Damage Mechanisms and the Mechanical Properties of a Laminated 0/90 Ceramic/Matrix Composite

The tensile properties of a 0/90 laminated CAS matrix composite reinforced with Nicalon fibers have been measured. Some effects of notches have also been explored. Changes in modulus and permanent strain caused by matrix cracking have been measured and compared with available models. For this comparison, independent measurements have been made of the constituent properties and the residual stress. The ultimate tensile strength has also been measured and compared with a global load-sharing model. It is concluded that lower-bound matrix cracking models provide good predictability of the stresses at which various matrix cracking mechanisms first operate. Also, the ultimate tensile strength is found to be consistent with a global load-sharing model, based on the in situ strength properties of the fibers. Conversely, the evolution of matrix cracks at stresses above the lower bound has yet to be adequately modeled. In addition, a need is identified for improved models relating elastic properties and permanent strains to matrix crack spacing.     

Polyurethane‐infiltrated carbon foams: A coupling of thermal and mechanical properties

The thermal and mechanical properties of polyurethane‐infiltrated carbon foam of various densities were investigated. By combining the high thermal conductivity of the carbon foam with the mechanical toughness of the pure polyurethane, a mechanically tough composite (relative to the unfilled foam) that could be used at higher temperatures than the polyurethane's degradation was formed. Both the tensile strength and the modulus increased by an order of magnitude for the composites compared to unfilled foam, while the compressive and shear strengths and moduli of the composites approached values exhibited by pure polyurethane. At both 300 and 400°C, the rectangular blocks of pure polyurethane lost their mechanical integrity due to decomposition in air. Thermogravimetric analysis confirms substantial initial weight loss above 290°C. Filled carbon foam blocks, however, maintain their mechanical integrity at both 300 and 400°C indefinitely, although the bulk of the rectangular block mass is polyurethane. Three different carbon foam densities are examined. As expected, the higher density foams show greater heat transfer. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2348–2355, 2003     

Chemistry of mandibular and Dufour's gland secretions of ants in genusMyrmecocystus

Males of several species ofMyrmecocystus produce mandibular gland secretions that contain 2,4-dimethyl-2-hexenoic acid and a variety of monoterpenes that include neral, geranial, citronellol, limonene, and 2,6-dimethyl-5-hepten-1-ol. Other components identified include methyl anthranilate, octanal, octanol, octyl octanoate, and 2-hexyl-2-decenal. Methyl salicylate has been identified as a mandibular gland constituent of workers of several species in addition to mellein and monoterpenes such as cymene, limonene, and the isomers of citral. The Dufour's gland secretions of workers and females of 14 species contain typical formicine alkanes (e.g., undecane), 2-alkanols (e.g., 2-tridecanol), and 2-alkanones (e.g., 2-tridecanone). Two species in the subgenusEremnocystus produce secretions that are distinguished by the presence of significant quantities of tridecyl esters. The functions of these compounds as well as their possible chemosystematic significance in the genusMyrmecocystus are discussed.     

Factors influencing the photofading of commercial anthraquinone dyes in solution

The photofading of two anthraquinone dyes has been studied in aqueous solution using ultraviolet-visible absorption spectroscopy and flash photolysis. The influence of alcohol concentration, pH, atmosphere, photosensitisers and stabilisers have been examined and these lead to some important conclusions on the mechanism of dye fading. Essentially, the results indicate the photoexcited triplet state of the dye undergoes a process of either electron or hydrogen-atom abstraction depending on the nature of the environment. Other factors such as aggregation and singlet oxygen also appear to play an important role in solution photofading. The relevance of these results to photofading in a polymeric phase is discussed.     

Adhesion of Polyethylene to Copper: Importance of Substrate Topography

In order to get good adhesion between polyethylene and copper previous workers have oxidized the metal in alkaline solution to give a matt black oxide film. In this paper it is shown that the good adhesion obtained is associated with the very rough, fibrous nature of the matt black oxide film. Adhesion rises as the layer develops on the copper. If the fibres are damaged to alter the topography without changing the chemical nature of the substrate, the adhesion falls markedly. If the chemical nature of the oxide film is changed by electrolytic reduction, with minimum change in topography, the adhesion is still substantial. Adhesion to these matt black oxide films is still good if oxidation of the polymer is suppressed either by incorporation of stabilizers or by coating in a nitrogen atmosphere. This further points to the importance of topography in adhesion to these surfaces.     

