Method for testing dynamic mechanical properties of brittle materials using high speed depth of cut

Abstract

This invention discloses a method for testing the dynamic mechanical properties of brittle materials using high-speed variable-depth cutting, relating to the field of dynamic mechanical property testing. It employs a diamond ball-end cutter to perform variable-depth cutting on the surface of the test material, obtaining deformation behavior under different loading conditions. Cutting stress and strain rate are calculated for the plastic region of the cutting area. The stress in the cutting area is dimensionlessly processed under different strain rates, and the relationship curve between dimensionless stress and dimensionless strain rate is fitted to obtain a strain rate-dependent material constitutive model. The cutting area is irradiated using a laser-assisted heating device, with the heating temperature as the cutting variable, to establish a material constitutive model that comprehensively considers the effects of temperature and strain rate. This invention transforms the processing method into a material property testing method, achieving a higher dynamic deformation strain rate than methods such as split Hopkinson bars or tension bars, providing a new solution for dynamic material property testing.

Description

Technical Field

[0001] This invention relates to the field of dynamic mechanical property testing, and more particularly to a method for testing the dynamic mechanical properties of brittle materials using high-speed variable depth cutting. Background Technology

[0002] For most engineering materials, the deformation and failure behavior under dynamic loading conditions differs significantly from their static or quasi-static loading deformation, indicating that the materials exhibit strain rate sensitivity. Effective dynamic mechanical property testing techniques and methods are crucial for accurately obtaining the mechanical response characteristics of materials within different strain rate ranges, and subsequently for establishing material constitutive models and failure models that consider the influence of strain rate.

[0003] Using a universal testing machine for tensile, compression, or bending tests is the most common method for testing the mechanical properties of materials. However, the highest test strain rate of conventional universal testing machines is only on the order of 0.1 / s–1 / s, and the highest test strain rate of high-speed hydraulic servo testing machines is usually less than 200 / s. Mechanical property testing with a higher strain rate range requires specialized equipment, such as split Hopkinson compression bars and split Hopkinson tension bars, which can achieve strain rates of 10... 3 / s-10 4 High strain rate testing in the range of / s.

[0004] The split Hopkinson compression / tension bar is mainly used to test the dynamic deformation behavior of ductile materials. For highly brittle materials, the application and testing accuracy of the split Hopkinson compression / tension bar are poor due to the difficulty in preparing small cylindrical specimens and the narrow plastic deformation range. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this invention is to provide a method for testing the dynamic mechanical properties of brittle materials using high-speed variable depth cutting. Based on commonly used cutting methods, this invention transforms the machining method into a material performance testing method. The resulting dynamic deformation strain rate of the material is higher than that of separate Hopkinson bar or tension bar testing methods, providing a new solution for testing the dynamic properties of materials.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0007] Embodiments of the present invention provide a method for testing the dynamic mechanical properties of brittle materials using high-speed variable depth cutting, comprising:

[0008] A diamond ball-end tool was used to perform variable-depth cutting on the surface of the test material to obtain the deformation behavior under different loading conditions;

[0009] Using the plastic cutting region as the stress analysis region, the cutting stress and cutting strain rate are calculated.

[0010] The stress in the cutting region under different strain rates is made dimensionless, and the relationship curve between the dimensionless stress and the dimensionless strain rate is obtained by fitting, thus obtaining a material constitutive model that depends on the strain rate.

[0011] With a fixed cutting speed, the area to be cut is irradiated using a laser-assisted heating device, and the heating temperature is used as the cutting variable to establish a material constitutive model that comprehensively considers the effects of temperature and strain rate.

[0012] As a further implementation method, the material to be tested is pre-processed, cut into sheet-like test samples, and the surface of the test samples is polished to a mirror finish.

[0013] As a further implementation, the force gauge is fixed to the surface of the worktable, and the test sample is placed on the upper side of the force gauge; the force gauge is used to measure the cutting force component during the variable depth of cut process.

[0014] As a further implementation, the worktable is a high-speed motion worktable, covering a range of 1mm / min-10. 4 The linear motion speed range is mm / min.

