Creation Of Voids Research Articles

On the formulation of boundary value problems with the incompressible constituents constraint in finite deformation poroelasticity

This paper considers the finite deformation theory of poroelasticity for the case in which a deformable solid constituent and an interpenetrating liquid constituent are each regarded as incompressible, and the mixing itself is regarded as taking place without the creation of voids. The resulting kinematical constraint gives rise to a Lagrange multiplier pressure in the resulting constitutive description. This pressure therefore enters into the separate momentum balance statements for each individual constituent. The formulation of boundary value problems in this context is well known in continuum mechanics. This paper examines how a systematic elimination of the Lagrange multiplier pressure from the mathematical formulation leads to a stress‐like tensor that generalizes a stress tensor concept introduced by Rajagopal and Wineman in the late 1980s, which they called the saturation stress. Here, by providing a rather complete development, it is discussed how boundary value problems are naturally formulated in terms of a single such stress tensor, how the constitutive theory is framed in terms of this stress tensor, and how certain questions concerning the formulation of boundary conditions are naturally addressed. Connections to the small deformation linear poroelastic (biphasic) theory are also provided. Copyright © 2012 John Wiley & Sons, Ltd.

Successful growth of Cu2Se-free CuGaSe2 by migration-enhanced epitaxy

CuGaSe2 films were grown on GaAs (001) substrates by migration enhanced epitaxy, where Cu + Ga and Se are alternately deposited. The in situ reflection high energy electron diffraction observation during growth revealed that the segregation of Cu2Se on CuGaSe2 can be detected by anomalous diffraction patterns. When the Cu2Se segregation takes place, a distorted pattern appears in both Cu + Ga and Se deposition periods. By optimizing the flux ratios, the anomalous diffraction disappears, and we succeeded in growing high quality CuGaSe2 single crystal layers free from Cu2Se segregation on GaAs (001) substrates. The authors also found that, in the CuGaSe2/GaAs wafers with Cu2Se segregation, a high density of voids is often observed at the substrate surface. These voids disappeared when the Cu2Se-free growth conditions were employed. Ga atoms near the GaAs substrate surface were probably drawn out by excess Cu atoms in the growing layer to form CuGaSe2, leading to the creation of voids with fairly large size.

A comparative study of the stress‐relaxation behavior of untreated and alkali‐treated jute fibers

AbstractIn this study, we examined the effect of alkali treatment and its variables, namely, the time (2, 4, 6, or 8 h) and the concentration of alkali (1, 5, or 17.5% w/w), on the linear density, strength, and stress‐relaxation properties of jute fiber. It was demonstrated that this kind of treatment led to the creation of several voids and fiber fibrillation. Properties were measured for the alkali‐treated and dewaxed fibers. The linear density and tenacity of the fibers were reduced at higher alkali concentration and at longer dipping times. The strength increased with treatment with mild alkali and decreased with treatment with the strong alkali. A very low alkali treatment (1%) rendered low relaxation. At a 5% alkali concentration, interfibrillar matrix softening also played an important role and was prominent in the stress‐relaxation behavior. The stress‐relaxation value was much higher in the fibers treated with 17.5% NaOH compared to the dewaxed fibers; this was probably due to a loss in the fibrillar arrangement. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Microstructure of damage in thermally activated fracture of Lennard-Jones systems

We investigate the effect of thermal fluctuations on the critical stress and the microstructure of damage preceding macroscopic fracture of Lennard-Jones solids under a constant external load. Based on molecular dynamics simulations of notched specimens at finite temperatures, we show that the crystalline structure gets distorted ahead of the crack in the secondary creep regime. The damage profile characterizing the spatial distribution of lattice distortions is well described by an exponential form. The characteristic length of the exponential form provides the scale of damage, which is found to be an increasing function of the temperature: At low temperatures, damage is strongly localized to the crack tip, while at high temperatures, damage extends to a broader range, leading to more efficient relaxation of overloads. As a consequence, the stress intensity factor decreases with increasing temperature. The final macroscopic failure of the system occurs suddenly and is initiated by the creation of vacancies and voids. The creep strength exhibits inverse square root scaling with the notch size corrected by the extension of the process zone.

Corrosion of pure aluminium and aluminium alloy: a comparative study using a slow positron beam

Corrosion-related defects in pure Al and AA 2037 Al alloy have been investigated by positron beam-based Doppler broadening energy spectroscopy. Defect profiles have been analyzed by measuring the S parameter as a function of incident positron energy up to 30 keV. When pure Al samples are immersed in 1M NaOH for various times, a significant increase in the S parameter near the surface is observed. This implies that the corrosion process involves the creation of defects and nanometer voids. In contrast, a significant decrease in the S parameter is observed after the corrosion of water-quenched Al alloy by the same method, which is interpreted as being a result of Cu enrichment near the metal-oxide interface layer.

