A method for measuring internal residual stress in building ceramics

Abstract

The present application discloses a method for measuring residual stress inside building ceramics, which includes prefabricating scratches at the measurement position on the ceramic surface, causing the ceramic to undergo brittle fracture along the scratches, forming two fracture surfaces, and then optimizing the contour data. The cross-sectional contour data is converted into stress along the normal direction of the fracture surface through finite element modeling calculation. The present application prefabricates scratches at the measurement position on the ceramic surface, causing the ceramic to undergo brittle fracture along the scratches, forming two fracture surfaces. By measuring the elastic deformation of the fracture surface caused by stress release, and then through finite element numerical simulation, the elastic deformation is reversely calculated to obtain a two-dimensional residual stress distribution cloud map of the fracture surface. The method has high measurement accuracy and good spatial resolution, realizes full-thickness stress measurement of the ceramic, provides rich and accurate residual stress distribution information, and can provide effective data support for ceramic composition design improvement, production process planning improvement, and later ceramic product service life prediction.

Description

Technical Field

[0001] The present application relates to the technical field of ceramic production, and more specifically, to a method for measuring residual stress inside building ceramics. Background Art

[0002] Architectural ceramics are plate-shaped ceramic products made from various inorganic non-metallic materials, such as clay and minerals, through a process of pressing, forming, and high-temperature calcination. Architectural ceramics, such as ceramic sheets and ceramic rock slabs, offer numerous green building material attributes, including low water absorption, large sizes, and thin thickness. They are also energy-efficient, environmentally friendly, lightweight, and highly strong.

[0003] Because building ceramics need to go through high-temperature calcination and rapid cooling processes during the production process, and they themselves have local uneven composition, residual stress is generated inside the ceramics. Residual stress is considered to be an important cause of cracking during ceramic cutting or cracking during later use. Among the various residual stress measurement methods, the main ones that can be used for ceramic measurement are X-ray diffraction, drilling strain method (also known as blind hole method) and ultrasonic method. However, these methods still have many limitations for the measurement of residual stress in building ceramics, resulting in the inability to achieve accurate measurement with high spatial resolution inside ceramics.

[0004] For example, X-ray diffraction measures residual stress in ceramics by using the interplanar spacing of crystals within the ceramic as a microstrain gauge. By adjusting the X-ray scanning angle, the relationship between the scanning angle and the interplanar spacing can be determined. Using a fitting method combined with the elastic stress equation, the residual stress at that measurement point can be calculated. However, due to the limited penetration depth of X-rays into ceramic materials of approximately 10 μm, this method can only measure surface residual stress. Furthermore, the presence of a glassy glaze layer on the surface of architectural ceramics can interfere with the diffraction signal, leading to significant measurement errors.

[0005] The hole-drilling strain method is also commonly used to measure residual stress in metal materials. A strain gauge is attached to the measurement point, and a blind hole is drilled through the center of the gauge to induce residual stress release. The strain gauge records the strain caused by stress release, and the magnitude and direction of the residual stress at that location are then calculated using the strain. However, when the hole-drilling strain method is applied to ceramics, due to the brittle nature of ceramics, defects such as microcracks can easily appear around the drill hole, affecting measurement reliability.

[0006] The ultrasonic method uses the phenomenon of acoustic birefringence—the acoustic elasticity of an isotropic, homogeneous material under stress—to measure residual stress in solids. The magnitude and direction of stress alter the propagation velocity of ultrasound waves in the material. By measuring the stress-induced changes in the ultrasonic birefringence spectrum and propagation velocity, the residual stress in the specimen can be calculated. However, the ultrasonic method measures the average stress within a specific range, resulting in poor spatial resolution. This is particularly true for ceramic materials with localized compositional inhomogeneities, where localized stress gradients cannot be accurately reflected.

[0007] Therefore, how to realize a method for measuring the internal residual stress of building ceramics with high precision and high spatial resolution is an urgent problem that needs to be solved in the field of building ceramics. Summary of the Invention

[0008] The purpose of this application is to provide a method for measuring the internal residual stress of building ceramics, aiming to solve the technical problem of how to achieve a method for measuring the internal residual stress of building ceramics with high precision and high spatial resolution.