[0015] As a further implementation, the cutting stress and strain rate under the lowest cutting speed condition are used as a benchmark, and the machining stress and strain rate under each cutting speed are made dimensionless; the relationship curve between dimensionless stress and dimensionless strain rate is obtained by fitting, and the functional relationship between material deformation stress and strain rate is established.

[0016] As a further implementation, the cutting stress is calculated based on the ratio of the cutting force component to the projected area in the corresponding direction; the cutting strain rate is calculated based on the ratio of the cutting speed to the cutting width.

[0017] As a further implementation method, a linear fitting method is used to obtain the relationship between dimensionless stress and dimensionless strain rate or temperature.

[0018] As a further implementation method, a variable depth cutting machining method is adopted, in which the cutting depth increases linearly from zero.

[0019] As a further implementation, the cutting speed range of the diamond ball end mill is 1 mm / min - 10 mm / min. 4 The cutting speed is mm / min and the maximum cutting depth is less than 5μm.

[0020] As a further implementation method, the plastic domain cutting area is determined based on the fluctuation of the cutting force curve or the morphology of the machined surface.

[0021] The beneficial effects of this invention are as follows:

[0022] (1) This invention uses a diamond ball-end cutter to perform variable depth cutting on the surface of the test material. By controlling the cutting depth range, the plastic domain of brittle materials is processed. By changing the cutting speed, material is removed under different strain rate conditions. The stress distribution law of the processed area under different strain rates is analyzed to obtain the influence law of the loading strain rate on the material flow stress, so as to realize the quantitative testing and characterization of the dynamic mechanical properties of brittle materials. The area to be cut is irradiated by a laser-assisted heating device to realize material removal at different cutting speeds under high temperature conditions, so as to obtain the dynamic mechanical properties of brittle materials under the combined effect of temperature and strain rate. Based on the commonly used cutting processing method, the processing method is transformed into a material performance testing method. The dynamic deformation strain rate of the material achieved is higher than that of the split Hopkinson bar or tension bar test methods, which will provide a new solution for the dynamic performance testing of materials.

[0023] (2) The present invention adopts a variable depth cutting process with the cutting depth increasing linearly from zero to obtain the deformation behavior under different loading conditions. As the cutting depth gradually increases, the material removal method will gradually change from plastic deformation to brittle fracture. In order to avoid problems such as the decrease in cutting force test accuracy and the inability to accurately identify the material deformation area caused by brittle fracture, the plastic domain processing interval will be selected as the object when analyzing the stress in the processing area. Attached Figure Description

[0024] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0025] Figure 1 This is a flowchart of the present invention according to one or more embodiments;

[0026] Figure 2 This is a schematic diagram of a test apparatus according to one or more embodiments of the present invention;

[0027] Figure 3 This is a schematic diagram of the high-speed variable depth cutting principle according to one or more embodiments of the present invention;

[0028] Figure 4 This is a schematic diagram of the contact area between the diamond ball-end tool and the surface being machined according to one or more embodiments of the present invention;

[0029] Figure 5 This is a graph showing the cutting force variation in a high-speed variable-depth cutting experiment of single-crystal silicon according to one or more embodiments of the present invention.

[0030] Figure 6 This is a dimensionless stress-strain rate fitting curve for high-speed variable depth cutting of single-crystal silicon according to one or more embodiments of the present invention.

[0031] Figure 7 This is a dimensionless stress-temperature fitting curve for high-speed variable depth cutting of monocrystalline silicon according to one or more embodiments of the present invention.

