Automatic testing system and method for single fiber interfacial shear strength

Abstract

The application discloses an automatic testing system for single-fiber interfacial shear strength, which comprises a single fiber with a resin drop, a clamp assembly for vertically fixing the single fiber and stretching the resin drop, and a testing system for detecting the single-fiber interfacial shear strength; the clamp assembly comprises a fixing frame for fixing two ends of the single fiber and movable along the direction of a single-fiber fixing shaft, and a pair of cutters located on both sides of the connection between the fiber and the resin drop; the testing system comprises a resin drop length acquisition module, a shearing force acquisition module, a motion control module and a calculation module. The application further provides an automatic testing method. The system provided by the application can effectively improve the detection accuracy and efficiency of the single-fiber interfacial shear strength.

Description

Technical Field

[0001] This invention belongs to the field of mechanical property testing technology, and in particular relates to an automatic testing system and method for the interfacial shear strength of a single fiber. Background Technology

[0002] Compared with traditional metallic materials, composite materials possess advantages such as high specific strength, high specific modulus, and fatigue resistance, making them widely used in aerospace, transportation / manufacturing, civil construction, and sporting goods. Since the macroscopic mechanical properties and durability of these materials are closely related to the interfacial properties between the fiber and the matrix—which are the primary reason for stress transfer from the matrix to the reinforcing fibers—accurately detecting and evaluating the resin / fiber interface state to obtain the interfacial properties of carbon fiber composites and guide fiber surface modification to regulate the interfacial properties of composites is an effective and essential approach to improving the mechanical properties of fiber composites and developing novel structural / functional carbon fiber composites.

[0003] Currently, commonly used methods for testing the interfacial properties between fibers and the matrix include fiber pull-out, microdroplet debonding, ejection, and monofilament breakage. Among these techniques, the microdroplet debonding method is relatively convenient for measuring the embedding length, with advantages such as easy observation and low equipment manufacturing cost. This method involves applying axial force to the upper end of a fiber monofilament with resin droplets through a testing machine to detach the monofilament from the resin matrix, and recording the maximum load during the pull-out process to obtain the interfacial shear strength.

[0004] Currently, fiber interface shear strength testing can only be performed manually, step by step. Operators need to undergo professional training before they can take up their posts. The testing process can cause visual fatigue, and the test results obtained by different personnel operating the equipment are inconsistent and fluctuate greatly.

[0005] Patent document CN106596296A discloses a method and apparatus for testing the interfacial shear strength of a single fiber, including a monofilament tensile tester, a fixed clamp, a movable clamp, and a single fiber pull-out auxiliary device. The single fiber pull-out auxiliary device includes a support assembly, an auxiliary clamp, a display, and a telescopic adjustment assembly. The support assembly consists of a sliding support, a fixed support, and a support base plate. A display is installed on the auxiliary clamp. A telescopic adjustment assembly is installed on each side of the auxiliary clamp, and the two telescopic adjustment assemblies are mirror-symmetrical with respect to the auxiliary clamp. Each telescopic adjustment assembly consists of a telescopic end, a fixed end sleeve, and a graduated rotating end arranged in sequence. The rotating end, partially fitted inside the fixed end sleeve, is threadedly connected to the fixed end sleeve, and the telescopic end, partially fitted inside the fixed end sleeve, is fixedly connected to the rotating end. The telescopic end is connected to the auxiliary clamp. This device is designed for a fixed length of the monofilament embedded in the resin in composite materials, and its final test results are not accurate.

[0006] Patent document CN105547851A discloses a compact composite material interfacial shear strength testing device and a method for testing the interfacial shear strength of composite materials using the same. The device includes a fixed base, a micro-tensile testing system and a microdroplet clamping system. It achieves interfacial shear strength testing by longitudinally stretching the composite material. However, the device does not consider the influence of the resin droplet's own weight causing deformation of the composite material during the stretching process, which leads to errors in the final test results. Summary of the Invention

[0007] The purpose of this invention is to provide an automatic testing system and method for single-fiber interfacial shear strength, which can effectively improve the detection accuracy and efficiency of single-fiber interfacial shear strength.

