Andrew T. Anderson

Laser powder-bed fusion additive manufacturing: Physics of complex melt flow and formation mechanisms of pores, spatter, and denudation zones

Abstract This study demonstrates the significant effect of the recoil pressure and Marangoni convection in laser powder bed fusion (L-PBF) of 316L stainless steel. A three-dimensional high fidelity powder-scale model reveals how the strong dynamical melt flow generates pore defects, material spattering (sparking), and denudation zones. The melt track is divided into three sections: a topological depression, a transition and a tail region, each being the location of specific physical effects. The inclusion of laser ray-tracing energy deposition in the powder-scale model improves over traditional volumetric energy deposition. It enables partial particle melting, which impacts pore defects in the denudation zone. Different pore formation mechanisms are observed at the edge of a scan track, at the melt pool bottom (during collapse of the pool depression), and at the end of the melt track (during laser power ramp down). Remedies to these undesirable pores are discussed. The results are validated against the experiments and the sensitivity to laser absorptivity is discussed.

Concussion, microvascular injury, and early tauopathy in young athletes after impact head injury and an impact concussion mouse model

The mechanisms underpinning concussion, traumatic brain injury (TBI) and chronic traumatic encephalopathy (CTE) are poorly understood. Using neuropathological analyses of brains from teenage athletes, a new mouse model of concussive impact injury, and computational simulations, Tagge et al. show that head injuries can induce TBI and early CTE pathologies independent of concussion.

X-Ray Response of National Ignition Facility First Surface Materials

The ablation of first surface materials by x rays is a primary threat to the final optics in the NIF target chamber. To meet the operational goals of the facility, the designs of the chamber wall, ...

Ablation of NIF Targets and Diagnostic Components by High Power Lasers and X-Rays from High Temperature Plasmas

The National Ignition Facility (NIF) will consist of 192 laser beams that have a total energy of up to 1.8 MJ in the third harmonic ((lambda) equals 0.35 micrometer) with the amount of second harmonic and fundamental light depending on the pulse shape. Material near best focus of the third harmonic light will be vaporized/ablated very rapidly, with a significant fraction of the laser energy converted into plasma x rays. Additional plasma x rays can come from the imploding/igniting capsule inside Inertial Confinement Fusion (ICF) hohlraums. Material from outer portions of the target, diagnostic components, first-wall material, and optical components, are ablated by the plasma x rays. Material out to a radius of order 3 cm from target center is also exposed to a significant flux of second harmonic and fundamental laser light. Ablation can accelerate the remaining material to high velocities if it has been fragmented or melted. In addition, the high velocity debris wind of the initially vaporized material pushes on the fragments/droplets and increases their velocity. The high velocity shrapnel fragments/droplets can damage the fused silica shields protecting the final optics in NIF. We discuss modeling efforts to calculate vaporization/ablation, x-ray generation, shrapnel production, and ways to mitigate damage to the shields.

Target Area Design Basis and System Performance for the National Ignition Facility

The NIF Target Area is designed to confine the ICF target experiments leading up to and including fusion ignition and gain. The Target Area will provide appropriate in-chamber conditions before, during, and after each shot. The repeated introduction of large amounts of laser energy into the chamber and emission of fusion energy from targets represents a new challenge in ICF facility design. Prior to a shot, the facility provides proper illumination geometry, target chamber vacuum, and a stable platform for the target and its diagnostics. During a shot, the impact of the energy introduced into the chamber is minimized, and workers and the public are protected from excessive prompt radiation doses. After the shot, the residual radioactivation is managed to allow required accessibility. Tritium and other radioactive wastes are confined and disposed of. Diagnostic data is also retrieved, and the facility is readied for the next shot. The Target Area will accommodate yields up to 20 MJ, and its design lifetime is 30 years. The Target Area provides the personnel access needed to support the use precision diagnostics. The annual shot mix for design purposes is shown. Designing to this experimental envelope ensures the ability and flexibility to move through the experimental campaign to ignition efficiently.

Computer design, 3D printing, testing, and commercialization of a revolutionary machine gun suppressor (silencer) design*

Since their invention over 100 years ago, firearm suppressors have achieved acoustic suppression using baffles and chambers to trap and delay propellant gases from exiting the muzzle of a weapon. A modern suppressor is functionally identical to the original 1908 design, with most of the improvements made by lawyers trying to circumvent extant patents. We have produced a flow-through suppressor that functions completely differently from all previous suppressors. We used a few rapid design cycles of high performance computing, 3D printing of titanium prototypes, testing, and analysis to create our suppressor, which has been patented and licensed for commercialization. Ours is the only design to simultaneously limit blowback, flash, noise, and temperature. It will last the lifetime of the barrel on single shot and fully automatic weapons, requires minimal maintenance, and therefore, is the first practical suppressor for battlefield use. If adopted for general use, the main benefit would be the reduction of d...

