Brown University School of Engineering

Engineering Seminar: Joint Materials/Solid Mechanics

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Monday, November 13, 2017 4:00pm - 5:00pm

Professor Krishnaswamy Ravi-Chandar, Center for Mechanics of Solids and Structures, University of Texas at Austin, will present a talk: "Damage in Elastomers: Nucleation, Growth, and Healing of Cavities and Micro-cracks". Abstract: The study of the nucleation and growth of cavities in elastomers and rubbers as a precursor to eventual failure has a long and rich history; this topic has occupied the interest of many analytic investigators and a few experimental investigator. The prevailing viewpoint is that cavitation is a purely elastic instability phenomenon governed by the elastic properties of the material. In this presentation, the focus is on experiments where the initiation and propagation of internal damage are designed to occur in between two spherical or cylindrical glass beads that are firmly embedded within a matrix of the polymethylsiloxane (PDMS) elastomer and are placed close to each other in order to generate a high triaxial stress state. An optical microscope is used to monitor the various processes of nucleation and growth of cavities and cracks at a spatial resolution of about 1 um and a temporal resolution of about 66.7 ms. In combination with corresponding full-field simulations, the experiments show that the nucleation of cavities — that is, the onset of cavitation — is an extremely fast process that is controlled primarily by the stiffening at large deformations of the underlying elastomer and, more critically, by its fracture properties. The experiments and simulations also show that cavitation is followed by two distinct events upon further macroscopic loading: the transition of the nucleated cavities to micro-cracks, and the further transition of some micro-cracks to macro-cracks. These two distinct events are also controlled primarily by the fracture properties of the underlying elastomer. Further, recent experiments that show the healing response of the cavities/cracks will also be discussed. It will be demonstrated that these interior cavities or cracks can recover completely upon unloading and reestablish their initial strength. Supporting numerical simulations will be presented as an aid to understanding the mechanical state under which such damage and healing occur. Bio: Professor Ravi-Chandar received his bachelor’s degree in Physics from Bangalore University in 1973; and his diploma in Aeronautical Engineering, with honors, from the Madras Institute of Technology in 1976. He received his MS and Ph.D. in Aeronautics from the California Institute of Technology, in 1977 and 1982. He started his academic career at the University of Houston in 1983, and moved to The University of Texas at Austin in September 2000 as a Professor in the Department of Aerospace Engineering and Engineering Mechanics. Since 2007 he holds the Temple Foundation Endowed Professorship No. 1. He has also held numerous visiting positions in Europe and India. Dr. Ravi-Chandar’s research interests are in the general area of mechanics of materials. He is well-recognized for his fundamental work on mechanisms and mechanics of deformation and failure. He has published more than 150 archival journal articles on fracture, instabilities, fragmentation, and authored a book titled Dynamic Fracture.