This article aims to design an innovative polishing method that can do polishing job to a complicated axial symmetric free surface. The main task of the system is to increase the precision of a middle size (diameter range from 50mm to 150mm) free surface with low precision (form error is larger than 10£gm, even reach few hundred £gm. By using the developed polishing system, the precision is expected to reach and order of sub-micron. It is a machining method which able to outcome a precise free surface, and also a high efficient free surface machining method compared to machining technique nowadays. At the beginning of this article, a logical thinking method will be used to set up a number of sub-targets from the task of the article. From those sub-targets, the keys of the polishing method would come out to accomplish the task. They are: 1.The machining tool is deformable and able to match up the shape of the surface of the tool to enlarge the polishing area. This will increase the efficiency of the machining method; 2.The pressure distribution between the tool and work piece is controllable to let the surface area with larger error form has larger machining rate. By accomplish the sub-targets above, a set of form error compensate strategy can be use to remove the error profile of the free surface with high efficiency. To increase the efficiency of the polishing system, the analysis of the force guide by ANSYS (a finite element analysis software) will be done to create a relation between the force applied and the pressure distribution. This will make the pressure distribution construction task easy and the efficiency of polishing will be increased. According to the machining method designed above, a prototype polishing machine will be designed, and a series of experiments will be done on the designed prototype polishing machine to test the workability of the polishing method. The outcome of the experiments shows that the machine not only has good repeatability, but also has a very high machining efficiency. Besides, the machining distribution experiment shows that the machining method has ability to remove the error distribution from the free surface. It means that is able to do precision machining job to the free surface.

Recently, the high-power light-emitting diodes (LEDs) have been used from the traditional indicator purpose to general illumination purpose. The operating environment and requirement has been more severe. The long operating life high efficiency and high reliability are its main feature attracting the lighting community to this technology. The effect of operating temperature on the degradations of high-power blue LEDs is studied in this thesis. The experiment, measurements, and finite element simulations were conducted to investigate the possible causes of LED degradation. The influence of LED material degeneration on the radiometric pattern was analyzed by tracing rays simulation. Different groups of sample LEDs produced by Lumileds, Unity opto technology Co., and Everlight electronics Co. were studied. Different operating ambient temperatures, e.g. 80oC, 100 oC, and 120 oC, were considered in the accelerated aging test. Experimental results indicated that yellowing, carbonization, gel degeneration, lens chapping and deformation were observed during the test. Results also indicated that the operating temperature is the key factor for LED failure mechanism, that is, different operating ambient temperature may lead to different degradation phenomenon. Numerical simulation results shown that the creep caused by high temperature and thermal stress would cause solder takeoff. This takeoff defects were observed in experimental results. Through ray tracing simulation, it is assured that gel degeneration would change the radiometric pattern of the LED significantly.

There are many causes of structural failure. One of the most important factors leading to material failure is residual stress. This stress represents effects left in structures after processing or removal of external loads including changes in shape and crystallite size. In aggregate, residual stress changes the mechanical behaviour of materials. Various measurement techniques encompassing destructive, semi destructive, and non-destructive testing can be used to measure residual stresses. Thin plates are common in engineering applications. This thesis analyzes residual stresses on circular AISI 1020 steel alloy plates after removal of external loads using two-dimensional X-ray diffraction. Two identical thin circular plates are used in this experiment; one of which is statically loaded. The other plate is used as a control specimen. Residual stresses in the plates are measured using two-dimensional X-ray diffraction and the measurements are compared to those obtained using finite element analysis. It was found that experimentally measured residual stress occurred due to manufacture processing. Also, modules A and B showed the external effect of applying not enough to reach the plastic region to deform specimen 2 and obtain residual stress results distribution.

The objective of this research was to better understand how impact angle influences headform dynamic response and brain tissue deformation. A bare headform was impacted using a pneumatic linear impactor at 5.5 m/s. The impacts were directed on the front and side location at angles of 0, 5, 10 and 15° rightward rotations as well as -5, -10 and -15° (leftward) rotations at the side to examine the characteristics of the head and neckform on the results. Peak resultant linear and rotational accelerations from the headform as well as peak maximum principal strain (MPS) and von Mises stress (VMS) estimated from a brain finite element model were used to measure the effect of impact angle. Significant results were dependent upon the impact angle and location as well as the dependent variable used for comparison (p <0.05). Impact angle produced significant differences in rotational acceleration and MPS at both the front and side; however angle only had an effect on VMS and linear acceleration at the front and side locations, respectively. These findings show that the effect of impact angle is asymmetrical and is specific to the dependent variable. This study suggests that varying impact angle alone may not be as influential on headform dynamic response and brain tissue deformation and that the severity of an impact may be more of a function of how both location and angle create high risk conditions.

