H. Lakiss

Ultrafine Grinding of MgTiO3 Based Ceramic Influencing the Material Properties

The effect of grinding MgTiO3 on the particle size and electrical properties was studied. Initially, good dispersion conditions were optimized via rheological characterizations of the aqueous slurry in variant dispersant amounts. Then, 50% MgTiO3 slurry was grinded using balls of different diameter sizes (0.8 and 0.4 mm) for two consecutive cycles. The milled powder was characterized using laser granulometry, BET method, X-ray diffraction and scanning electron microscopy techniques. The crystallite size was calculated using Halder-Wagner methods. The electrical and dielectrical properties were also monitored for different particle size. These results revealed impurities from the zirconium balls, however, without affecting the particle size even if prepared with different grinding operations.

Dynamical properties of random fibrous networks based on generalized continuum mechanics

ABSTRACT The dynamic analysis of random fibrous networks (RFNs) is a novel topic, which has many applications since these networks are very often subjected to dynamical loading conditions such as mechanical vibrations. In order to bypass the complexity of performing dynamic computations at the microscopic scale of RFN, we develop and identify couple-stress and second gradient models as effective continua at the mesoscopic level of windows of analysis. The static mechanical properties which are at the basis of the dynamical analysis are computed thanks to FE simulations performed over windows of analysis subjected to mixed boundary conditions allowing to capture the classical and non-classical effective moduli. The acoustic properties are captured by the dispersion diagrams and phase velocity plots; we analyze the influence on the dynamic properties of the fiber bending length, and the fiber network density. The impact of these parameters is successively assessed for the couple-stress and strain gradient substitution continua. A comparison of the acoustic properties of the two effective media is provided, showing that the couple-stress medium is essentially non-dispersive for the longitudinal mode and dispersive for the shear mode, whereas the strain gradient medium behaves in a dispersive manner for both modes.

Analysis of Nonlinear Wave Propagation in Hyperelastic Network Materials

We analyze the acoustic properties of microstructured repetitive network material undergoing configuration changes leading to geometrical nonlinearities. The effective constitutive law of the homogenized network is evaluated successively as an effective first nonlinear 1D continuum, based on a strain driven incremental scheme written over the reference unit cell, taking into account the changes of the lattice geometry. The dynamical equations of motion are next written, leading to specific dispersion relations. The inviscid Burgers equation is obtained as a specific wave propagation equation for the first order effective continuum when the expression of the energy includes third order contributions, whereas a perturbation method is used to solve the dynamical properties for the effective medium including fourth order terms. This methodology is applied to analyze wave propagation within different microstructures, including the regular and reentrant hexagons, and plain weave textile pattern.