The effect of damage on the energy absorption potential of composite structures

This thesis describes work undertaken to investigate the effects of damage on the energy absorption potential of composite tubes. Tubes of various geometries and manufactured from either continuous filament random mat (CoFRM) or glass braid and polyester resin were subjected to various types of damage before testing. Damage types consisted of drilled holes, to simulate the use of drilling components for the need of assembly, impacts, to simulate damage that may occur through tool drops or items being kicked up during use and PET inserts to simulate delamination. Large glass CoFRM/polyester tubes with an outer diameter of 89.1mm and varying wall thicknesses were crushed quasi-statically at a speed of 5mmlmin. Small CoFRM and braided glass/polyester tubes with an outer diameter of 38.1mm and a 2mm wall thickness were tested quasi statically and dynamically at a speed of 5m1s. Tubes were tested undamaged and containing various sizes of holes, simulated delamination and impacts. Specific energy absorptions (SEA) and failure modes were compared. Threshold values of damage size have been found for each tube and test type, above which unstable failures and subsequent unpredictable reductions in energy absorptions occur. The small CoFRM tubes showed a decrease in SEA as the test rate increased and this was attributed to the rate dependency of the resin, causing greater fragmentation allowing fibres to bend more easily and without fracturing. The braided small tubes showed an increase in SEA as the test rate increased due to a change in the mode of failure attributed to a higher compressive strength at the increased rate. Relatively small hole sizes and impacts, of 5mm and 1.5J-3J, were seen to reduce the energy absorption of the materials tested at quasi-static test speeds. However, an increase in damage tolerance was identified as test rate increased and this was attributed to an increase in compressive strength and fracture toughness, and reduction in crush load, as the speed of test increased

The effect of damage on the energy absorption potential of composite structures

This thesis describes work undertaken to investigate the effects of damage on the energy absorption potential of composite tubes. Tubes of various geometries and manufactured from either continuous filament random mat (CoFRM) or glass braid and polyester resin were subjected to various types of damage before testing. Damage types consisted of drilled holes, to simulate the use of drilling components for the need of assembly, impacts, to simulate damage that may occur through tool drops or items being kicked up during use and PET inserts to simulate delamination. Large glass CoFRM/polyester tubes with an outer diameter of 89.1mm and varying wall thicknesses were crushed quasi-statically at a speed of 5mmlmin. Small CoFRM and braided glass/polyester tubes with an outer diameter of 38.1mm and a 2mm wall thickness were tested quasi statically and dynamically at a speed of 5m1s. Tubes were tested undamaged and containing various sizes of holes, simulated delamination and impacts. Specific energy absorptions (SEA) and failure modes were compared. Threshold values of damage size have been found for each tube and test type, above which unstable failures and subsequent unpredictable reductions in energy absorptions occur. The small CoFRM tubes showed a decrease in SEA as the test rate increased and this was attributed to the rate dependency of the resin, causing greater fragmentation allowing fibres to bend more easily and without fracturing. The braided small tubes showed an increase in SEA as the test rate increased due to a change in the mode of failure attributed to a higher compressive strength at the increased rate. Relatively small hole sizes and impacts, of 5mm and 1.5J-3J, were seen to reduce the energy absorption of the materials tested at quasi-static test speeds. However, an increase in damage tolerance was identified as test rate increased and this was attributed to an increase in compressive strength and fracture toughness, and reduction in crush load, as the speed of test increased

Invasion risk of active and diapausing invertebrates from residual ballast in ships entering Chesapeake Bay

ABSTRACT: We examined the invasion risk posed by active invertebrates and their diapausing stages (e.g. resting eggs, quiescent adults) carried in residual sediment and water of non-ballasted ships to Chesapeake Bay. Many taxa were recorded that are not native to Chesapeake Bay, supporting the contention that residual ballast represents an invasion vector of some risk to marine systems. Composition and propagule supply differed relative to that in ships entering the Laurentian Great Lakes (e.g. marine taxa dominated in Chesapeake Bay ships), indicating that risk varies geographically. Average abundances of active invertebrates in residual sediment (1002.1 ind. kg–1) and water (2.7 ind. l–1), and diapausing eggs in sediments (779.4 eggs kg–1), were typically low relative to those in ships entering the Great Lakes (1322.5 ind. kg–1, 10.9 ind. l–1 and 3650.0 eggs kg–1, respectively). However, due to high variability among ships, differences were not statistically significant. The major cause of composition and abundance differences is dissimilar trade routes between each system, with vessels entering Chesapeake Bay primarily originating from marine rather than freshwater ports, and because diapausing stages are less commonly found among marine invertebrates. Low propagule supplies, predominant intra-continental ship movements, and salinity disparity between the upper (20 to 28‰) and lower (3 to 8‰) regions of Chesapeake Bay (where ballast water is loaded and offloaded) may greatly reduce invasion risk and be a contributing factor to the bay’s low invasion rate: invasion risk from non-ballasted ships here may be low relative to hull fouling or ballast water discharge. Other marine coastal areas may be at greater risk from this vector

Modelling the future of the Hawaiian honeycreeper : an ecological and epidemiological problem

The Hawaiian honeycreeper (Drepanididae) faces the threat of extinction; this is believed to be due primarily to predation from alien animals, endemic avian malaria (Plasmodium relictum) and climate change. A deterministic SI modelling approach is developed, incorporating these three factors and a metapopulation approach in conjunction with a quasi-equilibrium assumption to simplify the vector populations. This enables the qualitative study of the behaviour of the system. Numerical results suggest that although (partial) resistance to avian malaria may be advantageous for individual birds, allowing them to survive infection, this allows them to become carriers of infection and hence greatly increases the spread of this disease. Predation obviously reduces the life-expectancy of honeycreepers, but in turn this reduces the spread of infection from resistant carriers; therefore the population-level impact of predation is reduced. Various control strategies proposed in the literature are also considered and it is shown that predation control could either help or hinter, depending upon resistance of the honeycreeper species. Captive propagation or habitat restoration may be the best feasible solution to the loss of both heterogeneity within the population and the loss of the species as a whole

