Method for applying speckle patterns to measure deformation of samples made of ceramic materials

Abstract

FIELD: technical physics.SUBSTANCE: invention relates to the field of technical physics, specifically to methods for applying speckle structures to measure the deformation of samples made of ceramic materials using the digital image correlation method, and can be used in mechanical engineering for mechanical testing of structural and composite ceramic materials at high and low temperatures. The method for applying speckle structures to measure the deformation of samples consists in using a material carbide as the speckle powder material, the density of which exceeds the density of the sample material, and the coefficient of thermal expansion is at least close to the coefficient of thermal expansion of the sample material. First, a layer of adhesive is applied to the surface of the sample, and the carbide material of the sintered powder is coated with a cladding layer of a refractory material of medium activity. To form a speckle structure, a template is installed concentrically relative to the sample surface, ensuring a gap between the inner surface of the latter and the adhesive layer used to fix the speckle powder on the sample surface before heat treatment of the latter. The sample is heat‑treated at a temperature of up to 0.8 times the test temperature, and deformation measurements are carried out in the X‑ray frequency range.EFFECT: technical result lies in the reliability of applying speckle structures to the sample surface when the latter is loaded during the testing process.1 cl, 5 dwg

Description

[0001] The invention relates to the field of technical physics, namely to methods for applying speckle structures for measuring the deformation of samples made of ceramic materials using digital image correlation, and can be used in mechanical engineering for mechanical testing of structural and composite ceramic materials at high and low temperatures.

[0002] The method relates to the field of technical physics, namely, to methods of applying speckle structures to measure the deformation of samples made of ceramic materials, and can be used in mechanical engineering in mechanical testing of structural and composite ceramic materials, including those based on silicon (nitride, oxide, carbide) when applying speckle structures to measure the deformation of samples during loading at high and low temperatures using the digital image correlation method.

[0003] The use of structural ceramic materials and ceramic composites requires studies of their mechanical properties, including at high (close to 1800°C) and low (down to -150°C) temperatures. One of the measured parameters is the deformation on the sample surface. Measurements are conducted using various methods, one of which is Digital Image Correlation (DIC), which allows for contactless deformation measurement. Using DIC requires a random contrast pattern, which is created using marks (patterns) or speckles on the sample surface. Deformations are determined by recalculating the displacement of contrast marks pre-applied to the surface of the part under the applied load.The location of marks on the surface is recorded using optical means operating in different spectral ranges, depending on the test conditions.

[0004] When testing gaseous or contaminated environments at high and low temperatures, taking into account the influence of optical interference associated with changes in gas density and its convection at different temperatures near the object, the most effective method for obtaining images with markers is to use X-rays. In this case, the markers must be radiopaque, and the contrast is created not by the ink, but by the difference in the radiation transmittance of the test object and the marker. Radiation transmittance depends on the density of the sample and marker materials, and the path length of the X-ray beam from the source to the detector. Using the DIC method in the X-ray range places the following requirements on the markers that form the images:

[0005] - marks should not peel off or fade during testing;

[0006] - marks should not act as a stress concentrator;

[0007] - the temperature resistance of the label material must comply with the test range;

[0008] - There must be sufficient contrast between the background and the label.

[0009] A known method for applying speckle structures to measure the deformation of samples during high-temperature tests using digital image correlation consists in the fact that high-temperature ceramics in the form of powders are selected for the manufacture of marks, mixed with high-temperature paints and varnishes that are thermally stable at high temperatures, applied by airbrushing and subjected to heat treatment, during which adhesive adhesion of the material of the marks and the part occurs (Y. Don. Temperature deformation measurement using optical imaging digital image correlation: Status, challenge and future Chinese Journal of Aeronautics Volume 38, Issue 6, 6 2025, 103472, https: / / doi.org / 10.1016 / j.cja.2025.103472).

