No abstract provided / Thesis / Master of Science (MSc)

Osteoporosis is a disease characterized by reduced bone strength leading to an increased fracture risk. Current diagnostic best practice involves measuring the bone mineral density (BMD) of a patient using absorptiometric imaging tools. This measurement is compared to a known value in order to compute fracture risk. This assessment of bone quality is based solely on the BMD, which has been shown to make up only a portion of the explanation of bone strength. The extent of BMD's contribution to bone strength is also extensively debated and widely varying in the scientific literature. This thesis work encompasses a preliminary investigation into factors in addition to density that contribute to bone strength. The geometric and material properties of 21 vertebral functional unit specimens were measured using dual energy absorptiometry (DXA), pQCT (peripheral quantitative computed tomography) and HCT (helical computed tomography) techniques. The strength of the functional units was assessed through mechanical testing under compressive loading conditions. These measurements were amalgamated into multiple linear regression models to characterize vertebral strength in terms of a few key variables. The model developed for failure load had a coefficient of determination of 0.725 and indicated that the volume of the vertebral body as well as the cross-sectional area of the cortical region were significant in the explanation of failure load. A model was also developed for stress at failure which indicated that the vertebral body height and cortex concavity were important parameters. The coefficient of determination for this model was 0.871. The goal of this study was to provide a foundation on which further investigation into the explanation of bone strength could be built. Ultimately, a better understanding of the parameters that affect bone strength will provide a basis for more accurate clinical tools for the diagnosis of osteoporosis. / Thesis / Master of Applied Science (MASc)

Resistance exercise training (RET) can lead to muscle hypertrophy; however, the relative contribution that exogenous (protein supplementation and specific training variables) versus endogenous (biology inherent to the individual) factors have on RET-induced muscle hypertrophy is controversial. In Study 1, we provided an evidence-based conclusion that protein supplementation during periods of RET results in a small but statistically significant increase in RET-induced muscle hypertrophy. In Study 2, we corroborate previous research and observed that the amount of mass lifted per repetition (load) did not determine RET-induced muscle hypertrophy in resistance-trained men when RET was performed to volitional fatigue. In Study 4, we observed similar muscle fibre activation following resistance exercise with lighter versus heavier loads when both were lifted until volitional fatigue. In Studies 2 and 3, we observed no relationship between circulating anabolic hormones (e.g., testosterone) and RET-induced muscle hypertrophy. Nonetheless, in Study 3, we found significantly greater muscle androgen receptor content in the top versus the bottom quintile of respondents for muscle hypertrophy following 12 weeks of RET indicating that androgen receptor content, and not circulating androgen concentration, may be an important determinant of hypertrophy. Finally, in Study 5, we observed that RET-induced muscle hypertrophy was an consistent within an individual (independent of load and limb) but considerably different between participants. Together, these data suggest that the exogenous factors we studied – protein supplementation and load (when RET was performed to volitional fatigue) – had a relatively small influence on RET-induced muscle hypertrophy. In contrast, we found that endogenous variables, such as intramuscular androgen receptor content and likely other genetic influences, appear to contribute more to the significant heterogeneity seen in RET-induced muscle hypertrophy. Future research in this area should prioritize understanding the biology that underpins the individual variability in RET-induced muscle hypertrophy. / Thesis / Doctor of Philosophy (PhD) / Resistance exercise training (RET) increases muscle size (hypertrophy); however, the relative influence that protein supplementation, specific training variables, and individual (genetic) variation have on the RET-induced hypertrophy is controversial and largely unknown. Broadly, data in this thesis show that protein supplementation slightly augments RET-induced hypertrophy, and that the magnitude of RET-induced hypertrophy may be related to the number of androgen (e.g., testosterone) receptors inside an individual’s muscle. In contrast, we found that neither load nor hormones affect RET-induced hypertrophy. Interestingly, data in this thesis also show that RET-induced hypertrophy is consistent within an individual but varies considerably between people, which illustrates the greater influence that individual variation has on RET-induced hypertrophy. We conclude that when RET is performed with a high degree of effort, protein supplementation and specific training variables confer a relatively small benefit on RET-induced hypertrophy compared to the influence of biological variability between people.

