Thermal expansion measuring device and method for gradient material

Abstract

The invention relates to the field of material thermal expansion testing, and provides a thermal expansion measuring device and method for gradient materials, and the device comprises an array probe module, a machine vision system, a temperature control system, a driving mechanism, a control module and a housing. The probe array module comprises probes arranged at equal intervals, and the bottom ends of the probes are in direct contact with the surface of a sample; the driving mechanism drives the probe array to scan along a sample component gradient direction; the machine vision system is used for collecting a probe top end image and combining an image processing algorithm to achieve full-area analysis of gradient components. Compared with existing equipment, the thermal expansion behavior of samples such as component gradient materials and composite materials can be represented, the thermal expansion behavior characterization device is particularly suitable for thermal expansion behavior characterization of key components such as aerospace gradient coatings and nuclear reactor cladding materials, and a reliable testing means is provided for design optimization of functionally gradient materials.

Description

Technical Field

[0001] The present invention relates to the field of material thermal expansion testing, and in particular to a thermal expansion measuring device and method for gradient materials. Background Art

[0002] The coefficient of thermal expansion (CTE) of a material, as a key physical property parameter, directly affects the thermal matching performance of core components such as aerospace engine turbine blades, electronic packaging substrates, and precision optical devices. New functional composition-gradient materials occupy an important position in aerospace and nuclear applications. Accurately measuring the CTE of composition-gradient materials is of great significance for designing stable material structures, avoiding structural buckling, and predicting the internal stress of material structures during service in thermal environments. However, traditional thermal expansion testing methods for homogeneous materials can no longer meet the requirements for characterizing their thermal-mechanical coupling behavior. Therefore, measuring the CTE of composition-gradient materials has become a key link in materials research and development and engineering practice.

[0003] Existing thermal expansion measurement techniques are generally only suitable for testing homogeneous materials. For example, the most widely used push-rod dilatometers, thermal expansion analyzers, and strain gauges are limited to regional measurements when measuring novel compositionally gradient functional materials. These methods can only measure the overall average expansion of the specimen. In particular, given the physical property differences of gradient structures, traditional testing methods cannot fully reflect the anisotropic expansion behavior of compositionally gradient materials and cannot resolve local CTE jumps within micron-scale composition gradient regions. This severely restricts the design and optimization of novel composite materials. Given these limitations, it is necessary to design a device and method for measuring the thermal expansion of gradient materials. Summary of the Invention

[0004] The purpose of the present invention is to overcome the shortcomings of the existing technology and provide a thermal expansion measurement device and method for gradient materials, which can realize the thermal expansion measurement and analysis of the full component area of the gradient material, thereby improving the accuracy and efficiency of the test.

[0005] The present invention adopts the following technical solutions:

[0006] In one aspect, the present invention provides a device for measuring thermal expansion of gradient materials, comprising an array probe module, a machine vision system, a temperature control system, a drive mechanism, a control module, and a housing;

[0007] The array probe module includes a plurality of probes perpendicular to the sample surface and arranged in parallel with equal spacing, which is used to calibrate the displacement of multiple set points on the sample surface at one time; the array direction of the array probe is perpendicular to the material gradient direction of the sample;

[0008] The machine vision system is used to capture an image of the top needle tip of the array probe and calculate the actual position and displacement of each probe based on the needle tip image;

[0009] The driving mechanism is used to drive the array probe module to move in a set manner along the gradient direction of the sample material and to adjust the position and angle of the machine vision system;

[0010] The temperature control system is used to heat and maintain the sample at a set temperature;

[0011] The control module is used to control the operation of the machine vision system, temperature control system, and drive mechanism;

[0012] The array probe module, machine vision system, temperature control system, and driving mechanism are all arranged in the housing.

