Calendar

Apr
25
Thu
Graduate Seminar: Rohan Abeyaratne (MIT)
Apr 25 @ 12:00 pm – 1:00 pm

Growth of an Elastic Solid on a Rigid Substrate 

Rohan Abeyaratne
Berg Professor of Mechanics
Massachusetts Institute of Technology

 In this talk I will illustrate and discuss certain issues pertaining to the continuum mechanical formulation of problems that involve growth on a rigid impermeable surface. One characteristic of the problem we consider is that accretion takes place on the interior surface that separates the body from its support (rather than on its exterior surface). As a result, each new layer formed must push away the layers formed previously. This leads to a build-up of stress in the growing body. Simultaneously, ablation takes place at the outer surface where material is removed from the body. In addition, as a material unit moves through the body, after accretion but before ablation, it undergoes a phase transition.

The issues that I will address include (a) choosing a reference configuration that allows one to cope with the continually evolving material structure; (b) the nonstandard boundary conditions that couple diffusion to growth; (c) the driving force associated with surface growth; and (d) the phase transition that happens within the interior of the growing body. I will illustrate the theory by a problem involving growth on a spherical bead. I will show in particular that the build-up of stress at the inner surface slows down accretion, while the increase in strain energy at the outer surface promotes ablation. Eventually, the system may reach a point where internal accretion is balanced by external ablation, a regime referred to as “treadmilling”. We derive conditions under which such a state exists, and show that when it does exist, it is unique. Finally (d) we will use mixture theory to derive a (more detailed) coupled model of the solid that accounts for the affect of diffusion on the solid.

Parts of this work were carried out jointly with Rami Abi-Akl (MIT), Tal Cohen (MIT) and Giuseppe Tomassetti (University of Rome).

Rohan Abeyaratne is the Berg Professor of Mechanics at MIT.   From 2009-2013 he was the CEO & Director of the Singapore-MIT Alliance for Research and Technology (SMART). Prior to this, he was the Head of the Department of Mechanical Engineering at MIT from 2001-2008. He is a Fellow of ASME and the American Academy of Mechanics, and is the recipient of ASME’s 2010 Daniel Drucker Medal. He served a two-year term as President of the American Academy of Mechanics. Professor Abeyaratne’s research interest is in the field of theoretical mechanics with a focus on material instabilities such as phase transitions and cavitation, and more recently on growth. He is the author of three books, the “Evolution of Phase Transitions”, Mechanics of Elastic Solids  “Volume I: Mathematical Preliminaries” and “Volume II: Continuum Mechanics”.  Professor Abeyaratne received his B.Sc. in Mechanical Engineering from the University of Ceylon (1975), and his M.Sc. (1976) and Ph.D (1979) degrees from the California Institute of Technology.

All civil engineering graduate seminars are FREE and open to the public. Attendance is required for all enrolled Civil Engineering graduate students.

For directions and information on parking please see Maps & Directions link at www.jhu.edu and select information on Homewood Campus.

Apr
26
Fri
Special Seminar: Outbreakiomics
Apr 26 @ 3:00 pm – 4:00 pm

The Department of Civil Engineering and Center for Systems Science and Engineering are proud to co-sponsor the following seminar:

Outbreakiomics
Kristian Andersen, PhD
Associate Professor, Immunology and Microbiology
The Scripps Research Institute

Friday, April 26, 2019
3:00-4:00 pm

W5030
Wolfe Street Building

 

May
2
Thu
Graduate Seminar: Jordan Raney (UPenn)
May 2 @ 12:00 pm – 1:00 pm

3D printing multifunctional fibrous composites with controlled microstructure

Jordan Raney
Assistant Professor, Dept. of Mechanical Engineering and Applied Math
University of Pennsylvania 

The internal structural features of material systems greatly affect their macroscopic mechanical properties. For example, natural structural materials such as wood possess highly heterogeneous mesoscale architectures, with hierarchical structure, spatially-varying fiber alignment, non-uniform density, and graded porosity. These features are the result of localized structural and compositional optimization, producing maximal bulk mechanical properties that greatly exceed those of the constituent materials as well as fascinating stimuli-responsiveness. Researchers have long sought the ability to produce synthetic composites of comparable microstructural complexity. Additive manufacturing techniques have begun to enable more nuanced control of the internal structure of engineering materials, but many challenges remain, including notable process-intrinsic limits to the palette of printable materials. Here, direct write 3D printing is used to print short fiber composites with controlled fiber orientation, with the goal of enabling a new degree of control over their mechanical properties and responsiveness to their environment.  Ink materials with fibrous fillers are developed based on epoxies, elastomers, and natural matrices, producing highly anisotropic materials during extrusion through a deposition nozzle.  Using this approach, we control the fiber alignment to produce 3D printed parts that demonstrate both enhanced damage tolerance and “embodied logic” based on instability-induced shape change.

Jordan R. Raney is an assistant professor in the Department of Mechanical Engineering & Applied Mechanics at the University of Pennsylvania. He received a B.S. in Physics and a B.S. in Computer Science from the University of Minnesota, before joining the staff at MIT Lincoln Laboratory. Subsequently, he attended Caltech for graduate school, where he received a M.S. and Ph.D. in Materials Science.  Before joining Penn, he was a postdoctoral fellow at Harvard, in the John A. Paulson School of Engineering & Applied Sciences and the Wyss Institute for Biologically Inspired Engineering.  His research focuses on the mechanics and additive manufacturing of novel composites and material architectures, including hierarchical, heterogeneous, fibrous, and soft systems.

All civil engineering graduate seminars are FREE and open to the public. Attendance is required for all enrolled Civil Engineering graduate students.

For directions and information on parking please see Maps & Directions link at www.jhu.edu and select information on Homewood Campus.

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