Seminar: Ductile Failure of Aluminum Alloys at Low Triaxialities: Experimental and Modeling Challenges

Seminar by Stelios Kyriakides

Research Center for Mechanics of Solids,

Structures and Materials

The University of Texas at Austin

E-mail: skk@mail.utexas.edu

Recent experimental studies on the extent to which aluminum alloys can deform under combined shear and axial loadings, have reported failure strains to be monotonically decreasing as the triaxiality increases, a trend that is contrary to some recent published results. Furthermore, strains inside narrow localization zones that precede failure were found to be much higher than previously reported. In addition, scanning electron microscopic evaluation of the failure zones showed that void formation and coalescence is delayed until very close to the onset of failure for this material. This lecture will first review the tension-torsion experiments and associated experimental challenges such as measurement of strains in narrow zones of the order of the wall thickness of the specimen. Numerical simulations of the experiments are used to evaluate the extent to which continuum plasticity can reproduce the measured responses and the associated localization. The numerical results demonstrate the crucial role played in the reproduction of the measured responses by the constitutive model and its calibration, the need for a properly extracted material hardening response to large strains, and the demands placed on the discretization of the structure in order to capture the large strains and high strain gradients in the localization zones.  

References:

Scales, M., Chen, K., Kyriakides, S., “Material Response, Localization and Failure of an Aluminum Alloy Under Combined Shear and Tension: Part I Experiments.” Int’l J. Plasticity 120, 340-360, 2019.

Chen, K., Scales, M., Kyriakides, S., “Material Response, Localization and Failure of an Aluminum Alloy Under Combined Shear and Tension: Part II Analysis.” Int’l J. Plasticity 120, 361-379, 2019.

Dr. Kyriakides received a B.Sc. degree in Aeronautical Engineering with first class honors from the University of Bristol in the U.K., and M.S. and Ph.D. degrees in Aeronautics from the California Institute of Technology. He is Professor of Aerospace Engineering and Engineering Mechanics at The University of Texas at Austin and holds the John Webb Jennings Chair in Engineering. Kyriakides' major technical interests are in the mechanics of solids, structures and materials, with an emphasis on instability at both the macro (structural) and micro (material) levels. His work is motivated by practical problems and usually involves combined experimental, analytical and numerical efforts. He has more than 200 publications, has co-authored one book, and has lectured extensively both nationally and internationally. He has pioneered propagating instabilities in structures and materials and has maintained a long-term interest in plastic instabilities and crushing of structures, plasticity, forming problems in manufacturing, localization and ductile failure of metals, the mechanical behavior of composites, etc. He is recognized as a major contributor to these areas. He served as chair of the Executive Committee of the Applied Mechanics Division-ASME, as President of the American Academy of Mechanics (AAM), as chair of the US National Committee of Theoretical and Applied Mechanics, and is Editor of the International Journal of Solids and Structures. His recognitions include the 2009 Warner T. Koiter Medal from the American Society of Mechanical Engineers (ASME), Member of the US National Academy of Engineering, and Fellow of ASME and AAM.