A high strain rate nanoindentation testing device and method

Abstract

The present invention relates to a high strain rate nano-indentation testing device and method, comprising a laser focuser, facing an indentation mechanism, for emitting a short pulse laser beam to the top of the indentation mechanism and inducing an explosive plasma; the indentation mechanism, comprising a guide rod located inside a housing and moving along a vertical axis, the guide rod head end being connected to a pressure head, the guide rod tail end facing the laser focuser, the generated explosive plasma pushing the guide rod and the pressure head, the pressure head pressing against a material to be tested carried on a stage; the stage, located in the space below the pressure head, for carrying the material to be tested, the material to be tested receives the pressure of the pressure head to generate an indentation. The process of the explosive plasma pushing the guide rod and the pressure head to press against the material to be tested can simulate the dynamic response process of the material under the influence of high-speed loading such as explosion, high-speed collision and dynamic fracture, thereby realizing high-speed loading of the material, that is, dynamic performance testing under high strain rate.

Description

Technical Field

[0001] The invention relates to the technical field of material mechanics, and in particular to a high strain rate nanoindentation testing device and method. Background Art

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] Nanoindentation technology is an indentation measurement technology for microscale materials. It obtains the material's load-displacement (Ph) curve by measuring the load on the indenter and the depth of the indentation into the sample surface. Combined with the indentation shape, the material's microhardness, elastic modulus, fracture toughness, creep performance and other parameters are obtained using related functions.

[0004] During nanoindentation measurement, the loading process of the indenter can be regarded as a quasi-static process. Although it can be used to measure the mechanical properties of materials under static or low-speed loading, it is difficult to measure the dynamic properties under high-speed loading, that is, high strain rate. This makes it difficult to use accurate performance parameters when studying the dynamic response of materials under high strain rates such as explosions, high-speed collisions, and dynamic fractures, and thus it is difficult to analyze the dynamic mechanical properties of materials. Summary of the invention

[0005] In order to solve the technical problems existing in the above-mentioned background technology, the present invention provides a high strain rate nanoindentation testing device and method, which utilizes the shock wave pressure of the explosion plasma induced by laser as the indentation load, and presses the indenter into the material to be tested at high speed through a guide rod. The high strain rate plastic deformation of the material to be tested under the action of the indenter is used to measure the hardness, elastic modulus, hardening index, yield strength and other mechanical properties of the material under high strain rate, and has high measurement efficiency and measurement accuracy.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] A first aspect of the present invention provides a high strain rate nanoindentation testing device, comprising:

[0008] A laser focuser is directed toward the indentation mechanism and is used to emit a short pulse laser beam to the top of the indentation mechanism and trigger an explosive plasma;

[0009] The indentation mechanism includes a guide rod located inside the housing and moving along a vertical axis, the front end of the guide rod is connected to the indenter, and the rear end of the guide rod faces the laser focuser. The explosive plasma generated pushes the guide rod and the indenter, and the indenter presses against the material to be tested carried on the stage;

[0010] The stage is located in the space below the indenter and is used to carry the material to be tested. The material to be tested receives the pressure of the indenter to produce an indentation.

[0011] The stage, the indentation mechanism and the laser focuser are all connected to the frame.

[0012] The stage is connected to a clamping device, and the material to be tested is fixed on the upper surface of the stage through the clamping device.

[0013] The laser focuser is connected to the pulse laser through a light guide mechanism, and the pulse laser is connected to the control module.

[0014] The pulse laser is a short pulse YAG laser or a transverse excitation high intensity TEA-CO2 laser.

[0015] The control module is connected to a signal detection unit for detecting and collecting displacement and load signals. The signal detection unit includes a displacement sensor and an acceleration sensor connected to the bottom end of the guide rod. The displacement sensor and the acceleration sensor are connected to the control module through a signal collector.

[0016] A gap is provided on the inner side of the shell, the top of the gap is connected to the gas supply port, the gas supply port is filled with gas to form an air cavity, the outer side of the guide rod is coaxially connected to the guide sleeve, the guide sleeve is coaxially connected to the inner side of the shell and covers the area where the air cavity is located.

