Abstract:

Lattice structures are architected cellular materials composed of periodic unit cells formed by rods, plates, or other structural elements. Advances in additive manufacturing have enabled precise control of lattice geometry, allowing these materials to achieve exceptional stiffness-to-weight ratios, strength, and energy-absorption capabilities. Architected lattice metamaterials with spatial property gradients offer new opportunities for tailoring stress-wave propagation, energy dissipation, and failure mechanisms under dynamic loading. This seminar examines the high-strain-rate behavior of polymeric lattice structures using split-Hopkinson pressure bar and direct impact experiments combined with high-speed imaging and digital image correlation. Quasi-static and dynamic tests on Kelvin lattices reveal the formation of localized deformation bands that initiate near the specimen center. The influence of lattice topology on transient dynamic response and the transition to shock compression is investigated through comparative studies of cubic, Kelvin, and octet-truss architectures. Full-field DIC measurements enable the definition of local shock parameters, while continuum shock analysis based on Rankine-Hugoniot jump conditions is used to quantify shock behavior. Results from density-graded lattices spanning bending-dominated, stretching-dominated, and auxetic topologies provide new insight into how topology, gradient design, and loading rate interact to govern stress-wave propagation, energy absorption, and failure evolution in architected materials. Explicit finite element simulations incorporating tensile failure are used to validate observed deformation modes and scaling trends.

Biography:

Guruswami (Ravi) Ravichandran is the John E. Goode, Jr., Professor of Aerospace and Mechanical Engineering at the California Institute of Technology. He received his 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, and a Fellow of ASME, SEM, and AAM. His honors include the ASME Timoshenko Medal, SES Eringen Medal, and SEM Murray Lecture Award. His research interests are in mechanics of materials, including dynamic behavior, wave propagation, composites, multifunctional materials, micro/nano-mechanics, cell mechanics, and experimental methods