No description available.

No description available.

No description available.

Ice hockey players are at a high risk to sustain a concussion. Most of the concussion-inducing hits are to the jaw region, nevertheless, most players do not wear any protective gear shielding the jaw.  This parametric study used finite element simulations in LS-Dyna to evaluate the potential of foam materials in a jaw guard that could be attached to a helmet to reduce the concussion risk.  Here, it was investigated how nine different foam materials influence the ability of the jawguard to protect against concussion. Furthermore, aspects like foam thickness, shell thickness, and the impacting object were evaluated. In a second part, the formerly used HIII head model was exchanged with the KTH HBM, a FE model with a detailed representation of a jaw, and it was looked at how a movable jaw affects the head kinematics. Stiffer foams with a certain stress-strain behavior tend to aid best in energy absorption in the simulated crash scenarios and therefore lower the risk of sustaining a concussion. Impact angle and location influence the result significantly. Two simulated impacts show a decrease in concussion risk by up to 8.2\% and 6.9\% respectively when the jawguard was implemented, while the two other impacts resulted in an increase in concussion risk. Shell and foam thickness variation results depend mostly on the impact scenarios. However, it was found that a soft impactor helps tremendously in avoiding concussions. The hits on the KTH HBM tend to produce higher linear and angular accelerations but no significant difference is seen in angular velocity.  In conclusion, using stiff foams in ice hockey jawguards is a promising approach to attenuate impact energy caused by a collision during an ice hockey game. However, the effect of the jawguard on the concussion risk is very sensitive to the impact location and direction.

<p> The foaming process has received increased attention by the rotational molding industry in recent years. The use of metallocene catalyzed polyethylenes for producing a cellular structure is a new development in rotational molding. The objective of this work was to investigate the effects of different chemical blowing agents, resin properties and processing conditions on the structure of foamed metallocene polyethylene and obtain a fundamental understanding of the parameters governing the foam structure and part properties.</p> <p> An experimental study was conducted to produce metallocene polyethylene foams in dry-blending-based rotational foam molding. The physical and cell structure properties of the final foamed parts were examined. The critical processing parameters that optimize the foam structure have been identified through adjustments to the molding conditions.</p> <p> The foaming performance of exothermic and endothermic chemical blowing agents were examined and it was revealed that selecting an appropriate chemical blowing agent was crucial as the foam structure depends significantly on the properties of the blowing agent. Exothermic blowing agents resulted in greater foam density reduction compared to endothermic blowing agents.</p> <p> The effect of rheological properties on the foaming process and foam properties was also examined. Rotomolding experiments were performed in monolayer and skin-foam moldings. Observations indicated that the final foam properties were profoundly influenced by the rheological properties of the polymer materials. There was a good correlation between the foam properties produced in both monolayer and two layer moldings. It was discovered that polymer materials with higher extensional viscosity could provide a promising foaming performance at different processing conditions.</p> <p> The effect of the surface tension of the polymer materials was investigated. It was found that type of reaction of the blowing agent (exothermic/endothermic) and composition of gas generated determine whether the surface tension of the resin contributes to the trend of changes in foam properties.</p> / Thesis / Master of Applied Science (MASc)

The development of postural stability in children with and without visual impairments (VI) was compared. Thirty eight subjects (4- 12 years old) without VI and 12 subjects with VI (5- 12 years) took part. Stability was measured in 4 quiet standing tasks (normal or foam surface, eyes open (EO) or eyes closed (EC)) and by measuring stability limits (SL) in the anterio-posterior (a-p) and lateral (lat) planes. Results for control subjects were compared using Pearson correlation coefficients, analysis of variance, and analysis of covariance (height as the covariate). For quiet standing tasks, outcome parameters were the standard deviation (SO) of the centre of pressure (CP) in the a-p and lat planes, and mean velocity (vel) of CP movements. For the leaning tasks, SL was measured (normalized to the base of support) in the a-p and lat planes, and SL was compared to CP. Individual results for subjects with VI were compared qualitatively to control subjects. For control subjects, stability increased with age. Subjects with VI were less _stable than controls on all outcome parameters. Differences between groups were more apparent as age increased, particularly for EO conditions. This could indicate a slower pattern of development for subjects with VI compared to controls. The groups were different both in the EO and EC conditions, indicating that postural control with EC is not the same as postural control with a VI, and that vision is important to the development of postural control in children. / Thesis / Master of Science (MSc)

No description available.