[0009] To achieve the above objectives, the technical solution adopted in this application is:

[0010] The present application provides a method for measuring residual stress inside architectural ceramics, which includes:

[0011] Prefabricate scratches at the measuring position on the ceramic surface;

[0012] Applying external force to the ceramic causes brittle fracture along the scratch, forming two fracture surfaces;

[0013] Scan the two fracture surfaces to obtain the contour data of the two fracture surfaces;

[0014] Optimizing the two fracture surface profile data so as to synthesize the two fracture surface profile data into fracture surface profile data;

[0015] Through finite element modeling calculation, the cross-section profile data is converted into stress along the normal direction of the fracture surface, and a two-dimensional distribution cloud map of residual stress in the ceramic cross section is obtained.

[0016] In one embodiment, in the step of pre-forming scratches at the measuring position on the ceramic surface, the scratches are formed at the measuring position on the ceramic surface by cutting, engraving or carving.

[0017] In one embodiment, in the step of pre-forming scratches at the measuring position on the ceramic surface, the scratches are in a straight line shape.

[0018] In one embodiment, the step of applying an external force to the ceramic to cause brittle fracture of the ceramic along the scratch to form two fracture surfaces includes:

[0019] A three-point bending fixture was clamped on both sides of the ceramic scratch;

[0020] External force is applied to the ceramic through a three-point bending fixture, causing the ceramic to undergo brittle fracture along the scratch, forming two fracture surfaces.

[0021] In one embodiment, in the step of clamping the three-point bending fixture on both sides of the ceramic scratch, the three-point bending fixture is clamped on both sides of the ceramic scratch, and the scratch is located in the middle of the two clamping positions.

[0022] In one embodiment, in the step of applying an external force to the ceramic using a three-point bending fixture to cause the ceramic to undergo brittle fracture along the scratch to form two fracture surfaces, the difference in contour fluctuation between the two fracture surfaces is no more than 5 mm.

[0023] In one embodiment, the step of scanning the two fracture surfaces to obtain the contour data of the two fracture surfaces includes:

[0024] Use surface measuring instruments to measure the contours of the two fracture surfaces respectively;

[0025] The two fracture surface profile data are outputted by the surface measuring instrument, thereby obtaining the two fracture surface profile data.

[0026] In one embodiment, the step of optimizing the two fracture surface profile data to synthesize the two fracture surface profile data into fracture surface profile data includes:

[0027] Align the two fracture surface profile data: perform matrix translation and flipping of one set of fracture surface profile data along the fracture direction in the Cartesian coordinate system so that the two sets of fracture surface profile data overlap, and then set the matrix average value as the reference surface height of the surface profile;

[0028] Establish a common coordinate network: Use linear interpolation to form a common network with a similar spacing to the reference surface data, and correspond the two fracture surface contour data to the points on the common network one by one;

[0029] Calculate the contour edge data of the two fracture surfaces to obtain complete contour data of the two fracture surfaces;

[0030] Data averaging: take the average of the above two fracture surface profile data to obtain the average profile data;

[0031] Data optimization to obtain cross-sectional profile data: the average profile data is cleaned and then smoothed.

[0032] In one embodiment, the data optimization step of performing data cleaning and smoothing on the average profile data is as follows:

[0033] Data cleaning includes: replacing abnormal data in the average profile data, where abnormal data is defined as data with a deviation of more than 15% from the mean of adjacent data points;

[0034] Data smoothing includes: processing the average profile data using a fitting equation to further eliminate data noise, wherein the fitting equation includes quadratic spline function fitting, Fourier function fitting and polynomial fitting.

[0035] In one embodiment, the step of converting the cross-sectional profile data into stress along the normal direction of the fracture surface by finite element modeling calculation to obtain a two-dimensional distribution of residual stress in the ceramic cross section includes:

[0036] Based on the fracture profile data of the ceramic, finite element 3D modeling was performed using Abaqus software. This included: establishing a finite element model of the fractured half of the ceramic sample based on its original dimensions; using the fracture profile data as the displacement boundary conditions of the finite element model; and selecting an appropriate finite element mesh based on the size of the ceramic sample to complete the finite element 3D modeling.

