Québec Université Laval, Bibliothèque 2015

Experiments were conducted on smooth specimens to study the closure behavior of short cracks at high cyclic strains under completely reversed cycling. Testing procedures and methodology, and closure measurement techniques, are described in detail. The strain levels chosen for the study cover from predominantly elastic to grossly plastic strains. Crack closure measurements were made at different crack lengths. The study reveals that, at high strains, cracks close only as the lowest stress level in the cycle is approached. The crack opening was observed to occur in the compressive part of the loading cycle. The applied stress needed to open a short crack, under high strain was found to be less than for cracks under small scale yielding. For increased plastic deformations, the value of σ_op/σ_max is observed to decrease and approaches the value of R. Comparison of the experimental results with existing analysis has been made and indicates the limitations of the small scale yielding approach where gross plastic deformation behavior occurs. / M.S.

A series of four water-blown flexible polyurethane foams was produced in which the water content was varied from 2 to 5 pph at a constant isocyanate index of 110. A portion of each foam was thermally compression molded into a plaque. The morphology of the foams and plaques was investigated using DMS, DSC, FTIR, TEM, SEM, swelling, WAXS, and SAXS. A high degree of phase separation occurs in these foams and the degree of phase separation is independent of water (hard segment) content. In the foam with the lowest water content the morphology is similar to that of typical segmented urethane elastomers. Small hard segment domains are present with a correlation distance of roughly 7.0 nanometers. When the water content is increased a binodal distribution of hard segments appears. There are the small hard segment domains typical of segmented urethane elastomers as well as large hard segment aggregates greater than 100 nanometers in diameter. The large domains are thought to be aggregates of polyurea that precipitated during the manufacture of the foam. The foam making process successfully incorporated the trifunctional polyols into a network indicating a high degree of polymerization for the hydroxyl-isocyanate reaction. Unreacted isocyanate is present in the foams a month after curing. It is believed to be trapped in the large urea aggregates. WAXS patterns of the foams suggest hard segment ordering that may be of a paracrystalline nature but certainly lacking in true crystallinity. / Master of Science

A series of lateral load tests were conducted on assemblies of four, 4 foot long U.S. Steel PS32 (regular strength) and PSX32 (high strength) straight web sheet pile sections. The instrumentation adopted in the testing program was geared toward monitoring the assembly displacements, load transfer characteristics, and interlock response. Average effective E-ratios over three different pressure ranges were computed, interlock force versus pressure relationships were derived, the stress states in the pile webs were examined, and interlock force versus interlock displacement trends were obtained from the resulting data. A total of 12 assemblies were tested, 6 each of the PS32 and PSX32 types. Three tests from each lot of 6 incorporated pretensioning of the assembly prior to application of the lateral pressure; whereas, the remaining tests initiated lateral loading of the assemblies while they were in a slacked state. The results from the tests were generally grouped according to assembly designation (PS32 or PSX32) and type of test (pretensioning or no pretensioning). The tabulation of E-ratios and pile web stresses, and interlock force versus pressure plots revealed consistent relationships among tests in a particular grouping over the 0-30 psi loading range. Interlock force versus interlock displacement trends were physically correct, but provided no conclusive information regarding the response at an interlock connection. / M.S.

«Thèse [...] pour l'obtention du grade de maître ès lettres (M.L.) »

Models of multiple component, multiple phase adhesives were developed to examine the conflicting demands placed on modern adhesion technology. Styrene and isoprene based block copolymers were investigated 511 order to understand their adhesive properties. The structure of the microphase separated morphology of the materials studied was found to influence the adhesive behavior in applications as hot melt/structural type adhesives and as pressure sensitive adhesives. The thermal and the dynamic mechanical behavior of linear styrene/isoprene/styrene triblock copolymers (40% and 50% by weight styrene) was determined for free films and for films bonding together two rigid adherends. Damping phenomena indicated a broader mechanical relaxation spectrum occurring at higher i temperatures in the bonded assemblies. Microphase separation in the melts of these triblock materials was interpreted as contributing to the formation of residual stresses in both free films and bonded joints under appropriate thermal and pressure histories, illustrating the importance of sample preparation. in the evaluation of multiple phase adhesive systems. / Ph. D. / incomplete_metadata

