Brittleness material fracture toughness measurement method and device based on laser thermal induced crack propagation

Abstract

The present application is based on the brittle material fracture toughness measurement method and device of laser thermal induced crack propagation. The method comprises the following steps: firstly, a crack is prepared on a brittle material sheet; then the laser power is adjusted, and the laser action point is adjusted to the position 1.5 mm behind the crack tip of the tested sample for irradiation; next, the length of the crack after propagation is measured, and the crack area is calculated combined with the material thickness; the laser action time, the laser input power, the laser action energy are recorded, and the energy for crack propagation is calculated by theoretical derivation combined with simulation analysis; next, the material energy release rate and fracture toughness are calculated according to the crack area and energy. The present application has the advantages of simple measurement device, simple operation, widely recognized formula in the industry, good universality and strong reliability.

Description

Technical Field

[0001] This invention belongs to the field of experimental testing technology, specifically relating to a method and device for measuring the fracture toughness of ceramic materials based on laser-induced crack propagation. Background Technology

[0002] Ceramic materials are mainly composed of oxides, carbides, nitrides, halogen compounds, borides, and silicates, aluminates, phosphates, and borates of certain elements. Typical ordinary ceramic materials are sintered from natural raw materials such as feldspar, clay (e.g., kaolin), and quartz. The main constituent elements are silicon, aluminum, and oxygen, which together make up 90% of the Earth's crust. Ordinary ceramics are made from natural raw materials through sintering, making them abundant, low-cost, and technologically mature. Based on performance characteristics and uses, they can be further divided into daily-use ceramics, building ceramics, electrical insulation ceramics, and chemical ceramics. Special ceramics are made from high-purity artificially synthesized raw materials, formed and sintered using precise controlled processes, possessing certain special properties to meet various needs. Based on their main components, they include oxide ceramics (e.g., alumina ceramics), nitride ceramics (e.g., silicon nitride ceramics), carbide ceramics (e.g., silicon carbide ceramics), and cermets. Based on different uses, special ceramic materials can be divided into structural ceramics, tool ceramics, and functional ceramics.

[0003] Ceramic materials, as a new type of material, are widely used in nuclear power, chemical industry, biology, metallurgy, and other fields. During the processing and transportation of ceramic materials, defects and scratches are unavoidable. In actual use, due to their inherent brittleness, once internal cracks form, they quickly propagate under test loads, leading to material failure and causing significant harm to public safety and national economic development. Therefore, how to better and faster measure the fracture toughness of ceramic materials, and how to design them more rationally for use in suitable industrial environments, is one of the important issues currently facing the industry.

[0004] In fact, there are many methods for measuring the fracture toughness of ceramic materials. These include: the indentation method, which uses an indenter to apply pressure to the ceramic surface to create cracks, and then calculates the fracture toughness based on the crack length, shape, and direction; the notched beam method, which involves cutting a notch in the middle or edge of the ceramic, applying bending force to create cracks at the notch, and calculating the fracture toughness based on the crack length and stress intensity factor; and the pre-cracked beam method, which involves pre-creating a crack in the middle or edge of a ceramic beam, applying bending force to cause the crack to propagate, and calculating the fracture toughness based on the crack length and stress intensity factor. All these methods require mechanical loading and measurement of force-displacement curves. Measuring these curves requires multiple sensors working together, and the material must be held in a suitable position by a clamp. High clamp hardness can cause material deformation, making the fracture toughness measurement experiments time-consuming, labor-intensive, and resulting in highly variable experimental data. Summary of the Invention

[0005] To overcome the shortcomings of the existing technology, the present invention aims to provide a method and apparatus for measuring the fracture toughness of ceramic materials based on laser-induced crack propagation. The present invention is based on the laser-induced expansion effect, utilizing the Griffith energy release concept, the Griffith fracture criterion, and the relationship between stress intensity factor and energy release rate to obtain a formula suitable for describing the fracture process of ceramic materials under thermo-mechanical coupling, and establishes a method for measuring its fracture toughness.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] Methods for measuring the fracture toughness of brittle materials based on laser-induced crack propagation include:

[0008] The test sample has a crack that penetrates the board surface. A laser probe and a thermal imager are installed on both sides of the end of the crack on the test sample. The laser beam is perpendicular to the board surface and converges 1.5 mm behind the crack tip.