[0008] To achieve the above objectives, the present invention provides an automatic testing system for the interfacial shear strength of a single fiber, comprising a single fiber with a resin droplet, a clamp assembly for vertically fixing the single fiber and stretching the resin droplet, and a testing system for detecting the interfacial shear strength of the single fiber.

[0009] The clamping assembly includes a fixing frame for securing both ends of a single fiber and movable along the fixing axis of the single fiber, and a pair of cutters located on both sides of the connection between the fiber filament and the resin droplet.

[0010] The testing system includes a resin drop length acquisition module, a shear force acquisition module, a motion control module, and a calculation module. The resin drop length acquisition module is used to obtain the length of the single fiber embedded in the resin drop as the resin drop length. The shear force acquisition module is used to obtain the maximum shear force when the resin drop debonds from the single fiber. The motion control module is used to control the clamp assembly to perform directional movement. The calculation module is used to output the interfacial shear strength of the single fiber based on the input resin drop length and shear force.

[0011] Specifically, the resin droplet length acquisition module includes a camera, which acquires stable single-fiber images and processes them to obtain the resin droplet length.

[0012] Preferably, the processing of the single fiber image includes image stabilization and pre-erosion followed by dilation. The image stabilization is used to eliminate length errors, and the pre-erosion followed by dilation is used to enhance the resin droplet image information in the image. This can effectively avoid errors caused by fiber shaking due to interference from the surrounding environment during the measurement process.

[0013] Specifically, the image stabilization process involves the following steps:

[0014] Acquire continuously captured images of a single fiber to obtain the set of resin droplet lengths corresponding to all resin droplets embedded in the single fiber in each image;

[0015] Determine whether the length of each resin droplet in the resin droplet length set meets the detection requirements, and calculate the average length of the resin droplet lengths that meet the detection requirements.

[0016] The length fluctuation value of each resin droplet in each image is calculated based on the average length.

[0017] After reducing the length fluctuation of the resin droplets by adjusting the tool position, the set of resin droplet lengths in the single fiber image is then obtained.

[0018] Preferably, the length fluctuation value is adjusted based on the electrostatic field of the single fiber itself and the adsorption force generated by the blades on both sides. The specific process is as follows:

[0019] If the length fluctuation value exceeds the threshold, the motion control module drives the left or right cutter to move slowly towards the direction of the fiber monofilament. The electrostatic attraction force generated by the left and right cutter tips when they approach the fiber eliminates the jitter effect of the single fiber in the image until the fluctuation value of the length of each resin droplet meets the requirements. Since the jitter amplitude of the single fiber exceeds the depth of field range of the camera lens, it will cause image instability. Therefore, non-contact adjustment is adopted to eliminate jitter without affecting the physical state of the material being tested, thereby further improving the accuracy of the final result.

[0020] Specifically, the steps of the corrosion followed by expansion treatment are as follows:

[0021] Visual erosion is performed on the original single-fiber image to reduce the feature edges in the image until the single fibers in the single-fiber image are eliminated;

[0022] The edges of the visually etched single-fiber image are enlarged until the size of the expanded resin droplet image is consistent with the size of the original resin droplet image before etching.

[0023] Specifically, the directional movement speed of the fixed frame is in the range of 0.002mm / s to 0.004mm / s, thereby avoiding errors in the test results due to the loading speed.

[0024] Preferably, the directional movement speed of the fixing frame is 0.002 mm / s.

[0025] Specifically, the calculation formula of the calculation module is as follows:

[0026]

[0027] Where D is the fiber diameter in μm, L is the resin droplet length in μm, F is the maximum shear force when the resin droplet debonds from the single fiber in mN, π is pi, and τ is the interfacial shear strength of the single fiber in MPa.