Background: Osteoarthritis (OA) is a debilitating joint disease marked by cartilage and bone changes. Morphological and mechanical changes to bone, which are thought to increase overall bone stiffness, result in distorted joint mechanics and accelerated cartilage degeneration. Using a parametric finite element (FE) model of the proximal tibia, the primary objective of this study was to determine the relative and combined effects of OA-related osteophyte formation, and morphological and mechanical alterations to subchondral and epiphyseal bone on overall bone stiffness. The secondary objective was to assess how simulated bone changes affect load transmission in the OA joint. Methods: The overall geometry of the model was based on a segmented CT image of a cadaveric proximal tibia used to develop a 2D, symmetric, plane-strain, FE model. Simulated bone changes included osteophyte formation and varied thickness and stiffness (elastic modulus) in subchondral and epiphyseal bone layers. Normal and OA related values for these bone properties were based on the literature. “Effective Stiffness (K)” was defined as the overall stiffness of the proximal tibia, calculated using nodal displacement of the loaded area on the subchondral cortical bone surface and the load magnitude. Findings: Osteophyte formation and thickness or stiffness of the subchondral bone had little effect on overall bone stiffness. Epiphyseal bone stiffness had the most marked effect on overall bone stiffness. Load transmission did not differ between OA and normal bone. Interpretation: Results suggest that epiphyseal (trabecular) bone is a key site of interest in future analyses of OA and normal bone. Results also suggest that observed OA-related alterations in epiphyseal bone may result in OA bone being more flexible than normal bone.

The use of energy methods and variational principles is widespread in many fields of engineering of which structural mechanics and curve and surface design are two prominent examples. In principle many different types of function can be used as possible trial solutions to a given variational problem but where piecewise polynomial behaviour and user controlled cross segment continuity is either required or desirable, B-splines serve as a natural choice. Although there are many examples of the use of B-splines in such situations there is no common thread running through existing formulations that generalises from the one dimensional case through to two and three dimensions. We develop a unified approach to the representation of the minimisation equations for B-spline based functionals in tensor product form and apply these results to solving specific problems in geometric smoothing and finite element analysis using the Rayleigh-Ritz method. We focus on the development of algorithms for the exact computation of the minimisation matrices generated by finding stationary values of functionals involving integrals of squares and products of derivatives, and then use these to seek new variational based solutions to problems in the above fields. By using tensor notation we are able to generalise the methods and the algorithms from curves through to surfaces and volumes. The algorithms developed can be applied to other fields where a variational form of the problem exists and where such tensor product B-spline functions can be specified as potential solutions.

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This thesis presents a numerical model for determining piezoelectric and non-linear elastic properties of piezoelectric composites consisting of nanotubes in a polymer matrix. Finite Element Analysis (FEA), in conjunction with the Embedded Fiber Method (EFM), is used, and variable nanotube geometry, alignment, and waviness are taken into account. First, a random morphology of a user-defined volume fraction of nanotubes is generated, and their properties are incorporated into the polymer matrix using the EFM. Next, the system is solved and the values are post-processed to determine the effective elastic and piezoelectric properties of the composite. Finally, incremental FEA approaches are used for the determination of the non-linear properties of the nanocomposite. Monte Carlo Analysis of five hundred random microstructures is performed to capture the stochastic nature of the fiber generation and to derive statistically reliable results. The models are validated by comparison with theoretical and experimental data reported in recent literature.

The project is a research on liquid methane. It is stored in a standing and static pressure vessel specially calculated for cryogenic purposes. All the simulations have been done using the finite element method.  The  finite  element  method  (FEM)  or  finite  element  analysis  (FEA)  is  a  numerical technique to find approximate solutions for partial differential equations and it is used to simulate the strength of materials. FEM allows the user to visualize the distribution of stresses and displacements. There is a wide range of software to do FEM simulations, the software chosen for the project is Pro/Engineer Wildfire 4.0.  Pro-Engineer  is  a  CAD/CAM/CAE  software  developed  by  Parametric  Technology Corporation (PTC).  It provides solid modeling, assembly modeling and finite element analysis.  The  results  obtained  in  the  mechanical  analysis  executed  with  the  application  Pro-mechanica show that the designed container holds the loads applied and stands stable.  The thermal analysis of the insulation verifies that the amount of heat exchanged with the environment is on acceptable levels. Finally, to protect the integrity of the structure the proper paints have been selected.