A high-precision Brinell hardness measurement method based on digital holographic microscopy

Abstract

The present invention belongs to the technical field of Brinell hardness measurement of materials, and specifically is a high-precision Brinell hardness measurement method based on digital holographic microscopy, which includes recording a hologram of the Brinell hardness indentation of a hardness test block; using a method of adaptively positioning the holographic positive first-order spectrum at the maximum value of the spectrum phase to obtain the positive first-order spectrum region of the hardness test block; using Fresnel diffraction method to numerically reproduce and holographically reconstruct the three-dimensional microscopic morphology of the Brinell hardness indentation of the hardness test block; using super-resolution fuzzy clustering and sub-pixel methods to achieve high-precision extraction and measurement of Brinell hardness indentation morphological features, and obtain the circular diameters of all Brinell hardness indentations in the current field of view; and calculating the Brinell hardness values of all Brinell hardness indentation areas in the current field of view based on the Brinell hardness measurement principle and calculation formula. The method described in the present invention can achieve high-resolution, high-precision holographic microscopic detection of Brinell hardness indentation morphologies in different shapes and surface conditions.

Description

Technical Field

[0001] The present invention belongs to the technical field of Brinell hardness measurement of materials, and in particular relates to a high-precision Brinell hardness measurement method based on digital holographic microscopy. Background Art

[0002] The mechanical properties of materials are crucial for the design, manufacture, operation, and maintenance of large-scale equipment, including aerospace, power equipment, high-speed rail equipment, pressure vessels, weaponry, heavy engineering equipment, advanced ships, and offshore platforms. Determining a material's mechanical properties requires appropriate performance tests, such as tensile strength, compressive strength, deformation resistance, and hardness. Hardness, among other things, is a material's ability to resist elastic deformation, plastic deformation, and failure. It reflects both elastic and plastic deformation. Objectively speaking, hardness is related not only to the material's elastic limit, elastic modulus, yield point, and brittleness, but also to its crystallization state, molecular structure, and interatomic bonding strength. In other words, hardness is a comprehensive indicator reflecting a material's mechanical properties, including elasticity, plasticity, strength, toughness, and wear resistance. Consequently, hardness testing has gained widespread attention and application in fields such as machinery manufacturing, metallurgy, and materials science.

[0003] As one of the earliest hardness measurement methods, Brinell hardness has been widely used for its advantages of high resolution, high reliability and high objectivity in reflecting material properties, and occupies a large proportion in production and research. Figure 1 As shown, a carbide ball of a specific diameter D is pressed into the surface of the specimen, and a load force is applied for a certain period of time. After the load force F is removed, the diameter d of the circular indentation on the surface of the specimen is read through an optical microscope, and finally the Brinell hardness value is determined by using the ratio of the load force to the indentation surface area. Since the load force F and the diameter of the steel ball D are both known parameters, the Brinell hardness measurement problem can be converted into the measurement problem of the indentation circle diameter d. At present, the measurement method of d is mainly to use an optical reading microscope and a microscale for manual measurement, compare the indentation circle with the microscale, read the diameter value twice in the horizontal and vertical directions of an indentation circle, and calculate the average value as the measurement value of d. However, this measurement method faces bottleneck problems such as large measurement error, low measurement efficiency, and poor adaptability, and it is difficult to meet the requirements of modern enterprises for digitalization, automation, and intelligence of material testing.

[0004] Digital holographic microscopy is a three-dimensional, real-time, high-precision measurement technology that combines digital holography and microscopy. Compared to commonly used three-dimensional optical inspection techniques such as laser confocal microscopy, white light interferometry, scanning tunneling microscopy, and atomic force microscopy, digital holographic microscopy offers advantages in microstructure detection, including full-field, non-invasive, high-resolution, real-time, scanning-free operation, and the absence of a conductive sputtering layer on the sample. Currently, digital holographic microscopy has been widely applied in fields such as microstructure measurement, microelectromechanical systems, biological detection and measurement, particle tracking, and radar systems. Therefore, applying digital holographic microscopy to Brinell hardness measurement research is expected to address the aforementioned bottlenecks and limitations of Brinell hardness measurement. Summary of the Invention

[0005] The present invention aims to solve the bottleneck problems of large measurement error, low measurement efficiency and poor adaptability faced by the current Brinell hardness measurement method, and provides a high-precision Brinell hardness measurement method based on digital holographic microscopy.

