The problem of damage accumulation in laminated composite materials hasreceived much attention due to their widespread application in the aerospace, automotive,civil, and sports industries. In the aerospace industry, composites are usedto make light weight and efficient structural components. In the Boeing 787, forexample, more than 50% of the structure is made of composite materials. Althoughthere have been significant developments in analyzing cross-ply laminates, none ofthe present approaches provides reasonable predictions for multidirectional laminatesin which intralaminar cracks may form in multiple orientations. Nevertheless, theprediction of damage accumulation and its effect on structural performance is a verydifficult problem due to complexity of the cracking processes.This study presents a synergistic damage mechanics (SDM) methodology to analyzedamage behavior in multidirectional composite laminates with intralaminarcracks in plies of multiple orientations. SDM combines the strengths of micro-damagemechanics (MDM) and continuum damage mechanics (CDM) in predicting the stiffness degradation due to these cracks. The micromechanics is performed on a representativeunit cell using a three-dimensional finite element analysis to calculate thecrack opening displacement accounting for the influence of the surrounding plies, theso-called constraint effect. This information is then incorporated in the CDM formulationdealing with laminates containing cracks in different ply orientations through a `constraint parameter'. Following CDM, a separate damage mode is defined for eachtype of crack and the expressions for engineering moduli of the damaged laminateare then derived in terms of crack density and the constraint parameter. The SDMmethodology is implemented for [0m/±θn/0m/2]s laminates containing cracks in ±θplies. It is then extended to [0m/±θn/90r]s and [0m/90r/±θn]s laminates with cracksadditionally in the 90°-plies. The predictions agree well with published experimentaldata as well as independent FE computations. Limited parametric studies areperformed to show usability of SDM for more general laminates.To predict the initiation and growth of intralaminar cracks, an energy basedmodel is proposed in which these cracks initiate and multiply when the work requiredto form new set of cracks exceeds a laminate dependent critical energy release rate.The approach requires determination of average crack opening and sliding displacementsat varying crack spacing. This task is performed through a suitable 3-D FEanalysis. In case of off-axis ply cracking, a mixed mode fracture criterion is utilized,where the critical energy release rates in normal and shear modes are determinedby fitting the damage model with the experimental data for a reference laminate.The predictions from the model for [0/± θ4/01/2]s and [0/90/ ± 45]s laminates showremarkable agreement with the experimental results.The methodology and the results covered in this dissertation will be of interest tomechanics of materials researchers as well as to engineers in industry where compositematerials for structural applications are of interest.

This work focuses on a new beta metastable titanium alloy, Ti-5553, for aeronautical applications. The goals of this study are the characterization of the two phases (alpha and beta) of this titanium alloy and the numerical modeling of representative cells of this material, which will be used to determine the appropriate microstructure. This thesis is divided into several parts. First, the numerical tools necessary to characterize this alloy and to model representative cells using the periodic homogenization theory will be presented. Secondly, the body-centered cubic beta phase will be identied. Then, the third part will concentrate on the characterization of the hexagonal close-packed alpha phase. Finally, the last part of this thesis will focus on choosing and modeling representative cells containing the phases identfied in the previous parts. The experimental tensile tests performed at different strain rates have demonstrated the necessity of using an elastic-viscous-plastic constitutive law. Guided by macroscopic (tensile and simple shear) experiments, a microscopic plasticity-based constitutive law was chosen to characterize this alloy instead of a macroscopic Norton-Hoff's constitutive one. It will be shown that the beta phase can be fully maintained in macroscopic samples at room temperature, making the characterization of the material behavior of this phase possible from macroscopic experiments. The optimized set of parameters was validated on nanoindentation tests performed in different beta grain orientations. In addition, a sensitivity analysis of several parameters from nanoindentation tests was performed and shows the importance of accurately defining some parameters, such as the exact shape of the indenter, and the negligible influence of other parameters, such as Poisson's ratio. From this study of experimental and numerical nanoindentation tests, it also appears that the orientation of the beta grain indented hardly affects the nanoindentation results. The characterization of the alpha phase was performed using nanoindentation experimental tests available for different grain orientations. This choice was influenced by the impossibility of maintaining only an alpha phase in a macroscopic Ti-5553 sample at room temperature and by the failure to represent the phase accurately from macroscopic (alpha+beta) samples. The material characterization of this phase is complex and difficulties occur when the behavior of this phase has to be characterized for different orientations by only one set of parameters. Finally, experimental microstructures were chosen and their simplied corresponding representative cells were meshed. Numerical simulations of these representative cells were performed and the influence of several parameters will be studied, such as the effect of the appearance of the alpha phase in the beta matrix and the effect of the shape of the alpha phase on the behavior of the cell.

Ground-borne vibrations from railway systems not only pose threats to structural integrity of nearby buildings and cause annoyance on people but also contribute into environmental noise levels. It is of utmost importance to predict these vibrations at the design stage of such systems. This thesis attempts to reach this goal through finite elements analysis. Commercial software is used to develop a finite element model of an existing railway system. The model is based on the work of Forrest and Hunt [11]. It is also aimed to perform transient analysis in time domain to complement vibration information already obtained in frequency domain. The model is validated by checking maximum element size and comparing results with the infinite boundary condition case. Parametric studies are designed to investigate effects of soil type, railpad type and train speed on vibrations induced by underground train traffic. Results acquired through the finite element analysis are found to be in good harmony with the ones by existing numerical methods. The study demonstrates that the approach can be applied to predict ground-borne vibration from any configuration of railway systems.

