In many cases, it is impractical or prohibitively expensive to develop new instrumentation to study tribological phenomena in situ, but with the application of elastic averaging, to accurately locate two surfaces with respect to one another, this can be realized with existing peripheral diagnostic equipment. A sample fixture was designed using the principles of elastic averaging that allows for the separation and repeatable repositioning of a tribological test specimen. Using an optical interferometer and digital image correlation, the fixture was determined to have average repositioning errors of <2 µm, in both the x and y directions. The application of these simple design principles could provide an accurate, repeatable, and low-cost solution for interrupted tribological studies.

As the number of digital retinal fundus images taken each year grows at an increasing rate, there exists a similarly increasing need for automatic eye disease detection through image-based analysis. A new method has been developed for classifying standard color fundus photographs into both healthy and diseased categories. This classification was based on the calculated network fluid conductance, a function of the geometry and connectivity of the vascular segments. To evaluate the network resistance, the retinal vasculature was first manually separated from the background to ensure an accurate representation of the geometry and connectivity. The arterial and venous networks were then semi-automatically separated into two separate binary images. The connectivity of the arterial network was then determined through a series of morphological image operations. The network comprised of segments of vasculature and points of bifurcation, with each segment having a characteristic geometric and fluid properties. Based on the connectivity and fluid resistance of each vascular segment, an arterial network flow conductance was calculated, which described the ease with which blood can pass through a vascular system. In this work, 27 eyes (13 healthy and 14 diabetic) from patients roughly 65 years in age were evaluated using this methodology. Healthy arterial networks exhibited an average fluid conductance of 419 ± 89 μm3/mPa-s while the average network fluid conductance of the diabetic set was 165 ± 87 μm3/mPa-s (p < 0.001). The results of this new image-based software demonstrated an ability to automatically, quantitatively and efficiently screen diseased eyes from color fundus imagery.

A model for the elastic contact between a rigid sphere and an ideal elastic foundation with adhesion has been developed. The model was derived by integrating the full Lennard-Jones potential to arrive at a closed-form equilibrium condition that balances surface energy with strain energy. It was found that the separation height is not a function of the penetration. Using this energy criterion for separation of contact in an elastic foundation, a model for the force displacement relationship was then developed. In this derivation there exists a tensile zone of deformation along the perimeter of the contact. The model also reveals a number of unique aspects of the adhesive contact, including: the maximum adhesion occurs when the apex of the sphere is tangent to the plane of the undeformed surface, the maximum adhesion force \( F_{\text{adh}} = - 2\pi R\Updelta \gamma \), and the contact area is linearly dependent on penetration. The ability to fit high fidelity indentation data from finite-element analysis and molecular dynamics simulation for thin films was demonstrated. Additionally, experiments were performed on thin films (~40 μm) of PDMS using a custom-built microtribometer with in situ optical interferometry that enabled simultaneous measurements of contact area, penetration depths, externally applied force, and the detailed measurements of the free-surface deformations, which include the predicted tensile zone along the perimeter of contact.

Virtual Office Hours through Video Conferencing: Lessons LearnedThe ability to hold academic office hours via video conferencing technology has been greatly enhancedwith the development of widely distributed, free platforms over the last few years. It is now possible torender academic assistance at a high level of effectiveness in both real-time/asynchronous settingsacross remote locations using platforms such as Google+ with Hangouts, Facetime, and Skype. Thelessons learned over the last two years of using this technology in the area of distance education andprofessional development will be shared.

Applying Distance Education Technologies to a Large-Scale EngineeringMechanics CourseA traditional engineering mechanics course with a very large enrollment (500 students) was enhancedby leveraging existing technologies originally purposed to serve distance engineering students in onlineprograms. The use of high-definition recorded lectures, online homework tools, social media, and coursemanagement systems allowed for an efficient delivery of engineering curriculum content by a singleprofessor and several teaching assistants. This increased instructional efficiency, in the form of fewerinstructors and support personnel required to teach such a large student population, did not come atthe expense of student learning experience as evidenced by student performance as compared toprevious semesters as well as student self-assessment of pedagogical efficacy.

Cells sense and respond to their environment. Mechanotransduction is the process by which mechanical forces, stress, and strains are converted into biochemical signals that control cell behavior. In recent decades it has been shown that appropriate mechanical signals are essential to tissue health, but the role of friction and direct contact shearing across cell surfaces has been essentially unexplored. This, despite the obvious existence of numerous biological tissues whose express function depends on sliding contacts. In our studies on frictional interactions of corneal cells we find that the friction coefficients are on the order of mu = 0.03-0.06 for in vitro and in vivo experiments. Additionally, we observe cell death after single cycles of sliding at contact pressures estimated to be approximately 12 kPa. These experimental results suggest that frictional contact forces produce mechanical stresses and strains that are in the cellular mechanosensing ranges.

