Title:

High Pressure Hugoniot Measurements in Solids using Mach Reflections

Speaker:

Prof. Guruswami Ravichandran

Affiliation:

Graduate Aerospace Laboratories (GALCIT) at the California Institute of Technology

When:

Thursday, January 19, 2012 at 3:30:00 PM   Add to Calendar

Where:

Montgomery Knight Building, Room G442

Host:

Aerospace Engineering Chair’s Office
melody.foster@me.gatech.edu

Abstract

It has long been recognized that high pressure equation of state (Hugoniot) measurements in solids can be determined by subjecting the material to a one dimensional plane shock wave. Shock waves of this type are usually generated by the planar impact of two flat plates and, as a result, the shock amplitude is inherently limited by the velocity of the impacting plate. In an effort to dramatically increase the range of pressures, which can be studied with available impact velocities, a new experimental technique has been developed. A target consisting of two concentric cylinders aligned with the axial direction parallel to the loading is subjected to planar impact. The target is designed such that upon initial impact, the outer cylinder will have a higher shock velocity than the inner material of interest. Conically converging shocks are generated at the interface between the two materials due to the impedance mismatch. Upon convergence, an irregular reflection occurs and the conical analog of a Mach reflection develops and grows until it reaches a steady state. The resulting high pressure Hugoniot state behind the Mach stem is measured using velocity interferometry (VISAR). The new technique is demonstrated using a planar mechanical impact generated by a powder gun to study the shock response of copper. Two systems are examined which utilize either a low impedance (6061-T6 aluminum) or a high impedance (molybdenum) outer cylinder. The results from the experiments are presented and compared to both numerical simulations and a hydrodynamic model based on shock polars. The feasibility of measuring an entire Hugoniot curve using full field velocity interferometry (ORVIS) is discussed, and initial experimental results are presented.

Biography

Guruswami Ravichandran is the John E. Goode, Jr. Professor of Aerospace and Professor of Mechanical Engineering and Director of the Graduate Aerospace Laboratories (GALCIT) at the California Institute of Technology. He received his B.E. (Honors) in Mechanical Engineering from the University of Madras in 1981, Sc.M. in Engineering and Applied Mathematics in 1983 and 1984, respectively, and Ph.D. in Solid Mechanics and Structures from Brown University in 1986. He is a Fellow of the American Society of Mechanical Engineers (ASME) and the Society for Experimental Mechanics (SEM). He was awarded Doctor honoris causa by Paul Verlaine University in 2006 and Chevalier de l'ordre des Palmes Academiques by the Republic of France in 2011. His awards also include Charles Russ Richards Memorial Award from Pi Tau Sigma and ASME and Lazan and Hetenyi awards from SEM. His research interests are in mechanics of materials with emphasis on deformation, damage and failure, micro/nano mechanics, active materials, biomaterials and experimental methods.