A polymer-based composite reinforced with a mixture of Ni and Al powders was investigated as an example of a multifunctional structural energetic material. Micron-sized Ni powder, nano/micron-sized Al powders, and Teflon or epoxy were fabricated as bulk materials by pressing or casting. The thermally initiated reaction response of these materials was evaluated using differential thermal analysis coupled with x-ray diffraction. The analyses showed evidence of thermally initiated reactions between Ni and Al powders, as well as between Ni+Al and Teflon. Nano-sized Al powder showed a preference for reaction with Teflon over Ni, while micron-sized Al reacted strongly with Ni regardless of the presence of a binder. Teflon was shown to be very reactive with the Ni+Al/nano Al mixture, whereas epoxy was not reactive with the metallic powders, and also inhibited reaction between Ni and nano Al. The structural/mechanical behavior of these materials was evaluated using elastic and plastic property measurements via static and dynamic compression tests. Dynamic mechanical testing using reverse Taylor anvil-on-rod impact tests combined with velocity interferometry gave qualitative and quantitative information about the transient deformation and failure response of the composites. The material containing 20wt% epoxy and nano-sized Al powder showed the most superior mechanical properties in terms of elastic modulus and static and dynamic compressive strength. The addition of Ni and Al powders to the epoxy matrix increased the strength of the composites, and their tendency toward brittle fracture, as evidenced by Ni particle pullout in SEM analysis. The results illustrate that nano-sized Al particles provide significant enhancement to strength of epoxy composites, but at the expense of reactivity. The nano-Al particles get dissociated from the Ni and Al mixture and swept into the epoxy, generating a nano-Al containing epoxy matrix with embedded Ni particles. The chemical reactivity of the system is thus sacrificed as contacts between Ni and Al powders are minimized. A mixture of nano-sized Ni and Al particles may however provide the best combination of high strength and reactivity.

This investigation represents a comparative study of the flexural behavior of lightweight and normal weight concrete. Both theoretical and experimental moment-curvature characteristics of the tested specimens were used to study the flexural behavior. A generalized computer program to determine the moment-curvature relationships of a singly reinforced rectangular concrete beam was developed. For this limited study it was observed that lightweight concrete beams when compared to normal concrete beams achieve comparable moment capacity (about 92% of normal weight concrete) but exhibit higher deflections (about 40% more than normal weight concrete).

<p>With the poor room temperature formability of magnesium, rare earth (RE) additions have proven a promising avenue for wrought magnesium products. However, not much is known regarding the effect of these elements on strength and ductility. Stanford et al. (2010b) summarized it best: “Although the addition of rare earth elements offers the possibility of greatly improved mechanical properties, we still lack fairly basic knowledge about the behaviour of these alloying elements”[p.6773]. Through a systematic study across three Mg-RE binary systems, the effect of gadolinium, samarium and scandium on solution strengthening, work hardening behaviour and strain rate sensitivity of Mg-RE binary alloys have been characterized.</p> <p>The results suggest that samarium offers the greatest solid solution strengthening in both tension and compression relative to the other two binary systems. For the binary alloys explored, only gadolinium and samarium in compression followed the Labusch theory of solution strengthening; in which the yield strength scales with c^2/3 . Gadolinium additions provide the largest strength and ductility in tension and compression. Increasing solute content in the binary systems leads to a decrease of the strain rate sensitivity of the alloys. At the highest level of solute, both Mg-Gd and Mg-Sm exhibit negative strain rate sensitivity under tension. In compression, Mg-Gd also exhibits a negative strain rate sensitivity at the highest level solute, whereas Mg-Sm has a low, but positive value. The asymmetry in work hardening behaviour and the form of the flow curves between tension and compression is the result of the difference in the dominating modes of deformation at a given stage of the plastic flow. The extent of the work performed established the hardening levels and thermodynamic deformation parameters which control the flow stress and work hardening behaviour, that can be applied in future work.</p> / Master of Applied Science (MASc)

