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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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The construction and processing of four test lasers are discussed, and the test results are assessed. Tests show that the best performance was obtained from cathodes made from internally oxidized Ag-Cu alloys or pure Cu. Due to the cold cathode technology developments, sealed-off 1 w CO2 lasers with gas volumes of only 50 cu cm were duplicated, and have performed satisfactorily for more than 6000 hours.
The present conference discusses topics in line broadening and shift phenomena in low-to-moderately dense plasmas, resonances in the continuum, hot and dense laser-produced plasmas, collisional broadening and intermolecular potentials, molecular broadening and collision-induced spectroscopy, collisional redistribution and laser-assisted collision processes, coherent and nonlinear spectroscopy, astrophysical line-shapes, and short-wavelength lasers. Attention is given to the widths and shifts of Be ion lines, the Stark broadening of Xe II and Fe I lines, perturbed and unperturbed series in the line-shapes of autoionizing Rydberg series, the line-broadening of hydrogenic ions in dense plasmas, Doppler-free line-shapes, the Franck-Condon principle, the dynamics of laser-assisted reactive collisions, the gas-kinetic effects of light, collision-induced processes in nonlinear optics, and line-shaping phenomena in cool stars.
Laser ablation is the removal of material by laser pulses through photochemical, photothermal, or photophysical mechanisms, which is useful to prepare an adherend surface for adhesive bonding. Laser surface treatment is a method that has been under research for the past decade at NASA Langley Research Center (LaRC) to prepare surfaces for adhesive joining of aerospace composite materials and metallic alloys. Laser ablation of composite materials increases surface area and removes the surface contaminants introduced during material handling and fabrication processes. By adjustment of laser parameters, it is possible to obtain repeatable surface conditions, and superficial contaminants can be selectively and efficiently removed without damaging the underlying carbon fibers or the carbon fiber reinforced polymer (CFRP) substrate. Laser induced breakdown spectroscopy (LIBS) is a surface characterization and inspection technique that can be seamlessly integrated into the laser surface treatment process. At NASA LaRC, a single laser system has been used for both laser surface treatment and LIBS, which enables in-situ monitoring of surface contaminants. This work focuses on the advancements at LaRC using LIBS to detect surface silicone contaminants on aerospace CFRP materials and to provide surface quality control in adhesive bonding.
Laser ablation is the removal of material by laser pulses through photochemical, photothermal, or photophysical mechanisms, which is useful to prepare an adherend surface for adhesive bonding. Laser surface treatment is a method that has been under research for the past decade at NASA Langley Research Center (LaRC) to prepare surfaces for adhesive joining of aerospace composite materials and metallic alloys. Laser ablation of composite materials increases surface area and removes the surface contaminants introduced during material handling and fabrication processes. By adjustment of laser parameters, it is possible to obtain repeatable surface conditions, and superficial contaminants can be selectively and efficiently removed without damaging the underlying carbon fibers or the carbon fiber reinforced polymer (CFRP) substrate. Laser induced breakdown spectroscopy (LIBS) is a surface characterization and inspection technique that can be seamlessly integrated into the laser surface treatment process. At NASA LaRC, a single laser system has been used for both laser surface treatment and LIBS, which enables in-situ monitoring of surface contaminants. This work focuses on the advancements at LaRC using LIBS to detect surface silicone contaminants on aerospace CFRP materials and to provide surface quality control in adhesive bonding.