[0013] According to any possible implementation described above, there is further provided an implementation, wherein the array probe module includes a frame, a first clamping bar, a second clamping bar, a calibration block, and a plurality of probes;

[0014] The frame is provided with a first plywood strip and a second plywood strip on the upper and lower sides respectively. The first plywood strip and the second plywood strip are provided with vertical guide channels distributed at equal intervals along the length direction. Probes of the same length are vertically installed in each guide channel to form a probe array. The bottom ends of the probes are in direct contact with the sample surface. The calibration blocks are respectively installed at the top ends of the probe array. The calibration blocks have known dimensions and are used to provide a reference for calculating the position of the probes.

[0015] The frame is connected to the driving mechanism and moves along the gradient direction of the sample material with the driving mechanism.

[0016] Any possible implementation as described above, further provides an implementation, wherein the probe is made of Invar alloy, the top end is coated with matte alumina and both the top end and the bottom end are hemispherical, and the two ends of the probe are provided with radially extending limiting protrusions to prevent the probe from sliding downward from the guide channel along the axial direction, and the outer diameter of the limiting protrusion is larger than the inner diameter of the guide channel.

[0017] According to any possible implementation described above, there is further provided an implementation, wherein the driving mechanism includes a guide rail, a displacement sensor, and a mechanical arm assembly;

[0018] One end of the mechanical arm assembly is fixed to the housing, and the other end is rigidly connected to the frame to drive the array probe module to move; the displacement sensor is arranged on the frame to record the displacement of the array probe module;

[0019] The guide rail is used to adjust the position and angle of the machine vision system.

[0020] According to any possible implementation described above, there is further provided an implementation, wherein the machine vision system includes a coaxial backlight unit, an image acquisition unit, and an image processing unit;

[0021] The image acquisition unit is a high-resolution CCD camera, whose field of view covers the entire top of the probe and the upper part of the first splint; the coaxial backlight unit is arranged opposite to the CCD camera and is used to provide backlight illumination, so that a high contrast is formed between the probe and the background in the collected image;

[0022] The image processing unit is an image processing system based on a distributed computing framework, equipped with a sub-pixel displacement analysis algorithm based on a convolutional neural network, which is used to perform sub-pixel segmentation and data calculation and statistics tasks of the image to obtain the actual spatial position coordinates of the probe.

[0023] As for any possible implementation method described above, an implementation method is further provided, wherein the temperature control system includes a multi-layer thermal insulation structure, a magnetic induction coil and a temperature sensor; the multi-layer thermal insulation structure is composed of an innermost ferromagnetic alloy sleeve, an insulation cotton layer located outside the alloy sleeve, and an outermost high-temperature cloth layer; the magnetic induction coil is located outside the multi-layer thermal insulation structure; and the temperature sensor is arranged outside the multi-layer thermal insulation structure.

[0024] In any of the possible implementations described above, further provided is an implementation in which the spacing between adjacent guide channels is ≤ 0.5 mm, and the center-to-center distance error is ≤ ± 0.05 mm. The inner diameter of the guide channel is 0.5-1.5 mm. The number of probes is 20-50, and the spacing between the steel needles and the length of the probe array can be adjusted by adjusting the arrangement of the probes in the channel.

[0025] As for any possible implementation described above, a further implementation is provided, wherein the housing includes an air inlet valve, an air outlet valve, an oxygen sensor, and an air pressure sensor, which are used to form a closed test environment and perform atmosphere adjustment.

[0026] On the other hand, the present invention also provides a method for measuring thermal expansion of a gradient material, the method using the above-mentioned device, the method comprising:

[0027] S1. The sample to be tested is placed in the temperature control system. The drive mechanism adjusts the array probe module to the test starting end X0, so that the bottom of the probe is in close contact with the upper surface of the sample. The coaxial backlight unit and CCD camera are adjusted so that the camera image shows high contrast and clear noise-free between the top of the probe, the calibration block, and the background. The temperature control system adjusts the sample to the initial temperature T0.

