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Full-Text Articles in Mechanical Engineering

Predicting The Hydrogen Pressure To Achieve Ultralow Friction And Diamondlike Carbon Surfaces From First Principles, Haibo Guo, Yue Qi, Xiaodong Li Jun 2008

Predicting The Hydrogen Pressure To Achieve Ultralow Friction And Diamondlike Carbon Surfaces From First Principles, Haibo Guo, Yue Qi, Xiaodong Li

Faculty Publications

Hydrogen atmosphere can significantly change the tribological behavior at diamond and diamondlike carbon (DLC) surfaces and the friction-reducing effect depends on the partial pressure of hydrogen. We combined density functional theory modeling and thermodynamic quantities to predict the equilibrium partial pressures of hydrogen at temperature T, PH2 (T), for a fully atomic hydrogen passivated diamondsurface. Above the equilibrium PH2 (T), ultralow friction can be achieved at diamond and DLC surfaces. The calculation agrees well with friction tests at various testing conditions. We also show that PH2 (T) increases with temperature; therefore, the temperature effect ...


An Optimization-Based Framework For Designing Robust Cam-Based Constant-Force Compliant Mechanisms, John Christian Meaders Jun 2008

An Optimization-Based Framework For Designing Robust Cam-Based Constant-Force Compliant Mechanisms, John Christian Meaders

Theses and Dissertations

Constant-force mechanisms are mechanical devices that provide a near-constant output force over a prescribed deflection range. This thesis develops various optimization-based methods for designing robust constant-force mechanisms. The configuration of the mechanisms that are the focus of this research comprises a cam and a compliant spring fixed at one end while making contact with the cam at the other end. This configuration has proven to be an innovative solution in several applications because of its simplicity in manufacturing and operation. In this work, several methods are introduced to design these mechanisms, and reduce the sensitivity of these mechanisms to manufacturing ...


Friction And Wear Characteristics Of Electrodeposited Nanocrystalline Nickel-Tungsten Alloy Films Jan 2008

Friction And Wear Characteristics Of Electrodeposited Nanocrystalline Nickel-Tungsten Alloy Films

A.S. Md Abdul Haseeb

Electrodeposited nanocrystalline nickel-tungsten alloys are being investigated as an attractive alternative to electrodeposited nickel for applications involving fabrication of micro electro mechanical systems (MEMS). Ni-W alloys are also being considered as an environmentally friendly alternative to hard chrome plating in some cases. In applications involving sliding contacts such as in micro-gears in MEMS, mould inserts, etc., tribological properties of Ni-W alloys would be of relevance. In this work, the sliding friction and wear characteristics of Ni-W alloys with different tungsten contents were investigated and compared with that of nickel film deposited from sulphamate bath commonly used in microfabrication. For wear ...


Investigation Of Tribological Properties Of Biobased Polymers And Polymeric Composites, Satyam Kumar Bhuyan Jan 2008

Investigation Of Tribological Properties Of Biobased Polymers And Polymeric Composites, Satyam Kumar Bhuyan

Graduate Theses and Dissertations

Worldwide potential demands for replacing petroleum derived raw materials with renewable plant-based ones in the production of valuable polymeric materials and composites are quite significant from the social and environmental standpoints. Therefore, using low-cost renewable resources has deeply drawn the attention of many researchers. Among them, natural oils are expected to be ideal alternative feedstock since oils, derived from plant and animal sources, are found in profusion in the world. The important feature of these types of materials is that they can be designed and tailored to meet different requirements. The real challenge lies in finding applications which would use ...


Effect Of Conformational Change On Nanoscale Friction Behavior Of Organic Thin Films, Kanaga Karuppiah Kanaga Subramanian Jan 2008

Effect Of Conformational Change On Nanoscale Friction Behavior Of Organic Thin Films, Kanaga Karuppiah Kanaga Subramanian

Graduate Theses and Dissertations

The overarching theme of this dissertation is to probe relationships between structure of organic thin films and their specific functional property of friction in the context of various engineering applications. Two specific thin film systems were studied - biological macromolecules in total joint replacements and self-assembled alkanethiol monolayers for microdevice applications. Before delving into the actual systems, a thorough understanding of friction at small length scales was required. To address this, a friction study of two material pairs (Si3N4/mica and Si3N4/ultra-high molecular weight polyethylene) was conducted using a microtribometer and atomic force microscope (AFM) at the micro- and nanometer ...