"The purpose of this project is to design a non-snagging guardrail post. The procedure will be to first develop a simple finite element (FE) model of a single post, wheel and suspension to explore the snag potential for some existing standard guardrail posts. The next step in the procedure will be to develop appropriate design changes that could prevent wheel snagging and investigate if they do by using a one-post sub-model. An attempt to validate the used material model for wood will also be done by comparison between laboratory tests and finite element simulations."

This paper presents a static analysis of functionally graded single and sandwich beams by using an efficient 7DOFs quasi-3D hybrid type theory. The governing equations are derived by employing the principle of virtual works in a weak form and solved by means of the Finite Element Method (FEM). A C1 cubic Hermite interpolation is used for the vertical deflection variables while C0 linear interpolation is employed for the other kinematics variables. Convergence rates are studied in order to validate the finite element technique. Numerical results of the present formulation are compared with analytical and FEM solutions available in the literature. / Revisión por pares

This thesis investigates the characteristics of static torsional mesh stiffness, load sharing ratio, and transmission errors of gears in mesh with and without a localised tooth crack.Gearing is perhaps one of the most critical components in power transmission systems. The transmission error of gears in mesh is considered to be one of the main causes of gear noise and vibration. Numerous papers have been published on gear transmission error measurement and many investigations have been devoted to gear vibration analysis. There still, however, remains to be developed a general non-linear Finite Element Model capable of predicting the effect of variations of gear torsional mesh stiffness, transmission error, transmitted load and load sharing ratio. The primary purpose of this study was to develop such a model and to study the behaviour of the static torsional mesh stiffness, load sharing ratio, and transmission error over one completed cycle of the tooth mesh.The research outlined in this thesis considers the variations of the whole gear body stiffness arising from the gear body rotation due to tooth bending deflection, shearing displacement, and contact deformation. Many different positions within the meshing cycle were investigated and then compared with the results of a gear mesh having a single cracked tooth.In order to handle contact problems with the finite element method, the stiffness relationship between the two contact areas must be established. Existing Finite Element codes rely on the use of the variational approach to formulate contact problems. This can be achieved by insertion of a contact element placed in between the two contacting areas where contact occurs. For modelling of gear teeth in mesh, the penalty parameter of the contact element is user-defined and it varies through the cyclic mesh. A simple strategy of how to overcome these difficulties is ++ / also presented. Most of the previously published finite element analysis with gears has involved only partial teeth models.In an investigation of gear transmission errors using contact elements, the whole body of the gears in mesh must be modelled, because the penalty parameter of the contact elements must account for the flexibility of the entire body of the gear not just the local stiffness at the contact point.

Many soft food materials, including vegetable shortening, exhibit complex rheological behaviour with properties that resemble those of a solid and a liquid simultaneously. The fundamental parameters used to describe the rheological response of vegetable shortening were obtained from uniaxial compression tests, including monotonic and cyclic compression, as well as creep and stress relaxation tests. The fundamental parameters obtained from the various compression tests were then used in two mechanical models (viscoelastic and elasto-visco-plastic) to predict the compression and conical indentation response of vegetable shortening. The accuracy of the two models was studied with the help of the commercially available finite element analysis software package Abaqus. It was determined that the viscoelastic model was not suitable for the prediction of the rheological response of shortening. On the other hand, the proposed elasto-visco-plastic model predicted with reasonable accuracy the uniaxial compression and indentation experimental response of vegetable shortening. / February 2009