[0028] S2, the driving mechanism drives the array probe module to move from the test starting end X0 to the test ending end X z, each time it moves a specific step length Δm, the dwell time t0, Δm can be 0.2-2mm, take an image and mark the image number a, a=1,2,3,……;

[0029] S3, the image processing module divides the calibration block width pixel size, and defines the image coordinate reference point (x a (0),y a (0)); Use the image processing module to segment the probe tip and the background and calibrate the coordinates (x a (i),y a (i)), where i is the number of each probe, i = 1, 2, 3...;

[0030] S4, the temperature control system heats the sample to the target temperature T k , T k >T0; repeat steps S2 and S3;

[0031] S5. Based on the results of steps S3 and S4, the thermal expansion coefficient of each measuring point of the sample and the overall thermal expansion distribution diagram are calculated.

[0032] For any of the possible implementations described above, a further implementation is provided, in which the specific method of step S5 is:

[0033] S51, calculate the calibration block width pixel size P a Conversion ratio coefficient K between the actual width dimension L a , K a =L / P a , where K a The unit is: micrometer / pixel;

[0034] S52, calculate the temperature as T k The pixel displacement of the probe tip ΔP a (i), ΔP a (i) = y a (i)(T k )-y a (i)(T0),y a (i)(T k ) is the temperature T k The vertical coordinate of the i-th probe in the a-th image, y a (i)(T0) is the ordinate of the i-th probe in the a-th image at temperature T0;

[0035] S53, according to the conversion ratio coefficient K a Convert pixel displacement to actual displacement ΔL a (i), ΔL a (i) = K a ×ΔP a (i);

[0036] S54. Calculate the temperature change ΔT, ΔT = T k -T0; Calculate the local thermal expansion coefficient α of each probe corresponding to the sample position based on the initial longitudinal thickness dimension L0 of the sample measured at the probe position (which can be the dimension of the probe initially contacting the sample or a pre-determined reference dimension) i , α i =ΔL a (i) / (L0×ΔT);

[0037] S55, according to the probe at T k The known thermal expansion coefficient α under invar Perform thermal compensation calculation, α i '=α i -α invar ; α i ' is the thermal expansion coefficient after compensation.

[0038] The beneficial effects of this invention include: by constructing a probe array module and combining an adjustable number of probe arrays, simultaneous multi-point high-throughput characterization is achieved, replacing traditional single-point measurements. This enables high-throughput thermal expansion analysis of composition gradients across the entire region, from points to lines to surfaces, significantly improving test accuracy and research efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 FIG2 is a schematic structural diagram of a thermal expansion measurement device for gradient materials according to an embodiment of the present invention.

[0040] Figure 2 Shown is a schematic structural diagram of the array probe module in the embodiment.

[0041] Figure 3 FIG. 1 is a schematic top view of the array probe module in the embodiment.

[0042] Figure 4 Shown is a schematic diagram of the relationship between the probe array direction and the sample gradient direction in the embodiment.

[0043] Figure 5 Shown is a grayscale change diagram of a single probe characteristic area and visual identification in an embodiment.

[0044] Figure 6 Shown is a diagram showing the displacement of a single position of the probe array in an embodiment.

[0045] Figure 7 Shown is a diagram showing the overall displacement of the probe array in the embodiment.

[0046] Figure 8 The figure shows the relationship between the thermal expansion coefficient and elements of the Invar-316L gradient alloy in Application Example 1.

[0047] In the figure: 1-1, probe, 1-2, first splint, 1-3, first calibration block, 1-4, frame, 1-5, second splint, 1-6, second calibration block, 1-7, guide channel, 2-1, coaxial backlight unit, 2-2, image acquisition unit, 2-3, image processing unit, 3-1, robotic arm assembly, 3-2, first guide rail, 3-3, second guide rail, 3-4, third guide rail, 4-1, multi-layer insulation structure, 4-2, magnetic induction coil, 4-3, temperature sensor, 5-1, air inlet valve and air outlet valve, 5-2, stage, 5-3, oxygen sensor and air pressure sensor, 5-4, cover, 6, composition gradient material sample. DETAILED DESCRIPTION

[0048] The following will describe in detail specific embodiments of the present invention with reference to the accompanying drawings. It should be noted that the technical features or combinations of technical features described in the following embodiments should not be considered isolated, and they can be combined with each other to achieve better technical effects.