[0006] The present invention solves the technical problem by adopting a high-precision Brinell hardness measurement method based on digital holographic microscopy, comprising the following steps:

[0007] Step 1: Record the holograms of all Brinell hardness indentations in the current field of view of the hardness test block;

[0008] Step 2: Using the method of adaptively locating the holographic positive first-order spectrum by the maximum value of the spectrum phase, the negative first-order and zero-order spectrum regions of the hardness test block are filtered out to obtain the positive first-order spectrum region of the hardness test block;

[0009] Step 3: Use Fresnel diffraction method to numerically reproduce and holographically reconstruct the three-dimensional micromorphology of all Brinell hardness indentations in the current field of view of the hardness test block;

[0010] Step 4: Use super-resolution fuzzy clustering and sub-pixel methods to achieve high-precision extraction and measurement of Brinell hardness indentation morphological features, and obtain the diameter of all Brinell hardness indentation circles in the current field of view;

[0011] Step 5: Calculate the Brinell hardness value based on the Brinell hardness measurement principle and calculation formula.

[0012] Preferably, in step 1, a measuring device based on digital holographic microscopy is constructed, which includes a frequency-stabilized linearly polarized He-Ne laser, a first 1 / 2 wave plate, a second 1 / 2 wave plate, a polarization beam splitter prism PBS, a beam splitter prism BS and an industrial camera CCD. The output light of the frequency-stabilized linearly polarized He-Ne laser passes through the first 1 / 2 wave plate and is incident on the polarization beam splitter prism PBS. The polarization beam splitter prism PBS splits the laser into two paths. The first path of laser light passes through the first spatial filter BE1, the first lens L1 and the first reflecting mirror M1 in sequence. The second laser beam is incident on the beam splitter prism BS as the reference light R; the second laser beam passes through the second 1 / 2 wave plate, the second spatial filter BE2, the second lens L2 and the second reflector M2 in sequence and then enters the beam splitter prism BS as the object light O. After being emitted from the beam splitter prism BS, the object light O is irradiated on the Brinell hardness indentation of the hardness test block. The reflected light of the hardness test block is reflected back into the beam splitter prism BS. The reflected light and the reference light R are combined by the beam splitter prism BS and interfere on the CCD surface of the industrial camera to form a hologram of the Brinell hardness indentation of the hardness test block.

[0013] Preferably, in step one, a reflective digital holographic optical path is designed based on the constructed measuring device to determine whether the reflective digital holographic optical path meets the holographic recording conditions. If not, the optical path is redesigned. If so, the holograms of all Brinell hardness indentations in the current field of view are recorded.

[0014] Preferably, step 4 also includes iterative multiple measurements to obtain all Brinell hardness indentation circle diameters in the current field of view, and judging whether the measurement error converges. If so, proceed to step 5; otherwise, continue iterative multiple measurements.

[0015] Preferably, in step five, after calculating all the Brinell hardness values in the current field of view, if the current field of view does not measure all areas of the hardness test block, the remaining fields of view can be converted and steps one to five can be repeated for measurement until the Brinell hardness values of all Brinell hardness indentation areas of the hardness test block are obtained.

[0016] The beneficial effects of the present invention are as follows: the present invention adopts digital holographic microscopy technology to achieve high-precision measurement of Brinell hardness, with the characteristics of three-dimensional, full-field, real-time and high precision; compared with traditional Brinell hardness measurement methods, the present invention meets the requirements of modern enterprises for digitalization, automation and intelligence of materials; and achieves high-resolution and high-precision holographic microscopy detection of Brinell hardness indentation morphology under different forms (such as normal morphology, ridge effect, depression effect, etc.) and different surface conditions (such as highlight, smoothness, scratches, roughness, mottled color, texture, etc.); the method of the present invention is feasible in principle, mature in technology, simple in operation, highly automated, and has important engineering application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0018] Figure 1 It is a structural schematic diagram of the Brinell hardness measurement principle described in the background technology of the present invention.

[0019] Figure 2 This is the technical roadmap of the high-precision Brinell hardness measurement method based on digital holographic microscopy of the present invention.

[0020] Figure 3 This is a schematic structural diagram of a measurement device based on digital holographic microscopy according to the present invention.

[0021] Figure 4 This is a flow chart of a high-precision Brinell hardness measurement method based on digital holographic microscopy described in the present invention.

[0022] In the figure: 1- frequency-stabilized linearly polarized He-Ne laser; 2- first 1 / 2 wave plate; 3- second 1 / 2 wave plate; 4- hardness test block; PBS- polarization beam splitter; BE1- first spatial filter; L1- first lens; M1- first reflector; R- reference light; BS- beam splitter; CCD- industrial camera; BE2- second spatial filter; L2- second lens; M2- second reflector; 0- object light. DETAILED DESCRIPTION

[0023] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0024] In the description of the present invention, it should be noted that the terms “first” and “second” are only used for descriptive purposes and should not be understood as indicating or implying relative importance.

