An in-situ loading three-point bending fixture and method for aiding micro-characterization

Abstract

The present application relates to a kind of in-situ loading three-point bending clamps and methods for assisting micro characterization, belong to three-point bending clamp technical field.In which in-situ loading three-point bending clamps include base plate, sliding block, pressing plate, lock nut, the base plate is equipped with sliding slot, the base plate center is equipped with the semicylindrical support perpendicular to the direction of the sliding slot;Two The sliding block is placed in the sliding slot of the semicylindrical support two sides respectively, and one pressing plate is fixed on each sliding block by one or more lock nuts respectively, and there is also a gap between the pressing plate and the sliding block;Based on the above device, the present application also provides a kind of auxiliary micro characterization method, can be directly observed to different strain after once unloading, wide application range, practical and convenient.

Description

Technical Field

[0001] This invention relates to an in-situ loading three-point bending fixture and method for assisting microscopic characterization, belonging to the technical field of three-point bending fixtures. Background Technology

[0002] With the development of science and technology, more and more experiments require in-depth exploration of the properties and laws of materials. However, experimental research methods significantly influence the progress of experimental results. For materials science, the most crucial aspect of experimental materials research is the characterization of material properties. This characterization depends on research at both the macroscopic and microscopic scales, especially at the microscopic scale, where research is significantly constrained by experimental methods. Traditional, single-instrument equipment is insufficient to meet the requirements for in-depth exploration of microscopic properties. Therefore, it is necessary to add auxiliary equipment to existing instruments to advance the experiment.

[0003] For example, in-situ loading scanning electron microscopy involves loading a device with tensile, compressive, or bending loading effects onto a scanning electron microscope to investigate the evolution of the microstructure of materials under loading, thus providing a foundation for the study of the mechanical properties of materials.

[0004] In-situ loading scanning electron microscopy (SEM) has many drawbacks, including extremely high cost (US$50,000 to US$100,000, such as the corresponding products from MTI in the United States), large instrument size and weight, etc. At the same time, traditional microstructure characterization methods can only detect the initial state of the sample and cannot perform deformation processing and microscopic morphology imaging of the sample in real time. It is also impossible to observe different strains under a single loading condition. Therefore, it is difficult to study the deformation process during observation, especially for many dynamically changing experiments (such as stress-induced martensitic transformation), where the dynamic deformation process can cause inconvenience to observation and research.

[0005] For example, CN106526241B discloses an in-situ loading device based on a scanning electron microscope. However, this device has a complex structure and suffers from high cost and limited applicability. Furthermore, it cannot accurately observe and study deformation during dynamic loading, nor can it obtain precise data to aid subsequent research. Summary of the Invention

[0006] To address the aforementioned problems, this invention provides an in-situ loading three-point bending fixture for assisting microscopic characterization, comprising a substrate, sliding blocks, pressure plates, and locking nuts. The substrate has a sliding groove, and a semi-cylindrical support perpendicular to the sliding groove is located at the center of the substrate. Two sliding blocks are respectively placed in the sliding grooves on both sides of the semi-cylindrical support. Each sliding block is fixed with one or more locking nuts to a pressure plate, and a gap is left between the pressure plate and the sliding block.

[0007] In one embodiment of the present invention, the slide groove has a trapezoidal cross section; each of the pressure plates is fixed by two locking nuts.

[0008] In one embodiment of the present invention, the substrate is rectangular.

[0009] This invention also provides an auxiliary microscopic characterization method.

[0010] Includes the following steps:

[0011] Step 1: Select a sheet-like sample capable of elastic deformation, fix both ends of the sheet-like sample to the gap between the two pressure plates and the sliding block, and lock them with the locking nut; at the same time, place the middle area of ​​the sheet-like sample on the semi-cylindrical support, so that the sheet-like sample bends at three points and deforms;

[0012] Step 2: Take any observable deflection change starting point at 1 / 2 thickness of the left fixed end of the sheet sample as the origin O, take the direction parallel to the long side of the substrate as the X-axis direction, and take the direction perpendicular to the long side of the substrate as the Y-axis direction, and establish an XOY plane coordinate system.