[0049] like Figure 1 As shown, an embodiment of the present invention provides a thermal expansion measurement device for gradient materials, comprising an array probe module, a machine vision system, a temperature control system, a drive mechanism, a control module, and a housing;

[0050] The array probe module includes a plurality of probes 1-1 perpendicular to the surface of the sample 6 and arranged parallel to each other at equal intervals, and is used to calibrate the displacement of multiple set points on the surface of the sample 6 at one time; the array direction of the array probe is perpendicular to the material gradient direction of the sample 6, such as Figure 4 As shown;

[0051] The machine vision system is used to capture the top needle tip image of the array probe 1-1 and calculate the actual position and displacement of each probe 1-1 based on the needle tip image;

[0052] The driving mechanism is used to drive the array probe module to move along the material gradient direction of the sample 6 in a set manner and to adjust the position and angle of the machine vision system;

[0053] The temperature control system is used to heat and maintain the sample 6 at a set temperature;

[0054] The control module is used to control the operation of the machine vision system, temperature control system, and drive mechanism;

[0055] The array probe module, machine vision system, temperature control system, and driving mechanism are all arranged in the housing.

[0056] In a specific embodiment, Figure 2 、 Figure 3As shown, the array probe module includes a frame 1-4, a first clamping strip 1-2, a second clamping strip 1-5, a calibration block 1-3, 1-6 and a plurality of probes 1-1;

[0057] The first plywood strip 1-2 and the second plywood strip 1-5 are respectively provided on the upper and lower parts of the frame 1-4, and the first plywood strip 1-2 and the second plywood strip 1-5 are both provided with vertical guide channels 1-7 distributed at equal intervals along the length direction, and the guide channels 1-7 provided by the first plywood strip 1-2 and the second plywood strip 1-5 correspond to each other one by one; a probe 1-1 of the same length is vertically installed in each guide channel 1-7 to form a probe array, and the bottom end of the probe 1-1 is in direct contact with the surface of the sample 6; the calibration blocks (the first calibration block 1-3 and the second calibration block 1-6) are respectively installed at the top two ends of the probe array, and the sizes of the calibration blocks 1-3 and 1-6 are known, and are used to provide reference objects for solving the position of the probe 1-1;

[0058] The frame 1-4 is connected to the driving mechanism and moves along the material gradient direction of the sample 6 with the driving mechanism.

[0059] In a specific embodiment, the probe 1-1 is made of Invar alloy, the top end is coated with matte alumina and both the top end and the bottom end are hemispherical. The two ends of the probe 1-1 are provided with radially extending limiting protrusions to prevent the probe 1-1 from sliding downward from the guide channel 1-7 along the axial direction. The outer diameter of the limiting protrusion is larger than the inner diameter of the guide channel 1-7.

[0060] In a specific embodiment, Figure 1 As shown, the driving mechanism includes guide rails (a first guide rail 3-2, a second guide rail 3-3, and a third guide rail 3-4), a displacement sensor, and a robotic arm assembly 3-1;

[0061] One end of the robotic arm assembly 3-1 is fixed to the housing, and the other end is rigidly connected to the frame 1-4 to drive the array probe module to move; the displacement sensor is provided on the frame 1-4 to record the displacement of the array probe module;

[0062] The guide rails, the first guide rail 3-2, the second guide rail 3-3, and the third guide rail 3-4, provide fixed movement directions for adjusting the position and angle of the machine vision system.

