No description available.

A study of the effect of shear rate on the inherent and intrinsic viscosities of polystyrene fractions, in dilute solution was carried out. Inherent viscosities were determined for five fractions (of molecular weights ranging from 2.9 x 10 to 4.8 x 106); in three solvents (Benzene, Toluene and Methyl Ethyl Ketone); at five temperatures (from 15°C to 85°C); and shear rates ranging from 1.0 x 103 to 2.8 x 104 sec.-1. Inherent viscosities thus determined were extrapolated to zero rate of shear and the extrapolated values plotted against concentration to determine intrinsic viscosities at zero rate of shear, [N] D=0 The inherent viscosity decreased with increasing shear rate. The slope of the curve of inherent viscosity vs shear rate was found to increase (ie become more negative) with increasing concentration, temperature and molecular weight and to be less in a poor solvent than in a good solvent. At very high molecular weights the value of inherent viscosity was found to decrease non-linearly with shear rate. The intrinsic viscosity was found to decrease with increasing shear rate. The slope of the [N] vs D curve was found to increase with increasing molecular weight and decreasing temperature; the slopes were smaller the poorer the solvent. For the three lower fractions the intrinsic viscosity was found to decrease with increasing temperature, very slightly in Methyl Ethyl Ketone and appreciably in Benzene and Toluene, the relative being greater at higher molecular weights. With the two highest fractions this trend was reversed. The slope of the [N] D=0 vs T curve becoming less negative (and actually positive for Benzene end Toluene). The [N] vs T curves ( [N] at free fall) for the three lower fractions were parallel to those at zero rate of shears but of lower intrinsic viscosity values. With the two highest fractions, the slope of the [N] vs T curve became less negative but not to as great a degree as was found with [N] D=0 vs curves. Intrinsic viscosities obtained at zero rate of shear were applied to the Flory-Fox theory. Calculated intrinsic viscosities for polystyrene fractions in Benzene and Toluene were found to agree to within+-4% of the experimental results. For Methyl Ethyl Ketone a wide variation in values was obtained. / Thesis / Master of Science (MS)

This thesis investigates Stochastic Separated Flow (SSF) models for particle dispersion in turbulent shear flows. A new model is presented that accounts for anisotropy and incorporates a temporal and a spatial autocorrelation in the description of the fluctuating component of the turbulent gas-phase velocity. This model and three SSF models available in the literature are evaluated by comparing predictions with the shear layer experiments of Lazaro and Lasheras (1989), Hishida et al (1992) and the turbulent round jet experiment of Yuu et al (1978). Results are discussed and deficiencies in the models explored. The new model of Evinou and Lightstone compensates for the crossing trajectory effect with the inclusion of a spatial correlation based on the relative velocity of the particle and the time step employed. / Thesis / Master of Applied Science (MASc)

We present the results of our study of the shear deformation zone in free-standing thin polymer films as a probe of entanglement in confined systems. A stretching system was used to uniaxially strain thin polystyrene (PS) films. Atomic force microscopy was used to measure the thicknesses of the shear deformation zone (SDZ), hc, and the film thicknesses h. The maximum extension ratio 2 - h/hc, was measured as a function of film thickness. The results show that A increases with the decreasing film thickness which implies an increase in the entanglement molecular weight in confinement. The same experiments were carried out for thin PS film with different molecular weights. A tentative model was developed to explain the experimental results and found to be in good agreement with the data. More exciting is the fact that the model predicts a scaling dependence on the polymer molecular weight which was also observed. / Thesis / Master of Applied Science (MASc)

No description available.

No description available.

This study consists of three self-standing parts, each dealing with a different aspect of design of composite steel-concrete flexural members. The first part deals with a new type of shear connection in composite joists. Composite steel-concrete flexural members have increasingly become popular in design and construction of floor systems, structural frames, and bridges. A particularly popular system features composite trusses (joists) that can span large lengths and provide empty web space for installation of typical utility conduits. One of the prominent problems with respect to composite joists has been the installation of welded shear connection due to demanding welding requirements and the need for significant welding equipment at the job site. This part of the study presents a new type of shear connection developed at Virginia Tech— standoff screws. Results of experimental and analytical research are presented, as well as the development of a recommended design methodology. The second part deals with reliability of composite beams. Constant research advances in the field of composite steel-concrete beam design have resulted in numerous enhancements and changes to the American design practice, embodied in the composite construction provisions of the AISC Specification (AISC 1999). Results of a comprehensive reliability study of composite beams are presented. The study considers specification changes since the original reliability study by Galambos et al. (1976), considers a larger database of experimental data, and analyses recent proposals for changes in design of shear connection. Comparison of three different design methods is presented based on a study of 15,064 composite beam cases. A method to consider effect of degree of shear connection on strength reduction factor is proposed. Finally, while basic analysis theories between the two are similar, requirements for determining the strength of composite beams in Eurocode 4 (CEN 1992) and 1999 AISC Specification (AISC 1999) differ in many respects. This is particularly true when considering the design of shear connections. This part of the dissertation explores those differences through a comparative step-by-step discussion of major design aspects, and accompanying numerical example. Several shortcomings of 1999 AISC Specification are identified and adjustments proposed. / Ph. D.