[0028] This invention also provides an automatic testing method, implemented using the aforementioned automatic testing system for single-fiber interfacial shear strength, comprising:

[0029] Step 1: After fixing the single fiber vertically, start the test from the first resin droplet at the bottom where the resin droplet length meets the testing requirements.

[0030] Step 2: Adjust the positional relationship between the two blades and the upper fiber filament of the bottom resin droplet, and record the motion parameters during adjustment.

[0031] Step 3: Control the fixture to move vertically upwards and collect the shear force change between the resin droplet and the fiber filament. At the same time, calculate the maximum value. Stop moving the fixture when the current shear force is less than the previously collected maximum shear force within a set time, so as to obtain the maximum shear force.

[0032] Step 4: Calculate the corresponding single-fiber interfacial shear strength based on the fiber diameter, resin droplet length, and the maximum shear force.

[0033] Step 5: Based on the motion parameters recorded in Step 2, adjust the positions of the two blades to test the second resin droplet to obtain the corresponding single fiber interface shear strength.

[0034] Step 6: Repeat steps 3 to 5 to obtain the single-fiber interfacial shear strength between all resin droplets and fiber filaments.

[0035] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0036] (1) The fiber monofilament and resin droplet are separated by corrosion and expansion processing. The interference of the fiber monofilament on the boundary features of the resin droplet is removed from the original image. The image only retains the discrete resin droplets, making the target features clearer and the target surface smoother.

[0037] (2) The fiber drift and shaking phenomenon during the test was solved by visual anti-shake treatment. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of an automatic testing system for the interfacial shear strength of a single fiber provided in this embodiment;

[0039] Figure 2 This is a schematic diagram of the fixing frame structure of the clamp assembly provided in this embodiment;

[0040] Figure 3 This is a schematic diagram of the cutting tool and shearing force acquisition module provided in this embodiment;

[0041] Figure 4 This is a magnified view of a portion of the area where the cutting tool is close to the single fiber, as provided in this embodiment.

[0042] Figure 5 This is a schematic diagram of the resin droplet length acquisition module provided in this embodiment;

[0043] Figure 6 The original image acquired in this embodiment;

[0044] Figure 7 The image provided in this embodiment after erosion processing;

[0045] Figure 8 The image provided in this embodiment after dilation processing;

[0046] Figure 9 This is a schematic diagram showing the discrete position distribution of resin droplets after processing the original image provided in this embodiment. Detailed Implementation

[0047] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this application as detailed in the appended claims.

[0048] The terminology used in this application is for the purpose of describing characteristic embodiments only and is not intended to limit the application.

[0049] The singular forms “a,” “the,” and “the” used in this application and the appended claims are also intended to include multiple forms unless the context clearly indicates their meaning.

[0050] It should be understood that although the terms first, second, third, etc., may be used in this application to describe various parameters, these parameters should not be limited to these terms. These terms are used only to distinguish parameters of the same type from one another. For example, without departing from the scope of this application, a first resin drop may also be referred to as a second resin drop, and similarly, a second resin drop may also be referred to as a first resin drop. Depending on the context, the word "if" as used herein may be interpreted as "when," "when," or "in response to determination."

[0051] like Figure 1 As shown, an automatic testing system for the interfacial shear strength of a single fiber includes a single fiber with a resin droplet, a clamp assembly for vertically fixing the single fiber and stretching the resin droplet, and a testing system for detecting the interfacial shear strength of the single fiber, wherein the testing system is mounted on an industrial control computer.

[0052] The clamping assembly includes a fixing frame for fixing both ends of a single fiber and movable along the fixing axis of the single fiber, as well as a left and right cutter located on both sides of the connection between the fiber filament and the resin droplet.

[0053] The testing system includes a resin droplet length acquisition module, a shear force acquisition module, a motion control module, and a calculation module.

[0054] The shear force acquisition module includes a force sensor and a weighing display.

