Biofidelity of finite element head model (FEHM) includes geometric and material aspects. A FEHM with inhomogeneous material properties was proposed to improve material biofidelity. The proposed FEHM was validated against experimental data and good agreements were observed. The capability of the proposed model in simulating large tissue deformation was also demonstrated. Influences of inhomogeneous material properties on the mechanical responses of head were investigated by comparing with homogeneous material model. The inhomogeneous material properties induce large peak strains in head constituents, which are probably the cause of various brain injuries. Helmets are effective in preventing head injuries. Parametric studies were conducted to investigate how changes in helmet shell stiffness, foam density and pad thickness influence the performance of a helmet in protecting the brain. Results showed that strain energy absorbed by foam component, contact stress on the interfaces and intracranial responses are significantly affected by foam density and pad thickness.

This thesis studies the application of a multi-objective niched Pareto genetic algorithm on the design optimization of an electric field mill sensor. The original sensor requires resonant operation. The objective of the algorithm presented is to optimize the geometry eliminating the need for resonant operation which can be difficult to maintain in the presence of an unpredictable changing environment. The algorithm evaluates each design using finite element simulations. A population of sensor designs is evolved towards an optimal Pareto frontier of solutions. Several candidate solutions are selected that offer superior displacement, frequency, and stress concentrations. These designs were modified for fabrication using the PolyMUMPs abrication process but failed to operate due to the process. In order to fabricate the sensors in-house with a silicon-on-glass process, an anodic bonding apparatus has been designed, built, and tested.

Forging operations are widely used for manufacturing processes. Forging process is done hot, warm or cold. All three temperature ranges have advantages and disadvantages. The aim of this study is to combine the advantages of hot and cold forging in a flange forming process with cylindirical workpieces in a single step. The process idea is the partial heating of the workpiece at locations where large deformations occur and to keep the parts of the workpiece cold at regions where high precision forming is required. Firstly, the process idea has been investigated virtually by the finite element method supplying the theoretical verification of the feasibility of the novel process. By this analysis also the process limits have been estimated. All analysis are based on an elastoplastic large strain material law with thermomechanical coupling. The experimental part of the study served to realize the new process idea and to verify the process window. In the experimental study two different materials, three different part geometries and different initial conditions such as temperature field, lubrication etc. have been investigated. The specifimens are heated by induction.

This thesis focuses on the investigation of behavior of thick and moderately thick laminates under transverse and horizontal loading for different boundary conditions and configurations. An efficient finite element solution is proposed for analyzing composite laminates. Based on a combination of composite theory and 3-D Elasticity Theory, a 3-D finite element program is developed in MATLAB for calculating the stresses, strains and deformations of composite laminates under transverse and/or horizontal loading for different boundary conditions. The applicability of the formulation to analysis of laminated rubber bearings is also examined in this study. Since it is very important to calculate the correct stress state when developing models for composite behavior, the 3-D Elasticity Theory is used in this research. Numerical results are presented for various problems with different lamination schemes, loading and boundary conditions. In order to verify the analysis and the numerical calculations, numerical solutions obtained in this study are compared with available closed form solutions in the literature, experiment results and a commercial finite element program, namely ANSYS. The results obtained using the present finite element is found to be in acceptable and good agreement with the closed form solutions in the literature for thick and moderately thick rectangular and square plates.

Bolts and rivets are produced by cold forging technique. A great majority of metal forming companies prefer to use their dexterity rather than science and technology. The main aim of this thesis is to establish an environment for developing technology in bolt production by reducing trial and error. In this thesis finite element method is utilized to model bolt forming for correcting tooling designs, removing production defects and estimating forging forces. Material characterization, precise determination of boundary conditions and verification of numerical results are also investigated. It is shown how efficient the finite element method is for technology development in metal forming industry. Furthermore, two anomalies in extrusion process are presented: The hump and the force hill in extrusion force-displacement curve. Reasons of these two anomalies are studied using finite element simulations and verified by experiments. Thesis also explains reduction methods of three-dimensional problems to axisymmetric models and compares the results.

This thesis is for the investigation of the design and analysis processes of filament wound composite tubes under combined loading. The problem is studied by using a computational tool based on the Finite Element Method (FEM). Filament wound tubes are modeled as multi layered orthotropic tubes. Several analyses are performed on layered orthotropic tubes by using FEM. Results of the FEM are examined in order to investigate characteristics of filament wound tubes under different combined loading conditions. Winding angle, level of orthotropy and various ratios of the loading conditions were the main concerns of the study. The results of the FEM analysis are discussed for each loading condition. Both pure loading and combined loading analysis results were consistent with the ones mentioned in literature, such as optimum winding angles, optimum loading ratios and optimum level of orthotropy. Modeling parameters, assumptions and source of errors are also discussed. Finally, the required data is obtained for the design of filament wound composite tubes under combined loading.

Friction is one of the important parameters in metal forming processes since it affects metal flow in the die, forming load, strain distribution, tool and die life, surface quality of the product etc. The range of coefficient of friction in different metal forming applications is not well known and the factors affecting variation are ambiguous. Commercially available FEA packages input the coefficient of friction as constant among the whole process which is not a realistic approach. In this study, utility of user-subroutines is integrated into MSC SuperForm v.2004 and MSC Marc v.2003 FEA packages, to apply a variable coefficient of friction depending on the contact interface conditions. Instead of using comparatively simple friction models such as Coulomb, Shear (constant) models, friction models proposed by Wanheim-Bay and Levanov were used to simulate some cold forging operations. The FEA results are compared with the experimental results available in literature for cylinder upsetting. Results show that, large variation on the coefficient of friction is possible depending on the friction model used, the part geometry and the ratio of contact normal pressure to equivalent yield stress. For the ratio of contact normal pressure to equivalent yield stress values above 4, coefficient of friction values are approximately same for both friction models.

As metals have high formability at elevated temperatures, hot forming is preferred and widely used in manufacturing of complicated geometries. The term hot forming is usually used if the whole workpiece is processed at elevated temperatures. However, for certain products high formability is required only locally. Forming by local heating is proposed to provide ease of manufacturing of local forms on the workpiece. Also, tools can be simplified by this method. In this study, local laser heating procedures are applied to obtain local forms on cylindrical bulk metal products in a single step. Locally heated workpieces are formed between two flat dies. Both solid and hollow products have been investigated experimentally and by finite element modeling. The experimental studies and finite element analyses are done simultaneously in order to obtain optimum local deformation characteristics. Three different materials together with different initial geometries and various local laser-heating procedures are applied to search for the process window. The limits of applicability are determined and examples of application are supplied.

The aim of this study is to design a computer interface, which links the user to commercial Finite Element Analysis (FEA) program, MSC.Marc-Mentat to make automatic FE analysis of an excavator boom by using DELPHI as platform. Parametrization of boom geometry is done to add some flexibility to interface called OPTIBOOM. Parametric FE analysis of a boom shortens the design stages and helps to find the optimum design in terms of stresses and mass.

Roll-forging is a metal forming process and mainly used for preform forging of long parts prior to press or hammer forging in the industry. Variable cross sections through the length of billet can be obtained by roll-forging to acquire an adequate distribution of material to the next forging stages. In the design of process and dies used in roll-forging, there are some empirical techniques in literature. However these techniques only provide approximate reduction ratio and elongation during the process and the geometry of the workpiece at the end of each stage cannot be determined exactly by using these techniques. In this study, multistage roll-forging process has been analyzed by using a finite element analysis software to examine material flow, temperature, stress and strain distribution at each roll-forging step. The geometries at the intermediate stages have been determined. Computer results have been compared to experimental results and good agreement has been observed.