EM modelling of arbitrary shaped anisotropic dielectric objects using an efficient 3D leapfrog scheme on unstructured meshes.

The standard Yee algorithm is widely used in computational electromagnetics because of its simplicity and divergence free nature. A generalization of the classical Yee scheme to 3D unstructured meshes is adopted, based on the use of a Delaunay primal mesh and its high quality Voronoi dual. This allows the problem of accuracy losses, which are normally associated with the use of the standard Yee scheme and a staircased representation of curved material interfaces, to be circumvented. The 3D dual mesh leapfrog-scheme which is presented has the ability to model both electric and magnetic anisotropic lossy materials. This approach enables the modelling of problems, of current practical interest, involving structured composites and metamaterials.

A micropolar anisotropic constitutive model of cancellous bone from discrete homogenization.

Cosserat models of cancellous bone are constructed, relying on micromechanical approaches in order to investigate microstructure-related scale effects on the macroscopic properties of bone. The derivation of the effective mechanical properties of cancellous bone considered as a cellular solid modeled as two-dimensional lattices of articulated beams is presently investigated. The cell walls of the bone microstructure are modeled as Timoshenko thick beams. The asymptotic homogenization technique is involved to get closed form expressions of the equivalent properties versus the geometrical and mechanical microparameters, accounting for the effects of bending, axial, and transverse shear deformations. Considering lattice microrotations as additional degrees of freedom at both the microscopic and macroscopic scales, an anisotropic micropolar equivalent continuum model is constructed, the effective mechanical properties of which are identified. The effective elastic moduli of various periodic cell structures are computed in situations of low and high effective densities to assess the impact of the transverse shear deformation. The stress distribution in a cracked bone sample is computed based on the effective micropolar model, highlighting the regularizing effect of the Cosserat continuum in comparison to a classical elasticity continuum model.

Micromechanically-based formulation of the cooperative model for the yield behavior of starch-based nano-biocomposites.

The tensile yield stress of plasticized starch filled with montmorillonite has been studied as a function of the temperature and the strain rate and has been compared to the yield behavior of the original matrix. Aggregated/intercalated and exfoliated nano-biocomposites, obtained from different nanofillers, have been produced and tested under uniaxial tension (tensile test). To model the nanocomposite tensile yield stress behavior, a preexisting micro-mechanically based cooperative model, which describes properly the yield of semi-crystalline polymers has been modified. According to our development, the yield behavior of nano-biocomposites is strongly dependant on the clay concentration and exfoliation ratio. Based on the thermodynamics properties, an effective activation volume and effective activation energy are computed through the Takayanagi homogenization model. The predicted results for the yield stress at low strain rates and at different temperatures are in agreement with our experimental results.

Prediction of the mechanical properties of hydroxyapatite/polymethyl methacrylate/carbon nanotubes nanocomposite.

In this work carbon nanotubes (CNTs) were used to increase the strength and toughness of the hydroxyapatite (HA) and consequently to reduce its brittleness. The combination of CNT, HA and polymethyl methacrylate (PMMA) has led to a new composite material, which has mechanical properties superior to those of conventional HA/PMMA for biomedical scaffold in tissue engineering. PMMA is a well known bone cement which is highly compatible with HA and also it can act as a functionalizing/linking material with HA. The mechanical properties of the new nanocomposite were predicted with a self-consistent computational model taking into account the structure morphology and the orientation of the CNTs. CNT reinforced HA composite is shown to be a promising coating material for high-load-bearing metal implants. The development of this new nanocomposite based on HA/PMMA and CNTs, may significantly contribute to the bond strength of the HA/PMMA metal interface and the overall mechanical properties of the HA/PMMA coating.