No description available.

Photocopy of typescript. / Digitized by Kansas Correctional Industries

Typescript. / Digitized by Kansas Correctional Industries

No description available.

Thesis (M. Ing.)--University of Stellenbosch, 1997. / Bibliography. Also available via the Internet.

No description available.

No description available.

A study of the constitutive equations of the flow of cohesionless granular materials at large rates of deformation and low stress levels is presented. The interstitial fluid effects are assumed negligible and the particles approximately incompressible. / Dimensional arguments and experimental observations suggest that two different regimes of flow may occur. At low rates of deformation, the Coulomb friction gives rise to stresses that are rate independent (of the plastic type). At large rates of deformation, momentum transfer arises from particles collisions and the resulting stresses become rate dependent (of the viscous type). A continuum model that includes both types of behaviour is proposed. The equilibrium part of the stress tensor satisfies the Mohr-Coulomb yield criterion and a non-coaxial flow rule. The viscous part is assumed to have a form corresponding to an isotropic Reiner-Rivlin fluid. / Experiments of simple shear flow flow in an annular shear cell were performed on several types of dry granular materials. The purpose of the tests was to obtain the information needed for the continuum description of the material behaviour. At lower solids concentrations and high shear rates where the inter-particle collisions are dominant, both shear and normal stresses were proportional to the square of the shear rate. At higher concentrations and lower shear rates, Coulomb friction between particles became increasingly important and the stresses were proportional to the shear rate raised to a power less than two. All tests showed a strong dependence upon solids concentration.

A repetitive low-pressure die casting technique has been developed for casting high quality Mg6SCU2SY10 bulk metallic glass (BMG) samples. Using these as-cast samples, the thermal and mechanical behaviour of the BMG in the supercooled liquid (SCL) region was investigated principally by uniaxial tensile testing, differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Using the die casting facility, charge temperature, injection pressure and injection velocity were found to be important parameters for controlling the length, porosity and degree of crystallinity in the as-cast samples. A processing map was generated which showed that a melt temperature and casting pressure in the range 560-580°C and 0.4-0.5 bar, respectively, generated the highest quality samples. The static crystallization behaviour of the as-cast BMG was investigated in detail. It was found that the kinetics of both anisothermal and isothermal crystallization were adequately represented by a number of transformation models. Using the Johnson-Mehl-Avrami-Kolmogorov (JMAK) relation in conjunction with isothermal DSC, the Avrami exponent was found to vary from 2.2 to 2.5 with increasing annealing temperature which implies that, at high annealing temperatures, nucleation occurs at a constant rate accompanied by diffusion-controlled growth of spherical grains. A comparable Avrami exponent of 2.34 was also calculated by anisothermal DSC using the Ozawa method. The tensile flow behaviour of the BMG was investigated over a range of strain rates (10.3to 10.1S•1) and deformation temperatures (150 to 170 QC) in the SCL region using standardized tensile test samples. It was found that, the flow stress increased rapidly to a maximum value followed by a decrease to a very low steady-state value. In the SCL region, the relationship between peak flow stress, strain rate and absolute deformation temperature was described adequately by the classic Sellars-Tegart constitutive relationship. There was also a good correlation between the Zener-Hollomon parameter, Z, and the flow characteristics of the BMG such as the transition from Newtonian to non-Newtonian flow at Z>1 031 S•1 and optimum superplasticity for Z-values in the range 5 x 1030 to 5 x 1031 S•1 where tensile elongations in excess of 1400% were achieved.

Thesis (M.S.)--University of North Texas, Dec., 2009. / Title from title page display. Includes bibliographical references.