Tribological behaviors of lubricated interfaces are strongly affected by the interactions between mating surfaces and the rheological properties of the lubricant between them. This research aims to improve lubrication through two approaches: 1) designing surface textures for lubrication enhancement and adhesion reduction, and 2) developing lubricants of desired rheology.
Molecular...
With the advances in electronics and communication devices over the last several decades, radio-frequency antennas have miniaturized from externally mounted “rabbit ears” on our grandma’s televisions to devices small enough to be concealed within the body of the cellphone itself, corresponding to the carrier frequencies used from on the order...
Effective and reliable material and structure as bone implant have been a continuing challenge for scientists from bioengineering, material science and mechanical engineering. Porous titanium has reduced stiffness comparable to bone and open pores to allow complete bone infiltration, thus making it attractive for bone-replacement implants in biomedical engineering. To...
Three critical problem areas pertinent to the development of precision high-speed spindles for meso-scale machine tools (mMTs), driven by air turbines, constitute the focus of this work. These are the development of the spindle, of a new tool clamping device, and of a measurement system for spindle error motions.
For...
Spectral elements are p-type element which can provide better accuracy
and faster convergence. However, applications of these elements make
conformation to discontinuities in the function or its derivative
difficult. The eXtended Finite Element Method (XFEM) recently
developed at Northwestern University can easily treat the arbitrarily
aligned discontinuities, i.e. independent of...
An understanding of how two people anticipate, adapt, and react to each other's forces and motions could aid in designing machines to work cooperatively with humans and further explain how a single human interacts with the world. Tasks, such as lifting and moving a bulky object, teaching manual skills, dancing,...
Motivated by applications to microfluidic separation systems like Capillary Electrophoresis (CE) and Capillary Electrochromatography (CEC), the research described in this dissertation analyzes through numerical and asymptotic methods the effect of variation in the wall zeta potential (or surface charge) on the electroosmotic flow field in a microchannel and the effect...
The combined trends of decreasing application size and increasing requirements for energy efficiency have driven a need for improved understanding and better predictive tools for thin film lubricated systems. Research on such systems is complicated by the involvement of both larger scale phenomena such as fluid flow, material deformation, and...
There is a need for cyclic robots that interact with lower limbs. Such robots will bring new programmability to exercise, rehabilitation, psychophysiology, and physiology, allowing for complete customization of the foot pedal path and dynamics. These robots are novel to the robotics research ¯eld as well, since conventional robotic designs...
The macroscale mechanical and physical properties of materials are inherently linked to the underlying microstructure. Traditional continuum mechanics theories have focused on approximating the heterogeneous microstructure as a continuum, which is conducive to a partial differential equation mathematical description. Although this makes large scale simulation of material much more efficient...
In a highly competitive market, it is becoming increasingly important to view product design as an enterprise-level profit-driven activity. Demand models have become central to enterprise-driven design approaches since they help estimating the economic impact (e.g., revenues, profits, and cost) of a product's design. The primary contribution of this dissertation...
Various methods for solving the partial contact of surfaces with regularly periodic profiles-- which might arise in analyses of asperity level contact, serrated surfaces or even curved structures--have previously been employed for elastic materials. A new approach based upon the summation of evenly spaced Flamant's solution is presented here to...
Cells are known to respond to external stimuli such as chemical, physical and mechanical cues from their microenvironments. In this work, we developed the technology to to complement the previously reported studies that deal with substrates' mechanical property by developing thin polydimethlysiloxane (PDMS) membrane microdevices using microfabrication technology. Typically, multiples...
In this research, the optical and electrical properties of graphene-based materials are investigated. In particular, "graphene oxide", which is an individual layer of graphite oxide, and its chemically reduced form, is probed in terms of its properties, and the properties of graphene oxide and chemically modified graphene oxide are compared...
The addition of nanoparticles into polymer materials has been observed to dramatically change the mechanical, thermal, electrical, and diffusion properties of the host polymers, promising a novel class of polymer matrix composite materials with superior properties and added functionalities that are ideal candidates in many applications, including aerospace, automobile, medical...
We present several multiscale quantum mechanical (QM), molecular mechanical (MM), and continuum mechanical (CM) schemes to study the strength properties of carbon nanotubes (CNTs) and graphene sheets. A bridging domain method based on overlapping domain-decomposition schemes using the Lagrange multipliers field is developed to couple an atomistic domain with a...
A major challenge in the field of Structural Health Monitoring (SHM) of safety-critical structures is how to effectively and efficiently detect fatigue damage, especially before there is macrocrack initiation. In this dissertation, a local ultrasonic technique is developed to assess pre-crack fatigue damage in structures. The novel feature of this...
A dynamic model of the rolling process that includes the material strain-hardening and work roll flattening effects was developed based on homogeneous deformation theory. By coupling this new dynamic rolling process model with a structural model for a mill stand, a single-stand chatter model expressed through a state-space representation was...
Novel materials and nanostructures with superior electro-mechanical properties are emerging in the development of novel devices. Engineering application of these materials requires accurate electro-mechanical characterization, which in turn requires development of novel experimental techniques. This dissertation outlines the investigation of the mechanical and electrical properties of one-dimensional nanomaterials.
One-dimensional nanomaterials...
In the last two decades the number of innovative applications for advanced materials has been rapidly increasing. Shape memory alloys (SMAs) are an exciting class of these materials which exhibit large reversible stresses and strains due to a thermoelastic phase transformation. SMAs have been employed in the biomedical field for...