Interest in multi-axis additive manufacturing has grown significantly in recent years due to associated benefits that range from improved quality to support for greater geometric complexity. A method of 5-axis Laser Hot-Wire Directed Energy Deposition is developed and demonstrated in this study using an 8-axis industrial robot, comprised of a 6-axis serial link robot and a 2 degree-of-freedom positioner. Coordinated 5-axis motion is used to print Ti-6Al-4V objects predominantly through build plate rotation. Methods of slicing and toolpath generation are presented, including the use of an alternating toolpath direction philosophy and the manipulation of the CAD model surface normal vectors for determining the required build plate tilt angles for maintaining consistent deposition orientations relative to gravity. Another objective of the study was to determine the limits of conventional slicing and layer height control techniques for printing geometries with significant unsupported overhangs. A comparison is made between the behavior of normal and conformal bead alignment in this regard, and the performance of the layer height controller is reported as it relates to process stability and the limits of printing overhang geometries. Unsupported overhangs were successfully printed at 35° without build plate tilt and 45° with build plate tilt. Toolpath velocity and net-shape printing performance are reported as well, with 3D scans of the printed surfaces used for net-shape characterization. In all, the printing of three geometries is presented, including the overhang geometry, a 5-axis toolpath geometry, and a large-scale, multi-bead demonstrator part, which exceeded 500 mm in height and weighed 44 kg (97 lbs).
General systems design and optical and signal processing requirements for laser velocimetric measurement of flows are reviewed. Bias errors which occur in measurements using burst (counter) processors are discussed and particle seeding requirements are suggested.
Additive Manufacturing (AM) has significantly evolved over the last decade for use in the aerospace industry, particularly for liquid rocket engines. AM offers a considerable departure from traditional manufacturing to rapidly fabricate components with complex internal features. High performance liquid rocket engine combustion chambers that operate in a high heat flux environment are fabricated using a copper-alloy liner with a series of integral coolant channels. Copper-alloys provide the necessary conductivity and material strength for adequate design margins offering high performance without the need for film coolant. Copper-alloys present unique challenges to properly melt the powder in laser-based AM processes due to their high reflectivity and conductivity. Starting in 2014, NASA’s Marshall Space Flight Center (MSFC) and Glenn Research Center (GRC) have developed a process for AM of GRCop (Copper- Chrome-Niobium) alloys using Selective Laser Melting (SLM). GRCop, originally developed at GRC, is a high conductivity, high-strength, dispersion strengthened copper-alloy for use in high-temperature, high heat flux applications. NASA has completed significant material characterization and testing, along with hot-fire testing, to demonstrate that GRCop-42 and GRCop-84 alloys are suitable for use in combustion chambers. Additional development and testing has been completed on AM bimetallic chambers using GRCop-84 liners and superalloy jackets, fabricated using two Directed Energy Deposition (DED) processes: Electron Beam Freeform Fabrication (EBF³) and Blown Powder DED. NASA completed hot-fire testing on various AM chambers using GRCop-84, GRCop-42, and bimetallic chambers in Liquid Oxygen (LOX)/Hydrogen, LOX/Methane, and LOX/Kerosene propellants.
Abstract In this study, the evolution of solidification texture during LPBF of Ti-free grade 300 maraging steel, and its effect on texture development during subsequent post-fabrication heat treatments was characterized using Electron Backscatter Diffraction (EBSD). It was found that in the as-fabricated state, no texture was observed in the room temperature martensitic phase. However, the reconstructed parent austenite phase displayed a Cube texture with a minor fraction of Rotated Goss texture. During subsequent aging treatments involving two different routes, namely direct aging of the as-fabricated samples, and conventional solution treatment + aging of the as-fabricated samples, significant changes in the texture components of parent austenite were observed, whereas no changes in texture were observed in the room temperature martensitic phase. During direct aging, it was found that with an increase in the aging temperature up to 520 °C, the texture components of the parent austenite changed from Cube/Rotated Goss to Brass, whereas during the conventional solution treatment and aging cycle, interestingly a change in texture component to rotated copper was observed. The transitions in texture components have been discussed using the concepts of recrystallization and twinning in austenite during annealing and/or aging, and strain energy release maximization (SERM) theory. Furthermore, the importance of these preferred orientations on the mechanical properties was quantified using transformation potential diagrams.
A semi-analytical model for deterministic surface smoothing of fused silica below the evaporation temperature threshold is presented. Using this model, a method for calculating deterministic track depths for laser polishing fused silica is derived and validated with experiments. In this work, model predictions were in good agreement with experiment across varying laser preheating temperature and power. With the semi-analytical method presented here, deterministic laser smoothing can be achieved in the densification regime to close the process loop of laser polishing.
