Method and device for testing mechanical property of fabric membrane material

Abstract

The invention provides a method and device for testing the mechanical property of a fabric membrane material, and the method comprises the steps: collecting real illumination data and real temperature data in a real environment within a preset time period, and generating a simulation environment containing test temperature data; placing a standard sample in the simulation environment, and performing dynamic tearing test based on different temperature data to obtain a tearing damage image, a load displacement relation curve, a membrane surface displacement field and a strain field of the fabric membrane material; on the basis of three types of preset actual measurement data, the test result data are analyzed, and an analysis result can provide a reference basis for tearing mechanical property research and safety evaluation of the photovoltaic film structure.

Description

Technical Field

[0001] The present invention belongs to the technical field of mechanical property testing, in particular to a method and device for testing the mechanical properties of fabric membrane materials at high temperatures, which is applicable to engineering fields such as building photovoltaic integration and large-span membrane structures. Background Art

[0002] High-strength composite membranes, due to their lightweight and aesthetically pleasing properties, are widely used in sports stadiums, transportation facilities, and other fields. Integrated photovoltaic membrane structures, combined with photovoltaic technology, utilize the membrane surface to generate electricity using photovoltaic panels, helping to reduce building energy consumption and achieve dual carbon goals. However, in actual projects, membranes are exposed to long-term solar radiation and the high temperatures of photovoltaic modules, coupled with complex loads. This can lead to stress concentration and tearing at membrane defects, ultimately causing structural failure.

[0003] Existing tear tests are mostly based on room temperature environments (such as GB / T 3917.3-2009, "Tear Properties of Textile Fabrics"), ignoring the cumulative effects of environmental factors on material damage. This results in test results that fail to truly reflect actual service performance. Therefore, there is an urgent need to develop a test method that can simulate complex environments and accurately quantify tear mechanical parameters. Summary of the Invention

[0004] The purpose of the present invention is to provide a method and device for testing the mechanical properties of fabric membrane materials at high temperatures, so as to simulate a complex environment and accurately quantify the tearing mechanical parameters.

[0005] The technical solutions for achieving the purpose of the present invention are:

[0006] A method for testing the mechanical properties of a fabric membrane material, comprising:

[0007] Within a preset time period, real light data and real temperature data in a real environment are collected, light-thermal analysis is performed, and the light data is converted into temperature data;

[0008] The membrane sample is placed in the simulated environment of the above temperature data, and dynamic tearing tests are performed under different temperature conditions. The test results under different temperature conditions are recorded, including the failure image, load and displacement data of the tearing process of the fabric membrane material;

[0009] The tearing failure image is processed to obtain the displacement field and strain field of the membrane surface. The load-displacement relationship curve is established through the load and displacement data. Three types of measured data are obtained: the tearing failure image of the fabric membrane material, the load-displacement relationship curve, and the membrane surface displacement field and strain field. Based on these three types of measured data, the results of the membrane material tearing mechanical response and deformation are analyzed.

[0010] Based on the above analysis results, the tearing mechanical properties of the photovoltaic membrane structure are analyzed and protective measures are taken.

[0011] A device for testing the mechanical properties of a fabric membrane material, comprising:

[0012] The data acquisition module is used to collect real light data and real temperature data in a real environment within a preset time period, perform light-thermal analysis, and convert the light data into temperature data;

[0013] The test module is used to place the membrane sample in the simulated environment of the above temperature data, perform dynamic tearing tests under different temperature conditions, and record the test results under different temperature conditions, including the failure image, load and displacement data of the tearing process of the fabric membrane;

[0014] The analysis module is used to process the tearing failure image to obtain the membrane surface displacement field and strain field. The load-displacement relationship curve is established through the load and displacement data. The three types of measured data are obtained: the tearing failure image of the fabric membrane material, the load-displacement relationship curve, and the membrane surface displacement field and strain field. Based on these three types of measured data, the results of the membrane material tearing mechanical response and deformation are analyzed;

[0015] The generation module analyzes the tearing mechanical properties of the photovoltaic membrane structure and provides protective measures based on the above results analysis.

[0016] Compared with the prior art, the present invention has the following significant advantages:

[0017] Aiming at the problem of tearing and damage of membrane materials at high temperatures in the actual application of photovoltaic membrane structures, a complete set of high-temperature textile membrane mechanical property testing methods was designed. Starting from the collection of real light data and real temperature data in a real environment within a preset time period, dynamic tearing tests of membrane materials at different temperatures were carried out, and a formula for the temperature line stiffness degradation of membrane materials was established. A solution was given to the problem of blurry photos taken through a high and low temperature test chamber used to simulate different temperature conditions. The membrane tearing damage image, load-displacement relationship curve, and membrane surface displacement field and strain field were analyzed. The conclusions can provide an important reference basis for the study of high-temperature tearing mechanical properties of textile membrane materials and the safety assessment of photovoltaic membrane structures. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A schematic flow chart of a method for testing the mechanical properties of a fabric membrane at high temperature provided by the present invention is shown;

[0019] Figure 2 A schematic diagram showing the collection of real light data and real temperature data according to the present invention is shown;

[0020] Figure 3 A picture of an actual working scene where real light data and real temperature data are collected is shown.