[0037] The linear elastic model is used to calculate the corresponding residual stress of each data point on the fracture surface, and a two-dimensional distribution cloud map of the residual stress of the entire section is obtained.

[0038] The beneficial effects of the method for measuring internal residual stress of architectural ceramics provided by this application are at least:

[0039] The present application discloses a method for measuring residual stress inside building ceramics, which includes prefabricating a scratch at a measurement position on the ceramic surface; applying an external force to the ceramic so that the ceramic undergoes brittle fracture along the scratch, forming two fracture surfaces; scanning the two fracture surfaces to obtain two fracture surface contour data; optimizing the two fracture surface contour data so that the two fracture surface contour data are synthesized into cross-section contour data; converting the cross-section contour data into stress along the normal direction of the fracture surface through finite element modeling calculation to obtain a two-dimensional residual stress distribution cloud map of the ceramic cross section. The present application prefabricates a scratch at a measurement position on the ceramic surface so that the ceramic undergoes brittle fracture along the scratch, forming two fracture surfaces; measuring the elastic deformation of the fracture surface caused by stress release; and using finite element numerical simulation to reversely calculate the elastic deformation to obtain a two-dimensional residual stress distribution cloud map of the fracture surface. The method has high measurement accuracy and good spatial resolution, realizes full-thickness stress measurement of the ceramic, and provides rich and accurate residual stress distribution information, which can provide effective data support for ceramic composition design improvement, production process planning improvement, and later ceramic product service life prediction. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments or descriptions of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0041] Figure 1 A schematic diagram of a flow chart of a method for measuring residual stress in architectural ceramics according to an embodiment of the present application;

[0042] Figure 2 A schematic diagram of the structure of a prefabricated scratch on a ceramic sample provided in an embodiment of the present application;

[0043] Figure 3 A schematic diagram of a three-point bending fixture provided in an embodiment of the present application holding a ceramic sample;

[0044] Figure 4 A schematic diagram of scanning a fracture surface provided in an embodiment of the present application;

[0045] Figure 5 A schematic diagram showing a comparison of smoothed contour data provided in an embodiment of the present application;

[0046] Figure 6 Schematic diagram of the data processing flow in residual stress measurement provided in an embodiment of the present application.

[0047] Wherein, the reference numerals:

[0048] 1. Scratch; 2. Clamping point; 3. Ceramic specimen; 4. Three-point bending fixture; 5. Optical probe; 6. Fracture surface. DETAILED DESCRIPTION

[0049] In order to make the technical problems, technical solutions and beneficial effects to be solved by this application more clearly understood, the present application is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0050] It should be noted that when a component is referred to as being "fixed on" or "disposed on" another component, it may be located directly or indirectly on the other component. When a component is referred to as being "connected to" another component, it may be directly or indirectly connected to the other component. The directions or positions indicated by the terms "upper", "lower", "left", "right", "front", "back", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc. are based on the directions or positions shown in the accompanying drawings and are only for the convenience of description and cannot be understood as limitations on this technical solution. The terms "first" and "second" are only used for the purpose of convenience of description and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features. "Multiple" means two or more, unless otherwise clearly and specifically defined.

[0051] Conventional profilometry is commonly used on metal materials. However, architectural ceramics are made from fired inorganic, non-metallic materials like clay. They are generally opaque and poorly conductive, sometimes even insulators. This makes them difficult to cut using techniques like wire cutting, making the profilometry method difficult to implement.

[0052] In order to realize a method for measuring the internal residual stress of building ceramics with high precision and high spatial resolution, the present application provides a method for measuring the internal residual stress of building ceramics, which measures the elastic deformation of the fracture surface caused by stress release, and then uses finite element numerical simulation to reversely calculate the elastic deformation to obtain a two-dimensional residual stress distribution cloud map of the fracture surface. Specifically, a scratch is pre-made at the measurement position on the ceramic surface, and then an external force is applied to the ceramic to cause brittle fracture of the ceramic along the scratch, forming two fractures. The two fracture surfaces are then scanned to obtain two fracture surface contour data, and then the two fracture surface contour data are optimized to synthesize the two fracture surface contour data into cross-section contour data. The cross-section contour data is then converted into stress along the normal direction of the fracture surface through finite element modeling calculation to obtain a two-dimensional distribution cloud map of the residual stress of the ceramic cross section.

