This paper presents the behaviour and design of axially loaded elliptical steel hollow sections filled with normal and high strength concrete. The experimental investigation was conducted with three nominal wall thickness (4mm, 5mm and 6.3mm) and different infill concrete cube strengths varied from 30 to 100 MPa. The effect of steel tube thickness, concrete strength, and confinement were discussed together with column strengths and load-axial shortening curves were evaluated. The study is limited to cross-section capacity and has not been validated at member level. Comparisons of the tests results together with other available results from the literature have been made with current design method used for the design of composite circular steel sections in Eurocode 4 and AISC codes. It was found that existing design guidance for concrete filled circular hollow sections may generally be safely applied to concrete filled elliptical steel tubes.

This thesis outlines a methodology for formatting and applying stress models, collecting visco-elastic material properties, and presenting the material data for use in adhesive joint designs. There are a number of models/theories that can be applied to the design of Pressure Sensitive Adhesive (PSA) joints. Unfortunately, few design engineers are familiar with these models and the models are not formatted in a manner that can easily be applied to joint designs. By developing a format that is based on the existing knowledge of the designer and presenting them in a familiar manner the theories/models can easily be used in joint designs. This technique was demonstrated with Beam-on-Elastic Foundation, Shear Lag, and Shape Factors. Design examples successfully demonstrated the application of all of these models in the analysis and design of simple adhesive joints. The material properties of PSAs are a function of loading/displacement rate, temperature, relative humidity, and stress state. The Arcan_m fixture was used to test VHB™ 4950 over a range loading and stress states including fixed load and displacement rates. Several bond widths were tested to determine the extent of the shape factor effect. A second fixture was used to determine the impact of gradient-tensile stresses on the failure strength. All of the collected data was used to generate design plots. The strength data was presented as allowable strength envelopes with respect to rate. The moduli were calculated from the load-displacement data and plotted with respect to the displacement rate. The failure strength from the fixed load and displacement data were used to transform from one loading case to the other and a plot was generated. These three plots were used in the design and analysis of several adhesive joints. The methods demonstrated in this thesis show a great deal of promises as a design tool, but there is still a large amount of work to be done. The design space for this material is much larger than what was covered by this work. Additional strength testing needs to be conducted to fully characterize the material for all key applications. The principle of time-temperature superposition, beam-on-elastic foundation, shear lag, and shape factors all need to be validated for this material. / Master of Science

No description available.

The purpose of this study was to examine the acute effects of cycling exercise at different intensities and rest intervals on strength performance. Ten males, engaged in concurrent training for at least one month prior to testing, comprised the subject group for this study. Results show only leg press torque and leg press work to be decreased after cardiorespiratory exercise of moderate intensity. Leg extension average power, chest press torque, chest press power, and chest press work after cycling were not decreased from pre-exercise values. No significant effects were found for exercise intensity, testing times, or intensity by testing times. These results indicate that lower body strength is decreased by cycling and that one hour is not sufficient to restore leg strength.

Scientists have been well aware of the complexity of Martian and lunar regoliths. There are vast unexplored areas on both, the Moon and Mars, as well as uncertainties in our understanding of the physicochemical properties of their regoliths. Lunar and Martian regoliths differ from terrestrial soils in that they appear granular, but are expected to contain some cohesion. As such, cohesion in regolith poses challenges for future space operations, more specifically for landing, settlement, and mobility purposes. The ability to induce prescribed levels of cohesion in regolith simulants and reliably measure it would allow scientists to evaluate space technology limitations under different operational scenarios on Earth prior to a mission. Therefore, the objectives of this research were to (1) develop methods to induce prescribed levels of cohesion in dry granular media, and (2) evaluate accessible and reliable testing methods to measure cohesion. We developed and evaluated several methods to induce cohesion in two types of dry sand, F-75 silica sand and generic play sand. The methods to induce cohesion included play sand mixed with sugar-water, polymeric sand, and nanocellulose fibers, as well as F-75 sand mixed with polydimethylsiloxane, polyvinyl acetate, crystalline silica, agar, zero-valent iron, adhesive spray, and sand surface modification using a plasma gun. Each method was assessed for advantages and disadvantages, and laboratory specimens produced using the most promising methods were tested at different compositions and densities to measure cohesion. The laboratory methods used to measure the cohesion included direct shear test, simple direct shear test, and vertical cut test. The results from these tests were then compared to tensile strength tests, using a split box test. In addition, these tests were also performed on lunar simulants JSC-1A and GRC-3 at different densities. The direct shear apparatus was available, but the other three devices were fabricated as part of this work. Based on the research results, simple methods to potentially induce low levels of cohesion in dry granular media are suggested along with suitability of laboratory methods to measure the added cohesion.

