Multiscale Analysis of Elastic Properties of Nano-Reinforced Materials Exhibiting Surface Effects. Application for Determination of Effective Shear Modulus

This work concerns a multiscale analysis of nano-reinforced heterogeneous materials. Such materials exhibit surface effects that must be taken into account in the homogenization procedure. In this study, a coherent imperfect interface model was employed to characterize the jumps of mechanical properties through the interface region between the matrix and the nanofillers. As the hypothesis of scale separation was adopted, a generalized self-consistent micromechanical scheme was employed for the determination of the homogenized elastic moduli. An explicit calculation for the determination of effective shear modulus is presented, together with a numerical application illustrating the surface effect. It is shown that the coherent imperfect interface model is capable of exploring the surface effect in nano-reinforced materials, as demonstrated experimentally in the literature.

Neutron star crust in Voigt approximation: general symmetry of the stress–strain tensor and an universal estimate for the effective shear modulus

ABSTRACT I discuss elastic properties of neutron star crust in the framework of static Coulomb solid model when atomic nuclei are treated as non-vibrating point charges; electron screening is neglected. The results are also applicable for solidified white dwarf cores and other materials, which can be modelled as Coulomb solids (dusty plasma, trapped ions, etc.). I demonstrate that the Coulomb part of the stress–strain tensor has additional symmetry: contraction Bijil = 0. It does not depend on the structure (crystalline or amorphous) and composition. I show as a result of this symmetry the effective (Voigt averaged) shear modulus of the polycrystalline or amorphous matter to be equal to −2/15 of the Coulomb (Madelung) energy density at undeformed state. This result is general and exact within the model applied. Since the linear mixing rule and the ion sphere model are used, I can suggest a simple universal estimate for the effective shear modulus: $\sum _Z 0.12\, n_Z Z^{5/3}e^2 /a_\mathrm{e}$. Here summation is taken over ion species, nZ is number density of ions with charge Ze. Finally, ae = (4πne/3)−1/3 is electron sphere radius. Quasi-neutrality condition ne = ∑ZZnZ is assumed.