[0032] Among them, 1. Tool holder; 2. Diamond ball-end tool; 3. Laser beam heat source; 4. Laser; 5. Test sample; 6. Bolt; 7. Worktable; 8. Force gauge. Detailed Implementation

[0033] Example 1:

[0034] This embodiment provides a method for testing the dynamic mechanical properties of brittle materials using high-speed variable depth cutting. A diamond ball-end cutter 2 is used to perform variable depth cutting on the surface of the material under test to obtain deformation behavior under different loading conditions. The plastic domain cutting area is used as the stress analysis area to calculate cutting stress and cutting strain rate. The stress in the cutting area under different strain rates is dimensionlessly processed, and the relationship curve between dimensionless stress and dimensionless strain rate is obtained by fitting, resulting in a strain rate-dependent material constitutive model. With the cutting speed fixed, the cutting area is irradiated using a laser-assisted heating device, and the heating temperature is used as the cutting variable to establish a material constitutive model that comprehensively considers the effects of temperature and strain rate.

[0035] Specifically, such as Figure 1 As shown, it includes the following steps:

[0036] Step (1): The material to be tested is pre-processed, cut into sheet-shaped test sample 5, and the surface of the test sample 5 is polished to a mirror surface (surface roughness Ra<1nm) to ensure the cutting test accuracy.

[0037] In this embodiment, the test sample 5 is a rectangular sheet structure; it is understood that in other embodiments, the test sample 5 can also be processed into a circular sheet or other thin sheet workpiece sample.

[0038] Step (2): As Figure 2 As shown, the force gauge 8 is fixed to the upper surface of the worktable 7 by bolts 6, and the test sample 5 is placed on the force gauge 8. The force gauge 8 is used to measure the cutting force components during the variable depth of cut process, including the tangential force F. x lateral force F y and normal force F z .

[0039] The force gauge 8 used in this embodiment is a piezoelectric crystal triaxial force gauge with a natural frequency greater than 1000Hz to ensure the accuracy of cutting force testing.

[0040] In this embodiment, the worktable 7 is a high-speed motion worktable, covering a range of 1mm / min-10. 4The linear motion speed range is mm / min, and the motion accuracy needs to reach the nanometer level. Variable cutting depth machining tests can be achieved using a linear motor motion platform or an ultra-precision machine tool.

[0041] Step (3): Use diamond ball end mill 2 to perform high-speed cutting on the test sample 5 at different speeds. Use a variable depth cutting method where the cutting depth increases linearly from zero to obtain the deformation behavior under different loading conditions.

[0042] like Figure 2 As shown, the diamond ball end mill 2 is positioned above the test sample 5 and is used for cutting the test sample 5; the diamond ball end mill 2 is connected to the tool holder 1. The ball end radius of the diamond ball end mill 2 ranges from 1μm to 10μm; the cutting speed ranges from 1mm / min to 10... 4 The maximum cutting depth can be selected from mm / min, and can be determined according to the type of material being tested, generally less than 5μm; the linear variation law of the cutting depth can be selected as 0.1μm / mm-0.5μm / mm (that is, the cutting depth variation of 1mm cutting length can be set to 0.1μm-0.5μm).

[0043] Step (4): Taking the plastic cutting area as the research scope (ensuring that only the material is plastically removed and there is no brittle fracture failure), derive and calculate the values ​​of cutting stress and cutting strain rate based on the measured cutting force and cutting parameters.

[0044] Furthermore, the cutting region in the plastic domain can be determined based on the fluctuation of the cutting force curve or the surface morphology. Regarding cutting force, within the plastic domain, the cutting force steadily increases with the depth of cut, while in the brittle domain, the cutting force fluctuates drastically. As for surface morphology, within the plastic domain, material is removed through plastic deformation, while in the brittle domain, brittle fracture defects such as microcracks and chipping occur.

[0045] The contact area between the diamond ball-end tool 2 and the machined surface is as follows: Figure 4 As shown, the cutting stress can be obtained from the ratio of the cutting force component to the projected area in the corresponding direction, as shown in equations (1) and (2). The normal stress σ can be calculated from these equations. z and tangential stress σ x Cutting strain rate It can be derived from the ratio of cutting speed v to cutting width w, as shown in equation (3).

[0046]

[0047]

[0048]

[0049] Since the cutting tool used in the test is an axisymmetric ball-head shape, the values ​​of transverse force and transverse stress are 0, and are not considered here.

[0050] Step (5): Based on the cutting stress and strain rate under the lowest cutting speed v0 condition used in the test, the machining stress and strain rate under each cutting speed are dimensionless.