[0009] A laser is used to inject energy of magnitude W into the crack tip, and the temperature change ΔT(x,y) on the plate surface is read on a thermal imager and recorded in a computer.

[0010] The energy release rate G of the material is obtained by using energy W, temperature change ΔT(x,y) and crack length change Δa, and by using Griffith's energy release theory.

[0011] The fracture toughness K of a material is determined based on the relationship between energy release rate and fracture toughness.

[0012] A further improvement of the present invention is that the test sample has a crack that penetrates the plate surface, and the crack surface is perpendicular to the material surface.

[0013] A further improvement of the present invention is that, taking the surface of the plate as a plane, the crack tip on the test sample as the origin, the crack propagation direction as the x-axis, the direction perpendicular to the crack as the Y-axis, and the direction perpendicular to the plate surface as the Z-axis, a three-dimensional right-handed rectangular coordinate system is established, and the laser action point is 1.5mm inside the crack tip, with specific coordinates (-1.5, 0, 0).

[0014] By using the energy formula and applying Griffith's energy balance theory and the basic laws of elasticity, the proportion of crack propagation energy to the total laser injection energy is determined to be a constant.

[0015] The required formula is as follows:

[0016]

[0017] dQ=cdmΔT=cρ(T-T0)dV

[0018] In the formula: ∈_ij^e represents elastic strain; ∈_ij^T represents thermal strain; α is the coefficient of thermal expansion; W is the strain energy; Q is the heat absorbed by the material; E is the elastic modulus; c is the specific heat capacity; ρ is the density.

[0019] A further improvement of this invention is that the ratio of crack propagation energy to laser injection energy is calculated using the following formula:

[0020]

[0021] In the formula: α is the coefficient of thermal expansion; W is the strain energy; Q is the heat absorbed by the material; E is the elastic modulus; c is the specific heat capacity; ρ is the density.

[0022] A further improvement of the present invention is that the location of the crack on the test sample is known, and the crack on the test sample is a crack that penetrates the plate and the crack surface is perpendicular to the surface of the plate.

[0023] A further improvement of this invention is that the diameter of the laser application point is 0.1 mm, the laser power is 100 W, and the laser application time is 0.1 s.

[0024] A further improvement of this invention is that the thickness of the material being tested is 0.5 mm.

[0025] A device for measuring the fracture toughness of brittle materials based on laser-induced crack propagation includes a carbon dioxide laser, a reflector, a convex lens, a camera, a thermal imager, and a data processing computer.

[0026] The laser emitted by the carbon dioxide laser is adjusted through a reflector to reach directly above the test specimen. After being focused by a convex lens, it acts on the trailing edge of the crack tip on the material surface at 1.5 mm. A thermal imager records the change in surface temperature distribution of the test specimen over time, and a camera records the crack propagation process and the final length of the crack. The data processing computer calculates the crack area using the crack length and the thickness of the test specimen, and calculates the energy used for crack propagation using the energy ratio formula.

[0027] A further improvement of this invention is that the carbon dioxide laser is a 150W carbon dioxide laser.