[0055] The resin droplet length acquisition module includes an industrial camera, lens, and light source.

[0056] The motion control module includes a first stepper motor for controlling the opening and closing motion of the left cutter, a second stepper motor for controlling the opening and closing motion of the right cutter, a third stepper motor for loading the resin droplets up and down, and a focusing stepper motor for moving the camera back and forth.

[0057] The calculation module includes a calculator and a results display. It performs calculations based on parameters obtained from other modules to obtain the single-fiber interfacial shear strength. The specific formula is as follows:

[0058]

[0059] Where D is the fiber diameter in μm, L is the resin droplet length in μm, F is the maximum shear force when the resin droplet debonds from the single fiber in mN, π is pi, and τ is the interfacial shear strength of the single fiber in MPa.

[0060] like Figure 2 The diagram shows a single fiber fixed on a mounting frame, including resin droplets 1 on the fiber monofilament, fiber monofilament 2 on the carrier, carrier 3, and tape 4. The resin droplets 1 are granular and adhered to the fiber monofilament 2. The two ends of the fiber monofilament 2 are fixed to the carrier 3 by tape 4. L1, L2, ... Lm represent resin droplets that meet the test length requirements from bottom to top, and code 5 represents resin droplets that do not meet the length requirements.

[0061] like Figure 3 The diagram shows a cutting tool and a cutting force acquisition module, including a left cutting tool 6 and a first stepper motor 6.1 that drives the left cutting tool 6 to move, a right cutting tool 7 and a second stepper motor 7.1 that drives the right cutting tool 7 to move, a force sensor 8, and a stepper motor 9 for loading resin droplets and fibers.

[0062] The left cutter 6 and the right cutter 7 are distributed on the two sides of the fiber monofilament. The carrier 3, on which the fiber monofilament 2 is installed, is mechanically fixed to the upper end of the force sensor 8. The force sensor 8 is mechanically connected to the loading stepper motor 9, and the moving speed of the loading stepper motor 9 is set to 0.002 mm / s.

[0063] like Figure 4 The image shown is a magnified view of the area where the cutting tool is close to the single fiber. The horizontal distance from the tip of the left cutting tool 6.2 to the center of the fiber is dm1, and the horizontal distance from the tip of the right cutting tool 7.2 to the center of the fiber is dm2. The vertical distance from the lower end of the lowest qualified resin drop L1 on the fiber monofilament 2 to the line connecting the left and right cutting tips is e0. The left and right cutting tips need to be manually adjusted to the same horizontal plane before testing. The focusing scale 10 is arranged on the left cutting tool 6. Before using the system, the vision needs to be calibrated and adjusted to ensure that the height value of the scale in the vision image is consistent with the actual height. The calibrated height of the scale image is m. When the system automatically focuses, the focusing stepper motor is moved back and forth until the vision acquisition system reads the height of the scale image m' = m in real time, and the image focusing is completed. The distance from the tip of the left cutting tool 6.2 to the center of the fiber is d11… / dm1, and the distance from the tip of the right cutting tool 7.2 to the center of the fiber is d12… / dm2.

[0064] like Figure 5 The diagram shows a resin droplet length acquisition module. The lens 13 is fixed on the camera 12, and the camera and the light source 14 are distributed on the two sides of the fiber monofilament. The camera 12 is mechanically connected to the focusing stepper motor 11, and the focusing stepper motor 11 drives the camera 12 to move back and forth to achieve the automatic focusing function.

[0065] Because fibers are lightweight and small in size, they are prone to shaking and drifting during resin drop length measurement, which causes image instability and large length errors during visual acquisition. This embodiment adds image stabilization processing.

[0066] like Figure 6 As shown, this is the original image captured by the camera without image processing. The theoretical width and height dimensions of each resin droplet are L1h\L1w, L2h\L2w... Since each resin droplet is bonded to the fiber monofilament, the visual system cannot automatically identify the features. The conventional method is to manually click on the display screen with a mouse based on the user's sense of touch.

