Method for measuring high-strain-rate dynamic hardness of material surface based on AFM knocking

Abstract

A method for measuring high-strain-rate dynamic hardness of a material surface based on AFM knocking belongs to the technical field of solid mechanical property testing and high-speed machining, and comprises the following steps: S1, enabling a material to generate plastic deformation at a high strain rate by an AFM probe; s2, accurately measuring an applied load and a material deformation amount; and S3, performing post-processing analysis to calculate the dynamic hardness of the material. Compared with an existing method for testing the mechanical property of the material under the high strain rate, the method has the advantages that the strain rate of plastic deformation is increased on the basis of ensuring nanoscale deformation of the material, and the dynamic mechanical property response condition of the surface of the material is accurately measured. Therefore, the test method provided by the invention promotes the development of the high-strain-rate mechanical property of the surface of the test material under the nanoscale.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of material surface mechanical property characterization or the field of material surface high-speed machining technology, and particularly relates to a method for measuring high-strain-rate dynamic hardness of a material surface based on AFM knocking. BACKGROUND

[0002] Materials are in a high-strain-rate deformation state under high-speed dynamic load (for example, impact, high-speed machining, etc.), which is different from a traditional quasi-static loading process, and the intrinsic mechanical properties and deformation response of the materials change, especially for strain-rate sensitive materials.

[0003] Conventional macroscopic test methods, such as Hopkinson pressure bar tests and drop hammer impact tests, can provide strain and stress changes under high strain rates (10 3 ~10 4 / s), but these test methods are difficult to measure the high-strain-rate response of nanoscale materials on the basis of considering the microstructure of the materials. Traditional nanoindentation test methods can characterize the mechanical properties of materials at the nanoscale, but due to the limited loading speed, the mechanical properties of materials under high strain rates cannot be characterized. This has seriously restricted the application of cross-scale analysis of material mechanical properties and machining manufacturing. Therefore, it is urgent to invent a method for measuring the mechanical properties of materials at the nanoscale under high strain rates. SUMMARY

[0004] The purpose of the application is to solve the problem of measuring the mechanical properties of materials at the nanoscale under high strain rates, and to provide a method for measuring the high-strain-rate dynamic hardness of materials at the nanoscale based on the dynamic response of AFM microcantilever knocking.

[0005] To achieve the above purpose, the technical solutions adopted by the application are as follows:

[0006] A method for measuring the high-strain-rate dynamic hardness of a material surface based on AFM knocking, the method comprising:

[0007] S1: causing plastic deformation of the material under high strain rate by means of an AFM probe;

[0008] S2: accurately measuring the applied load and the deformation amount of the material;

[0009] S3: post-processing analysis and calculation of the dynamic hardness of the material. The post-processing analysis and calculation of the dynamic hardness of the material are as follows: after the plastic deformation of the material caused by the AFM probe knocking, one is to calculate by the peak force and the normal area, and the other is to calculate by the consumed energy and the deformed volume.

[0010] Further, the step S1 specifically comprises:

[0011] S11: A microcantilever with a diamond indenter is used as the testing tool, and high-frequency vibration is provided by exciting the microcantilever; the measurement method can be used on a commercial AFM or on a self-built AFM system, requiring a stable testing environment and no other special requirements.

[0012] S12: By scanning the ceramic tube to drive the micro cantilever, the diamond indenter is cyclically contacted with the sample surface at high frequency;

[0013] S13: The vibration amplitude is controlled in a closed loop by a sensor (e.g., a photoelectric receiving screen) to cause plastic deformation of the sample material under test;

[0014] S14: To determine the strain rate of material deformation, the vibration amplitude of the microcantilever needs to be provided. A Vibration frequency Ω and material indentation depth h s The strain rate is then calibrated according to the following formula:

[0015]

[0016] The AFM probe induces plastic deformation in the material under high-frequency loading of 5–700 kHz. The deformation strain rate is determined by measuring the loading frequency. Here, the material deformation strain rate should be within 10... 3 ~10 5 The range varies between orders of magnitude of / s.

[0017] S15: The microcantilever is driven by the scanning ceramic tube to detach the diamond indenter from the sample surface, thus completing the test.

[0018] Furthermore, in step S11, the tip radius of the diamond indenter is 10~100 nanometers.

[0019] Furthermore, in step S12, the frequency of the high frequency is 5~700kHz.

[0020] Furthermore, in step S12, the sample includes metals, polymers, semiconductors, optical crystals, and ceramics, etc.