Cell-cell adhesion is important to understanding the mechanics of cell-cell interactions. A recent study of cell adhesion was conducted by others using an Atomic Force Microscopy to measure forces when two cells are brought together and then pulled apart. When the two cells come in contact, the adhesion molecules of one cell bind to molecules of the other cell throughout the contact region. When the two cells are then pulled apart, some of these bonds break off while others lead to the formation of tethers which also eventually also break. These phenomena create a force-time curve, which is difficult to interpret. In order to model this experiment and understand details of the experiments, a series of modules were added to a 2D finite element model used previously to model cells and their mechanical interactions. These new modules were designed to replicate mechanical processes associated with molecular detachments at the cell-cell interface. The enhanced model includes several new types of elements including an InterfaceTruss, which characterizes individual adhesion bonds between two cells. Parametric studies carried out using the new finite element model showed that cytoplasmic viscosity, actin cortex stiffness, and the lifetime of the molecular attachments at the cell-cell interface all affect one or more portions of the force time curve. The model was able to model virtually all of the significant features of the experimental force-time curve, and when suitable parameter values are chosen, the model closely approximates the observed features of the experimental curves. The new finite element model provides an effective tool for investigating features of the cell-cell interface. It also provides a powerful tool for learning about the mechanical properties of the cells and their bonds and tethers and for the design of new cell adhesion experiments.

Cell-cell adhesion is important to understanding the mechanics of cell-cell interactions. A recent study of cell adhesion was conducted by others using an Atomic Force Microscopy to measure forces when two cells are brought together and then pulled apart. When the two cells come in contact, the adhesion molecules of one cell bind to molecules of the other cell throughout the contact region. When the two cells are then pulled apart, some of these bonds break off while others lead to the formation of tethers which also eventually also break. These phenomena create a force-time curve, which is difficult to interpret. In order to model this experiment and understand details of the experiments, a series of modules were added to a 2D finite element model used previously to model cells and their mechanical interactions. These new modules were designed to replicate mechanical processes associated with molecular detachments at the cell-cell interface. The enhanced model includes several new types of elements including an InterfaceTruss, which characterizes individual adhesion bonds between two cells. Parametric studies carried out using the new finite element model showed that cytoplasmic viscosity, actin cortex stiffness, and the lifetime of the molecular attachments at the cell-cell interface all affect one or more portions of the force time curve. The model was able to model virtually all of the significant features of the experimental force-time curve, and when suitable parameter values are chosen, the model closely approximates the observed features of the experimental curves. The new finite element model provides an effective tool for investigating features of the cell-cell interface. It also provides a powerful tool for learning about the mechanical properties of the cells and their bonds and tethers and for the design of new cell adhesion experiments.

Small and efficient energy harvesters, as a renewable power supply, draw lots of attention in last few years. This thesis presents a planar rotary electromagnetic generator with copper coils fabricated by printed circuit board (PCB) as inductance and Nd-Fe-B magnets as magnetic member. Coils are fabricated on PCB, which is presumably cost-effective and promising methods. 28-pole Nd-Fe-B magnets with outer diameter of 50 mm and thickness of 2 mm was sintered and magnetized, which can provide magnetic field of 1.4 Tesla. This harvester consists of planar multilayer with multi-pole coils and multi-pole permanent magnet, and the volume of this harvester is about 50x50x2.5 mm3. Finite element analysis is used to design energy harvesting system, and simulation model of the energy harvester is established. In order to confirm the simulation, experiment data are compared with simulation result. The PCB energy harvester prototype can generate induced voltage 1.11 V and 26.54mW output power at rotary speed of 4,000 rpm, and the efficiency of this energy harvester is 31.5%.