Drainage ratio impact on void creation in gold interconnect

This articles details investigation into metal voiding observed on electroplated gold interconnect during high temperature wafer-scale bake. The test structures and methodology to measure this effect are discussed in detail. Various factors affecting a metal voiding phenomenon were examined and measured. A drainage ratio is defined to quantify the effects of test structure layout proportions on gold void formation. Different metal formulations were also investigated to better comprehend the influence of metal composition on gold void formation. Furthermore the effect of temperature on void formation was studied and an activation energy of 2.0 eV was estimated for this phenomena. Several methods are proposed to minimize any reliability impact from this phenomenon.

Vertical Landscraping, a Big Regionalism for Dubai

Dubai's ecologic and economic complications are exacerbated by six years of accelerated expansion, a fixed top-down approach to urbanism and the construction of iconic single-phase mega-projects. With recent construction delays, project cancellations and growing landscape issues, Dubai's tower typologies have been unresponsive to changing environmental, socio-cultural and economic patterns (BBC, 2009; Gillet, 2009; Lewis, 2009). In this essay, a theory of "Big Regionalism" guides an argument for an economically and ecologically linked tower typology called the Condenser. This phased "box-to-tower" typology is part of a greater Landscape Urbanist strategy called Vertical Landscraping. Within this strategy, the Condenser's role is to densify the city, facilitating the creation of ecologic voids that order the urban region. Delineating "Big Regional" principles, the Condenser provides a time-based, global-local urban growth approach that weaves Bigness into a series of urban-regional, economic and ecological relationships, builds upon the environmental performance of the city's regional architecture and planning, promotes a continuity of Dubai's urban history, and responds to its landscape issues while condensing development. These speculations permit consideration of the overlooked opportunities embedded within Dubai's mega-projects and their long-term impact on the urban morphology.

Simulation and verification of void transfer patterning (VTP) technique for nm-scale features

This paper investigates simulation of a patterning technique for defining sub-lithographic features. The technique studied involves intentional creation of voids using a conformal chemical vapor deposition (CVD) followed by controlled etch-back to form nanoscale pores. This method provides features that are independent of lithographically defined parent holes and exhibit lower critical dimension (CD) variations. It offers efficient low thermal budget and backend process compatible integration scheme that requires just one additional mask level. The void diameter obtained in this work is 74 nm i.e. ∼10× reduction from lithographically defined hole of 714 nm using i-line lithography. Critical parameters affecting the void formation and the final pore size have been identified and modeled. Simulation of the void transfer process has been investigated using plasma etch module of ‘Elite’ by Silvaco that employs 2-D Monte Carlo ion transport modeling. The results of this investigation show that the geometrical design parameters can be coupled with the plasma process simulations to develop an efficient module for the void transfer process.

Kyphoplasty

The advent of the use of kyphoplasty in 1998 was the result of the expected evolution of materials and methods related to the successful introduction of vertebroplasty as a valid treatment of painful vertebral compression fractures. Kyphoplasty introduced a method of creating bilateral bone voids and in many cases elevation (reduction) of depressed end plates with variable degrees of height restoration. This was achieved by using bilateral balloon bone tamps capable of pressures significantly higher than conventional angioplasty balloons. This allows creation of bilateral bone voids, resulting in the ability to apply a much thicker cement mixture. This is felt to be the reason for fewer cement-related complications compared with vertebroplasty including extravasation and embolization. Although the procedural cost presently is higher for kyphoplasty, this is expected to decrease as patents expire and industry competition increases. Kyphoplasty indications include all those of vertebroplasty plus additional ones either contraindicated or not recommended for treatment with vertebroplasty. Kyphoplasty achieves the same degree of pain relief as vertebroplasty but may offer additional benefits of fewer complications, more indications, better biopsy specimens, and potential for height restoration of compression fractures of the spine. Further studies regarding potential benefits are warranted to assess any added value of kyphoplasty compared with vertebroplasty.

