Eddy current testing is a non-destructive testing method, which is usually used for an examination of thin metal material. It can acquire the coil impedance variety between the eddy current magnetic field and the coil magnetic field by electromagnetic induction. By prognosticating its phase angle, testing can exam the influence of the examination through the impedance plane diagram. However, the eddy current testing is usually influenced by different types of the defects and factors of examination. The purpose of this study is to analyze the examination factors of eddy current testing accuracy by means of the finite element method (FEM). This study is to create two dimensional axial symmetry model of simplification in eddy current testing by finite element software package Femlab. After that, the researcher applied the mathematics software package Matlab to plot the impedance plane diagram and evaluation curve. Furthermore, the researcher analyzed the impedance plane diagram and evaluation curve in different examination factors. After the FEM simulation in different types of the defects and the examination factors, this study can provide many comparable data for experimentalists, to judge the condition of the defects more correctly and to reduce testing errors more effectively in the eddy current testing.

Sutures are the joints between the bones of skull, a tiny amount of movement is permitted at sutures, which contributes to the compliance of skull. Craniosynostosis is a disease in which some or all of the sutures in the skull of an infant close too early, causing problems with normal growth of brain and/or skull. Craniosynostosis can only be cured with operation, but someone has try to use helmet to adjust this condition. This study uses cranial from 2-month-old mice with shadow Moiré to measure its 3-D profile, and use this result to build ANSYS model, and to simulate the condition of Craniosynostosis with ANSYS. The results are then compared with existed symptom of Craniosynostosis.

This dissertation work is focused on the analytical and numerical examination of the mechanical response of polypropylene (PP) under scratch deformation by a semispherical indenter. The finite element (FE) method is employed as the analysis technique and ABAQUS??, a commercial FE package is adopted to perform the analysis. Important physical and computational considerations on the implementation of FE analyses for the scratch problem are reviewed. It is shown through the discussion of the generated results that a good understanding can be gained on how different scratch conditions can affect scratch behavior of PP. A phenomenological deduction of the scratch damage process and mechanisms is also established. Considering the two main damage modes of polymers, shear yielding and crazing, it is shown that the two damage modes not only exist in the scratch deformation, and moreover, that they may compete against each other for dominance. A parametric study is also performed to assess the influence of material and surface properties on scratch response of material. A secondary research effort is also made to investigate the material constitutive modeling of polymers. Focusing on elastomeric or rubbery materials, a new mixed network model between the Gaussian and eight-chain non-Gaussian models is proposed. This mixed model inherently preserves the good predictive power of these two models and yields better predictions over a wider range of deformation than that of the rubber model adopted by ABAQUS??.

This research is concerned with the modeling and failure analysis of closed cell foam with various scales of microstructure that is disordered due to defects. This foam material is used for the forward bipod closeout on the space shuttle external tank. Three dimensional finite element simulations of closed cell foams with various microstructures are performed to study the influence of the geometric character of the microstructure (eg. defect size and distribution) on the stiffness and failure behavior of the foam. First, regularly arrayed cells are modeled for a reference to compare with the disordered microstructure. For studying the effect of cellular microstructure, a discrete model is developed where in every edge and face of each cell are modeled. Two types of defects, point defects (void) and area defects (knot), are indicated from the examination of BX250 and BX265 polyurethane foams. However, this research is focused on the point defect. Analyzing a material with such complex microstructure is especially challenging in terms of computation power as well as required modeling techniques. A finite element model consisting of only beam and shell elements was developed. Certain complications that arise from using beam and shell elements were resolved using novel techniques. Stiffness predictions from the model agreed with data from the literature for a wide range of relative densities. Parametric studies were performed to examine the effect of different properties, such as relative densities and edge fraction, on the effective stiffness, Von Mises stress, and buckling stress. The thickness of the face plays an important role in the behavior of the foam material. Linear buckling and postbuckling analyses were performed to understand the effect of local buckling on the effective properties of the foam and stress concentrations. A distorted multicell model was developed to analyze the effect of point defects on the foam behavior. In particular, two geometric parameters, the defect size and the defect density (or the distance between two defects) were varied to find their effect on the stress concentrations and the effective stiffness of the foam. It is seen that the discrete model that accounts for the foam microstructure reveals much more about the foam behavior than a homogenous model.

Changes in the mechanics of the lens capsule of the eye arising from alterations of its native configuration can lead to undesirable clinical results. One example is the surgical introduction of a hole into the lens capsule and subsequent removal of the cloudy lens during cataract surgery. The adverse effect is secondary cataract on the posterior lens capsule, brought about by a sudden proliferation of lens epithelial cells in the region. Understanding the biomechanics of the anterior lens capsule is necessary in order to model its behavior under various physiological conditions and predict its response to alterations and perturbations such as those during cataract surgery. Such knowledge will help in the improvement of techniques during cataract surgery, and in the design of artificial intraocular lens. In this study we present, for the first time, results that demonstrate that the anterior lens capsule exhibits non-homogeneity and regionally varying anisotropy. We also compute stresses in the lens capsule due to normal loading conditions and procedures such as a capsulorhexis.

