) of a biaxial dynamic tearing performance testing device for a membrane material provided by an embodiment of the present invention.

[0035] Explanation of reference numerals:

[0036] 1. Hydraulic cylinder; 2. Fixed bracket; 3. Energy storage tank; 4. Slide block; 5. Fixture; 6. Cross-shaped specimen; 7. Tensile force sensor; 9. Tooth plate; 10. Slide rail support plate; 11. Slide rail; 12. Support pillar; 13. Connecting rod. Detailed implementation manners

[0037] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0038] As Figures 1 to 3 shown, a biaxial dynamic tearing performance testing device for a membrane material includes a cross-shaped frame composed of two crossbeams. At both ends of the upper end surface of the crossbeam, slide blocks 4 capable of sliding along its length direction are respectively provided;

[0039] A fixture 5 for clamping the cross-shaped specimen 6 is slidably connected to the slide block 4. Three of the fixtures are connected to the fixing device, and the other fixture 5 is connected to the loading device;

[0040] The fixing device includes a slide rail support plate 10 fixed at the end of the cross-shaped frame;

[0041] A driving motor is fixed on the slide rail support plate 10 and is slidably connected to the tooth plate 9. The output end of the driving motor meshes with the tooth plate 9 to control its movement;

[0042] One end of the toothed plate 9 away from the slide rail support plate 10 is connected to the fixture 5 through a tension sensor 7;

[0043] The loading device includes a hydraulic cylinder 1 fixed to the end of the cross-shaped frame;

[0044] The hydraulic cylinder 1 is provided with an energy storage tank 3, and the extending end of the hydraulic cylinder 1 is fixedly connected to the fixture 5 on the same side.

[0045] Preferably, the fixture 5 includes a cross bar, the cross bar penetrates through the slider 4 and is slidably connected thereto, one end of the cross bar is connected to a clamping plate, and the other end of the cross bar is connected to the tension sensor 7 or the extending end of the hydraulic cylinder 1.

[0046] Preferably, support columns 12 for supporting the cross-shaped frame are fixed at the four ends and the middle of the cross-shaped frame, and a connecting rod 13 is connected between the support columns 12 arranged in the middle and the other support columns 12.

[0047] Preferably, a slide rail 11 for the slider 4 to slide is provided on the cross beam.

[0048] The present invention also provides a method for using a biaxial dynamic tearing performance testing device for film materials, including the following steps:

[0049] Step 1: Use the fixture 5 to clamp the four ends of the cross-shaped specimen 6 respectively, arrange a high-speed camera facing the cross-shaped specimen 6 to record the whole process of dynamic tearing of the specimen, and the tension sensor 7 is connected to a computer to record the dynamic tearing load;

[0050] In Step 1, a high-speed camera with 250 frames per second and a high-frequency and high-sensitivity tension sensor are adopted. To ensure that each frame of image can correspond to a load value, the acquisition frequencies of the high-speed camera and the tension sensor 7 should be consistent;

[0051] Step 2: The driving motor is connected to the computer, and the computer controls the rotation of the driving motor to control the lateral movement of the toothed plate 9 until the value of the tension sensor 7 reaches the size of the pre-load;

[0052] Step 3: The loading device starts to work at this time. After the energy stored in the energy storage tank 3 reaches the designed value, its built-in solenoid valve is controlled to open, and the energy is instantaneously released into the hydraulic cylinder 1 to realize a tensile test under high strain rate conditions; the solenoid valve can be connected to the computer to control its opening; the energy storage tank 3 selects an existing energy storage tank capable of displaying its internal pressure, and the energy storage tank 3 is fixed to the hydraulic cylinder 1 through a fixing bracket 2 to prevent it from shaking.

[0053] Step 4: The computer reads the value of the tension sensor 7 in real time and draws a load-time curve to extract test data;

[0054] Step 5: After the test, use a computer to read the content captured by the high-speed camera, read each frame image of the video through a frame extraction tool, identify the cracks in the picture based on Opencv image processing technology, and calculate the transverse size of the cracks, the crack opening size, and the crack propagation rate.