[0017] The cross sections of the guide sleeve and the guide rod are both non-circular.

[0018] A reset port is arranged at the bottom of the shell, and the reset port is connected to the space reserved inside the shell, and the guide rod is reset by letting in air.

[0019] The second aspect of the present invention provides a method for implementing an indentation test based on the above device, comprising the following steps:

[0020] The material to be tested is fixed on the stage; gas is introduced through the gas source supply port, and the gas enters the gas cavity to form an air cushion between the guide sleeve and the guide rod;

[0021] The pulse laser emits pulsed laser, which acts on the tail end of the guide rod through the light guide mechanism and the laser focuser to generate explosive plasma. The explosive plasma generates shock wave pressure, which transmits kinetic energy to the indenter through the guide rod, causing the indenter to press down and generate an indentation on the surface of the material to be tested.

[0022] The signal collector synchronously conditions and collects the detected acceleration and displacement output signals, and sends them to the control module to obtain the load-displacement curve;

[0023] The gas guide rod is introduced into the reset port to reset;

[0024] The indentation geometric parameters are obtained, and combined with the load-displacement curve, the dynamic mechanical properties parameters of the material under high strain rate are obtained.

[0025] Compared with the prior art, one or more of the above technical solutions have the following beneficial effects:

[0026] 1. The process in which the explosive plasma pushes the guide rod and the pressure head to press against the material to be tested can simulate the dynamic response process of the material under the influence of high-speed loading such as explosion, high-speed collision and dynamic fracture, thereby realizing high-speed loading of the material, that is, dynamic performance testing under high strain rate.

[0027] 2. The air cushion formed by the air cavity and the guide sleeve on the side of the guide rod is used as a gas lubricant. The cooperation between the guide sleeve and the guide rod can not only ensure the linear motion of the guide rod and the pressure head, but also minimize the loss of kinetic energy caused by friction, and prevent the pressure head from being affected by the lateral load when contacting the material to be measured, thereby ensuring the measurement accuracy.

[0028] 3. The tail end of the guide rod absorbs almost all laser radiation and can generate plasma immediately. It does not require complex pretreatment layers and ablation layers. It can generate kinetic energy to push the guide rod in a very short time. The measurement speed is fast and can meet the requirements of high-throughput experiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0030] Figure 1 is a structural schematic diagram of an indentation testing device provided in Embodiment 1 of the present invention;

[0031] Figure 2 is a structural schematic diagram of an indentation mechanism in an indentation testing device provided in Embodiment 1 of the present invention;

[0032] Figure 3 They are schematic diagrams of the structure of a triangular pyramid Berkovich indenter provided in Example 1 of the present invention;

[0033] In the figure: 1 stage, 2 clamping device, 3 laser focuser, 4 light guide mechanism, 5 pulse laser, 6 control module, 7 signal collector, 8 acceleration sensor, 9 displacement sensor, 10 air valve, 11 pressure head, 12 air cavity, 13 guide sleeve, 14 guide rod, 15 air supply port, 16 reset port. DETAILED DESCRIPTION

[0034] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0035] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0036] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0037] With the application of new materials, the characteristic size of materials is getting smaller and smaller, and the stress conditions are becoming more and more complicated. For samples with a size below 100μm, many traditional mechanical property testing methods, such as hardness measurement or tensile testing, can no longer meet the requirements of material testing, so nanoindentation technology has gradually been applied.

[0038] As described in the background technology, although nanoindentation measurement can be used to measure the mechanical properties of materials under static or low-speed loading, it is difficult to measure the dynamic properties under high-speed loading, that is, high strain rate. This makes it difficult to use accurate performance parameters when studying the dynamic response of materials under high strain rates such as explosions, high-speed collisions, and dynamic fractures, and thus it is difficult to analyze the dynamic mechanical properties of materials.

[0039] Therefore, the following embodiment provides a high strain rate nanoindentation testing device, which uses the laser-induced explosion plasma shock wave pressure as the indentation load, presses the indenter into the material to be tested at high speed through the guide rod, and measures the hardness, elastic modulus, hardening index, yield strength and other mechanical properties of the material under high strain rate through the high strain rate plastic deformation generated by the material to be tested under the action of the indenter, with high measurement efficiency and measurement accuracy.

