Eddy current testing is a widely-used examination of the nondestructive testing method. According to the theory of electromagnetic induction, the coil impendence varies with the interaction between the coil magnetic field and the eddy current magnetic field. By observing the variations of the phase angle and the impendence plane diagram, the influence of different defects and factors are evidently presented. The purpose of this study is to analyze the three-dimensional defects of eddy current testing by means of the finite element method. To begin with, a complete 3-D electromagnetic model in eddy current testing by finite element software package COMSOL Multiphysic was created. Then the impendence plane diagram and evaluation curves are drawn by the mathematics software package MATLAB to show the variations of the impendence and the phase angle. Moreover, the results show the effect of reducing testing errors. The simulation of 3-D defect model can provide more comparable data for experimentalists. So that the problem of inappropriate judgement can be prevented, and then the accuracy in eddy current testing can be enhanced.

Extruded products with precision shape have been used widely to 3C products, electronic equipment, communicatory installation, precision instrument, automobile industry. The tolerance for this kind of asymmetric products with small size is strictly required. During extrusion, the plastic flow of the billet inside the die cavity is complicated. The temperature distribution of the billet, the elastic deformation of the die, and the design of the flow guide affect the final dimension of the product. This paper uses the finite element code ¡§DEFORM 3D¡¨ to simulate the plastic flow of the billet inside the die cavity and the stress, strain, temperature distributions of the die during extrusion of a 3C product, Clip and Housing. From the simulation results, a die design guideline is proposed and the temperature, stress, strain distributions are discussed systematically. Furthermore, extrusion experiments are conducted. From the comparisons of the temperature at the die exit, the product sizes and the extrusion force, the validity of the die design rule is verified.

Magnesium alloy tubes have good formability at elevated temperatures. In this study, a finite element code DEFORM 3D is used to simulate the result of T-shape hydroforming at working temperatures 150¢J and 250¢J with magnesium alloy AZ61 tubes and then conducts the hydroforming experiments. By modifying the loading paths, products with uniform thickness and branch height are obtained 49mm. The results of simulation are compared with the experimental results to verify the validity of this modeling. On the other hand, the effects of the die fillet radius on tube formability during y-shape hydroforming are discussed. With the right die fillet radius r1¡×10mm and the left die fillet radius r2¡×30mm, a better formability of the tube is obtained.

The purpose of this study is to explore the biological effects of ultrasound exposure on growth of Saccharomyces cerevisiae. The result shows the biological effects of ultrasound exposure. The resonance frequencies and a non-resonance frequency were used with different intensities to find the relations between ultrasonic and cell growth. The methods of this study adopted finite element method and Rayleigh-Plesset theory to calculate the resonance frequencies. And then, the study set a diffuse field to exposure the yeast cells. In the experiment, cell growths were analyzed by a 600 nm ultraviolet spectrophotometer measuring the cell mass concentration. The results show that the restrained time under high intensity ultrasonic exposure was longer than low intensity in 0.306 and 11.6625 MHz. However, the restrained effects were the same between high and low irradiation intensity in 2.4079 MHz. By 10 MHz low irradiation intensity, the restrained time was 0.5 hr after sonication. The restrain effects were not obvious under low and high irradiation intensity in 16.124 MHz.

The goal of this thesis is to develop a novel polishing tool system. This system can be attached to a CNC machine and execute a precision polishing job mainly for an axially symmetric free surface. The precision polishing job is to remove the error surface profile on the work to improve its form precision, which was left by the previous machining process. An inferential rule, which was based on a top-down planning strategy, was utilized to gradually decompose the design goals of the tool system to facilitate the process for generating all of the possible design proposals. The major design goal is to render all the rotational axes of the tool system to exactly intersect at the tool center. To analyze the effects of the structure and interface stiffness of tool system on the major goal, the finite element method was adopted. Further, the homogeneous transformation scheme is applied to establish the forward kinematic error of the designed system and to analyze the effect of different manufacturing and assembly errors on the major goal.Accordingly, two novel polishing tool systems were developed. The simulation study indicated that the total errors after assembly at the tool center and the two rotation axes were dominated by the stiffness at the interfaces of the tool system, in addition to the influence of structure stiffness. An assembly strategy was then proposed in the study to reduce the total error.

