Plastic deformation and residual stresses in amorphous silica pillars under uniaxial loading

We have carried out uniaxial compression of micron-scale amorphous silica pillars. We have measured load–displacement curves and observed the morphology of the pillars after unloading, providing strong evidence for large plastic deformations. Minor cracking is also observed, with a well-defined pattern. We find that the van Mises stress in compression is comparable to the intrinsic tensile strength of silica. Precise analysis of the deformation of the pillars has been carried out by finite element modeling (FEM) using the constitutive equation determined previously (G. Kermouche et al., Acta Materialia, 56 (2008) 3222), which quantitatively takes into account densification, shear flow and strain hardening. The residual stress distribution we predict by FEM matches the observed crack pattern well. Finally the calculated stress fields in pillar compression and cone indentation are compared. We propose an interpretation of the contrasts in terms of confinement.     

Modal method in deep metal-dielectric gratings: the decisive role of hidden modes

The modal method is well adapted for the modeling of deep-groove, high-contrast gratings of short period, possibly involving metal parts. Yet problems remain in the case of the TM polarization in the presence of metal parts in the corrugations: whereas most of the diffraction features are explained by the interplay of an astonishingly small number of true propagating and low-order evanescent modes, the exact solution of the diffraction problem requires the contribution of two types of evanescent modes that are usually overlooked. We investigate the nature and the role of these modes and show that metal gratings can be treated exactly by the modal method.     

Rayleigh wave interaction with,and the extension of,microcracks

Intense Rayleigh waves produced by the impact of high-velocity liquid jets on brittle solids were arranged to interact with well-defined surface flaws of dimensions 50 to 200 μm. The extent of crack growth was monitored as a function of distance from the impact site. It was found that considerable crack growth as well as crack branching occurred for cracks parallel to the incident wavefront and little or no growth for orthogonal cracks. The form of the surface wave was monitored using piezoelectric crystals attached to the surface. The results are discussed in terms of recent fracture mechanics analysis of stress-wave interaction with cracks. The significance of this study to strength degradation of brittle bodies subjected to rain-drop impact is pointed out.     

Epitaxial growth of anatase TiO2 thin films on LaAlO3(100) prepared using pulsed laser deposition

Titanium dioxide thin films were grown on a lattice-matched LaAlO₃(100) surfaces using pulsed laser deposition (PLD) in oxygen atmosphere. The films were characterized using X-ray diffraction (XRD), reflection high-energy electron diffraction (RHEED) and atomic force microscopy (AFM). The crystal structure of all the films was anatase. Preferred oriented films with a c-axis normal to the substrate surface were obtained. RHEED analysis also revealed that the films had the preferential in-plane orientation, demonstrating that anatase films were epitaxially grown on the substrate. The flatness of the films depended on their growth conditions and thickness.     

Thermal parameter components of building envelope

A procedure is presented for analyzing the effective thermal capacitance, the time constant and the thermal delay of buildings into components corresponding to discrete sections of the envelope (i.e. the roof or a whole wall of a specified orientation), to envelope parts of different compositions (i.e. the brickwork and the concrete parts of the envelope), or even to the layers of the exterior multilayer walls. Correlations are also developed, which express the dynamic thermal parameters of buildings in terms of the thickness of exterior wall layers and the surface percentage of envelope parts with different compositions. The effective layer thickness is introduced, the increase of which causes negligible increase in the building thermal capacitance. The developed procedure is based on finite-difference solution of a rigorous set of coupled differential equations describing the dynamic thermal behaviour of buildings. The analysis made quantifies the thermal contribution of every element of the envelope and may improve its thermal behaviour if the related conclusions are taken into consideration in the design of buildings.     

Determination of the Isoelectric Point of Planar Oxide Surfaces by a Particle Adhesion Method

A particle adhesion method for the determination of the isoelectric point (iep) of planar oxide surfaces in aqueous media is described. The experiment consists in measuring the rate of deposition of latex particles as a function of pH. We have measured the iep of fused silica, soda-lime silicate glass and thin films of different metal oxides: tin, aluminum, iridium and tungsten. We find our results in good agreement with data from the literature obtained with other experimental techniques.     

Role of zirconium in nucleation and crystallization of a (SiO2, Al2O3, MgO,ZnO) glass

Journal of Materials Science Letters -     

Kinetic fracture of glass at the nanometer scale

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.