September 18
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12:00 PM
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1:00 PM
The Mechanics Seminar Series is a weekly seminar given by campus and visiting speakers on topics across the spectrum of mechanics research (solids, fluids, and dynamics). Professor Guruswami Ravichandran is a professor at Caltech.
Presentation Title: Shock Induced Deformation and Failure during Pore Collapse in PMM
Abstract: Porosity is prevalent in engineering materials and strongly influences their response to dynamic loading. Under shock compression, localized deformation near pores can govern failure in lattice structures, additively manufactured components, and energetic materials, yet the underlying mesoscopic mechanisms remain poorly understood. An internal digital image correlation (DIC) technique is developed for transparent materials, enabling in situ, high-speed, full-field measurements of displacement and strain at strain rates of 10³ – 10⁶ s⁻¹. Using specimens with embedded internal speckle patterns, the technique is applied to investigate shock-induced pore collapse in PMMA at impact stresses up to 1 GPa. For single spherical pores, measurements reveal intense strain localization surrounding the collapsing cavity. As shock stress increases, the response transitions from classical strain concentration to adiabatic shear band formation and ultimately dynamic shear fracture. Explicit finite element simulations incorporating thermo-viscoplastic constitutive behavior identify thermal softening-induced instability as the governing mechanism. Experiments on pore pairs show that pore interactions alter strain localization, modify failure thresholds, and influence crack propagation through baroclinic effects and shear-wave interactions. These results provide new insights into shock-driven shear localization and failure in porous materials.
Bio: 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 National Academy of Engineering and Academia Europaea, and a Fellow of ASME, SEM, and AAM. He was named Chevalier de l’Ordre des Palmes Académiques by the Republic of France. 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.