The interfaces of bubbles and droplets imbue foams and emulsions with extraordinary mechanical and chemical properties. The remarkably large interfacial area of these structures controls their thermodynamics and makes them practical and functional materials. When these interfaces are forced to touch, they can turn a dispersion of one fluid in another into a solid. These solid-like properties are evident in common household products such as shaving foam and mayonnaise, and our ability to control the fluid and solid properties of these materials is essential to their function. / Physics

The focus of this research is characterizing a new material system composed of carbon and graphite foams, which has potential in a wide variety of applications encompassing aerospace, military, offshore, power production and other commercial industries. The benefits of this new material include low cost, light weight, fire-resistance, good energy absorption, and thermal insulation or conduction as desired. The objective of this research is to explore the bulk material properties and failure modes of the carbon foam through experimental and computational analysis in order to provide a better understanding and assessment of the material for successful design in future applications. Experiments are conducted according to ASTM standards to determine the mechanical properties and failure modes of the carbon foam. Sandwich beams composed of open cell carbon foam cores and carbon-epoxy laminate face sheets are tested in the flexure condition using a four point setup. The primary failure mode is shear cracks developing in the carbon foam core at a critical axial strain value of 2,262 με. In addition to flexure, the carbon foam is loaded under tensile and shear loads to determine the respective material moduli. Computational analysis is undertaken to further investigate the carbon foam's failure modes and material characteristics in the sandwich beam configuration. Initial estimates are found using classical laminated plate theory and a linear finite element model. Poor results were obtained due to violation of assumptions used in both cases. Thus, an additional computational analysis incorporating three dimensional strain-displacement relationships into the finite element analysis is used. Also, a failure behavior pattern for the carbon foam core is included to simulate the unique failure progression of the carbon foam on a microstructure level. Results indicate that displacements, strains and stresses from the flexure experiments are closely predicted by this two parameter progressive damage model. The final computational model consisted of a bond line (interface) study to determine the source of the damage initiation, and it is concluded that damage initiates in the carbon foam, not at the bond line.

This study addresses the flexural performance of sandwich panels composed of a polyurethane foam core and glass fibre-reinforced polymer (GFRP) skins. Panels with and without GFRP ribs connecting the skins have been studied. While the motivation of the study was to develop new insulated cladding panels for buildings, most of the work and findings are also applicable to other potential applications such as flooring, roofing and light-weight decking. The study comprises experimental, numerical, and analytical investigations. The experimental program included three phases. Phase I is a comprehensive material testing program of the polyurethane core and GFRP skins and ribs. In Phase II, six medium size (2500x660x78 mm) panels with different rib configurations were tested in one-way bending. It was shown that flexural strength and stiffness have increased by 50 to 150%, depending on the rib configuration, compared to a panel without ribs. In Phase III, two large-scale (9150x2440x78 mm) panels, representing a cladding system envisioned to be used in the field, were tested under a realistic air pressure and discrete loads, respectively. The deflection under service wind load did not exceed span/360, while the ultimate pressure was about 2.6 times the maximum factored wind pressure in Canada. A numerical study using finite element analysis (FEA) was carried out. The FEA model accounted for the significant material nonlinearities, especially for the polyurethane soft core, and the geometric nonlinearity, which is mainly a reduction in thickness due to core softness. Another independent analytical model was developed based on equilibrium and strain compatibility, accounting for the core excessive shear deformation. The model also captures the localized deformations of the loaded skin, using the principals of beam-on-elastic foundation. Both models were successfully validated using experimental results. Possible failure modes, namely core shear failure, and compression skin crushing or wrinkling were successfully predicted. A parametric study was carried out to explore further the core density, skin thickness, and rib spacing effects. As the core density increased, flexural strength and stiffness increased and shear deformations reduced. Also, increasing skin thickness became more effective as the core density increased. The optimal density was 95-130 kg/m3. Reducing the spacing of ribs enhanced the strength up to a certain level; It then stabilized at a spacing of 2.9 times the panel thickness. / Thesis (Ph.D, Civil Engineering) -- Queen's University, 2010-09-21 16:29:00.315

No description available.

