Chengli Shi

A novel driving principle by means of the parasitic motion of the microgripper and its preliminary application in the design of the linear actuator.

This paper presents a novel driving principle by means of the parasitic motion of the microgripper. Actuators based on this principle can realize the large displacement range and high speed easily. Also the structure can be simple. A parasitic motion principle linear actuator mainly consisting of two piezoelectric stacks, two microgrippers and a mover was designed. Experimental results indicate that at a low driving frequency of 5 Hz, large velocity over 40 μm/s is obtained with the driving voltage of 100 V. Backward motion was observed and analyzed. Experimental results verify the feasibility of the new principle and it can be used to design new linear or rotary actuators.

Effect of residual chips on the material removal process of the bulk metallic glass studied by in situ scratch testing inside the scanning electron microscope

Research on material removal mechanism is meaningful for precision and ultra-precision manufacturing. In this paper, a novel scratch device was proposed by integrating the parasitic motion principle linear actuator. The device has a compact structure and it can be installed on the stage of the scanning electron microscope (SEM) to carry out in situ scratch testing. Effect of residual chips on the material removal process of the bulk metallic glass (BMG) was studied by in situ scratch testing inside the SEM. The whole removal process of the BMG during the scratch was captured in real time. Formation and growth of lamellar chips on the rake face of the Cube-Corner indenter were observed dynamically. Experimental results indicate that when lots of chips are accumulated on the rake face of the indenter and obstruct forward flow of materials, materials will flow laterally and downward to find new location and direction for formation of new chips. Due to similar material removal processes, in situ scratch testi...

Randomness and Statistical Laws of Indentation-Induced Pop-Out in Single Crystal Silicon

Randomness and discreteness for appearance of pop-out of the single crystal silicon with a (100) orientation were studied by a self-made indentation device. For a given maximum penetration load, the load Ppo for appearance of pop-out fluctuates in a relatively large range, which makes it hard to study the effect of the loading/unloading rate on the load Ppo. Experimental results with different maximum penetration loads indicate that the critical penetration load for appearance of pop-out is in the range of 15 mN~20 mN for the current used single crystal silicon. For a given maximum penetration load, the load Ppo for appearance of pop-out seems random and discrete, but in the point of statistics, it has an obviously increasing trend with increase of the maximum penetration load and also the fraction Ppo/Pmax approximately keeps in the range of 0.2~0.5 for different maximum penetration loads changing from 15 mN to 150 mN.

Molecular Dynamics Simulation of the Crystal Orientation and Temperature Influences in the Hardness on Monocrystalline Silicon

A nanoindentation simulation using molecular dynamic (MD) method was carried out to investigate the hardness behavior of monocrystalline silicon with a spherical diamond indenter. In this study, Tersoff potential was used to model the interaction of silicon atoms in the specimen, and Morse potential was used to model the interaction between silicon atoms in the specimen and carbon atoms in the indenter. Simulation results indicate that the silicon in the indentation zone undergoes phase transformation from diamond cubic structure to body-centred tetragonal and amorphous structure upon loading of the diamond indenter. After the unloading of the indenter, the crystal lattice reconstructs, and the indented surface with a residual dimple forms due to unrecoverable plastic deformation. Comparison of the hardness of three different crystal surfaces of monocrystalline silicon shows that the (0 0 1) surface behaves the hardest, and the (1 1 1) surface behaves the softest. As for the influence of the indentation temperature, simulation results show that the silicon material softens and adhesiveness of silicon increases at higher indentation temperatures.

A study on phase transformation of monocrystalline silicon due to ultra-precision polishing by molecular dynamics simulation

A three-dimensional molecular dynamics (MD) simulation is conducted to investigate the material removal mechanism of monocrystalline silicon by mechanical polishing at atomistic scale with diamond abrasives. By monitoring relative positions of atoms in the monocrystalline silicon specimen, the microstructure transformation of monocrystalline silicon is clearly identified and analyzed. The phase transformation is accomplished under extreme conditions with high temperature and huge hydrostatic pressure, and as a result the silicon microstructure transforms from the four-coordinated diamond cubic structure (Si-I) to the six-coordinated body-centered tetragonal structure (β-silicon). The values of local pressure and temperature are consistent with previous experimental results. In addition, the force between the diamond abrasive and specimen indicates the occurrence of phase transformation in the specimen. The potential energy of each atom is also calculated, which provides us an effective approach to analyze the energy variation of atoms in the mechanism of material deformation and the formation of machined surface after ultra-precision polishing.