A dielectric study of hydrolytic ageing and the effects of periodic freezing in carbon fibre reinforced plastic jointed structures

The effect of water on the dielectric properties of adhesively bonded carbon fibre reinforced plastic [CFRP/AF 163-2K] structures aged at 75 °C for 162 weeks in deionised water is reported. Joints were exposed at regular intervals to cryogenic temperatures to explore the effect of periodic freezing of water on the ageing of these joints. In addition to dielectric measurements, gravimetric and mechanical analysis was carried out. The absorption, desorption and then re-absorption behaviour of the joints was studied. The adhesive and adherend layers were found to adsorb significant amounts of water. Initially, the majority of water uptake occurs in the CFRP layers, with the adhesive taking much longer to reach high levels of water content. Initial water uptake was greatest in the cryogenically frozen samples; however, over time the greater leaching and desorption suffered by frozen joints resulted in a drop in weight relative to non-frozen samples. High dielectric permittivities observed at very low frequencies after the initial exposure to moisture indicated the presence of microvoids in the frozen joint samples. Time domain data as well as mechanical testing show the development of defects and loss of strength during water ingress. Desorption and further re-absorption of samples indicated that significant differences exist between non-frozen and frozen joints. During re-absorption, frozen samples were found to absorb more water than their non-frozen counterparts. The irreversible creation of micro-cracks and voids ensures that re-absorption produced much greater weight, thickness and dielectric increases, compared with the original adsorption cycle.

Development of CAD-to-MCNP Model Conversion System and Its Application to ITER

We developed a conversion system from three-dimensional computer-aided design (CAD) drawing data to MCNP geometry input data. This system consists of programs of “void creation” and “conversion into MCNP input data.” By using this system, it is possible to convert large and complicated CAD drawing data such as a fusion reactor into MCNP geometry input data. We applied this system to ITER CAD drawing data and created MCNP input data for ITER nuclear analysis. We calculated the neutron flux and nuclear heating using this input data. The calculation results agreed well with those by the other parties participating in this ITER research and development.

Influence of alkali treatment on creep properties and crystallinity of jute fibres

In this work, the effect of the alkali-treatment and its variables viz., time and concentration of alkali, on the creep properties of jute fibre were studied. It was demonstrated that this kind of treatment leads to several changes in fine structure, such as voids creation and fibre fibrillation. The creep behaviour was measured for the alkali treated as well as the dewaxed fibres. Creep value was much higher in the 17.5% NaOH treated fibres compared to the dewaxed fibres. In the 8 hrs treated fibres, the creep was slightly more than the 20 mins treated fibres. XRD study revealed that experimental alkali treatment conditions resulted in closer packing of cellulose chains or rather increased crystallinity. Hence closer arrangement of the molecular chains (higher crystallinity) will reduce the creep extension, as expected.

Bonding state evaluation of tunnel shotcrete applied onto hard rocks using the impact-echo method

Shotcrete is an important primary support for tunnelling in rock. The bonding state of shotcrete on excavated rock surfaces is a core issue in the safe construction and maintenance of tunnels. Although shotcrete may be applied well initially onto excavated rock surfaces, it is affected by blasting, rock deformation, and shrinkage and can debond from the excavated surface, causing problems such as corrosion, buckling, fracturing and the creation of internal voids. This study suggests an effective non-destructive evaluation method of the tunnel shotcrete bonding state applied onto hard rocks using the impact-echo (IE) method. Various bonding conditions (i.e., fully bonded, debonded, and void) were simulated using numerical and experimental models. The signals obtained from the numerical and experimental IE tests were analyzed at the time domain, frequency domain, and time–frequency domain (i.e., the short-time Fourier transform). Both the numerical and experimental results suggest that the bonding state of shotcrete can be evaluated through changes in the resonance frequency and geometric damping ratio in a frequency domain analysis, and through changes in the contour shape and correlation coefficient in a time–frequency analysis. Limited field tests were also performed for practical applications.

Sorption irreversibility of 1,4‐dichlorobenzene in two natural organic matter–rich geosorbents

Hysteresis, a frequently observed phenomenon in sorption studies, is inconsistent with the key assumption of sorption reversibility in most fate and bioavailability models. Therefore, a study of the underlying causes of hysteresis is essential. Carbon-radiolabeled 1,4-dichlorobenzene (DCB) isotope tracer exchange was carried out at select points along the isotherms of DCB in a brown coal and a peat soil, holding total DCB concentration constant. Tracer exchange was performed both in the forward (sorption) and reverse (desorption) directions at the bulk sorption points and in the desorption direction at the corresponding bulk desorption points. Bulk DCB isotherms showed concentration-dependent hysteresis. However, tracer reequilibration in all cases was consistent with free exchange between sorbed and aqueous-phase molecules. These results rule out common experimental artifacts and demonstrate that sorption of bulk DCB is truly hysteretic (i.e., irreversible). The differences in rates between bulk and tracer sorption and desorption are consistent with the coupling of bulk DCB diffusion to other processes that retard equilibration, which we assign to matrix swelling or shrinking. Hysteresis is attributed to matrix deformation--specifically, to inelastic expansion and creation of voids accommodating sorbate molecules in the matrix, which leads to enhanced affinity in the desorption step. Comparing the results to previous results for naphthalene in the coal, we find that irreversible effects are similar for DCB and naphthalene in the coal but differ for DCB between the two sorbents. An explanation based on the different physical properties of these sorbents is provided. Solid-phase extraction of equilibrated DCB with Tenax revealed a highly desorption-resistant fraction. While too small to account for the observed hysteresis, this fraction may represent molecules that become trapped as the matrix collapses and simultaneously stiffens during abrupt desorption.