This study deals with the vibration and stability analyses of laminated plates and shells, using classical, first-order and third-order equivalent single-layer theories and the layer-wise theory of Reddy. Analytical solutions of these theories for natural frequencies and critical buckling loads of plates and shells under various boundary conditions are developed using an improved analytical procedure. A solution for the transient response of viscously damped cross-ply laminated plates, subjected to a sonic-boom type loading, is developed using the third-order shear deformation plate theory of Reddy and the first-order shear deformation plate theory. The nonlinear dynamic equations of the first-order shear deformation plate theory and the third-order shear deformation plate theory of Reddy are reformulated in terms of a pair of equations describing the interior and the edge-zone problems of rectangular plates laminated of transversely isotropic layers. The pure—shear frequencies of the plate in linear and nonlinear problems are identified from the edge—zone equation. For certain boundary conditions the original system of equations are reduced to three in number, as in the classical plate theory. The frequency and buckling equations of symmetric plates laminated of transversely isotropic layers are obtained using the Levinson’s third—order shear deformation plate theory. Using the interior and the edge—zone equations, the frequency and buckling equations are also obtained according to the first—order shear deformation plate theory. The solution contribution of the edge—zone equation is analyzed. By introducing a mixed approach, the bending problem of laminated plates with various boundary conditions is studied according to the first—order and Reddy’s third-order shear deformation plate theories. / Ph. D.

The assessment of the shear strength of soil deposits after the occurrence of large strains is an important issue for geotechnical engineers. One method for doing so, the steady state approach, is based on the assumption that the steady state undrained shear strength is a unique function of the in situ void ratio and effective stress. This method, which has been applied to liquefaction and flow failures, has been criticized because it may overestimate the in situ shear strength. The key to the steady state approach is accurate determination of the relationship between void ratio and effective stress at steady state. This is typically accomplished using conventional isotropically consolidated undrained (ICU) triaxial tests. The triaxial test was developed for measuring peak strengths, which typically occur at small strains, but steady state conditions typically occur at much larger strains. At large strain levels, the suitability of conventional triaxial testing procedures and error corrections is uncertain. The measured response at large strains may be inaccurate due to the influence of various testing errors. Furthermore, the true material response in the test specimen at large strains may not accurately represent in situ material behavior at large strains. This research effort consisted of an experimental and analytical study to examine the validity of steady state undrained shear strength determination using conventional ICU triaxial tests. The analytical study addressed triaxial testing errors and conventional corrections that are applied to test data and their influence on the measured steady state parameters. Finite element analyses were conducted to investigate the influence of variations in restraint at the end platens on stress distributions in the sample and measured stress-strain response. The finite element analyses incorporated axisymmetric interface elements to model the friction characteristics between the end platens and the specimen ends. The experimental study focused on several sands that are susceptible to liquefaction. An interface direct shear test program was conducted in order to evaluate various schemes for reducing end platen friction. ICU triaxial tests were conducted on each material using both conventional and lubricated end platens. / Ph. D.

In this study, a new and efficient numerical algorithm is developed to solve both the two-dimensional and three-dimensional compressible hydrodynamic stability problem. A parametric study of free shear flows with two or more supersonic streams is performed. Flows examined included shear layers, jets/wakes, and various geometrical combinations of these flows. The effect of Mach number on the stability characteristics of the flow is studied and found to confirm the work of other researchers who found that increasing the relative (or convective) Mach number increases the stability of the flow. For 2-D mean flows, the most amplified disturbance is shown to be axial for M<1.2 and fully three-dimensional for M> 1.2. Disturbances for three-dimensional mean flows are found here to be axial in the presence of side walls. The variation of the eigenfunctions and flow field disturbances as a function of Mach number and the flow geometry was also studied. Comparisons of the stability code results are also made to several turbulent mixing experiments. The stability code correctly predicts which parameters will accelerate mixing. New correlations of the effects of some important parameters on stability are developed. / Ph. D.