Ball bonding with gold wire has been the preferred choice to connect semiconductor chip and a lead frame. Recently, copper wires have been increasingly used to replace gold wires because of the rising price of gold. However, copper is harder than gold and has the tendency to induce the damage of bond pad or other underlying layers. Herein, Al pad material has to be changed from bulk to single crystal with (100) surface orientation in order to improve bonding reliability. Firstly, finite element method was adopted to simulate 3D wire bonding. Also, from the impact of gold wire bonding, the stress concentration was found on pad and underlying layers due to the higher elastic modulus of bulk Al. During copper ball impact, there is not only the serious stress concentration at pad, but also a pad splash due to the insufficient strength of bulk Al, even though bulk Al has a lower elastic modulus. Secondly, material properties of Al(100) were obtained by uniaxial tensile tests at constant speed. With molecular dynamics method, the incorporated result showed that Al(100) has the lower elastic modulus and higher yield strength than those of bulk material. Finally, single crystal Al(100) was used, instead of bulk material, to carry out copper ball impact process by using multi-scale simulation. Al(100) material is able to transform impact energy into the resilience of strain energy effectively owing to its high yield stress and low elastic modulus. Results show that the application of Al(100) material reduces the effects of stress concentration and pad ¡§splashing¡¨ successfully during copper ball impact process.

The mechanical and electrical properties of thin films have been become important and urgent in recent years, especially, the laminated structure made by films stacked over hundreds of layers. For example, the Multi-Layered Ceramic Capacitors (MLCCs) are such structures fabricated by one layer ceramic film interleaves with one layer electrode film repeatedly a hundred times. Thus, the advantages of MLCCs include small volume, mass product, and high capacity. That makes the MLCCs the necessary part of passive components. The Finite element method is adopted in the study. The model is built by the simulation program of ANSYS. After meshing and setting boundary conditions, the numerical process is performed. The numerical simulation was started first by applying a uniformly distributed pressure on the top of near hundred layers of MLCCs before sintering process with the bottom plate fixed. Then, the displacement and stress fields of MLCCs under five pressures were obtained and discussed. In order to visualize the results, the data of displacement and the stress fields were listed in Tables and plot in Figures. In addition to the MLCCs under vertically and uniformly distributed pressure, the slightly slant distributed pressure and gradient distributed pressure had been simulated. Next, the results of changing Young¡¦s modulus had also been received. It is found that the vertical distributed pressure and slant distributed pressure were not the main factor led to the side deformation. The lateral constraint of gradient distributed pressure would influence the deformation of the MLCCs significantly.

This study involves analyses and experiments of magnesium¡¦s hot extrusion of thin sheets and tubes. At first, hot compression tests are conducted to obtain the magnesium¡¦s plastic flow stresses in high tempearatures, which will be used in the finite element analysis. In the FE simulations of thin sheet extrusion, the flow pattern of the magnesium billet within the die, the temperature history at die exit and the elastic deformation of the die is analyzed. Sound and good thin sheets are obtained by appropriate die design, initial billet temperature and extrusion velocity¡¦s control. The goal of constant temperature extrusion is expected to achieved by controlling the extrusion velocity which will influences the billet temperature at die exit. In FE simulations of thin tube extrusion, the flow pattern of the magnesium billet within the port-holes, welding chamber and die bearing is analyzed. The elastic deformation of the die is dicussed. Extrusion of sound thin tubes is achieved by appropriate extrusion conditions. Finally, hot extrusion experiments are conducted and the experimental values of the extrusion load and dimensions of the products are compared with the analytical values to verify the validity of the analytical models.

ABSTRACT Eddy Current Test (ET) is one of the widely-used method in the nondestructive testing (NDT). It is used to examine thinner sheet metal. According to the theory of electromagnetic induction, the researcher used a coil to make the surface of the metal pipe bring much eddy current. In addition, he investigated the variations of the coil impendence by the interaction between the coil magnetic field and the eddy current magnetic field. By observing the variations of the phase angle and the impendence plane diagram, the researcher also found factors for different defects. The purpose of this study is to research the influence of the diversity of the geometry when examining metal pipe. According to Eddy Current Test, the magnetic field is a major factor in testing. So the researcher generalized a 3-D electromagnetic model with software and analyzed the results of the magnetic field by the finite element method. By drawing the impendence plane diagram, evaluating curves and by observing the variations of the influence by diversity of the geometry, the researcher found the possibility of preventing the inaccuracy and errors in testing with a 3-D electromagnetic model. Later on, he found some influential factors, confirmed the tendency, and then increased the accuracy in examining thin sheet metal.

The purpose of this research is to provide a systematic design of a reciprocating tubular linear generator, which is suitable for harvesting solar thermal energy and ocean wave energy. For the structure design of this generator, the stator utilizes a slotless structure, while the mover utilizes the quasi-Halbach permanent magnet array. The operational magnetic fields are first estimated by magnetic equivalent circuit analysis, and then confirmed by three-dimensional finite element analysis. Also, parameters of the machine structure are optimized by Taguchi¡¦s method. The stator windings are selected iteratively by operational specifications and constraints. Finally, assessments of the machine operational behaviors are performed to achieve a complete and systematic design.