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Mechanical Engineering

Faculty Publications

2002

Articles 1 - 13 of 13

Full-Text Articles in Engineering

On-Chip Actuation Of An In-Plane Compliant Bistable Micromechanism, Michael S. Baker, Larry L. Howell Dec 2002

On-Chip Actuation Of An In-Plane Compliant Bistable Micromechanism, Michael S. Baker, Larry L. Howell

Faculty Publications

A compliant bistable micromechanism has been developed which can be switched in either direction using on-chip thermal actuation. The energy storage and bistable behavior of the mechanism is achieved through the elastic deflection of compliant segments. The Pseudo-Rigid-Body Model was used for the compliant mechanism design, and for analysis of the large deflection flexible segments. To achieve on-chip actuation, the mechanism design was optimized to allow it to be switched using linear motion thermal actuators. The modeling theory and analysis are presented for three design iterations, with two iterations fabricated in the MUMP's process and the third in the SUMMiT …

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Mapping The Mesoscale Interface Structure In Polycrystalline Materials, Brent L. Adams, C. L. Bauer, D. Casasent, A. Morawiec, S. Ozdemir, A. Talukder, Chialin T. Wu Nov 2002

Mapping The Mesoscale Interface Structure In Polycrystalline Materials, Brent L. Adams, C. L. Bauer, D. Casasent, A. Morawiec, S. Ozdemir, A. Talukder, Chialin T. Wu

Faculty Publications

This work was supported primarily by the MRSEC Program of the National Science Foundation under Award Numbers DMR-9632556 and DMR-0079996. A new experimental approach to the quantitative characterization of polycrystalline microstructure by scanning electron microscopy is described. Combining automated electron backscattering diffraction with conventional scanning contrast imaging and with calibrated serial sectioning, the new method (Mesoscale Interface Mapping System, MIMS) recovers precision estimates of the 3-dimensional idealized aggregate function G(x). This function embodies a description of lattice phase and orientation (limiting resolution ~ 1 degree) at each point x (limiting spatial resolution ~ 100 nanometers), and therefore contains a complete …

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Distributions Of Noble Metal Pd And Pt In Mesoporous Silica, J. Arbiol, A. Cabot, J. R. Morante, Fanglin Chen, Meilin Liu Oct 2002

Distributions Of Noble Metal Pd And Pt In Mesoporous Silica, J. Arbiol, A. Cabot, J. R. Morante, Fanglin Chen, Meilin Liu

Faculty Publications

Mesoporous silica nanostructures have been synthesized and loaded with Pd and Pt catalytic noble metals. It is found that Pd forms small nanoclusters (3–5 nm) on the surface of the mesoporous structure whereas Pt impregnation results in the inclusion of Pt nanostructures within the silica hexagonal pores (from nanoclusters to nanowires). It is observed that these materials have high catalytic properties for CO–CH4 combustion, even in a thick film form. In particular, results indicate that the Pt and Pd dispersed in mesoporous silica are catalytically active as a selective filter for gas sensors.

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Distributions Of Nobel Metal Pd And Pt In Mesoporous Silica, J. Arbiol, A. Cabot, J. R. Morante, Fanglin Chen, Meilin Liu Oct 2002

Distributions Of Nobel Metal Pd And Pt In Mesoporous Silica, J. Arbiol, A. Cabot, J. R. Morante, Fanglin Chen, Meilin Liu

Faculty Publications

Mesoporous silicananostructures have been synthesized and loaded with Pd and Pt catalytic noble metals. It is found that Pd forms small nanoclusters (3–5 nm) on the surface of the mesoporous structure whereas Pt impregnation results in the inclusion of Pt nanostructures within the silica hexagonal pores (from nanoclusters to nanowires). It is observed that these materials have high catalyticproperties for CO–CH4CO–CH4CO–CH4 combustion, even in a thick film form. In particular, results indicate that the Pt and Pd dispersed in mesoporous silica are catalytically active as a selective filter for gas sensors.

