Adjacent Holes Research Articles

Diffusion of gases in PEEKs membranes: molecular dynamics simulations

Results of molecular dynamics (MD) simulations on transport process of small molecules in amorphous cardo poly-ether-ether-ketone membranes, namely PEEK-WC, sulfonated PEEK-WC and nitrated PEEK-WC are discussed. Atomistic simulations techniques have proven to be a useful tool for the understanding of structure–property relationships of materials and in particular MD can be used for detailed descriptions of the complex morphologies and transport mechanisms associated with rigid glassy structures. The diffusion process results from jumps of penetrant molecules between adjacent holes in the polymer matrix. The occurring jump mechanism is characterised and visualised. Constants of diffusion and solubility coefficients have been calculated by the transition state Gusev–Suter Monte Carlo (MC) method.

Proposal of an extendedt−JHamiltonian for high-Tccuprates fromab initiocalculations on embedded clusters

A series of accurate ab initio calculations on Cu_pO-q finite clusters, properly embedded on the Madelung potential of the infinite lattice, have been performed in order to determine the local effective interactions in the CuO_2 planes of La_{2-x}Sr_xCuO_4 compounds. The values of the first-neighbor interactions, magnetic coupling (J_{NN}=125 meV) and hopping integral (t_{NN}=-555 meV), have been confirmed. Important additional effects are evidenced, concerning essentially the second-neighbor hopping integral t_{NNN}=+110meV, the displacement of a singlet toward an adjacent colinear hole, h_{SD}^{abc}=-80 meV, a non-negligible hole-hole repulsion V_{NN}-V_{NNN}=0.8 eV and a strong anisotropic effect of the presence of an adjacent hole on the values of the first-neighbor interactions. The dependence of J_{NN} and t_{NN} on the position of neighbor hole(s) has been rationalized from the two-band model and checked from a series of additional ab initio calculations. An extended t-J model Hamiltonian has been proposed on the basis of these results. It is argued that the here-proposed three-body effects may play a role in the charge/spin separation observed in these compounds, that is, in the formation and dynamic of stripes.

Crosstalk between acoustic sensors in a MEMS array

The sensor array considered is in bare essentials a regular rectangular array of square holes in a slab of single crystalline silicon. The actual sensing of an incident pressure wave is achieved by optical sensing of the acoustically induced vibrations of recessed membranes (plates) within the holes. The present study addresses the crosstalk question by investigating the effect of the spacing between the holes (sensors) on the vibration of the individual membranes. The no crosstalk limit is taken as when adjacent holes are asymptotically very far apart. When they are closer together the amplitude changes because of two primary effects: (1) elastic waves originating at each of the individual holes and stimulating vibrations of the membranes in adjacent holes, and (2) reradiation of sound from one hole and subsequent diffraction into an anjacent hole. Complementary analyses are carried out using a finite element program and the geometrical theory of diffraction. For the array under study the dominant effect results from diffraction through the fluid itself; structure-borne sound has a minor effect.

Stress intensity factors and crack interaction in adjacent holes

In this analytical investigation, stress intensity factors, K, are calculated for oblique part-elliptical through cracks nucleating and growing from an array of collinear holes subjected to remote tension, bending, and pin loading. The finite element method is used with model validation through comparisons to known stress concentration factors solutions. The three-dimensional virtual crack closure technique is used to calculate the new K solutions. This work was motivated by the need to predict fatigue crack growth in transport aircraft fuselage lap-splice skin joints. Fatigue crack growth of adjacent through cracks with oblique crack fronts can now be predicted using the results of this investigation.

Deformations and stresses in pin-loaded tubes: Multiple holes and effects of various loadings

Deformations and stresses have been determined experimentally in a pin-loaded tube configuration comprising two adjacent and identical hole pairs with fitted pins in a cylindrical tube. The tube was loaded in axial tension applied through one or both of the pins; both parallel and crossed (i.e. perpendicular) pin-axis combinations have been studied. The results are presented in non-dimensional form and discussed. Results are also given for two typical pin-tube configurations subjected, in turn, to axial tension, axial compression, bending in the plane containing the axes of the tube and pin, and torsion about the tube axis.

A molecular simulation study on gas diffusion in a dense poly(ether–ether–ketone) membrane

Results of molecular dynamics (MD) simulations on transport and solubility of small molecules in amorphous cardo poly–ether–ether–ketone membranes are discussed. Atomistic simulation techniques have proven to be a useful tool for the understanding of structure–property relationships of materials. Although MD are still not an ideal tool for the quantitative prediction of gas permeation properties, this methodology can be used for a detailed description of the complex morphologies and transport mechanisms associated with rigid glassy structures.The diffusion process results from jumps of penetrant molecules between adjacent holes in the polymer matrix. The free volume and the occurring jump mechanism are characterized and visualized with different methods. Constants of diffusion and solubility coefficients have been calculated by the Transition State Gusev–Suter Monte Carlo method revealing a considerable agreement between simulated and calculated data.

