Search Results (6)

Artificial satellites are widely used in different areas such as communication, position systems, and agriculture. The number of satellites orbiting Earth is becoming huge, and many are set to be launched soon. This huge number of satellites in addition to space debris are sources of concern. Indeed, some incidents have occurred either between satellites or because of space debris. These incidents are a threat for the hit satellite and can be a source of irreversible damages. A hit satellite may diverge to a chaotic motion with all the entailed consequences. The inertia moment of a satellite is a main factor to determine if the hit satellite is heading toward a chaotic motion or not. The inertia moment is determined over the mass density function. In this paper, a circularly orbiting artificial satellite was modeled as a thin rotating rod. The objective was to determine a suitable mass density function for this satellite allowing the prevention as much as possible of the chaotic motion after being hit. This unknown density mass function satisfies a system of equations reflecting some physical constraints. Conventional procedures are not applicable to solve this system of equations. The presented resolution method is based on several mathematical transformations, allowing converting this system into a highly nonlinear one with several unknowns. Several mathematical techniques were applied, and an analytical solution was obtained. Finally, from the mechanical engineering point of view, the obtained mass density function corresponds to a Functionally Graded Material (FGM). Full article

We formulate equations governing flows of suspensions of rod-like particles. Such suspensions include linear polymer solutions, FD-virus, and worm-like micelles. To take into account the particles that form and their rotation, we treat the suspension as a Cosserat continuum and apply the theory of micropolar fluids. Anisotropy of suspensions is determined through the inclusion of the microinertia tensor in the rheological constitutive equations. We check that the model is consistent with the basic principles of thermodynamics. In addition to anisotropy, the theory also captures gradient banding instability, coexistence of isotropic and nematic phases, sustained temporal oscillations of macroscopic viscosity, shear thinning and hysteresis. For the flow between two planes, we also establish that the total flow rate depends not only on the pressure gradient, but on the history of its variation as well. Full article

The friction surfacing technique is an advanced method for creating coatings of various materials onto the surface of a similar or dissimilar material substrate. In this method, there is no external source of heat energy, and all the heat energy required in this method is generated by friction. In this paper, a novel method of friction surfacing from the side of the consumable tool is introduced. The most significant difference in this technique is that material transfer will occur from the radial surface of the consumable tool as opposed to the end of the tool as in conventional friction surfacing. In lateral friction surfacing, the side of the rotating consumable tool is pressed against the substrate surface, which generates frictional heating and shear forces at the interface between tool and substrate. A layer of tool material is transferred from the consumable rod to the substrate surface as the tool moves across. In this study, 6063 aluminum alloy and AISI 1018 carbon steel are used as the materials of consumable tool and substrate, respectively. The impact of process factors, surface roughness values, tool mass loss, and deposition thickness are discussed in detail. The experimental results of this study reveal that lateral friction surfacing produces a very smooth ultra-thin deposition with full coverage, with coating layers with roughness values in the order of 1 µm. Additionally, there is no flash formed in this technique which reduces material consumption. Moreover, temperatures at the interface between the consumable tool and workpiece were measured to be lower than for that in friction surfacing from the end of the tool, which is beneficial for the metallurgical characteristics of the deposited material. Full article

Porosity-free bulk nanostructured nickel cannot be fabricated by conventional electroplating due to hydrogen bubbling at the cathode. Here, we developed a cathode-rotating electroplating technique to remove the bubbles in order to obtain millimeter-scale nanostructured nickel rods with low porosity. The grain sizes ranged from 20 to 300 nm. The range produced by the new technique was broader than those that have been reported. The heterogeneous microstructure contributed to high work hardening rate, yield strength, and ductility of the rods in tension. The ductility was larger than electroplated thin nickel film with comparable ultimate strength in the literature. Dislocations accumulated at pre-existing twins, grain boundaries, and at the grain interior mediated the plastic deformation of the rods. Full article

The complete orientational ordering tensor of quasi-ideal colloidal rods is obtained as a function of shear rate by performing rheo-SANS (rheology with small angle neutron scattering) measurements on isotropic fd-virus suspensions in the two relevant scattering planes, the flow-gradient (1-2) and the flow-vorticity (1-3) plane. Microscopic ordering can be identified as the origin of the observed shear thinning. A qualitative description of the rheological response by Smoluchowski, as well as Doi–Edwards–Kuzuu theory is possible, as we obtain a master curve for different concentrations, scaling the shear rate with the apparent collective rotational diffusion coefficient. However, the observation suggests that the interdependence of ordering and shear thinning at small shear rates is stronger than predicted. The extracted zero-shear viscosity matches the concentration dependence of the self-diffusion of rods in semi-dilute solutions, while the director tilts close towards the flow direction already at very low shear rates. In contrast, we observe a smaller dependence on the shear rate in the overall ordering at high shear rates, as well as an ever-increasing biaxiality. Full article

Analysis of the induced stress on undoped and boron-doped diamond (BDD) thin films by confocal Raman microscopy is performed in this study to investigate its correlation with sample chemical composition and the substrate used during fabrication. Knowledge of this nature is very important to the issue of long-term stability of BDD coated neurosurgical electrodes that will be used in fast-scan cyclic voltammetry, as potential occurrence of film delaminations and dislocations during their surgical implantation can have unwanted consequences for the reliability of BDD-based biosensing electrodes. To achieve a more uniform deposition of the films on cylindrically-shaped tungsten rods, substrate rotation was employed in a custom-built chemical vapor deposition reactor. In addition to visibly preferential boron incorporation into the diamond lattice and columnar growth, the results also reveal a direct correlation between regions of pure diamond and enhanced stress. Definite stress release throughout entire film thicknesses was found in the current Raman mapping images for higher amounts of boron addition. There is also a possible contribution to the high values of compressive stress from sp² type carbon impurities, besides that of the expected lattice mismatch between film and substrate. Full article