[0021] Figure 4A schematic diagram of a dynamic tearing test of a film material at different temperatures according to the present invention is shown;

[0022] Figure 5 Shows pictures of actual working scenes of dynamic tearing test of membrane materials at different temperatures;

[0023] Figure 6 A schematic diagram showing the modification and installation of a high and low temperature test chamber according to the present invention is shown;

[0024] Figure 7 The real light data and real temperature data collected in a real environment according to the embodiment of the present application are shown;

[0025] Figure 8 Shows the tearing and damage images of the fabric film material at the typical temperature provided in the embodiments of the present application;

[0026] Figure 9 A schematic diagram showing the load-displacement relationship curves of the fabric membrane material at different temperatures provided in the embodiment of the present application is shown;

[0027] Figure 10 A schematic diagram showing the degradation of the linear stiffness of the fabric membrane material at different temperatures provided in an embodiment of the present application is shown;

[0028] Figure 11 A schematic diagram of the displacement field and strain field of the membrane surface of the fabric membrane material provided in an embodiment of the present application at a typical temperature of 75°C is shown.

[0029] Among them: 1. Photovoltaic-fabric membrane composite material; 2. Solar irradiation tester; 3. Ultra-thin adhesive platinum resistor; 4. Multi-channel paperless recorder; 5. Bracket; 6. Membrane material sample with speckle; 7. High and low temperature test chamber; 8. Uniaxial stretching equipment; 9. Image acquisition equipment; 10. High-temperature lamps; 11. Electrical wiring. DETAILED DESCRIPTION

[0030] The present invention is further described below with reference to the accompanying drawings and examples.

[0031] Specific implementation: Figure 1 As shown, this embodiment describes a method for testing the mechanical properties of a fabric membrane at high temperature, the method comprising the following steps:

[0032] Step 1: Data collection: Collect real light data and real temperature data in a real environment within a preset time period, perform light-thermal analysis, and convert the light data into temperature data;

[0033] The schematic diagram of the device for collecting real light data and real temperature data in step 1 is as follows Figure 2 As shown, Figure 3 This is a picture of the actual working scene for data collection.

[0034] Based on the composite method of photovoltaic modules and membrane structures in actual applications of photovoltaic membrane structures, the photovoltaic modules and membrane materials are composited to prepare a photovoltaic-fabric membrane composite material 1. With reference to the geographical location and climatic conditions of the actual application of the photovoltaic membrane structure, the photovoltaic-fabric membrane composite material 1 is placed in a real environment, and real light data under different weather conditions are collected within a preset time period. Real temperature data of the photovoltaic module surface, the fabric membrane surface, and the composite interface between the photovoltaic module and the fabric membrane are collected. The real light data and temperature data are analyzed, and the light data under various weather conditions are converted into temperature data. Based on the relationship between the measured light and temperature, the temperature range and temperature change gradient of the dynamic tear test are determined.

[0035] There is no restriction on the collection equipment used. In this embodiment, a solar radiation tester 2 is used to collect light radiation intensity, i.e., light data. An ultra-thin adhesive platinum resistor 3 and a multi-channel paperless recorder 4 automatically collect temperature data, which can be collected as quickly as once per second. The bracket 5 can tilt the photovoltaic-fabric film composite material 1 so that the photovoltaic module faces the sun.

[0036] Step 2: Dynamic tear test: Place the speckled membrane sample 6 in the simulated environment of the aforementioned temperature data, perform dynamic tear tests under different temperature conditions, and record the test results, including a damage image of the fabric membrane tearing process and mechanical response data such as load and displacement data;

[0037] The schematic diagram of the dynamic tearing test device in step 2 is as follows Figure 4 As shown, Figure 5 This is a picture of the actual working scene of the dynamic tearing test;

[0038] Based on the temperature data obtained in step 1, the prepared film sample 6 with speckles is placed in a high and low temperature test chamber 7 that simulates different temperature environments. A certain pre-tension is applied to the sample, and sealing, heat preservation, and thermal insulation are performed to keep the film sample 6 with speckles in a tensioned state at a predetermined temperature for a long period of time. The uniaxial stretching device 8 and the image acquisition device 9 are simultaneously started. The uniaxial stretching device 8 can automatically collect and record load and displacement data. The image acquisition device 9 collects photos of the film sample 6 with speckles during the tearing process at the same time interval. The shorter the time interval, the better. For example, 10 photos can be collected per second.

[0039] There are no restrictions on the acquisition equipment used. Regarding speckle patterns, it is recommended to use a CNC speckle spraying machine to spray ink speckles. This can avoid distortion of the speckle sticker and damage to the speckles caused by large displacements and deformations in high-temperature environments. Using a CNC speckle spraying machine to generate randomly distributed speckle patterns on the film surface significantly improves the accuracy of speckle recognition obtained in high-temperature environments, allowing the acquired image data to be processed to obtain film surface strain. It is worth noting that the speckle diameter is extremely small, such as 0.5 mm, and the photos taken through the high and low temperature test chamber are relatively blurry. The present invention provides the following solutions:

[0040] like Figure 6 As shown, a high-temperature lamp 10 that can operate normally within a range including temperature data is installed in the high-temperature and low-temperature test chamber 7, and the wire line 11 is connected through the holes at the upper and lower ends of the test chamber. The high-temperature lamp 10 makes the light in the chamber bright and uniform, and can achieve full-angle non-reflection when combined with matte ink, greatly improving the correlation of speckle in continuous photos and avoiding the loss of speckle in some areas. However, certain modifications to the high-temperature and low-temperature test chamber are required.

[0041] Step 3, data analysis: Based on the load and displacement data collected in step 2, a load-displacement relationship curve is established. The damage image of the tearing process of the fabric membrane collected in step 2 is further converted into a data file of membrane surface displacement field and strain field information with the help of digital image related technology software. Specifically, an image of the center measurement area of the surface of the membrane sample 6 with speckles before deformation is collected as a reference image, as well as a sequence of deformation images under uniaxial tension, with the help of an image acquisition device 9. The collected reference image and all deformation images are imported into the digital image software for analysis. With the reference image as a benchmark, the displacement field and strain field of the deformation image measurement area are analyzed using the characteristic speckle matching method and the linear strain calculation method respectively. Finally, a data file containing all displacement field and strain field information is exported.

