Surface energy effects on the yield strength of nanoporous materials containing nanoscale cylindrical voids

Surfaces and interfaces behave differently from their bulk counterparts especially when the dimensions approach small scales. The recent studies have shown that the surface/interface free energy (surface stress) plays an important role in the effective mechanical properties of solids with nanosized inhomogeneities. In this work, within a micromechanical framework, the effect of surface stress is taken into account to obtain a macroscopic yield function for nanoporous materials containing cylindrical nanovoids. Gurtin-Murdoch model of surface elasticity is incorporated in the generalized self-consistent method to obtain a closed-form expression for the transverse shear modulus of transversely isotropic nanoporous materials. Using the transverse shear modulus of a nanoporous material along with the other effective elastic properties, an energy-type overall yield function for such a nanoporous material is derived. Additionally, performing numerical examples for various loading cases, it is shown that the surface stress has a significant influence on the yield surfaces of the nanoporous material comprised of compressible/incompressible matrices, especially for voids radii less than 10 nm.