[0010] The existing technical solution doesn't take into account the thermal expansion coefficients of the mixture components during the manufacturing process, leading to chipping of the markers when the sample is heated during testing. Furthermore, the low density of the marker material, characteristic of this technical solution, precludes its use for X-ray measurements due to their low radiopacity.

[0011] A known method for applying speckle patterns to measure the deformation of samples during high-temperature testing using digital image correlation consists of applying laser engraving on the surface of the sample (YJ. Hu, YJ Wang, JB Chen, JM Zhu. / / A New Method of Creating High-Temperature Speckle Patterns and Its Application in the Determination of the High-Temperature Mechanical Properties of Metals. / / Experimental Techniques Volume 42, pages 523-532 5.6.2018 / / DOI: 10.1007 / s40799-018-0256-z).

[0012] A well-known technical solution allows for the creation of speckle structures resistant to temperatures reaching the melting point of the sample material. However, marks applied to the sample surface lead to the formation of stress concentrators, crack initiation under cyclic loading, and ultimately, distortion of test results.

[0013] The closest to the proposed invention in terms of the set of essential features and purpose to the claimed technical solution is a method for applying speckle structures for measuring the deformation of samples during high-temperature tests using digital image correlation, which consists in sequentially preparing the surface of the sample to increase its roughness and adhesion, applying a layer of glue to the surface of the sample, placing a template on the surface of the sample to organize the speckle structure, applying carbide material of speckle powder to the template and subjecting the sample with the speckle powder applied to its surface to heat treatment (N. Lu, L. Yu, Q. Wang, B. Pan. / / Fabrication of Ultra-Stable and Customized High-Temperature Speckle Patterns Using Air Plasma Spraying and Flexible Speckle Templates. / / Sensors Journal:, 2023, Volume: 23 Number: 7656 / / DOI:10.3390 / s23177656).

[0014] A known technical solution for applying markings eliminates the possibility of a chemical reaction between the primer and the speckle structure components and ensures sufficient color contrast between the sublayer and the speckle mark components. Specifically, it is proposed to use white zirconium dioxide as the sublayer and black silicon carbide as the marking material. However, this method is characterized by insufficient adhesion between the speckle structure material and the sample material, resulting in low durability.

[0015] Thus, a significant drawback of the known technical solutions mentioned above is the low reliability of the method of applying speckle structures to the surface of the sample material.

[0016] The technical problem solved by the claimed invention consists in expanding the arsenal of technical means, namely, in creating a method for applying speckle structures for measuring the deformation of samples made of structural and composite ceramic materials during testing using the digital image correlation method.

[0017] The technical result achieved by implementing the present invention consists in realizing its purpose, i.e. in creating a method for applying speckle structures for measuring the deformation of samples made of structural and composite ceramic materials during testing using the digital image correlation method, ensuring the reliability of applying speckle structures to the surface of the sample when loading the latter during testing.

[0018] The claimed technical result is achieved due to the fact that when implementing the method for applying speckle structures for measuring the deformation of samples made of ceramic materials, the surface of the sample is successively prepared to increase its roughness and adhesion, a layer of glue is applied to the surface of the sample, a template for organizing the speckle structure is placed on the surface of the sample, the carbide of the speckle powder material is applied to the template and the sample with the speckle powder applied to its surface is subjected to heat treatment, according to the proposed technical solution, the carbide of the speckle powder material is preliminarily coated with a cladding layer of a refractory material of medium activity, designed to ensure the diffusion of the speckle powder material into the sample material, the speckle powder is a material whose density exceeds the density of the sample material,and the coefficient of thermal expansion is at least close to the thermal expansion coefficient of the sample material, a template for organizing the speckle structure is installed concentrically relative to the surface of the sample, providing a gap between the inner surface of the template and the adhesive layer, and the adhesive is used to fix the speckle powder on the surface of the sample before heat treatment of the latter, the heat treatment of the sample is carried out at a temperature of up to 0.8 of the test temperature, and the deformation measurements are carried out in the range of X-ray frequencies.

