Carbon fiber reinforced polymers (CFRP) are widely used in advanced industry, like aerospace, modern sports, and automobile. Compared to traditional metals, CFRP laminates have a higher strength to weight ratio and better corrosion resistance. Because of the heterogeneous and anisotropic behavior of CFRP laminates, their damage mechanisms include fiber/matrix debonding, diffuse matrix damage, matrix cracking, fiber breakage, and delamination. These damage mechanisms develop in different length scales and are deeply coupled with each other, especially the intra/interlaminar damage coupling. Therefore, a well understanding of intra/interlaminar damage coupling is vital for predicting integrity of laminated structures. The dissipation during delamination process includes the intrinsic (depends on local material) and extrinsic (depends on non-local structural effect) parts. The intrinsic part could be straightly calibrated through standard test, while the non-local extrinsic part is usually not fully elaborated. In this work, we will devote to fill the gap, both in experiments and simulation, which will encounter the effect of intra/inter laminar damage coupling on the extrinsic dissipation during delamination process. The non-local extrinsic dissipation is usually triggered by the intra/inter laminar damage coupling, depending the loading conditions and curing process. In this thesis, we first design a two step test (tensile-DCB) on a cross ply to quantitatively study the influence of intralaminar damage on interlaminar performance. The intralaminar damage effect has proven to be two-fold on the interlaminar performance as the preset transverse cracks could lead to fiber bridging and also local delamination. Secondly, we proposed a hybrid cohesive element to encounter the intra/interlaminar coupling in a pragmatic local way. The hybrid cohesive element not only calculate the out-of-plane separation but also the in-plane strain of the two surfaces of the interface elements, which could be used to estimate the intralaminar damage of adjacent layers. Meanwhile, the coupling damage in multidirectional delamination is also investigated through a modified double cantilever beam (DCB) test. A general hybrid cohesive element is developed, in which the influence of delamination direction on the local apparent toughness is also considered. Last but not least, we implement an experimental campaign to study the curing process effect on fiber bridging development in unidirectional mode I fracture. Through these studies, the intra/interlaminar damage coupling mechanism is better understood and the hybrid cohesive element prove its potential on simulation efficiency and robustness.

Listeria monocytogenes is an enteric pathogen that can replicate within bile, yet this capability differs between strains. This project analyzed whether the pathogenic potential of the strain affects the ability to resist bile. We tested this hypothesis by examining the effect of bile on the morphology of a virulent strain (EGD-e) and an avirulent strain (HCC23) under aerobic and anaerobic conditions. Our data showed that exposure to bile greatly impacted the growth of HCC23. Additionally, scanning electron microscopy and transmission electron microscopy analyses indicated that bile affects the cell envelope of EGD-e and HCC23 differently. Our results suggest that differences exist in the ability of EGD-e and HCC23 to survive and replicate in the presence of bile. We propose that the virulence capability of L. monocytogenes directly correlates to its ability to resist the detergent properties of bile.

No description available.

No description available.

Although young in its existence, graphene has already shown many potential uses in nuclear engineering. Graphene has unique electrical, mechanical and optical properties that give it unmatched potential for applications raging from sensors to composites. Before these applications can be fully developed, the response to neutron and gamma irradiation must be understood. In this study, graphene grown from chemical vapor deposition was irradiated by the High Flux Isotope Reactor at Oak Ridge National Laboratory and characterized using Raman spectroscopy. It was found that the amount of structural damage was minimal, but that the graphene was doped reversibly with H₂0₂ and irreversibly. The irreversible doping is a type of soft etching process related to the exposure to O₂ as well as ionizations and heating caused by irradiation. The reversible doping is related to the products generated through the radiolysis of the water trapped between the sample and the substrate. By removing the water through evaporation the dopants related to the radiolysis products were found to be removed as well. These results are promising as they show that graphene is resilient and sensitive to the effects of irradiation simultaneously. / Master of Science

The serious consequence of ship collisions necessitates the development of regulations and requirements for the subdivision and structural design of ships to reduce damage and environmental pollution from collision, and improve safety. The on-going revision of IMO regulations on oil outflow performance and damage stability in grounding and collision is focused on a transition to probabilistic performance-based standards. This thesis addresses one aspect of this problem, a simplified collision model sufficient to predict collision damage, and fast enough to be used in probabilistic analysis requiring thousands of collision simulations. The simplified collision model (SIMCOL) developed and evaluated in this thesis is based on a time domain simultaneous solution of external dynamics and internal deformation mechanics. The external sub-model uses a three-degree of freedom system for ship dynamics. The internal sub-model determines reacting forces from side and bulkhead structures using mechanisms adapted from Rosenblatt and McDermott, and absorbed energy by decks, bottoms and stringers calculated using the Minorsky correlation as modified by Reardon and Sprung. SIMCOL is applied to a series of collision scenarios. Results are compared with MIT's DAMAGE, a Danish Technical University (DTU) model and ALPS/SCOL. SIMCOL provides a fast, consistent and reasonable result for ship collision analysis. An actual collision case is used in an initial attempt to validate the model. This research is sponsored by the Society of Naval Architects and Marine Engineers (SNAME) and the Ship Structure Committee (SSC). / Master of Science

