Research On Design And Experiments Of Precision In-situ Indentation And Scrach Testing System From Micro-to Nano-scale

With the development of microelectronics,micro-electro-mechanical system and precision optics, Microstructure and nanostructure are widely used in information storage, precision optical lens, IC, composite film and novel semiconductor. It has been encountered a lot of mechanical problems inevitably in the process of using the various types of materials and their products, such as deformation, damage and failure.There has been commercialization of nano-indentation, nano-scratch testing equipments at present which are used to study the micro-mechanical properties of materials and their products. However, there are still some problems to be resolved. The main problem is that the testing datas are dispersed and precision deficiency. Moreover, Existing testing equipments can not be carried out high-resolution in-situ monitoring.So they can not be use to study the correlation law between the deformation, damage status and loading conditions, material properties. To solve the main problems of existing nano-indentation/scratch testing device, this paper put forward a precision in-situ nanoindentation and nanoscrach testing system which carried on driving, loading, testing, micro-mechanical properties of nano-scale testing, ultra-precision scratch-machining and in-situ observation.First, the smart materials used for precision-driven are introduced. Compared to other smart materials,the piezoelectric elements have much more advantages such as small bulk, large generated force, high frequency response and high resolution of displacement. The structure and working principle of piezoelectric stack are analyzed. Besides, the basic characteristics of piezoelectric stack are studied in this paper,such as,capacitance characteristics, response characteristics, output characteristics, hysteresis characteristics. The working principle of VCM(Voice Coil Motor) are analyzed and the mathematical model of a Linear Voice Coil Motor is established. Measurement methods of micro-displacement and micro-load are analyzed.Second,Oliver and Pharr method,classical mechanics method of nano-indentation,is introduced. Many models and laws which describe and explain Indentation Size Effect (ISE) are analyzed,such as, Meyer Equation, Hays-Kendall Equation, Elastic Plastic Deformation( EPD) Model, Proportional Specimen Resistance(PSR) Model,Residual Area Maximum Depth Model,Energy Balance Method, Strain Gradient Plasticity(SGP) Model; Indentation deformation features of classic materials in nanoindentation experiments are discussed.Subsequently, utilizing the piezoelectric straight drive theory, flexible hinge theory, driving technology of VCM and precise detection technique, to design a precision In-situ indentation and scrach testing system from micro- to nano-scale which carried on driving, loading, testing, micro-mechanical properties of nano-scale testing, ultra-precision scratch-machining and in-situ observation.The device consists of precision positioning stage in the X/Y-axis direction, adjusting mechanism in the Z-axis direction, precision driving unit and precision microscopic imaging system which is used to observe and store material deformation and damage status on mechanical testing process. In the testing, specimen is fixed up on precision positioning stage. Adjust precision positioning stage in the X/Y-axis direction to locate the test point's position. The piezoelectric stack in precision driving unit reacts firstly and pushes the indentation unit contact with sample. The imposing load value is measured by precision force sensor and indentation depth is measured by precision displacement sensor.The signals from force sensor and displacement sensor are collected by multi-channel A/D data acquisition card and then transported to computer. Materials'deformation and damage status effected by diamond indenter is dynamic monitored by precision microscopic imaging system and stored by computer. Specimen materials'microhardness and elastic modulus are calculated through corresponding algorithm from the signals. Furthermore, materials'deformation and damage status in different force could be monitored and in-situ testing would be achieved.Driving the precision positioning stage in the X/Y-axis direction when diamond indenter inpress intio the specimen, nano-scratch testing would be achieved.By means of designing and analyzing the each unit of the device,this paper adopts piezoelectric element as kernel driver power source and adopts flexible hinge as precision transmission mechanism to implement precision positioning of loading mechanism.Statics analysis and modal analysis are done to the flexible hinge in software ANSYS. The result shows that the flexible hinge has sufficient strength and strong anti-interference ability. This paper select resistance strain precision force sensor to measure micro-load and select laser displacement sensor based on laser triangulation to measure micro-displacement by means of analyzing detecting demand of load signal and displacement signal.Finally,precision in-situ nanoindentation and nanoscrach testing system has been fabricated.,assembling and debugging of which have been done.The experimental calibration of precision force sensor and precision displacement sensor have been done. The calibration result shows that the force sensor can measure the micro-load and the displacement sensor can measure the micro-displacement in nano-indentation test. The linear correlation of the force sensor's calibration curve is 1 and the linear correlation of the displacement sensor's calibration curve is 0.9999. They both have high linearity and stability. The nanoindentation test for a kind of glass was carried out via the device with the sensors calibrated developed by ourselves, and the relation curves between normal load and penetration depth were obtained. The nanoindentation test result shows that the precision In-situ nanoindentation and nanoscrach testing system has been able to carry out a high accuracy nanoindentation test.