The theory of soft variable structure control, which produces robustness to parameter variation and fast transient response, is discussed in this thesis. The digital implementation techniques are presented in the aspects of sample rate, prefilter design, hardware selection, and microprocessor arithmetic operation. Simulation and experimental results showed good performance in negative speed range, but this controller created unwanted high armature current fluctuation in positive speed range. The reasons turned out to be the limitation of sample rate, noise from the tachometer, and high gain at positive speed. / Master of Science / incomplete_metadata

Construction of braced excavations in major urban areas has increased over the last few decades. It is a major concern of the designer to limit ground movement around an excavation in order to prevent damage to adjacent structures, utilities and roads. Existing design methods can accurately predict ground and wall movement of a braced excavation, but the calculations become complex when multiple construction stages are considered, or if different design schemes are compared. This thesis presents an interactive personal computer program (called MOVEX) to facilitate braced excavation design. Using input variables for wall stiffness, strut stiffness, and strut spacing, MOVEX includes four design options that allow the designer to adjust the variables in order to develop the optimal bracing design. Details of the design theory, input and output data, and a user's guide are included in this thesis. In addition, the settlement of sand due to pile driving was investigated. A predictive method is presented that relates sand densification to the ground acceleration caused by pile driving. / Master of Science

Ribosomal 5.85 RNA is a component of the large (605) ribosomal subunit in eucaryotes. Studies of 5.85 rRNA in solution have shown that under certain conditions, including standard isolation procedures, the molecule complexes with itself to form dimers and higher multimers. Two models have been proposed in the literature to explain the intermolecular interactions responsible for 5.85 rRNA dimer formation. The terminal interaction model of Sitz et al. (Biochem. 17, 5811-5815, 1978) proposes that the dimer forms through base-pairing of the 5' and 3' terminal sequences of two 5.85 rRNA molecules. Pavlakis et al. (Nucl. Acids Res. 7, 2213-2237, 1978) showed that 5.85 rRNA lacking the 3' terminal region was capable of forming dimer. They proposed an alternative model for 5.85 rRNA dimer formation in which an entirely different part of the molecule interacts to form a double-stranded palindrome. In this study, enzymatic probing techniques and stability measurements (both experimental and theoretical) were used to determine which model most accurately describes the intermolecular interactions of the 5.88 rRNA dimer. The methods used for determining stability were not able to discriminate between the models for 5.88 rRNA dimer formation. Results from the structural probing studies, however, support the terminal interaction model and indicate that the palindrome interaction does not occur in 5.88 rRNA dimer formed from the intact molecule. / Master of Science / incomplete_metadata

The flotation of sphalerite has been demonstrated without the use of collectors. The effect of redox potential, pH, and copper-activation have been investigated in tests using samples of pure mineral. It has been found that in general, collectorless flotation of sphalerite can be accomplished at potentials greater than -200 mV, SHE, and is more readily carried out in acidic solutions. It has also been shown that although copper-activation was necessary to achieve flotation recoveries above 35%, an excessive addition of cupric ions may result in a decrease in floatability. Batch flotation experiments conducted using Elmwood Mine sphalerite ore have shown that in addition to copper-activation, the addition of sodium sulfide was required to obtain high grades and recoveries. If the ratio of the addition of these reagents is maintained such that the atomic ratio of cupric ions to sulfide ions is 0.31, good flotation is observed over a range of reagent dosages. X-ray photoelectron spectroscopy (XPS) was conducted on pure mineral samples after microflotation testing. Based on the sulfur species identified on highly flotable samples, possible mechanisms for collectorless flotation of sphalerite have been suggested. These include: i) elemental sulfur formed under oxidizing conditions is responsible for collectorless flotation; ii) polysulfides or metal-deficient sulfides formed as a result of mineral oxidation are responsible for collectorless flotation; and iii) removal of HS- ions, which may render the surface hydrophilic, under oxidizing conditions. The third mechanism is based on the assumption that clean, unoxidized sphalerite surfaces are naturally hydrophobic. Evidence has been presented to suggest that the first mechanism may be responsible for collectorless flotation in acidic solutions, while the second mechanism may be of greater importance in nearly neutral or basic solutions where elemental sulfur is thermodynamically less stable. / Master of Science