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During the course of this grant, research focused on using available theoretical tools to explore and elucidate complex dynamics of impurities in Si. In particular, we studied clustering of As in heavily doped Si, segregation of As in Si grain boundaries and the migration of oxygen in Si. In addition we carried out atomic scale nonequilibruim heat flow simulations and mesoscopic calculations of void growth in polycrystalline metal lines.

During the course of this grant, research focused on using available theoretical tools to explore and elucidate complex dynamics of impurities in Si. In particular, we studied clustering of As in heavily doped Si, segregation of As in Si grain boundaries and the migration of oxygen in Si. In addition we carried out atomic scale nonequilibruim heat flow simulations and mesoscopic calculations of void growth in polycrystalline metal lines.

Fibrous structures of increasing complexity, as introduced by ply and twist, were subjected to high and low speed tensile tests. The ratio of the strength at high speed to that at low speed is always greater than one but decreases with increasing complexity. The ratio of the elongation to break at high speed to that at low speed is always less than one and also decreases with increasing complexity of structure. The ability to absorb energy markedly increases with increasing complexity of geometry at the low strain rates characteristic of the Instron. The reasons for this additional energy absorption are discussed. Tests at high rates of straining point out the inability of many complex textile structures to translate their superior energy absorption characteristics to high strain rates. The results obtained and the principles demonstrated are applied to the development of improved materials for use in aerial delivery and ballistic applications.

A summary of the most important findings on the thermal decomposition of five cyclic nitramines is presented. The compounds studied include: octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), hexahydro-1,3,5- trinitro-striazine (RDX), hexahydro-l-nitroso-3,5-dinitro-s-triazine (ONDNTA), 1,3,5-trinitro-1,3,5-triazacycloheptane (TNCHP), and 2-oxo- 1,3,5-trinitro- 1,3, 5-triazacyclohexane (K6). The thermal decomposition processes were studied using simultaneous thermogravimetric modulated beam mass spectrometry (STMBMS) to identify the decomposition products and to determine their gas formation rates and using mixtures of isotopically labeled analogues of the compounds to track the decomposition mechanisms by analyzing the extent of isotopic scrambling and the deuterium kinetic isotope effect (DKIE). Extensive results on the thermal decomposition of RDX and HMX in the solid and liquid phases show that their decomposition is controlled by several parallel decomposition pathways. One pathway involves the loss of HONO and the formation of oxy-s-triazine (OST) from the RDX ring. The other pathway occurs via the mononitroso intermediate of the parent compound. The decomposition of the mononitroso-RDX intermediate, ONDNTA, has been extensively studied and a summary of the highlights of its decomposition is presented. The results on TNCHP show that it is the only one of the cyclic nitramines studied that is stable in the liquid phase. Thermal decomposition, Thermal stability, Mass spectrometry, Isotopic labels, Deuterium kinetic isotope effect, DKIE, Nitramines, Nitroso compounds, Cyclic nitramines, RMX, RDX, K6, TNCHP, ONDNTA, Kinetics, Reaction mechanisms, Reaction rates, Sensitivity, Explosives, Propellants, Energetic materials.

A summary of the most important findings on the thermal decomposition of five cyclic nitramines is presented. The compounds studied include: octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), hexahydro-1,3,5- trinitro-striazine (RDX), hexahydro-l-nitroso-3,5-dinitro-s-triazine (ONDNTA), 1,3,5-trinitro-1,3,5-triazacycloheptane (TNCHP), and 2-oxo- 1,3,5-trinitro- 1,3, 5-triazacyclohexane (K6). The thermal decomposition processes were studied using simultaneous thermogravimetric modulated beam mass spectrometry (STMBMS) to identify the decomposition products and to determine their gas formation rates and using mixtures of isotopically labeled analogues of the compounds to track the decomposition mechanisms by analyzing the extent of isotopic scrambling and the deuterium kinetic isotope effect (DKIE). Extensive results on the thermal decomposition of RDX and HMX in the solid and liquid phases show that their decomposition is controlled by several parallel decomposition pathways. One pathway involves the loss of HONO and the formation of oxy-s-triazine (OST) from the RDX ring. The other pathway occurs via the mononitroso intermediate of the parent compound. The decomposition of the mononitroso-RDX intermediate, ONDNTA, has been extensively studied and a summary of the highlights of its decomposition is presented. The results on TNCHP show that it is the only one of the cyclic nitramines studied that is stable in the liquid phase. Thermal decomposition, Thermal stability, Mass spectrometry, Isotopic labels, Deuterium kinetic isotope effect, DKIE, Nitramines, Nitroso compounds, Cyclic nitramines, RMX, RDX, K6, TNCHP, ONDNTA, Kinetics, Reaction mechanisms, Reaction rates, Sensitivity, Explosives, Propellants, Energetic materials.

