Micro-nano speckle preparation method for digital image correlation measurement

Abstract

The invention provides a micro-nano speckle preparation method for digital image correlation measurement, which comprises the following steps: preparing a doped photoresist doped with non-organic powder and a glass binding phase; coating a photoresist on the substrate; exposing and developing the coated photoresist to form a speckle pattern; and sintering the speckle pattern to form the micro-nano speckle. According to the technical scheme, the speckle pattern is accurately formed through the photoetching technology, and the speckle pattern has excellent high-temperature stability after high-temperature sintering and is suitable for digital image correlation measurement.

Description

Technical Field

[0001] The present invention relates to the technical field of digital image correlation measurement, and in particular to a method for preparing micro-nano speckles for digital image correlation measurement. Background Art

[0002] Digital image correlation (DIC) is a non-contact, full-field, high-precision optical measurement technique widely used in material mechanics testing, strain analysis, thermal expansion measurement, and other fields. DIC tracks the displacement of speckle patterns on the sample surface before and after deformation, calculates the strain distribution, and enables quantitative analysis of material properties. In high-temperature environments, DIC can be used to study the thermal expansion coefficient, thermal strain distribution, and mechanical properties of high-temperature alloys, ceramics, coatings, and other materials, and has important applications in aerospace, energy, and nuclear industries.

[0003] The accuracy and stability of high-temperature DIC analysis are highly dependent on the quality of the speckle pattern. Currently, in processes such as spraying and sputtering, it is impossible to pre-design the speckle pattern, resulting in completely unpredictable random speckle patterns each time. This uncertainty necessitates subjective adjustments to parameters such as the number of subregions and calculation step size during DIC analysis, increasing experimental instability and data uncertainty. A designable and reproducible random speckle pattern would not only solidify DIC parameter settings and improve analytical stability, but also allow for calibration of the DIC measurement and analysis process using standards, correcting potential errors and improving the measurement accuracy of thermal strain and thermal expansion.

[0004] On the other hand, the accuracy of thermal strain and thermal expansion measurements in DIC analysis depends on the resolution and size of the speckle pattern. High-precision thermal strain and thermal expansion measurements require the generation of ultra-high-resolution micro- and nano-speckle patterns. For example, measurements of ultra-low thermal expansion coefficients generally require speckle sizes below the micron level. Combining photolithography and deposition techniques is a common method for generating micro- and nano-speckle patterns, but this approach is costly and time-consuming. Furthermore, the resulting micro- and nano-speckle patterns have poor temperature resistance, making them difficult to meet the demands of high-temperature testing. Summary of the Invention

[0005] In view of the problems in the prior art, the present invention aims to provide a method for preparing micro-nano speckles for digital image correlation measurement with excellent high-temperature stability.

[0006] The present invention provides a method for preparing micro-nano speckles for digital image correlation measurement, comprising the following steps:

[0007] Step 1, preparing a doped photoresist, wherein the photoresist is doped with non-organic powder and a glass bonding phase;

[0008] Step 2, coating photoresist on the substrate;

[0009] Step 3, exposing and developing the coated photoresist to form a speckle pattern;

[0010] Step 4: Sintering the speckle pattern to form micro-nano speckles.

[0011] Preferably, the particle size of the non-organic powder and the glass binder phase in step 1 is in the range of 30-500 nm.

[0012] Preferably, the content of the non-organic powder in step 1 is 60-80 wt%.

[0013] Preferably, the non-organic powder in step 1 is inorganic or metal powder.

[0014] Preferably, the non-organic powder is Al2O3, Fe3O4, SiC, CuO, W or Pt.

[0015] Preferably, the components of the glass bonding phase in step 1 include SiO2 or B2O3.

[0016] Preferably, the content of the glass bonding phase in step 1 is 3-10 wt %.

[0017] Preferably, a solvent is further added to the photoresist in step 1, and the solvent is propylene glycol methyl ether acetate or ethylene glycol butyl ether acetate.

[0018] Preferably, the photoresist in step 1 is a suspension.

[0019] Preferably, in step 4, the sintering temperature is 800-1600° C., the sintering time is 1-6 hours, and the heating rate is 5-10° C. / min.

[0020] The technical solution of the present invention has the following beneficial effects:

[0021] 1. The technical solution of the present invention can control speckle at the micro-nano scale and improve the high-temperature reliability of speckle, thereby improving DIC measurement accuracy and meeting the testing requirements of low strain and low expansion;

[0022] 2. The technical solution of the present invention can pre-design the pattern of micro-nano speckles, so that the speckle pattern formed each time remains consistent, thereby solidifying the DIC parameter settings and improving analysis stability. It can also calibrate the DIC measurement and analysis process through standard samples, correct potential errors, and improve the measurement accuracy of thermal strain and thermal expansion. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Other features, objects and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings.

