Nanoscale ripples on the compressive fracture surface of a bulk metallic glass with microscale crystals

Some periodic and straight strips with about 60 nm spacing were observed on the compressive fracture surface of Ni₄₂Cu₅Ti₂₀Zr_21.5Al₈Si_3.5 bulk metallic glass (BMG) rods containing minor microscale crystals. The characteristic difference between amorphous matrix and microscale crystals also reveal why periodic corrugations could not be observed on the fracture surface of metal crystals. The dynamic crack instability may be explained by the interaction of the propagating crack and the internal micro-cracks. This kind of periodic morphologies showed in-plane feature, which may be attributed to the non-intense interaction between dynamic crack and micro-crack.     

Size-dependent longitudinal and transverse wave propagation in embedded nanotubes with consideration of surface effects

In this article, the size-dependent free vibration of nanotubes with surface effects is investigated. An efficient shell-core-shell model is introduced to simulate the structure which includes the effect of additional surface elasticity and surface residual stresses. Love??s continuum model for longitudinal wave propagation is employed, which accounts for the effects of lateral contractions on the axial vibration of the structure. On the other hand, the Timoshenko beam model is modified to include the surface effects as well as shear deformations for transverse vibration of nanotubes under axial load. Temperature effects on material properties are also investigated to show the general trend of size dependencies. The generalized differential equation for each case is derived under general external loadings using Hamilton??s principle. The axial vibration is analyzed for different material types and boundary conditions. The linear stiffness modulus is assumed for the elastic bed in both directions with due dependence on the size of the nanotubes.     

Finite element analysis of resonant properties of silicon nanowires with consideration of surface effects

We developed a 3D finite element model taking into account the surface effects which is considered significant in nanostructures and used the model to study the resonant frequencies and Young??s modulus of silicon nanowires on both fixed/fixed and fixed/free boundary conditions with diameters between 50 and 200?nm. We found that Young??s modulus and resonant frequencies significantly decreased with decreasing diameter when the diameter was less than 100?nm for fixed/free boundary condition, while they slightly decreased for fixed/fixed boundary condition. When the diameter is larger than 200?nm, the surface stresses may be neglected.     

Branch cracking and debonding at an end of a rigid stiffener under anti-plane shear stress

A semi-infinite body with a rigid stiffener on a part of the surface under uniform anti-plane shear stress is considered. This is a mixed boundary value problem, and a closed and exact solution is obtained. Stress concentration occurs at the ends of the stiffener; therefore a crack or a debonding may occur at the end of the stiffener. This paper investigates the competition between a crack or a debonding occurrence. It also investigates how far the debonding will extend. The maximum strain energy release rate is used as criterion for detecting a crack and a debonding initiation. Also the strain energy release rate just after crack initiation is investigated and the crack initiation angle is 140.8°. As the applied load, the following three kind of loading conditions are considered; constant loading, increasing loading and small cyclic loading.     

Functionally graded piezoelectric materials for modal transducers for exciting bulk and surface acoustic waves

We show that functionally graded piezoelectric materials can be used to make modal actuators through theoretical analyses of the excitation of extensional motion in an elastic rod and Rayleigh surface waves over an elastic half-plane. The results suggest alternatives with certain advantages for the excitation of bulk and surface acoustic waves.     

Nanoscale ion beam polishing of optical materials

A method of ion beam polishing is described, the special features of which consist in (i) preferential ion beam assisted deposition of a nanometer-thick layer into depressions of the initial relief by oxygen-ion sputtering of a target with a composition identical to that of the processed object; (ii) sputtering of the resulting surface structure by a normally incident low-energy oxygen ion beam to a depth reaching approximately two layers of the deposited material; and (iii) deposition-sputtering cycles repeated with gradually decreasing thickness of the deposited layer until the necessary final state of the surface is attained. Examples of the surface of quartz, sitall (glass ceramic), and BK-7 optical glass processed using the proposed ion beam polishing method show a more than twofold decrease in the height of the relief protrusions as compared to that on the initial surface. On the ion beam processed quartz surface areas with dimensions 2.5×2.5 μm, the maximum roughness height did not exceed 0.8 nm.     

Nanoscale surface engineered living cells with extended substrate spectrum

We report on cell surface engineering of living microorganisms by using Layer-by-Layer (LbL) technology to extend the substrate spectrum. The yeast Arxula adeninivorans LS3 (Arxula) was employed as a model organism and biological template. By using LbL technology, Arxula cells were encapsulated by polyelectrolyte and enzyme layers. The biological activity of the Arxula was retained after the encapsulation process. The polymeric capsule surrounding the Arxula provides a stable interface for surface engineering of living cells. LbL of polyelectrolytes followed by an enzyme layer of lactate oxidase were assembled. The outer enzyme layer provides an additional biological function for Arxula to convert the unfavourable substrate lactate into the favourable substrate pyruvate, thus extending the substrate spectrum of the organism. Moreover, capsule stability and enzyme conjugate stability of the surface engineered Arxula were studied.     

Evaluation of materials to reduce pavement cracking

The materials characterization for a new procedure to reduce pavement cracking was presented. The viscoelastic properties of several mixes were determined to ascertain optimum bitumen content and composition of aggregates.     