[0067] like Figure 7 The image shown is the result of visual erosion processing on the original image. Visual erosion reduces the size of various features in the image until the fibrous monofilaments are eliminated. Consequently, the dimensions of the resin droplets L1h'\L1w', L2h'\L2w', etc., will be reduced, i.e., L1h'... <L1h,L1w’<L1w…。

[0068] like Figure 8 The image shown is the result of dilation processing. The purpose of dilation processing is to expand the feature edges of the image so that the size of the resin droplet after dilation is the same as that before the image was eroded and dilated, i.e., L1h”=L1h, L1w”=L1w….

[0069] The purpose of erosion followed by dilation of the original image captured by the camera is to eliminate the fiber filaments in the original image, so that only discrete resin droplets are retained in the image, creating conditions for automatic visual acquisition.

[0070] like Figure 9 As shown, this is a schematic diagram of the discrete position distribution of resin droplets after processing the original image. That is, Lmh is the length of the m-th fiber embedded in the resin droplet from bottom to top in the image that meets the requirements, Lmw is the width of the m-th fiber embedded in the resin droplet, g1 represents the distance between resin droplets L1 and L2, and so on.

[0071] This embodiment also provides an automatic testing method, implemented using the automatic testing system for single-fiber interface shear strength described in the above embodiment, including the following steps:

[0072] Step 1: The focusing stepper motor drives the camera and lens to slowly approach the fiber monofilament. The camera collects and compares the height m' of the scale used for focusing the image on the left cutter with the height m marked on the scale. This continues until the camera collects the size m' of the focusing scale, where m' is the height of the focusing scale image collected by the camera and m is the height of the image marked on the focusing scale. At the same time, the distance moved is recorded as Lf.

[0073] Step 2: Move the left and right cutters away from the fiber direction by a distance H1; H1 = max(L1w / L2w… / Lmw);

[0074] The stepper motor drives the resin droplet to move a distance e0, and at the same time, the saved resin droplet length L1h is retrieved.

[0075] Step 3: Move the left cutter a distance d closer to the fiber filament. 11 +H1-D / 2, the distance d the right cutter moves closer to the fiber filament. 12 +H1-D / 2;

[0076] The left and right tool positions are maintained, and the resin droplet is loaded. The stepper motor drives the resin droplet to move downward, and the moving resin droplet generates a load relative to the stationary tool.

[0077] The shear force acquisition system collects the shear force between the resin droplet and the fiber in real time and calculates the maximum value of the shear force F0. When the collected shear force f0 is less than the shear force F0, the loading stepper motor stops moving downward.

[0078] Step 4: The system calculates the interfacial shear strength of the resin droplet: τ1=F0 / (πDL1h);

[0079] Step 5: Load the stepper motor to drive the fiber clamp to move upward until the shearing force collected by the cutting force acquisition system is less than a certain set value. Then, load the stepper motor to stop rising and the left and right cutters move outward a distance H1.

[0080] Step 6: Repeat steps 2 to 5, replacing e0 with gn-1 for the stepper motor movement distance, and replacing the resin droplet length L1h with Lmh. Replace d11+H1-D / 2 with the left cutter moving distance dm1+H1-D / 2 towards the fiber filament, and replace dm2+H1-D / 2 with the right cutter moving distance d12+H1-D / 2 towards the fiber filament. Replace F0 with the collected shear force Fm; calculate the interfacial shear strength τ of the resin droplet. m =Fm / (πDLmh) until all qualified resin droplets on the image have been tested; after all resin droplets of monofilament fibers have been tested, the focusing stepper motor drives the camera and lens to move backward by a set distance Lf.

[0081] Furthermore, it should be understood that after reading the above description of the present invention, those skilled in the art can make various alterations or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims.