The monotonous and strenuous shoulder moving pattern during throwing may result in microtrauma and fibrous adhesions between the layers of fascia among athletes. In the last decade, self myofascial release (SMR) has gained good reputation as a way to treat these adhesions. However, there is limited data demonstrating the effects on upper body performance among athletes. PURPOSE: The purpose was to examine the effects from an acute bout of upper body SMR or from dynamic stretch (DS), on shoulder range of motion (ROM), throwing velocity and throwing accuracy. Also to examine correlations between shoulder ROM and throwing velocity/accuracy and between playing experience (PE) and changes in throwing velocity/accuracy and ROM. METHODS: 20 elite male handball players (age 20 ± 5 years, weight 84 ± 9 kg) were included in the study. The study had an experimental cross-over design in which participants first performed baseline measures. They also performed SMR and DS in two different trials. The trials were supervised and separated by 14 days. During SMR, the athletes performed a series of foam rolling exercises during two minutes for the muscles surrounding the shoulder joint. The same muscles were stretched for two minutes during the DS trial. Directly after foam rolling and DS, shoulder ROM, throwing velocity and throwing accuracy were measured using a gravity reference goniometer, radar gun and a high speed videocamera. ANOVA with repeated measures and t-tests were used to analyze differences between and within groups. RESULTS: There were no statistically significant differences in either shoulder ROM, throwing velocity or throwing accuracy between the three trials. There was a moderate correlation between shoulder extension and mean accuracy (r = 0.62; p = 0.004) after DS. When dividing the group into high and low experienced players, among the players in the PE-low group, the most experienced players elicited the greatest increase in peak throwing velocity after DS (r = 0.58; p = 0.10). Change in peak accuracy showed moderate but conflicting correlations after SMR (r = -0.53; p = 0.09) and DS (r = 0.50; p = 0.11) for the players in the PE-high group, indicating a better result after SMR. CONCLUSION: An acute bout of upperbody SMR does not affect ROM and does not improve throwing velocity or throwing accuracy compared to baseline or DS among elite male handball players. Nor could any correlation between ROM and throwing velocity or throwing accuracy be observed. The associations between PE and throwing performance was inconclusive. Further studies is needed to define if PE should be taken into consideration when using SMR or DS in order to improve throwing performance.

Background: Self-myofascial release is widely used by athletes but the scientific evidence of its supposedly positive effects is limited. This study was conducted to investigate the effects of foam rolling as a warm-up routine in comparison with a dynamic stretching routine and how it may affect the jumping performance among subjects familiar with weight training. Aim: The aim of this study was to investigate the acute effect of foam rolling vs. a standardized dynamic stretch warm-up routine on jumping performance. Method: Twelve subjects, mean (SD) age 25.1 (± 3.0) years, participated in a randomized, controlled, crossover study. All subjects completed a standardized foam rolling (FR) and a dynamic stretch (DS) warm-up routine on separate days of testing. Squat jump (SJ), counter movement jump (CMJ) and loaded counter movement jump (L-CMJ) all performed bilaterally and unilaterally were conducted to investigate the acute effect of the two warm-up routines. A dependent T-test was used to investigate differences between the warm-up routines. Results: A statistical significant difference in favor of the DS was found for SJ performed bilaterally among males (p = 0.009). The mean (SD) jumping height for SJ FR was 35.6 (± 4.7) cm and for SJ DS 37.9 (± 5.2) cm. The male group also improved more in L-CMJ performed on the right leg with an external load of 54kg after DS compared to FR. No other statistical significant differences were found between the two interventions. A near statistical significant difference was found for SJ performed bilaterally for the total sample (p = 0.057) also in favor of the DS. The mean (SD) jumping height for SJ FR was 29.3 (± 8.7) cm and for SJ DS 30.5 (± 9.9) cm. Conclusion: Findings from this study supports a dynamic stretch warm-up routine prior to performing high intensity bilateral plyometrics instead of a foam rolling warm-up routine. However the data was inconsistent and more research with larger sample sizes is needed to further investigate the possible effects of foam rolling as a warm-up routine on jumping performance performed both bilaterally and unilaterally.