[0013] Step 3: Let c be any point on the sheet sample at half thickness in the XOY plane coordinate system during the deformation process, and let w be the deflection of point c in the Y-axis direction. The deflection w is used to represent the linear displacement of point c after bending compared to before bending. Assume that point c is always on the deflection curve, and the equation f(x) of the deflection curve is used to represent the functional relationship between the deflection w and the X coordinate of point c: w = f(x).

[0014] Step 4: Calculate the radius of curvature R at any point c on the deflection curve, and then use the formula... Calculate the tensile strain ε corresponding to any point c in the sheet-like sample; where the radius of curvature... r represents half the thickness;

[0015] Step 5: Apply the formulas from Step 3 respectively. and Establish distribution maps of radius of curvature R as a function of X coordinate and tensile strain ε as a function of X coordinate. With the help of these two distribution maps, the characteristics of the sample under different positions and different deformation conditions can be observed in real time.

[0016] In one embodiment of the present invention, the distribution maps of the radius of curvature R as a function of the X-coordinate and the tensile strain ε as a function of the X-coordinate are established using Origin software.

[0017] This invention also provides an auxiliary microscopic characterization method for in-situ loading three-point bending fixture in the study of maximum strain. By adjusting the fixed position between the two sliders and the pressure plate, the length of the bent portion of the sheet sample is adjusted, thereby obtaining the maximum strain value under different deformation conditions. The sheet sample only needs to be loaded once for analysis and observation.

[0018] In one embodiment of the present invention, when the X coordinate of point c is the same as that of the highest point of the semi-cylindrical support, the maximum strain εmax can be obtained. The maximum strain εmax is compared with the strain test requirement value of metallic materials and shape memory alloys to determine whether the sheet sample meets the requirements. Preferably, the sheet sample is a sheet Ti-Ni (CR15%) sample.

[0019] In one embodiment of the present invention, when the sheet-like sample undergoes plastic deformation after reaching maximum strain, a microscopic tensile strain calculation method, namely the microscopic feature point DIC (Digital Image Correlation) method, is employed. The specific method is as follows:

[0020] First, obtain a SEM image of the microstructure of the central region of the sheet-like sample before deformation;

[0021] Secondly, obtain the microstructure SEM image of the location of the maximum strain εmax during loading;

[0022] Next, the deformation was unloaded, and a microscopic SEM image was obtained again at the same location where the maximum strain was located;

[0023] Finally, by comparing with the DIC analysis software GOM Correlate, a micro-strain distribution cloud map in the Y direction was obtained, which was then used for further analysis.

[0024] It should be noted that although there is a certain error in selecting the origin O through human observation, the accuracy of the selection of the origin O only affects the accuracy of the absolute value of deflection, and will not affect the first and second derivatives of the deflection curve imported into the curvature calculation formula. Therefore, it is sufficient to choose any observable starting point of deflection change. The accuracy error of the selection of the origin O will not affect the size of the calculated radius of curvature, especially within ±10mm of the area near the maximum deflection, which is the main microscopic observation area.

[0025] The beneficial effects of this invention are:

[0026] 1. This invention utilizes an in-situ loading three-point bending fixture, which facilitates intuitive real-time observation of different strains after a single unloading.

[0027] 2. The present invention is equipped with a locking nut and a pressure plate, which can not only adjust the length of the bent part of the sheet sample to obtain different maximum strains, but also ensure that the unbent parts at both ends are flat and do not deform.

[0028] 3. This invention facilitates the continued study of the same location of maximum strain in subsequent microstructure characterization experiments, and allows for the observation of microscopic morphological characteristics under different strains.

[0029] 4. This invention sets a deflection curve equation to reflect the degree of deformation. The formula makes the results and analysis methods more intuitive and accurate.

[0030] 5. This invention uses a microscopic tensile strain calculation method to reflect plastic deformation, and at the same time uses microscopic SEM images and DIC analysis software GOM Correlate for comparison to provide an analytical basis for subsequent research.

[0031] 6. The in-situ loading three-point bending clamp of this invention has a small volume, light weight, and low processing cost. It can be used to observe and study the microstructure evolution caused by sample deformation during the deformation process, and is practical and convenient.

[0032] 7. This invention can study both elastic and plastic deformation, and has a wide range of applications. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the overall structure of an in-situ loading three-point bending fixture in one embodiment of the present invention.

