Foldable and Responsive Soft Metamaterials

Shu Yang
Department of Materials Science and Engineering, University of Pennsylvania

Materials that can expand and collapse, fold, and transform into a variety shapes have attracted significant interest and have obvious applications in flexible electronics, color displays, smart windows, actuators, sensors, and both photonic and phononic devices. But how can we render a rigid device super-flexible so that it can wrap around a sphere without bending and stretching? How can flat surfaces be transformed into any desired 3D structure without disruptive stretching and deformation?
In my talk, I will show several examples how we introduce holes and cuts in periodically structured materials, so called metamaterials, exhibiting dramatic shape change (e.g. ~800% areal expansion) and super-conformability via expanding or collapsing of the periodic hole arrays without deforming individual lattice units. When choosing the cuts and geometry correctly, we show folding into the third dimension, known as kirigami. The kirigami structures can be rendered pluripotent, that is changing into different 3D structures from the same 2D sheet. We then pre-program the buckling direction and curvatures by introducing notches on existing kirigami structures or by embedding cues in surface patterns of liquid crystal elastomers with internal strains. Lastly, I will show our initial success in additive manufacturing toward textile based self-folding devices.

Seminar will be held at 3:30 PM in Malone Hall G 33/35.

Development of Micro-Architected Materials for Space Propulsion and Pulsed Power Applications

Nasr M. Ghoniem, University of California, Los Angeles

Advances in electrode, chamber, and structural materials will enable breakthroughs in future generations of electric propulsion and pulsed power (EP & PP) technologies. Although wide ranges of electric propulsion and pulsed power technologies have witnessed rapid advances during the past few decades, much of the progress was based on empirical development of materials through experimentation and trial-and-error approaches. To enable future technologies and to furnish the foundations for quantum leaps in performance metrics of these systems, a science-based materials development effort is required. We aim to develop new plasma-resilient material architectures that will enable future generations of electric propulsion and pulsed power technologies through an integrated research approach that combines multiscale modeling of plasma-material interactions, experimental validation, and material characterization. The range of materials of interest in EP & PP include refractory metals, such as tungsten and its alloys (W-Re) and molybdenum, ceramic composites, such as BN and Al2O3, high-strength copper alloys, and carbon-carbon composites. These classes of materials serve various design functions; primarily in cathode and anode applications, in accelerator grids, and in beam dumps of HPM sources. The presentation will give a review of our fundamental understanding for the limits of using these materials in EE & PP, and the opportunity to design material architectures that may dramatically improve their performance. We discuss the results of recent research related to three questions: (1) How can we control the thermomechanical response of materials in extreme heat flux and mitigate failure? (2) What are the phenomena that determine the unstable erosion of material surfaces in plasma and ion environments? and (3) How can we design materials that beneficially influence the plasma through Secondary Electron Emission (SEE)? We first review the status of our experimental facilities for simulation of the space environment. Then, we present results of our understanding of the thermomechanics of materials in severe pulsed plasma environments, and the factors that control the erosive instabilities of surfaces. Finally, results of the effects of surface architectures on secondary electron emission will be given.

Seminar will be held at 11:00 AM in Malone Hall, G33/35.

Dynamic Behavior of Earth Materials Subjected to Pressure-Shear Loading

Dr. John Borg, Prof. of Mechanical Engineering, Marquette University

The dynamic behavior of earth materials, such as wet and dry sand, is of interest to a variety of research fields such as defense, mining and planetary science. Plane-strain experiments are necessary to obtain the Hugoniot response of such systems however such loading is not indicative of most loading scenarios of interest.  Thus understanding oblique impact configuration (pressure-shear) can lead to a better understanding of the role of strength in the dynamic response of earth materials.  Figure 1 illustrates the basic configuration of the impact experiment and sand of interest.  A key aspect of this experiment is obtaining an accurate measurement of the normal and transverse velocity of the anvil.  For these experiments a photon Doppler velocimetry (PDV) will be used.  The configuration and the inherent difficulties of applying such a diagnostic technique to this experiment will be discussed.

Seminar will be held at 3:30 PM in Malone G33/35.

Fig. 1. (a) Oblique impact configuration with assembly with a thin sand sample with incident and reflected probes (b) Oklahoma #1 pure sand (425 – 500 μm diameter)