Nickel super alloy Inconel 718 was tested and compared to Haynes 230 using Gleeble and Varestraint mechanical test methods. Hot cracking susceptibility was examined in either alloy using a sub-scale Varestraint test method at 5 augmented strain levels: 0.25%, 05.%, 1%, 2%, and 4%. Maximum crack length, total crack length, and number of cracks were measured for each strain level. Gleeble hot ductility on-heating and on-cooling tests were performed on both alloys. Inconel 718 was tested on-heating at target temperatures of 1600˚F, 2000˚F, 2100˚F, 2200˚F, and on cooling at 1600˚F, 1700˚F, 1800˚F, 1900˚F, and 2100˚F. Haynes 230 was tested on-heating at target temperatures of 2050 ˚F, 2200 ˚F, 2240 ˚F, 2330 ˚F, and on-cooling at 1800 ˚F, 1900 ˚F, 1990 ˚F, 2040 ˚F, 2090 ˚F, 2100 ˚F, 2140 ˚F, and 2190 ˚F. Ductility in Gleeble samples was measured in a reduction of surface area. A nil-strength temperature was established for either alloy. The nil-strength temperature was 2251˚F and 2411˚F, for Inconel 718 and Haynes 230, respectively. The nil ductility temperature <5% R/A) was 2188˚F for Inconel 718 and 2341˚F for Haynes 230. Ductility recovery temperature occurred at 1924˚F for Inconel 718 and 2147˚F for Haynes 230. The brittle temperature range was determined to be 326˚F for Inconel 718 and 228˚F for Haynes 230. Varestraint testing revealed that Inconel 718 had a lower threshold strain for crack initiation than Haynes 230 (0.5% vs 1%), and a higher number of cracks, as well as a larger maximum crack length, at every strain level. These results show a greater tendency for liquation cracks to form in Inconel 718 than in Haynes 230.

In this project, we have successfully joined MA956 Oxide Dispersion-Strengthened (ODS) steel plates using Friction Stir Welding (FSW). ODS steels are prime candidate materials for the fuel cladding in Generation IV nuclear fission reactors and as first wall components in nuclear fusion reactors. This is due to their exhibiting excellent high temperature strength and creep behaviour, together with enhanced resistance to radiationinduced void swelling. ODS steels are heavily reliant on a fine dispersion of (Y-Al-O) nanooxide particles to provide the aforementioned properties. This, however, makes ODS steels particularly problematic to join. Most joining techniques melt the material along the joint line, but this would severely alter or deplete the nano-oxide dispersion and hence be highly detrimental to the material’s performance in a nuclear environment. FSW is a solid-state joining technique, and therefore can join ODS steel without melting the material. Although FSW can potentially alter the microstructure of the base material and affect the distribution of nano-oxide particles, if a sufficient number of nano-sized particles and a sufficiently homogeneous dispersion remain after the welding process, then a major roadblock for the implementation of ODS steels will have been removed. The research of this thesis focused on the impact of FSW on: i) the microstructure, ii) the mechanical properties, iii) the residual stresses, and iv) the abnormal grain growth behaviour of ODS steels; utilizing a wide array of techniques to assess the micro-to-nano scale structure and the properties of the base material and welds, including optical, scanning and transmission and electron microscopy, X-ray and neutron diffraction, small-angle neutron scattering, tensile testing and micro-hardness measurements. We also produced welds with systematic changes to the tool traverse speed and rotation speed to investigate the impact of changing the welding parameters on the weld microstructure, and therefore optimise the process parameters for enhanced radiation and mechanical performance of the ODS steel welds.

Metal-organic frameworks (MOFs) have been extensively studied because of their amazing applications in gas storage, purification, photocatalysis, chemical sensing, and imaging techniques. Ruthenium polypyridyl complexes have been broadly considered as photosensitizers for the conversion of solar energy and photoelectronic materials. With this aspect, we have synthesized three new ruthenium polypyridyl based MOFs ([Ru(H2bpc)Cu(bpc)(Hbpc)2(H2O)]·5H2O (1), [Ru(H2bpc)(Fe(bpc)(Hbpc)2(H2O)2]·6H2O (2) and [Ru(H2bpc)Ni(bpc)(Hbpc)2(H2O)2]·6H2O (3)) from ruthenium(III) chloride, bpc (2,2’- bipyridine-4,4’-dicarboxylic acid) ligand, and 3d M(II) metal ions (M(II)= Cu(II), Fe(II), Ni(II)). These MOFs were synthesized under hydro or solvothermal conditions by using water, ethanol or methanol as solvents. The crystal structures of the new compounds contains zigzag chains of [Ru(bpc)3]n- complex ions linked by Cu, Fe or Ni complex ions individually. Above synthesized crystal structures were characterizing by single-crystal Xray and powder X-ray diffraction strategies, UV-vis and IR spectroscopy. Thermal properties were determining by thermogravimetric analysis. Magnetic properties were also studied.

The efficacy of dispersed reduced graphene oxide (rGO) as a nucleation site for the growth of mesophase in an isotropic pitch was investigated and quantified in this study. Concentrations of rGO were systematically tested in an isotropic petroleum and coal-tar pitch during thermal treatments and compared to pitch without rGO. The mesophase content of each thermally treated pitch was quantified by polarized light point counting. Further characterization of softening temperature and insolubles were quantified. Additionally, the pitches with and without rGO were melt spun, graphitized, and tensile tested to determine the effects of rGO on graphitized fiber mechanical properties and fiber morphology.