[0024] Figure 1are mask designs for positive and negative photoresists, respectively, according to an embodiment of the present invention;

[0025] Figure 2 This is a photograph of Fe3O4 speckles formed on a stainless steel substrate in Example 1 of the present invention;

[0026] Figure 3 This is a photograph of SiC speckles formed on an alumina substrate according to Example 2 of the present invention;

[0027] Figure 4 The average thermal strains are measured at 500°C (a), 700°C (b), 900°C (c), and 1100°C (d) using the DIC technique after the speckle pattern is prepared in Example 2 of the present invention. DETAILED DESCRIPTION

[0028] Example embodiments will now be described more fully. However, the example embodiments can be implemented in many forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete and will fully convey the concepts of the example embodiments to those skilled in the art.

[0029] The present invention provides a method for preparing micro-nano speckles for digital image correlation measurement, comprising the following steps:

[0030] 1. Preparation of photoresist doped with nanopowder and glass binder phase.

[0031] According to the material type and color of the measured object, high-temperature resistant inorganic or metal non-organic powders such as Al2O3, Fe3O4, SiC, CuO, W, and Pt are selected as the main raw materials to prepare high-contrast speckle patterns.

[0032] Glass powder with SiO2, B2O3 and the like as main components is selected as the glass bonding phase to make the speckle have adhesion after sintering.

[0033] The particle size range of the non-organic powder and the glass bonding phase is controlled between 30-500 nm.

[0034] The selected nanopowder is preferably added to a photoresist such as SU-8 or S1813, and an appropriate solvent is preferably added, such as propylene glycol methyl ether acetate, ethylene glycol butyl ether acetate, or the like.

[0035] Furthermore, the photoresist doped with nanopowder and glass bonding phase preferably contains 60-80 wt% of inorganic or metal powder, 3-10 wt% of glass bonding phase, 10-20 wt% of photoresist, and 5-10 wt% of solvent.

[0036] Ultrasonic dispersion and magnetic stirring are then used to mix the materials to ensure that the powder is evenly distributed in the photoresist, and finally vacuum defoaming is performed to form a stable suspension.

[0037] 2. Mask processing.

[0038] Masking is performed based on the properties of the selected photoresist. If a positive photoresist is selected, a speckle pattern should form in the photoresist layer; if a negative photoresist is selected, the photoresist layer should retain exposed areas, forming a speckle pattern. Preferably, a single speckle can have any shape and be less than 1000 μm in size.

[0039] 3. Apply photoresist.

[0040] The photoresist doped with nanopowder is coated on the surface of the substrate to be processed. Preferably, a spin coating process is used, with the rotation speed set at 1000-4000 rpm, and the spin coating time is adjusted according to the substrate size and the required thickness.

[0041] 4. Exposure.

[0042] According to the characteristics of the selected photoresist, select the corresponding wavelength of ultraviolet light for exposure, and the exposure dose is preferably 100-300mJ / cm 2 , ensuring that the speckle pattern is formed clearly and with the required resolution.

[0043] 5. Development.

[0044] Select a developer that matches the photoresist to remove the photoresist outside the speckle pattern. Positive photoresist developers are preferably sodium hydroxide solution or tetramethylammonium hydroxide solution, while negative photoresist developers are preferably dimethyl sulfoxide and acetone.

[0045] The development process is controlled by adjusting the concentration, temperature and time of the developer to ensure the clarity and edge sharpness of the speckle pattern and avoid damaging the solidified speckle pattern.

[0046] 6. Clean.

[0047] The measurement substrate was cleaned with deionized water and dried at 120°C, and then the integrity of the speckle pattern was checked.

[0048] 7. High temperature sintering.

[0049] The dried substrate is placed in a sintering furnace and sintered preferably at a high temperature of 800-1600° C. for 1-6 hours at a heating rate of 5-10° C. / min.

[0050] After sintering, the photoresist is removed and the final speckle pattern has good temperature resistance and mechanical strength.

[0051] The micro-nano speckle preparation method based on photolithography and high-temperature sintering in the embodiment of the present invention realizes high-precision DIC measurement in a high-temperature environment

[0052] The present invention is described below with specific embodiments:

[0053] Example 1:

[0054] A method for preparing Fe3O4 nano-speckle on a stainless steel substrate using a positive photoresist (S1813) comprises the following steps:

[0055] (1) Preparation of photoresist doped with Fe3O4 nanopowder.

