Efficient engineering design and development of high precision and reliable surgical simulators, like haptic devices for surgical training benefits from model-based and simulation driven design. The complexity of the design space, multi-domains, multicriteria requirements and multi-physics character of the behavior of such a product ask for a model based systematic approach for creating and validating compact and computationally efficient simulation models to be used for the design process.The research presented in this thesis describes a model-based design approach towards the design of haptic devices for simulation of surgical procedures, in case of hard tissues such as bone or teeth milling. The proposed approach is applied to a new haptic device based on TAU configuration.The main contributions of this thesis are: Development and verification of kinematic and dynamic models of the TAU haptic device. Multi-objective optimization (MOO) approach for optimum design of the TAU haptic device by optimizing kinematic performance indices, like workspace volume, kinematic isotropy and torque requirement of actuators.  A methodology for creating an analytical and compact model of the quasi-static stiffness of haptic devices, which considers the stiffness of; actuation system;flexible links and passive joints. / QC 20120611

This research investigates two principal characteristics that are of primary importance in Fiber Reinforced Polymer (FRP) bridge deck applications: STIFFNESS and STRENGTH. The research was undertaken by investigating the stiffness and strength characteristics of the multi-cellular FRP bridge deck systems consisting of pultruded FRP shapes. A systematic analysis procedure was developed for the stiffness analysis of multi-cellular FRP deck systems. This procedure uses the Method of Elastic Equivalence to model the cellular deck as an equivalent orthotropic plate. The procedure provides a practical method to predict the equivalent orthotropic plate properties of cellular FRP decks. Analytical solutions for the bending analysis of single span decks were developed using classical laminated plate theory. The analysis procedures can be extended to analyze continuous FRP decks. It can also be further developed using higher order plate theories. Several failure modes of the cellular FRP deck systems were recorded and analyzed through laboratory and field tests and Finite Element Analysis (FEA). Two schemes of loading patches were used in the laboratory test: a steel patch made according to the ASSHTO's bridge testing specifications; and a tire patch made from a real truck tire reinforced with silicon rubber. The tire patch was specially designed to simulate service loading conditions by modifying real contact loading from a tire. Our research shows that the effects of the stiffness and contact conditions of loading patches are significant in the stiffness and strength testing of FRP decks. Due to the localization of load, a simulated tire patch yields larger deflection than the steel patch under the same loading level. The tire patch produces significantly different failure compared to the steel patch: a local bending mode with less damage for the tire patch; and a local punching-shear mode for the steel patch. A deck failure function method is proposed for predicting the failure of FRP decks. Using developed laminated composite theories and FEA techniques, a strength analysis procedure containing ply-level information was proposed and detailed for FRP deck systems. The behavior of the deck's unsupported (free) edges was also investigated using ply-level FEA. / Ph. D.

Aging is characterized by a progressive stiffening of large elastic arteries in the cardiothoracic region. Importantly, large artery stiffness is an independent predictor of cardiovascular events and mortality in both healthy and diseased populations. The results of several studies suggest that obesity, particularly visceral adiposity, is associated with the accelerated stiffening of central elastic arteries in middle-aged and older adults. Despite the widely recognized association between obesity, aging and arterial stiffness, there remains a paucity of information regarding both the initiation of arterial stiffening and effective treatment strategies. To address these issues, we tested the hypotheses that weight gain increases arterial stiffness in nonobese young males, and atorvastatin treatment reduces large artery stiffness in overweight and obese middle-aged and older adults. Consistent with our first hypothesis, weight gain increased arterial stiffness in nonobese young men. In addition, we demonstrated that, independent of total body fat, those individuals with relatively larger increases in abdominal visceral fat also experienced correspondingly larger increases in arterial stiffness. Regarding our second hypothesis, atorvastatin treatment decreased arterial stiffness in overweight and obese middle-aged and older adults. Importantly, the reduction in arterial stiffness with atorvastatin appeared to be independent of the reduction in C-reactive protein. The findings of the present studies could potentially lead to the identification of effective strategies for the prevention and treatment of arterial stiffening in the population. / Ph. D.

The purpose of this study was to assess the validity, as well as to test novel approaches to improving the reliability, of mechanical response tissue analysis (MRTA). Twenty composite tibiae underwent MRTA testing on three separate days to determine intra- and inter-day reliability of bending stiffness. The bones were then subjected to three-point bending tests to directly determine elastic modulus. Within- and between-day reliability of tibial bending stiffness with MRTA was moderate (CV = 24%) and poor (CV = 74%), respectively. No relationship was observed between the two testing methods due to the wide variation in tibial bending stiffness values with MRTA. The second part of the study sought to determine within- and between-day reliability of MRTA in young women with the current testing protocol and compare the results with those from newly-designed protocols. Twelve women (23 ± 2 yr, 162 ± 7 cm, 57 ± 7kg, 19 ± 4 % fat) were tested for tibial bending stiffness with MRTA over 5 days. The current protocol was compared to protocols where day-to-day subject positioning was quantified, subjects were tested in a supine position, and various bending stiffness prediction models were used. Within- (CV = 20%) and between-day (CV = 19%) reliability of tibial bending stiffness with MRTA was moderate using the original methodology. Modifications to this protocol either resulted in similar or worse reliability. / Ph. D.