[0040] Embodiment 1:

[0041] A laser focuser is used to emit a short pulse laser beam, which acts on the tail end of the indenter guide rod and generates explosive plasma. The shock wave pressure generated by the explosive plasma pushes the guide rod and the indenter, causing the indenter to press into the material to be tested within tens of nanoseconds or microseconds, generating an indentation and obtaining a load-displacement curve. The dynamic mechanical properties of the material under high strain rates can be determined through the load-displacement curve and the indentation geometric parameters extracted from the indentation.

[0042] like Figure 1-3 As shown, a high strain rate nanoindentation testing device comprises:

[0043] The laser focuser 3 is directed toward the indentation mechanism and is used to emit a short pulse laser beam to the top of the indentation mechanism and trigger an explosive plasma;

[0044] The indentation mechanism includes a guide rod 14 located inside the housing and moving along a vertical axis, the bottom end of the guide rod 14 is connected to the indenter 11, and the top end of the guide rod 14 faces the laser focuser 3. The generated explosive plasma pushes the guide rod 14 and the indenter 11, and the indenter 11 presses against the material to be tested carried on the stage 1;

[0045] The stage 1 is located in the space below the pressure head 11 and is used to carry the material to be tested. The material to be tested receives the pressure of the pressure head 11 to generate an indentation.

[0046] In this embodiment, the indenter needs to have a high rigidity. Commonly used indenters include spherical indenters, conical indenters, quadrangular pyramid Vickers indenters and triangular pyramid Berkovich indenters. Figure 3 The triangular pyramid Berkovich indenter shown can also be replaced with indenters of other shapes according to needs.

[0047] The stage 1, the indentation mechanism and the laser focuser 3 are all connected to the frame.

[0048] The stage 1 is connected to the clamping device 2 , and the material to be tested is fixed on the upper surface of the stage 1 through the clamping device 2 .

[0049] In this embodiment, the pressing device 2 is not limited to a specific structure, and the stage 1 and the pressing device 2 form a workbench for placing and fixing the material to be tested during the test process.

[0050] The laser focuser 3 is connected to the pulse laser 5 through the light guide mechanism 4 , and the pulse laser 5 is connected to the control module 6 .

[0051] In this embodiment, the pulse laser 5 is preferably a short pulse YAG laser or a transverse excitation high-intensity TEA-CO2 laser. The pulse laser can adjust various process parameters according to the test requirements, such as laser pulse energy, pulse duration, laser spot size and other parameters.

[0052] The control module 6 is connected to a signal detection unit for detecting and collecting displacement and load signals. The signal detection unit includes a displacement sensor 9 and an acceleration sensor 8 connected to the bottom end of the guide rod 14 . The displacement sensor 9 and the acceleration sensor 8 are connected to the control module 6 via a signal collector 7 .

[0053] A gap is provided on the inner side of the shell, the top of the gap is connected to the gas supply port 15, and the gas supply port 15 is filled with gas of a certain pressure to form an air cavity 12. The outer side of the guide rod 14 is coaxially connected to the guide sleeve 13, and the guide sleeve 13 is coaxially connected to the inner side of the shell and covers the area where the air cavity 12 is located.

[0054] In this embodiment, the gas introduced into the gas source supply port 15 is air, which forms an air cushion on the peripheral side of the guide rod 14 through the air cavity 12 and the guide sleeve 13, and acts as a gas lubricant to reduce the friction on the outer side of the guide rod 14 and the resistance to the axial movement of the guide rod 14.

[0055] In this embodiment, the guide sleeve 13 may be made of a porous carbon material, and the guide rod 14 may be made of a high-carbon steel material.

[0056] In this embodiment, the cross-sections of the guide sleeve 13 and the guide rod 14 are both non-circular to prevent the guide rod from rotating. In this embodiment, they are square.

[0057] In this embodiment, the inner wall of the guide sleeve 13 and the outer wall of the guide rod 14 are clearance-matched, and the air cavity 12 also serves as a retaining frame of the guide sleeve 13 for fixing the guide sleeve 13 .