[0028] A further improvement of this invention is that the energy ratio calculation formula is as follows:

[0029]

[0030] dQ=cdmΔT=cρ(T-T0)dV (5)

[0031] In the formula:

[0032] ∈_ij^e represents elastic strain;

[0033] ∈_ij^T represents thermal strain;

[0034] α is the coefficient of thermal expansion;

[0035] W represents strain energy;

[0036] E is the elastic modulus;

[0037] Q represents the heat absorbed by the material;

[0038] c is the specific heat capacity;

[0039] ρ is the density;

[0040] The energy ratio formula is calculated as follows:

[0041]

[0042] Compared with the prior art, the present invention has at least the following beneficial technical effects:

[0043] This invention provides a method and apparatus for measuring the fracture toughness of brittle materials based on laser-induced thermal expansion. It introduces a defined external energy source, utilizing the thermal expansion generated within the material. The surface changes are measured using simple detection methods. Based on a derived formula, the energy is converted into the energy driving crack propagation. Then, using classical Griffith theory, the fracture energy is calculated, and the fracture toughness is further determined. This measurement method features simple equipment, easy operation, and the formulas used are widely accepted in the industry, demonstrating good versatility and high reliability. Attached Figure Description

[0044] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0045] Figure 1 This is a schematic diagram of crack propagation in the fracture toughness measurement of brittle materials based on laser-induced thermal expansion, according to the present invention.

[0046] in, Figure 1 (a) is a schematic diagram before laser irradiation. The blue part is the laser, a crack is pre-made on the plate-shaped sample, and the red dot is the point where the laser will be applied. Figure 1 (b) is a schematic diagram after laser irradiation. The added transparent cone represents the converged laser beam, which irradiates the red position, and the crack extends by a length of Δa.

[0047] Figure 2 This is a schematic diagram showing the arrangement of the laser, measuring device, and test sample of the present invention.

[0048] Figure 3 These are effect diagrams of an embodiment of the present invention, wherein... Figure 3 (a) Before laser treatment Figure 3 (b) is after laser treatment.

[0049] Explanation of reference numerals in the attached figures:

[0050] 1-Carbon dioxide laser, 2-Reflector, 3-Computer, 4-Thermal imager, 5-Convex lens, 6-Camera, 7-Ceramic plate sample, 8-Test bench. Detailed Implementation

[0051] In the following description, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit or scope of the invention. Therefore, the drawings and description are considered to be exemplary in nature and not restrictive.

[0052] It should be understood that, when used in this specification and the appended claims, the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0053] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0054] It should also be further understood that the term "and / or" as used in this specification and the appended claims refers to any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0055] The accompanying drawings illustrate various structural schematic diagrams according to embodiments disclosed in this invention. These drawings are not to scale, and some details have been enlarged for clarity, and some details may have been omitted. The shapes of the various regions and layers shown in the drawings, as well as their relative sizes and positional relationships, are merely exemplary and may deviate from reality due to manufacturing tolerances or technical limitations. Furthermore, those skilled in the art can design regions / layers with different shapes, sizes, and relative positions as needed.

[0056] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0057] Example 1

[0058] The present invention provides a method for measuring the fracture toughness of brittle materials based on laser-induced crack propagation. This method involves inputting laser radiation energy to the crack tip of the material in a non-contact manner. The material absorbs the laser energy and converts it into heat energy, causing it to expand and drive the crack forward, thus injecting fracture energy. The fracture toughness of the material is calculated based on the crack propagation length and the amount of input energy. The method includes the following steps:

[0059] The test sample has a crack that penetrates the board surface. A laser probe and a thermal imager are installed on both sides of the end of the crack on the test sample. The laser beam is perpendicular to the board surface and converges about 1.5 mm behind the crack tip.

[0060] A laser is used to inject energy of magnitude W into the crack tip, and the temperature change ΔT(x,y) on the plate surface is read on a thermal imager and recorded in a computer.

[0061] The energy release rate G of the material is obtained by using energy W, temperature change ΔT(x,y), and crack length change Δa, and by applying Griffith's energy release theory.

[0062] The fracture toughness K of a material is determined based on the relationship between energy release rate and fracture toughness.

[0063] In this embodiment, the crack on the test sample penetrates the material surface, and the crack surface is perpendicular to the material surface;

[0064] In this embodiment, a three-dimensional right-handed rectangular coordinate system is established with the surface of the plate as the plane, the crack tip on the test sample as the origin, the crack propagation direction as the x-axis, the direction perpendicular to the crack as the Y-axis, and the direction perpendicular to the plate surface as the Z-axis. The laser action point is about 1.5 mm inside the crack tip, with specific coordinates of (-1.5, 0, 0).