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Modeling The Thermal Behavior Of A Surface-Micromachined Linear-Displacement Thermomechanical Microactuator, Christian D. Lott, Timothy W. Mclain, John N. Harb, Larry L. Howell Sep 2002

Modeling The Thermal Behavior Of A Surface-Micromachined Linear-Displacement Thermomechanical Microactuator, Christian D. Lott, Timothy W. Mclain, John N. Harb, Larry L. Howell

Faculty Publications

Thermomechanical microactuators possess a number of desirable attributes including ease of fabrication and large force and displacement capabilities relative to other types of microactuators. These advantages provide motivation for improving thermomechanical microactuator designs that are more energy efficient and thus better suited for low-power applications. To this end, this paper describes the development and experimental validation of a finite-difference thermal model of a thermomechanical in-plane microactuator (TIM). Comparisons between the model and experimental results demonstrate the importance of including the temperature dependence of several parameters in the model. Strategies for reducing the power and energy requirements of the TIM were …

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Experimental Demonstration Of Multiple Robot Cooperative Target Intercept, Timothy W. Mclain, Randal W. Beard, Jed M. Kelsey Aug 2002

Experimental Demonstration Of Multiple Robot Cooperative Target Intercept, Timothy W. Mclain, Randal W. Beard, Jed M. Kelsey

Faculty Publications

This paper presents experimental results for the simultaneous intercept of preassigned targets by a team of mobile robots. The robots are programmed to mimic the dynamic behavior of unmanned air vehicles in constant-altitude flight. In proceeding to their targets, robots must avoid both known static threats and pop-up threats. An overview of the cooperative control strategy followed is given, as well as a description of the robot hardware and software used. Experimental results demonstrating simultaneous intercept of targets by the robot team are presented.

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Viewpoint: Experimental Recovery Of Geometrically Necessary Dislocation Density In Polycrystals, Brent L. Adams, Bassem S. El-Dasher, Anthony D. Rollett Aug 2002

Viewpoint: Experimental Recovery Of Geometrically Necessary Dislocation Density In Polycrystals, Brent L. Adams, Bassem S. El-Dasher, Anthony D. Rollett

Faculty Publications

The authors wish to thank The Alcoa Technical Research Center for supplying the specimens and performing the compression tests. This work was supported primarily by the MRSEC program of the National Science Foundation under DMR-0079996. Application of electron backscattering diffraction methods to recover estimates of the geometrically necessary dislocation density is described. The limitations of the method arising from the opacity of crystalline materials and the spatial and angular resolution limits are discussed.

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Autonomous Hierarchical Control Of Multiple Unmanned Combat Air Vehicles (Ucavs), Timothy Mclain, Randal W. Beard, Sai-Ming Li, Jovan D. Boskovic, Sanjeev Seereeram, Ravi Prasanth, Jayesh Amin, Raman K. Mehra Jun 2002

Autonomous Hierarchical Control Of Multiple Unmanned Combat Air Vehicles (Ucavs), Timothy Mclain, Randal W. Beard, Sai-Ming Li, Jovan D. Boskovic, Sanjeev Seereeram, Ravi Prasanth, Jayesh Amin, Raman K. Mehra

Faculty Publications

In this paper we present a hierarchical control scheme that enables multiple UCAVs to achieve demanding missions in hostile environments autonomously. The objective is to use a swarm of UCAVs for a SEAD type mission: fly the UCAVs in a formation to an enemy territory populated with different kinds of threats, collect enemy information or destroy certain targets, and return to the base, all without human intervention. The scheme is an integration of four distinct components, including: (1) high level Voronoi diagram based path planner to avoid static threats; (2) low level path planner to avoid popup threats; (3) differential …

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Nanofatigue Studies Of Ultrathin Hard Carbon Overcoats Used In Magnetic Storage Devices, Xiaodong Li, Bharat Bhushan May 2002

Nanofatigue Studies Of Ultrathin Hard Carbon Overcoats Used In Magnetic Storage Devices, Xiaodong Li, Bharat Bhushan