Individual Data Acquisition and Experimentation in Undergraduate Mechanical Engineering LaboratoriesUndergraduate teaching laboratories in mechanical engineering curriculum are traditionallygroup-oriented courses with activities centered on large, one-off experimental apparatus. Thepredominance of single-instanced experimental laboratories is largely due to the balancebetween having sufficient curricular diversity and the cost and maintenance constraints of labinstructors and support personnel. This work summarizes the experiences over the last two yearswhere a model of all individually-based data acquisition and experimentation laboratoryactivities was established in two separate teaching laboratory courses: mechanics of materialslaboratory and dynamic and controls systems laboratory. All students used self-owned personallaptops combined with student-owned low-cost universal serial bus data acquisition (USBDAQ) devices for interfacing with each individual experimental station. The experimentalactivities would be changed out each week but with the thread of commonality being that thesoftware programs written for the USB DAQ device from the previous week’s activity wereemployable in subsequent activities. Since data was acquired on an individual basis, individualreports recounting the laboratory procedures, results, and discussion were submitted and graded.Assessment of this approach was performed via anonymous student course evaluation surveyscomparable to previous traditional group-experimentation laboratory courses where similarsurveys were given. The potential ramifications of this model adoption on undergraduateteaching laboratories will be discussed in relation to increased student engagement anddepartmental resource allocations.

A model for the lateral contact stiffness for an elastic foundation was developed. The model was evaluated using a low force and low contact pressure microtribometer capable of performing indentation and reciprocated sliding experiments. The slope of lateral force versus the lateral displacement was used to fit the shear modulus. When complementary elastic indentation measurements are made to determine the composite modulus of the elastic foundation, there is sufficient data to fit elastic modulus, shear modulus, and Poisson ratio for these thin films. Using these models, the elastic properties for a thin (~65 μm) vertically aligned multiwall carbon nanotube film were evaluated. The experiments were performed with a silicon nitride indenter (radius = 1.6 mm) over a range in loads from 100 to 800 μN. The resulting values of the elastic modulus, shear modulus, and Poisson ratio were E = 429 kPa, G = 156 kPa, and ν = 0.37, respectively.

Considerable research has been done on the tribological properties of cosputtered metal/MoS2 solid lubricant films with low metal content (<20 at.%) because of their usefulness in applications at high Hertzian contact stress (around 1 GPa). However, cosputtered Au-MoS2 coatings with a much higher range of metal contents up to (95 at.%) have shown surprisingly good performance at low contact stresses (as low as 0.1 MPa). In the present study, transmission electron microscopy, X-ray diffraction and electrical resistance measurements of cosputtered Au-MoS2 coatings reveal them to be composites of nanocrystalline Au particles within an amorphous MoS2 matrix. Electrical conductivity images of the coatings displayed metallic (Au) and semi-conducting (MoS2) domains of nanometer dimensions. Auger Nanoprobe analyses confirmed that sliding on the coatings causes the formation of a pure MoS2 layer about a nanometer thick on top of the bulk of the coatings. Lattice resolution atomic force microscopy revealed that this nanometer-thick MoS2 layer is crystalline, and oriented with the basal plane (0001) parallel to the coating surface. Electrical resistance obtained during sliding and pull-off force measurements was consistent with the structure of the coatings. Sliding friction data on the coatings support previous results showing that performance at different Hertzian contact stresses correlated strongly with Au content (C) 2009 Elsevier B.V. All rights reserved.

Electrical contact materials deposited via thin-film processes enable the structuring of interfaces that optimize electrical contact performance. The performance gains are accomplished by structuring the contact material such that a conductive pathway is always present in the composite, a phenomenon related to the percolation threshold. The relationship between film composition and percolation threshold was explored by combined three-dimensional contact area and resistance modeling as well as experimental efforts. An optimal composite structure was found based on deposition parameters and compositional phase selections.

Direct computation of interfacial contact area for microelectromechanical-system applications was performed numerically using the measured device surface topography and the material hardness to define the flow stress of an individual element. The simulation results compared well with the established contact-area determination methods and also introduced new capabilities that enabled the visualization of the spatial distribution of contact spots to be computationally mapped and rendered directly onto device surfaces.

Electrical contact resistance testing was performed by hot-switching a simulated gold-platinum metal microelectromechanical systems contact. The experimental objective was to determine the sensitivity of the contact resistance degradation to current level and environment. The contact resistance increased sharply after 100hot-switched cycles in air. Hot-switching at a reduced current and in nitrogen atmosphere curtailed contact resistance degradation by several orders of magnitude. The mechanism responsible for the resistance degradation was found to be arc-induced decomposition of adsorbed surface contaminants