[0034] Figure 2 This is a front view of an in-situ loading three-point bending fixture according to one embodiment of the present invention.

[0035] Figure 3 This is a side view of an in-situ loading three-point bending fixture according to one embodiment of the present invention.

[0036] Figure 4 This is a top view of an in-situ loading three-point bending fixture according to one embodiment of the present invention.

[0037] Figure 5 This is a schematic diagram of the XOY coordinate system and reference quantities for each physical quantity in an embodiment of the present invention, which utilizes an in-situ loaded three-point bending fixture to construct an auxiliary microscopic characterization method.

[0038] Figure 6 This is a macroscopic photograph of a sheet-like Ti-Ni (CR15%) sample under an electron microscope in a deformed state, according to one embodiment of the present invention.

[0039] Figure 7 This is a distribution diagram of the radius of curvature R as a function of x and the distribution diagram of strain ε as a function of x, generated by using Origin software to take points in one embodiment of the present invention.

[0040] Figure 8 The maximum strain ε was obtained at the point where the sheet-like Ti-Ni (CR15%) sample was subjected to loading and deformation. 中心 Microscopic SEM image.

[0041] Figure 9 ε was obtained for a sheet-like Ti-Ni (CR15%) sample under deformed unloading conditions. 中心 Microscopic SEM image.

[0042] Figure 10 The image shows the micro-strain distribution cloud map in the y-direction obtained by comparison using the DIC analysis software GOM Correlate.

[0043] In the figure, 1: substrate, 2: sliding block, 3: pressure plate, 4: locking nut, 5: sheet-like sample, 1-1: semi-cylindrical support, 1-2: groove. Detailed Implementation

[0044] Example 1

[0045] like Figures 1-4 As shown, the present invention provides an in-situ loading three-point bending fixture for assisting microscopic characterization, comprising a substrate 1, a sliding block 2, a pressure plate 3, and a locking nut 4.

[0046] The substrate 1 is a rectangular plate with a trapezoidal groove 1-2 inside. A semi-cylindrical support 1-1 perpendicular to the groove 1-2 is provided at the center of the substrate 1.

[0047] The two sliding blocks 2 are respectively placed in the sliding grooves 1-2 on both sides of the semi-cylindrical support 1-1. Each sliding block 2 is fixed with a pressure plate 3 by two locking nuts 4. There is a gap between the pressure plate 3 and the sliding block 2.

[0048] The two ends of the sheet sample 5 are respectively fixed in the gap between the pressure plate 3 and the sliding block 2 at both ends, and the deformed part of the sheet sample 5 is adjusted to a suitable length and locked with the locking nut 4. The middle part of the sheet sample 5 is placed on the semi-cylindrical support 1-1 in a convex state.

[0049] Example 2

[0050] The present invention also provides an auxiliary microscopic characterization method, comprising the following steps:

[0051] Step 1: Fix the sheet-like sample 5 onto the in-situ loading three-point bending fixture in Example 1. The semi-cylindrical radius R0 of the semi-cylindrical support is 6mm, causing the sheet-like sample 5 to bend at three points and deform. Then proceed with the following steps:

[0052] Step Two: As Figure 5 As shown, with the origin O at the starting point of the deflection change at 1 / 2 thickness of the left fixed end of the sheet sample 5, the XOY plane coordinate system is established with the direction parallel to the long side of the substrate as the X-axis direction and the direction perpendicular to the long side of the substrate as the Y-axis direction.

[0053] Step 3: Let c be any point on the sheet sample 5 at half its thickness in the XOY plane coordinate system during the deformation process, and let w be the displacement of point c in the Y-axis direction. The deflection w is used to represent the linear displacement of point c after bending compared to before bending. Assume that point c is always on the deflection curve, and the equation f(x) of the deflection curve is used to represent the functional relationship between the deflection w and the X coordinate of point c: w = f(x).

[0054] Step 4: Calculate the radius of curvature R at any point c on the deflection curve, and then use the formula... Calculate the tensile strain ε corresponding to any point c in the sheet-like sample; where the radius of curvature...