[0053] Various non-limiting embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0054] See also Figure 1 This embodiment provides a method for measuring residual stress inside building ceramics, which includes:

[0055] S100. Pre-form scratches at the measuring position on the ceramic surface.

[0056] In order to achieve the measurement of residual stress inside building ceramics, the embodiment of the present application uses prefabricated scratches at the measurement position on the ceramic surface. Since building ceramics are not necessarily crystalline materials, they may also be amorphous materials. Crystalline materials must meet the requirements of linear elasticity. For amorphous materials, the key to the successful application of the contour method lies in the linear elasticity requirements, that is, amorphous ceramic materials must meet the linear elasticity requirements, that is, obey the generalized Hooke's law, and its verification can be carried out in open source technology. The embodiment of the present application measures the elastic deformation of the fracture surface of the ceramic caused by stress release, and then uses finite element numerical simulation to reversely calculate the elastic deformation to obtain a two-dimensional residual stress distribution cloud map of the fracture surface.

[0057] Optionally, in step S100 , scratches are made at the measurement position on the ceramic surface by cutting, engraving or carving.

[0058] See also Figure 2 , a hard tool roller cutter can be used to carve a scratch 1 running through both ends in the middle of the surface of the ceramic sample 3 to be measured.

[0059] Preferably, the scratch is a straight line and belongs to a line of the measuring surface. The scratch represents the maximum length of the measuring surface.

[0060] The tool for making scratches can be any tool with a hardness greater than that of the ceramic being measured. Preferably, the tool for making scratches is a diamond graver.

[0061] For example, clean the surface of the ceramic sample along the scratch path to ensure there are no visible particles that could interfere with the scratch. After securing the cleaned ceramic sample with hot melt adhesive, use a hard roller to create a scratch through the center of the surface to be measured. The scratch depth should be between 2 and 5 μm, primarily to initiate cracking. Excessive scratches should be avoided, as these can affect the final surface stress calculation.

[0062] S200, applying external force to the ceramic, causing the ceramic to undergo brittle fracture along the scratch, forming two fracture surfaces.

[0063] In order to measure the residual stress inside building ceramics, the embodiment of the present application applies an external force to the ceramics, causing the ceramics to undergo brittle fracture along the scratch, forming two fracture surfaces. Specifically, step S200 includes:

[0064] S210. Clamp a three-point bending fixture on both sides of the ceramic scratch.

[0065] S220. Apply external force to the ceramic through a three-point bending fixture, so that the ceramic undergoes brittle fracture along the scratch, forming two fracture surfaces.

[0066] See also Figure 3In this embodiment, a three-point bending fixture 4 is clamped at the clamping points 2 on both sides of the ceramic scratch, with the scratch located in the middle of the two clamping positions. The three-point bending fixture then applies an external force to the ceramic, causing the ceramic to undergo brittle fracture along the scratch, forming two fracture surfaces. For example, the three-point bending fixture is installed at both ends of a prefabricated scratch on the ceramic, with the prefabricated scratch located in the middle of the three-point bending fixture. Force is gradually applied to the ceramic through the three-point bending fixture until the ceramic undergoes brittle fracture along the prefabricated scratch, resulting in a fracture surface along the scratch.

[0067] The three-point bending fixture is bilaterally symmetrical and a combination of two three-point bending fixtures can be used separately. When in use, the two three-point bending fixtures are at the same height level and are distributed bilaterally symmetrically.

[0068] When force is applied to the three-point bending fixture, the two rotating arms rotate at the same speed and in opposite directions, causing the arms to descend and exert pressure on the ceramic. When the applied force exceeds the static strength of the ceramic, the ceramic fractures along the scratch, resulting in a fracture surface.

[0069] In step S220, the difference in contour fluctuation between the two fracture surfaces is no more than 5 mm.