Long term storage of soybean and cottonseed salad oils

Commercially prepared and packaged soybean and cottonseed salad oils from several different processors were evaluated periodically during storage for 12 months. Partially hydrogenated and winterized soybean oils, as well as unhydrogenated soybean salad oils, were stored in bottles and cans at 78 and 100 F. Control samples of all oils were held at 0 F during the entire test. Some lots in bottles and cans were packaged under nitrogen to improve storage stability. Agreement was good between organoleptic and oxidative evaluation of aged oils. After 26 weeks of storage at 100 F, the flavor of partially hydrogenated-winterized oils packaged under nitrogen showed a minimum loss. These same oils did not exhibit much, if any, reduction in their oxidative stability as indicated by storage peroxide values (active oxygen method). Soybean oil not protected with nitrogen demonstrated progressive flavor deterioration at 100 F. After 10 weeks of storage, the deterioration became marked and the flavor score was below 5. From limited observations, bottled oils appear to have a better stability than oils packaged in screw-cap tin cans. Hydrogenated oils packaged under nitrogen in cans had good oxidative stability, but some lowering of the flavor score was observed. Nonhydrogenated soybean oils packaged in tin cans not under nitrogen exhibited the most rapid flavor deterioration of all lots of oil investigated. Presented in part at the AOCS meeting, New York, October 1968 ARS, USDA     

The Oxidation of NdFeB Magnets

The oxidation kinetics in air of a commercial NdFeB magnet have been investigated over the temperature range 335–500°C. The oxide microstructure has been characterized by SEM, XRD and cross-sectional TEM. The results show that the external scale formed consists of an outer layer of Fe₂O₃ and an inner layer of Fe₃O₄ but that the principal degradation process is the formation of an extensive zone of internal oxidation. HREM has been used to show that this zone contains NdO particles embedded in an -Fe matrix. These particles are discrete and very small, approximately 2 nm in diameter, and have an amorphous structure. The -Fe matrix has a columnar grain structure with a grain width of approximately 100 nm. It is argued that the high rates of internal oxidation arise because the external-oxide layers are not protective at the oxidation temperature, and oxygen penetrates to the zone front by fast diffusion along the columnar -Fe grain boundaries.     

On the mechanical performance of closed cell Al alloy foams

The mechanical properties of three different commercially available closed cell Al alloys all made by foam casting are examined. The objective is to assess the roles of cell morphology and of imperfections in governing the basic properties: stiffness, yield strength and fracture resistance. This assessment provides goals for manufacturing strategies that enable attainment of good mechanical performance with affordable process technologies. A prevalent role of curves and wiggles in the cell walls on stiffness and strength (anticipated by models) is affirmed by the present measurements. Systematically larger stiffnesses and yield strengths found in tension than in compression are consistent with a prominent role exerted by such imperfections. Moreover, foam casting is apparently capable of cell morphologies that impart properties approaching the best achievable values for an isotropic closed cell solid, devoid of imperfections. There are associated implications for performance and affordability. Fracture measurements indicate crack growth occurring along the cell walls by a mechanism analogous to the plastic tearing of thin sheets. The crack growth resistances are in the range of 1 kJm⁻². This mechanism infers a toughness that scales with the cell wall thickness and its yield strength.     

PID controller tuning for a multivariable glass furnace process by genetic algorithm

Standard genetic algorithms (SGAs) are investigated to optimise discrete-time proportional-integral-derivative (PID) controller parameters, by three tuning approaches, for a multivariable glass furnace process with loop interaction. Initially, standard genetic algorithms (SGAs) are used to identify control oriented models of the plant which are subsequently used for controller optimisation. An individual tuning approach without loop interaction is considered first to categorise the genetic operators, cost functions and improve searching boundaries to attain the desired performance criteria. The second tuning approach considers controller parameters optimisation with loop interaction and individual cost functions. While, the third tuning approach utilises a modified cost function which includes the total effect of both controlled variables, glass temperature and excess oxygen. This modified cost function is shown to exhibit improved control robustness and disturbance rejection under loop interaction.     

Reviewing VTAM and NetView Security Controls

Abstract

The basic premise of developing any information system is to increase efficiency and manage information in an improved manner. Based on the definitions above, an information system is “a group of devices or artificial objects serving a common purpose to communicate knowledge or intelligence.” Most information systems evolve from processes that either manipulate much information or rely on complex calculations. In other words, information systems are developed either to manage information or to manipulate it. Systems are meant to receive input, manipulate the input, and provide output.