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Results for “Spalling”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Trajectories of solid particles spalled from a carbonaceous heat shield

Trajectories are calculated of solid carbon particles that spall from a carbonaceous heat shield and travel through a given flow field. The mathematical model takes into account mass, momentum, and energy conservation during evaporation of the particles in an effort to understand spallation phenomena and their consequences in a physical way. The solution technique is applied to available Galileo Probe flow field solutions. Plots of trajectories and other particle parameters are presented for a range of initial particle sizes and velocities. It is shown that a significant amount of gaseous carbon is deposited in the inviscid region and ahead of the bow shock as well as in the ablation layer.

Davies, C. B.↗
NASA NTRS1989

Techniques for reduced spalling and increased operating life of xenon ion engines

Erosion measurements were performed on a modified J-series 30 cm ion engine operating on xenon propellant. The data indicate that a factor of 15 reduction in erosion of the upstream baffle face can be obtained by introducing nitrogen into the xenon propellant. Minor design changes to reduce spalling coupled with the reduction in baffle erosion may increase the operating life of xenon ion engines.

Garner, Charles E.↗
NASA NTRS1990

Rolling-Contact Spalling In Bearings

Report describes experimental and theoretical studies of effects of thermal and mechanical contact stresses and attendant plastic deformations responsible for rolling-contact spalling of the 440C-steel bearings in high-pressure-oxygen turbopump.

Kumar, A. M.↗
DOE OSTI2023

A spall and diffraction study of nanosecond pressure release across the iron ε-α phase boundary

The extreme response of polycrystalline iron at high pressures and high strain rates is revealed by means of high-power laser pulses. The compression portion of the pulse coupled with x-ray diffraction identifies the expected body-centered cubic (α) to hexagonal close packed (ε) displacive transformation. Upon release, observation shows that the complete reverse transformation takes approximately 8 ns and that the structure returns to its initial microstructural configuration, in a reversible transformation path. This is in good agreement with molecular dynamics (MD) simulations which predict an inverse dependence between transformation time and strain rate. The grain size is reduced from μm to nm range during compression and begins increasing back to the original grain size on decompression. The kinetics of the transition is dictated by heterogenous nucleation as it follows the Johnson-Mehl-Avrami-Kolmogorov equation with the appropriate time exponent of ~1. This is confirmed by MD simulations which also identify profuse twinning and dislocation generation. Here, the tensile pulse generated upon reflection at the free surface is captured by time-resolved free surface velocity measurements from which a peak tensile stress of 7 GPa is obtained, in stark contrast with its quasi-static value of ~200 MPa. At these strain rates, the strength of grain interiors, which is determined by twinning and slip exceeds the strength of the boundaries, and failure initiates preferentially in the latter.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Repair of Cracks and Spalls within the Concrete Façade Covering the Runit Island Waste Containment Structure (V.2.0)

The concrete repair shall be performed using a combination of pre-packaged cement-based mortar (Structural Concrete® V/O) supplied by Five Star Products, Inc., and CRACKBOND® products from Adhesive Technology Corp., Pompano Beach, Florida. Five Star Structural Concrete® V/O is a high strength, rapid setting, one component, permanent concrete repair material used primarily for vertical and overhead structural repairs. The material produces a repair which is dimensionally stable, develops an integral bond to existing concrete, and restores structural integrity within hours of placement (Five Star DESIGN-A-SPEC™ Guidelines). The CRACKBOND® family of products are two component, high strength structural epoxy formulations specifically designed to repair cracks in concrete.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1975

Solutions for discharge chamber sputtering and anode deposit spalling in small mercury ion thrusters

Small electron bombardment mercury ion thrusters are considered for attitude-control and station-keeping operations in the case of earth synchronous satellites. The required operational lifetimes of the order of 20,000 hours could present problems because of the occurrence of sputter erosion of thruster discharge chamber components. The investigation reported is concerned with a study of these problems and the development of approaches for overcoming them.

Power, J. L.↗