[0070] Preferably, the fracture surface includes a pre-prepared scratch, and its deviation ξ is ≤ 3%. The calculation method of the deviation ξ is defined as follows:

[0071]

[0072] S300 , scanning two fracture surfaces to obtain two fracture surface contour data.

[0073] In order to measure the residual stress inside building ceramics, the embodiment of the present application scans two fracture surfaces to obtain two fracture surface contour data.

[0074] Specifically, step S300 includes the following steps:

[0075] S310. Use a surface measuring instrument to measure the contours of the two fracture surfaces respectively.

[0076] S320 , outputting two fracture surface profile data through a surface measuring instrument, thereby obtaining two fracture surface profile data.

[0077] See also Figure 4 In this embodiment, the two fracture surfaces are profiled using a surface measurement instrument. The surface measurement instrument then outputs two fracture surface profile data, thereby obtaining two fracture surface profile data. For example, a three-dimensional topography measurement instrument can be used to scan the fracture surface, such as by fixing a ceramic sample to a workbench of the instrument and performing profile measurement on the obtained ceramic fracture surface.

[0078] Optionally, the 3D topography instrument used to measure the ceramic fracture surface profile data can be a combination of one or more instruments with 3D topography measurement capabilities, such as a 3D laser confocal microscope, an Alicona confocal microscope, and a coordinate measuring machine. When measuring the fracture surface profile, the measuring equipment is preferably non-contact. The measurement accuracy of different instruments is selected according to Table 1.

[0079] Table 1

[0080]

[0081] Optionally, when optically measuring the fracture surface profile of the ceramic, the distance between the optical probe 5 and the fracture surface 6 of the ceramic is 0.1 mm to 100 mm. Preferably, the distance between the optical probe 5 and the fracture surface 6 of the ceramic is 1 mm to 20 mm.

[0082] In this embodiment, the measurement process requires scanning and measuring the fracture surfaces. The scanning process requires establishing a correct three-dimensional coordinate system so that the two surface contour results can be symmetrically overlapped along a certain coordinate axis.

[0083] The above three-dimensional coordinate system (the three-dimensional coordinate system refers to the Cartesian coordinate system) is an artificially defined coordinate system with relative meaning. To facilitate the front-end steps of subsequent data processing, the X direction of the three-dimensional coordinate system is parallel to the maximum long side of the ceramic, the Y direction is parallel to the thickness direction of the ceramic, and the Z direction is parallel to the normal direction of the fracture surface.

[0084] When performing profile scanning measurement, the measurement direction is preferably the Y direction.

[0085] S400 , optimizing the two fracture surface profile data so as to synthesize the two fracture surface profile data into fracture surface profile data.

[0086] In order to measure the residual stress inside building ceramics, the embodiment of the present application optimizes the two fracture surface profile data so that the two fracture surface profile data are synthesized into fracture surface profile data.

[0087] Specifically, step S400 includes:

[0088] S410: Align the two fracture surface profile data sets: Perform a matrix translation and flipping of one set of fracture surface profile data along the fracture direction in a Cartesian coordinate system so that the two sets of fracture surface profile data overlap. The matrix average is then set as the reference height of the surface profile. For example, the two side profile data sets obtained in step 300 can be combined into a single profile representing the fracture surface deformation by mirroring, flipping, rotating, and averaging the two side profile data sets.

[0089] Due to the large surface roughness caused by the brittle fracture of ceramics, there are obvious bumps and undulations. In order to remove the influence of the surface roughness caused by the fracture and make the deformation caused by the residual stress release more obvious, during data alignment, the discreteness of the various alignment parameter results is compared by variance, and the root mean square parameter with the smallest discreteness is obtained as the final alignment parameter, which can minimize the influence of the surface undulation caused by the ceramic fracture.

[0090] S420, establishing a common coordinate network: forming a common network with a spacing similar to that of the reference surface data by linear interpolation, and making one-to-one correspondence between the two fracture surface contour data and the points on the common network.

[0091] S430: Calculate the contour edge data of the two fracture surfaces to obtain complete contour data of the two fracture surfaces.