[0021] Further, step S2 specifically includes:

[0022] S21: Measure the peak contact force of the material during plastic deformation or the free amplitude of the free end of the microcantilever using a sensor (e.g., a photoelectric receiving screen);

[0023] S22: Measure the morphology of the plastic deformation region on the sample surface using an atomic force microscope probe, and accurately determine the normal area of ​​the deformation region. A p ) or the volume of material deformation ( V ).

[0024] Furthermore, the applied load is the peak load or the energy consumed by the plastic deformation of the material.

[0025] Furthermore, the amount of material deformation is the normal area of ​​the residual indentation after the material undergoes plastic deformation or the volume of the material deformation.

[0026] Further, step S3 specifically includes:

[0027] S31: Dynamic hardness of the material at high strain rates ( H D There are two calculation methods: one is based on peak force ( P ) and material normal deformation area ( A p Another method is based on the energy dissipation between the diamond indenter and the sample. E ) and material deformation volume ( V The calculation formulas for the two methods are as follows:

[0028]

[0029]

[0030] S32: If the first method is adopted, the calculation and analysis are performed directly using the data measured in S13 and S22;

[0031] S33: If the second method is adopted, the energy dissipation between the diamond indenter and the sample needs to be analyzed based on the excitation conditions.

[0032] Further, step S33 specifically involves: exciting the microcantilever to high-frequency vibration and measuring the amplitude change of the microcantilever; the elastic coefficient of the microcantilever is... k The quality factor is given by the vibration frequency of Ω. The free amplitude is A 0, the vibration amplitude is when close to the sample surface. A The phase difference between the excitation and response of the microcantilever is The energy calculation formula is as follows:

[0033] .

[0034] The advantages of this invention over existing technologies are as follows: The measurement method disclosed in this invention can be implemented on traditional commercial AFM or on non-commercial AFM, requiring a conventional tapping measurement mode. While ensuring nanoscale deformation of the material, it improves the strain rate of plastic deformation and accurately measures the dynamic mechanical property response of the material surface, i.e., dynamic hardness. Attached Figure Description

[0035] Figure 1 is a schematic diagram of measuring the high strain rate mechanical properties of material surface by AFM tapping mode;

[0036] Figure 2 is a three-dimensional topography map of the plastic deformation of material surface measured by scanning detection and a cross-section extraction condition map of material deformation area;

[0037] Figure 3 is a frequency map measured by the contact of AFM cantilever and sample surface.

[0038] Wherein: 1 is a displacement control scanning ceramic tube, 2 is a piezoelectric ceramic, 3 is an AFM probe, 4 is a laser, 5 is a sample, 6 is a photoelectric receiving screen, and 7 is a closed-loop feedback control system. DETAILED DESCRIPTION

[0039] In order to make the person in the art better understand the present application, the technical solutions in the embodiments of the present application will be described clearly and completely in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by the person in the art without creative labor are within the scope of protection of the present application.

[0040] Embodiment 1:

[0041] (1) The AFM probe 3 with a diamond tip (tip radius of 10-100 nanometers) is used as a testing tool, and the piezoelectric ceramic 2 is used to provide high-frequency vibration.

[0042] (2) The displacement control scanning ceramic tube 1 drives the micro-cantilever to make the AFM probe 3 cyclically contact the surface of the sample 5 under high frequency.

[0043] (3) The sensor (for example, the photoelectric receiving screen 6) and the closed-loop feedback control system 7 are used to adjust the constant vibration amplitude, so that the sample material to be tested is plastically deformed.

[0044] (4) The displacement control scanning ceramic tube 1 drives the micro-cantilever to make the AFM probe 3 separate from the surface of the sample 5, and the test is completed.

[0045] (5) The peak contact force or the free amplitude of the free end of the micro-cantilever during the plastic deformation of the material is measured.

[0046] (6) The topography of the plastic deformation area of the sample surface is measured by the AFM probe, and the normal area of the deformation area (A) or the volume of the material deformation (V) is accurately determined, as shown in FIG. A p V Figure 2 .​​

[0047] (7) To determine the strain rate of material deformation, the vibration amplitude of the microcantilever needs to be provided. A ), vibration frequency (Ω) and material indentation depth ( h s The vibration frequency can be used to perform frequency domain analysis on the test signal of the photoelectric receiving screen 6, such as... Figure 3 As shown, the strain rate can be calibrated using the following formula:

[0048]

[0049] When the vibration frequency varies between 5 and 700 kHz, the strain rate of the material deformation is 10. 3 ~10 5 / s.

