to be done in this area. Face recognition is a problem that scarcely clamoured for attention before the computer age but, having surfaced, has involved a wide range of techniques and has attracted the attention of some fine minds (David Mumford was a Fields Medallist in 1974). This singular application of mathematical modelling to a messy applied problem of obvious utility and importance but with no unique solution is a pretty one to share with students: perhaps, returning to the source of our opening quotation, we may invert Duncan's earlier observation, 'There is an art to find the mind's construction in the face!'.

Linear and nonlinear waves, by G. B. Whitham. Pp.636. £50. 1999. ISBN 0 471 35942 4 (Wiley).

Ballistic impact into fabric and compliant composite laminates

Stab resistance of shear thickening fluid (STF)-treated fabrics

https://digital.csic.es/bitstream/10261/136295/5/10.1016_j.progpolymsci.2015.08.002.pdf

Increasing the performance of dielectric elastomer actuators: A review from the materials perspective

Structural power composites

Space-based astronomy and remote sensing systems would benefit from extremely large aperture mirrors that can permit greater-resolution images. To be cost effective and practical, such optical systems must be lightweight and capable of deployment from highly compacted stowed configurations. Such gossamer mirror structures are likely to be very flexible and therefore present challenges in achieving and maintaining the required optically precise shape. Active control based on dielectric elastomers was evaluated in order to address these challenges. Dielectric elastomers offer potential advantages over other candidate actuation technologies including high elastic strain, low power dissipation, tolerance of the space environment, and ease of commercial fabrication into large sheets. The basic functional element of dielectric elastomer actuation is a thin polymer film coated on both sides by a compliant electrode material. When voltage is applied between electrodes, a compressive force squeezes the film, causing it to expand in area. We have explored both material survivability issues and candidate designs of adaptive structures that incorporate dielectric elastomer actuation. Experimental testing has shown the operation of silicone-based actuator layers over a temperature range of -100 °C to 260 °C, suitable for most earth orbits. Analytical (finite element) and experimental methods suggested that dielectric elastomers can produce the necessary shape change when laminated to the back of a flexible mirror or incorporated into an inflatable mirror. Interferometric measurements verified the ability to effect controllable shape changes less than the wavelength of light. In an alternative design, discrete polymer actuators were shown to be able to control the position of a rigid mirror segment with a sensitivity of 1800 nm/V, suggesting that sub-wavelength position control is feasible. While initial results are promising, numerous technical challenges remain to be addressed, including the development of shape control algorithms, the fabrication of optically smooth reflective coatings, consideration of dynamic effects such as vibration, methods of addressing large-numbers of active areas, and stowability and deployment schemes.

Shape control of large lightweight mirrors with dielectric elastomer actuation

: Because fragments from in-flight engine failures can damage critical aircraft components and produce catastrophic consequences, the Federal Aviation Administration is sponsoring research to mitigate the effects of uncontained engine bursts. SRI International is evaluating the ballistic effectiveness of fabric structures made from advanced polymers and developing a computational ability to design fragment barriers. In this reporting period, SRI solved several numerical problems associated with modeling the crimped geometry and interaction of woven yarns. When an orthotropic model is invoked and direction-dependent yarn properties specified, the yarn, as it is loaded, exhibits no appreciable stiffness until it straightens. The model behaved properly in simple simulations of single yarn response to axial and transverse loads. Laboratory and field site tests were performed to provide data for developing and validating the computational model. The ballistic response of fabrics to fragment impact was evaluated; the phenomenology of fabric deformation and failure was elucidated in quasi-static penetration tests; and the tensile properties of yarns and fibers were measured. Three high-strength polymer materials were examined: PBO (Zylon), aramid (Kevlar), and polyethylene (Spectra). Future work will include verification of the microstructural fabric model by implementing it into the DYNA3D code, simulating the static and dynamic penetration tests, and comparing the results. The material properties most important in resisting penetration will be identified and the effects of boundary conditions investigated. SRI will also perform fragment impact tests to generate data on boundary condition effects, measure yarn-on-yarn friction, and participate in full-scale fragment barrier tests at the Navy Air Warfare Center.

Improved Barriers to Turbine Engine Fragments: Interim Report III

The cut resistance of three high-strength yarns under tension-shear loading conditions was measured by pressing a knife blade transversely at a constant rate against a yarn gripped at its ends. The load-deflection relation and the energy required to cut through the yarn were determined for Kevlar (aramid), Spectra (polyethylene), and Zylon (polybenzobisoxazole, or PBO). The cut energy and strain to initiate cutting were highest for Zylon, least for Kevlar, and depended on the slicing angle, the sharpness of the blade, and the pre-tension in the yarn. The dependencies are explained by changes in failure mode of the fibers within the yarn. The test provides input needed for computational simulations of ballistic response of fabrics to sharp fragments and should be useful in designing slash-resistant gloves and clothing.

Cut Resistance of High-strength Yarns

Plastic flow behavior of Inconel 718 under dynamic shear loads

https://cyberleninka.org/article/n/866157.pdf

Jeffrey W. Simons

Papers

Shape control of large lightweight mirrors with dielectric elastomer actuation

Improved Barriers to Turbine Engine Fragments: Interim Report III

Cut Resistance of High-strength Yarns

Plastic flow behavior of Inconel 718 under dynamic shear loads

Effect of composite covering on ballistic fracture damage development in ceramic plates