Rahmi Yazici

Degree of Mixing Analyses of Concentrated Suspensions by Electron Probe and X-Ray Diffraction

Abstract Two x-ray based techniques involving energy-dispersive analysis and diffractometry were introduced to the analyses of the degree of mixedness, i.e. the “goodness of mixing” of concentrated suspensions. A hydroxyl terminated polybutadene matrix was mixed with aluminum and ammonium sulfate. In the analysis, the ratio of the relative volume fractions of the two solid components was used as the basis of the analytical evaluation. Both characterization techniques are capable of determining the relative volume fraction of the two solid components as a representative measurement of the distributive mixing efficiency and both are sensitive to the scale of examination. The introduced techniques should be useful in the better definition of the degree of mixedness as well as in resolving differences in mixing efficiencies of various mixers used in processing of concentrated suspensions.

Capillary Flow Behaviour of Microcrystalline Wax and Silicon Carbide Suspension

Suspensions of ceramic particles in low or high molecular weight polymers are shaped into various three-dimensional parts using various moulding and extrusion technologies. Such bodies are subsequently fired-up and sintered to remove the binder. The utilities of such three-dimensional ceramic bodies depend on the restrictions related to the shapeability of the ceramic suspension, hence to the flow and deformation behaviour of the suspension. In this study, factors affecting the flow and deformation behaviour of a 50% by volume of silicon carbide in a wax binder was investigated. Consistent with the previously observed behaviour of other highly filled materials, the ceramic suspension exhibited viscoplasticity, plug flow and wall slip. Furthermore, flow instabilities associated with the axial migration of the low viscosity binder under the imposed pressure gradient were observed. These results pinpoint to the various difficulties associated with the collection of rheological data and emphasize the relevance of various flow mechanisms, including wall slip and mat formation and filtration based flow instabilities, which would also occur in processing/shaping flows of such ceramic suspensions including extrusion and moulding.

Quantitative characterization of degree of mixedness of lova grains

Abstract A wide-angle x-ray diffraction technique developed earlier by the authors to characterize the degree of mixing in concentrated suspensions is applied to the quantitative characterization of the distributive mixing achieved in extruded LOVA grains, to demonstrate the applicability of the technique towards total quality assessment of energetic grains. The samples included LOVA grains which were either processed in a batch mixer and ram extruded or processed and extruded using co-rotating twin screw extrusion.

Microstrain and Defect Analysis of CL-20 Crystals by Novel X-Ray Methods.

ABSTRACT Microstrains and defects are introduced during synthesis and crystal-growth stages of energetic particles and increase during processing stages such as grinding, mixing, and extrusion. The detection and quantification of these microstrains and defects in a given particle population is a difficult task that requires highly sensitive techniques. In this study a novel X-ray diffraction technique (XAPS) based on simultaneous rocking-curve analysis of individual particles was successfully applied to CL-20 powders. The effects of synthesis, grinding, and static loads on the extent of microstrain and defect development in CL-20 particles were quantitatively determined as frequency versus half-width of rocking curves. The greater half-width values observed for the samples subjected to grinding and static loads indicated greater microstrain and defect density in comparison to the as-received samples of CL-20. It may be possible to relate the findings of such analysis to combustion calculations for energetic particles in general and to CL-20 particles in particular.

Uniaxial Extensional Flow Behavior of a Glass Fiber-Filled Engineering Plastic

The extensional flow behavior of a Nylon 6 based engineering plastic filled with short glass fibers was characterized using a Meissner-type uniaxial extensional rheometer. The fiber orientation distributions of the resin samples at various Hencky strains were also determined by X-ray microradiography and image analysis techniques. The uniaxial extensional stress growth function was found to be intimately related to the orientation distribution function of the fibers.

Predicting crack growth in continuous-fiber composite materials

Pre-notched composite lamina with unidirectional fibers were studied experimentally and using finite element analysis. Experiments were conducted on notched graphite/aluminum and glass/epoxy panels and the results were compared to a finite element method. Under remote tensile loading, cracks in the graphite/aluminum panels propagated perpendicular to the applied load without stable crack growth. In the glass/epoxy panels, crack propagation was initially stable and parallel to the fibers. A nonlinear damage zone method (DZM) was used to predict the crack growth directions, estimate damages, model stable and unstable crack growths, and predict the loads at failure. For both materials, the predicted loads at failure were within 20% of experimental loads.

Dissolution study of BAMO/AMMO thermoplastic elastomer for the recycling and recovery of energetic materials

Abstract This study involves the characterization and dissolution of a thermoplastic elastomer copolymer used as binder in the new generation of energetic materials. The thermoplastic binder is an oxetane based elastomer manufactured by Thiokol Corporation. Since the binder encapsulates other components in an energetic material formulation, its controlled dissolution is crucial to the recovery and recycle of all the energetic material ingredients. The polymeric binder was found to be highly soluble in ethyl acetate and THF. The dissolution rate data obtained under well defined flow dynamics was satisfactorily correlated with the film model. External mass transfer resistance was found to be generally important but became negligible for Reynolds numbers above 6.0×104. The mass transfer coefficients calculated on the basis of the film model were found to be an Arrhenius function of temperature. The activation energy for the dissolution rates was estimated to be 4.8 kcal/mol.

Evaluation of elastic-plastic fracture in aluminum panels

Abstract An experimental and numerical study of failure in 6061-T6 aluminum panels was completed. The experimental effort included generation of GRcurves and collection of data from static fracture tests on thin aluminum panels with cracks and notches. The numerical effort centered on predicting the crack opening displacement as a function of applied load, predicting applied load at failure, and predicting the nature of failure: either yield or fracture. A finite element model, referred to in this paper as the damage zone model (DZM), incorporates a cohesive stress zone adjacent to a crack or notch. The predicted failure loads using the DZM were within 9.0% of experimental values for yield failure. Predicted failure loads were within 11.0% of experimental failure loads when stable crack growth preceded unstable fracture. In all cases, the DZM predicted the nature of the final failure.

Relative Magnetic Permeability of Injection Molded Composites as Affected by the Flow Induced Orientation of Ferromagnetic Particles

Publisher Summary The objective of this chapter is to experimentally examine the effects of processing on the orientation distributions of ferromagnetic fibers in injection molded composites and to elucidate the effects of the resultant fiber orientation distributions on the magnetic properties of the injection moldings. Furthermore, the effects of the concentration and the aspect ratio of the ferromagnetic particles are also investigated. Magnetic properties of composites are influenced by concentration, fiber length, and orientation of the ferromagnetic particles, which are incorporated into a polymeric binder. Since fibers are anisotropic their preferential orientation will impart anisotropy in the composite material properties. Anisotropic magnetic composites are produced by injection molding of suspensions consisting of a high-viscosity polymeric binder and various fillers in two custom designed molds, which produced differences in fiber orientation distributions. The magnetic properties of the composites are characterized in terms of their relative permeability values and related to their microstructure. It is determined that composites with a higher degree of orientation generate higher permeability values. Quantitative data, which link orientation distribution functions to magnetic permeability values of composites, are provided for the first time. It is also shown that various processing conditions and die diameter influence the orientation, hence the permeability. These findings can be utilized to tailor injection moldings with desired relative magnetic permeability values for various industrial applications.