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September 2021

MEAM Seminar: “Kirigami: Programming Cutting and Folding from Microscale to Meter Scale”

September 28 at 10:00 AM - 11:30 AM
Zoom – Email MEAM for Link, peterlit@seas.upenn.edu

Programmable shape-shifting materials can take different physical forms to achieve multifunctionality in a dynamic and controllable manner. By introducing holes and cuts in 2D sheets, we demonstrate dramatic color and shape change and super-conformability via collapsing or expanding of the hole arrays in the micro- and macroscales. When choosing the cuts and geometry correctly, we show folding into the third dimension, known as kirigami. By programming the geometry of cuts and folding angles, we explore their potential applications in water…

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MEAM PhD Thesis Defense: “A Differential Homogenization Framework for Precipitation-Strengthened Metals”

September 30 at 2:00 PM - 3:00 PM
Zoom – Email MEAM for Link, peterlit@seas.upenn.edu

Composite materials, such as metal- and polymer-matrix composites, exhibit both elastic and dissipative effects when subjected to macroscopic loadings. Even when the phases of the composite are characterized by a simple Maxwell rheology, the complex viscoelastic interactions between the phases give rise to emergent behavior at the macroscopic scale. Incorporating these ``long-memory'' effects in the context of analytical homogenization is the subject of this thesis. In particular, I will present a novel differential homogenization framework for particulate composites comprised of…

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October 2021

MEAM Seminar: “Electrets, Magnetics and Deformation in Soft Materials”

October 5 at 10:00 AM - 11:30 AM
Zoom – Email MEAM for Link, peterlit@seas.upenn.edu

Soft robotics, energy harvesting, large-deformation sensing and actuation, are just some of the applications that can be enabled by soft dielectrics that demonstrate substantive electromechanical coupling. Imagine now also a material that will produce electricity and deform substantively via a contactless, wireless magnetic signal. Unfortunately, truly soft, naturally occurring piezoelectric or magnetoelectric materials essentially do not exist. In this presentation, I will illustrate how mechanics and the concept of electrets i.e. materials with immobile embedded charges and dipoles, may be…

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MEAM PhD Thesis Defense: “Analytical Homogenization Estimates for the Effective Properties and Field Statistics of Viscoplastic Composites and Particle Suspensions”

October 5 at 1:00 PM - 2:00 PM
Zoom – Email MEAM for Link, peterlit@seas.upenn.edu

Heterogeneous materials are commonly found in nature (e.g. soil, rock, blood) and engineering applications (e.g. paints, lubricants, sintered materials). Understanding the microstructure-properties relations is crucial to predicting how these materials fail and behave during processing. In this thesis, we develop semi-analytical homogenization estimates for the macroscopic properties and field statistics of viscoplastic composites. A generalization of classical homogenization estimates for anisotropic linear two-phase composites is proposed. The generalized estimates are consistent with known bounds for the effective properties and satisfy…

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MEAM Seminar: “Computational Mechanics for Landing on Mars”

October 19 at 10:00 AM - 11:30 AM
Zoom – Email MEAM for Link, peterlit@seas.upenn.edu

Current technology for decelerating a spacecraft from the high speed of atmospheric entry to the final stages of landing on Mars is based on low-density supersonic decelerators such as low mass and high packaging efficiency parachute systems. To enable future exploration missions featuring sophisticated robots and safely land heavier spacecraft on Mars, larger than before high-speed parachutes and inflatable drag devices are needed. The design, development, and maturing of such devices for future use at Mars require guidance from predictive…

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PICS Colloquium: “Kinetic theory for superparameterization of sea ice dynamics”

October 22 at 2:00 PM - 3:00 PM
PICS Conference Room 534 – A Wing , 5th Floor, 3401 Walnut Street
Philadelphia, PA 19104 United States
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Arctic sea ice comprises of many ice floes whose dynamics is driven by oceanic/atmospheric currents and floe-floe interaction. Models of the effective sea ice dynamics  at large scales typically employ hydrodynamic equations of motion, such as mass and momentum conservation, with complex constitutive laws attempting to capture the rheology of sea ice as a continuum. Although hydrodynamic sea ice models have enjoyed some successes, they have well-documented limitations in capturing phenomena such as fracture and lead formation, which are direct manifestation of the granular nature of sea…

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MEAM Seminar: “Robotics Goes Soft: Challenges and Achievements, for New Robotics Scenarios”

October 26 at 10:00 AM - 11:30 AM
Zoom – Email MEAM for Link, peterlit@seas.upenn.edu

Largely inspired by the observation of the role of soft tissues in living organisms, the use of soft materials for building robots is recognized as one of the current challenges for pushing the boundaries of robotics technologies and building robotic systems for service tasks in natural environments. The study of living organisms sheds light on principles that can be fruitfully adopted to develop additional robot abilities or to facilitate more efficient accomplishment of tasks, because living organisms exploit soft tissues…

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November 2021

MEAM Seminar: “Time and Rate Dependent Fracture of Polymer Gels and Interfaces”

November 9 at 10:00 AM - 11:30 AM
Zoom – Email MEAM for Link, peterlit@seas.upenn.edu

Fracture of materials and interfaces is often time and rate dependent. The underlying mechanisms for the time and rate dependent fracture may include local molecular processes, viscoelasticity, and poroelasticity (solvent diffusion coupled with deformation). In this talk, I will present our recent works on two different mechanisms. First, the effects of poroelasticity on fracture of polymer gels will be discussed. A path-independent, modified J-integral approach is adopted to define the crack-tip energy release rate as the energetic driving force for…

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