[0065] By using the energy formula and applying Griffith's energy balance theory and the basic laws of elasticity, the proportion of crack propagation energy to the total laser injection energy is determined to be a constant.

[0066] The required formula is as follows:

[0067]

[0068] dQ=cdmΔT=cρ(T-T0)dV

[0069] In the formula: ∈_ij^e represents elastic strain; ∈_ij^T represents thermal strain; α is the coefficient of thermal expansion; W is the strain energy; Q is the heat absorbed by the material; E is the elastic modulus; c is the specific heat capacity; ρ is the density.

[0070] In this embodiment, the ratio of crack propagation energy to laser injection energy is calculated using the following formula:

[0071]

[0072] In the formula: α is the coefficient of thermal expansion; W is the strain energy; Q is the heat absorbed by the material; E is the elastic modulus; c is the specific heat capacity; ρ is the density.

[0073] In this embodiment, the location of the crack on the test sample is known, and the crack on the test sample is a crack that penetrates the plate and the crack surface is perpendicular to the surface of the plate.

[0074] In this embodiment, the diameter of the laser application point is 0.1 mm, the laser power is 100 W, and the laser application time is 0.1 s.

[0075] In this embodiment, the thickness of the material being tested is 0.5 mm.

[0076] In this embodiment, the fracture toughness of brittle materials is measured using a measuring device such as a laser.

[0077] In this embodiment, the fracture toughness measuring device includes a camera, a thermal imager, and a data processing computer.

[0078] Example 2

[0079] See Figures 1-2 The present invention relates to a method for measuring the fracture toughness of brittle materials based on laser-induced thermal expansion, which involves a test sample, a laser, and a measuring device assembly.

[0080] The laser and measuring device assembly includes a 150W carbon dioxide laser 1, a reflector 2, a convex lens 5, a thermal imager 4 for detecting the temperature field, a camera 6 for recording crack propagation, a computer 3 for controlling the laser and collecting experimental data, a test bench 8, and a ceramic plate sample 7. The laser emitted by the carbon dioxide laser is guided by the reflector to a point directly above the test piece. After being focused by the convex lens, it acts on the trailing edge of the crack tip on the material surface, approximately 1.5 mm away. The thermal imager records the temperature distribution on the test piece surface over time, and the camera records the crack propagation process, recording the final crack length.

[0081] Among them, the carbon dioxide laser is a gas laser that uses CO2 gas as its working medium. Its working principle is based on the molecular vibration and rotation caused by electronic energy level transitions, specifically as follows:

[0082] Gas mixture: The laser is filled with a mixture of CO2, nitrogen and helium, with CO2 being the main laser-generating substance.

[0083] Lamp pump: Uses high-voltage current to pass through a gas mixture, thereby exciting the gas to a high-energy state, producing ionization and discharge processes.

[0084] Energy level transition: During the discharge process, electrons in CO2 molecules are excited to a higher energy level and then rapidly transition back to a lower energy level. This transition releases energy and causes molecular vibration and rotation.

[0085] Resonance feedback: These vibrations and rotations cause the laser energy level in the CO2 molecule to resonate with the energy levels in the other two gases, thereby causing the CO2 molecule to emit a laser beam of a specific wavelength.

[0086] Beam amplification and output: The beam is amplified as it travels repeatedly between the convex mirrors, and is finally transmitted out through the reflecting mirror.

[0087] The main characteristics of carbon dioxide lasers are:

[0088] High power output: Carbon dioxide lasers can generate high-power laser beams, with continuous mode producing laser power of over 20 kilowatts, and pulsed mode producing equally powerful beams.

[0089] Specific wavelength: The laser it emits has a wavelength of 10.6 micrometers, which is in the infrared region and cannot be detected by the naked eye.