Mechanical response tissue analysis (MRTA) provides a noninvasive means of estimating the cross-sectional bending stiffness (EI) of long bones, and thus can serve as a predictor of bone strength. Estimates of bone bending stiffness are derived from the point impedance response of a long bone to low frequency (70-500Hz) stimulation according to beam vibration theory. MRTA has demonstrated the ability to reliably estimate human ulnar bending stiffness with between-test coefficients of variation of 5%, and in vivo measurements of monkey tibiae have been validated with ex vivo 3-point mechanical bending tests. Human tibial MRTA measurement has achieved between-trial coefficients of variation of only 12%, so a new physical MRTA configuration and improved computer algorithms have been developed in an attempt to improve upon this level of reliability. The new configuration removes the rigid proximal and distal tibial restraints and models the tissue behavior with a 12-parameter algorithm that accounts for free vibration at the ankle and knee joints. Initial testing with only the hardware changes and application of the 7-parameter model of tissue behavior used in earlier systems yielded unacceptable variation. Subsequent reliability testing with application of 6-, 9-, and 12-parameter models demonstrated modest improvements, prompting the development of the more robust 12-parameter model used in the present study. Evaluation of 110 college-age females (age 20.2±1.8 yr, height 163.3±5.9 cm, weight 60.7±9.3 kg, BMI 22.8±3.1 kg·m⁻²) with the current MRTA system has demonstrated an improvement in within-trial reliability for unsupported tibial EI measurement with a coefficient of variation of 11.2%. These results demonstrate the ability of the system to measure tibial response characteristics when both proximal and distal ends are free of rigid support. Long-term measurement reliability is still problematic with a coefficient of variation of 36.5% for a set of 4 measurements spanning 21 months. / Ph. D.

The main goal for my research was to challenge the long held belief that the mechanical properties of maturing dystrophic compared to control skeletal muscle membranes are weaker, leading to onset of Duchenne muscular dystrophy (DMD). We built on a previous report from our lab that suggested sarcolemmal membranes from dystrophic mice are not more susceptible to damage early in maturation (i.e., age 9-12 days) and determined if and when muscle mechanical properties change as the mice mature. Across four studies, I have helped define the role of dystrophin-deficient skeletal muscle membranes in the onset of DMD. A linear viscoelastic muscle model was used to determine passive stiffness and damping in control and dystrophic muscles from maturing mice aged 14-35 days. Results confirmed my hypothesis that there are no differences in passive mechanical properties between normal and dystrophic mice. Recognizing the limitations of the linear model, a nonlinear model was developed to determine the stiffness and damping of active and passive dystrophic muscles from maturing mice aged 21 and 35 days. The nonlinear model achieved a significantly better fit to experimental data than the linear model when muscles were stretched to 15% strain beyond resting length. Active and passive mechanical properties of dystrophic mice were not different than control at 14 and 28 days of age. The previously developed nonlinear model was used to determine a more complete time-course (14-100 days of age) of dystrophic muscle mechanical properties. There was no difference in passive stiffness between mdx and control muscles at each age. However, the mdx:utrn-/- muscles showed increased stiffness compared to control and mdx muscles at 21 and 28 days, suggesting a temporary change within the muscle that only occurs with a lack of both utrophin and dystrophin. Fast-twitch and slow-twitch muscle mechanical properties were compared in control and dystrophic mice aged 3, 5, and 9 weeks of age. Dystrophic and control slow-twitch muscles did not have different mechanical properties, suggesting that a lack of dystrophin does not affect slow-twitch muscles during maturation (3-5 weeks) or well after maturation (9 weeks). / Ph. D.

This thesis presents two studies related to head injury. The study presented in Chapter 1 reviewed findings of cranial movement in animal and human specimens and evaluate the validity of cranial movement due to manual manipulation in humans through engineering analysis. The study had two parts. In Part I, the literature was reviewed to determine the cranial motion in animals and humans. Engineering analysis was done in Part II to determine the amount of force necessary to cause cranial motion in the studies from Part I using skull stiffness values from published studies. Chapter 2 explored data collection methodologies used in frontal sled tests. Several data collection methodologies exist for collecting kinematic data, such as Vicon motion analysis, video analysis, and sensors. Head trajectories from motion data and accelerometer data were plotted up to maximum forward excursion of the head for eight frontal sled tests, four conducted at Virginia Tech and four at the University of Virginia. In addition, the percent difference between maximum forward excursion values from sensor and motion data were calculated. Finally, Chapter 3 discusses the literary contributions of each study and to which journals they will be submitted. / Master of Science