Diffusion anisotropy and void development under cascade irradiation

Cascade irradiation of metals gives rise to swelling as a result of the creation of voids and the evolution of the void ensemble. Under suitable circumstances, the originally disordered void distribution transforms into to a void lattice. As demonstrated previously, the understanding of the evolution and the unique features of the void ensemble requires a difference in the anisotropy of the diffusion (DAD) of vacancies and self-interstitial atoms (SIAs), which is achieved by one-dimensional diffusion of the SIAs. On the other hand, void swelling has been successfully modeled in terms of three-dimensional diffusion of both vacancies and SIAs. In the present paper it is shown that these seemingly contradicting interpretations and all related observations can be quantitatively reconciled by a small DAD created by only ∼1% of SIAs diffusing one-dimensionally. It is also demonstrated that at the initial stage of void-lattice formation, ordering occurs mainly on close-packed crystal planes, which is in contrast to the naive expectation that one-dimensional diffusion of SIAs should result in a void ordering along close-packed directions. Finally it is found that, in the case of a small DAD, voids annihilate via stochastic shrinkage much faster than by coalescence. This falsifies the argument in the literature that one-dimensional diffusion of SIAs would necessarily lead to the coalescence of voids and destabilization of the void lattice.

High lateral strain ratio in jointed rock masses

Rock masses encountered in the field are jointed and highly anisotropic. An important manifestation of this characteristic of rock masses is that the blocks, when slipping, separate and create voids in the mass resulting in high lateral strain even under low axial stress. It has been shown in this study that the ratio of lateral to axial strain may be very high, especially, if the joints are critically oriented. The assumption of isotropic linearly elastic material is not applicable in such situations. This observation is based on the outcome of an extensive laboratory testing programme, in which a large number of specimens of a jointed rock mass with various joint configurations were tested under uniaxial loading conditions. The trends of experimental results for both lateral strain ratio and rock mass strength have also been verified through distinct element modelling. The reason for high lateral strains has been attributed to the creation of voids and also to the fact that permanent deformations due to slip commence along rock joints right from the start of loading process. A simple mechanistic model has also been suggested to explain the high values of lateral strain for rough and dilatant rock joints. The lateral strains in such situations are important in the design of rock bolts. An example from a recently completed hydroelectric project has also been discussed where high lateral strain was found to be responsible for excessive wall closure and failure of rock bolts.

Nanoscale in situ investigation of ultrathin silicon oxide thermal decomposition by hightemperature scanning tunneling microscopy

A surface chemical reaction—the thermal decomposition of ultrathin silicon oxide(∼1 nm) by ultrahigh vacuum (UHV) thermal annealing at600–800 °C—is in situ investigated on a nanometer scale by high temperature scanning tunnelingmicroscopy (STM). The reaction is initiated by the creation of circular voids which exposethe underlying silicon substrate. Growth kinetics of the voids is scrutinized via time-lapseSTM movies. It is verified that the void perimeters grow linearly with time beforecoalescence and the reaction occurs peripherally around the void perimeters. It is alsodemonstrated that the decomposition rate varies concomitantly with the local environmentnear the reaction fronts. The observed low–high–low rate evolution is qualitativelyexplained. Increased reaction activation energy is found in the final decomposition stageand the origin of the increase is proposed to be due to the local morphological evolution.