A technique for obtaining values of the stress intensity factor from photoelastic data for three dimensional cracked body problems is described. The stress intensity determination is accomplished without resorting to stress separation methods through employing an expression for the maximum in-plane shearing stress consisting of a singular term which is related to the stress intensity factor and a constant term which is related to the regular stress field. The technique itself identifies the zone dominated by the singular stresses. The effects of using artificial cracks and a model material which exhibits a Poisson's ratio v = 0.5 are assessed. The application of the technique to a variety of technologically important three dimensional problems is illustrated for Mode I loading and combined Mode I - Mode II loading. The major advantages and limitations of the technique are discussed. Replications of identical test geometries indicate a scatter of the stress intensity factor determination of less than ± 5%. It is concluded that the method is a valid means for the independent determination of values of the stress intensity factor. / Ph. D.

Carbon/epoxy laminates are receiving greater attention by the infrastructure, marine, and offshore oil industries due to the need for superior performance capabilities. Such applications generally involve subjecting materials to harsh temperature and moisture conditions. The objective of this study was to provide a greater understanding of how temperature and moisture affect the strength and fatigue behavior of carbon/epoxy composites and the issues involved in modeling these effects. Results from thermal analysis and quasi-static testing on neat resin and unidirectional laminates as a function of temperature and moisture are presented which provide insight into how material properties vary with temperature and moisture and form the inputs necessary to evaluate composite strength and damage models. Fatigue life and damage accumulation testing results provide further insight into the effects of temperature and moisture and also provide a means for model validation. Generally, composite strength was found to be compromised by temperature but enhanced with moisture, while fatigue life was reduced by both temperature and moisture. Crack density with fatigue cycles was found to decrease with temperature but increase for immersed fatigue. Testing also revealed discrepancies between the edge replication and radiography methods for determining crack density. The analytical phase of the work considered a composite strength model and a damage evolution model to predict crack density. The composite strength model was found to provide an accurate dry, room temperature prediction which could be extended to an accurate prediction of wet specimen strength, but the results at elevated temperature fell conservative. The validation of the damage model proved inconclusive as it was found that the results are very sensitive to quantities such as thermal residual stresses and first ply failure. Currently, no reliable methods are available in the literature to determine these values accurately. However, the model was able to predict the decrease in crack density at elevated temperatures. The increase in crack density for immersed fatigue was not predicted. Overall, the study revealed that a more basic understanding of "in-situ" ply properties are needed before one can consider the use of predictive models in practical applications, especially in varying environments. / Ph. D.

Porous silica-based nanocomposites are promising ceramics, as they exhibit high specific surface area, highly porous network, and a surface that can be easily functionalized. This dissertation describes the results of a study on the formation and properties of porous silica nanoparticle-based composites, using techniques of freeze casting and sintering. Kaolinite platelets and silica nanorods were added into the nanoparticle system, and their effects on modifying the porous microstructures and physical properties were investigated. During freeze casting, homogeneous microstructures with highly interconnected porosity are fabricated. Kaolinite addition results in large and more interconnected pores, while added silica nanorods cause a pore morphology evolution from circular to elongated spherical pores with increasing aspect ratio. The specific surface areas (area/mass) of the particles are conserved during freeze casting and values for the resulting composites can be accurately predicted using the area and mass of the components assuming conservation of area. Both kaolinite platelets and silica nanorods effectively improved the strength of the freeze cast green composites as they distribute any applied stress over a larger portion of the sample. Upon sintering, added kaolinite is found to modify the sintering behavior of the silica nanoparticles and a transitioning interfacial phase is identified when sintering temperature is above 1250 °C. This new phase contributes to the further enhancement of strength and this strengthening effect depends on composition and initial solids loading. After sintering at 1250 °C for 1 h, a ceramic containing 10 vol% kaolinite and 8 vol% silica has a maximum strength while maintaining a ~69% porosity. The kaolinite-silica composites with lower solids loading exhibit faster sintering (e.g. larger shrinkage, more extensive thickening of the pore walls), which, in turn, results in a rapid increase in mechanical strength. Based on the understanding of the composite properties and the underlying principles, a novel method for creating nanocomposites with precisely controllable specific surface area is developed. With repeated nanoparticle suspension infiltration, freeze drying, and sintering, the specific surface area can be varied from less than one to well over 100 m2/g, demonstrating potential application as liquid membranes. / Ph. D.

