Coarse Slip Bands in a Single-Crystalline Aluminum Alloy
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Coarse Slip Bands in a Single-Crystalline Aluminum Alloy Seung-Yong Yang, Xianghong Li and Wei Tong1 Department of Mechanical Engineering, Yale University, New Haven, CT 06520-8284, USA ABSTRACT The effect of crystal orientation on the discontinuous deformation and coarse slip bands in aluminum single crystals has been investigated by finite element simulation. The numerical analysis is based on a rate-dependent crystal plasticity model recently formulated by us with modifications made here that explicitly accounts for the three strain hardening stages and the effect of the interaction of dislocations and alloying elements on setting the hardening rules on the individual slip systems of the aluminum alloy crystal. The dependence of the magnitude of the serrations of tensile stress-strain curves on orientation and its evolution over the three strain hardening stages of Al-0.3%Mg single crystals observed experimentally has been successfully explained in this investigation. INTRODUCTION Plastic deformation in crystals is inherently nonuniform in a microscopic sense. It is common for plastic flow in crystals deformed to finite plastic strains to become localized macroscopically also in the form of a shear band. Such local deformations influence the mechanical properties and lead to poor surface finishing. Various experiments have been carried out on different materials in an attempt to explore the relation between the characteristics of moving deformation band and the experimental conditions and material properties. Propagating deformation bands on specimen surfaces and serrations in the force-displacement curves were observed in steel and aluminum alloys [1, 2]. Estrin and Kubin investigated discontinuous yielding and the propagation of bands of localized plastic strain (the Portevin-Le Chatelier effect). It is accepted that PLC effect is consequence of dynamic strain ageing (DSA) [3]. An increase in the flow stress is caused by the local concentration of solute atoms at temporarily arrested dislocations. A high accuracy whole-field strain measurement technique was developed to directly measure the whole-field localized deformation band patterns of the aluminum sheet metals during uniaxial tensile test [4]. A crystal plasticity model [5] and a dynamic strain-aging model [3] were recently combined to account for the interaction between solute atoms and mobile dislocations on crystal slips in a continuum perspective [6] to explain the formation of the coarse slip bands in aluminum alloys. As a continuation of our constitutive modeling and finite element simulation efforts, the model has been further modified here in terms of two important aspects: namely, the dynamic strain aging effect on each individual slip system and the three strain hardening stages are explicitly incorporated for Al-Mg crystals. A summary of the modified crystal plasticity model is given and numerical simulation results of the serrated plastic flows of single crystals of Al-Mg alloys are discussed and compared with experimental observation [8] in t
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