[0092] S440, data averaging: averaging the two fracture surface profile data to obtain average profile data. The two fracture surface profile data are averaged, that is, the average value is taken for every two corresponding points in the data matrix.

[0093] S450, data optimization, obtaining cross-sectional profile data: performing data cleaning on the average profile data, and then performing data smoothing processing.

[0094] Data cleaning includes: replacing abnormal data in the average contour data, where the abnormal data is the deviation from the mean of adjacent data points greater than 15%; due to the presence of dust on the surface during the measurement of fracture surface contour data, there will be some abnormal data points in the averaged contour data, and data cleaning is required to remove these abnormal data points.

[0095] Data smoothing includes: using fitting equations to process the average contour data to further eliminate data noise, where the fitting equations include quadratic spline function fitting, Fourier function fitting, and polynomial fitting. Due to the roughness of the fracture surface and the error of contour measurement, the fracture surface contour data will contain many "noise" signals. The contour data needs to be smoothed by the radius filtering method. The smoothed contour data can better display the contour deformation characteristics (such as Figure 6 ).

[0096] In this embodiment, the fracture surface contour data obtained in S300 is synthesized into a contour representing the cross-sectional deformation after mirror flipping, rotation, translation alignment and averaging, and further smoothed by a filtering algorithm to obtain smooth contour surface data. For details, please refer to Figure 5 .

[0097] The mirror flipping is based on the three-dimensional coordinate system established in step S300, and preferably the Y axis is used as the symmetry axis for the mirror flipping symmetry processing.

[0098] The rotation operation is to align one end of the two cross-section contours first, and then rotate to align the other end.

[0099] Translation is based on one cross-section profile and aligns another cross-section profile by moving it as a whole.

[0100] During data processing, rotation is an optional process and depends on the specific situation.

[0101] If a rotation operation exists, the rotation and translation may be performed asynchronously, but preferably, the rotation and translation are performed synchronously.

[0102] The rotation (if any) and translation process is considered as a whole operation, and this operation is preferably performed at least 9 times. The symmetric root mean square difference of all points in the symmetry plane is then calculated. The operation corresponding to the smallest root mean square difference is selected as the optimal operation, and the symmetric profile formed by this operation is the final profile. For example, the rotation and translation are performed simultaneously, and this operation is performed at least 9 times. The symmetric root mean square difference of all points in the symmetry plane is then calculated. The operation corresponding to the smallest root mean square difference is selected as the optimal operation, and the symmetric profile formed by this operation is the final profile.

[0103] The root mean square error is preferably less than 9.99×10 -3 .

[0104] The filtering algorithm includes but is not limited to a combination of one or more open source filtering technologies such as quadratic spline function filtering, homogeneous filtering, Gaussian filtering, radius filtering and bilateral filtering, preferably radius filtering.

[0105] S500, converting the cross-section profile data into stress along the normal direction of the fracture surface through finite element modeling calculation, and obtaining a two-dimensional distribution of residual stress in the ceramic cross section.

[0106] In order to measure the residual stress inside building ceramics, the embodiment of the present application converts the cross-sectional profile data into stress along the normal direction of the fracture surface by using finite element modeling calculation to obtain a two-dimensional distribution cloud map of the residual stress of the ceramic cross section.

[0107] Specifically, step S500 includes the following steps:

[0108] S510, using Abaqus software to perform finite element three-dimensional modeling based on the fracture surface profile data of the ceramic, which includes: establishing a finite element model of the half sample after the ceramic tile is fractured based on the original size of the ceramic tile sample; using the cross-section profile data as the displacement boundary condition of the finite element model; selecting an appropriate finite element mesh based on the size of the ceramic sample to complete the finite element three-dimensional modeling;

[0109] S520. Calculate the corresponding residual stress of each data point on the fracture surface using a linear elastic model to obtain a two-dimensional distribution cloud map of the residual stress of the entire cross section.