[0042] At this point, three types of measured data can be obtained: the tearing damage image of the membrane material, the tearing load-displacement relationship curve, and the membrane surface displacement field and strain field. Based on these three types of measured data, the results of the membrane material tearing mechanical response and deformation are analyzed:

[0043] By observing the damage images during the tearing process of the membrane material, and according to the characteristic states such as the extension of the incision and whether the first main load-bearing yarn breaks, the tearing process of the membrane material at high temperature is divided into different tearing stages, such as the "incision tensioning stage" with initial load and the "initial tearing stage" when the first main load-bearing yarn breaks.

[0044] Through the damage images of the membrane tearing process, the fracture patterns of the yarns at the cut are observed. There are two fracture patterns: the first main stress-bearing yarn breaks, followed by the subsequent yarns breaking one after another, or the first main stress-bearing yarn breaks, and the rest of the main stress-bearing yarns break almost simultaneously. Based on the yarn fracture pattern, the membrane tearing failure is divided into "ductile fracture" with warning and "brittle fracture" without warning.

[0045] Through the damage image of the membrane tearing process, the key nodes of the tearing process, such as the starting point and the end point, are captured, the overall expansion trend of the cut, such as the direction and length, is observed, and the regularity is analyzed, such as whether the starting points are consistent, whether the cracks always go in one direction, such as along the yarn direction or perpendicular to the force direction. The membrane tearing peak load F can be obtained through the membrane tearing load-displacement relationship curve. C and fracture displacement δ C Based on the stiffness evolution law, the entire curve can be divided into four typical stages through the quasi-yield point A, the stiffness strengthening point B, and the starting tearing point C: the linear elastic stage OA segment, which characterizes the initial elastic response of the material; the quasi-yield stage AB segment, which reflects the yarn slippage and redistribution process; the stiffness strengthening stage BC segment, which corresponds to the yarn cooperative load-bearing mechanism; and the post-tear segment CD segment, which indicates the final destruction of the material. Among them, in MATLAB, the quasi-yield point A and the stiffness strengthening point B in the load-displacement relationship curve can be identified through piecewise linear regression combined with the residual minimization method. The starting tearing point C can be directly obtained from the load-displacement relationship curve. Then, the load and displacement data of points A, B, and C are used to calculate the linear stiffness K of the linear elastic stage OA segment, the quasi-yield stage AB segment, and the stiffness strengthening stage BC segment at different temperatures. OA , K AB , K BC , the temperature line stiffness degradation formula is obtained by fitting, which can be in the form of polynomial function, exponential function, logarithmic function, etc. The temperature line stiffness degradation formula in polynomial form is as follows:

[0046] K OA =A1*T n +A2*T n-1 +A3*T n-2 +…+A n *T+P OA

[0047] K AB =B1*T n +B2*T n-1 +B3*T n-2 +…+B n *T+P AB

[0048] K BC =C1*Tn +C2*T n-1 +C3*T n-2 +…+C n *T+P BC

[0049] Where T is temperature; n represents the linear stiffness K OA , K AB , K BC The highest order of the polynomial, n, can be the same or different: if n is the same in each segment, it means that the degradation law complexity of the linear stiffness at different stages under high temperature is consistent; if n is different, it means that the degradation mechanism of the linear stiffness at high temperature is more complicated; A1-A n 、B1-B n 、C1-C n Represents the linear stiffness K OA , K AB , K BC The polynomial coefficient reflects the weight of the influence of temperature on stiffness and needs to be determined by fitting the test data. OA 、P AB 、P BC Represents the linear stiffness K OA , K AB , K BC The constant term of the polynomial represents the reference value of the stiffness in this temperature range at T=0, and its unit is consistent with the stiffness.

[0050] Through the data file containing all the displacement field and strain field information, the cloud map of the horizontal and vertical displacement, strain and shear strain of the membrane surface during the tearing process of the fabric membrane material is obtained. In the cloud map, blue generally indicates small deformation and red indicates large deformation. The horizontal stretching or contraction of the membrane material is analyzed by the horizontal displacement cloud map, the deformation of the membrane material in the vertical direction is analyzed by the vertical displacement cloud map, the elongation or compression rate of the membrane material in the horizontal direction is analyzed by the horizontal strain cloud map, the elongation or compression rate of the membrane material in the vertical direction is analyzed by the vertical strain cloud map, and the degree of local shear slip of the membrane material is analyzed by the shear strain cloud map. Whether out-of-plane buckling occurs; the horizontal and vertical displacement cloud maps can be used to determine the maximum displacement area, such as near the crack tip and the boundary constraint; the horizontal and vertical strain cloud maps can be used to determine the strain concentration area, such as the slit tip and around the membrane surface defects. The high strain area indicates that the crack may extend in this direction; the shear cloud map can be used to determine whether there is a strain localization zone on the membrane surface, indicating out-of-plane buckling deformation of the membrane material. At the same time, if the shear strain cloud map has an oblique high-value zone, it means that the material has shear slip, which will affect the tearing direction; for areas with relatively uniform strain distribution, it means that the material in this area is under uniform stress and deformation is also relatively uniform;

[0051] Through the destruction image of the membrane tearing process, various displacement and strain cloud maps of the membrane surface during the membrane tearing process can be obtained. By analyzing the cloud maps, the deformation characteristics of the membrane surface during the membrane tearing process, as well as the displacement and strain data values of the membrane surface during the membrane tearing process can be obtained.

