Superelastic Deformation of Adaptive Nano-Composites
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Superelastic Deformation of Adaptive Nano-Composites Alexander L. Roytburd1 and Julia Slutsker Materials Science & Engineering Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899 1 Department of Materials and Nuclear Engineering, University of Maryland, College Park, MD, 20742 ABSTRACT An adaptive composite containing a shape memory alloy as an active component is the subject of the paper. The elastically heterogeneous nano-composite containing ultra-thin layers of a passive material and thin layers of an active material is investigated in this paper. The superelastic modulus of the composite depends on the fraction of the active layer and can be negative if relative thickness of the active layer exceeds some critical value depending on the ratio between the elastic moduli of the layers and the characteristics of transformation. The negative superelastic modulus corresponds to the thermodynamic instability of superelastic deformation and results in stress-strain hysteresis. The relation between the elastic properties of the composite’s components and relative thickness of the layers, which enable to stabilize the superelastic deformation, is obtained. INTRODUCTION A concept of the superelastic polydomain adaptive composite is proposed in the paper. The adaptive composite containing a shape memory alloy as an active component utilizes the unique adaptive properties of shape memory alloys to change their crystalline structure in response to the external stimuli such as temperature or stress. In the adaptive polydomain composite deformation of an active component proceeds through the evolution of a polydomain martensitic microstructure. Since the microstructure evolution in thin constrained layer can be well controlled, the multilayer composite consisting of thin (
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