The aim of this study was to investigate drying characteristics (temperature gradient, rate of drying and temperature change, drying time, diffusivity values, shrinkage) of isotropic and anisotropic foods by observing the changes in temperatures at four different locations and moisture contents and to build an appropriate model for simulation of temperature and moisture distribution using finite element method. The lean meat samples (anisotropic) with three fiber configurations (v / flow normal to fiber, drying along the fiber, h1 / flow normal to fiber, h2 / flow along to fiber) and minced meat (isotropic) were dried at two different temperatures (48

Mitigating injury in side impact has been an important topic of research for decades. In the mid 1980’s the American government began a program intended to improve the crashworthiness of vehicles in side impact. This program ultimately led to the introduction of a dynamic side impact test (Federal Motor Vehicle Safety Standard (FMVSS) 214), which new vehicles must pass, along with a very similar test aimed at consumer awareness (New Car Assessment Program (NCAP) side impact test). The work presented in this thesis involved the study and simulation of these tests to evaluate occupant response in side impact, with a focus on the thoracic response. In the first portion of the work presented here, an in-depth study of the National Highway Traffic Safety Administration (NHTSA) crash test database was performed. In this study the results of the side impact crash tests of 72 vehicles were examined to understand the general trends seen in this type of testing with regards to vehicle velocity, side intrusion, and occupant injury prediction. A series of average velocity profile curves was created from accelerometer data at 18 measurement points on each vehicle crash tested. Additionally the injury criterion measured by the front seat occupant was plotted against several vehicle variables (such as mass and occupant arm to door distance) to study the effect these variable had on the injury predicted by the occupant. No single variable was shown to have a strong correlation to injury, although increasing door intrusion distance, peak lateral velocity, the Head Injury Criterion (HIC), and pelvic acceleration were found to positively correlate to thoracic injury. In addition, increasing vehicle model year, vehicle mass, and arm to door (AD) distance showed negative correlations with thoracic injury. Following the survey of the NHTSA database, a finite element model of the NHTSA side impact test was developed. This model included a full scale Ford Taurus model, a NHTSA barrier model and three side impact anthropometric test device (ATD) occupant models, each representing a different 50th percentile male dummy. Validation of this model was carried out by comparing the simulated vehicle component velocity results to the corridors developed in the NHSTA crash test database study as well as comparing these velocities, the vehicle deformation profile, and the occupant velocity, acceleration and rib deflection to several Ford Taurus crash tests from a similar vintage to the finite element model. As this model was intended as a ‘baseline’ case to study side impact and occupant kinematics in side impact, side airbags were not included in this model. A lack of experimental data and a lack of consensuses within the automotive crash community on the proper method of modeling these devices and their effectiveness in real world impacts also led to their exclusion. Following model validation, a parametric study was carried out to assess the importance of the initial position of the occupant on the vehicle door velocity profile and the predicted occupant injury response. Additionally the effect of the door trim material properties, arm rest properties and the effect of seat belt use were studied. It was found that the lateral position of the occupant had an effect on the door velocity profile, while the vertical and longitudinal position did not. The use of seatbelts was shown to have no significant effect in these simulations, due to minimal interaction between the restraint system and occupant during side impact. Furthermore, there was a general decreasing trend in the injury predicted as the initial position of the occupant was moved further inboard, down and forward in the vehicle. Stiffer interior trim was found to improve the injury prediction of the occupant, while changing the material of the foam door inserts had no effect. It was found that in general the occupant remained in position, due to the inertia of the occupant, while the seat began moving towards the centerline of the vehicle. Future considerations could include more advanced restraint systems to couple the occupant more effectively to the seat, or to develop side interior trim that engages the occupant earlier to reduce the relative velocity between the occupant and intruding door. Overall, the model correlated well with experimental data and provided insight into several areas which could lead to improved occupant protection in side impact. Future work should include integrating side airbags into the model, widening the focus of the areas of injury to include other body regions and integrating more detailed human body models.