[0052] Step 4. Result summary: Based on the analysis of the three types of measured data in step 3, the analysis results are summarized to provide a reference for the study of the tearing mechanical properties and safety assessment of photovoltaic membrane structures;

[0053] Based on step 3, the tearing failure stage of the membrane material at different temperatures, the yarn fracture form and the expansion path of the cut were obtained:

[0054] By observing the morphological characteristics of the tearing of the membrane material of the photovoltaic membrane structure and corresponding it with the membrane material tearing damage stage obtained in step three, it is possible to effectively judge the damage stage of the membrane material at this time. If it is in the "cut tensioning section" of the initial load, it is necessary to use the parent material (the same membrane material used in the photovoltaic membrane structure) for welding reinforcement at the cut to prevent the cut from continuing to expand. If it is in the "starting tearing section" where the first main load-bearing yarn breaks, in addition to welding reinforcement of the tear, it is recommended to use a fabric membrane material with higher strength than the parent material for welding reinforcement. In addition, the photovoltaic membrane structure needs to be unloaded and the deposits on the membrane surface (snow, fallen leaves, etc.) are cleared to reduce the tension. The surrounding steel cables can be moderately relaxed, but the morphological changes of the membrane structure need to be monitored simultaneously to avoid structural failure caused by excessive relaxation.

[0055] Through step three, the fracture forms of the yarn at different temperatures can be obtained, and the fracture characteristics of different temperature ranges can be divided by the temperature threshold point T1: in the temperature range below the temperature threshold point T1, the membrane material presents ductile fracture with obvious warning characteristics, and in the temperature range above the temperature threshold point T1, the membrane material is prone to brittle fracture without obvious warning. Although the geographical location and weather conditions of photovoltaic membrane structures are different, the temperature threshold point T1 should be used as a key temperature detection point. When the membrane surface temperature is higher than the temperature threshold point T1, it is necessary to strengthen the monitoring and maintenance of the membrane material status, monitor whether there are cracks on the membrane surface, the crack extension, and the tearing damage stage. According to the monitoring results, welding reinforcement or unloading and unloading can be carried out to prevent sudden structural failure caused by brittle fracture.

[0056] By capturing the starting point of the tearing process through step three, local reinforcement can be carried out at the starting point through welding of the base material to prevent the crack from expanding. By accurately analyzing the expansion path characteristics of the cut, the regularity of crack expansion can be found, such as perpendicular to the force direction. On the one hand, precise repairs can be carried out on the torn path, and on the other hand, preventive reinforcement measures can be implemented on the untorn expansion path perpendicular to the force direction, which can significantly improve the reliability and service life of the membrane structure.

[0057] Step 3: The temperature linear stiffness degradation formula is established through the load-displacement relationship curve of the membrane tearing test. Based on this, the linear stiffness of the membrane material at different tearing stages at different temperatures can be calculated. In addition, due to the limitations of materials or test equipment, when conducting dynamic tearing tests, if the temperature range is only selected from 25 to 100°C, the temperature linear stiffness degradation formula can also be used to predict the linear stiffness of the fabric membrane material at higher temperatures, such as 120°C, or lower temperatures, such as -10°C. This ensures that the linear stiffness of the fabric membrane material is within the allowable range of the project, ensures the safety of photovoltaic membrane structures in different geographical locations and under different weather conditions, and provides a reference for engineering applications. At the same time, the membrane tearing peak load F can be extracted from the load-displacement relationship curve. C and fracture displacement δ C For areas with higher load, such as crack holes, high-frequency heat-sealed weld edges, boundary anchor points (such as cable connections, fixture periphery), and surface mutation areas (such as valley lines, ridge lines, and other locations with large curvature), the load in these areas is close to 0.8F. C , immediate support reinforcement, local reinforcement or unloading should be carried out; LVDT displacement sensors can be arranged in the tearing area to record the displacement changes of the membrane surface in real time, or a laser rangefinder can be used to monitor the dynamic deformation of the tearing area at a fixed point using non-contact method. If the displacement growth rate of the tearing area exceeds δ C 10% / hour or when the measured displacement approaches 0.8δ C When the tearing area is broken, immediately strengthen the support, local reinforcement or unload the load. In addition, if the load of the tearing area is close to 0.9F C Or the displacement is close to 0.9δ C When the membrane material is about to tear and fail, it can be judged that the membrane material is about to tear and fail, and the safety of the photovoltaic membrane structure should be maintained in time to avoid damage to the photovoltaic membrane structure;

[0058] In step 3, by analyzing the displacement field and strain field of the membrane surface, the distribution characteristics of the horizontal and vertical displacement, strain and shear strain of the membrane surface and the deformation characteristics of the membrane material are obtained, and the membrane surface cloud map of each picture in the tearing and damage process of the membrane material collected by the image acquisition device 9 and the displacement and strain values of the entire membrane surface are obtained. At the same time, in step 3, the tearing and damage stage of the membrane material obtained can now be measured by LVDT displacement sensor, laser rangefinder or strain gauge to quantitatively judge the tearing stage of the membrane material. If the measured displacement is less than 0.2δ C It can be determined that the initial load is in the "slit tension section". At this time, the parent material can be welded for reinforcement. When the measured displacement is close to 0.9δ C, it can be judged that it is about to enter the "beginning of tearing stage". In addition to using higher strength fabric membrane materials for welding reinforcement, the photovoltaic membrane structure also needs to be unloaded and reduced, and repaired and reinforced; the strain concentration area can be identified through the strain cloud map. The high strain area is generally the crack initiation location or the crack may extend in this direction. Strengthen the design or maintenance of the strain concentration area to avoid structural failure. The deformation characteristics of the membrane surface in the membrane material tearing process can be obtained through the membrane surface horizontal and vertical displacement cloud map, horizontal and vertical strain cloud map and shear cloud map. The red area in the cloud map is along the yarn direction, which means that the yarn fiber is pulled apart. The red area spreads like a spider web, which means that the coating or substrate of the membrane material may be damaged first, and an oblique red area (large shear strain) appears, which may crack or wrinkle. This can better understand and analyze the deformation behavior of the membrane material, and take protective measures such as welding reinforcement and local reinforcement in advance.