Stress analysis of door and window of a passenger aircraft

AbstractThe stresses around the passenger door, emergency door and window of an aircraft, Airbus A300B, are considered in this paper. By idealising these opening as rectangular holes with rounded corners in an infinite plate subjected to inplane loads and considering the presence of adjacent holes the stresses are determined using the complex variable method along with Schwarz Alternating Method. The results of the analytical solution are found to be in good agreement with those of the finite element analysis using ANSYS 5.0 software within 5%.

Controlled dewetting processes on microstructured surfaces – a new procedure for thin film microstructuring

We describe a new experimental attempt to generate defined ultrathin microstructured polymer films. Microcontact printing of 11-undecanoic acid has been used to modify the wetting properties of bare gold surfaces to prepare poor wettable surface domains downward to 4 μm size. Film formation of polystyrene films thinner than 20 nm was achieved by dip-coating from a solution of polystyrene in chloroform. The nucleation of holes and the dewetting process was completely controlled by the heterogenity of the surface. Large areas with well defined hole patterns were achieved by the controlled dewetting during the dip-coating process. The remaining film showed no indications for dewetting on the bare gold surface. Especially at higher polymer concentrations Rayleigh instabilities within coalescent rims of adjacent holes are shown to influence the film morphology. Some criteria which are relevant for the design of surface film patterns by controlled dewetting are discussed. Low voltage scanning electron microscopy (LVSEM) which is used appears to be an excellent method for the characterisation of ultrathin films and organic layers downward to 5 nm thickness.

Effects of assist gas on the physical characteristics of spatter during laser percussion drilling of NIMONIC 263 alloy

The effects of different assist gases, O 2, Ar, N 2 and compressed air, during laser percussion drilling are investigated with regard to the physical features, i.e., thickness and surface geometry, of the resulting spatter and its bonding strength. Laser drilling was conducted on NIMONIC 263 alloy sheets, 2.6 mm thick, using a fibre-optic delivered 400-W Nd:YAG laser. The work has revealed that the spatter generated with O 2 assist gas is distinctly different from those produced with N 2, Ar and compressed air. The influence of the assist gas type on the mechanism of material ejection/removal is reported. The spatter bonding strength has been found to be associated with the ‘inertness’ of the assist gas employed, in which a progressive increase was observed in the order of O 2, compressed air, and N 2 and Ar. It appears that the spatter bonding strength is dependent on the assist gas type and the workpiece material composition. In addition, it was found that the overlapping of spatter between adjacent holes, in closely spaced array holes, possessed higher bonding strengths. Consequently, the removal of overlapped spatter produced with inert assist gases is difficult to achieve without causing undesired modification to the material surface and hole geometry.

A scanning electron microscopic study of biliary stent materials

Background: Clogging of biliary stents remains an important problem. In vitro studies have shown less sludge formation in Teflon stents. Recently, clinical studies with Teflon stents have produced contradictory results. The aim of this study was to investigate whether the surface properties of the endoprostheses could explain the variation observed in clinical studies. Methods: A total of 9 different types of unused 10F endoprostheses were examined by scanning electron microscopy (SEM): polyethylene Amsterdam-type, polyurethane Amsterdam-type, Teflon Amsterdam-type, Teflon Tannenbaum-type and a Tannenbaum-type stent with a thin stainless steel mesh between inner and outer layers. Results: All polyethylene stents had a relief with tiny lumps. All Teflon stents had multiple shallow pits and ridges along the entire longitudinal axis. Both Tannenbaum-type stents also had multiple particles protruding into the stent lumen with adjacent holes in the wall of the stent. The polyurethane stent had an extremely smooth surface. Conclusion: SEM of Teflon made stents showed a markedly irregular inner surface, which may explain the controversial results of clinical studies. Our results indicate that the inner surface of a new stent should first be evaluated by SEM before clinical trials are initiated. (Gastrointest Endosc 2000;51:19-22.)

Analysis of curved cracks emanating from adjacent holes

This article provides a new method for the comprehensive treatment of cracks of curved trajectory, emanating from adjacent holes under constant amplitude fatigue loading. The theoretical formulations of the newly formed curved crack are based upon the use of a piece-wise subcrack model and the superposition of single dislocation solutions, which reduce the original problem into the solution of singular integral equations in terms of dislocation density functions. The resulting integral equations are then solved using Chebyshev polynomial expansions, yielding the stress intensity factor (SIF). The SIF solutions are used in conjunction with the strain energy release rate criterion to determine the potential incremental fatigue crack growth experienced by a plate containing two adjacent holes. The theoretical predictions are verified with the experimental results of an aluminum 7075 plate containing two arbitrarily oriented adjacent holes subject to constant amplitiude fatigue loading. The results reveal good agreement between the theoretical predictions and the experimental findings.

