Modification of mechanical properties of Kevlar fibre by polymer infiltration

While high-performance organic fibres such as poly (para phenylene benzobisthiazole) and Kevlar possess excellent mechanical properties under axial tension, their strength under compression is generally poor. This study focuses on a polymer infiltration approach to modify the mechanical properties of the Kevlar 49 fibre in tension as well as compression, in which various polymeric resins are infiltrated in an opened fibrillar network of Kevlar single filaments. Opening was achieved using concentrated sulfuric acid, which resulted in a strength loss at high acid concentrations. However, compared to the acid-treated fibre, both the tensile strength and strain-to-failure of the fibres were found to increase after infiltration with epoxy resins and bismaleimide polymers. Polymer infiltration also resulted in a significant improvement in the compressive strength of the Kevlar fibre, with the bismaleimide performing better than the epoxy resins. Plasma modification using ammonia was also used to enhance interfibrillar adhesion by incorporating reactive amine groups on the fibril surface     

Digital television: a perspective

Commercial television was standardized originally mainly for entertainment, sports, and news, using over-the-air broadcasts. While a few upward compatible changes have been added over the years, the standard has remained essentially unchanged. Moreover, no other standard has had so many products and services built around it and withstood such a period of rapid technological change. Digital television promises to disturb the current equilibrium in consumer television and in the broader media industries. It is forcing a convergence with the simultaneous expansion of personal computing into the home and the commercialization of research networks. Digitizing television in a cost-effective manner and integrating it with computers, telecommunication networks, and consumer products will produce a large array of new products and services. The paper describes digital television, factors affecting it, its potential, and some major issues in its evolution     

An enhanced,acoustic emission-based,single-fiber-composite test

In the single-fiber-composite (SFC) test, a fiber imbedded in a matrix is loaded in tension, resulting in a fragmentation of the fiber. In the conventional version of this test, the final fiber fragmentation length distribution is used with a micro-mechanical model to determine the average fiber/matrix interfacial shear stress. In the enhanced version of this test, one also determines the applied stress at each fiber fracture, and from this, one can evaluate the strength of the fiber at short gage lengths. In our measurement system, we utilize an acoustic emission (AE) technique to detect the fiber fractures and to locate the fiber breaks and so determine both the fiber failure stresses as well as the fiber fragmentation lengths while the test is in progress. Critical to the success of this test is a broadband AE system that utilizes point-like AE sensors, procedures for evaluatingin situ, the wavespeed of the first wave arrival and signal processing techniques for determining the arrival time of this signal as precisely as possible for a broad range of wave shapes. Here we describe the application of such an enhanced SFC test procedure to investigate the failure of a Nicalon fiber in an epoxy matrix.     

Iterative algorithm for optimal fiducials under weak perspective projection

In previous work, we designed space fiducials with the aim of making camera pose determination as noise‐insensitive as possible. These fiducials turned out to be sets of points that formed concentric regular polyhedra. Here, we apply an idea of Dementhon and Davis and test and analyze an iterative linear algorithm in conjunction with our optimal fiducials to increase the accuracy of the computed camera pose. We also analyze under what circumstances this iterative algorithm is guaranteed to converge to the correct solution. Comprehensive computer simulations illustrate the behavior of the algorithm and the degree of improvement in pose determination in case of convergence. © 2009 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 19, 27–36, 2009     

Dilated Networks for Photonic Switching

We present some novel architectures for rearrangeably nonblocking multistage photonic space switches implemented using arrays ofTi:LiNbO_{3}directional couplers. Multistage networks, studied mostly in the electronic domain, are obtained by minimizing the number of 2 × 2 elements needed to implement a switch. Unfortunately, straightforward extensions of these networks to the photonic domain show that the switch size has to be severely limited by the crosstalk in each of theTi:LiNbO_{3} 2 times 2switching elements. Our networks, on the other hand, have a controllable (including almost zero) amount of crosstalk, low optical path loss, and an asymptotically optimal number of directional coupler switches for a given switch size. In addition, the switch has a simple control algorithm and its performance for light loading appears very promising. The switch is easily decomposable into smaller arrays of no more than two types, making it easy to partition the switch into chips. At the cost of a slight increase in crosstalk, the switch can be made single fault tolerant in terms of its ability to connect any input to any output.     

