MEAM Seminar Series Summer 2018

For Spring 2018 Seminars, click here.

Seminars are held on Tuesday mornings beginning at 10:45 am in Room 337, in the Towne Building (unless otherwise noted).

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June 6

Zac Milne, Ph.D. Candidate, Department of Mechanical Engineering and Applied Mechanics, University of Pennsylvania
Advisor: Robert Carpick

Title:

"Sliding and Stress Modulate Nanoscale Adhesion of Silicon-Silicon and Silicon-Diamond Contacts"

Abstract:

The Jost report estimates that approximately 3% of a developed nation’s GDP is wasted on friction and wear-related losses, whether through frictional energy loss, mechanical abrasion, machine downtime, and replacing failed parts. For the United States, this equates to hundreds of billions of dollars annually . Nanotribology, the nanoscale study of friction, wear, adhesion, and lubrication, seeks to understand the fundamental causes of these phenomena in an effort to not only reduce the immense costs involved, but to also find ways to manipulate and control frictional and adhesive properties of surfaces where desired.

In this talk, I present the results of experimental studies exploring nanoscale adhesion. Adhesion on the nanoscale is still not well understood and the typically strong adhesion on this scale currently prevents the manufacturing of MEMS devices with contacting and sliding surfaces. Silicon is the primary material used in nano lithography and MEMS development and diamond provides an ideally hard surface to test silicon adhesion against. Using our in situ transmission electron microscopy nanoindentation methodology, we find that cohesion of silicon and adhesion of silicon and diamond depend significantly on both the sliding speed and normal contact stress. Together, these results suggest that shear stress modulates the reactivity of the surfaces. This is the first time that tunable adhesion of hard contacts has been explored in situ.



June 12

NO SEMINAR



June 19

NO SEMINAR


June 26

TBA



July 3

TBA



July 9 (Monday)

MEAM Thesis Defense

Mohammed Asaduzzaman, MSE Candidate, University of Pennsylvania
Advisor: Howard H. Hu

"Interfacial Wave Dynamics of Core-annular Flow of Two Fluids"

10:00 a.m., Room 307, Levine Hall

Abstract:

In core-annular flow of two different fluids, for a set of suitable flow conditions, various shapes of saturated waves such as bamboo, snake and corkscrew waves are observed. Some of the dominant parameters such as thickness ratio of the fluid, Reynolds number, viscosity ratio, density ratio, interfacial surface tension, and the direction of gravitational forces determine the final shape of the saturated wave and their ultimate stability in a nonlinear regime.
When the flow rate ratio is high, sometimes it is difficult to determine the differences between the final shape of the waves for up-flow and down-flow. For some combinations of thickness ratio, viscosity ratio, density ratio, Reynolds number and surface tension, waves tend to break down and bubbles start to form. Interfacial surface tensions between these two fluids play a very important role to stabilize the waves from breaking down.
In this study, new sets of waves were discovered for core-annular flow, which modulate at certain flow parameter ranges. The critical parameter ranges are identified where the waves shift from saturated bamboo waves and bifurcate into modulated bamboo waves. A thorough analysis is performed for the first time to depict the windows of these critical parameters at which this transition takes place. A bifurcation diagram is constructed to capture the regime. A detailed wave shape analysis is performed to characterize these wave shapes and their periods of oscillation.
Due to challenges associated with large computational domain and an enormous computational power requires to resolve the interfacial instability, a three-dimensional true non-axisymmetric model was never studied before. For the first time, effort is being undertaken to construct a viable 3-D Core-annular flow. A general purpose computational fluid dynamics package ANSYS Fluent is used for this analysis. Three dimensional models for both up-flow and down-flow were constructed and a novel explanation is presented to distinguish between the Bamboo waves, Cork-Screw waves, and Snake waves. The sensitivity of down-flow on initial conditions was also verified with 3-D models on some parameter space from selected publication.

July 17

TBA


July 24

Gavin Kenneally


July 31

John Cortes


August 7

Lisa Mariani


August 14

TBA


August 21

TBA