Solving anti-plane problems of piezoelectric materials by the Trefftz finite element approach

Applications of the Trefftz finite element method to anti-plane electroelastic problems are presented in this paper. A dual variational functional is constructed and used to derive Trefftz finite element formulation. Special trial functions which satisfy boundary conditions are also used to develop a special purpose element with local defects. The performance of the proposed element model is assessed by an example and comparison is made with results obtained by other approaches. The Trefftz finite element approach is demonstrated to be ideally suited for the analysis of the anti-plane problem.The work was performed under the auspices of an Australian Professorial Fellowship Program with grant number DP0209487 and 21st Century Education Promotion Key project from Tianjin University.     

A model for predicting grain boundary cracking in polycrystalline viscoplastic materials including scale effects

A model is developed herein for predicting the mechanical response of inelastic crystalline solids. Particular emphasis is given to the development of microstructural damage along grain boundaries, and the interaction of this damage with intragranular inelasticity caused by dislocation dissipation mechanisms. The model is developed within the concepts of continuum mechanics, with special emphasis on the development of internal boundaries in the continuum by utilizing a cohesive zone model based on fracture mechanics. In addition, the crystalline grains are assumed to be characterized by nonlinear viscoplastic mechanical material behavior in order to account for dislocation generation and migration. Due to the nonlinearities introduced by the crack growth and viscoplastic constitution, a numerical algorithm is utilized to solve representative problems. Implementation of the model to a finite element computational algorithm is therefore briefly described. Finally, sample calculations are presented for a polycrystalline titanium alloy with particular focus on effects of scale on the predicted response. This revised version was published online in July 2006 with corrections to the Cover Date.     

Nanoscale surface photovoltage of organic semiconductors with two pass Kelvin probe microscopy

Kelvin probe microscopy implemented with controlled sample illumination is used to study nanoscale surface photovoltage effects. With this objective a two trace method, where each scanning line is measured with and without external illumination, is proposed. This methodology allows a direct comparison of the contact potential images acquired in darkness and under illumination and, therefore, the surface photovoltage is simply inferred. Combined with an appropriate data analysis, the temporal and spatial evolution of reversible and irreversible photo-induced processes can be obtained. The potential and versatility of this technique is applied to MEH-PPV thin films. Photo-physical phenomena such as the mesoscale polymer electronic light-induced response as well as the local nanoscale electro-optical properties are studied.     

Nanoscale fluid transport: size and rate effects

The transport behavior of water molecules inside a model carbon nanotube is investigated by using nonequilibrium molecular dynamcis (NMED) simulations. The shearing stress between the nanotube wall and the water molecules is identified as a key factor in determining the nanofluidic properties. Due to the effect of nanoscale confinement, the effective shearing stress is not only size sensitive but also strongly dependent on the fluid flow rate. Consequently, the nominal viscosity of the confined water decreases rapidly as the tube radius is reduced or when a faster flow rate is maintained. An infiltration experiment on a nanoporous carbon is performed to qualitatively validate these findings.     

Simulation of capillary shrinkage cracking in cement-like materials

In drying suspensions, water loss leads to a capillary pressure build-up in the liquid phase. This effect may also be observed in fresh cement-based materials subjected to evaporation at an open surface. If under decreasing water content the near-surface solid particles are no longer covered by a plane water film, menisci develop along with an associated build-up of negative capillary pressure, resulting in shrinkage and possibly in cracking. A 2D model for simulating the described physical process is presented. For arranging the particles in the 2D specimen a stochastic–heuristic algorithm is used. Subsequently, the course of the water front between the particles is calculated by assuming a constant curvature of the water surface. Particle mobility is taken into account by adopting interparticle forces and performing equilibrium iterations. The model allows one to study the influences of the particle size distribution as well as of the properties of the liquid phase on the capillary pressure build-up and on the cracking risk.     

Nanoscale effects in discrete-pulse transformation of energy

The physical principles of the discrete-pulse transformation of energy in fluid disperse heterogeneous systems have been investigated. A classification of the working elements and physical processes realizing the temporal and linear nanoscale effects is given. Examples of physicochemical nanoprocesses have been considered.__________Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 78, No. 1, pp. 15–22, January–February, 2005.     

Transient response of a surface crack subjected to dynamic anti-plane concentrated loadings

In this study, the transient response of a surface crack in an elastic solid subjected to dynamic anti-plane concentrated loadings is investigated. The angles of the surface crack and the half-plane are 60° and 90°. In analyzing this problem, an infinite number of diffracted and reflected waves generated by the crack tip and edge boundaries must be taken into account and it will make the analysis extremely difficult. The solutions are determined by superposition of the proposed fundamental solution in the Laplace transform domain and by using the method of image. The fundamental solution to be used is the problem for applying exponentially distributed traction on the crack faces. The exact transient solutions of dynamic stress intensity factor are obtained and expressed in formulations of series form. The solutions are valid for an infinite length of time and have accounted for the contribution of an infinite number of diffracted waves. The explicit value of the dynamic overshot for the perpendicular surface crack is obtained from the analysis. Numerical results are evaluated which indicate that the dynamic stress intensity factors will oscillate near the correspondent static values after the first three or six waves have passed the crack tip.     

Angle-resolved ellipsometry of light scattering: discrimination of surface and bulk effects in substrates and optical coatings

Angle-resolved ellipsometry of light scattering is an original technique developed at the Fresnel Institute to identify scattering processes in substrates and multilayers. We extend the investigation because numerous experimental results proved that the technique can be of major interest for analysis of microcomponents and their scattering origins. Surface and bulk effects can be separated in most situations, as well as the oblique growth of materials and the presence of first-order contaminants.