Design And Experiment Of Nanoindentation And Scratch Test Device

Miniaturization, integration and precision is the development trend of high-tech products. A variety of micro-devices and micro-nano structure have been widely used in precision optics, semiconductors, thin film technology, integrated circuit and information stored as well as other fields. However, all materials, parts, components and equipments ,large to key components of the space shuttle, aircraft carriers and small to micro/nano electromechanical systems (MEMS / NEMS) and even cells, can not avoid the external load resulting in the deformation, damage, degradation and up to the failure and destruction during their work. In order to ensure their reliability, stability and durability, the research on deformation and damage mechanism of materials under the load must be done. Among the micro/nano mechanical testing methods, nanoindentation and scratch test shows good prospects, and gradually developes into a basic method of micro/nano-mechanical testing. Based on piezoelectric stack and flexible hinge technology as well as precision displacement detection technology, this paper presents a precision nanoindentation and nanoscrach testing device to solve the main problems of existing nano-indentation/scratch test device. The device relates to mechanics, testing technology, piezoelectric, electrical, mechanical and other related knowledge. Integrating displacement amplification platform , flexible hinge amplification device and self-sensing function , the device takes advantages of high accuracy,wide testing range,compact structure and has the function of indentation and scratch testing as well as micro-nanofabrication, such as micro-optical arrays and micro-groove machining.The design of this device provides profitable accumulation and evidence of feasibility for in-situ nanoindentation and scratch testing inside scanning electron microscope and high resolution optical microscope.First, the popular micro-mechanical test methods—bending test, tensile test, torsion test and the indentation and scratch test are introduced and the advantages and disadvantages of each test method are given. There are some shortcomings during the bending test, tensile test, torsion test, such as difficult to make the specimen, difficult to clamp the specimen and so on. So they are not suitable to carry out micro/nano-mechanical testing of materials. Taking many advantages of a wide range of applications, rich content of test, convenience to make the specimen, easy to operate, indentation and scratch test has played an increasing role in precision instruments, microelectronics, information science, metallurgy, manufacturing, MEMS, biomedical engineering, design and manufacture of key parts for automotive and aircraft, and shows a good prospect.Research status of nano-indentation and scratch test device at home and abroad is analyzed in detail. The analysis results show that the abroad has done this work earlier than the domestic, and also has achieved a lot. Up to now, the abroad has appeared some commercial nanoindentation and scratch test devices, while in domestic work about the test device is nearly no done. Although there are commercial nanoindentation and scratch testing instruments in abroad, there is no uniform testing standards and the test data is decentralized. In addition, there are some problems to buy the test device from abroad, such as high price, long time-consuming, key technology embargoed and so on.So, it is of great significance to develop nanoindentation and scratch test device which has independent intellectual property rights.Classical mechanics method of nanoindentation—Oliver and Pharr is introduced in detail. The theoretical method of indentation test is presented and the typical deformation behavior and deformation characteristics of materials are analyzed. Many models or laws which describe and explain indentation size effect are analyzed, mainly consisting of Elastic Plastic Deformation( EPD) Model, Meyer Equation, Hays-Kendall Model, Residual Area Maximum Depth Model, Energy Balance Method, Proportional Specimen Resistance(PSR) Model, Strain Gradient Plasticity(SGP) Mode. These establishes solid the oretical foundations for the design of device and analysis of test results.Then, the two key technologies of nanoindentation and scratch test—precision driven and precision detection are introduced. Materials usually used to drive are analyzed. Compared to other materials, piezoelectric element has the advantages of small size, large generated force and high frequency response, high resolution, and can be used to realize precision driven and positioning. The structure and work principle of piezoelectric stack is presented. Besides, this paper analyzes the basic characteristics of piezoelectric stack, such as, response characteristics, capacitance characteristics, hysteresis characteristics. The flexible hinge technology is introduced and its advantages comparing to conventional transmission are found. Mechanics analysis model of right-hinge is established which provides reference for the design and optimize of flexible hinge. The work principle of laser displacement sensor and capacitive sensor is introduced and the analysis shows that it is feasible to use these two sensors to realize precision detection.Then, main components of the test device mainly including X, Y precision positioning platform, displacement amplification platform and Z axis hinge are designed and analyzed. Static analysis and modal analysis is carried out for these components by finite element analysis software ANSYS10.0.And results of deformation and stress distribution as well as the first three order frequencies and mode shapes are obtained. Through these results intensity and frequency response of these key parts are analyzed and the conclusion is that X, Y precise positioning platform and Z axis hinge have good strength and stability for low frequency work.Also, the Z axis hinge has enough strength and displacement-load conversion capacity, but it is not stability for low frequency work. So measures should be taken to prevent resonance.Z axis coarse adjusting mechanism and auxiliary device for laser displacement sensor are designed which provide convenience for position adjustment of diamond pressure head and sensor head. Finally based on flexible hinge, piezoelectric stack and two displacement sensors, nanoindentation and scratch test device is designed and its CATIA model is also established.Finally, the nanoindentation and scratch test device is processed and assembled. Model of the test system is established and the theory of testing is described. Calibration experiments of laser displacement sensor, capacitive displacement sensor and displacement amplification platform are carried out and the results show that they all have good linearity and their linear correlation coefficients are close to 1 or equal to 1 which indicates that the sensors and the designed platform have good stability. Displacement outputs of X, Y precise positioning platform and Z axis hinge are tested and curves show that the outputs of X, Y precision positioning platform are uniform and stable both in X and Y directions but the stiffness is a little large while not affecting the indentation test. Displacement output of Z axis hinge is so large that can be used to realize coarse adjustment and precision motion by changing the step length of load voltage. Then nanoindentation test of a kind of optics glass material is carried out using designed nanoindentation and scratch test device. The relation curve between normal load and penetration depth is obtained, from which the hardness of the optics glass material is figured out. The indentation morphology is obtained through high resolution optical microscope. The indentation results show that the device presented in this paper can be able to realize high precision indentation test but the testing resolution should be improved and the device also should be calibrated precisely.