Presented by Professor William Curtin
W. A. Curtina , Zhaoxuan Wub, Rasool Ahmada, and Binglun Yinc
a Institute of Mechanical Engineering, École Polytechnique Fédérale de Lausanne,
b Dept. of Materials Science, City University of Hong Kong
cDept. of Materials Science, Zhejiang U., China
Pure Mg has low ductility due to strong plastic anisotropy and due to a transition of <c+a> pyramidal dislocations to a sessile basal-oriented structure . Alloying generally improves ductility; for instance, Mg-3wt.%RE (RE=Y, Tb, Dy, Ho, Er) alloys show relatively high ductility , and typically larger than most commercial Mg-Al-Zn alloys at similar grain sizes. Possible concepts for ductility in alloys include the reduction of plastic anisotropy due to solute strengthening of basal slip, the nucleation of <c+a> from basal I1 stacking faults, the prevention of the detrimental <c+a> transformation to sessile structures, and the weakening of strong basal texture by some solute/particle mechanisms. Experiments and modeling do not strongly support these concepts, however. Here, we introduce a new mechanism of pyramidal cross-slip from the lower-energy Pyr. II plane to the higher energy Pyr. I plane as the key to ductility in Mg and alloys . Certain alloying elements reduce the energy difference between Pyr. I and II screw dislocations, accelerating cross-slip that then leads to rapid dislocation multiplication and alleviates the effects of the undesirable pyramidal-to-basal dissociation. A theory for the cross-slip energy barrier is presented, and first-principles density functional theory (DFT) calculations, following methods in , are used to compute the necessary pyramidal stacking fault energies as a function of solute type for many solutes in the dilute concentration limit. Predictions of the theory then demonstrate why Rare Earth solutes are highly effective at very low concentrations, and generally capture the trends in ductility and texture evolution across the full range of Mg alloys studied to date. The new mechanism is used to guide alloy design for achieving enhanced ductility across a range of non-RE alloys .
Professor William Curtin earned a 4 yr. ScB/ScM degree in Physics from Brown University in 1981 and a PhD in theoretical physics from Cornell University in 1986. He worked as staff researcher at British Petroleum until 1993 and then joined Virginia Tech as an Associate Professor in both Engineering Mechanics and Materials Science. In 1998 he returned to Brown as Full Professor of Engineering in the Solid Mechanics group, where he was appointed Elisha Benjamin Andrews Professor in 2006. He joined Ecole Polytechnique Federale de Lausanne as the Director of the Institute of Mechanical Engineering in 2011 and officially as Full Professor in 2012. His research successes include predictive theories of optical properties of nanoparticles, statistical mechanics of freezing, hydrogen storage in amorphous metals, strength and toughness of fiber composites, dynamic strain aging and ductility in lightweight Al and Mg metal alloys, solute strengthening of metal alloys including high entropy alloys, and hydrogen embrittlement of metals, along with innovative multiscale modeling methods to tackle many of these problems. Professor Curtin was a Guggenheim Fellow in 2005-06, was Editor-in-Chief of “Modeling and Simulation in Materials Science and Engineering” from 2006-2016, has published over 300 journal papers that have received over 19000 citations with an h-index of 75 (Google Scholar), and has been the Principal Investigator on over $37M of funded research projects.
 Z. Wu, W.A. Curtin, Nature 526 (2015) 62-67
 S. Sandlobes, et al., Acta Materialia 59 (2011) 429-439; Acta Materialia 70 (2014) 92–104
 Z. Wu, R. Ahmad, B. Yin, S. Sandlobes, and W. A. Curtin, Science 359, 447-452 (2018).
 B. Yin, Z. Wu, and W. A. Curtin, Acta Materialia 136 (2017) 249-261.
 R. Ahmad, B. Yin, Z. Wu, and W. A. Curtin, Acta Materialia 172 (2019) 161-184.
“Magnetic Soft Composites with Integrated Multiphysics Responses”
Presented by Professor Renee Zhao
Assistant Professor, Department of Mechanical and Aerospace Engineering
The Ohio State University
Magnetic soft composites are a type of stimuli-responsive materials that can generate large deformation and locomotion under external magnetic fields. They have recently attracted great interest due to the increasing demand for programmable materials that can be easily controlled to achieve complex functionalities for untethered morphing and reconfigurable structures. In particular, these composites are considered to be competitive candidates for developing soft robots as biomedical devices for drug delivery and minimally invasive surgeries for two major reasons: the magnetic untethered control (1) offers a safe and effective operation method for biomedical applications, which typically require remote actuation in enclosed and confined spaces; and (2) separates the power source and controller from the device, making miniaturized robots possible. However, it is still a great challenge to design and fabricate high performance multifunctional magnetic soft composites for advanced engineering applications, due to the lack of design guidance on materials, fabrication, and stimulation control. In this talk, a mechanics-guided methodology is first introduced and integrated with advanced fabrication such as 3D printing to guide the design of structures with precise actuation control for multifunctionality of magnetic soft composites. It is accomplished by implementing a new constitutive model for magnetic soft composites into finite element analysis. This methodology is used to guide the design for a few novel applications, including symmetry-breaking actuation for soft robots, magnetic shape memory polymers for untethered shape morphing and locking, and magnetic origami robots for functional deformation and locomotion. Then, the artificial intelligence is integrated with the finite element analysis to guide the 3D printing of magnetic soft composites for desired shape morphing during magnetic actuation. At the end of this talk, future directions in fundamental research and novel applications of magnetic soft composites will be discussed.
Ruike (Renee) Zhao is currently an Assistant Professor in the Department of Mechanical and Aerospace Engineering at The Ohio State University. She received her PhD degree in solid mechanics from Brown University in 2016. She was a postdoc associate at MIT during 2016-2018 prior to joining OSU in August 2018. Her research concerns the fundamental science and the development of stimuli-responsive polymeric soft composites for soft robotic systems with integrated multifunctionality including shape-changing, locomotion, and navigation. By combining mechanics, polymer engineering, and advanced material manufacturing techniques, the functional soft composite systems will enable biomedical applications with a focus on developing miniaturized biomedical devices for minimally invasive surgeries. Renee is a recipient of the ASME Haythornthwaite Research Initiation Award (2018) and the NSF Career Award (2020).