Faculty Publications

A technique to perform nanofatigue experiments was developed. This technique utilizes a depth-sensing nanoindenter with harmonic force. The nanofatigue behavior of 20 nm thick amorphous carbon coatings was studied. The contact stiffness was monitored continuously throughout the test. The abrupt decrease in the contact stiffness indicates fatigue damage has occurred. The critical load amplitude, below which no fatigue damage occurs, was identified. It was found that the filtered cathodic arc coating exhibits longer fatigue life than a direct ion beam coating. Failure mechanisms of the coatings during fatigue are also discussed in conjunction with the hardness,elastic modulus, and fracture toughness, …

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In-Plane Linear-Displacement Bistable Microrelay, Troy Gomm, Larry L. Howell, Richard H. Selfridge May 2002

In-Plane Linear-Displacement Bistable Microrelay, Troy Gomm, Larry L. Howell, Richard H. Selfridge

Faculty Publications

This paper investigates the Linear Displacement Bistable Mechanism (LDBM) for use in microrelays. The LDBM, thermal actuators, and contacts are integrated to demonstrate a relay design. The performance of the relay is characterized using relay performance metrics, including size (1.92 mm2), contact force (23.4 μN), switching time (340 μs), breakdown voltage (> 475 V), and isolation (> 235 V). The actuation voltage and current are 11 V and 85 mA, respectively. AC characteristics, including contact-to-contact crosstalk and AC isolation are also measured. The testing results demonstrate that it is feasible to use the LDBM as a microrelay and that it …

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Surface Micromachined Force Gauges: Uncertainty And Reliability, Jonathan W. Wittwer, Troy Gomm, Larry L. Howell Jan 2002

Surface Micromachined Force Gauges: Uncertainty And Reliability, Jonathan W. Wittwer, Troy Gomm, Larry L. Howell

Faculty Publications

Surface micromachining of micro-electro-mechanical systems (MEMS), like all other fabrication processes, has inherent variation that leads to uncertain material and dimensional parameters. By considering the effects of these variations during the design of micro force gauges, the gauge uncertainty and reliability can be estimated. Without means of calibrating micro gauges, these effects are often significant when compared to experimental repeatability. The general force gauge model described in this paper can be used to measure a wide range of forces, and simple design changes can lead to improved accuracy in measurement. A method of probabilistic design is described that is not …

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Spectral Integration Of Microstructure And Design, Brent L. Adams, B. Henrie, M. Lyon, H. Garmestani, Surya R. Kalidindi Jan 2002

Spectral Integration Of Microstructure And Design, Brent L. Adams, B. Henrie, M. Lyon, H. Garmestani, Surya R. Kalidindi

Faculty Publications

Support of the Army Research Office is greatly appreciated. Mechanical design can be conducted in a framework where consideration of microstructure as a continuous design variable is facilitated by the use of a Fourier space. Selection of the mechanical framework for the problem (e.g., mechanical constitutive model and homogenization relations) dictates the dimensionality of the pertinent microstructure representation. Microstructure is comprised of basic elements that belong to the local state space. Local state includes crystallographic phase and orientation, and other parameters such as composition. The local state space is transformed into an isomorphic set in Fourier space. The universe of …

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Effect Of Residual Thermal Stresses On Fracture Behavior And Mechanical Properties Of Al Sub 2 O Sub 3/Ni Cermets, Guo Jin Li, Da Ming Chen, Xiao Xian Huang, Jing Kun Guo Jan 2002

Effect Of Residual Thermal Stresses On Fracture Behavior And Mechanical Properties Of Al Sub 2 O Sub 3/Ni Cermets, Guo Jin Li, Da Ming Chen, Xiao Xian Huang, Jing Kun Guo

Faculty Publications

Effect of residual thermal stresses on fracture behavior and mechanical properties of Al2O3/Ni cermets was qualitatively explained by using theory on residual thermal stresses. When Ni particles are located within Al2O3 grains or Ni content is relatively low, tensile stresses are exerted at Al2O3-Al2O3 grain boundary. While fracturing, intergranular fracture is easily produced. When Ni particles are dispersed at Al2O3 grain boundary or Ni content is relatively high, compressive stresses are exerted at Al2O3-Al2O3grain boundary. …

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