Woodruff School of Mechanical Engineering

Faculty Candidate Seminar


Nonlinear mechanics, morphology and instability of thin structures: from slap bracelets to the Venus flytrap and beyond


Dr. Zi Chen


Washington University in St. Louis


Tuesday, May 7, 2013 at 11:00:00 AM


MRDC Building, Room 4211


Min Zhou


Mechanical forces play a key role in the shaping of versatile morphologies of thin structures in natural and synthetic systems. The morphology and deformation of thin ribbons, plates and rods and their instabilities are systematically investigated, through both theoretical modeling and table-top experiments. An elasticity theory combining differential geometry and stationarity principles is developed for the spontaneous bending and twisting of ribbons with tunable geometries in presence of mechanical anisotropy. Closed-form predictions are obtained from this theory with no adjustable parameters, and validated with simple, table-top experiments that are in excellent agreement with the theoretical predictions. For large deformation of ribbons and plates, a more general theory is developed to account for mechanical instability (slap-bracelet type) induced by geometric nonlinearity, due to the competition between inhomogeneous bending and mid-plane stretching energy. This comprehensive, reduced parameter model leads to unique predictions about multistability that are validated with a series of table-top experiments. Furthermore, this study can be extended to investigate a different type of snap-through instability that the Venus flytrap has been actively employing to capture insects for millions of years, and the learnt principle is used to guide the design of bio-mimetic flytrap robot. The study of large deformation and instability of thin objects will facilitate understanding of morphology generation in natural and synthetic systems, and benefit the ongoing efforts in developing programmable micro-fabrication techniques and novel functional devices including artificial muscles, stretchable electronics and bio-inspired robots.


Dr. Zi Chen is currently a Society in Science Branco Weiss Fellow and Research Scientist at Washington University in St. Louis, working with Dr. Larry A. Taber on developmental mechanics. Dr. Chen received a BS and MS in Materials Science and Engineering from Shanghai Jiaotong University in 2002 and in 2005, and his Ph.D. from Department of Mechanical and Aerospace Engineering at Princeton University under Dr. Mikko Haataja and David J. Srolovitz in 2012. His research interests range from computational materials science and solid mechanics to biomechanics, covering topics such as mechanical instabilities of materials and energy harvesting, structural evolution in materials, morphogenesis in plant and animal development, rapid motion of plants, biomimetic materials/devices and nanofabrication. Dr. Chen has received a number of prestigious awards including Society in Science Branco Weiss fellowship, American Academy of Mechanics Founder's Award, Materials Research Society Graduate Student Award, Outstanding Paper Award at ASME NEMB, etc.


Refreshments will be served.