[0019] The significance of the distinctive features of the technical solution is confirmed by the fact that only the totality of all features describing the proposed technical solution allows for the solution of the stated technical problem with the achievement of the stated technical result.

[0020] The invention is explained by the following detailed description and illustrations, where:

[0021] - Fig. 1 shows the original sample with carbide of speckle powder material applied to its surface;

[0022] - Fig. 2 shows a sample after heat treatment at 1100°C;

[0023] - Fig. 3 shows a sample after heat treatment at 1200°C;

[0024] - Fig. 4 shows a sample after heat treatment at 1300°C;

[0025] - Fig. 5 shows a sample after heat treatment at 1400°C;

[0026] The following designations are used in the drawing:

[0027] 1 - sample;

[0028] 2 - speckle powder carbide.

[0029] The method is implemented as follows.

[0030] To improve the roughness and adhesive properties, the surface of sample 1 is pre-treated with an abrasive material for the application of a speckle structure, and a layer of adhesive (not shown in the drawing) is applied to the surface of the sample. This adhesive is intended to fix speckle powder 2 to the surface of sample 1 prior to heat treatment. The speckle is selected from a material (including a carbide of this material) whose radiopacity exceeds that of the sample material and the test equipment components, and whose coefficient of thermal expansion is at least close to that of the sample material. A powder is produced from the selected material, the particles of which are pre-coated with a cladding layer (not shown in the drawing) of a refractory material of medium activity, designed to ensure the diffusion of speckle powder 2 into the material of sample 1.A template (not shown in the drawing) is installed concentrically relative to the surface of the latter to organize the speckle structure, ensuring a gap between the inner surface of the template and the adhesive layer. Speckle powder 2 is then applied to the template (see Fig. 1), and sample 1, with speckle powder 2 applied to its surface through the template, is subjected to heat treatment. Next, to ensure diffusion of speckle powder 2 into the material of sample 1, heat treatment is performed at a temperature of up to 0.8 times the test temperature (see Figs. 2-5), which eliminates the possibility of material alteration due to high temperatures prior to testing.As the heating temperature increases, the adhesive used to fix speckle powder 2 to the surface of sample 1 burns away. The refractory cladding layer transitions to a liquid phase. Given its moderate activity, it partially reacts chemically with speckle powder 2, forming new carbide and intermetallic compounds characterized by high strength, ensuring their diffusion into the sample 1 material and the fixation of the speckle structure. Sample 1 is then cooled and tested according to specified conditions, monitoring its deformation using X-rays and digital image correlation. A radiopaque image of sample 1 and the markings is obtained directly through the chamber walls and thermal insulation, without the use of viewing windows and independent of the sample's surrounding environment.

[0031] Example of the method implementation.

[0032] For the production of marks, sample 1 was used in the form of a flat square plate measuring 30×30 mm made of silicon carbide (SiC), the coefficient of thermal expansion of which is 3.8-4x10 -6 1 / K. Tungsten carbide (WC) with a particle size of ≈20 μm and a thermal expansion coefficient of 3.84-3.9x10 was chosen as speckle powder 2. -6 1 / K. Metallic nickel (Ni) was used as the cladding material. Sample surface preparation consisted of mechanical cleaning to achieve the required roughness and degreasing with a solvent. Cyanoacrylate adhesive was applied to the surface with a brush, and speckle powder was randomly applied to it, without using a template, in the form of individual marks approximately 1 mm in diameter (see Fig. 1). The marks, glued in this manner, allowed the sample to be moved without risk of damage.

[0033] The heat treatment process is as follows:

[0034] Original condition (see photo a):

[0035] - WC (or W2C) - tungsten carbide;

[0036] - Ni - plating material.