[0063] In a specific embodiment, Figure 1 As shown, the machine vision system includes a coaxial backlight unit 2-1, an image acquisition unit 2-2 and an image processing unit 2-3;

[0064] The image acquisition unit 2-2 may be a high-resolution CCD camera, the field of view of which covers the entire top of the probe 1-1 and the upper portion of the first splint 1-2; the coaxial backlight unit 2-1 is disposed opposite to the CCD camera 2-2 and is used to provide backlight illumination, so that a high contrast is formed between the probe 1-1 and the background in the captured image;

[0065] The image processing unit 2-3 is an image processing system based on a distributed computing framework, which is equipped with a sub-pixel displacement analysis algorithm based on a convolutional neural network, and is used to perform sub-pixel level segmentation and data calculation and statistical tasks of the image to obtain the actual spatial position coordinates of the probe 1-1.

[0066] In a specific embodiment, Figure 1 As shown, the temperature control system includes a multi-layer insulation structure 4-1, a magnetic induction coil 4-2 and a temperature sensor 4-3; the multi-layer insulation structure 4-1 is composed of an innermost ferromagnetic alloy sleeve, an insulation cotton layer located outside the alloy sleeve and an outermost high-temperature cloth layer; the magnetic induction coil 4-2 is located outside the multi-layer insulation structure; the temperature sensor is arranged outside the multi-layer insulation structure 4-1.

[0067] In one embodiment, the spacing between adjacent guide channels 1-7 is ≤0.5 mm, and the center-to-center distance error is ≤±0.05 mm. The inner diameter of the guide channel 1-7 is 0.5-1.5 mm. The number of probes 1-1 is 20-50. The spacing between the probes 1-1 and the length of the probe array can be changed by adjusting the arrangement of the probes 1-1 in the channel 1-7.

[0068] In a specific embodiment, Figure 1 As shown, the shell includes an air inlet valve and an air outlet valve 5-1, an oxygen sensor and an air pressure sensor 5-3, which are used to form a closed test environment and adjust the atmosphere. The sample 6 is placed on the stage 5-2.

[0069] An embodiment of the present invention provides a method for measuring thermal expansion of a gradient material, the method using the above-mentioned device, and the method comprising:

[0070] S1. Place the sample 6 to be tested in the temperature control system. The drive mechanism adjusts the array probe module to the test starting end X0, so that the bottom of the probe 1-1 is in close contact with the upper surface of the sample 6. Adjust the coaxial backlight unit 2-1 and the CCD camera 2-2 so that the camera image shows high contrast and clear noise-free between the top of the probe 1-1, calibration blocks 1-3 and 1-6, and the background. The temperature control system adjusts the sample 6 to the initial temperature T0.

[0071] S2, the driving mechanism drives the array probe module to move from the test starting end X0 to the test ending end X z , each move has a specific step length Δm, such as Figure 4 As shown, at the dwell time t0, an image is captured and marked with image number a, where a=1, 2, 3, ...;

[0072] S3, the image processing module divides the calibration blocks 1-3 and 1-6 into width pixel sizes, and defines the image coordinate reference point (x a (0),y a (0)); Use the image processing module to segment the probe 1-1 tip and the background and calibrate the coordinates (x a (i),y a (i)), where i is the number of each probe 1-1, i = 1, 2, 3...; Figure 5 As shown, the tip coordinates (x1(i), y1(i)) of a single probe 1-1 are obtained by visually identifying the grayscale change, and the integration is as follows Figure 6 Array coordinates of the tip of probe 1-1 at temperature T0 shown in FIG;

[0073] S4, the temperature control system heats the sample 6 to the target temperature T k , T k >T0; repeat steps S2 and S3; repeatedly drive the array probe module to move a distance Δm, collect multiple sets of images numbered a (a=1, 2, 3, ...) and complete the image segmentation task, and obtain the overall position distribution map of the probe 1-1 tip, such as Figure 7 shown.

[0074] S5. Based on the results of steps S3 and S4, the thermal expansion coefficient of each measuring point of sample 6 and the overall thermal expansion distribution diagram are calculated.