A total of thirty-five publications have been generated from this research appearing in thirteen primary journals. The connection between two traditional theoretical approaches to the treatment of rubber elasticity has been bridged. One of these is the theory of 'phantom' networks, developed originally by James and Guth, in which the integrity of the chains is ignored and the junctions (cross linkages) are allowed to seek their preferred positions without regard for the entanglements of chains that severely limit configurational rearrangements in real systems. The other follows the precepts of W. Kuhn, elaborated by Wall, Treloar, Flory and Rehner and others, according to which the cross linkages are firmly embedded in their surroundings and hence must undergo ('affine') displacements in proportion to the macroscopic strain. This research suggests that the unswollen network at small deformations conforms approximately to the affine behavior, but that it approaches the phantom model at high elongations and/or high degrees of swelling. Decreases with strain and dilution may account for departures from the theoretical relationship. The theory of order-disorder in systems of rigid extended polymer chains and of phase equilibria in such systems (Proc. Roy. Soc. London, A234, 73 (1956) has been adapted without difficulty to semiflexible chains consisting of rigid rod-like segments connected by flexible joints. (Author)

*The research covered herein was performed to (1) Establish the microstructures and intrinsic properties characteristic of materials with enhanced use performance and the capability of reliably and predictably retaining this performance in aerospace systems applications, and (2) Obtain information about microstructural and property parameters associated with the achievement of improvements in structural strength and stability through the characterization of materials from AFML in-house investigations. The principal techniques employed in this characterization included optical, electron and scanning electron microscopy, x-ray analysis, electron microprobe analysis and numerous physical test methods. Sample preparation, including forming, heat treatment, grinding, polishing and etching, was required and represented a substantial part of the effort. Much of the program was directed toward the study of the structure and properties of titanium and aluminum alloys. (Author)

Contents: Columbium creep at high stresses; Specific features of alloying, structure, and phase composition of nickel-chromium heat-resistant alloy with columbium; Comparative study of oxidability and heat resistance of columbium-base alloys.

Contents: Columbium creep at high stresses; Specific features of alloying, structure, and phase composition of nickel-chromium heat-resistant alloy with columbium; Comparative study of oxidability and heat resistance of columbium-base alloys.

Book digitized by Google from the library of the University of Wisconsin - Madison and uploaded to the Internet Archive by user tpb.

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Layered transition metal dichalcogenide (LTMD) compounds constitute a class of materials with unique and unusual properties based on the extreme degree of anisotropy in their layered crystal structures. LTMDs are formed by stacking sandwiches consisting of a layer of transition metal between two layers of chalcogen. There is strong covalent bonding within the sandwiches but weak (van der Waals') bonding between them. Details of the exact crystal type within this general structure vary and result in some LTMDs being very good lubricants and others being poor lubricants or abrasives. Coincidentally, the electrical properties vary greatly also, ranging from insulators to semiconductors, and finally to metals with evidence of superconductivity in some of the class members. Keywords: Electronic structure; Molybdenum disulfide; Solid lubricants; Tribology; Materials properties; Thin films.

Research on the theory of liquid crystalline systems has been continued with special emphasis on systems of semiflexible polymer chains. Experiments on low molecular analogs have been carried out with the primary object of assessing the effects of anisotropic phase. It has been demonstrated that anisotropy of the molecular polarizability, which can be evaluated by optical measurements of depolarized Rayleigh scattering (DRS), is directly responsible for the effect. The density of the fluid has been found to play an important role, not hitherto recognized. It must be taken into account in any quantitative treatment of liquid crystallinity in low molecular substances at high temperatures. The theory of rubber elasticity of real polymeric networks has been refined and generalized. In its revised form the theory gives a good account of the relationship of stress to strain for all strains, including biaxial deformations, throughout experimentally accessible ranges. The principal parameter required, apart from the degree of interlinking that characterizes the network structure, appears to be related to the degree of interpenetration in the network. This parameter, too, may be subject to evaluation, also from molecular characteristics. Thus, the theory provides an essential link between molecular structure and properties. (Author)

Nanocrystalline and nanocomposite materials are polycrystalline materials with grain sizes of up to about 100 nm. This survey reviews the current state-of-the-art in nanoscale design of magnetic materials and identifies new opportunities for future research and applications of these systems. A variety of preparative techniques that lead to magnetic materials with nanometer dimensions are discussed. These techniques include chemical self-assembly processes as well as mechanical fabrication techniques. This is followed by a discussion of the structures. theory and modeling concepts, and novel physical properties with emphasis given to the differences between course and fine grained magnetic materials. Finally, there is a discussion of the current and potential applications of nanophase materials that are likely to fuel research into the coming decades.

Book digitized by Google from the library of the University of Michigan and uploaded to the Internet Archive by user tpb.

Book digitized by Google from the library of the University of Michigan and uploaded to the Internet Archive by user tpb.

Book digitized by Google from the library of the University of Michigan and uploaded to the Internet Archive by user tpb.

Book digitized by Google from the library of the University of Michigan and uploaded to the Internet Archive by user tpb.

Book digitized by Google from the library of the University of Michigan and uploaded to the Internet Archive by user tpb.

Book digitized by Google from the library of the University of Michigan and uploaded to the Internet Archive by user tpb.

Book digitized by Google from the library of the University of California and uploaded to the Internet Archive by user tpb.