[0037] The sample prepared in this manner was placed in a high-temperature furnace for heat treatment and subjected to sequential heating to temperatures of 1100°C - 1300°C for 10 minutes (see Figs. 2, 3, 4). The following chemical processes occur during the heating process:

[0038] 1. At a temperature close to 1100°C in air, oxidation of WC and Ni occurs:

[0039] WC + 2.5O2→ WO3+CO2

[0040] (WO3 is formed - volatile at high temperature).

[0041] 2Ni + O2 → 2 NiO

[0042] (NiO is formed).

[0043] 2. Solid phase reaction: When heated to a temperature of 1200°C to 1300°C, Ni reacts with SiC and WC to form new high-strength carbide and intermetallic compounds.

[0044] NiO + WO3 → NiWO4 (nickel tungstate NiWO4 is formed).

[0045] Final products:

[0046] - WO3- basic tungsten oxide;

[0047] - NiO - nickel oxide;

[0048] - NiWO4- mixed oxide (with long-term heating);

[0049] - Carbon is released as CO2.

[0050] Color change

[0051] - WO3: bright yellow, lemon yellow;

[0052] - NiO: dark gray;

[0053] - NiWO4: dark green-black.

[0054] The surface of WC-Ni first turns yellow (WO3), then darkens to green-black (NiO + NiWO4).

[0055] After holding in a furnace at 1100°C, a reaction occurs, after which the gray powder turns yellow (see Fig. 2). As a result of holding at a temperature of 1400°C, the yellow powder sinters into a gray film with good adhesion (see Fig. 5). The WC-Ni surface first turns yellow (WO3), then darkens to green-black (NiO + NiWO4).

[0056] The test of the sample for which the implementation of the speckle structure application method was developed was carried out in a nitrogen atmosphere at an operating temperature of 1800°C.

[0057] To apply speckle structures to ceramic and composite metal-ceramic samples during testing in a vacuum or in furnaces with an inert atmosphere, it is advisable to use metal powders (Pt, W, Ta, Mo) or their compounds with high heat resistance as speckle materials.

[0058] Thus, preliminary application of a layer of adhesive to the surface of the sample, coating the speckle powder material with a cladding layer of a refractory material of medium activity, the density of which exceeds the density of the sample material, and the coefficient of thermal expansion is at least close to the thermal expansion coefficient of the sample material, fixing the speckle powder on the surface of the sample and carrying out heat treatment at a temperature of up to 0.8 of the test temperature, and measuring the deformation in the X-ray frequency range provides a solution to the technical problem of expanding the arsenal of technical means, namely, the creation of a method for applying speckle structures for measuring the deformation of samples made of structural and composite ceramic materials during testing using the digital image correlation method, with the achievement of a technical result consisting in the implementation of its purpose, i.e.in the creation of a method for applying speckle structures to measure the deformation of samples made of structural and composite ceramic materials during testing using the digital image correlation method, ensuring the reliability of applying speckle structures to the surface of the sample when the latter is loaded during testing.

Claims

A method for applying speckle structures for measuring the deformation of samples made of ceramic materials, which consists in sequentially preparing the surface of the sample to increase its roughness and adhesion, applying a layer of adhesive to the surface of the sample, placing a template on the surface of the sample for organizing the speckle structure, applying the carbide of the speckle powder material to the template and subjecting the sample with the speckle powder applied to its surface to heat treatment, characterized in that the carbide of the speckle powder material is first coated with a cladding layer of a refractory material of medium activity, designed to ensure the diffusion of the speckle powder material into the sample material, the speckle powder being a material whose density exceeds the density of the sample material and whose coefficient of thermal expansion is at least close to the thermal expansion coefficient of the sample material,a template for organizing a speckle structure is installed concentrically relative to the surface of the sample, ensuring a gap between the inner surface of the template and the adhesive layer, and the adhesive is used to fix the speckle powder on the surface of the sample before heat treatment of the latter, the heat treatment of the sample is carried out at a temperature of up to 0.8 of the test temperature, and the deformation measurements are carried out in the range of X-ray frequencies.

Images