[0059] Based on the above-mentioned testing method, the present invention also provides a device for testing the mechanical properties of fabric membrane materials, comprising:

[0060] The data acquisition module is used to collect real light data and real temperature data in a real environment within a preset time period, perform light-thermal analysis, and convert the light data into temperature data;

[0061] The test module is used to place the membrane sample in the simulated environment of the above temperature data, perform dynamic tearing tests under different temperature conditions, and record the test results under different temperature conditions, including the failure image, load and displacement data of the tearing process of the fabric membrane;

[0062] The analysis module is used to process the tearing failure image to obtain the membrane surface displacement field and strain field. The load-displacement relationship curve is established through the load and displacement data. The three types of measured data are obtained: the tearing failure image of the fabric membrane material, the load-displacement relationship curve, and the membrane surface displacement field and strain field. Based on these three types of measured data, the results of the membrane material tearing mechanical response and deformation are analyzed;

[0063] The generation module analyzes the tearing mechanical properties of the photovoltaic membrane structure and provides protective measures based on the above results analysis.

[0064] The processing procedures of the above modules refer to steps 1 to 4 in the test method respectively, and will not be repeated in this embodiment.

[0065] The specific test plan is as follows:

[0066] The first step is to collect light and temperature data, such as Figure 3 The actual environment of this embodiment is shown in the table below. The detailed data of the solar radiation intensity and the temperature of three measuring points on the membrane surface changing with time in the actual environment are obtained, and the changing trend is shown in the table below. Figure 6 shown.

[0067]

[0068] Weather conditions have a significant impact on solar radiation intensity and photovoltaic module performance. Specifically, on sunny days, the radiation intensity is high (800-1000W / m 2 ), the membrane surface temperature rises rapidly. For example, in the test on October 29, the maximum membrane surface temperature reached 43.9℃, 24℃ higher than the ambient temperature; when the specimen is continuously exposed to direct sunlight (such as on November 3), the maximum membrane surface temperature can reach 53.1℃, with a temperature rise of 30℃. Under cloudy conditions, the radiation intensity is low (200-400W / m 2 ), the temperature rise is limited, such as the highest temperature of the membrane surface on October 28 was 31℃, and the temperature rise was only 12℃. In cloudy weather, the irradiation intensity fluctuates greatly (400~800W / m 2 ), resulting in temperature fluctuations. For example, on October 30th, the maximum membrane surface temperature reached 38.4°C, an 18°C rise. Weather conditions significantly affect the output voltage and membrane surface temperature of PV modules by changing solar radiation intensity and ambient temperature.

[0069] By analyzing the irradiation intensity, output voltage, membrane surface temperature and temperature increment of photovoltaic modules under different weather conditions, key data are summarized as shown in the table below. The light data under different weather conditions can be converted into temperature data.

[0070]

[0071] The second step is to conduct a tear test of the membrane material under high temperature and record the digital image, load and displacement data of the sample tearing process: determine the type and size of the membrane material, the size of the speckle diameter, the temperature range and gradient, and the test equipment. Specifically: the material used is a typical fabric composite membrane with PVDF coating, the membrane thickness is 0.73mm, and the surface density is 949g / m 2 The yarn density in the warp and weft directions is 8.8 × 7.6 yarns / cm (warp × weft); the specimen dimensions are 152.4 mm × 101.6 mm (length × width), and the effective target area dimensions are 76.2 mm × 101.6 mm. The slit is located in the center of the specimen, and the target area is sprayed with a 0.5 mm diameter speckle.

[0072] Based on the above temperature data and taking into account the integrity of the test, the lower limit of the test temperature data is smaller than the minimum value of the actual temperature data, and the upper limit of the test temperature data is larger than the maximum value of the actual temperature data. The test temperature data range is set to 25°C to 100°C, with a gradient of 25°C. Preferably, after the test data range is generated based on the actual temperature data, it can be supplemented according to actual needs, for example, two more temperatures of 40°C and 60°C can be added.

[0073] The tensile tearing equipment used is the UTM4000 electronic universal testing machine with a displacement rate of 0.001 to 500.000 mm min -1 , the deformation measurement range is 0~800mm, the accuracy is ±1‰, and it is equipped with a tension and pressure sensor with an accuracy of 0.1N and a range of 10kN. The image acquisition device uses a Nikon camera with a 24-megapixel camera, which can effectively achieve accurate non-contact full-area measurement. In this example, a 150W lighting system is built into the high and low temperature test chamber, which is suitable for temperatures of 0~150℃. A G-type clamp is used to assist clamping to reduce slippage. The speckle pattern is generated by a CNC speckle machine, and 20,000 to 30,000 specks can be identified. The standard specimen is placed in a simulated environment for dynamic tearing test, such as Figure 5 As shown;

[0074] The test process was carried out according to the following steps: ① The membrane material specimen 6 with speckles was installed on the fixture in the high and low temperature test chamber to complete the sealing, insulation and heat preservation work; ② The temperature in the test chamber was controlled to a predetermined value and stabilized for 10 minutes, during which a pre-tension of 10N was always maintained; ③ The UTM4000 testing machine (constant rate of 25mm / min) and the D3200 camera (sampling frequency of 10Hz) were synchronously started to continuously capture digital images of the specimen's tearing and failure process; ④ The UTM4000 testing machine automatically collected and recorded the load and displacement data.