Vascular stents are medical devices used to treat stenoses blockages in arteries that restrict blood flow. Most commonly, stents are made out of stainless steel or nitinol, and are delivered to the afflicted sites via catheter-based delivery systems. Usually, stents are balloon-expandable or self-expanding. In order for the treated vessel to remain patent, it is necessary that the stents be oversized to prevent flow-induced or pressureinduced stent migration. Furthermore, stents must be rigid enough to prevent the collapse of the vessel, allowing the free passage of blood. However, it has been observed that the presence of the stent in the artery triggers adverse biological responses such as neointinal hyperplasia, often times culminating in restenosis. Extensive research external to this investigation has elucidated evidence to suggest that the abnormally high stresses imparted to the arterial wall as a result of stenting are an important factor in the treatment and development of cardiovascular diseases. Furthermore, normal physiologic diameter flcutuations between systole and diastole produce beneficial biological responses in the artery wall. The primary purpose of this study was to investigate specific stent design criteria that minimize the stress field in the arterial wall to mitigate the impact of restenosis. Commerically available finite element software was used to design the stents parametrically, and perform the stress analysis on a hyperelastic arterial model, including the effects of contact between the artery and stent. Seven stent geometries were uniquely defined by varying strut-spacing, ring amplitude, and crown radii of curvature. Stent designs with large strut spacing, large ring amplitude and a greater than zero radius of curvature imparted the less severe stress field in the arterial wall as well as maximizing vessel deflection between systole and diastole. In contrast, stents with small strut spacing, small amplitudes and zero radius of curvature at the crowns imparted significantly higher stresses. The small strut spacing and small amplitude created stiffer stents, prventing the artery from experiencing physiologic diameter fluctuations between systole and diastole. Evidence presented herein suggests that strut spacing should be as wide as possible without causing pillowing of the arterial wall into the stent.

The aim of this thesis paper, to create a numerical model to examine the residual stresses induced by orthogonal machining in the finished work piece and the model is validated by comparing with experimental result. The finite element method is used to simulate and analyze the residual stresses induced by a orthogonal metal cutting process. A Dynamics explicit time integration technique with Arbitrary Lagrangian Eulerian (ALE) adaptive meshing Finite Element Method (FEM) is employed to simulate the model. The Johnson-Cook material model is used to describe the work material behaviour and fully coupled thermal-stress analysis are combined to realistically simulate high speed machining with an orthogonal cutting. Finite Element modelling of Residual stresses and resultant surface properties induced by round edge cutting tools is performed as case studies for high speed orthogonal machining of 20NiCrMo5 steel. As a conclusion we can say that results from 2D simulations are very close to the experimental results at the surface level, but there is bit difference when we go down in the material. In 3D simulation, results agree with the experimental values in all levels So we can say that it is possible to model residual stresses, induced by orthogonal machining with accepted amount of accuracy. Keywords Residual stress, FE-modelling, ALE formulation,3D.ABAQUS/CAE / FEM,ALE, ABAQUS

This thesis mainly focuses on sensor nodes design. A small two-axis and three-axis accelerometer using optic fiber with FBG written in the core as sensing element were originally designed due to the advantages of FBG mentioned above. The proposed design has a concentrated mass sitting in the middle of a rigid frame, and a glass fiber with a FBG written in the fiber core as a stiff spring is connected between each side of the frame and the mass. The two accelerometers can decouple the ground motion along different axes, resulting in virtually zero cross-sensitivity, which exceeds currently available seismometers. The accelerometer or seismometer has a working bandwidth below the structure’s natural frequency and linearly responds to ground movement. COMSOL Multiphysics by using Finite Element Method (FEM) was used to analyze and simulate the two devices.

This thesis includes the modification and optimization to an electric field mill based on micromachining technology. The sensor was originally designed to overcome the disadvantages of the conventional macroscopic field mill. Although it achieved all these listed above with a minimum detectable field strength at 42 V/m, some drawbacks are yet to be settled. In order to overcome these drawbacks, modifications are studied and put forward. Metal coating of the sensor surface could lead to a good electrical grounding that addresses the charging problem. Non-resonant working design was established with a shutter displacement around 5μm. Finite element simulations were set up to look into the optimizations of the structure parameters of the sensor, focusing on the shutter and electrodes. Moreover, the fabrication process was also studied with attempts of each step carried out in the NSFL of University of Manitoba.

This thesis includes the modification and optimization to an electric field mill based on micromachining technology. The sensor was originally designed to overcome the disadvantages of the conventional macroscopic field mill. Although it achieved all these listed above with a minimum detectable field strength at 42 V/m, some drawbacks are yet to be settled. In order to overcome these drawbacks, modifications are studied and put forward. Metal coating of the sensor surface could lead to a good electrical grounding that addresses the charging problem. Non-resonant working design was established with a shutter displacement around 5μm. Finite element simulations were set up to look into the optimizations of the structure parameters of the sensor, focusing on the shutter and electrodes. Moreover, the fabrication process was also studied with attempts of each step carried out in the NSFL of University of Manitoba.