CONCUSSION, MICROVASCULAR INJURY, AND EARLY TAUOPATHY IN YOUNG ATHLETES AFTER IMPACT HEAD INJURY AND AN IMPACT CONCUSSION MOUSE MODEL

tauopathy in young athletes after impact head injury and an impact concussion mouse model 5 Chad A. Tagge,* Andrew M. Fisher,* Olga V. Minaeva,* Amanda GaudreauBalderrama, Juliet A. Moncaster, Xiao-Lei Zhang, Mark W. Wojnarowicz, Noel Casey, Haiyan Lu, Olga N. Kokiko-Cochran, Sudad Saman, Maria Ericsson, Kristen D. Onos, Ronel Veksler, Vladimir V. Senatorov, Jr, Asami Kondo, Xiao Z. Zhou, Omid Miry, Linnea R. Vose, Katisha R. Gopaul, Chirag Upreti, 10 Christopher J. Nowinski, Robert C. Cantu, Victor E. Alvarez, Audrey M. Hildebrandt, Erich S. Franz, Janusz Konrad, James A. Hamilton, Ning Hua, Yorghos Tripodis, Andrew T. Anderson, Gareth R. Howell, Daniela Kaufer, Garth F. Hall, Kun P. Lu, Richard M. Ransohoff,7,z Robin O. Cleveland, Neil W. Kowall, Thor D. Stein, Bruce T. Lamb, Bertrand R. Huber, 15 William C. Moss, Alon Friedman, Patric K. Stanton, Ann C. McKee, Lee E. Goldstein

Full length articleLaser powder-bed fusion additive manufacturing: Physics of complex melt flow and formation mechanisms of pores, spatter, and denudation zones

Abstract This study demonstrates the significant effect of the recoil pressure and Marangoni convection in laser powder bed fusion (L-PBF) of 316L stainless steel. A three-dimensional high fidelity powder-scale model reveals how the strong dynamical melt flow generates pore defects, material spattering (sparking), and denudation zones. The melt track is divided into three sections: a topological depression, a transition and a tail region, each being the location of specific physical effects. The inclusion of laser ray-tracing energy deposition in the powder-scale model improves over traditional volumetric energy deposition. It enables partial particle melting, which impacts pore defects in the denudation zone. Different pore formation mechanisms are observed at the edge of a scan track, at the melt pool bottom (during collapse of the pool depression), and at the end of the melt track (during laser power ramp down). Remedies to these undesirable pores are discussed. The results are validated against the experiments and the sensitivity to laser absorptivity is discussed.

Laser powder-bed fusion additive manufacturing: Effects of main physical processes on dynamical melt flow and pore formation from mesoscopic powder simulation

Abstract This study demonstrates the significant effect of the recoil pressure and Marangoni convection in laser powder bed fusion (L-PBF) of 316L stainless steel. A three-dimensional high fidelity powder-scale model reveals how the strong dynamical melt flow generates pore defects, material spattering (sparking), and denudation zones. The melt track is divided into three sections: a topological depression, a transition and a tail region, each being the location of specific physical effects. The inclusion of laser ray-tracing energy deposition in the powder-scale model improves over traditional volumetric energy deposition. It enables partial particle melting, which impacts pore defects in the denudation zone. Different pore formation mechanisms are observed at the edge of a scan track, at the melt pool bottom (during collapse of the pool depression), and at the end of the melt track (during laser power ramp down). Remedies to these undesirable pores are discussed. The results are validated against the experiments and the sensitivity to laser absorptivity is discussed.

Management of unconverted light for the National Ignition Facility target chamber

The NIF target chamber beam dumps must survive high x-ray, laser, ion, and shrapnel exposures without excessive generation of vapors or particulate that will contaminate the final optics debris shields, thereby making the debris shields susceptible to subsequent laser damage. The beam dumps also must be compatible with attaining and maintaining the required target chamber vacuum and must not activate significantly under high neutron fluxes. Finally, they must be developed, fabricated, and maintained for a reasonable cost. The primary challenge for the beam dump is to survive up to 20 J/cm2 of 1 micrometers light and 1-2 J/cm2 of nominally 200-350 eV blackbody temperature x-rays. Additional threats include target shrapnel, and other contamination issues. Designs which have been evaluated include louvered hot-pressed boron carbide or stainless steel panels, in some cases covered with transparent Teflon film, and various combinations of inexpensive low thermal expansion glasses backed by inexpensive absorbing glass.