[0025] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed, detachable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediate medium; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0026] A high-precision Brinell hardness measurement method based on digital holographic microscopy, such as Figure 2 As shown, the following steps are included:

[0027] Step 1: Record the holograms of all Brinell hardness indentations in the current field of view of the hardness test block 4;

[0028] Step 2: Using the method of adaptively locating the holographic positive first-order spectrum by the maximum value of the spectrum phase, the negative first-order and zero-order spectrum regions of the hardness test block 4 are filtered out to obtain the positive first-order spectrum region of the hardness test block 4;

[0029] Step 3: Use Fresnel diffraction method to numerically reproduce and holographically reconstruct the three-dimensional micromorphology of all Brinell hardness indentations of the hardness test block 4 in the current field of view;

[0030] Step 4: Use super-resolution fuzzy clustering and sub-pixel methods to achieve high-precision extraction and measurement of Brinell hardness indentation morphological features, and obtain the diameter of all Brinell hardness indentation circles in the current field of view;

[0031] Step 5: Calculate the Brinell hardness value based on the Brinell hardness measurement principle and calculation formula.

[0032] Among them, step one is the basis and prerequisite for all subsequent steps; step two is to eliminate the zero-order diffraction image and conjugate image in the reproduction phenomenon of the hardness test block 4 to achieve interference-free reproduction of the object light wave, in preparation for obtaining high-precision Brinell hardness micromorphology; in step three, the three-dimensional micromorphology of the Brinell hardness indentation of the hardness test block 4 is the reproduction phenomenon (intensity and phase) of the hardness test block 4, and the three-dimensional information of the hardness test block 4 is reconstructed; step four is to achieve high-precision measurement of the circular diameter of all Brinell hardness indentations in the current field of view based on the three-dimensional micromorphology obtained in step three; step five is to achieve high-precision measurement of the circular diameter of all Brinell hardness indentations in the current field of view based on the attached Figure 1 The Brinell hardness measurement principle, the Brinell hardness value can be expressed as:

[0033] ,

[0034] Where: HB is the Brinell hardness value (N / mm 2); F is the test load; S is the surface area of the indentation; D is the diameter of the carbide ball; d is the diameter of the indentation circle; h is the depth of the indentation circle; pi is π.

[0035] Furthermore, as a specific implementation of the embodiment of the present invention, in step 1, a measurement device based on digital holographic microscopy is constructed, such as Figure 3 As shown, it includes a frequency-stabilized linearly polarized He-Ne laser 1, a first 1 / 2 wave plate 2, a second 1 / 2 wave plate 3, a polarization beam splitter prism PBS, a beam splitter prism BS and an industrial camera CCD. The output light of the frequency-stabilized linearly polarized He-Ne laser 1 passes through the first 1 / 2 wave plate 2 and is incident on the polarization beam splitter prism PBS. The polarization beam splitter prism PBS splits the laser into two paths. The first path of laser light passes through the first spatial filter BE1, the first lens L1 and the first reflector M1 in sequence and then enters the beam splitter prism BS as the reference light R. The second laser beam passes through the second 1 / 2 wave plate 3, the second spatial filter BE2, the second lens L2 and the second reflector M2 in sequence and is incident on the beam splitter prism BS as the object light O. The object light O is emitted from the beam splitter prism BS and irradiates the Brinell hardness indentation of the hardness test block 4. The reflected light of the hardness test block 4 is reflected back into the beam splitter prism BS. The reflected light and the reference light R are combined by the beam splitter prism BS and interfere on the CCD surface of the industrial camera to form a hologram of all Brinell hardness indentations in the current field of view of the hardness test block 4.

[0036] In the measurement device based on digital holographic microscopy, the function of the frequency-stabilized linearly polarized He-Ne laser 1 is to generate the laser beam necessary for hologram recording; the function of the first 1 / 2 wave plate 2 and the second 1 / 2 wave plate 3 is to adjust the light intensity ratio between the object light O and the reference light R to ensure that the hologram has a high contrast. The function of the polarization beam splitter prism PBS is to split the laser beam emitted by the laser into two beams for subsequent use as the object light O and the reference light R. The function of the first spatial filter BE1 and the second spatial filter BE2 is to expand and collimate the light beam to increase the irradiation range of the parallel light beam. The function of the first lens L1 and the second lens L2 is to collimate the light beam passing through the lens to concentrate the energy in the direction of the light beam. The first reflector M1 and the second reflector M2 are used to adjust the propagation direction of the light. The reference light R serves as a reference. The function of the beam splitter prism BS is to combine the reflected light and the reference light R. The hardness test block 4 can have one or more Brinell indentations. The CCD of the industrial camera is the core optical device for recording holograms. The reflected object light and the reference light are combined to form an interference on the target surface of the industrial camera CCD to record the hologram.

