Speaker and Affliation:
Professor of Aerospace and Mechanical Engineering
Graduate Aerospace Laboratories
California Institute of Technology
Guruswami (Ravi) Ravichandran is the John E. Goode, Jr. Professor of Aerospace and Mechanical Engineering at the California Institute of Technology. He received his B.E. (Honors) in Mechanical Engineering from the University of Madras, Sc.M. in Engineering and Applied Mathematics and Ph.D. in Engineering (Solid Mechanics and Structures) from Brown University. He is a member of the U.S. National Academy of Engineering and Academia Europaea. He is a Fellow of the American Society of Mechanical Engineers (ASME), Society for Experimental Mechanics (SEM) and American Academy of Mechanics (AAM). He was named Chevalier de l’ordre des Palmes Academiques by the Republic of France. His awards include A. C. Eringen Medal from the Society of Engineering Science, Warner T. Koiter Medal from ASME, and William M. Murray Lecture Award from SEM. His research interests are in mechanics of materials including micro/nano mechanics, wave propagation, composites, active materials, biomaterials and cell mechanics, and experimental methods.
15th April, 2022 (Friday), 04:00 PM (India Standard Time)
Iron is an abundant metal featured in many applications and planetary physics involving dynamic loading. Constitutive models for the flow strength as a function of strain, strain rate, pressure, and temperature are needed to model and simulate applications. This talk focuses on the behavior of iron at high strain rates using a split Hopkinson (Kolsky) pressure bar (SHPB) and at high pressures using the pressure shear plate impact (PSPI) technique. A shear-compression specimen (SCS) used to attain high strain rates, large strains, and shear dominant deformation provides a seamless characterization of a-iron over a range of strain rates, 10-4 to 2x104 s-1. In addition to the mechanical response (stress-strain), a high-speed infrared detector is used to measure in-situ temperature rise during dynamic deformation. Strong strain rate sensitivity of flow stress is observed, with strengths exceeding 1 GPa, comparable to pre-shocked iron and high strength steels. The microstructural evolution characterized using optical, SEM, TEM, and EBSD provides insights into the strengthening and deformation mechanisms. Results from PSPI experiments on iron at pressures ranging from 10 to 43 GPa and strain rates ~105 s-1 are presented. The mechanical response of the low pressure a phase (bcc) and the high-pressure e phase (hcp) is obtained, with the a to e transformation occurring at ~13 GPa. A strong pressure hardening in strength is observed, and the possible mechanisms for the hardening are discussed.