KEYWORDS: Foam, Finite element methods, Neodymium, Composites, Electroluminescence, Performance modeling, Chemical elements, Surface conduction electron emitter displays, Solids, Vibration control
Structural assemblies incorporating negative stiffness elements have been shown to provide both tunable damping properties and simultaneous high stiffness and damping over prescribed displacement regions. In this paper we explore the design space for negative stiffness based assemblies using analytical modeling combined with finite element analysis. A simplified spring model demonstrates the effects of element stiffness, geometry, and preloads on the damping and stiffness performance. Simplified analytical models were validated for realistic structural implementations through finite element analysis. A series of complementary experiments was conducted to compare with modeling and determine the effects of each element on the system response. The measured damping performance follows the theoretical predictions obtained by analytical modeling. We applied these concepts to a novel sandwich core structure that exhibited combined stiffness and damping properties 8 times greater than existing foam core technologies.
Current seals used for vehicle closures/swing panels are essentially flexible, frequently hollow structures whose designs
are constrained by numerous requirements, many of them competing, including door closing effort (both air bind and
seal compression), sound isolation, prevention of water leaks, and accommodation of variations in vehicle build. This
paper documents the first portion of a collaborative research study/exploration of the feasibility of and approaches for
using active materials with shape and stiffness changing attributes to produce active seal technologies, seals with
improved performance. An important design advantage of an active material approach compared to previous active seal
technologies is the distribution of active material regions throughout the seal length, which would enable continued
active function even with localized failure. Included as a major focus of this study was the assessment of polymeric
active materials because of their potential ease of integration into the current seal manufacturing process. In Part 1 of
this study, which is documented in this paper, potential materials were evaluated in terms of their cost, activation
mechanisms, and mechanical and actuation properties. Based on these properties, simple designs were proposed and
utilized to help determine which materials are best suited for active seals. Shape memory alloys (SMA) and
electroactive polymers (EAP) were judged to be the most promising.
We detail the joint concept generation and embodiment development by HRL and GMR&D of shape memory
polymer (SMP) based reversible-on-demand attachments. In this initial study of active material enabled
reversible-on-demand attachments, our primary focus was on hook-and-loop type fasteners. The approach
followed, in broader context, was to incorporate an active material, defined as a material which changes a
fundamental mechanical property upon exposure to an appropriate field, in at least one component of the
hook-and-loop assembly, in this way allowing a field activated change in the stiffness (raising/lowering)
and/or geometry (straightening of the hook) of the component and thus on-demand release of the attachment
This paper describes the fabrication method and properties of one of the two principle classes of
embodiments made during the development of the concept. This class of embodiments, which utilized
thermally activated shape memory polymer materials, was shown to exhibit pull-off forces similar to
conventional "non-active" hook-and-loop fasteners, and significantly, as desired, was reversible with a
reduction in the pull-off force of a factor of ~100. This study was thus successful in demonstrating the
feasibility of a thermally activated SMP based reversible-on-demand distributed attachment.
Reversible electrochemical compound formation has considerable potential to form the basis of a high-strain high-force multifunctional actuator technology. We present preliminary experimental demonstrations of the reversible work capability of solid-state electroplating. Our experimental test case is the volume expansion incurred during the reversible electrochemical formation of thin-film Li metal from a ceramic lithium ion storage medium, LiCoO2 as part of the standard operation of a state-of-the-art Li-ion battery. Reversible work is accomplished through the plating or stripping of the pure Li film against an external load. With the active portion of the structure as a basis, we observe ~10% strain against loads up to 2 MPa, with the load being limited by battery failure. No change in actuation characteristics is observed up to failure.
Graphite intercalation compounds are a class of materials systems formed as ions diffuse into a host graphite structure. The volume expansion associated with this process has been shown to be capable of performing work up to 3.8 MJ/m3. To evaluate GICs for solid state actuation, this study explores some factors affecting the rate at which the volume expansion occurs. Given that diffusion length has an exponential effect on rate, we tested a graphite paper comprised of 7-micron diameter PAN fibers. We found that the paper had ultimate strain and loading properties comparable to HOPG. The paper was cycled under various loads and temperatures to examine the strain rate and repeatability of the material. Testing showed a strong correlation between rate and temperature, while pressure had relatively little effect.
Benjamin Shanabrook, W. Barvosa-Carter, Robert Bass, Brian Bennett, J. Boos, William Bewley, Allan Bracker, James Culbertson, E. Glaser, Walter Kruppa, R. Magno, W. Moore, Jerry Meyer, B. Nosho, Doewon Park, P. Thibado, M. Twigg, R. Wagner, James Waterman, Lloyd Whitman, Ming Yang
Heterostructures formed from III-V semiconductors with the 6.1 angstroms lattice spacing (InAs, GaSb, AlSb and related alloys) have attracted significant interest because of their potential to define a new `state of the art' in applications including 100 GHz high-speed logic circuits, terahertz transistors, sensitive infrared detectors and mid-infrared semiconductor lasers. In this paper, we describe the ongoing work at the Naval Research Laboratory to develop the materials growth and fabrication technology for a variety of 6.1 angstroms-based devices which have the potential to revolutionize infrared optoelectronics and low-power, high- speed electronics.
New methods for producing avoidance behavior among moving obstacles within the context of reactive robotic control are described. These specifically include escape and dodging behaviors. Dodging is concerned with the avoidance of a ballistic projectile while escape is more useful within the context of chase. The motivation and formulation of these new reactive behaviors are presented. Simulation results of a robot in a cluttered and moving world are also provided.
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