[0058] A reset port 16 is provided at the bottom of the housing. The reset port 16 is connected to a space reserved inside the housing, and air is introduced into the space to move the guide rod 14 upward and reset it.

[0059] In this embodiment, the lower part of the guide rod 14 has a circle of raised flanges, and the area from the raised flange to the top of the guide rod 14 forms a clearance fit with the guide sleeve 13. The bottom end of the raised flange forms a cavity with the outer shell and the pressure head 11, and the cavity is connected to the reset port 16. After air is introduced into the reset port 16, the air pushes the guide rod 14 and drives the pressure head 11 to move upward to achieve reset.

[0060] The above structure uses a laser to emit a short-pulse laser beam. The short-pulse laser beam acts on the tail end (top end) of the indenter guide rod and generates explosive plasma. The shock wave pressure generated by the explosive plasma pushes the guide rod and the indenter, so that the indenter is pressed into the material to be tested in an extremely short time (within tens of nanoseconds or microseconds) to produce an indentation. The dynamic mechanical properties of the material can be determined by the load-displacement curve obtained by the control module and the indentation geometric parameters extracted from the indentation.

[0061] In current nanoindentation tests, it is impossible to perform dynamic performance tests of materials at high strain rates because high-speed loading cannot be achieved. The above structure uses the process of explosive plasma pushing the guide rod and the indenter toward the material to be tested, which can simulate the dynamic response process of the material under the influence of explosion, high-speed collision, dynamic fracture, etc., thereby achieving high-speed loading of the material, that is, dynamic performance testing at high strain rates.

[0062] The above structure can not only realize high-speed loading by utilizing explosive plasma, but also use the air cushion formed by the air cavity and the guide sleeve on the side of the guide rod as a gas lubricant to minimize the friction effect during high-speed movement and reduce the loss of kinetic energy due to friction. Through the cooperation of the guide sleeve and the guide rod, the linear movement of the guide rod and the pressure head is realized, so that the pressure head is not affected by the lateral load when contacting the material to be tested, thereby ensuring the measurement accuracy.

[0063] Whether using YAG laser or TEA-CO2 laser, the tail end of the steel guide rod absorbs almost all laser radiation and can generate plasma immediately. It does not require complex pretreatment layers and ablation layers. It can generate kinetic energy to push the guide rod in a very short time and has a fast measurement speed, which can meet the requirements of high-throughput experiments.

[0064] Embodiment 2:

[0065] The method for implementing the indentation test based on the device of embodiment 1 comprises the following steps:

[0066] The material to be tested is fixed on the stage and fixed by adjusting the clamping force of the clamping device;

[0067] Under the action of the control module, gas is introduced into the gas source supply port, and the gas enters the gas cavity to form an air cushion between the guide sleeve and the guide rod;

[0068] The control module controls the pulse laser to emit pulse laser, and the laser acts on the tail end (top end) of the guide rod through the light guide mechanism and the laser focuser to generate explosive plasma. The explosive plasma generates shock wave pressure, and transmits kinetic energy to the indenter through the guide rod, so that the indenter is pressed down and generates an indentation on the surface of the material to be tested;

[0069] The acceleration sensor detects the acceleration signal of the pressure head, and the displacement sensor detects the downward stroke of the pressure head, which are returned to the control module as feedback signals to control the pulse laser and the guide rod to achieve a closed loop. At the same time, the detected acceleration and displacement output signals are synchronously conditioned and collected by the signal collector, and sent to the computer terminal for processing to obtain the load-displacement curve;

[0070] After the process is completed, gas is introduced into the reset port through the control module to move the guide rod upward and reset. The indentation geometric parameters are obtained with the help of a microscope, and the dynamic mechanical properties of the material are obtained based on the load-displacement curve and the relevant dynamic model.

[0071] The process of explosive plasma pushing the guide rod and the pressure head to press against the material to be tested can simulate the dynamic response process of the material under the influence of explosion, high-speed collision, dynamic fracture, etc., thereby realizing high-speed loading of the material, that is, dynamic performance testing under high strain rate.