Solids ablate under laser irradiation, but experiments have not previously characterized the initiation of this process at ultrarelativistic laser intensities. Here, we present first measurements of bulk ion velocity distributions as ablation begins, captured as a function of depth via Doppler-shifted x-ray line emission from two viewing angles. Bayesian analysis indicates that bulk ions are either nearly stationary or flowing outward at the plasma sound speed. The measurements quantitatively constrain the laser-plasma ablation mechanism, suggesting that a steplike electrostatic potential structure drives solid disassembly.
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Abstract not provided.
In powder bed fusion additive manufacturing, machines are often equipped with in-situ sensors to monitor the build environment as well as machine actuators and subsystems. The data from these sensors offer rich information about the consistency of the fabrication process within a build and across builds. This information may be used for process monitoring and defect detection; however, little has been done to leverage this data from the machines for more than just coarse-grained process monitoring. In this work we demonstrate how these inherently temporal data may be mapped spatially by leveraging scan path information. We then train a XGBoost machine learning model to predict localized defects—specifically soot–using only the mapped process data of builds from a laser powder bed fusion process as input features. The XGBoost model offers a feature importance metric that will help to elucidate possible relationships between the process data and observed defects. Finally, we analyze the model performance spatially and rationalize areas of greater and lesser performance.
Investigations continue of diode-laser-pumped solid-state laser oscillators and nonlinear processes using them as sources. Diode laser array pumped Nd:YAG and Nd:glass lasers have been demonstrated. Theoretical studies of non-planar oscillators have been advanced, producing new designs which should be more resistant to feedback and offer better frequency stability. A monolithic, singly resonant Optical Parametric Oscillator in MgO:LiNbO3 has been operated.
Laser-induced N2 ionization is accomplished using a commercially available Nd:YAG laser, and confirmed by means of ion-collection and spectral measurements. Neutral N2 is excited by six photons of the third harmonic frequency, or 355 nm, and is transformed to an ionized state. The radiation at 355 nm is separated from the fundamental and frequency-doubled Nd:YAG radiation to guarantee monochromatic incident radiation. Intense lines near 391.4 nm are found in the initial laser polarization and for a 90-degree rotation of polarization. The radiation at 391.4 nm is associated with an incoherent laser-induced flourescence process related to an ionized-state transition, and increases quadratically with laser power. A 45-mJ laser pulse focused to a diameter of 17 microns can produce an ion concentration of 3.25 x 10 to the 13th ions/cu cm. The large ion concentration and robust fluorescence signal make this technique an efficient method for time-of-flight velocimetry and in-flight testing.
This paper describes the experimental and numerical characterization of the capillary fuel injection, atomization, dispersion, and vaporization of liquid fuel in a coflowing air stream inside a single venturi tube. The experimental techniques used are all laser-based. Phase Doppler analyzer was used to characterize the atomization and vaporization process. Planar laser-induced fluorescence visualizations give good qualitative picture of the fuel droplet and vapor distribution. Limited quantitative capabilities of the technique are also demonstrated. A modified version of the KIVA-II was used to simulate the entire spray process, including breakup and vaporization. The advantage of venturi nozzle is demonstrated in terms of better atomization, more uniform F/A distribution, and less pressure drop. Multidimensional spray calculations can be used as a design tool only if care is taken for the proper breakup model, and wall impingement process.
We developed an all solid state laser ranging detector technology, which makes the goal of millimeter accuracy achievable. Our design and construction philosophy is to combine the techniques of single photon ranging, ultrashort laser pulses, and fast fixed threshold discrimination while avoiding any analog signal processing within the laser ranging chain. The all solid state laser ranging detector package consists of the START detector and the STOP solid state photon counting module. Both the detectors are working in an optically triggered avalanche switching regime. The optical signal is triggering an avalanche current buildup which results in the generation of a uniform, fast risetime output pulse.