Molecular Dynamics Simulation of Fracture in Rual
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MOLECULAR DYNAMICS SIMULATION OF FRACTURE IN RUAL
C.S. BECQUART, P.C. CLAPP and J.A. RIFKIN Centerfor MaterialsSimulations,Institute of MaterialsScience, University of Connecticut, Storrs, CT 06269-3136 ABSTRACT High temperature intermetallic compounds show promise for aerospace technology. Unfortunately many of them have the property of being brittle at low temperatures and have therefore to be modified to be used. However among the binary high temperature materials, stoichiometric RuAl has shown some significant room temperature toughness [1]. Computer simulations at the atomistic level have shown to be of significant help in the understanding of many phenomena (phase transformations, etc). In this work, Molecular Dynamics and potentials derived by the Embedded Atom Method (EAM) have been used to study the behavior of a microcrack embedded in a three-dimensional lattice of RuAl. Values of the critical toughness factor (value at which the crack starts propagating) have been established for different orientations of the crack and for different temperatures. Dislocation emission and propagation have been observed in some cases. Parameters such as the unstable stacking energy (which characterizes the resistance to slip) and the surface energy (which characterizes the resistance to cleavage) have also been calculated for this material. A recent theory developped by Rice [2] will be used to interpret the behavior of the crack upon orientation.
Introduction Since the advent of the Griffith criterion [1] which predicts the condition for stability of a crack in a purely brittle material, much research has been done to extend this criterion to ductile and semibrittle materials. A pionneering work by Rice and Thomson [2] in 1974 established the important contribution of dislocation emission and propagation at the crack tip to the understanding of the behavior of a microcrack under load. Since then many models have been proposed to predict the brittle versus ductile behavior. One of the most recent one was proposed recently by Rice [2]. Molecular Dynamics simulations give access to all the parameters needed in this theory and this paper will present the results of simulations performed on crack-embedded arrays of RuAl (a prospective candidate for high-temperature use) and compare them with Rice's predictions.
Conditions of the simulations The simulations were performed on arrays of approximately 8,000 particles with several different orientations. In this array an initial crack was created and a tensile load normal to the crack applied. Orientations are given as a the direction of crack propagation / crack plane pair. For example [001](1-10) means that the crack would normally propagate in the [001] direction (if crack propagation occurs at all) and (1-10) is the crack plane normal. In these two directions there are free surfaces at the array boundary. In the remaining direction there is a repeating boundary. The dimensions of the arrays were on the order of 70 A by 70 A by 20 A, where the shorter direction is the one wit
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