[0075] The third step is to post-process the tearing damage image to obtain the data file of the membrane surface displacement field and strain field information, establish the load-displacement relationship curve, and analyze the three types of measured data: the membrane material tearing damage image, the tearing load-displacement relationship curve, and the membrane surface displacement field and strain field:

[0076] Tearing damage to the image Figure 8 As shown: The test shows that the tearing failure process of the membrane material at different temperatures is basically similar, and four typical stages can be defined, as follows:

[0077] (i) Slit pre-tensioning section: Under 10N pre-tension and low load, the slit opens slightly;

[0078] (ii) The first formation of the tearing triangle: As the external load increases, the slit opens further; a stress concentration triangle is formed at the slit tip, and the tensile stress of the warp yarn in the triangle gradually increases and approaches its breaking strength; this section is before the critical tearing failure (the first yarn breaks);

[0079] (iii) Tearing failure: As the applied load increases, the stress in the membrane material gradually increases, and the maximum stress in the stress concentration area rises significantly. When the maximum stress in the yarn reaches the breaking strength, the yarn breaks, i.e., tearing failure occurs.

[0080] (iv) Full expansion: As the external load continues to increase, the load-bearing yarns break one after another, and the slit expands the width of the specimen. The load-bearing capacity of the membrane material decreases sharply until it loses its load-bearing capacity. The failure mode is mainly the neat breakage of fibers, with less yarn extraction and slippage failure. At different temperatures, the slit always expands along the direction of the main load-bearing yarn, that is, the warp yarn, and the final failure mode is a "straight" shape.

[0081] The yarn breakage forms are different. Taking 50℃ as the temperature threshold point, the degree of yarn breakage of the membrane material is divided into: "slow" breakage and "severe" breakage. The former corresponds to temperatures of 25℃ and 40℃. The stress field is evenly distributed in the yarn bundle, and the fiber has a strong collaborative bearing capacity. After the first warp yarn at the tip of the cut of this type of specimen breaks, its adjacent warp yarns respond quickly and bear the main external load. The stressed warp yarns break one after another, and the tearing triangle area gradually expands laterally. When the yarn breaks, some fibers are forcibly pulled out of the coating matrix. The overall destruction process has certain warning and evolution characteristics, which is called "ductile failure". Figure 8 (a). When the temperature is 50℃, 60℃, 75℃ and 100℃, only the stressed warp yarn at the tip of the cut is exposed and continuously stretched, and the width of the tearing triangle is slightly expanded. Figure 8 (b) After the first warp yarn breaks, the cut expands to the width instantly, lacking warning signs. Compared with the previous type of failure, this type of failure is characterized by "brittle failure";

[0082] The yarns all expand along the breaking direction of the main stress-bearing yarns, that is, the breaking direction of the warp yarns.

[0083] The load-displacement relationship curve is as follows Figure 9 As shown in the figure, based on the stiffness evolution law, the entire curve can be divided into four typical stages through the quasi-yield point A, the stiffness strengthening point B, and the starting tearing point C: the linear elastic stage OA segment, the quasi-yield stage AB segment, the stiffness strengthening stage BC segment, and the post-tear segment CD segment. Among them, in MATLAB, the three points A, B, and C in the load-displacement relationship curve can be identified by piecewise linear regression combined with the residual minimization method; the linear stiffness K of the linear elastic stage OA segment, the quasi-yield stage AB segment, and the stiffness strengthening stage BC segment at different temperatures can be calculated. OA , K AB , K BC , linear stiffness, peak load and fracture displacement are shown in the following table:

[0084]

[0085] Linear stiffness K of the OA segment in the linear elastic stage, the AB segment in the quasi-yielding stage, and the BC segment in the stiffness enhancement stage OA , K AB , K BC The law of change is shown in Figure 10 , the temperature stiffness degradation formula is obtained by fitting:

[0086] K OA =-0.0018*T 3 +0.285*T 2 -19.87*T+1149.38

[0087] K AB =0.0004*T 3 -0.0492*T 2 +0.171*T+228.89

[0088] K BC =-0.0005*T 3 +0.0954*T 2 -6.92*T+444.88

[0089] T is temperature.

[0090] Taking the typical temperature of 75℃ as an example, the displacement and strain nephograms of the membrane surface at the tearing point C are as follows: Figure 11 Its lateral displacement cloud diagram is shown as follows: Figure 11 As shown in (a), under the action of tensile load, the lateral displacement is mainly contraction displacement, and the larger displacement values appear on the left and right sides of the slit tip. The overall displacement field cloud diagram shows a "parabolic" distribution from the two sides to the middle slit, and the membrane surface is in a state of being squeezed from the two sides to the middle. Figure 11 (b) is the transverse strain cloud diagram. The vicinity of the slit tip shows obvious negative strain concentration. This phenomenon is mainly composed of two parts: one is the necking phenomenon caused by the transverse contraction effect near the slit tip during the stretching process; the other is that the vertical displacement of the central area of the elliptical slit is significantly greater than the vertical displacement of the slit tip, which involves the slit tip area, including the vertical strip area perpendicular to the slit tip, to shrink toward the center. Figure 11 (a) The state of the membrane surface being squeezed from both sides toward the center is consistent.