No

No / The purpose of the research was to describe a software package (Discus) for investigating clinicians' subjective assessment of optic disc damage [diagnostic accuracy in detecting visual field (VF) damage, decision criteria, and agreement with a panel of experts] and to provide reference data from a group of expert observers. Optic disc images were selected from patients with manifest or suspected glaucoma or ocular hypertension who attended the Manchester Royal Eye Hospital. Eighty images came from eyes without evidence of VF loss in at least four consecutive tests (VF negatives), and 20 images from eyes with repeatable VF loss (VF positives). Software was written to display these images in randomized order, for up to 60 s. Expert observers (n = 12) rated optic disc damage on a 5-point scale (definitely healthy, probably healthy, not sure, probably damaged, and definitely damaged). Optic disc damage as determined by the expert observers predicted VF loss with less than perfect accuracy (mean area under receiver-operating characteristic curve, 0.78; range, 0.72 to 0.85). When the responses were combined across the panel of experts, the area under receiver-operating characteristic curve reached 0.87, corresponding to a sensitivity of ∼60% at 90% specificity. Although the observers' performances were similar, there were large differences between the criteria they adopted (p < 0.001), even though all observers had been given identical instructions. Discus provides a simple and rapid means for assessing important aspects of optic disc interpretation. The data from the panel of expert observers provide a reference against which students, trainees, and clinicians may compare themselves. The program and the analyses described in this article are freely accessible from http://www.discusproject.blogspot.com/.

The serious consequence of ship collisions necessitates the development of regulations and requirements for the subdivision and structural design of ships so that damage and environmental pollution is reduced, and safety is improved. A simplified collision model (SIMCOL) is currently being developed at Virginia Tech to conduct probabilistic analysis of damage in ship collisions and ultimately optimize ship structural designs to improve crashworthiness. Collision data for validation of SIMCOL is very difficult to obtain, and model testing is very costly. Finite Element Analysis (FEA) provides an alternative to physical validation that can be used to increase confidence and insight in simplified model results. This thesis develops a complete methodology for ship-to-ship collision simulations using the explicit non-linear FE code LS-DYNA3D. Various modeling alternatives are considered. The ability to model a complete ship-to-ship collision is developed incrementally starting with bow collisions with a rigid wall. A super-element (intersection model) approach is considered to increase the calculation speed of bow models. A conventional fine mesh finite element bow model is also developed. Results from both models are compared with each other, and with a closed-form calculation from Pedersen. A fine mesh model is developed for a struck tanker cargo section and integrated in a total ship framework modeling external dynamics and ship-to-ship contact. A series of collision scenarios is simulated using the conventional bow model and a rigid bow model striking a double hull tanker. Results are compared with SIMCOL, DAMAGE, DTU and ALPS/SCOL models. LS-DYNA provides detailed and reasonable results for ship collision analysis and comparison to increase confidence in simplified models. / Master of Science

Self-healing materials have received considerable development in the last decade. Recent results have demonstrated healing in polymeric materials via a chemical reaction using a healing agent or response to thermal treatment. The goal of this research is to develop a new composite material, for application in wire insulation, that can detect damage and heal itself using resistance heating. The composite material is composed of a conductive network embedded in a polymer matrix. The conductive network is used for damage detection and resistive heating. A matrix material is used that melts when heated and flows to fill damage. External electronic circuitry is used to implement a damage detection algorithm and apply current for resistive heating. Surlyn 8940 is chosen as the polymer matrix and carbon fibers are selected for the resistive heating elements. Methods for melt processing Surlyn are developed and used to produce Surlyn films and composite samples where carbon fiber is embedded in a Surlyn matrix. A finite element model of the resistive heating process is developed to predict the temperature distribution. Thermal imaging is used to characterize resistive heating while optical microscopy and tensile testing are used to characterize healing. Damage detection using capacitive measurements is demonstrated and characterized. The self-healing composite is placed on top of another conductive material such as in the wire insulation application. Capacitance measurements are made using the conductive network inside the composite is used as one electrode and the wide conductor as the second electrode. / Master of Science