Physics Room 126, Lecture Hall
The MU Physics & Astronomy Department's O. M. Stewart Colloquium Series presents, "Beyond Hook’s Law," by Asst. Research Professor Hussein Nassar, MU College of Engineering on Tuesday, April 10 at 4:00 p.m. Refreshments will be served beginning at 3:30 p.m. in Rm. 236, Physics Lounge.
Nassar writes, "At one scale or another, what appears to be a homogeneous material can ultimately be resolved into a set of inhomogeneous constituents: a metal into a polycrystal, a piece of paper into pulp fibers, a wall into bricks and mortar, a bridge into a truss, a mountain into rocks or even a galaxy into stars. In all of these instances, the apparent physical behavior of the whole is less dependent on chemical composition and more anchored in the spatial order and distribution of constituents. Modern advances in fabrication techniques have enabled a similar approach in materials design where a material is architected, like a building, rather than “cooked” by chemical and thermodynamic processes. The purpose, as always, is to get the best of two worlds: a most common example is that of reinforced concrete, light and strong, whereas concrete alone is brittle and steel alone is heavy (and expensive). The talk will explore two topics revolving around the elastic behavior of mixtures where the global behavior of the whole drastically departs from the local behavior of the parts effectively rendering Hook’s law obsolete. In the first topic, we will describe polarization effects that emerge in a family of spatiotemporal composites whereby waves travel left and right at different speeds. This sort of left/right speed bias cannot be accounted for through Hook’s law and its full description will require the use of tools inspired from similar quantum mechanical systems known as topological insulators. In the second topic, we present a set of compliant shell mechanisms referred to as Origami tessellations. Based on the Japanese art of paper folding, these shells exhibit local folding mechanisms that aggregate on a global scale and bring on large changes in shape, elongation and curvature. Here too, Hook’s law, although valid on the scale of a single fold, fails in rendering changes in shape on the global scale. Last, relevant applications in various domains are presented along with an outlook and plans for future investigations."