[0091] During the tearing process, the cut expands into an elliptical hole, and the vertical displacement is mainly concentrated in the upper end of the cut, such as Figure 11 (c) As shown. The displacement value at the upper end of the slit is large, while the displacement value at the lower end is small, and an obvious displacement jump phenomenon occurs. This is because during the uniaxial center tearing failure process, the upper end of the slit is directly loaded and easily deformed, while the lower end of the membrane material is fixed, and due to the existence of the slit, the load path is destroyed and the deformation is small. The vertical displacement cloud diagram is symmetrical with the vertical extension line of the center point of the slit as the symmetry axis. Figure 11As can be observed in image (d), the maximum vertical strain on the membrane surface is concentrated near the slit tip, forming a symmetrical crescent shape corresponding to the tear triangle. This indicates that under critical tearing conditions, significant stress concentration occurs near the slit tip. The vertical strain is lowest at the upper and lower ends of the slit center, while the strain at the membrane edge is relatively uniform. The vertical strain contour shows a vertically symmetrical distribution, with the horizontal extension of the slit center as the axis of symmetry.

[0092] Near the kerf tip, the shear strain cloud diagram shows an "X"-shaped distribution, forming a bipolar distribution of positive and negative shear strains, such as Figure 11 (e) shows that one extreme point on the same side shows positive shear strain, while the other extreme point shows negative shear strain, indicating that shear deformation in two directions occurs on the same side near the slit tip. Under the action of shear force, the membrane material undergoes out-of-plane buckling in a local area, resulting in local concentration of shear strain and the formation of a local buckling zone. This phenomenon is the result of deformation coordination and reflects the complex mechanical response of the membrane material near the slit tip.

[0093] The above analysis can help understand and analyze the deformation behavior of the membrane material, identify the strain concentration area, and obtain the peak displacement and strain values of the membrane surface during the tearing process.

[0094] Step 4: Summary of results:

[0095] By observing the tearing morphology, it is possible to determine which of the four typical stages of tearing damage the membrane material is in, and to take reinforcement or maintenance measures in advance; by the fracture form of the yarn, the fracture characteristics of different temperature ranges are divided with 50°C as the temperature threshold: in the range of 25-50°C, the membrane material exhibits ductile fracture with obvious warning characteristics; while in the range of 50-100°C, the material is prone to brittle fracture without obvious warning. Under temperature conditions above 50°C, it is necessary to strengthen the monitoring and maintenance of the membrane material status to prevent sudden structural failure caused by brittle fracture; carry out precise repairs on the path where the yarn has torn, and take reinforcement measures in the direction of the main force-bearing yarn fracture;

[0096] Based on the load-displacement relationship curve of the membrane tearing test, a temperature linear stiffness degradation formula was established. This formula can predict the linear stiffness above 100°C or below 25°C, ensuring that it is within the allowable range of the project. In this way, support or local reinforcement is strengthened in areas with higher loads. Displacement changes are also detected to determine whether the membrane structure is about to tear and fail, and timely maintenance is carried out to avoid sudden damage.

[0097] By analyzing the displacement and strain fields on the membrane surface, identifying areas of concentrated stress and strain, strengthening design or maintenance in concentrated areas, and analyzing the deformation characteristics of the membrane material, we can better understand and analyze the deformation behavior of the membrane material. In the actual engineering application of photovoltaic membrane structures, the displacement and strain of membrane material tearing in real time are monitored. The tearing process is located through measured data, and early warning is given to avoid structural failure.

Claims

1. A method for testing the mechanical properties of a fabric membrane, characterized in that: include: Within a preset time period, real light data and real temperature data in a real environment are collected, light-thermal analysis is performed, and the light data is converted into temperature data; The membrane sample is placed in the simulated environment of the above temperature data, and dynamic tearing tests are performed under different temperature conditions. The test results under different temperature conditions are recorded, including the failure image, load and displacement data of the tearing process of the fabric membrane material; The tearing failure image is processed to obtain the displacement field and strain field of the membrane surface. The load-displacement relationship curve is established through the load and displacement data. Three types of measured data are obtained: the tearing failure image of the fabric membrane material, the load-displacement relationship curve, and the membrane surface displacement field and strain field. Based on these three types of measured data, the results of the membrane material tearing mechanical response and deformation are analyzed. Based on the above analysis results, the tearing mechanical properties of the photovoltaic membrane structure are analyzed and protective measures are taken.

2. The method according to claim 1, characterized in that Used in real environment, the result analysis process includes: According to the extension of the incision and whether the first main stress-bearing yarn breaks, the tearing process of the membrane material at high temperature is divided into different tearing stages, including the "incision tensioning stage" and the "initiation of tearing stage". Observe the fracture pattern of the yarn at the cut and classify the tearing failure of the membrane into "ductile fracture" with warning and "brittle fracture" without warning; Capture the key nodes of the tearing process, including the starting point and the end point; observe the overall expansion trend of the cut, and obtain the membrane tearing peak load F through the membrane tearing load-displacement relationship curve C and fracture displacement δ C ; Calculate the linear stiffness K of the linear elastic stage OA segment, the quasi-yield stage AB segment and the stiffness enhancement stage BC segment at different temperatures OA , K AB , K BC , the temperature line stiffness degradation formula is obtained by fitting; The cloud diagrams of the horizontal and vertical displacements, strains and shear strains of the membrane surface during the tearing process of the fabric membrane are obtained to obtain the deformation characteristics of the membrane material during the tearing process, as well as the displacement and strain data values of the membrane surface of various displacements and strains during the tearing process of the membrane material.