Self-cleaning, anti-corrosion, anti-icing, dropwise-condensation, and drag-reduction are some applications in which superhydrophobic surfaces are implemented. To date, all the studies associated with superhydrophobic surfaces have been dedicated to understanding the liquid interaction with surfaces that are macroscopically smooth. The current study investigates the solid-liquid interaction of such surfaces which are fully decorated with macroscopic ridges (ribbed surfaces). In particular, the drop motion and impact on our newly designed non-wettable ribbed surface have been investigated in this work. Our experimental investigations have shown that liquid drops move faster on the ribbed surfaces due to lower friction induced by such a surface pattern. Moreover, an impacting droplet shows shorter contact time on ribbed surfaces. This concludes that ribbed surface pattern can be an efficient alternative design for the related applications. Besides the experimental studies, the theoretical analyses done in this work have led to, firstly a scaling model to predict descent velocity of a rolling viscous drops on an inclined non-wettable surface more accurately. Secondly, for curved superhydrophobic surfaces a scaling model which correlates the contact time of the impacting drop to its impact velocity has been developed. At the end, the knowledge obtained from this work has led to a special surface design which exhibits a contact time shorter than the inertial-capillary time scale, an unprecedented phenomenon.

In this thesis, the relationship among friction stir processing (FSP) parameters, microstructure evolution, texture development, and mechanical hehavior of AZ31B Mg alloy was investigated. First of all, in order to reveal the correlation among the deformation conditions, dynamic recrystallization (DRX) mechanisms, and microstructure evolution in the Mg alloy, hot compression tests at a wide range of Zener-Hollomon parameter (Z) values were conducted. Through optical microscopic examination, it was found out that above a critical Z value, twinning influences the DRX process resulting in a more effective grain refinement, which is manifested in a significant change in the slope of the Z-drec relationship, where drec is the recrystallized grain size. Moreover, EBSD examination revealed that the twinning also contributed to a distinct change in the recrystallization texture. Compression tests were performed along both through-thickness and in-rolling-plane directions of the plate to study the orientation dependency of twinning activities and its influence on the DRX process. X-ray line profile analysis (XLPA) provides further insights by highlighting the differences in the dislocation density/types, subgrain sizes, and twin densities during the DRX processes operating with or without the twinning. Secondly, the constitutive behaviour study was applied to the investigation of microstructure evolution during FSP. By varying the key FSP parameters systematically, i.e. rotation and travel rates of the tool, a series of FSP specimens were prepared with a wide range of thermo-mechanical inputs in terms of Z. The resulting tensile behavior in the stir zone (SZ) showed a dramatic change as a function of Z, caused by a systematic change in the texture within SZ measured by neutron diffraction. A three-dimensional transient model was developed to investigate the detailed deformation history including the temperature and strain rate profiles and material flow pattern during FSP of the Mg alloy. Such deformation history can be combined with the constitutive study from the compression tests in order to analyze the developments of micro-texture and DRX grains during FSP, which will, in turn, dominate the mechanical properties. Based on the studies above, new fundamental understandings were gained on the governing mechanisms for the deformation and recrystallization processes during FSP and the influence of thermo-mechanical input during FSP on ductility enhancement in the Mg alloy.

Nanoporous carbons are among the widely studied and promising materials on hydrogen storage for on-board vehicles. However, the nature of nanoporous carbon structures, as well as the relationship between local structure and hydrogen adsorption are still unclear, and hinder the design of carbon materials for optimum hydrogen storage. This dissertation presents a systematic modeling effort of hydrogen storage in nanoporous carbon materials. Tight binding molecular dynamics simulations are utilized to simulate the amorphous carbons over a wide range of density. The resulting structures are in good agreement with experimental data of ultra-microporous carbon (UMC), a wood-based activated carbon, as indicated by a comparison of the microstructure at atomic level, pair distribution function, and pore size distribution. To estimate gas adsorption in complex geometries, an efficient numerical algorithm (based on a continuum gas adsorption model) is developed for calculating the gas uptake at room temperature and moderate pressures. This algorithm is a classical approximation of the quantum mechanical model by Patchkovskii et al.1 and proven to be much faster than other commonly used methods. The gas adsorption calculations in carbon structures from tight-binding simulations demonstrate both a promising hydrogen storage capacity (1.33 wt% at 298K and 5 MPa) and a reasonable heat of adsorption (12-21 kJ/mol). To our knowledge, this is the first work to directly calculate hydrogen adsorption capacity in amorphous carbon. This work demonstrates that increasing the heat of adsorption does not necessarily increase the hydrogen uptake. In fact, the available adsorption volume is as important as the isosteric heat of adsorption for hydrogen storage in nanoporous carbons.