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NASA NTRS2001

Particle Engulfment and Pushing (PEP): Past Micro-Gravity Experiments and Future Experimental Plan on the International Space Station (ISS)

The interaction of an insoluble particle with a growing solid-liquid interface (SLI) has been a subject of investigation for the four decades. For a metallurgist or a material scientist understanding the fundamental physics of such an interaction is relevant for applications that include distribution of reinforcement particles in metal matrix composites, inclusion management in castings, and distribution of Y2Ba1Cu1O5 (211) precipitates (flux pinning sites) in Y1Ba2Cu3O7 (123) superconducting crystals. The same physics is also applicable to other areas including geological applications (frost heaving in soils) and preservation of biological cells. Experimentally this interaction can be quantified in terms of a critical growth velocity, Vcr, of the SLI below which particles are pushed ahead of the advancing interface, and above which the particles are engulfed. Past experimental evidence suggests that this Vcr is an inverse function of the particle radius, R. In order to isolate the fundamental physics that governs such a relationship it is necessary to minimize natural convection at the SLI that is inherent in ground based experiments. Hence for the purpose of producing benchmark data (Vcr vs. R) PEP is a natural candidate for micro-gravity experimentation. Accordingly, experiments with pure Al containing a dispersion of ZrO2 particles and an organic analogue, succinonitrile (SCN) containing polystyrene particles have been performed on the LMS and USMP-4 mission respectively. In this paper we will summarize the experimental data that was obtained during these two micro-gravity missions and show that the results differ compared to terrestrial experiments. We will also discuss the basic elements of our analytical and numerical model and present a comparison of the predictions of these models against micro-gravity experimental data. Finally. we will discuss our future experimental plan that includes the ISS glovebox and MSRRl.

Sen, Subhayu↗

NASA NTRS2003

Particle Engulfment and Pushing By Solidifying Interfaces

The study of particle behavior at solid/liquid interfaces (SLI s) is at the center of the Particle Engulfment and Pushing (PEP) research program. Interactions of particles with SLI s have been of interest since the 1960 s, starting with geological observations, i.e., frost heaving. Ever since, this field of research has become significant to such diverse areas as metal matrix composite materials, fabrication of superconductors, and inclusion control in steels. The PEP research effort is geared towards understanding the fundamental physics of the interaction between particles and a planar SLI. Experimental work including 1-g and mu-g experiments accompany the development of analytical and numerical models. The experimental work comprised of substantial groundwork with aluminum (Al) and zinc (Zn) matrices containing spherical zirconia particles, mu-g experiments with metallic Al matrices and the use of transparent organic metal-analogue materials. The modeling efforts have grown from the initial steady-state analytical model to dynamic models, accounting for the initial acceleration of a particle at rest by an advancing SLI. To gain a more comprehensive understanding, numerical models were developed to account for the influence of the thermal and solutal field. Current efforts are geared towards coupling the diffusive 2-D front tracking model with a fluid flow model to account for differences in the physics of interaction between 1-g and -g environments. A significant amount of this theoretical investigation has been and is being performed by co-investigators at NASA MSFC.

Source record↗

NASA NTRS1994

Hyperpolarizabilities of Push-Pull Polyenes: Experimental Results and a New Two-State Model

Recent work has demonstrated a correlation between the geometry (i.e., the bond length alteration, BLA) and the first and second hyperpolarizabilities (betta and gamma) of donor-acceptor substituted (push-pull)polyenes.

valence bond model↗

NASA NTRS2011

Benefit of "Push-pull" Locomotion for Planetary Rover Mobility

As NASAs exploration missions on planetary terrains become more aggressive, a focus on alternative modes of locomotion for rovers is necessary. In addition to climbing steep slopes, the terrain in these extreme environments is often unknown and can be extremely hard to traverse, increasing the likelihood of a vehicle or robot becoming damaged or immobilized. The conventional driving mode in which all wheels are either driven or free-rolling is very efficient on flat hard ground, but does not always provide enough traction to propel the vehicle through soft or steep terrain. This paper presents an alternative mode of travel and investigates the fundamental differences between these locomotion modes. The methods of push-pull locomotion discussed can be used with articulated wheeled vehicles and are identified as walking or inchinginch-worming. In both cases, the braked non-rolling wheels provide increased thrust. An in-depth study of how soil reacts under a rolling wheel vs. a braked wheel was performed by visually observing the motion of particles beneath the surface. This novel technique consists of driving or dragging a wheel in a soil bin against a transparent wall while high resolution, high-rate photographs are taken. Optical flow software was then used to determine shearing patterns in the soil. Different failure modes were observed for the rolling and braked wheel cases. A quantitative comparison of inching vs. conventional driving was also performed on a full-scale vehicle through a series of drawbar pull tests in the Lunar terrain strength simulant, GRC-1. The effect of tire stiffness was also compared; typically compliant tires provide better traction when driving in soft soil, however its been observed that rigid wheels may provide better thrust when non-rolling. Initial tests indicate up to a possible 40 increase in pull force capability at high slip when inching vs. rolling.

robotics↗

NASA NTRS2014

NASA Green Propulsion Technologies Pushing Aviation to New Heights

Center Director Free is providing the Keynote at the Disruptive Propulsion Conference, sponsored by Cranfield University, Cranfield, Bedfordshire, England in November. Director Free will be presenting a PowerPoint presentation titled, NASA Green Propulsion Technologies Pushing Aviation to New Heights at both the conference and a meeting at the Royal Aeronautical Society.