[0037] Further, such as Figure 4As shown in FIG, in step 1, a reflective digital holographic optical path is designed based on the constructed measuring device to determine whether the reflective digital holographic optical path meets the holographic recording conditions. If not, the optical path is redesigned. If so, the holograms of all Brinell hardness indentations in the current field of view are recorded. Figure 3 As shown, in the present invention, the reference light R, the beam splitter prism BS and the industrial camera CCD are located on the same straight line, the object light O is perpendicular to the reference light R, and the object light O, the beam splitter prism BS and the hardness test block 4 are located on the same straight line.

[0038] Further, such as Figure 4 As shown, as a specific implementation method of the embodiment of the present invention, step four also includes iterative multiple measurements to obtain the diameters of all Brinell hardness indentation circles in the current field of view, and judge whether the measurement error converges. If so, go to step five, otherwise continue to iterate multiple measurements.

[0039] Further, such as Figure 4 As shown, in step 5, after all the Brinell hardness values in the current field of view are calculated, if the current field of view does not measure all areas of the hardness test block, the remaining fields of view can be converted and steps 1 to 5 can be repeated to measure until the Brinell hardness values of all Brinell hardness indentation areas of the hardness test block 4 are obtained.

[0040] Finally, a high-precision Brinell hardness measurement method based on digital holographic microscopy is described in detail in the following embodiments. Figure 4 shown.

[0041] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A high-precision Brinell hardness measurement method based on digital holographic microscopy, characterized in that: The following steps are involved: Step 1, record the hologram of all Brinell hardness indentations in the current field of view of the hardness test block (4); Step 2: using the method of adaptively positioning the holographic positive first-order spectrum using the maximum value of the spectrum phase, the negative first-order and zero-order spectrum regions of the hardness test block (4) are filtered out to obtain the positive first-order spectrum region of the hardness test block (4); Step 3: Use Fresnel diffraction method to numerically reproduce and holographically reconstruct the three-dimensional micromorphology of all Brinell hardness indentations in the current field of view of the hardness test block (4); Step 4: Use super-resolution fuzzy clustering and sub-pixel methods to achieve high-precision extraction and measurement of Brinell hardness indentation morphological features, and obtain the diameter of all Brinell hardness indentation circles in the current field of view; Step 5: Calculate the Brinell hardness value based on the Brinell hardness measurement principle and calculation formula.

2. The high-precision Brinell hardness measurement method based on digital holographic microscopy according to claim 1 is characterized in that: In step 1, a measuring device based on digital holographic microscopy is constructed, which includes a frequency-stabilized linearly polarized He-Ne laser (1), a first 1 / 2 wave plate (2), a second 1 / 2 wave plate (3), a polarization beam splitter prism PBS, a beam splitter prism BS and an industrial camera CCD. The output light of the frequency-stabilized linearly polarized He-Ne laser (1) passes through the first 1 / 2 wave plate (2) and is incident on the polarization beam splitter prism PBS. The polarization beam splitter prism PBS splits the laser into two paths. The first path of laser light passes through the first spatial filter BE1, the first lens L1 and the first reflector M1 in sequence and is used as a reference. The test light R is incident on the beam splitter prism BS; the second laser beam passes through the second 1 / 2 wave plate (3), the second spatial filter BE2, the second lens L2 and the second reflector M2 in sequence and then enters the beam splitter prism BS as the object light O. The object light O is emitted from the beam splitter prism BS and irradiates the Brinell hardness indentation of the hardness test block (4). The reflected light of the hardness test block (4) is reflected back to the beam splitter prism BS. The reflected light and the reference light R are combined by the beam splitter prism BS and interfere on the CCD surface of the industrial camera to form a hologram of the Brinell hardness indentation of the hardness test block (4) in the current field of view.

3. The high-precision Brinell hardness measurement method based on digital holographic microscopy according to claim 2 is characterized in that: In step 1, a reflective digital holographic optical path is designed based on the constructed measuring device to determine whether the reflective digital holographic optical path meets the holographic recording conditions. If not, the optical path is redesigned. If so, the holograms of all Brinell hardness indentations in the current field of view are recorded.

4. A high-precision Brinell hardness measurement method based on digital holographic microscopy according to any one of claims 1 to 3, characterized in that: Step 4 also includes iterative multiple measurements to obtain the diameters of all Brinell hardness indentation circles in the current field of view, and to determine whether the measurement error has converged. If so, proceed to step 5; otherwise, continue iterative multiple measurements.

5. The high-precision Brinell hardness measurement method based on digital holographic microscopy according to claim 4 is characterized in that: In step 5, after all Brinell hardness values in the current field of view are calculated, if the current field of view does not measure all areas of the hardness test block (4), the remaining fields of view can be converted and steps 1 to 5 can be repeated to measure until the Brinell hardness values of all Brinell hardness indentation areas of the hardness test block (4) are obtained.

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