Microstructure Evolution Across Interfaces of Heterogeneous Metal Systems Under Ultrasonic Impact
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Microstructure Evolution Across Interfaces of Heterogeneous Metal Systems Under Ultrasonic Impact Youhong Li1, Yinon Ashkenazy2, Robert S. Averback3 1 Computational Science and Engineering, University of Illinois at UrbanaChampaign,1304 W. Springfield Av. Urbana, IL 61801, USA. 2 Racah Institute of Physics, Hebrew University of Jerusalem, Israel. 3 Department of Materials Science and Engineering, University of Illinois at UrbanaChampaign, 1304 W. Green St. Urbana, IL 61801 USA. ABSTRACT Large-scale Molecular Dynamics (MD) studies on heterogeneous, model metal systems subjected to intense shock loading by a flyer plate were carried out. Of interest here is the effect of structural defects on interfacial strength under these extreme conditions. The metal target and flyer were essentially single crystals of Cu, but an interface layer was created by varying the mass of the Cu atoms in part of the sample. Interfacial defects in the form of vacancies, and at different concentrations, were introduced into the interfacial region. In addition to microstructural evolution of damage in this system, the shock induced temperature and pressure changes were also analyzed. INTRODUCTION The strength and structural stability of internal interfaces are often the deciding features in determining the lifetimes of engineering materials in service. This is particularly true for nanomaterials, which are normally more sensitive to such changes than are bulk materials [1-2]. In various situations, such as low earth orbit vehicles in space, thin protective coatings are often impacted by bits of space debris, which creates shock waves in the material, and often leads to delamination and fraction of the coating. Similar problems occur in devices attached to explosive devices. We present here results of our initial studies using Molecular Dynamics (MD) simulations to investigate these problems. Although quite a few MD simulations for shock wave and materials interactions were performed in late 80s and early 90s, most of this work employed twodimensional systems and very small three-dimensional systems limited to a few thousands of atoms [3]. In recent years, various reports on simulations describing the dynamics of plastic deformation in metals using MD have been published [4]. It was shown that spall is formed by a process where voids nucleate, grow, and coalesce by dislocation interaction and the formation of shear bands and amorphous regions [5-8]. This work describes the dynamics of spall formation at damaged heterogeneous interfaces.
METHODS In order to control the complexity of the interactions between shock wave and a heterogeneous system and to highlight the important aspects of such interactions, we
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begin our studies with very simple system, namely the Cu-“Au”, in order to create a mass mismatch at the interface. In these systems, however, interfacial stresses are completely removed by a potential for “Au” that is identical to Cu, but with Au’s mass. We adopt the EAM potential for copper developed by Cleri and Rosat
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