[0051] Furthermore, dimensionless processing of machining stress refers to using the machining stress at the lowest cutting speed in the range of cutting speeds as a benchmark, and comparing the machining stress at other cutting speeds with the benchmark value.

[0052] For example, when the cutting speed range used is 1 mm / min-10 4 When the cutting speed is 1 mm / min, the machining stress σ0 at the lowest cutting speed of 1 mm / min is used as the reference. The dimensionless processing of the machining stress σ at other cutting speeds is shown in Equation (4).

[0053]

[0054] Dimensionless treatment of strain rate refers to the material deformation strain rate at the lowest cutting speed within the range of cutting speeds used. Using this as a benchmark, the strain rate at other cutting speeds... Compared with the benchmark value, as shown in Equation (5).

[0055]

[0056] Step (6): Fit the curve of the relationship between dimensionless stress and dimensionless strain rate, and then establish the functional relationship between material deformation stress and strain rate.

[0057] This embodiment uses common linear fitting methods such as the least squares method.

[0058] Step (7): Fix the cutting speed, irradiate the area to be cut with a laser-assisted heating device, and obtain different temperature values ​​by changing the laser energy input.

[0059] Repeat steps (1) to (6), and change the cutting variable from cutting speed to heating temperature to obtain the functional relationship between deformation stress and temperature. Figure 2 As shown, laser 4 emits a laser beam heat source 3, which is tilted to irradiate the cut area of ​​the test sample 5.

[0060] Step (8): Based on the functional relationship between deformation stress, strain force and temperature, establish a material constitutive model that comprehensively considers the effects of temperature and strain rate.

[0061] This embodiment transforms the machining method into a material performance testing method, achieving a higher dynamic deformation strain rate than methods such as split Hopkinson bar or tension bar testing. This provides a new solution for dynamic performance testing of materials. It solves the problem of testing high strain rate dynamic mechanical properties of hard and brittle materials due to the narrow plastic deformation domain. The test sample preparation is simple, the testing process is simple and easy to perform, and the repeatability is high. It can be applied to hard and brittle materials such as semiconductors, ceramics, and diamonds, as well as plastic materials and composite materials.

[0062] Example 2:

[0063] In this embodiment, two diamond ball-end cutters with a ball-end radius of r = 3 μm were used to perform high-speed variable depth cutting on (100) crystal plane single crystal silicon. The variable depth cutting test was carried out on a high-speed motion platform driven by a linear motor, and the cutting speeds used were 1 mm / min, 10 mm / min, 100 mm / min, 1000 mm / min, and 10000 mm / min, respectively. Figure 3 As shown, the cutting depth increases from 0 to a over a cutting distance of l = 10 mm. c =3μm.

[0064] The component forces F in each of the three directions during the cutting process were measured using a triaxial piezoelectric crystal force gauge. x F y and F z ,according to Figure 5 The cutting force curve fluctuations shown reveal that within a cutting distance of less than 1.40 mm, the material is in the plastic processing stage, where the cutting force curve is smooth and increases steadily. When the cutting distance exceeds 1.40 mm, the material undergoes a ductile-brittle transition and is removed due to the proportionality between the cutting depth and the cutting distance. Therefore, a cutting distance of less than 1.40 mm is selected for stress analysis in the deformation region. By calculating the ratio of the cutting force component at different cutting positions to the contact area between the diamond tool and the machined surface, the cutting stress at different positions can be obtained.

[0065] Using the cutting stress and strain rate under the lowest cutting speed condition v0 = 1 mm / min as a benchmark, the machining stress and strain rate at each cutting speed were dimensionlessly processed using equations (4) and (5) in Example 1, and the relationship curve between dimensionless stress and dimensionless strain rate was obtained by fitting, as follows: Figure 6 As shown, the functional relationship between the deformation stress and strain rate of single-crystal silicon, as shown in equations (6) and (7), can then be established.