[0050] (8) Dynamic hardness of the material at high strain rates H D The peak force can be calculated in two ways: one is based on the peak force (…). P ) and material normal deformation area ( A p Another method is based on the energy dissipation between the diamond indenter and the sample. E ) and material deformation volume ( V The calculation formulas for the two methods are as follows:

[0051]

[0052]

[0053] (9) If the first method is adopted, the calculation and analysis are performed directly using the data measured in S13 and S22.

[0054] (10) If the second method is adopted, the energy dissipation between the AFM probe 3 and the sample 5 surface needs to be analyzed according to the excitation situation. Here, an analysis method for the excitation system is given, namely, exciting the microcantilever to vibrate at high frequency and measuring the amplitude change of the microcantilever. The elastic coefficient of the microcantilever is k The quality factor is given by the vibration frequency of Ω. The free amplitude is A 0, the vibration amplitude is 0 when close to the sample surface. A The phase difference between the excitation and response of the microcantilever is The energy calculation formula is as follows:

[0055]

[0056] In summary, the application provides a method for determining the mechanical properties of a material surface under high strain rate, using an AFM probe to control the plastic deformation of the material surface under high frequency loading, and then measuring the contact peak force (or energy dissipation) and the normal deformation area (or deformation volume) respectively, and further determining the dynamic hardness of the material under high strain rate. Compared with the existing method for testing the mechanical properties of a material under high strain rate, the application improves the strain rate of plastic deformation on the basis of ensuring nanoscale deformation of the material, and accurately determines the dynamic mechanical property response of the material surface. Therefore, the test method of the application promotes the development of testing the mechanical properties of a material surface under high strain rate at the nanoscale.

[0057] The above merely describes preferred embodiments of the application and is not intended to limit the application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the application shall be included in the protection scope of the application.

Claims

1. A method for measuring high strain rate dynamic hardness of a material surface based on AFM tapping, characterized by: The method is: S1: plastic deformation of the material under high strain rate by AFM probe; S2: accurate determination of the applied load and the amount of material deformation; S3: post-processing analysis and calculation of the dynamic hardness of the material.

2. The method of claim 1, wherein: The step S1 is specifically: S11: using a micro-cantilever with a diamond indenter as a testing tool, providing high-frequency vibration by exciting the micro-cantilever; S12: driving the micro-cantilever by scanning the ceramic tube to make the diamond indenter cyclically contact the sample surface under high frequency; S13: plastic deformation of the sample material to be tested by closed-loop control of the vibration amplitude through the sensor; S14: The strain rate of the material deformation is determined, requiring the vibration amplitude of the microcantilever, the vibration frequency Ω and the penetration depth of the material A h s The strain rate is then calibrated according to the following formula:​ S15: driving the micro-cantilever by scanning the ceramic tube to make the diamond indenter separate from the sample surface, and completing the test.

3. The method of claim 2, wherein: In step S11, the tip radius of the diamond indenter is 10-100 nanometers.

4. The method of claim 2, wherein: In step S12, the frequency of the high frequency is 5-700 kHz.

5. The method of claim 2, wherein: In step S12, the sample includes metal, polymer, semiconductor, optical crystal and ceramic, etc.

6. The method of claim 1, wherein: The step S2 is specifically: S21: measuring the peak contact force or the free amplitude of the free end of the micro-cantilever during the plastic deformation of the material by a sensor (such as a photoelectric receiving screen); S22: The morphology of the plastic deformation region on the sample surface is measured by an atomic force microscope probe, and the normal area of the deformation region is accurately determined (S22) A p ) or the volume of material deformation ( V ).

7. The method of claim 1, wherein: The applied load is the peak force or the energy consumed by the plastic deformation of the material.

8. The method of claim 1, wherein: The amount of material deformation is the normal area of the residual indentation after the plastic deformation of the material or the volume of the material deformation.

9. The method of claim 1, wherein: The step S3 is specifically: S31: Dynamic hardness of the material at high strain rate H D There are two calculation methods: one is according to the peak force (Fp) P ) and the normal deformation area (A) A p ) of the material, and the other is according to the energy dissipation (W) E ) between the diamond indenter and the sample and the deformation volume (V) V ) of the material, and the calculation formulas of the two methods are as follows: S32: if the first method is used, the data measured by S13 and S22 are directly used for calculation and analysis; S33: if the second method is used, the energy dissipation between the diamond indenter and the sample needs to be analyzed according to the excitation condition.

10. The method of claim 9, wherein: The step S33 is specifically: exciting the micro-cantilever to high-frequency vibration, and measuring the amplitude change of the micro-cantilever; the elastic coefficient of the micro-cantilever is k , the quality factor is , the free amplitude is A , the vibration amplitude is A , and the phase difference between the excitation and the response of the micro-cantilever is The energy calculation formula is as follows: 。

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