  Functionally graded material (FGM) is a class of advanced materials,
consisting of two (or more) different constituents, that possesses a
continuously varying composition profile. With the advancement of
nanotechnology, applications of FGMs have shifted from their conventional usage
towards sophisticated micro and nanoscale electronics and energy conversion
devices. Therefore, the study of mechanical and vibrational properties of
different FGM nanostructures is crucial in exploring their feasibility for
different applications. In this study, for the first time, we employed
molecular dynamics (MD) simulations to investigate the mechanical and
vibrational properties of radially graded Cu-Ni FGM nanowires (NW).
Distribution of Cu and Ni along the radial direction follows power-law,
exponential and sigmoid functions for FGM NWs under consideration. Our results
demonstrate that, distribution function parameters play an important role in
modulating the mechanical (elastic modulus and ultimate tensile strength) and
vibrational (natural frequency and quality factor) properties of FGM NWs. The
study also suggests that, elastic moduli of FGM NWs can be predicted with
relatively good accuracy using Tamura and Reuss micromechanical models,
regardless of NW diameter. We found that, Euler-Bernoulli beam theory
under-predicts the natural frequencies of FGM NWs, whereas He-Lilley model
closely approximates the MD results. Interestingly, FGM NWs are always found to
exhibit beat vibration because of their asymmetrical cross sections. Finally,
this is the first atomistic scale study of FGMs that directly compares MD
simulations with continuum theories and micromechanical models to understand
the underlying mechanisms that govern the mechanical and vibrational properties
of FGM NWs in nanoscale.