Critical currents in Josephson junctions, with unconventional pairing symmetry: dx2−y2+isd_{x^2-y^2}+is versus dx2−y2+idxyd_{x^2-y^2}+id_{xy}

Phenomenological Ginzburg-Landau theory is used to calculate the possible spontaneous vortex states that may exist at corner junctions of $d_{x^2-y^2}+ix$-wave, (where $x=s$ or $x=d_{xy}$) and s-wave superconductors. We study the magnetic flux and the critical current modulation with the junction orientation angle $\theta$, the magnitude of the order parameter, and the magnetic field $H$. It is seen that the critical current $I_c$ versus the magnetic flux $\Phi$ relation is symmetric / asymmetric for $x=d_{xy}/s$ when the orientation is exactly such that the lobes of the dominant $d_{x^2-y^2}$-wave order parameter points towards the two junctions, which are at right angles for the corner junction. The conclusion is that a measurement of the $I_c(\Phi)$ relation may distinguish which symmetry ($d_{x^2-y^2}+is$ or $d_{x^2-y^2}+id_{xy}$) the order parameter has.Comment: 11 pages with 11 figures, Changed conten

Harvesting Environmental Microalgal Blooms for Remediation and Resource Recovery: A Laboratory Scale Investigation with Economic and Microbial Community Impact Assessment

A laboratory based microflotation rig termed efficient FLOtation of Algae Technology (eFLOAT) was used to optimise parameters for harvesting microalgal biomass from eutrophic water systems. This was performed for the dual objectives of remediation (nutrient removal) and resource recovery. Preliminary experiments demonstrated that chitosan was more efficient than alum for flocculation of biomass and the presence of bacteria could play a positive role and reduce flocculant application rates under the natural conditions tested. Maximum biomass removal from a hyper-eutrophic water retention pond sample was achieved with 5 mg·L-1 chitosan (90% Chlorophyll a removal). Harvesting at maximum rates showed that after 10 days, the bacterial diversity is significantly increased with reduced cyanobacteria, indicating improved ecosystem functioning. The resource potential within the biomass was characterized by 9.02 μg phosphate, 0.36 mg protein, and 103.7 μg lipid per mg of biomass. Fatty acid methyl ester composition was comparable to pure cultures of microalgae, dominated by C16 and C18 chain lengths with saturated, monounsaturated, and polyunsaturated fatty acids. Finally, the laboratory data was translated into a full-size and modular eFLOAT system, with estimated costs as a novel eco-technology for efficient algal bloom harvesting

Magnetic-interference patterns in Josephson junctions with d+is symmetry

The magnetic interference pattern and the spontaneous flux in unconventional Josephson junctions of superconductors with d+is symmetry are calculated for different reduced junction lengths and the relative factor of the d and s wave components. This is a time reversal broken symmetry state. We study the stability of the fractional vortex and antivortex which are spontaneously formed and examine their evolution as we change the length and the relative factor of d and s wave components. The asymmetry in the field modulated diffraction pattern exists for lengths as long as L=10\lambda_J.Comment: 8 pages, 6 eps files, submitted to PR

Metabolic Futile Cycles and Their Functions: A Systems Analysis of Energy and Control

It has long been hypothesized that futile cycles in cellular metabolism are involved in the regulation of biochemical pathways. Following the work of Newsholme and Crabtree, we develop a quantitative theory for this idea based on open-system thermodynamics and metabolic control analysis. It is shown that the {\it stoichiometric sensitivity} of an intermediary metabolite concentration with respect to changes in steady-state flux is governed by the effective equilibrium constant of the intermediate formation, and the equilibrium can be regulated by a futile cycle. The direction of the shift in the effective equilibrium constant depends on the direction of operation of the futile cycle. High stoichiometric sensitivity corresponds to ultrasensitivity of an intermediate concentration to net flow through a pathway; low stoichiometric sensitivity corresponds to super-robustness of concentration with respect to changes in flux. Both cases potentially play important roles in metabolic regulation. Futile cycles actively shift the effective equilibrium by expending energy; the magnitude of changes in effective equilibria and sensitivities is a function of the amount of energy used by a futile cycle. This proposed mechanism for control by futile cycles works remarkably similarly to kinetic proofreading in biosynthesis. The sensitivity of the system is also intimately related to the rate of concentration fluctuations of intermediate metabolites. The possibly different roles of the two major mechanisms for cellular biochemical regulation, namely reversible chemical modifications via futile cycles and shifting equilibrium by macromolecular binding, are discussed.Comment: 11 pages, 5 figure

The structural analysis of Cu(111)-Te (√3 × √3) R30° and (2√3 × 2√3)R30° surface phases by quantitative LEED and DFT,

The chemisorption of tellurium on atomically clean Cu(111) surface has been studied under ultra-high vacuum conditions. At room temperature, the initial stage of growth was an ordered 23×23R30° phase (0.08 ML). An ordered 3×3R30° phase is formed at 0.33 ML coverage of Te. The adsorption sites of the Te atoms on the Cu(111) surface at 0.08 ML and 0.33 ML coverages are explored by quantitative low energy electron diffraction (LEED) and density functional theory (DFT). Our results indicate that substitutional surface alloy formation starts at very low coverages

Thinking about growth : a cognitive mapping approach to understanding small business development

School of Managemen