As advances in solid rocket technology push rocket motors to more extreme operating speeds and temperatures, it becomes increasingly important to have well-designed material systems capable of surviving these harsh conditions. One common component in these systems is the use of a fiber- and particle-reinforced EPDM insulation layer between the motor casing and the solid fuel to shield the casing from the temperatures of the burning fuel and from the high velocity of gas particles traveling within the motor. This work studies several insulation materials to determine which exhibits the highest shear strength after being charred. Double-notch shear test specimens of three materials, ARI-2718, ARI-2719, and ARI-2750, were charred and tested to measure the failure strength of each charred material. The ARI-2750 showed the highest shear strength when loaded along the material orientation, but the ARI-2719 was strongest when transversely loaded. The strength measurements for ARI-2750 were highly sensitive to loading direction, unlike ARI-2718 and ARI-2719. Extensive scanning electron microscopy to identify correlations between shear strength and microstructure revealed that the amount of fiber orientation and amount of residual matrix material may have significant impacts on charred shear strength in these materials. / Master of Science

It has been observed that the normal process of aging is associated with a decline in muscle strength and mass. It has also been observed that total body potassium and intracellular water (ICW) decrease with age, reflecting a loss of body cell mass (BCM), 60% of which is the skeletal muscle. It is generally accepted that traditional high-intensity strength training (ST) regimens can not only attenuate, but in some cases, reverse some of these aging-related changes. Periodization, a nontraditional approach to strength training, has been demonstrated to stimulate more rapid increases in muscle strength than traditional approaches in young adults; however, it has not been comprehensively evaluated in postmenopausal women. Investigators have consistently reported an increase in muscle strength in older adults undergoing both short- and long-term traditional ST programs. It is fairly well accepted that early increases in muscle strength are attributable to neurologic adaptations. There has been less consistency in the literature regarding the timing and nature of changes in muscle quality and mass with ST. Although several investigators have reported increased muscle protein synthesis rates as early as 2 weeks after ST initiation in older adults, the majority of published reports support the notion that significant NET gains in intracellular protein, and thus, gains in muscle mass/volume/hypertrophy do not occur before 9-10 weeks. Changes in intracellular water, which would be expected to occur with changes in intracellular protein, have not been studied during short-term ST interventions in older adults. Bioimpedance spectroscopy (BIS) has been validated as a field technique to accurately measure ICW (and BCM) changes in HIV infected individuals. The primary aim of the current study was to determine if muscle strength would increase in postmenopausal women undergoing a novel (periodized) ST intervention of 10 weeks duration. A secondary aim was to determine if BIS would detect a change in ICW in the study subjects from baseline to study conclusion. Study participants were eleven, healthy postmenopausal women between the ages of 60 and 74 (mean age: 65 ± 4.4 y) who had not engaged in ST in the six months preceding the study. ICW and muscle strength were assessed at baseline and at study conclusion. The ST program was conducted twice a week for 10 weeks at the Senior Center in Blacksburg, VA. Participants performed seven different exercises incorporating upper body and lower body muscle groups. The women performed one set of 8-12 repetitions at an intensity of 80% of one repetition maximum (1 RM) the first week, progressing to 2 sets of 8-12 repetitions at the same intensity during the second week. The remaining weeks consisted of three sets of 8-12 repetitions, performed at an intensity of 80%, 75%, and 70% of their current 1 RM, respectively. One RM was reassessed every other week. The major result from this study was that muscle strength of all trained muscle groups increased in postmenopausal women undergoing 10 weeks of pyramid ST (P<0.05). In addition, the pyramid ST protocol utilized in this study was well-tolerated and resulted in no injuries in any of the older women in the study, indicating that this approach may be used safely in this population. Mean ICW measured by the field method BIS did not change over the course of the study. This result was consistent with other published data reporting no changes in lean body mass or muscle volume/area by more sophisticated techniques. / Master of Science