[0055] r represents half the thickness;

[0056] Step 5: Apply the formulas from Step 3 respectively. and Establish distribution maps of radius of curvature R as a function of X coordinate and tensile strain ε as a function of X coordinate. With the help of these two distribution maps, the characteristics of the sample under different positions and different deformation conditions can be observed in real time.

[0057] Example 3

[0058] This invention also provides an auxiliary microscopic characterization method for in-situ loading three-point bending fixture in the study of maximum strain. Based on Example 2, the length of the deformed part of the sheet sample is adjusted by adjusting the fixed position between the two sliders and the pressure plate, thereby obtaining the maximum strain value under different deformation conditions. The sheet sample only needs to be loaded once for analysis and observation.

[0059] According to the formula It can be seen that the smaller the radius of curvature R, the larger the strain ε. Therefore, referring to... Figure 5 The intersection point B of the center line of the three-point bend and the upper surface of the sheet sample 5 is the point of maximum strain ε. 中心 As the distance from the center line of the three-point bend increases, the strain ε gradually decreases. Let point C be the point where the strain reaches its maximum, BC = d / 2, and the center of curvature of point B be A. At this time, point A coincides with the center of curvature of the semi-cylindrical support 1-1.

[0060] The maximum strain εmax can be obtained when the X coordinate of point c is the same as that of the highest point of the semi-cylindrical support.

[0061] Select a sheet-like Ti-Ni (CR15%) with a thickness d of 2 mm as sheet-like sample 5. Substitute the thickness d = 2 mm and the radius of curvature R = R0 = 6 mm for sheet-like sample 5, and calculate the maximum strain at this time: For general metallic materials (ε) el ≤1%) and shape memory alloys (ε SE ≤10% all meet the test requirements.

[0062] Example 4

[0063] A sheet-like Ti-Ni (CR15%) sample with a thickness d of 0.5 mm was selected. After performing steps one, two, three, and four in Example 2, step five was carried out as follows:

[0064] The loading deformation of sheet-like sample 5 is shown under an electron microscope, such as... Figure 6 As shown in (a), points were obtained using Origin software;

[0065] like Figure 7 As shown in (a), 50 points were selected using Origin software, and polynomial fitting was performed (output data set to 500) to obtain the variation of the deflection curve f(x) with x. Based on the fitted deflection curve and the formula... and like Figure 7 As shown in (b), the strain distribution trend with x was obtained. It can be seen from the figure that the position of the center line of the three-point bend is the location of the maximum strain: ε max =4.57%;

[0066] according to Figure 7 The calculation results shown in the figure, in subsequent microstructure characterization experiments, such as Figure 6 As shown in (b), by selecting different microscopic characterization locations, the microscopic morphology characteristics of a sample at a certain location and under a certain strain can be studied in real time.

[0067] This embodiment 4 demonstrates that the simple three-point bending fixture for assisting microstructure characterization can help researchers rationally design strain distribution before the experiment, encompassing all strains to be studied; during the experiment, it avoids the cumbersome loading and unloading process, enabling real-time observation of different positions and strains with a single loading, saving a significant amount of research costs; after the experiment, based on the high-resolution image of the macroscopic loading, the strain distribution curve of the sample can be accurately obtained, facilitating subsequent comparative analysis of the influence of different strains on the microstructure characteristics of the sample.

[0068] Example 5

[0069] When the sheet sample in Example 4 undergoes plastic deformation after reaching the elastic limit, it cannot be observed using the above method. This is because the maximum strain described in this invention is limited by the semi-cylindrical radius of the semi-cylindrical support 1-1, which is also the maximum strain that can be observed macroscopically. After plastic deformation, the strain will exceed this, so it cannot be observed macroscopically.

[0070] Therefore, a microscopic tensile strain calculation method is needed, namely the microscopic feature point DIC (Digital Image Correlation) method.

[0071] First, obtain a SEM image of the microstructure of the central region of the sheet-like sample before deformation.

[0072] Secondly, such as Figure 8 As shown, the maximum strain ε at which the sheet-like Ti-Ni (CR15%) sample was obtained under loaded deformation is shown. 中心 Microscopic SEM image.

[0073] Again, such as Figure 9 As shown, the sheet-like Ti-Ni (CR15%) sample obtained after deformation and unloading was similar to... Figure 8 ε 中心 Microscopic SEM images of the same location.