[0110] In this embodiment, Abaqus software is used to perform finite element three-dimensional modeling based on the fracture surface contour data of the ceramic, which includes: establishing a finite element model of half of the sample after the ceramic tile is fractured based on the original size of the ceramic tile sample; using the cross-sectional contour data as the displacement boundary condition of the finite element model; selecting a suitable finite element grid according to the size of the ceramic sample to complete the finite element three-dimensional modeling; using a linear elastic model to calculate the corresponding residual stress of each data point on the fracture surface, and obtaining a two-dimensional distribution cloud map of the residual stress of the entire section.

[0111] In this embodiment, finite element numerical simulation software is used to establish a finite element model of the ceramic tile based on the actual size of the sample, assign material properties, and use the cross-sectional contour data of step S400 as the cross-sectional displacement boundary condition. The linear elastic model is used to calculate the corresponding residual stress of each data point on the cross section to obtain a two-dimensional residual stress distribution cloud map of the cross section.

[0112] The finite element simulation software can be any open source software that can perform simulations.

[0113] The actual dimensions mentioned above are the dimensions after breaking.

[0114] When establishing a model, the grid elements can be selected as fully integrated elements, linear elements, quadratic elements and reduced elements, preferably quadratic elements.

[0115] When assigning material properties, the required parameters are the material's elastic modulus and Poisson's ratio, while the thermal expansion coefficient is an optional parameter.

[0116] 1. This embodiment uses finite element numerical simulation software to establish a ceramic finite element model, and uses cross-section profile data as the displacement boundary condition of the cross section of the model to perform linear elastic calculation to obtain residual stress distribution results.

[0117] 2. In the embodiments of the present application, the method for measuring ceramic residual stress is no longer limited to conductive crystalline ceramic materials, but can be extended to non-conductive non-holocrystalline ceramic materials.

[0118] 3. In the embodiment of the present application, a three-point bending fixture is used for the first time to "cut" ceramics, utilizing the fracture characteristics of ceramic materials to obtain a natural fracture surface rather than an artificial cutting surface.

[0119] 4. In the embodiment of the present application, a single three-point bending fixture is combined into a composite processing tool for the first time and applied to the “cutting” of ceramic materials.

[0120] 5. The symmetric method under the coordinate system disclosed in the embodiments of this application can greatly save data processing time and prevent alignment errors.

[0121] 6. In the embodiment of the present application, when aligning and averaging, the root mean square error is calculated by using sample statistics to find the optimal alignment method, rather than traditional human eye observation, thereby improving measurement accuracy.

[0122] This application prefabricates scratches at the measurement position on the ceramic surface, causing the ceramic to undergo brittle fracture along the scratches, forming two fracture surfaces. By measuring the elastic deformation of the fracture surface caused by stress release, and then using finite element numerical simulation, the elastic deformation is reversely calculated to obtain a two-dimensional residual stress distribution cloud map of the fracture surface. The measurement has high accuracy and good spatial resolution, and can achieve full-thickness stress measurement of the ceramic, providing rich and accurate residual stress distribution information, which can provide effective data support for ceramic composition design improvement, production process planning improvement, and later ceramic product service life prediction.

[0123] In summary, the present application discloses a method for measuring residual stress inside building ceramics, which includes prefabricating scratches at a measuring position on the surface of the ceramic; applying external force to the ceramic so that the ceramic undergoes brittle fracture along the scratches, forming two fracture surfaces; scanning the two fracture surfaces to obtain two fracture surface contour data; optimizing the two fracture surface contour data so that the two fracture surface contour data are synthesized into cross-section contour data; converting the cross-section contour data into stress along the normal direction of the fracture surface through finite element modeling calculation to obtain a two-dimensional residual stress distribution cloud map of the ceramic cross section. The present application prefabricates scratches at a measuring position on the surface of the ceramic so that the ceramic undergoes brittle fracture along the scratches, forming two fracture surfaces, and measures the elastic deformation of the fracture surface due to stress release, and then uses finite element numerical simulation to reversely calculate the two-dimensional residual stress distribution cloud map of the fracture surface. The method has high measurement accuracy and good spatial resolution, realizes full-thickness stress measurement of the ceramic, and provides rich and accurate residual stress distribution information, which can provide effective data support for ceramic composition design improvement, production process planning improvement, and later ceramic product service life prediction.

