129 research outputs found
Recovering the Principle of Relativity from the Cosmic Fabric Model of Space
We extend the descriptive power of the Cosmic Fabric model of space developed
by Tenev and Horstemeyer (2018) to include moving observers by demonstrating
that all reference frames are phenomenologically equivalent with one another
and transform between each other via the Lorentz transformations. Our approach
is similar to that of Lorentz (1892), which was used to explain the negative
outcome of the Michelson-Morley {\ae}ther detection experiment (Michelson and
Morley 1887), except that we deduce the notions of length contraction and time
dilation from the postulates of the Cosmic Fabric model. Our result is valid
for the continuum length scale at which, by definition, the cosmic fabric can
be described mathematically as a continuum. Herein, we also discuss the
length-scale dependent nature of the Cosmic Fabric model as a possible way to
relate gravitational and quantum theories
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Numerical Simulation of the Temperature Distribution and Solid-Phase Evolution in the LENS™ Process
A three-dimensional finite element model was developed and applied to analyze the
temperature and phase evolution in deposited stainless steel 410 (SS410) during the Laser
Engineered Net Shaping (LENSTM) rapid fabrication process. The effect of solid phase
transformations is taken into account by using temperature and phase dependent material
properties and the continuous cooling transformation (CCT) diagram. The laser beam is modeled
as a Gaussian distribution of heat flux from a moving heat source with conical shape. The laser
power is optimized in order to achieve a pre-defined molten pool size for each layer. It is found
that approximately 5% decrease of the laser power for each pass is required to obtain a steady
molten pool size. The temperature distribution and cooling rate surrounding the molten pool are
predicted and compared with experiments. Based upon the predicted thermal cycles and cooling
rate, the phase transformations and their effects on the hardness are discussed.Mechanical Engineerin
Microstructure-Sensitive Fatigue Modeling of AISI 4140 Steel
A microstructure-based fatigue model is employed to predict fatigue damage in 4140 steel. Fully reversed, strain control fatigue tests were conducted at various strain amplitudes and scanning electron microscopy was employed to establish structure-property relations between the microstructure and cyclic damage. Fatigue cracks were found to initiate from particles near the free surface of the specimens. In addition, fatigue striations were found to originate from these particles and grew radially outward. The fatigue model used in this study captured the microstructural effects and mechanics of nucleation and growth observed in this ferrous metal. Good correlation of the number of cycles to failure between the experimental results and the model were achieved. Based on analysis of the mechanical testing, fractography and modeling, the fatigue life of the 4140 steel is estimated to comprise mainly of small crack growth in the low cycle regime and crack incubation in the high cycle fatigue regime
The effect of Fe atoms on the adsorption of a W atom on W(100) surface
We report a first-principles calculation that models the effect of iron (Fe)
atoms on the adsorption of a tungsten (W) atom on W(100) surfaces. The
adsorption of a W atom on a clean W(100) surface is compared with that of a W
atom on a W(100) surface covered with a monolayer of Fe atoms. The total energy
of the system is computed as the function of the height of the W adatom. Our
result shows that the W atom first adsorbs on top of the Fe monolayer. Then the
W atom can replace one of the Fe atoms through a path with a moderate energy
barrier and reduce its energy further. This intermediate site makes the
adsorption (and desorption) of W atoms a two-step process in the presence of Fe
atoms and lowers the overall adsorption energy by nearly 2.4 eV. The Fe atoms
also provide a surface for W atoms to adsorb facilitating the diffusion of W
atoms. The combination of these two effects result in a much more efficient
desorption and diffusion of W atoms in the presence of Fe atoms. Our result
provides a fundamental mechanism that can explain the activated sintering of
tungsten by Fe atoms.Comment: 9 pages, 2 figure
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