Design and Analysis of a Compact Precision Positioning Platform Integrating Strain Gauges and the Piezoactuator

Miniaturization precision positioning platforms are needed for in situ nanomechanical test applications. This paper proposes a compact precision positioning platform integrating strain gauges and the piezoactuator. Effects of geometric parameters of two parallel plates on Von Mises stress distribution as well as static and dynamic characteristics of the platform were studied by the finite element method. Results of the calibration experiment indicate that the strain gauge sensor has good linearity and its sensitivity is about 0.0468 mV/μm. A closed-loop control system was established to solve the problem of nonlinearity of the platform. Experimental results demonstrate that for the displacement control process, both the displacement increasing portion and the decreasing portion have good linearity, verifying that the control system is available. The developed platform has a compact structure but can realize displacement measurement with the embedded strain gauges, which is useful for the closed-loop control and structure miniaturization of piezo devices. It has potential applications in nanoindentation and nanoscratch tests, especially in the field of in situ nanomechanical testing which requires compact structures.

Note: A novel rotary actuator driven by only one piezoelectric actuator

This paper presents a novel piezo-driven rotary actuator based on the parasitic motion principle. Output performances of the rotary actuator were tested and discussed. Experiment results indicate that using only one piezoelectric actuator and simple sawtooth wave control, the rotary actuator reaches the rotation velocity of about 20,097 μrad/s when the driving voltage is 100 V and the driving frequency is 90 Hz. The actuator can rotate stably with the minimum resolution of 0.7 μrad. This paper verifies feasibility of the parasitic motion principle for applications of rotary actuators, providing new design ideas for precision piezoelectric rotary actuators.

Using residual indent morphology to measure the tilt between the triangular pyramid indenter and the sample surface

The tilt between the indenter and the sample surface will affect the measuring results and the accuracy of nanoindentation and scratches. In this paper, the potential factors leading to the tilt are firstly discussed. Then, based on the Cartesian coordinate system at the tip of the triangular pyramid indenter established by Kashani and Madhavan, a theoretical approach is proposed to measure the tilt angle η and the rotation angle ξ of the surface normal using the residual indent morphology. In order to reduce the input parameters for solving the equations and also make the equations dimensionless, two coefficients m and n are defined. One practical application is given to verify the feasibility of the theoretical approach. The theoretical approach is simplified and unified by analyzing the calculation results. The presented theoretical approach can be used to measure the tilt between the indenter and the sample surface indirectly, which is the premise for the adjustment of indentation instruments or the practical correction of the tilt.

A novel two-axis load sensor designed for in situ scratch testing inside scanning electron microscopes.

Because of a lack of available miniaturized multiaxial load sensors to measure the normal load and the lateral load simultaneously, quantitative in situ scratch devices inside scanning electron microscopes and the transmission electron microscopes have barely been developed up to now. A novel two-axis load sensor was designed in this paper. With an I-shaped structure, the sensor has the function of measuring the lateral load and the normal load simultaneously, and at the same time it has compact dimensions. Finite element simulations were carried out to evaluate stiffness and modal characteristics. A decoupling algorithm was proposed to resolve the cross-coupling between the two-axis loads. Natural frequency of the sensor was tested. Linearity and decoupling parameters were obtained from the calibration experiments, which indicate that the sensor has good linearity and the cross-coupling between the two axes is not strong. Via the decoupling algorithm and the corresponding decoupling parameters, simultaneous measurement of the lateral load and the normal load can be realized via the developed two-axis load sensor. Preliminary applications of the load sensor for scratch testing indicate that the load sensor can work well during the scratch testing. Taking advantage of the compact structure, it has the potential ability for applications in quantitative in situ scratch testing inside SEMs.

Influence of friction on the residual morphology, the penetration load and the residual stress distribution of a Zr-based bulk metallic glass

In this paper, friction between the Cube-Corner indenter and the sample surface of a Zr-based bulk metallic glass (BMG) was analyzed and discussed by the experimental method, the theoretical method and the finite element simulation. Linear residua are observed on the surface of the indenter for the first time, which gives the direct evidence that strong interaction processes exist between the indenter surface and the sample surface because of strong friction and local high contact press. A simplified model was developed to correct the penetration load with the consideration of friction. Effects of friction on the penetration load-depth curves, plastic flow, surface deformation and residual stress distribution of the sample with different friction coefficients were investigated by the finite element simulation.