[0075] In a specific embodiment, the specific method of step S5 is:

[0076] S51, calculate the pixel size P of the width of calibration blocks 1-3 and 1-6 a Conversion ratio coefficient K between the actual width dimension L a , K a =L / P a , where K a The unit is: micrometer / pixel;

[0077] S52, calculate the temperature as T k The pixel displacement ΔP at the tip of probe 1-1 is a (i), ΔP a (i) = y a (i)(T k )-y a (i)(T0),y a (i)(T k ) is the temperature T kThe vertical coordinate of the i-th probe 1-1 in the a-th image, y a (i)(T0) is the ordinate of the i-th probe 1-1 in the a-th image at temperature T0;

[0078] S53, according to the conversion ratio coefficient K a Convert pixel displacement to actual displacement ΔL a (i), ΔL a (i) = K a ×ΔP a (i);

[0079] S54. Calculate the temperature change ΔT, ΔT = T k -T0; Calculate the local thermal expansion coefficient α of each probe 1-1 corresponding to the position of the sample 6 according to the initial longitudinal thickness dimension L0 of the sample 6 measured at the probe 1-1 position (which can be the dimension of the sample when the probe 1-1 initially contacts the probe 1-1 or a pre-determined reference dimension). i , α i =ΔL a (i) / (L0×ΔT);

[0080] S55, according to probe 1-1 in T k The known thermal expansion coefficient α under invar Perform thermal compensation calculation, α i '=α i -α invar ; α i ' is the thermal expansion coefficient after compensation;

[0081] The calculation and integration generate the distribution cloud map of the thermal expansion behavior of the composition gradient material in the whole area.

[0082] Application examples of the present invention:

[0083] In fields such as aerospace, microelectronics, and precision instruments, there is an urgent need to control the thermal expansion of key components. That is, the relevant materials need to have a linear or designable coefficient of thermal expansion (CTE) to ensure high precision and long service life of the equipment and reduce unnecessary power consumption (temperature compensation, etc.).

[0084] When designing the CTE of compositionally gradient composite materials, traditional single-point thermal expansion instruments are unable to meet practical testing requirements due to sample preparation issues. Resistive strain gauges are commonly used to measure the CTE data of each layer of gradient materials. However, these methods also face challenges such as time-consuming and labor-intensive attachment, cumbersome operational procedures with inconsistent compliance, and high economic and time costs. Furthermore, strain gauge accuracy is severely affected by various factors related to high-temperature environments, including dependence on temperature sensitivity and complex thermal output compensation. Consequently, these strain gauges cannot meet the high-throughput data characterization requirements for compositionally gradient materials in research and engineering.

[0085] Application Example 1

[0086] In key fields such as aviation, aerospace, and nuclear energy, Invar-316L dissimilar materials are crucial functional components in control and sensing systems. The thermal expansion coefficient of 316L is approximately 10 times that of Invar, resulting in thermal stress mismatch. Gradienting dissimilar materials is an effective solution to this problem.

[0087] Because strain gauges essentially measure the average CTE of a specific area, they can only accurately screen gradient material components to the smallest strain gauge size (millimeter level). Their measurement results and accuracy fall far short of meeting research and practical needs. This application, however, employs a probe array with adjustable precision. By adjusting the axial displacement of the probe module along the composition gradient, micron-level measurement can be achieved, increasing accuracy by more than ten times. This measurement method offers exceptionally high resolution and efficiency, perfectly replacing traditional strain gauge measurement methods.

[0088] like Figure 8 As shown, the present application conducted a full-area analysis of the composition gradient CTE of Invar-316L. In the study of the correspondence between the element distribution and CTE of Invar alloy, it was found that the thermal expansion coefficient of the gradient alloy showed a nonlinear correspondence with the elements. The high-throughput full-area measurement of the present application can directly screen out the appropriate gradient composition, which can solve the problem of significant thermal stress caused by mismatched thermal expansion coefficients between different components. The high-throughput testing characteristics of the present application greatly improve the efficiency of the gradient composition alloy screening work, and guide the study of the thermal expansion property mechanism in the transition range from zero expansion alloy to high thermal expansion metal.