[0074] Finally, as Figure 10 As shown, the GOM Correlate software was used to... Figure 8 and Figure 9 DIC analysis was performed, and the distribution cloud map of micro-strain along the tensile direction was obtained.

[0075] This embodiment 5 demonstrates that the simple three-point bending fixture for assisting microstructure characterization can help researchers analyze and compare high-resolution microscopic SEM images of the same location before, during, and after loading using DIC software after the experiment, obtain microscopic strain distribution cloud maps, and thus analyze the influence of microscopic strain on microstructure evolution.

[0076] In addition, by combining the macroscopic strain distribution measurement of Example 4 with the comparison of macroscopic and microscopic strain at any location, the potential microscopic mechanism of macroscopic performance changes can be revealed through the evolution law of microscopic organization.

[0077] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Anyone skilled in the art can make various modifications and alterations without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the claims.

Claims

1. An auxiliary microscopic characterization method using an in-situ loaded three-point bending fixture, characterized in that, The in-situ loading three-point bending fixture includes a base plate, sliding blocks, pressure plates, and locking nuts. The base plate has a groove, and a semi-cylindrical support perpendicular to the groove is located at the center of the base plate. Two sliding blocks are respectively placed in the grooves on both sides of the semi-cylindrical support. Each sliding block is fixed with one or more locking nuts to a pressure plate, and a gap is left between the pressure plate and the sliding block. The groove has a trapezoidal cross-section, and each pressure plate is fixed with two locking nuts. The auxiliary microscopic characterization method includes the following steps: Step 1: Select a sheet-like sample capable of elastic deformation, fix both ends of the sheet-like sample to the gap between the two pressure plates and the sliding block, and lock them with the locking nut; at the same time, place the middle area of ​​the sheet-like sample on the semi-cylindrical support, so that the sheet-like sample bends at three points and deforms; Step 2: Take any observable deflection change starting point at 1 / 2 thickness of the left fixed end of the sheet sample as the origin O, take the direction parallel to the long side of the substrate as the X-axis direction, the direction parallel to the short side of the substrate as the Z-axis direction, and the direction perpendicular to the substrate as the Y-axis direction, and establish an XOY plane coordinate system. Step 3: Let c be any point on the sheet sample at half thickness in the XOY plane coordinate system during the deformation process, and let w be the deflection of point c in the Y-axis direction. The deflection w is used to represent the linear displacement of point c after bending compared to before bending. Assume that point c is always on the deflection curve, and the equation f(x) of the deflection curve is used to represent the functional relationship between the deflection w and the X coordinate of point c: w = f(x). Step 4: Calculate the radius of curvature R at any point c on the deflection curve, and then use the formula... Calculate the tensile strain at any point c of the sheet sample. ε ;wherein the radius of curvature ; r represents half the thickness value; Step 5: Apply the formulas from Step 3 respectively. and Establish distribution maps of radius of curvature R as a function of X coordinate and tensile strain ε as a function of X coordinate, and use the two distribution maps to observe the characteristics of the sample in real time under different positions and different deformation conditions; The length of the bent portion of the sheet-like sample is adjusted by changing the fixed position between the two sliding blocks and the pressure plate, thereby obtaining the maximum strain value under different deformation conditions. The maximum strain is obtained when the X-coordinate of point c is the same as that of the highest point of the semi-cylindrical support. εmax ; The sheet-like sample is a sheet-like Ti-Ni sample. When the sheet-like Ti-Ni sample undergoes plastic deformation after reaching maximum strain, a microscopic tensile strain calculation method, namely the microscopic feature point (DIC) method, is used. The specific method is as follows: First, obtain a SEM image of the microstructure of the central region of the sheet-like sample before deformation; Secondly, obtain the microstructure SEM image of the location of the maximum strain εmax during loading; Next, the deformation was unloaded, and a microscopic SEM image was obtained again at the same location where the maximum strain was located; Finally, by comparing with the DIC analysis software GOM Correlate, a micro-strain distribution cloud map in the Y direction was obtained, which was then used for further analysis.

2. The auxiliary microscopic characterization method according to claim 1, characterized in that, The distribution maps of radius of curvature R as a function of the X-coordinate and tensile strain ε as a function of the X-coordinate were established using Origin software.

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