Macrophage foam cells are the major culprits in atherosclerotic lesions, having a prominent role in both lesion initiation and progression. With atherosclerosis being the main factor underlying cardiovascular complications, there is a long-standing interest on finding ways to reverse lipid buildup in plaques. Studies have shown that promoting reverse cholesterol transport (RCT) from macrophage foam cells is anti-atherogenic because it alleviates the cholesterol burden of the plaques. The goal of this thesis was to gain insight into the mechanisms that govern cholesterol efflux from macrophage foam cells. The first part of this study looked at the ability of different oxysterols to promote cholesterol efflux in unloaded as compared to lipid-loaded macrophages, and our major finding here is that epoxycholesterol decreases efflux in lipid-loaded macrophages. It appears that epoxycholesterol does so by impairing the release cholesterol from its cellular storage site, the lipid droplet (LD), where it accumulates in the form of cholesteryl esters (CE). These results highlighted the importance of cholesterol release from LDs for efflux; indeed, this process is increasingly being recognized as the rate-limiting step for RCT in vivo. Subsequent experiments aimed at elucidating the mechanisms that govern LD CE hydrolysis in macrophage foam cells lead to the discovery of a novel pathway involved in cholesterol efflux. Macrophage CE hydrolysis is classically defined as being entirely dependent on neutral CE hydrolases. In the second part of this study, we demonstrate that in addition to the canonical CE hydrolases, which mediate neutral lipid hydrolysis, lysosomal acid lipase (LAL) also participates in the hydrolysis of cytoplasmic CE. Autophagy is specifically triggered in macrophages by atherogenic lipoproteins and delivers LD CE to LAL in lysosomes, thus generating free cholesterol for efflux. This autophagy-mediated cholesterol efflux is a process that is primarily dependant on the ABCA1 transporter and, importantly, is important for whole-body RCT. Overall, the studies presented in this thesis support that macrophage LD CE hydrolysis is rate-limiting for cholesterol efflux and shed light on the mechanisms of cholesterol mobilization for efflux in macrophage foam cells.

This thesis examines the development of a high efficiency heat pump system using thermoelectric (TE) and reticulated metal foam (RMF) technologies to power a vehicle`s battery thermal management system. The focus is split into two areas: first a review of TE???s sourcing or removing heat, second an examination of compact heat exchanger (HX) design. Five TE suppliers were investigated to understand the performance and limitations of their TE modules. Testing showed the Kyrotherm product to be superior so it was used as a design basis. RMF???s are known to be an effective means to improve the performance of compact heat exchangers, thus HX???s were evaluated with RMF foams compressed to varying densities in order to understand their potential in conjunction with thermoelectric devices. Experimental results showed performance was limited due to adequate bonding, yet still on par with the highest efficiency technologies currently on the market.

This study investigates the possibility of fabricating periodic cellular materials (PCMs) via the lost foam casting (LFC) process using aluminum alloy A356 and magnesium alloy AZ91. This approach combines the structural efficiency of PCM architectures with the processing advantages of near-net-shape LFC. An initial feasibility study fabricated corrugated A356 panels. This was followed by a study of casting variables such as pattern design, vacuum assistance, and alloying additions in order to improve the fillability of the small cross-section struts. Finally, integrated pyramidal sandwich panels having different relative densities were subjected to artificial aging treatments and subsequently tested in uniaxial compression. The A356 PCMs experienced a continuous increase after yielding while the AZ91 PCMs exhibited strut fracture after peak strength. The results showed the compressive yield strengths of this study are comparable with those previously reported PCMs produced by different fabrication methods.

Two novel hybrid materials for use in sandwich cores of structural materials are designed, manufactured and mechanically tested. Each material is a hybrid of metal and polymer foam. One set of hybrids is fabricated using an aluminium micro-truss filled with varying densities of polyurethane foam. Increases up to 120% in stiffness, 372% in strength, 740% in resilience and 106% in impact energy over the aluminium micro-truss are obtained from compression and impact testing. Furthermore, the stiffness of these hybrids can be tailored according to the density of the polyurethane foam. Another set of hybrids is fabricated using a rapid prototyped ABS polymer truss that is foamed and electroplated with nanocrystalline nickel. Increases up to 1525% in stiffness, 1165% in strength and 650% in energy absorption over the foamed ABS truss are obtained. Furthermore, the gain in strength, stiffness and energy absorption outweigh the gain in density in these hybrid materials.