3. The method according to claim 2, characterized in that Analyze the tearing mechanical properties of photovoltaic membrane structures and implement protective measures, including: By observing the morphological characteristics of membrane tearing in the photovoltaic membrane structure and comparing them with the membrane tearing failure stage in the dynamic tearing test, the damage stage of the membrane material can be determined. If it is in the "slit tensioning stage" where the initial load is applied, welding reinforcement with parent material is required at the slit to prevent the slit from further expanding. If it is in the "initial tearing stage" where the first main load-bearing yarn breaks, in addition to welding reinforcement at the tearing site, the photovoltaic membrane structure also needs to be unloaded and unloaded. The fracture characteristics of different temperature ranges are divided by the temperature threshold point T1: in the temperature range below the temperature threshold point T1, the membrane material exhibits ductile fracture with obvious warning characteristics, and in the temperature range above the temperature threshold point T1, the membrane material is prone to brittle fracture without obvious warning. When the membrane surface temperature is higher than the temperature threshold point T1, it is necessary to strengthen the monitoring and maintenance of the membrane material status, monitor whether there are cracks on the membrane surface, the crack propagation, and the tearing damage stage. Based on the monitoring results, welding reinforcement or unloading and unloading can be carried out to prevent sudden structural failure caused by brittle fracture. The starting point of the tearing process is captured and local reinforcement is carried out at the starting point through welding of the base material. According to the overall expansion trend of the cut, on the one hand, repairs are carried out on the torn path, and on the other hand, preventive reinforcement measures are implemented on the untorn expansion path perpendicular to the force direction. According to the temperature linear stiffness degradation formula, the linear stiffness of the membrane material at different temperatures and different tearing stages is calculated to ensure that the linear stiffness of the fabric membrane material is within the allowable range of the project; at the same time, the membrane material tearing peak load F can be extracted from the load-displacement relationship curve C and fracture displacement δ C Immediately strengthen the support, local reinforcement or unloading and reducing the load in the area with higher load; monitor the dynamic deformation of the torn area, strengthen the support, local reinforcement or unloading and reducing the load in the torn area; and judge whether the membrane material is about to tear and fail; By measuring the displacement and strain values of the tearing area, the tearing stage and deformation behavior of the membrane material can be quantitatively determined, and welding reinforcement can be prepared in advance; the strain concentration area can be identified through the strain cloud map, and the design or maintenance of the strain concentration area can be strengthened.

4. The method according to claim 2, characterized in that "Ductile fracture" and "brittle fracture" are two types of fracture forms: after the first main stress-bearing yarn breaks, the subsequent yarns break one after another; and at the moment the first main stress-bearing yarn breaks, the remaining main stress-bearing yarns all break almost at the same time.

5. The method according to claim 2, characterized in that The temperature line stiffness degradation formula is: K OA =A1*T n +A2*T n-1 +A3*T n-2 +…+A n *T+P OA K AB =B1 / T n +B2*T n-1 +B3*T n-2 +…+B n *T+P AB K BC =C1*T n +C2*T n-1 +C3*T n-2 +…+C n *T+P BC Where T is temperature; n represents the linear stiffness K OA , K AB , K BC The highest order of the polynomial, A1-A n 、B1-B n 、C1-C n Represents the linear stiffness K OA , K AB , K BC Polynomial coefficients, P OA 、P AB 、P BC Represents the linear stiffness K OA , K AB , K BC The constant term of a polynomial.

6. The method according to claim 3, characterized in that Unloading and reducing the load of photovoltaic membrane structures includes clearing the deposits on the membrane surface, reducing the tension and simultaneously monitoring the morphological changes of the membrane structure.

7. The method according to claim 1, characterized in that The membrane sample was sprayed with ink speckles using a CNC speckle machine, and matte ink was used to generate a randomly distributed speckle pattern. The image acquisition equipment was used to collect photos of the membrane sample with speckles during the tearing process at the same time intervals.

8. The method according to claim 1, characterized in that In the process of collecting real light data and real temperature data under real environment, photovoltaic modules and film materials are compounded to prepare photovoltaic-fabric film composite materials. The photovoltaic-fabric film composite materials are placed in real environment, and real light data under different weather conditions are collected within a preset time period. The real temperature data of the photovoltaic module surface, the fabric film surface and the composite interface of the photovoltaic module and the fabric film material are collected, the real light data and temperature data are analyzed, the light data under various weather conditions are converted into temperature data, and the temperature range and temperature change gradient of the tear test are determined based on the relationship between the measured light and temperature.

9. A device for testing the mechanical properties of fabric membranes, characterized in that: include: The data acquisition module is used to collect real light data and real temperature data in a real environment within a preset time period, perform light-thermal analysis, and convert the light data into temperature data; The test module is used to place the membrane sample in the simulated environment of the above temperature data, perform dynamic tearing tests under different temperature conditions, and record the test results under different temperature conditions, including the failure image, load and displacement data of the tearing process of the fabric membrane; The analysis module is used to process the tearing failure image to obtain the membrane surface displacement field and strain field. The load-displacement relationship curve is established through the load and displacement data. The three types of measured data are obtained: the tearing failure image of the fabric membrane material, the load-displacement relationship curve, and the membrane surface displacement field and strain field. Based on these three types of measured data, the results of the membrane material tearing mechanical response and deformation are analyzed; The generation module analyzes the tearing mechanical properties of the photovoltaic membrane structure and provides protective measures based on the above results analysis.

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