The problem of damage accumulation in laminated composite materials hasreceived much attention due to their widespread application in the aerospace, automotive,civil, and sports industries. In the aerospace industry, composites are usedto make light weight and efficient structural components. In the Boeing 787, forexample, more than 50% of the structure is made of composite materials. Althoughthere have been significant developments in analyzing cross-ply laminates, none ofthe present approaches provides reasonable predictions for multidirectional laminatesin which intralaminar cracks may form in multiple orientations. Nevertheless, theprediction of damage accumulation and its effect on structural performance is a verydifficult problem due to complexity of the cracking processes.This study presents a synergistic damage mechanics (SDM) methodology to analyzedamage behavior in multidirectional composite laminates with intralaminarcracks in plies of multiple orientations. SDM combines the strengths of micro-damagemechanics (MDM) and continuum damage mechanics (CDM) in predicting the stiffness degradation due to these cracks. The micromechanics is performed on a representativeunit cell using a three-dimensional finite element analysis to calculate thecrack opening displacement accounting for the influence of the surrounding plies, theso-called constraint effect. This information is then incorporated in the CDM formulationdealing with laminates containing cracks in different ply orientations through a `constraint parameter'. Following CDM, a separate damage mode is defined for eachtype of crack and the expressions for engineering moduli of the damaged laminateare then derived in terms of crack density and the constraint parameter. The SDMmethodology is implemented for [0m/±θn/0m/2]s laminates containing cracks in ±θplies. It is then extended to [0m/±θn/90r]s and [0m/90r/±θn]s laminates with cracksadditionally in the 90°-plies. The predictions agree well with published experimentaldata as well as independent FE computations. Limited parametric studies areperformed to show usability of SDM for more general laminates.To predict the initiation and growth of intralaminar cracks, an energy basedmodel is proposed in which these cracks initiate and multiply when the work requiredto form new set of cracks exceeds a laminate dependent critical energy release rate.The approach requires determination of average crack opening and sliding displacementsat varying crack spacing. This task is performed through a suitable 3-D FEanalysis. In case of off-axis ply cracking, a mixed mode fracture criterion is utilized,where the critical energy release rates in normal and shear modes are determinedby fitting the damage model with the experimental data for a reference laminate.The predictions from the model for [0/± θ4/01/2]s and [0/90/ ± 45]s laminates showremarkable agreement with the experimental results.The methodology and the results covered in this dissertation will be of interest tomechanics of materials researchers as well as to engineers in industry where compositematerials for structural applications are of interest.

A nonlinear automated parameter fitted analytical model that numerically predicts the load-displacement response of wood frame shear walls subjected to static monotonic loading with and without vertical load is presented. This analytical model referred to as Analytical Model of wood frame SHEar walls subjected to Vertical load (AMSHEV) is based on the kinematic behavior of wood frame shear walls and captures significant characteristics observed from experimental testing through appropriate modeling of three failure mechanisms that can occur within a shear wall under static monotonic load: 1) failure of sheathing-to-framing connectors, 2) failure of vertical studs, and 3) uplift of end studs from bottom sill. Previous models have not accounted for these failure mechanisms as well as the inclusion of vertical load, which has shown to reveal beneficial effects such as increasing the ultimate load capacity and limiting uplift of the wall as noted in experimental tests. Results from the proposed numerical model capture these effects within 7% error of experimental test data even when different magnitudes of vertical load are applied to predict the ultimate load capacity of wood frame shear walls.

In this study, a design procedure incorporating a genetic algorithm (GA) is developed for optimization of the wing structure of a two seated trainer aircraft with single turboprop engine. The objective function considered is the total weight of the structure. The objective function is minimized subjected to certain strength requirements. In order to evaluate the design constraints and model the wing structure, finite element analysis is performed by using a conventional finite element solver (i.e. MSC/NASTRAN&reg / ). In addition, MSC/PATRAN&reg / commercial package program is used as preprocessor and postprocessor tool. VISUAL FORTRAN programming language is also utilized as the genetic algorithm implementation tool. Several conclusions drawn from the optimization results are presented.

This thesis focuses on the finite element modeling and analysis of wood shoring towers used by Urban Search and Rescue (US&R) teams during emergency response situations. These shores are constructed on site to provide temporary stabilization to a damaged structure. A high demand exists for experimental testing of the performance of these shores under non-ideal loading conditions, and for possible design modifications that could improve their overall behavior. To respond to this need, a total of thirteen vertical shores of the type laced post (LP) and plywood laced post (PLP) were constructed and tested at the Ferguson Structural Engineering Laboratory (FSEL) in Austin, Texas. The tests conducted on these shores aimed to investigate their performance under purely vertical load as well as various combinations of vertical and lateral loads. Finite element models for eight of the shores tested at FSEL were built and analyzed in Abaqus to compare the computed results with the actual linear elastic response of the shores. Material properties for the posts in each shore were obtained through further material testing at the conclusion of each shore test. Shore members were assumed to be isotropic. Solid elements were used to model each member, and Cartesian connector elements with a predefined nonlinear stiffness were used to model each nail. In general, the vertical load-displacement response computed from Abaqus exhibited good agreement with the laboratory results for the linear elastic range. The same general modeling scheme was then used to make design changes to the original shores based on observations gained during testing as well as modeling. Each design change was modeled, analyzed, and then compared with the computed results from the original shore design as well as the other design changes. The basis for evaluating the effectiveness of a given shore design involved comparing the bending moment diagrams for each post and the maximum first story nail slips (connector displacements). Recommendations were made for improved shore designs to be verified by experimental testing. / text

Cardiovascular stents are one of the most widely implanted medical devices, with over 1 million implanted each year in the United States alone. While stent failure modes of restenosis and thrombosis have been widely examined, there is an increasing appreciation of the propensity for stents to fracture and break after implantation. It remains unclear however what causes these fractures, which patients and devices are most susceptible, and whether fracture results in failure of device function. / Engineering and Applied Sciences