[0089] Application Example 2

[0090] The interface between dissimilar materials is a two-dimensional spatial region where physical and chemical properties suddenly change. It is also the source of stress and cracking during the service life of components. The interface problem of connecting materials with different thermal expansion is also a difficult and common problem in the current field of materials research. However, the interface area is different from the matrix of the connecting material and has an unknown thermal expansion coefficient. The problem that its area size is often small (micrometer level) and difficult to measure with traditional methods has further hindered the research progress of dissimilar materials in terms of interface failure, stress calculation, software simulation, etc. The high-precision analysis of this application can characterize the CTE of the interface area, improving the situation in which finite element simulation lacks micro-area data verification in previous interface research.

[0091] Compared with existing equipment, the present invention can characterize the thermal expansion behavior of samples such as compositionally gradient materials and composite materials. It is particularly suitable for characterizing the thermal expansion behavior of key components such as aerospace gradient coatings and nuclear reactor cladding materials, providing a reliable testing method for the design optimization of functionally gradient materials.

[0092] Although several embodiments of the present invention have been described herein, those skilled in the art will appreciate that modifications may be made to the embodiments herein without departing from the spirit of the present invention. The above embodiments are merely exemplary and should not be used as limitations on the scope of the present invention.

Claims

1. A thermal expansion measuring device for gradient materials, characterized in that: The device includes an array probe module, a machine vision system, a temperature control system, a driving mechanism, a control module and a housing; The array probe module includes a plurality of probes perpendicular to the sample surface and arranged in parallel with equal intervals, and is used to calibrate the displacement of multiple set points on the sample surface at one time; The array direction of the array probe is perpendicular to the material gradient direction of the sample; The machine vision system is used to capture an image of the top needle tip of the array probe and calculate the actual position and displacement of each probe based on the needle tip image; The driving mechanism is used to drive the array probe module to move in a set manner along the gradient direction of the sample material and to adjust the position and angle of the machine vision system; The temperature control system is used to heat and maintain the sample at a set temperature; The control module is used to control the operation of the machine vision system, temperature control system, and drive mechanism; The array probe module, machine vision system, temperature control system, and driving mechanism are all arranged in the housing.

2. The thermal expansion measuring device for gradient materials according to claim 1, wherein: The array probe module includes a frame, a first clamping strip, a second clamping strip, a calibration block and a plurality of probes; The frame is provided with a first plywood strip and a second plywood strip on the upper and lower sides respectively. The first plywood strip and the second plywood strip are provided with vertical guide channels distributed at equal intervals along the length direction. Probes of the same length are vertically installed in each guide channel to form a probe array. The bottom ends of the probes are in direct contact with the sample surface. The calibration blocks are respectively installed at the top ends of the probe array. The calibration blocks have known dimensions and are used to provide a reference for calculating the position of the probes. The frame is connected to the driving mechanism and moves along the gradient direction of the sample material with the driving mechanism.

3. The thermal expansion measuring device for gradient materials according to claim 2, characterized in that: The probe is made of Invar alloy, the top end is coated with matte alumina and both the top end and the bottom end are hemispherical. The two ends of the probe are provided with radially extending limiting protrusions to prevent the probe from sliding downward from the guide channel along the axial direction. The outer diameter of the limiting protrusion is larger than the inner diameter of the guide channel.

4. The thermal expansion measuring device for gradient materials according to claim 2, wherein: The driving mechanism includes a guide rail, a displacement sensor and a mechanical arm assembly; One end of the mechanical arm assembly is fixed to the housing, and the other end is rigidly connected to the frame to drive the array probe module to move; the displacement sensor is arranged on the frame to record the displacement of the array probe module; The guide rail is used to adjust the position and angle of the machine vision system.