This in vitro study evaluated the bond and compression strength of cemented leucite reinforced glass ceramics in bovine tooth enamel, comparing three etching times with hydrofluoric acid 10% of the ceramic surface (20, 60 and 90 seconds) and two adhesive treatments (adhesive system + silane and universal adhesive system). For the bond strength test, 120 ceramic cylinders (2mm diameter x 2mm length; n=20) were etched and cemented (80m thick) in enamel with a dual resin cement, varying the adhesive treatment, obtaining the groups: UEXC20s, UEXC60s, UEXC90s, USBU20s, USBU60s, USBU90s. After 24 hours, the shear bond strength test was performed on a universal test machine (0.5mm/min, 50kgf). For the compression test, 30 ceramic plates (5x5mm with 1mm thick, n=5) were etched, received the same adhesive treatments and were cemented (80m) in enamel, obtaining the following groups: CEXC20s, CEXC60s, CEXC90s, CSBU20s, CSBU60s, CSBU90s. After 24 hours of cementation, the compression test (0.5mm/min, 500kgf) was performed. Statistical analysis was performed using two-way ANOVA and Tukey test (=.05). For the shear bond strength test significant differences were found among the adhesives (p<.05). For the etching times there were no differences (p=.059). However, there was a significant interaction between the adhesives and the etching times (p=.021). At 60 seconds, the Silane + ExciTE F DSC Adhesive presented the highest bond strength values (47.53±16.70Mpa). And at 20 seconds, the Universal adhesive presented the lowest bond strength values (27.72±10.76Mpa). For the compression test there were no significant differences between the adhesives (p=.571) and between the times (p=.154). The group that presented the highest values of compression force was the Universal adhesive at 60 seconds (1757.89±200.47N). The lowest values were also the Universal adhesive, but at 90 seconds (1213.30±546.34N). The study concluded that the silane associated with the ExciTE F DSC adhesive showed the highest bond strength values at the etching time of 60 seconds with 10% hydrofluoric acid, without compromising the compressive strength of the leucite reinforced ceramic. / Este estudo in vitro avaliou a resistência de união e compressão da cerâmica reforçada por cimentada em esmalte de dentes bovinos, comparando-se três tempos de condicionamento com ácido fluorídrico 10% da superfície cerâmica (20, 60 e 90 segundos) e dois tratamentos adesivos (sistema adesivo + silano e sistema adesivo universal). Para o teste de resistência de união (U), 120 cilindros cerâmicos (2mm diâmetro x 2mm comprimento; n=20) foram condicionados e cimentados (80 m de espessura) em esmalte, com cimento resinoso dual, variando-se o tratamento adesivo, obtendo-se os grupos: UEXC20s, UEXC60s, UEXC90s, USBU20s, USBU60s, USBU90s. Após 24h, foi realizado o teste de cisalhamento (0,5mm/min, 50kgf). Para o teste de compressão (C), 30 placas cerâmicas (5x5mm com 1mm de espessura; n=5) foram condicionadas, receberam os mesmos tratamentos adesivos e foram cimentadas (80m) em esmalte, obtendo-se os grupos: CEXC20s, CEXC60s, CEXC90s, CSBU20s, CSBU60s, CSBU90s. Após 24h da cimentação, foi realizado o teste de compressão (0,5mm/min, 500kgf). Foi realizada a análise estatística por meio de ANOVA dois critérios e teste de Tukey (P < 0,05). Para o teste de cisalhamento diferenças significativas foram encontradas entre os adesivos (p<0,05). Para os tempos de condicionamento não houve diferenças significativas (p=0,059). No entanto, houve interação significativa entre os adesivos e os tempos de condicionamento (p=0,021). No tempo de 60 segundos, o silano + adesivo ExciTE F DSC apresentou os maiores valores de resistência de união (47,53±16,70Mpa). E no tempo de 20 segundos, o adesivo Universal apresentou os menores valores de resistência de união (27,72±10,76Mpa). Para o teste de compressão não houve diferenças significativas entre os adesivos (p=0,571) e entre os tempos (p=0,154). O grupo que apresentou maiores valores de força de compressão foi o adesivo Universal no tempo de 60 segundos (1757,89±200,47N). Já os menores valores, foi também o adesivo Universal, mas no tempo de 90 segundos (1213,30±546,34N). Pode-se concluir que, o Silano associado ao adesivo ExciTE F DSC, mostrou os maiores valores de resistência de união no tempo de condicionamento de 60 segundos com ácido fluorídrico a 10%, sem comprometer a resistência a compressão da cerâmica reforçada por leucita.

