Modeling and characterization of the mechanical behavior of nano-sized structural elements

Steady technological progresses in all fields of nanoscale technology and probe technology have enabled the synthesis, the assembly, the development, the characterization and the improvement of nanostructured materials. The lack of understanding of their macroscopic behavior is a major roadblock for inserting these materials into engineering applications. Partially due to these rapid advances in nanoscale and nano-structured materials, there has been a resurgence of interest in surface elastic properties such as surface energy, surface stresses, and surface elastic stiffness. Because of the large surface-to-volume ratio in nano-materials, surface elastic properties become more prominent. They have strong influence on the overall thermo-mechanical behavior of the nano-materials. In this paper, an innovative approach combining continuum mechanics and atomistic simulation is conducted to develop a nanomechanics theory for modeling and predicting the macroscopic behavior of nanomaterials. We first develop a framework to incorporate the surface free energy into the continuum mechanics theory. Based on this approach, it is shown that the effective elastic properties of nano-size particles (including nano-wires and nano-films) become size-dependent. Parallel to this methodology, we then introduce a semi-analytical method to calculate the surface elastic properties of groups 10-11 transition metals using the interatomic potentials directly without extensive atomistic simulations. In terms of engineering applications, this approach prove to be a useful tool for multi-scale modeling of heterogeneous materials with nanometer scale microstructures and provide insights on surface properties for several material systems; these will be very useful in many fields including surface science, tribology, fracture mechanics, adhesion science and engineering, and more. This will accelerate the insertion of nano-size structural elements, nano-composite and nanocrystalline materials into engineering applications.