[0124] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present application should be included in the scope of protection of the present application.

Claims

1. A method for measuring internal residual stress of building ceramics, characterized in that: include: Prefabricate scratches at the measuring position on the ceramic surface; Applying external force to the ceramic causes brittle fracture along the scratch, forming two fracture surfaces; Scan the two fracture surfaces to obtain the contour data of the two fracture surfaces; Optimizing the two fracture surface profile data so as to synthesize the two fracture surface profile data into fracture surface profile data; The cross-section profile data is converted into stress along the normal direction of the fracture surface through finite element modeling calculation, and a two-dimensional distribution cloud map of residual stress in the ceramic cross section is obtained; The scratch is in a straight line shape, and the scratch depth is 2-5 μm; The step of scanning the two fracture surfaces to obtain the contour data of the two fracture surfaces comprises: using a surface measuring instrument to measure the contours of the two fracture surfaces respectively; Outputting two fracture surface profile data through a surface measuring instrument, thereby obtaining two fracture surface profile data; The step of optimizing the two fracture surface profile data so as to synthesize the two fracture surface profile data into fracture surface profile data comprises: Align the two fracture surface profile data: perform matrix translation and flipping of one set of fracture surface profile data along the fracture direction in the Cartesian coordinate system so that the two sets of fracture surface profile data overlap, and then set the matrix average value as the reference surface height of the surface profile; Establish a common coordinate network: Use linear interpolation to form a common network with a similar spacing to the reference surface data, and correspond the two fracture surface contour data to the points on the common network one by one; Calculate the contour edge data of the two fracture surfaces to obtain complete contour data of the two fracture surfaces; Data averaging: take the average of the above two fracture surface profile data to obtain the average profile data; Data optimization to obtain cross-sectional profile data: the average profile data is cleaned and then smoothed; The data optimization step is to clean and smooth the average profile data. Data cleaning includes: replacing abnormal data in the average profile data, where abnormal data is defined as data with a deviation greater than 15% from the mean of adjacent data points; Data smoothing includes: processing the average profile data using a fitting equation to further eliminate data noise, wherein the fitting equation includes quadratic spline function fitting, Fourier function fitting, and polynomial fitting; The step of converting the cross-section profile data into stress along the normal direction of the fracture surface by finite element modeling calculation to obtain the two-dimensional distribution of residual stress in the ceramic cross section includes: Based on the fracture profile data of the ceramic, finite element 3D modeling was performed using Abaqus software. This included: establishing a finite element model of the fractured half of the ceramic sample based on its original dimensions; using the fracture profile data as the displacement boundary conditions of the finite element model; and selecting an appropriate finite element mesh based on the size of the ceramic sample to complete the finite element 3D modeling. The linear elastic model is used to calculate the corresponding residual stress of each data point on the fracture surface, and a two-dimensional distribution cloud map of the residual stress of the entire section is obtained.

2. The method for measuring internal residual stress of architectural ceramics according to claim 1, wherein: In the step of pre-forming scratches at the measuring position on the ceramic surface, the scratches are formed at the measuring position on the ceramic surface by cutting, carving or engraving.

3. The method for measuring internal residual stress of architectural ceramics according to claim 1, wherein: The step of applying an external force to the ceramic to cause brittle fracture of the ceramic along the scratch to form two fracture surfaces comprises: A three-point bending fixture was clamped on both sides of the ceramic scratch; External force is applied to the ceramic through a three-point bending fixture, causing the ceramic to undergo brittle fracture along the scratch, forming two fracture surfaces.

4. The method for measuring internal residual stress of architectural ceramics according to claim 3, wherein: In the step of clamping the three-point bending fixture on both sides of the ceramic scratch, the three-point bending fixture is clamped on both sides of the ceramic scratch, and the scratch is located in the middle of the two clamping positions.

5. The method for measuring internal residual stress of architectural ceramics according to claim 3, wherein: In the step of applying external force to the ceramic by a three-point bending fixture to cause brittle fracture of the ceramic along the scratch to form two fracture surfaces, the difference in contour fluctuation between the two fracture surfaces is no more than 5 mm.

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