Stress is a concept that can be studied using a variety of theoretical approaches, with a focus on the individual’s perceptions, the external stressor, or the physiological reactions of stress responding. However these approaches are often used independently, when they can be used complementarily to understand the nuanced relationship between the individual and the situation when appraising stressors as challenges or threats. The current study examined the relationship between individual differences in perceptions, situational strength (both as a categorical and a continuous predictor), and physiological reactions in a leadership task. Situational strength and leadership self-efficacy were found to interact, such that those high is LSE reported more appraisals of challenge as situational strength increased. / Master of Science / Stress is a widely known concept that has been studied in various ways (individual perceptions, situational characteristics, physiology, etc.). However these approaches are often used independently, when they can be used together to more fully understand the process of how individuals appraise stressors. The current study examined the relationship between the previously mentioned approaches within a leadership task. Situational strength and leadership self-efficacy (LSE), or one’s perceived capabilities to perform leadership duties, were found to interact, such that those high is LSE reported more appraisals of challenge as situational strength increased.

The most common fastening technique that is used to connect the components of wooden pallets together are helically or annularly threaded pallet nails. Pallet nails create a strong durable connection and increase manufacturing efficiency for a low cost. However, nails can also cause iron staining, wood splitting, and when exposed can cause product damage or personnel injury. Using adhesives could be a solution to these problems, but only if the adhesives' strength and durability is comparable or higher than nails. The objective of the study was to investigate the tensile and shear strength of pallet connections secured using commercially available wood adhesives and compare their performance to pallet connections secured using common pallet nails. The lowest pre-compression pressure resulted in the best tension and shear performance for a solvent based construction adhesive (SBCA). The pre-compression pressure did not have any practical effect on the performance of the two-part emulsion polymer isocyanate (EPI) adhesive. Samples made with the solvent based construction adhesive (SBCA) had greater strength and energy at failure than nailed samples. Meanwhile, the samples made with the two-part emulsion polymer isocyanate (EPI) adhesive had equal or greater strength than nailed samples, except for during the tension parallel to the grain tests in which they had equal or lower strength. / MS / The most common technique used to connect the components of wooden pallets together is nails. Pallet nails create a strong connection with high manufacturing efficiency for a low cost. However, nails can cause iron staining, wood splitting, and when exposed can cause product damage or personnel injury. Using adhesives could be a solution to these problems, but only if the adhesives’ strength and durability is comparable or higher than nails. The objective of this study was to investigate the tensile and shear strength of pallet connections when secured using commercially available wood adhesives and compare its performance to pallet connections secured by using common pallet nails. The lowest pre-compression pressure tested resulted in the best overall performance for a solvent based construction adhesive (SBCA); meanwhile, pre-compression pressure did not have any practical effect on the performance of the two-part emulsion polymer isocyanate (EPI) adhesive tested. Therefore, using a lower pre-compression pressure would provide adequate performance and could also improve the ease of manufacturing and potentially reduce overall costs. Based on the tests conducted it was found that the solvent based construction adhesive (SBCA) demonstrated the best performance of all connection methods and could be a potential replacement for nails. More tests, such as weathering and impact, should be conducted to determine the full limitations of the adhesive in use.