[0090] High efficiency conversion: As a commercial model, the conversion efficiency of carbon dioxide lasers can reach 10%, and the electro-optic conversion efficiency of some products can generally reach 15% to 25%, and some can even reach 30% to 40%, which exceeds that of other gas lasers.

[0091] High beam quality: It has the advantages of high optical quality of output beam, good coherence, narrow linewidth and stable operation.

[0092] The basic principle of thermal imagers is to utilize the infrared radiation emitted by the surface of an object. The intensity of this radiation is proportional to the object's temperature. Sensors capture this infrared radiation and convert it into digital signals, which are then processed to generate thermal images. These images use different colors or brightness levels to represent different temperature regions, thus visually displaying the temperature distribution on the surface of the target object.

[0093] The main features of thermal imagers are:

[0094] Non-contact temperature measurement: Thermal imagers can measure temperature without contacting the target object, avoiding the errors and interference that may be caused by traditional temperature measurement methods.

[0095] High-precision temperature measurement: Through advanced sensors and image processing technology, thermal imagers can achieve high-precision temperature measurement to meet the needs of various application scenarios.

[0096] Real-time monitoring: Thermal imagers can monitor the temperature distribution on the surface of target objects in real time, providing timely and accurate information for fault diagnosis and safety protection.

[0097] Visualized output: The thermal images generated by the thermal imager are intuitive and easy to understand, making it convenient for users to analyze, record, and export them.

[0098] Ceramic plate samples are prepared for testing the performance and quality of ceramic plates or for scientific research. Common ceramic plate materials include inorganic non-metallic materials such as alumina, zirconium oxide, and kaolin clay. Different ceramic plate materials have different physical and chemical properties, such as weather resistance, impact strength, and chemical corrosion resistance.

[0099] The crack area is calculated using the crack length and the thickness of the test sample, and the energy used for crack propagation is calculated using the energy ratio formula.

[0100] The formula for calculating the energy ratio is as follows:

[0101]

[0102] dQ=cdmΔT=cρ(T-T0)dV (5)

[0103] In the formula:

[0104] ∈_ij^e represents elastic strain;

[0105] ∈_ij^T represents thermal strain;

[0106] α is the coefficient of thermal expansion;

[0107] W represents strain energy;

[0108] E is the elastic modulus;

[0109] Q represents the heat absorbed by the material;

[0110] c is the specific heat capacity;

[0111] ρ is the density;

[0112] The energy ratio formula is calculated as follows:

[0113]

[0114] Example 3

[0115] The steps for using the laser-induced thermal expansion-based fracture toughness measurement method for brittle materials according to this invention are as follows:

[0116] Step 1: Prepare a thin ceramic plate of brittle material with pre-existing cracks. The crack length on the test sample is a.

[0117] Step 2: Place the test sample on the experimental table and fix it in place. Adjust the position of the laser so that the laser point of action is about 1.5 mm behind the crack tip on the test sample.

[0118] Step 3: Set up the thermal imager and camera so that their detection range can cover the entire sample surface, and measure the temperature distribution of the sample surface over time and the crack propagation.

[0119] Step 4: Determine the energy ratio as a constant in the total laser injection energy using formulas (1)-(5), and calculate the proportion of energy used for crack propagation in the total laser injection energy using formula (6) and simulation analysis.

[0120] Step 5: Calculate the crack surface area and calculate the material fracture toughness based on the energy obtained for propagation.

[0121] Example 4

[0122] like Figure 3 As shown, for yttrium-stabilized zirconium oxide, a sample with a length of 50 mm, a width of 50 mm, and a thickness of 0.5 mm was selected for testing, and the results are as follows:

[0123] Table 1 Laser irradiation time and calculated fracture toughness

[0124]

[0125] The reference "Preparation and Mechanical Properties of Zirconia Ceramics Doped with Different Y2O3 Contents" gives a fracture toughness measurement of 13 MPa*m. -0.5 It can be seen that this method is very accurate in calculating the fracture toughness of brittle materials.