Electrospun Hybrid Soy Protein/PVA Fibers

Rheological behavior and spinnability of biodegradable materials based on SPI and PVA were studied for the production of electrospun fibers. pH level, processing temperature, and heating time were adjusted to investigate the effects of denaturing of soy protein on the rheology of SPI/PVA solutions. The results show that zero shear viscosity and degree of shear thinning of the SPI solution can be controlled by adjusting pH level and thermal treatment. The continuous production of uniform SPI/PVA fibers was achieved by electrospinning. The presence and amount of soy protein in the electrospun fibers was determined by EMPA and elemental analysis, confirming that the SPI was well incorporated into the PVA and remained in the electrospun fibers.

     

Surface modification of UHSPE fibers through allylamine plasma deposition. I. Infrared and ESCA study of allylamine plasma formed polymers

Allylamine (CH₂?CH? CH₂? NH₂) was polymerized through rf generated plasma at varying powers and times. Chemical groups and elemental compositions in the polymers were studied using ESCA and infrared spectroscopy. It was observed that plasma derived polymers contained a significant number of primary amines, along with some secondary and tertiary amines, imines, and nitrile groups. Plasma derived polymers had a complex structure and contained unsaturated groups. A considerable amount of oxygen, primarily from residual air in the plasma reaction chamber, and possibly from atmosphere when plasma polymers were exposed to air, was responsible for carbonyl, amide, ether, and hydroxyl groups found in the polymer structure. Some silicon was also detected in the plasma deposited films.     

Design and implementation of a high-speed transport protocol

The design, analysis, and implementation of an end-to-end transport protocol that is capable of high throughput consistent with the evolving high-speed physical networks based on fiber-optic transmission lines and high-capacity switches are presented. Unlike current transport protocols in which changes in control/state information are exchanged between the two communicating entities only when some significant event occurs, this protocol exchanges relevant and full state information periodically and frequently. It is shown that this reduces the complexity of protocol processing by removing many of the procedures required to recover from network inadequacies such as bit errors, packet loss, and out-of-sequence packets and makes it more amenable to parallel processing. Also, to increase channel utilization in the presence of high-speed, long-latency networks and to support diagrams, and efficient implementation of the selective repeat method of error control is incorporated in the protocol. An implementation using a Motorola 68030-based multiprocessor as a front-end processor is described. The current implementation can comfortably handle 10-15 kpackets/s     

Characterization of interfacial and mechanical properties of “green” composites with soy protein isolate and ramie fiber

Environment-friendly fiber-reinforced composites were fabricated using ramie fibers and soy protein isolate (SPI) and were characterized for their interfacial and mechanical properties. Ramie fibers were characterized for their tensile properties and the parameters for the Weibull distribution were estimated. Effect of glycerol content on the tensile properties of SPI was studied. Interfacial shear strength (IFSS) was determined using the microbond technique. Based on the IFSS results and fiber strength distribution, three different fiber lengths and fiber weight contents (FWC) were chosen to fabricate short fiber-reinforced composites. The results indicate that the fracture stress increases with increase in fiber length and fiber weight content. Glycerol was found to increase the fracture strain and reduce the resin fracture stress and modulus as a result of plasticization. For 10% (w/w) of 5 mm long fibers, no significant reinforcement effect was observed. In fact the short fibers acted as flaws and led to reduction in the tensile properties. On further increasing the fiber length and FWC, a significant increase in the Young's modulus and fracture stress and decrease in fracture strain was observed as the fibers started to control the tensile properties of the composites. The experimental data were compared to the theoretical predictions made using Zweben's model. The experimental results are lower than the predicted values for a variety of reasons. However, the two values get closer with increasing fiber length and FWC.     

An automated testing machine for monitoring the evolution of fiber breaks

A cooperative agreement between the National Institute of Standards and Technology (NIST) and the Textile Research Institute/Princeton (TRI/Princeton) has resulted in the development of an automated tensile testing machine for determining the interfacial shear strength (IFSS) as determined by the single fiber fragmentation (SFF) test. The imaging capability of this new machine permits the archiving of data for additional analyses as new data reduction methods are developed and provides a framework for the sharing of fragmentation data among researchers. To keep pace with the changing directions of composite micromechanics research, the new machine was extended to obtaining archival data on fiber fragmentation in 2D multifiber arrays by utilizing a new fiber placement device that allows for the precise placement of these arrays within the dogbone specimen. This paper is declared a work of the U.S. Government and is not subject to copyright protection in the United States.

---