Subsonic aeronautics research↗

NASA NTRS2016

Ultrasonic Nondestructive Evaluation of Pultruded Rod Stitched Efficient Unitized Structure (PRSEUS) During Large-Scale Load Testing and Rod Push-Out Testing

The Pultruded Rod Stitched Efficient Unitized Structure (PRSEUS) is a structural concept developed by the Boeing Company to address the complex structural design aspects associated with a pressurized hybrid wing body (HWB) aircraft configuration. The HWB has long been a focus of NASA's environmentally responsible aviation (ERA) project, following a building block approach to structures development, culminating with the testing of a nearly full-scale multi-bay box (MBB), representing a segment of the pressurized, non-circular fuselage portion of the HWB. PRSEUS is an integral structural concept wherein skins, frames, stringers and tear straps made of variable number of layers of dry warp-knit carbon-fiber stacks are stitched together, then resin-infused and cured in an out-of-autoclave process. The PRSEUS concept has the potential for reducing the weight and cost and increasing the structural efficiency of transport aircraft structures. A key feature of PRSEUS is the damage-arresting nature of the stitches, which enables the use of fail-safe design principles. During the load testing of the MBB, ultrasonic nondestructive evaluation (NDE) was used to monitor several sites of intentional barely-visible impact damage (BVID) as well as to survey the areas surrounding the failure cracks after final loading to catastrophic failure. The damage-arresting ability of PRSEUS was confirmed by the results of NDE. In parallel with the large-scale structural testing of the MBB, mechanical tests were conducted of the PRSEUS rod-to-overwrap bonds, as measured by pushing the rod axially from a short length of stringer.

Johnston, Patrick H.↗

NASA NTRS1965

Where nothing falls without a push.

Zero-g simulation by parabolic aircraft flight for astronaut training

WEIGHTLESSNESS SIMULATION↗

NASA NTRS1968

Current pushing of the oscillation frequency of a 6328-angstrom units He-Ne laser.

Laser oscillation frequency shift dependence on discharge current in 6328 A He-Ne laser

Arrathoon, R.↗

NASA NTRS1979

Push test for switch welds

Pencil-like tool that applies low predetermined force, may be used to individually test switch welds for identification of poor or marginal welds without harming good ones.

Torborg, C. J.↗

NASA NTRS1985

Orbit on demand - In this century if pushed

Performance requirements and design features of the next generation of manned launch vehicles are discussed. The vehicles will launch within minutes of demand and will have a several-day turnaround time. Launch and landing sites will have minimal facilities. Baseline requirements comprise carriage and return of a 5000 lb, 7 ft diam, 15 ft long payload, a 160 n. mi. polar orbit, a 200 fps on-orbit delt-V capability, provisions for two men for 24 hr, an 1100 n. mi. cross range option, 500 flights/vehicle, land on 10,000 ft runways, and be acceptable passing over populated areas. Significant advances are needed in propulsion and fuel systems, lightweight durable structures and airbreathing acceleration engines. Trade-offs have yet to be fully explored among the number of stages and horizontal or vertical take-off.

Martin, J. A.↗

NASA NTRS1990

Pushing back the frontier - A mission to the Pluto-Charon system

A flyby mission to Pluto is proposed. The size, orbit, atmosphere, and surface of Pluto, and the Pluto-Charon system are described. The benefits of a planetary flyby compared to ground observations are discussed in terms of imaging capabilities. Planned payloads include a plasma science package, a UV spectrometer, and a thermal mapper. The advantages of a dual launch to Mars and the need for a Jupiter-Pluto transfer are considered. A diagram of a spacecraft for a flyby study of Pluto is provided.

Farquhar, Robert↗

NASA NTRS1991

Push Tester For Laminated Films

Small instrument used to measure brittleness of polymer film adhesively bonded to hard substrate. Penlike instrument has microball tip. Small pointer in slot on side of instrument used to calibrate and indicate spring force applied by point. Microball dents only small area of specimen. Such measurements used to measure rates of embrittlement in environmental tests of candidate laminated-film covers for photovoltaic modules. Not limited to transparent films; also used on opaque laminated films on back panels of photovoltaic modules.

Sugimura, Russell S.↗

NASA NTRS1948