This thesis investigates the stress inside Retroreflective Raised Pavement Markers (RRPMs) under tire-marker impact and laboratory testing scenarios. Many RRPMs have poor durability although they meet certain standards of the existing laboratory tests. It has been suspected that the current testing procedures might not be adequate to decide the field performance of RRPMs. Thus, it is necessary to evaluate the existing laboratory testing procedures and develop additional ones that could simulate the field performance of RRPMs more accurately. The tire-marker impact on rigid and flexible pavement will be investigated to identify the critical locations and magnitudes of stress inside markers during the impact. Various external factors, such as tire loading, tire speed, contact angle and contact location, might have effects on the stress inside markers during the impact and be considered as critical factors when developing a laboratory test. On the other hand, RRPMs have different profiles in terms of height, lens slope, and size etc, which affect the structure and field performance as well. The study explores the stress inside markers during the impact by varying the external factors and marker profile. In addition, the interface forces between RRPMs and pavement surface will be studied. Furthermore, the tire-marker impact simulation on rigid and flexible pavement will be compared so that specific testing procedures can be distinguished based on pavement type. Finally, the existing laboratory tests will be examined and additional tests be recommended based on the tire-marker impact analysis. The researcher found that the critical compressive stress is produced at the top edges of the markers on both types of pavement, while the patterns of critical tensile stress can be different between the two types of pavement. In addition, tire loading and contact location were determined to have effect on the stress inside the markers. Furthermore, different loading rates should be used in laboratory test based on pavement type. Finally, the researcher evaluated four laboratory tests and found that each test has its merit but none of them can test RRPMs comprehensively, so it is recommended that the four tests are used together to test RRPMs.

The ballistic impact of Twaron CT709® plain weave fabrics is studied using an explicit finite element method. Many existing approximations pertaining to woven fabrics cannot adequately represent strain rate-dependent behavior exhibited by the Twaron fabrics. One-dimensional models based on linear viscoelasticity can account for rate dependency but are limited by the simplifying assumptions on the fabric architecture and stress state. In the current study, a three-dimensional fabric model is developed by treating each individual yarn as a continuum. The yarn behavior is phenomenologically described using a three-dimensional linear viscoelastic constitutive relation. A user subroutine VUMAT for ABAQUS/Explicit® is developed to incorporate the constitutive behavior. By using the newly developed viscoelasticity model, a parametric study is carried out to analyze the effects of various parameters on the impact behavior of the Twaron fabrics, which include projectile shape and mass, gripping conditions, inter-yarn friction, and the number of fabric layers. The study leads to the determination of the optimal number of fabric layers and the optimized level of inter-yarn friction that are needed to achieve the maximum energy absorption at specified impact speeds. The present study successfully utilizes the combination of 3D weave architecture and the strain rate dependent material behavior. Majority of the existing work is based either on geometry simplification or assumption of elastic material behavior. Another significant advantage with the present approach is that the mechanical constitutive relation, coded in FORTRAN®, is universal in application. The desired material behavior can be obtained by just varying the material constants in the code. This allows for the extension of this work to any fabric material which exhibits a strain-rate dependent behavior in addition to Twaron®. The results pertaining to optimal number of fabric layers and inter-yarn friction levels can aid in the manufacturing of fabric with regard to the desired level of lubrication/additives to improve the fabric performance under impact.

Aluminum bond pads on semiconductor chips play an important role in IC device reliability and yield. In the paper, the vertical tension loading transferred from the capillary is clarified as the direct driving force for bond pad metal peeling. The crack on the bonding pad is identified as the root cause of the pad peeling. It is simulated by finite element method to find the effect of driving force resulting in the crack during the ultrasonic wire bonding process. It indicated that the horizontal vibration of the capillary controlled by ultrasonic power of the bonding machine was the main factors led to the crack on the bonding pad as well as its propagation into the oxide layers in chip. The degradation of Au wire/Al bond pad has become a major bonding failure problem. It is because that the molding resin with low thermal stability (e.g. bi-phenyl epoxy resin) and the IC devices under high thermal environments were used in packaging process. For the lifetime to bond failure, the bi-phenyl epoxy molding becomes shorter than that for cresol novolac epoxy due to the corrosion reaction of Au-Al intermetallics with bromine (Br) contained in the resin compounds. It was clarified that the reactive intermetallic was Au4Al phase formed in the bond interface. In addition, by utilizing the SEM, AES, EDS and XPS techniques, it could be carried out to reveal and identify defects underneath Al layer, and the contaminated Al bond pads could cause poor intermetallic growths led to the failed or unreliable connections from the chip to the outside world.