Mechanical Components

Swell Sleeves for Testing Explosive Devices

A device is detonated in a sleeve and the resultant swelling is measured.   A method of testing explosive and pyrotechnic devices involves exploding the devices inside swell sleeves. Swell sleeves have been used previously for measuring forces. In the present method, they are used to obtain quantitative indications of the energy released in explosions of the devices under test.  

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Mechanical Amplifier for a Piezoelectric Transducer

In addition to multiplication of stroke, the design affords momentum compensation. A mechanical amplifier has been devised to multiply the stroke of a piezoelectric transducer (PZT) intended for use at liquid helium temperatures. Interferometry holds the key to high angular resolution imaging and astrometry in space. Future space missions that will detect planets around other solar systems and perform detailed studies of the evolution of stars and galaxies will use new interferometers that observe at mid- and far-infrared wavelengths. Phase-measurement interferometry is key to many aspects of astronomical interferometry, and PZTs are ideal modulators for most methods of phase measurement, but primarily at visible wavelengths. At far infrared wavelengths of 150 to 300 µm, background noise is a severe problem and all optics must be cooled to about 4 K. Under these conditions, piezos are ill-suited as modulators, because their throw is reduced by as much as a factor of 2, and even a wavelength or two of modulation is beyond their capability. The largest commercially available piezo stacks are about 5 in. (12.7 cm) long and have a throw of about 180 µm at room temperature and only 90 μm at 4 K. It would seem difficult or impossible to use PZTs for phase measurements in the far infrared were it not for the new mechanical amplifier that was designed and built.

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Viscoelastic Vibration Dampers for Turbomachine Blades

These dampers can be retrofitted to existing machines. Simple viscoelastic dampers have been invented for use on the root attachments of turbomachine blades. These dampers suppress bending- and torsion-mode blade vibrations, which are excited by unsteady aerodynamic forces during operation. In suppressing vibrations, these dampers reduce fatigue (thereby prolonging blade lifetimes) while reducing noise. These dampers can be installed in new turbomachines or in previously constructed turbomachines, without need for structural modifications. Moreover, because these dampers are not exposed to flows, they do not affect the aerodynamic performances of turbomachines.

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Energy-Absorbing, Lightweight Wheels

Efficient structures would absorb impact energies and distribute contact loads. Improved energy- absorbing wheels are under development for use on special-purpose vehicles that must traverse rough terrain under conditions (e.g., extreme cold) in which rubber pneumatic tires would fail. The designs of these wheels differ from those of prior non-pneumatic energy-absorbing wheels in ways that result in lighter weights and more effective reduction of stresses generated by ground/wheel contact forces. These wheels could be made of metals and/or composite materials to withstand the expected extreme operating conditions.

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Soft Landing of Spacecraft on Energy-Absorbing Self-Deployable Cushions

A report proposes the use of cold hibernated elastic memory (CHEM) foam structures to cushion impacts of small (1 to 50 kg) exploratory spacecraft on remote planets. Airbags, which are used on larger (800 to 1,000 kg) spacecraft have been found to (1) be too complex for smaller spacecraft; (2) provide insufficient thermal insulation between spacecraft and ground; (3) bounce on impact, thereby making it difficult to land spacecraft in precisely designated positions; and (4) be too unstable to serve as platforms for scientific observations. A CHEM foam pad according to the proposal would have a glass-transition temperature (Tg) well above ambient temperature. It would be compacted, at a temperature above Tg, to about a tenth or less of its original volume, then cooled below Tg, then installed on a spacecraft without compacting restraints. Upon entry of the spacecraft into a planetary atmosphere, the temperature would rise above Tg, causing the pad to expand to its original volume and shape. As the spacecraft decelerated and cooled, the temperature would fall below Tg, rigidifying the foam structure. The structure would absorb kinetic energy during ground impact by inelastic crushing, thus protecting the payload from damaging shocks. Thereafter, this pad would serve as a mechanically stable, thermally insulating platform for the landed spacecraft.

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Bare Conductive Tether for Decelerating a Spacecraft

A document describes a prototype of electrically conductive tethers to be used primarily to decelerate spacecraft and/or generate electric power for the spacecraft. Like prior such tethers, this tether is designed so that when it is deployed from a spacecraft in orbit, its motion across the terrestrial magnetic field induces an electric current. The Lorentz force on the current decelerates the spacecraft. Optionally, the current can be exploited to convert some orbital kinetic energy to electric energy for spacecraft systems. Whereas the conductive portions of prior such tethers are covered with electrical insulation except for end electrodes that make contact with the ionosphere, this tether includes a conductive portion that is insulated along part of its length but deliberately left bare along a substantial remaining portion of its length to make contact with the ionosphere. The conductive portions of the tether are made of coated thin aluminum wires wrapped around strong, lightweight aromatic polyamide braids. The main advantages of the present partly-bare-tether design over the prior all-insulated-tether design include greater resistance to degradation by the impact of monatomic oxygen at orbital altitude and speed and greater efficiency in collecting electrons from the ionosphere.

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Staggering Inflation To Stabilize Attitude of a Solar Sail

A document presents computational simulation studies of a concept for stabilizing the attitude of a spacecraft during deployment of such structures as a solar sail or other structures supported by inflatable booms. Specifically, the solar sail considered in this paper is a square sail with inflatable booms and attitude control vanes at the corners. The sail inflates from its stowed configuration into a square sail with four segments and four vanes at the tips. Basically, the concept is one of controlling the rates of inflation of the booms to utilize in mass distribution properties to effect changes in the system’s angular momentum.

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