Papers by Author: Tie Lin Shi

Abstract: There are lots of practical problems which are related to the solution of Fredholm integral equations of the second kind. The present work proposes intervallic Coiflets for solving the equations. Illustrative problem involving dynamic stress and electric fields of a cracked piezoelectric excited by anti-plane shear wave is addressed. Permeable boundary condition has been used to obtain a pair of dual integral equations of the symmetric and antisymmetric parts which can be reduced to the solutions of two Fredholm integral equations of the second kind. The dynamic stress intensity factor is expressed in terms of the right-end values of two unknown functions in Fredholm integral equations. The two unknown functions are solved by intervallic Coiflets which have less the endpoints error. And intervallic Coiflets have low calculation cost and high accuracy due to the wavelet expansion coefficients are exactly obtained without calculating the wavelet integrations. The calculation results agree well with the existing method, which show the high accuracy of the estimation and demonstrate validity and applicability of the method.

Abstract: In order to enhance the application of bulk metallic glass (BMG) as engineer material, it is necessary to develop appropriate bonding technology to solve the problems of size limitation and weldability. In this work, a friction welding set-up was constructed, and the Zr₄₁Ti₁₄Cu_12.5Ni₁₀Be_22.5 BMG rods were joined. The joint interface zone was examined by X-ray diffraction, Scanning electron microscope, Vickers Micro-hardness and Transmission electron microscope. The results showed that the BMG rods were successfully joined, where no crystallization and visible defects were observed. The welding joint maintained the amorphous structure except few nanocrystallines occurred. Then the temperature field simulation was executed using ANSYS finite element software to optimize the welding parameters. It indicated that friction time cannot exceed 0.25s under the given experiment conditions, otherwise the crystallization would occurred, which is in good agreement with the experiment. It is concluded that the temperature field simulation can be used to guide the experiment and the friction welding can be used to join the BMG.

Abstract: Flip chip technology is one of the fastest growing segments of microelectronics packaging because of its ability to satisfy the increasing demands of high input/output density, package miniaturization, and reduced cost. A critical element in the successful application of flip chip technology is the reliability of solder bumps. In this paper, a nondestructive inspection method combining ultrasonic excitation with modal analysis is proposed for flip-chip solder bump defect detection. The signal generator and power amplifier are utilized to drive the capacitive air-coupled ultrasonic transducer to produce continuous ultrasonic waves for exciting the test chips. The vibration velocities of the chips are measured by the laser scanning vibrometer to extract the modal shapes and resonance frequencies. The results prove that the defective chips can be distinguished from the good chip by the modal shapes, and the resonance frequencies of the chips decrease with the increase of the open solder bumps. Therefore, this detection method may provide a new path for the improvement and innovation of flip chip on-line inspection systems.

Abstract: When friction pair contact with each other, self-generated voltage is a macroscopic potential difference manifested in the face of friction pair as a result of the interaction of diversified factor. It is consisted of contact potential between two different materials, thermal electromotive force in the friction process between two different materials, potential difference created by charge change in the contact and abruption process of friction pair and potential difference created by material transfer in the friction process. Self-generated voltage is measured in the paper through measuring system, and then the relation between self-generated voltage and frictional characteristic is analyzed. It is concluded useful to study observation and diagnosis of equipment friction with self-generated voltage signal of metal friction pair.

Abstract: Planetary mixers are indispensable to mixing of some cohesive mixture. The change of stream function is related to the shear velocity of the fluid flow of a mixer, and reveals the chaos feature of the mixing system. In this study, with assumptions of fluid being 2-D incompressible cohesive and mixing dynamic system quasi-static, stream function models of a single blade mixer and the twin blade one were presented. Research results show that: comparing with single blade mixer, the twin blade one decreases the area of zero shear velocity, which is good to the mixing process; there are areas of rapid change of stream function in mixing domain of the twin blade mixer, which is quite good to the mixing process and performance.

Abstract: Fluid flowing of mixing is mathematically expressed as mapping. The Smale horseshoe map is a typical model for cohesive mixing, and has a tremendously positive influence on mixing. Based on Smale Horseshoe Mapping Model, a method of defining move parameters of the mixing system of a planetary mixer was presented in this paper. The fluid flowing of the mixing system obtained shows good performance of ergodicity and mixing.

Abstract: Hydraulic drive mixers are widely employed to process the cohesive mixture, especially the dusty and energetic mixture. In this study, the modeling method of the AC frequency control speed regulating system of a planetary mixer was presented. The speed regulating system consists of links of frequency converter(FC), asynchronous motor(AM), and hydraulic circuit(HC). The stability analysis was conducted by applying specification parameters of the FC, AM and HC. Result shows that the speed regulating system is stable by Routh criterion with amplitude margin 21.4db and phase margin 17.9degree.

Abstract: The paper introduces a new approach to detect the fault of bearing based on wavelet grey moment vector and hidden Markov modeling (HMM). Because of non-stationary characteristics of vibration signals of faulty bearings, we propose a new method to extract the wavelet grey moment vectors from these signals. The grey moment vectors are used as feature parameters to train HMMs to establish the database. Fault modes of bearings can be identified by select the HMM with the highest probability. The experimental results show that the proposed approach is effective and accurate to detect the faulty bearing for every single fault.

Abstract: Nano-structures on the wing of Morpho butterflies generate bright blue color, and this color is sensitive to ambient gas, or more specifically, the refractive index of ambient gas. It was found that even slight change of the refractive index can lead to obvious change of the color. Such phenomenon has caught much attention and was employed as a sensing principle for detecting gas. In the present study, a typical nano-structure on the wing of Morpho butterflies is mimicked and simplified for constructing a refractive index based gas sensor. Moreover, partial derivative of the optical reflection efficiency with respect to the refractive index of ambient gas, i.e., sensitivity of the sensor, is utilized based on the rigorous coupled-wave analysis (RCWA) method. Finally, the effects of the nano-structure’s shape on the partial derivative are analyzed. The results can be applied to the design of the bioinspired refractive index based gas sensor.

Abstract: Multiphysics numerical simulation (MPNS) has certainly acquired a wide acceptance in the modeling, designing and fabrication fields and has been validated for various research applications. But it is important that the method should be thoroughly understood by students of the various fields. Keeping this aim in view, we demonstrate here the MPNS process as applied in several fields, such as: electrostatics, mechanics, chemistry, heat transfer and fluid flow. Four tasks are performed for fifteen hours in order to analyze simulation approaches such as modeling with geometrical parameters, meshing, solution and post-processing methods. Convection, buoyancy effects, microfiltration and flow analysis are investigated. This comprehensive study will enhance appreciation of the basic concepts of design and dimensioning of an object in MEMS for engineers, and help to guide workers in these fields when performing these tasks.