Claims

1. An automatic testing system for the interfacial shear strength of a single fiber, characterized in that, It includes a single fiber with resin droplets, a clamp assembly for vertically fixing the single fiber and stretching the resin droplets, and a test system for detecting the interfacial shear strength of the single fiber. The clamping assembly includes a fixing frame for fixing both ends of a single fiber and movable along the fixing axis of the single fiber, and a pair of cutters located on both sides of the connection between the fiber filament and the resin droplet. The testing system includes a resin drop length acquisition module, a shear force acquisition module, a motion control module, and a calculation module. The resin drop length acquisition module is used to obtain the length of the single fiber embedded in the resin drop as the resin drop length. The shear force acquisition module is used to obtain the maximum shear force when the resin drop debonds from the single fiber. The motion control module is used to control the clamp assembly to perform directional movement. The calculation module is used to output the interfacial shear strength of the single fiber based on the input resin drop length and shear force. The resin droplet length acquisition module includes a camera, which acquires stable single-fiber images and processes them to obtain the resin droplet length. The processing of the single-fiber image includes image stabilization and erosion followed by dilation. The image stabilization is used to eliminate length errors, and the erosion followed by dilation is used to enhance the resin droplet image information in the image. The specific steps of the image stabilization process are as follows: Acquire continuously captured images of a single fiber to obtain the set of resin droplet lengths corresponding to all resin droplets embedded in the single fiber in each image; Determine whether the length of each resin droplet in the resin droplet length set meets the detection requirements, and calculate the average length of the resin droplet lengths that meet the detection requirements. The length fluctuation value of each resin droplet in each image is calculated based on the average length. After reducing the length fluctuation of the resin droplets by adjusting the cutter position, the set of resin droplet lengths in the single fiber image is obtained. The length fluctuation is then adjusted based on the electrostatic field of the single fiber and the adsorption force generated by the cutters on both sides. The specific process is as follows: When the length fluctuation value exceeds the threshold, the motion control module drives one side of the cutter to approach the single fiber at a low speed until the length fluctuation value is lower than the threshold. The specific steps of the pre-corrosion followed by expansion treatment are as follows: Visual erosion is performed on the original single-fiber image to reduce the feature edges in the image until the single fibers in the single-fiber image are eliminated; The edges of the visually etched single-fiber image are enlarged until the size of the expanded resin droplet image is consistent with the size of the original resin droplet image before etching.

2. The automatic testing system for single-fiber interfacial shear strength according to claim 1, characterized in that, The directional movement speed of the fixed frame ranges from 0.002 mm / s to 0.004 mm / s.

3. The automatic testing system for single-fiber interfacial shear strength according to claim 1, characterized in that, The calculation formula of the calculation module is as follows: Where D is the fiber diameter, in units of... L is the length of the resin droplet, in units of... F represents the maximum shear force when the resin droplet debonds from the single fiber, expressed in mN. Pi; This represents the interfacial shear strength of a single fiber, expressed in MPa.

4. An automatic testing method, characterized in that, The automatic testing system for the single-fiber interfacial shear strength as described in any one of claims 1 to 3 is used, comprising: Step 1: After fixing the single fiber vertically, start the test from the first resin droplet at the bottom where the resin droplet length meets the testing requirements. Step 2: Adjust the positional relationship between the two blades and the upper fiber of the bottom resin droplet, and record the motion parameters during adjustment; Step 3: Control the fixture to move vertically upward and collect the shear force change between the resin droplet and the fiber filament. At the same time, calculate the maximum value. Stop moving the fixture when the current shear force is less than the previously collected maximum shear force within a set time, so as to obtain the maximum shear force. Step 4: Calculate the corresponding single-fiber interfacial shear strength based on the fiber diameter, resin droplet length, and the maximum shear force. Step 5: Based on the motion parameters recorded in Step 2, adjust the positions of the two blades to test the second resin droplet to obtain the corresponding single fiber interface shear strength. Step 6: Repeat steps 3 to 5 to obtain the single-fiber interfacial shear strength between all resin droplets and fiber filaments.

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