[0066]

[0067]

[0068] The results show that during high-speed variable-depth cutting of single-crystal silicon, the tangential stress and normal stress are positively correlated with the cutting strain rate, and the positive correlation coefficients between the tangential stress and normal stress and the strain rate are approximately equal.

[0069] Furthermore, the cutting speed was fixed at 1 mm / min, utilizing... Figure 2 The laser-assisted heating device irradiates the (100) crystal plane single-crystal silicon cutting area. By changing the laser energy input, four sets of temperature values ​​(100℃, 200℃, 400℃, and 800℃) are obtained, including five sets of temperature values ​​under room temperature conditions (i.e., 25℃). The cutting variable is transformed from cutting speed to heating temperature, thereby obtaining the corresponding relationship between deformation stress and temperature, as shown in the figure. Figure 7 As shown; the functional relationship is as follows:

[0070]

[0071]

[0072] In equations (8) and (9), T r and T m These represent ambient temperature and the melting point temperature of monocrystalline silicon, respectively.

[0073] Finally, based on the functional relationship between deformation stress, strain force and temperature, a material constitutive model that comprehensively considers the influence of temperature and strain rate is established, as shown in Equations (10) and (11).

[0074]

[0075]

[0076] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for testing the dynamic mechanical properties of brittle materials using high-speed variable depth cutting, characterized in that, include: Fix the force gauge to the upper surface of the workbench and place the test sample on the upper side of the force gauge; A force gauge is used to measure the cutting force components during variable depth of cut. A diamond ball-end tool was used to perform variable-depth cutting on the surface of the test material to obtain the deformation behavior under different loading conditions; Using the plastic cutting region as the stress analysis region, the cutting stress and cutting strain rate are calculated. The stress in the cutting region under different strain rates is dimensionlessly processed, and the relationship curve between dimensionless stress and dimensionless strain rate is obtained by fitting, thus obtaining a material constitutive model that depends on the strain rate. Based on the cutting stress and strain rate under the minimum cutting speed condition, the machining stress and strain rate under each cutting speed are dimensionlessly processed. The relationship curve between dimensionless stress and dimensionless strain rate is obtained by fitting, and the functional relationship between material deformation stress and strain rate is established. With a fixed cutting speed, the area to be cut is irradiated using a laser-assisted heating device, and the heating temperature is used as the cutting variable to establish a material constitutive model that comprehensively considers the effects of temperature and strain rate.

2. The method for testing the dynamic mechanical properties of brittle materials using high-speed variable depth cutting according to claim 1, characterized in that, The material to be tested is pre-processed, cut into sheet-like test samples, and the surface of the test samples is polished to a mirror finish.

3. The method for testing the dynamic mechanical properties of brittle materials using high-speed variable depth cutting according to claim 2, characterized in that, The worktable is a high-speed motion worktable with a coverage of 1 mm / min-10. 4 The linear motion speed range is mm / min.

4. The method for testing the dynamic mechanical properties of brittle materials using high-speed variable depth cutting according to claim 1, characterized in that, The cutting stress is calculated by the ratio of the cutting force component to the projected area in the corresponding direction; the cutting strain rate is calculated by the ratio of the cutting speed to the cutting width.

5. The method for testing the dynamic mechanical properties of brittle materials using high-speed variable depth cutting according to claim 1, characterized in that, The relationship between dimensionless stress and dimensionless strain rate or temperature is obtained by using a linear fitting method.

6. The method for testing the dynamic mechanical properties of brittle materials using high-speed variable depth cutting according to claim 1, characterized in that, A variable depth cutting method is adopted, in which the cutting depth increases linearly from zero.

7. The method for testing the dynamic mechanical properties of brittle materials using high-speed variable depth cutting according to claim 1 or 6, characterized in that, The cutting speed range of diamond ball end mills is 1 mm / min-10 mm / min. 4 The cutting speed is mm / min and the maximum cutting depth is less than 5μm.

8. The method for testing the dynamic mechanical properties of brittle materials using high-speed variable depth cutting according to claim 1, characterized in that, The plastic cutting zone is determined based on the fluctuation of the cutting force curve or the morphology of the machined surface.

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