[0055] The specific method for Step 5 is as follows:

[0056] S1. Using Opencv image processing technology, first define a ratio to measure the number of pixels per given unit of measurement, then balance the illumination of the captured image by the Mask equalization method, and then use the rectangle detection method to frame the cracks and perform perspective transformation for correction, so that the cracks in the image can be automatically extracted;

[0057] S2. Perform grayscale processing on the extracted crack area image by the weighted average method to reduce image information, then use Gaussian filtering to eliminate the influence of noise, and finally use the K-means clustering algorithm to enhance the contrast of this area to complete the image preprocessing work;

[0058] S3. For the preprocessed image, first use the Canny edge extraction algorithm to extract the crack edges, use dilation and erosion operations to eliminate any gaps between the edges, find the contour lines corresponding to the cracks in the picture, and draw the rectangular border circumscribing the contour;

[0059] S4. Calculate the transverse size and crack opening size of the cracks in the picture from the coordinates of the four corner points of the border and the initially set ratio;

[0060] S5. Calculate the crack propagation rate by the size change of the front and back frame pictures.

[0061] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these changes and modifications.

Claims

1. A biaxial dynamic tearing performance testing device for a membrane material, characterized in that it includes a cross-shaped frame composed of two crossbeams. At both ends of the upper end surface of the crossbeam, there are sliders (4) that can slide along its length direction; on the crossbeam, there are slide rails (11) for the sliders (4) to slide. A fixture (5) for clamping a cross-shaped specimen (6) is slidably connected to the slider (4). Among them, three of the fixtures are connected to a fixing device, and the other fixture (5) is connected to a loading device. The fixture (5) includes a crossbar. The crossbar passes through the slider (4) and is slidably connected to it. One end of the crossbar is connected to a clamping plate, and the other end of the crossbar is connected to the extending end of a tensile force sensor (7) or a hydraulic cylinder (1). The fixing device includes a slide rail support plate (10) fixed at the end of the cross-shaped frame. At the four ends and the middle of the cross-shaped frame, there are columns (12) that support it. A connecting rod (13) is connected between the column (12) arranged in the middle and the other columns (12). A force-applying motor is fixed on the slide rail support plate (10) and is slidably connected to a toothed plate (9). The output end of the force-applying motor meshes with the toothed plate (9) to control its movement. One end of the toothed plate (9) away from the slide rail support plate (10) is connected to the fixture (5) through a tensile force sensor (7). The loading device includes a hydraulic cylinder (1) fixed at the end of the cross-shaped frame. The hydraulic cylinder (1) is provided with an energy storage tank (3). The extending end of the hydraulic cylinder (1) is fixedly connected to the fixture (5) on the same side.

2. A method for using a biaxial dynamic tearing performance testing device for the film material as described in claim 1, characterized in that, It includes the following steps: Step 1: Use the fixture (5) to clamp the four ends of the cross-shaped specimen (6) respectively. Arrange a high-speed camera facing the cross-shaped specimen (6) to record the whole process of dynamic tearing of the specimen. The tensile force sensor (7) is connected to a computer to record the dynamic tearing load. A high-speed camera with 250 frames per second is used. To ensure that each frame of the image can correspond to a load value, the acquisition frequencies of the high-speed camera and the tensile force sensor (7) should be the same. Step 2: The force-applying motor is connected to a computer. The computer controls the rotation of the force-applying motor to control the lateral movement of the toothed plate (9) until the value of the tensile force sensor (7) reaches the size of the pre-load. Step 3: The loading device starts to work at this time. After the energy stored in the energy storage tank (3) reaches the designed value, its built-in solenoid valve is controlled to open, and the energy is instantly released into the hydraulic cylinder (1) to achieve a tensile test under high strain rate conditions. Step 4: The computer reads the value of the tensile force sensor (7) in real time and plots the load-time curve, and extracts the test data. Step 5: After the test is completed, use the computer to read the content captured by the high-speed camera. Read each frame of the video image through a frame extraction tool. Based on the Opencv image processing technology, identify the cracks in the picture and calculate the transverse size of the cracks, the opening size of the cracks, and the crack propagation rate. Specifically: S1. Using the Opencv image processing technology, first define a ratio to measure the number of pixels per given unit of measurement, then balance the illumination of the captured image by the Mask equalization method, and then use the rectangular detection method to frame the crack and perform correction using perspective transformation, so that the crack in the image can be automatically extracted; S2. Grayscale the extracted crack region image by the weighted average method to reduce image information, then use Gaussian filtering to eliminate the influence of noise, and finally use the K-means clustering algorithm to enhance the contrast of this region to complete the image preprocessing work; S3. For the preprocessed image, first use the Canny edge extraction algorithm to extract the crack edge, use dilation and erosion operations to eliminate any gaps between the edges, find the contour line corresponding to the crack in the figure, and draw the rectangular border circumscribing the contour; S4. Calculate the transverse dimension and the crack opening dimension of the crack in the picture from the coordinates of the four corner points of the border and the initially set ratio; S5. Calculate the crack propagation rate by the size change of the front and back frame pictures.

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