Vaughn College of Aeronautics and Technology

About: Vaughn College of Aeronautics and Technology is a education organization based out in New York, New York, United States. It is known for research contribution in the topics: Gravitational microlensing & Planetary system. The organization has 727 authors who have published 708 publications receiving 14082 citations. The organization is also known as: College of Aeronautics.

Thermotropic liquid-crystalline properties of extended viologen bis(triflimide) salts

Abstract: A series of extended, symmetric viologen triflimides were synthesised by the metathesis reaction of lithium triflimide with the respective viologen tosyalates in methanol. Their chemical st...

A study of free-jet and enclosed supersonic diffusion flames

Abstract: An experimental study has been made of supersonic diffusion flames produced by the subsonic and supersonic free-jet injection of hydrogen into a high-enthalpy air-stream. The air-stream was flowing at a Mach number=1.98 and had a total temperature of approximately 1900°K and a static pressure of 14.7 psia. An axial, mid-stream mode of fuel injection was adopted. For the case of hydrogen injected subsonically, combustion was found to be complete (i.e. the concentration of unreacted hydrogen was negligible), at a distance of approximately 9 inches from the point of injection. For the supersonic injection of hydrogen this distance was increased by approximately 30%, for the range of fuel velocities used. The tests were repeated with methane as the injected fuel, but ignition did not occur even with the methane preheated to 480°K, or when a bluff-body was inserted into the flow to create shock conditions. The above flames were then enclosed in various combustors of simple geometry, either of constant-area, constant-divergence or some combination of these two. For the conditions specified above, combustion in the diffusional mode was found to be impossible in a constantarea combustor. A diffusion flame was initiated in a combustor which consisted of a short parallel section followed by a section with a divergence of approximately 1°. However no combustion took place within a completely divergent duct even though the divergence was less than 1°. An exponential relationship between pressure, area and length has been proposed, and a one-dimensional analytical treatment for the case of heat addition in a non-constant-area duct is included in this paper. This assumption is shown to be experimentally reasonable and to result in gas dynamic equations which include the effect of process length.

Grain boundary sliding mechanism in plastic deformation of nano-grained YAG transparent ceramics: Generalized self-consistent model and nanoindentation experimental validation

Abstract: The elastic-plastic deformation behaviors of nano-grained and coarse-grained yttrium aluminum garnet (YAG) transparent ceramics are investigated using nanoindentation. An inverse Hall-Petch relation is observed for the nano-grained YAG ceramic and a forward Hall-Petch relation is observed for the coarse-grained YAG ceramic. In addition, the plastic work ratio as a function of applied load for the nano-grained YAG ceramic shows a different trend than that for the coarse-grained YAG ceramic. These observations suggest that the plastic deformation of the nano-grained YAG ceramic cannot be attributed to the normal dislocation mechanism and is controlled by grain boundary sliding. A generalized self-consistent model for studying the mechanical behavior of the nano-grained YAG ceramic is developed and validated by experimental results. The stress-strain relationship predicted by this model is embedded in finite element simulations which confirmed that the plastic deformation of the nano-grained YAG ceramic indeed can be attributed to grain boundary sliding.

Optimization of selective laser melting process parameters for surface quality performance of the fabricated Ti6Al4V

Abstract: The purpose of this study is to study the influence of the laser power and the scanning speed on the surface hardness, and top surface and side surface roughness of Ti6Al4V metal specimens fabricated via the selective laser melting (SLM) technique. The laser power was varied between 150 and 300 W while the scan speed was varied between 800 and 1400 mm/s. Response surface methodology (RSM) in the Design Expert 11 software environment was used for the design of experiment and results analysis. The distance for surface indentations were targeted at 10–20 μm for the top surface and 60–80 μm for the side surface while the surface hardness profiling was studied using an indenter with the indentation performed at a load of 500 gf and at a dwelling time of 15 s. The study revealed that as the laser power was increased, the surface hardness increases, while the top surface and side surface roughness reduces. Then, when the scanning speed increased, the surface hardness, and top surface and side surface roughness were found to also increase. The optimum range of the process parameters selected are laser speed 300 W and scan speed 1400 mm/s. This produces a minimum surface roughness of 13.006 μm for the top surface roughness and 62.166 μm for the side surface roughness with a corresponding hardness value of 409.391 HV. The findings of this study will assist manufacturers in the process design of the SLM of titanium alloy for aerospace applications.