[0126] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the scope of the invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0127] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can be appropriately combined to form other embodiments that can be understood by those skilled in the art. The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A method for measuring the fracture toughness of brittle materials based on laser-induced thermal crack propagation, characterized in that, The application relates to a method for measuring the fracture toughness of a material. The tested sample has a crack penetrating a plate surface, and laser probes and a thermal imager are arranged on both sides of the end of the crack on the tested sample, wherein a laser beam is perpendicular to the plate surface and converges at a position 1.5 mm behind the crack tip; The temperature change of the plate surface is read on a thermal imager recorded in a computer; Using the energy W, the temperature change and the crack length change and the energy release rate G of the material using the Griffith energy release theory. The fracture toughness K of the material is determined according to the relationship between the energy release rate and the fracture toughness; A three-dimensional right-handed rectangular coordinate system is established with the plate surface as a plane, the crack tip on the tested sample as an origin, the crack propagation direction as an x axis, the direction perpendicular to the crack as a Y axis and the direction perpendicular to the plate surface as a Z axis, and the laser action point is located at a position 1.5 mm inside the crack tip, and the specific coordinates are (-1.5, 0, 0); The proportion of the crack propagation energy to the total laser injection energy is a constant value through the energy formula, the Griffith energy balance theory and the basic law of elastic mechanics; The required formula is as follows: dW / dt = (1 / 2) * alpha * E * (deltaT / dt)2 wherein: wherein _ij^e represents elastic strain; _ij^T represents thermal strain; a is the thermal expansion coefficient; W is the strain energy; Q is the heat absorbed by the material; E is the elastic modulus; c is the specific heat capacity; Alpha is the thermal expansion coefficient; W is the strain energy; Q is the heat absorbed by the material; E is the elastic modulus; and c is the specific heat capacity. The tested sample has a crack penetrating a plate surface, and the crack surface is perpendicular to the material surface. The tested sample has a crack penetrating a plate surface, and the crack surface is perpendicular to the material surface.

2. The method of measuring the fracture toughness of brittle materials based on laser thermal crack propagation according to claim 1, characterized in that, The laser action point has a size of 0.1 mm in diameter, the laser action power is 100 W, and the laser action time is 0.1 s.

3. The method of claim 1, wherein the method is characterized by: The thickness of the measured material is 0.5 mm.

4. The method of measuring fracture toughness of brittle materials based on laser thermal induced crack propagation according to claim 1, wherein, The application relates to a carbon dioxide laser, a reflecting mirror, a convex lens, a camera, a thermal imager and a data processing computer.

5. The method of measuring fracture toughness of brittle materials based on laser thermal induced crack propagation according to claim 1, wherein, The laser emitted by the carbon dioxide laser reaches the upper side of the experimental piece after the light path is adjusted by the reflecting mirror, converges through the convex lens and then acts on a position 1.5 mm behind the crack tip on the material surface; the thermal imager records the change of the temperature distribution on the surface of the experimental piece with time, the camera records the crack propagation process and records the final length of the crack; the data processing computer calculates the crack area by using the crack length and the thickness of the tested sample and calculates the energy used for crack propagation by using the energy proportion formula; 6. A device for measuring the fracture toughness of a brittle material based on laser-induced thermal crack propagation, characterized in that, The energy proportion calculation formula is as follows: Alpha is the thermal expansion coefficient; W is the strain energy; E is the elastic modulus; Q is the heat absorbed by the material; c is the specific heat capacity; and rho is the density. The energy proportion formula is calculated as follows: The carbon dioxide laser adopts a 150 W carbon dioxide laser. ije represents the elastic strain; ijTrepresents thermal strain; ​ ​ ​ ​ ​ ​ ​ 。 7. The apparatus for measuring fracture toughness of brittle material based on laser thermal induced crack propagation according to claim 6, wherein, ​

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