[0056] The particle size of Fe3O4 is controlled at 40-120nm, and the glass bonding phase uses boron oxide (B2O3) glass powder, and the particle size is controlled at 50-100nm.

[0057] 65 wt % of Fe 3 O 4 and 7 wt % of B 2 O 3 powders were added to 18 wt % of S1813 positive photoresist, and 10 wt % of ethylene glycol butyl ether acetate was added as a solvent.

[0058] The mixture was placed in an ultrasonic disperser and ultrasonicated for 40 minutes, and then stirred with a magnetic stirrer at 600 rpm for 90 minutes to obtain a uniform nanopowder suspension.

[0059] After mixing, the suspension was placed in a vacuum defoamer and allowed to stand for 15 minutes to eliminate bubbles and improve coating uniformity. The air pressure was set to -0.1 MPa.

[0060] (2) Design and make a mask according to the characteristics of the selected S1813 positive photoresist, such as Figure 1 As shown in (a), 1 is the exposed area, 2 is the photoresist layer, and the unexposed area is a speckle pattern with a speckle size of 100 μm, a close packing of 45%, and a deviation of 60%.

[0061] (3) Applying speckle photoresist.

[0062] The S1813 photoresist doped with Fe3O4 powder was evenly drop-coated on the cleaned stainless steel substrate.

[0063] A spin coating process was used to obtain a uniform coating thickness. The spin speed was set to 2800 rpm for 40 seconds to obtain a photoresist coating with a thickness of about 5 μm, which was then pre-baked at 90°C for 5 minutes.

[0064] (4) Exposure.

[0065] Through the mask, the surface of the stainless steel substrate coated with photoresist was exposed using a UV exposure machine with a wavelength of 405nm. The exposure dose was set to 250mJ / cm 2 After exposure, the exposed areas of the positive photoresist can be removed by development, and the unexposed areas form a speckle pattern.

[0066] (5) Development.

[0067] The exposed stainless steel substrate was placed in a 2.5% tetramethylammonium hydroxide solution for development for 50 seconds. The solution was stirred slowly during the development process to ensure uniform development and a clear speckle pattern.

[0068] (6) Cleaning.

[0069] The developed stainless steel substrate was thoroughly washed with deionized water to remove the residual developer on the surface, and then dried at 120° C. for 10 minutes.

[0070] (7) High temperature sintering.

[0071] The dried substrate was placed in a tube furnace for sintering in a nitrogen atmosphere. The temperature was set to 800°C, the holding time was 2 hours, and the heating rate was 5°C / min. After sintering, the substrate was cooled to room temperature in the furnace to obtain the following Figure 2 The speckle image shown in .

[0072] Example 2:

[0073] A method for preparing SiC nano-speckle on an aluminum oxide (Al2O3) substrate using a negative photoresist (SU-8) comprises the following steps:

[0074] (1) Preparation of photoresist doped with SiC nanopowder.

[0075] The SiC particle size is controlled at 30-100 nm, and the glass bonding phase uses SiO2 glass powder with a particle size controlled at 50-100 nm.

[0076] 70 wt % SiC and 5 wt % SiO 2 powders were added to 15 wt % SU-8 negative photoresist, and 10 wt % propylene glycol methyl ether acetate was added as a solvent.

[0077] The mixture was ultrasonically treated in an ultrasonic disperser for 30 minutes and then stirred with a magnetic stirrer at 500 rpm for 1 hour to obtain a uniform nanopowder suspension. After mixing, the suspension was placed in a vacuum defoamer for 15 minutes to eliminate bubbles and improve coating uniformity. The air pressure was set to -0.1 MPa.

[0078] (2) Design and manufacture a mask based on the properties of the selected SU-8 negative photoresist.

[0079] like Figure 1 As shown in (b), 1' is the exposure area, and 2' is the photoresist layer. The exposure area of ​​the mask has a pre-designed speckle pattern with a speckle size of 50μm, a 40% density, and a 50% offset. The mask should be made of chrome-coated quartz, and high-precision pattern transfer is achieved through electron beam lithography.

[0080] (3) Applying speckle photoresist.

[0081] SU-8 photoresist doped with SiC powder was evenly drop-coated onto a cleaned alumina substrate. A spin coating process was used to achieve a uniform coating thickness. A spin coating of approximately 2 μm was obtained at a speed of 3000 rpm for 60 seconds. The coating was then pre-baked at 90°C for 5 minutes.

[0082] (4) Exposure.

[0083] Through the mask, the surface of the alumina substrate coated with photoresist was exposed using a UV exposure machine with a wavelength of 365nm. The exposure dose was set to 200mJ / cm 2 The exposure time is 10 seconds. After exposure, the speckle pattern in the exposed area will be cross-linked and solidified, and tightly adhere to the alumina substrate.