Dynamic void content prediction during radial injection in liquid composite molding

Abstract In liquid composite manufacturing, a resin is injected through a dry porous media previously placed in a closed mold. To reach aeronautic requirements or for short injection cycles in the automotive industry, entrapped air in the final part before curing has to remain as low as possible. Air entrapment will depend on the fibrous structure, such as fiber content or tow and preform architecture, and on the injection parameters, or more precisely on the fluid pressure and the flow front orientation with respect to the fibrous direction. Void content prediction during unidirectional flow in liquid composite molding processes was presented in a previous article [Gourichon B, Binetruy C, Krawczak P. A new numerical procedure to predict dynamic void content in liquid composite molding. Composites Part A 2006;37(11):1961–9]. In that article, it was shown that microvoids creation, evolution and elimination could be numerically predicted. Good agreement was obtained with experimental measurements of entrapped air volume for 1D flow. Usually, during injection of real parts, flow orientation is not constant, according to the part shape or to the injection scheme employed. The aim of this paper is to evaluate the importance of fiber orientation with respect to the flow front direction by taking as a reference a radial flow where any flow direction can be studied. A bidirectional model was thus developed based on the comparison of the direction of the flow front to the fiber orientation during radial injection by defining an entrapment angle. An experimental analysis of radial flow is conducted in order to analyze the voids creation process regarding fiber orientation by comparing experimental and numerical fluid pressure profiles during injection. Good agreement between numerical and experimental pressure profiles were obtained, thus validating the developed numerical code. However, the change in pressure level due to the presence of microvoids is not significant. In our case, pressure is thus not a reliable parameter to testify for microvoids creation.

Percutaneous vertebral augmentation: an elevation in adjacent-level fracture risk in kyphoplasty as compared with vertebroplasty

Background context Osteoporotic vertebral compression fractures (VCFs) are being increasingly treated with minimally invasive bone augmentation techniques such as kyphoplasty and vertebroplasty. Both are reported to be an effective means of pain relief; however, there may be an increased risk of developing subsequent VCFs after such procedures. Purpose The purpose of this study was to compare the effectiveness and complication profile of kyphoplasty and vertebroplasty in a single patient series. Study design/setting A clinical series of 36 patients with VCFs treated by vertebral augmentation procedures was retrospectively analyzed for surgical approach, volume of cement injected, cement extravasation (symptomatic and asymptomatic), the occurrence of subsequent adjacent level fracture, and pain relief. Patient sample Thirty-six patients with 46 VCFs underwent either kyphoplasty or vertebroplasty after failing conservative therapy. The mean patient age was not significantly different between the kyphoplasty group (70; range, 46–83) and vertebroplasty group (72; range, 38–90) (p=.438). Outcome measures Outcomes were assessed by using self-report measures (a comparative pain rating scale) and physiologic measures (pre- and postoperative radiographs). Methods Thirty-six patients with VCFs underwent 46 augmentation procedures (17 patients had 20 fractures treated via kyphoplasty, and 19 patients had 26 fractures treated via vertebroplasty). Seventeen patients in this series underwent kyphoplasty using standard techniques involving bone void creation with balloon tamps, followed by cement injection. Nineteen patients underwent a percutaneous vertebroplasty procedure using a novel cannulated, fenestrated bone tap developed to direct cement anteriorly into the vertebral body to avoid backflow of cement onto neural elements. Results Pain improvement was seen in >90% of patients in both groups. Mean cement injection per vertebral body was 4.65 mL and 3.78 mL for the kyphoplasty and vertebroplasty groups, respectively (p=.014). Ninety-five percent of the kyphoplasty procedures were performed bilaterally, whereas only 19% of the vertebroplasty procedures required bilateral augmentation (p<.001). There was no cement extravasation resulting in radiculopathy, or myelopathy in either group. Asymptomatic cement extravasation was seen in 5 of 46 (11%) of the total series (3/20 [15%] and 2/26 [7.7%] of kyphoplasty and vertebroplasty, respectively) (p=.696). Within a 3-month period, there were 5 new adjacent level fractures seen in 3 patients who underwent a kyphoplasty procedure (5/20 [25%]) and none in the vertebroplasty group (p<.05). Conclusions Vertebroplasty appears to offer a comparable rate of postoperative pain relief as kyphoplasty while using less bone cement more often via a unilateral approach and without the attendant risk of adjacent level fracture.

Hollow TS-1 crystals formed via a dissolution–recrystallization process

Post-synthesis treatment of a calcined TS-1 zeolite with aqueous solutions of tetrapropylammonium hydroxide leads to hollow TS-1 crystals. By contrast to conventional dissolution experiments using NaOH as mineralizing agent, the creation of intra-particle voids also involves a partial recrystallization of the zeolite. Hollow crystals possess the same chemical composition and approximately the same size as those of the original crystals, but the distribution of Ti species certainly differs. The method reported here is particularly attractive in the case of zeolites contaminated with extraframework Ti oxide species: the formation of the hollow structure is accompanied by a reincorporation of Ti in the zeolite framework, which considerably increases the catalytic activity.