Browsing by Author "Kumar, Dhananjay"

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    Durability Analysis of Helical Coil Spring in Vehicle Suspension Systems
    Kumar, Dhananjay (Virginia Tech, 2021-11-11)
    The suspension system in vehicles supports the vehicle's road stability and ride quality by scaling down the vibration responses resulting from road surface's roughness. This research focuses on fatigue life analysis of coil spring component. Static linear analysis is conducted on the 3D model of helical coil spring to investigate deformation and stress responses. Modal analysis evaluates the characteristics of vibration, i.e. natural resonance frequencies and corresponding mode shapes. The stress frequency response is generated after performing the harmonic analysis on the spring. Dynamics and performance of spring are analyzed over practical frequency range of 0 Hz to 200 Hz. Fatigue life estimation of vehicle suspension spring is performed using the stress data obtained from frequency response analysis. The stress-life (S-N) approach is utilized for fatigue life assessment of suspension spring. This durability analysis technique can be utilized in the automotive industry to improve reliability of vehicles. The outcome of this research can contribute in analysis and design of modern smart vehicles.
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    The effect of matrix and substrate on the coercivity and blocking temperature of self-assembled Ni nanoparticles
    Abiade, Jeremiah T.; Oh, Sang Ho; Kumar, Dhananjay; Varela, Maria; Pennycook, Stephen J.; Guo, Haizhong; Gupta, Arunava; Sankar, Jagannathan (American Institute of Physics, 2008-10-01)
    We have shown that the magnetic properties of nanoparticles may be tuned from superparamagnetic to ferromagnetic by changing the substrate or thin film matrix in which they are embedded. Nickel nanoparticles were embedded into alumina, titanium nitride, and cerium oxide matrices on both silicon and sapphire substrates via pulsed laser deposition. The laser ablation time on the nickel target was kept constant. Only nickel nanoparticles in cerium oxide showed characteristics of ferromagnetism (room temperature coercivity and remanence). Ni nanoparticles, in either alumina or titanium nitride, possessed blocking temperatures below 200 K. Detailed scanning transmission electron microscopy analysis has been conducted on the samples embedded into cerium oxide on both substrates and related to the magnetic data. (c) 2008 American Institute of Physics.
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    Effect of spacer layer thickness on magnetic interactions in self-assembled single domain iron nanoparticles
    Herndon, Nichole B.; Oh, Sang Ho; Abiade, Jeremiah T.; Pai, Devdas; Sankar, Jag; Pennycook, Stephen J.; Kumar, Dhananjay (American Institute of Physics, 2008-04-01)
    The magnetic characteristics of iron nanoparticles embedded in an alumina thin film matrix have been studied as a function of spacer layer thickness. Alumina as well as iron nanoparticles were deposited in a multilayered geometry using sequential pulsed laser deposition. The role of spacer layer thickness was investigated by making layered thin film composites with three different spacer layer thicknesses (6, 12, and 18 nm) with fixed iron particle size of similar to 13 nm. Intralayer magnetic interactions being the same in each sample, the variation in coercivity and saturation magnetization is attributed to thickness dependent interlayer magnetic interactions of three types: exchange, strong dipolar, and weak dipolar. A thin film composite multilayer structure offers a continuously tunable strength of interparticle dipole-dipole interaction and is thus well suited for studies of the influence of interaction on the magnetic properties of small magnetic particle systems.
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    Thermal transport in composites of self-assembled nickel nanoparticles embedded in yttria stabilized zirconia
    Shukla, Nitin C.; Liao, Hao-Hsiang; Abiade, Jeremiah T.; Murayama, Mitsuhiro; Kumar, Dhananjay; Huxtable, Scott T. (AIP Publishing, 2009-04-01)
    We investigate the effect of nickel nanoparticle size on thermal transport in multilayer nanocomposites consisting of alternating layers of nickel nanoparticles and yttria stabilized zirconia (YSZ) spacer layers that are grown with pulsed laser deposition. Using time-domain thermoreflectance, we measure thermal conductivities of k=1.8, 2.4, 2.3, and 3.0 W m(-1) K(-1) for nanocomposites with nickel nanoparticle diameters of 7, 21, 24, and 38 nm, respectively, and k=2.5 W m(-1) K(-1) for a single 80 nm thick layer of YSZ. We use an effective medium theory to estimate the lower limits for interface thermal conductance G between the nickel nanoparticles and the YSZ matrix (G>170 MW m(-2) K(-1)), and nickel nanoparticle thermal conductivity.