[0084] (5) Development.

[0085] The exposed alumina substrate was placed in acetone for development for 60 seconds. Stir slowly during development to ensure uniform development and a clear speckle pattern.

[0086] (6) Cleaning.

[0087] The developed alumina substrate was thoroughly washed with deionized water to remove residual acetone on the surface, and then dried at 120° C. for 10 minutes.

[0088] (7) High temperature sintering.

[0089] The dried substrate was placed in a box furnace for sintering in air at 1000°C, with a holding time of 2 hours and a heating rate of 5°C / min. After sintering, the substrate was cooled to room temperature in the furnace. The speckle image formed on the surface of the alumina substrate after sintering is shown in Figure 1. Figure 3 shown.

[0090] like Figure 4Figure 2 shows the DIC analysis results of thermal strain on the alumina substrate formed with speckles according to Example 2 of the present invention at 500°C, 700°C, 900°C, and 1100°C. It can be seen that the speckles at high temperatures do not show signs of detachment or discoloration, indicating that the sintered SiC speckles have good high-temperature stability and adhesion, accurately reflecting the thermal strain of the alumina substrate.

[0091] As shown in Table 1 below, the thermal strain of the alumina substrate with speckles formed in Example 2 of the present invention is measured by the DIC method and the ejector pin method. Taking the ejector pin method as a reference, the micro-nano speckles based on lithography and sintering in Example 2 of the present invention can maintain the accuracy of DIC measurement of thermal strain within ±3%.

[0092] Table 1: Thermal strain of the alumina substrate measured by DIC and ejector pin methods

[0093] temperature Thermal expansion reference value of ejector pin method DIC thermal expansion measurement value deviation 500℃ 0.363％ 0.365％ 0.6％ 700℃ 0.542％ 0.546％ 0.7％ 900℃ 0.732％ 0.731％ -0.2％ 1100℃ 0.944％ 0.919％ -2.6％

[0094] In summary, the embodiment of the present invention accurately forms a speckle pattern through photolithography technology, and after high-temperature sintering, it has excellent high-temperature stability and is suitable for digital image correlation measurement.

[0095] The above is a further detailed description of the present invention in conjunction with specific preferred embodiments, and the specific implementation of the present invention should not be considered to be limited to these descriptions. For those skilled in the art of the present invention, without departing from the concept of the present invention, several simple deductions or substitutions can be made, which should be considered to fall within the scope of protection of the present invention.

Claims

1. A method for preparing micro-nano speckles for digital image correlation measurement, characterized in that: The following steps are involved: Step 1, preparing a doped photoresist, wherein the photoresist is doped with non-organic powder and a glass bonding phase; Step 2, coating photoresist on the substrate; Step 3, exposing and developing the coated photoresist to form a speckle pattern; Step 4: Sintering the speckle pattern to form micro-nano speckles.

2. The method for preparing micro-nano speckles for digital image correlation measurement according to claim 1, characterized in that: The particle size range of the non-organic powder and the glass bonding phase in step 1 is 30-500 nm.

3. The method for preparing micro-nano speckles for digital image correlation measurement according to claim 1, characterized in that: The content of the non-organic powder in step 1 is 60-80 wt%.

4. The method for preparing micro-nano speckles for digital image correlation measurement according to claim 1, characterized in that: The non-organic powder in step 1 is inorganic or metal powder.

5. The method for preparing micro-nano speckles for digital image correlation measurement according to claim 4, characterized in that: The non-organic powder is Al2O3, Fe3O4, SiC, CuO, W or Pt.

6. The method for preparing micro-nano speckles for digital image correlation measurement according to claim 1, characterized in that: In step 1, the glass bonding phase comprises SiO2 or B2O3.

7. The method for preparing micro-nano speckles for digital image correlation measurement according to claim 6, characterized in that: The content of the glass bonding phase in step 1 is 3-10 wt %.

8. The method for preparing micro-nano speckles for digital image correlation measurement according to claim 1, characterized in that: A solvent is further added to the photoresist in step 1, and the solvent is propylene glycol methyl ether acetate or ethylene glycol butyl ether acetate.

9. The method for preparing micro-nano speckles for digital image correlation measurement according to claim 1, characterized in that: The photoresist in step 1 is a suspension.

10. The method for preparing micro-nano speckles for digital image correlation measurement according to claim 1, characterized in that: In step 4, the sintering temperature is 800-1600° C., the sintering time is 1-6 hours, and the heating rate is 5-10° C. / min.

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