5. The thermal expansion measuring device for gradient materials according to claim 2, wherein: The machine vision system includes a coaxial backlight unit, an image acquisition unit and an image processing unit; The image acquisition unit is a high-resolution CCD camera, whose field of view covers the entire probe tip and the upper portion of the first splint strip; the coaxial backlight unit is arranged opposite to the CCD camera and is used to provide backlight illumination, so that a high contrast is formed between the probe and the background in the captured image; The image processing unit is an image processing system based on a distributed computing framework, equipped with a sub-pixel displacement analysis algorithm based on a convolutional neural network, which is used to perform sub-pixel segmentation and data calculation and statistics tasks of the image to obtain the actual spatial position coordinates of the probe.

6. The thermal expansion measuring device for gradient materials according to claim 1, wherein: The temperature control system includes a multi-layer insulation structure, a magnetic induction coil and a temperature sensor; the multi-layer insulation structure is composed of an innermost ferromagnetic alloy sleeve, an insulation cotton layer located outside the alloy sleeve and an outermost high-temperature cloth layer; the magnetic induction coil is located outside the multi-layer insulation structure; and the temperature sensor is arranged outside the multi-layer insulation structure.

7. The thermal expansion measuring device for gradient materials according to claim 2, characterized in that: The spacing between adjacent guide channels is ≤0.5mm, and the center distance error is ≤±0.05mm; the inner diameter of the guide channel is 0.5-1.5mm, and the number of the probes is 20-50.

8. The thermal expansion measuring device for gradient materials according to claim 1, wherein: An air inlet valve, an air outlet valve, an oxygen sensor and an air pressure sensor are arranged on the shell to form a closed test environment and perform atmosphere adjustment.

9. A method for measuring thermal expansion of gradient materials, characterized in that: The method uses the device according to any one of claims 1 to 8, and the method includes: S1. The sample to be tested is placed in the temperature control system. The drive mechanism adjusts the array probe module to the test starting end X0, so that the bottom of the probe is in close contact with the upper surface of the sample. The coaxial backlight unit and CCD camera are adjusted so that the camera image shows high contrast and clear noise-free between the top of the probe, the calibration block, and the background. The temperature control system adjusts the sample to the initial temperature T0. S2, the driving mechanism drives the array probe module to move from the test starting end X0 to the test ending end X z , each time it moves a specific step length Δm, the dwell time t0, Δm is 0.2-2mm, an image is taken and marked with image number a, a=1, 2, 3, ...; S3, the image processing module divides the calibration block width pixel size, and defines the image coordinate reference point (x a (0),y a (0)); Use the image processing module to segment the probe tip and the background and calibrate the coordinates (x a (i),y a (i)), where i is the number of each probe, i = 1, 2, 3...; S4, the temperature control system heats the sample to the target temperature T k , T k >T0; repeat steps S2 and S3; S5. Based on the results of steps S3 and S4, the thermal expansion coefficient of each measuring point of the sample and the overall thermal expansion distribution diagram are calculated.

10. The method for measuring thermal expansion of gradient materials according to claim 9, wherein: The specific method of step S5 is: S51, calculate the calibration block width pixel size P a Conversion ratio coefficient K between the actual width dimension L a , K a =L / P a , where K a The unit is: micrometer / pixel; S52, calculate the temperature as T k The pixel displacement of the probe tip ΔP a (i), ΔP a (i) = y a (i)(T k )-y a (i)(T0),y a (i)(T k ) is the temperature T k The vertical coordinate of the i-th probe in the a-th image, y a (i)(T0) is the ordinate of the i-th probe in the a-th image at temperature T0; S53, according to the conversion ratio coefficient K a Convert pixel displacement to actual displacement ΔL a (i), ΔL a (i) = K a ×ΔP a (i); S54. Calculate the temperature change ΔT, ΔT = T k -T0; Calculate the local thermal expansion coefficient α of each probe corresponding to the sample position based on the longitudinal initial thickness dimension L0 of the sample measured at the probe position i , α i =ΔL a (i) / (L0×ΔT); S55, according to the probe at T k The known thermal expansion coefficient α under invar Perform thermal compensation calculation, α i '=α i -α invar ; α i ' is the thermal expansion coefficient after compensation.

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