An enhanced demand for lightweight materials in automotive applications has resulted in the growth of the use of injection molded discontinuous fiber-reinforced thermoplastics. During the intensive injection molding process, severe fiber breakage arises in the plasticating stage leading to a broad fiber length distribution. Fiber orientation distribution (FOD) is another highly anisotropic feature of the final injection molded parts induced by the mold filling process. The mechanical and other properties can be highly dependent on the fiber length distribution and fiber orientation distribution. The residual fiber length in the final part is of great significance determining the mechanical performances of injection molded discontinuous fiber reinforced thermoplastic composites. One goal of this research is to develop a fiber length characterization method with reproducible sampling procedure in a timely manner is described. In this work is also proposed an automatic fiber length measurement algorithm supported by Matlab®. The accuracy of this automatic algorithm is evaluated by comparing the measured results using this in-house developed tool with the manual measurement and good agreement between the two methods is observed. Accurate predictions of fiber orientation are also important for the improvement of mold design and processing parameters to optimize mechanical performances of fiber-reinforced thermoplastics. In various fiber orientation models, a strain reduction factor is usually applied to match the slower fiber orientation evolution observed experimentally. In this research, a variable strain reduction factor is determined locally by the corresponding local flow-type and used in fiber orientation simulation. The application of the variable strain reduction factor in fiber orientation simulations for both non-lubricated squeeze flow and injection molded center-gated disk, allows the simulated fiber re-orient rate to be dependent on the local flow-type. This empirical variable strain reduction factor might help to improve the fiber orientation predictions especially in complex flow, because it can reflect the different rates at which fibers orient during different flow conditions. Finally, the stiffness of injection-molded long-fiber thermoplastics is investigated by micro-mechanical methods: the Halpin-Tsai (HT) model and the Mori-Tanaka model based on Eshelby's equivalent inclusion (EMT). We proposed an empirical model to evaluate the effective fibers aspect ratio in the computation for the fiber bundles under high fiber content in the as-formed fiber composites. After the correction, the analytical predictions had good agreement with the experimental stiffness values from tensile tests on the composites. Our analysis shows that it is essential to incorporate the effect of the presence of fiber bundles to accurately predict the composite properties. / PHD / An enhanced demand for lightweight materials in automotive applications has resulted in the growth of the use of injection molded discontinuous fiber-reinforced thermoplastics. The injection molding process results in fiber length and fiber orientation distributions in the final parts. The mechanical and other properties can be highly dependent on the fiber length distribution and fiber orientation distribution. This work focuses on the process-structure-property relationship of fiber-thermoplastic composites. A novel fiber length measurement procedure and an automatic fiber length measurement tool were developed to improve the accuracy of fiber length measurement. The existing fiber orientation models have been improved by integration of the flow-type dependent fiber orientation kinetics. To improve the stiffness predictions, an empirical model has been developed to include the effects of fiber clumping on the elastic properties of injection molded fiber composites.

The purpose of this study was to compare the stiffness of a Type II external skeletal fixator (ESF) to a 3.5 mm locking compression plate (LCP) in axial compression, mediolateral, and craniocaudal bending in a fracture gap model. The hypothesis was that the Type II ESF would demonstrate comparable stiffness to the LCP. A bone simulant consisting of short fiber reinforced epoxy cylinders and a 40 mm fracture gap was used. The LCP construct consisted of a 12 hole 3.5 mm plate with three 3.5 mm bicortical locking screws per fragment. The Type II ESF construct consisted of 3 proximal full fixation pins (Centerface®) per fragment in the mediolateral plane, and 2 carbon fiber connecting rods. Five constructs of each were tested in non-destructive mediolateral and craniocaudal bending, and axial compression. Stiffness was determined from the slope of the elastic portion of force-displacement curves. A one-way ANOVA and a Tukey-Kramer multiple comparisons test were performed, with significance defined as p < 0.05. In mediolateral bending, the stiffness of the Type II ESF (mean ± standard deviation; 1584.2 N/mm ± 202.8 N/mm) was significantly greater than that of the LCP (110.0 N/mm ± 13.4 N/mm). In axial compression, the stiffness of the Type II ESF (679.1 N/mm ± 20.1 N/mm) was significantly greater than that of the LCP (221.2 N/mm ± 19.1 N/mm). There was no significant difference between the constructs in craniocaudal bending. This information can aid in decision-making for fracture fixation, although ideal stiffness for healing remains unknown. / Master of Science

Java applets are developed to assist in the learning of basic structural analysis concepts. In order for these programs to be easily available over the Internet, they are written in the object-oriented Java programming language. The Java programs known as applets are embedded in HTML documents. The HTML documents, part of a series of instructional units, present the topics demonstrated by the applets. The applets include truss and frame determinacy applets; a three-hinged arch bridge applet; determinate and indeterminate truss analysis applets; determinate and indeterminate frame analysis applets and an influence line analysis applet. These programs are available to any student or instructor with Internet access. The applets provide good examples of the application of object-oriented programming and the development of software for a graphical user interface. They also serve as excellent tools that facilitate the understanding of structural engineering concepts utilizing a medium that allows independent learning at an individual pace. / Master of Science