This study examined several features of flexible polyurethane foams from a structure-property perspective. A major part of this dissertation addresses the issue of connectivity of the urea phase and its influence on mechanical and viscoelastic properties of flexible polyurethane foams and their plaque counterparts. Lithium salts (LiCl and LiBr) were used as additives to systematically alter the phase separation behavior, and hence the connectivity of the urea phase at different scale lengths. Macro connectivity, or the association of the large scale urea rich aggregates typically observed in flexible polyurethane foams was assessed using SAXS, TEM, and AFM. These techniques showed that including a lithium salt in the foam formulation suppressed the formation of the urea aggregates and thus led to a loss in the macro level connectivity of the urea phase. WAXS and FTIR were used to demonstrate that addition of LiCl or LiBr systematically disrupted the local ordering of the hard segments within the microdomains, i.e., it led to a reduction of micro level connectivity or the regularity in segmental packing of the urea phase. Based on these observations, the interaction of the lithium salt was thought to predominantly occur with the urea hard segments, and this hypothesis was confirmed using quantum mechanical calculations. Another feature of this research investigated model trisegmented polyurethanes based on monofunctional polyols, or "monols", with water-extended toluene diisocyanate (TDI) based hard segments. The formulations of the monol materials were maintained similar to those of flexible polyurethane foams with the exceptions that the conventional polyol was substituted by an oligomeric monofunctional polyether of ca. 1000 g/mol molecular weight. Plaques formed from these model systems were shown to be solid materials even at their relatively low molecular weights of 3000 g/mol and less. AFM phase images, for the first time, revealed the ability of the hard segments to self-assemble and form lath-like percolated structures, resulting in solid plaques, even though the overall volume of the system was known to be dominated by the two terminal liquid-like polyether segments. In another aspect of this research, foams were investigated in which the ratios of the 2,4 and 2,6 TDI isomers were varied. The three commercially available TDI mixtures, i.e., 65:35 2,4/2,6 TDI, 80:20 2,4/2,6 TDI, and 100:0 2,4/2,6 TDI were used. These foams were shown to display marked differences in their cellular structure (SEM), urea aggregation behavior (TEM), and in the hydrogen bonding characteristics of the hard segments (FTIR). Finally, the nanoscale morphology of a series of 'model' segmented polyurethane elastomers, based on 1,4-butanediol extended piperazine based hard segments and poly(tetramethylene oxide) soft segments, was also investigated using AFM. The monodisperse hard segments of these 'model' polyurethanes contained precisely either one, two, three, or four repeating units. Not only did AFM image the microphase separated morphology of these polyurethanes, but it also revealed that the hard domains preferentially oriented with their long axis along the radial direction of the spherulites which they formed. / Ph. D.

No / This study presents the data elements to develop a new processing route to transform elastomeric waste residue (particulates) into acoustic and thermal insulation materials that can compete with commercial products. The approach is to bind these grain and fibre particulates with a foaming polyurethane or a similar polymer, the chemistry of which can be manipulated to control the structure stiffness and the evolution of the foaming gas into open or closed cells. Here the study uses two examples of such residues, tyre and carpet shreds both composed of fibres trapping grains of either rubber or PVC. Compounds were made from these systems with different PU binders and the structural properties (density, porosity, air flow resistivity, tortuosity and stiffness) and performance properties (sound absorption, sound transmission, impact sound insulation and thermal conductivity) were measured as a function of binder loading and chemistry. The data obtained show clearly that performance can be tailored by tailoring structural properties resulting with materials that match or even outperform commercial products. The data set obtained here can be usefully exploited with available acoustic and thermal insulation materials model to take the approach further and extended to other waste systems.

With the need for stealth in defense applications steadily increasing, noise reduction continues to play an important role in the world of aeronautics. With the ever increasing number of small UAV flight vehicle designs and their stringent weight requirements, acoustic solutions become progressively more complex. This thesis investigates the use of refractory foam, a new class of porous material, for designing effective silencers for small IC engines. The solution must be lightweight, compact, conformable, and capable of handling the rigors of flight. Throughout the course of this research, many silencer designs were fabricated to take advantage of refractory foam technology. These silencer designs were then tested against existing designs using both anechoic and outdoor testing techniques. These results proved refractory foam to be a superior broadband noise absorber that can survive harsh flight environment. Silencer designs using this material showed overall improvements in the areas of noise reduction, weight, size, and backpressure, compared to commercial designs. The final silencer design boasted an Aweighted overall sound pressure level that was 12.1 dBA lower than the reference case. This result was accomplished using nearly half the volume required by other designs to attain similar results. / Master of Science