[0072] In the process of realizing high-speed loading, the air cushion formed by the air cavity and the guide sleeve on the side of the guide rod is used as a gas lubricant to minimize the friction effect during high-speed movement and reduce the loss of kinetic energy due to friction. The guide sleeve and the guide rod cooperate to realize the linear motion of the guide rod and the pressure head, so that the pressure head is not affected by the lateral load when contacting the material to be tested, thereby ensuring the measurement accuracy.

[0073] Whether using YAG laser or TEA-CO2 laser, the tail end of the steel guide rod absorbs almost all laser radiation and can generate plasma immediately. It does not require complex pretreatment layers and ablation layers. It can generate kinetic energy to push the guide rod in a very short time and has a fast measurement speed, which can meet the requirements of high-throughput experiments.

[0074] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A high strain rate nanoindentation testing device, characterized in that: include: A laser focuser is directed toward the indentation mechanism and is used to emit a short pulse laser beam to the top of the indentation mechanism and trigger an explosive plasma; The indentation mechanism includes a guide rod located inside the housing and moving along a vertical axis, the front end of the guide rod is connected to the indenter, and the rear end of the guide rod faces the laser focuser. The explosive plasma generated pushes the guide rod and the indenter, and the indenter presses against the material to be tested carried on the stage; A gap is provided inside the shell, the top end of the gap is connected to the gas supply port, the gas supply port is filled with gas to form an air cavity, the outer side of the guide rod is coaxially connected to the guide sleeve, the guide sleeve is coaxially connected to the inner side of the shell and covers the area where the air cavity is located; The inner wall of the guide sleeve and the outer wall of the guide rod are in clearance fit, and the air cavity also serves as a retainer of the guide sleeve to fix the guide sleeve; The stage is located in the space below the indenter and is used to carry the material to be tested. The material to be tested receives the pressure of the indenter to produce an indentation.

2. A high strain rate nanoindentation testing device as claimed in claim 1, characterized in that: The object carrier, the indentation mechanism and the laser focuser are all connected to the frame.

3. A high strain rate nanoindentation testing device as claimed in claim 1, characterized in that: The stage is connected to a clamping device, and the material to be tested is fixed on the upper surface of the stage through the clamping device.

4. A high strain rate nanoindentation testing device as claimed in claim 1, characterized in that: The laser focuser is connected to the pulse laser through a light guide mechanism, and the pulse laser is connected to the control module.

5. A high strain rate nanoindentation testing device as claimed in claim 4, characterized in that: The pulse laser is a short pulse YAG laser or a transverse excitation TEA-CO2 laser.

6. A high strain rate nanoindentation testing device as claimed in claim 4, characterized in that: The control module is connected to a signal detection unit for detecting and collecting displacement and load signals. The signal detection unit includes a displacement sensor and an acceleration sensor connected to the bottom end of the guide rod. The displacement sensor and the acceleration sensor are connected to the control module through a signal collector.

7. A high strain rate nanoindentation testing device as claimed in claim 1, characterized in that: The cross sections of the guide sleeve and the guide rod are both non-circular.

8. A high strain rate nanoindentation testing device as claimed in claim 1, characterized in that: A reset port is arranged at the bottom end of the shell, and the reset port is connected to a space reserved inside the shell, and the guide rod is reset by letting in air.

9. A method for implementing an indentation test based on the device according to any one of claims 1 to 8, characterized in that: The following steps are involved: The material to be tested is fixed on the stage; gas is introduced through the gas source supply port, and the gas enters the gas cavity to form an air cushion between the guide sleeve and the guide rod; The pulse laser emits pulsed laser, which acts on the tail end of the guide rod through the light guide mechanism and the laser focuser to generate explosive plasma. The explosive plasma generates shock wave pressure, which transmits kinetic energy to the indenter through the guide rod, causing the indenter to press down and generate an indentation on the surface of the material to be tested. The signal collector synchronously conditions and collects the detected acceleration and displacement output signals, and sends them to the control module to obtain the load-displacement curve; The gas guide rod is introduced into the reset port to reset; The indentation geometric parameters are obtained, and combined with the load-displacement curve, the dynamic mechanical properties parameters of the material under high strain rate are obtained.

Images