Graduation date: 1993

Larger and stronger muscles are positively associated with bone strength in the growing skeleton; however, less is known about the role of muscle properties on bone strength later in life. The primary objective of this study was to examine the relationship between muscle cross sectional area (MCSA), muscle force and rate of torque development (RTD) with bone strength indices (bone strength index (BSI) and strength strain index (SSI)) in the radius of healthy middle-aged adults. All bone and muscle measurements were determined in the non-dominant forearm in a sample of 40 healthy adults (23 men, 17 women: mean age 49.5, SD 2.3 yrs). Peripheral quantitative computer tomography (pQCT) was used to scan the distal and shaft sites of the radius bone in the forearm. MCSA was determined from the forearm shaft scan. Forearm muscle force was measured by hand grip dynamometry and RTD was obtained from isometric wrist flexion from an isokinetic dynamometry protocol. Hierarchical regression analyses were used to identify whether muscle properties (MCSA, grip force, and RTD) independently predicted radius bone strength indices (BSI and SSI), after adjusting for the confounders of sex, height and weight. Steps of the regression models that included sex, height, weight and a muscle property explained between 66% and 71% of variance in distal radius BSI and between 74% and 78% variance of estimated bone strength (SSI) at the shaft site (all steps p<0.001). MCSA explained a significant amount of variance in BSI (R2=0.08; p<0.01) and SSI (R2=0.04; p<0.05) at the radius. Grip force was also a significant predictor of SSI (R2=0.05; p<0.01) but not distal radius BSI (R2=0.03; p=0.07). Conversely, RTD explained a significant amount of variance in bone strength at the distal radius (R2=0.04; p<0.05), but not at the shaft (R2=0.01; p=0.17). These cross sectional findings support the theory that regional muscle size, force, and rate of torque development are related to estimated bone strength in the forearm at midlife. Further research should focus on targeted interventions to help determine which muscle property elicits a greater osteogenic response to optimize bone strength at distal and shaft sites of the radius.

Larger and stronger muscles are positively associated with bone strength in the growing skeleton; however, less is known about the role of muscle properties on bone strength later in life. The primary objective of this study was to examine the relationship between muscle cross sectional area (MCSA), muscle force and rate of torque development (RTD) with bone strength indices (bone strength index (BSI) and strength strain index (SSI)) in the radius of healthy middle-aged adults. All bone and muscle measurements were determined in the non-dominant forearm in a sample of 40 healthy adults (23 men, 17 women: mean age 49.5, SD 2.3 yrs). Peripheral quantitative computer tomography (pQCT) was used to scan the distal and shaft sites of the radius bone in the forearm. MCSA was determined from the forearm shaft scan. Forearm muscle force was measured by hand grip dynamometry and RTD was obtained from isometric wrist flexion from an isokinetic dynamometry protocol. Hierarchical regression analyses were used to identify whether muscle properties (MCSA, grip force, and RTD) independently predicted radius bone strength indices (BSI and SSI), after adjusting for the confounders of sex, height and weight. Steps of the regression models that included sex, height, weight and a muscle property explained between 66% and 71% of variance in distal radius BSI and between 74% and 78% variance of estimated bone strength (SSI) at the shaft site (all steps p<0.001). MCSA explained a significant amount of variance in BSI (R2=0.08; p<0.01) and SSI (R2=0.04; p<0.05) at the radius. Grip force was also a significant predictor of SSI (R2=0.05; p<0.01) but not distal radius BSI (R2=0.03; p=0.07). Conversely, RTD explained a significant amount of variance in bone strength at the distal radius (R2=0.04; p<0.05), but not at the shaft (R2=0.01; p=0.17). These cross sectional findings support the theory that regional muscle size, force, and rate of torque development are related to estimated bone strength in the forearm at midlife. Further research should focus on targeted interventions to help determine which muscle property elicits a greater osteogenic response to optimize bone strength at distal and shaft sites of the radius.

ABSTRACT PEEK matrix reinforced by carbon fibers as one thermoplastic composite material is studied. Thermoplastic composites have the advantages of high specific stiffness and strength, longer fatigue life, good resistance to moisture absorption and high temperature condition. The thesis is aimed to investigate the mechanical properties and fracture mechanism of the centrally notched AS-4/PEEK composite laminates subjected to tension-tension fatigue loading at elevated temperature. We use three common types of laminates, such as cross-ply , quasi-isotropic and angle-ply . After centrally notched, we first obtain the base-line data of mechanical properties by tensile tests at five different temperatures, such as 25¢J¡B75¢J¡B100¢J¡B125¢J¡B150¢J. Then, the fatigue tests are conducted, we receive the fatigue strength and life and establish the stress-life curves. The fatigue characteristics and fracture mechanism of a centrally notched composite laminate at elevated temperature are also recorded and observed. The empirical results can be concluded as follows. At the same temperature, the laminate of cross-ply possesses the largest ultimate strength and fatigue strength, quasi-isotropic the second angle-ply the smallest. As for the elastic modulus, the laminate of cross-ply is larger than that of quasi-isotropic. However, the large strain of angle-ply is within the plastic range that is out of the limit of the study. Thus, a further investigation is needed for angle-ply laminates alone. After centrally notched, the net area is reduced of the specimen, and then the elastic modulus is raised and the ultimate strength and fatigue strength of composite materials are lower. As the temperature increasing, the ultimate strength, fatigue strength and elastic modulus are all decreasing.