Elasto-plastic finite-element analysis of the cold expansion of adjacent fastener holes

This investigation is devoted to the modelling and simulation of the residual stress field resulting from the cold expansion of two adjacent fastener holes. In this two-dimensional elasto-plastic analysis, the development and growth of the plastic zone and unloading residual stresses were examined using the finite-element method. Attention was devoted to two related issues. The first is concerned with the effect of the separation distance between the two holes, the mechanical properties of workpiece and the expansion level upon the field variables; and the second with the effect of the order of cold working of the two holes upon the residual stress field. The results reveal the important role played by the geometry of the workpiece and the expansion parameters upon the quality of the treatment, as measured by the mechanically-induced residual stresses. The shortcomings of the two-dimensional analysis are highlighted and compared with the results of a three-dimensional model.

NUMERICAL SIMULATION OF GROUTING BY TWO GROUT ANALYSIS METHODS

本論文はグラウチングに対する二つの解析手法, モンテカルロシミュレーションを利用したフラクチャーネットワーク解析 (MSFN) とリアルタイムインバージョン解析 (RTIA) の妥当性を検証する. MSFNは所定の仕様のグラウチングによる改良効果を予測するもので, コンソリデーションとカーテングラウチングのシミュレーションの結果, 1) 注入圧-注入量関係, 2) ルジオン値の低下, 3) グラウト剤の流出, に関して実測データとある程度の一致をみた. RITAは計測された注入圧-注入量関係をもとにグラウト孔近くの水みちとグラウト剤到達距離を逆解析するもので, コンソリデーショングラウチングに対するシミュレーションを行った.

Effects of Orientation Angles on Film Cooling Over a Flat Plate: Boundary Layer Temperature Distributions and Adiabatic Film Cooling Effectiveness

Presented are experimental results describing the effects of orientation angle of film cooling holes on boundary layer temperature distributions and film cooling effectiveness. Film flow data were obtained from a row of five film cooling holes on a flat test plate. The inclination angle of the hole was fixed at 35 deg and four orientation angles of 0, 30, 60, and 90 deg were investigated. The velocity ratios surveyed were 0.5, 1.0, and 2.0. The boundary layer temperature distributions were measured at three downstream locations using 1μm platinum wire. Detailed adiabatic film cooling effectiveness distributions were measured using thermochromic liquid crystal. Results show that the increased lateral momentum in the case of large orientation angle injection strongly affects boundary layer temperature distributions. Temperature distribution characteristics are, in general, explained in the context of the interactions between injectant and free-stream fluid and between injectants issuing from adjacent holes. The adiabatic film cooling effectiveness distributions are discussed in connection with the boundary layer temperature distributions. Spanwise-averaged effectiveness distributions and space-averaged effectiveness distributions are also presented with respect to the velocity ratios and the orientation angles. [S0889-504X(00)01701-3]

Study of the structure of streamer belts and chains in the solar corona

A comparison is made of polarization brightness distributions of the white-light corona based on the data from Mark III (MLSO) with calculated magnetic configurations in the corona (a potential-field approximation) between adjacent coronal holes (or associated open magnetic tubes) with magnetic fields of single polarity. It is shown that in these coronal regions, which were referred to as ‘chains of streamers’ in earlier papers of these authors, magnetic structures in meridional and azimuthal cross-sections typically have the aspect of helmet streamers. The calculated magnetic field configurations under the helmets of chains of streamers have an even number of systems of arched features closely adjacent to each other (unlike the structure of the streamer belt with a neutral line where their number is odd). The height of the helmet top of chains of streamers remains smaller than that of the source surface but changes along the length of the chain and reaches maximum values at the ends of the chain.

Three-dimensional finite element analysis of cold expansion of adjacent holes

Three-dimensional elasto-plastic finite element analysis was conducted to evaluate the development and growth of the plastic zone and unloading residual stresses resulting from the cold expansion of two adjacent holes. The contact between the mandrel and the hole was modelled using special contact elements. The work examined the effect of the geometry of two adjacent cold-expanded holes upon the resulting three-dimensional residual stress field. Both simultaneous and sequential expansion of the two holes was considered. It was shown that the compressive residual stress varies across the thickness of the specimen and that two-dimensional finite element models are incapable of accurately predicting the residual stresses resulting from the cold expansion process. It was further shown that sequential expansion reduces dramatically the compressive residual stresses. The validity of the developed finite element model was verified with existing experimental results.

Pore geometry in woven fiber structures: 0°/90° plain-weave cloth layup preform

Composite preform fiber architectures range from the very simple to the complex, and the extremes are typified by parallel continuous fibers and complicated three-dimensional woven structures. Subsequent processing of these preforms to produce dense composites may depend critically on the geometry of the interfiber porosity. The goal of this study is to fully characterize the structure of a 0°/90° cloth layup preform using x-ray tomographic microscopy (XTM). This characterization includes the measurement of intercloth channel widths and their variability, the transverse distribution of through-cloth holes, and the distribution of preform porosity. The structure of the intercloth porosity depends critically on the magnitude and direction of the offset between adjacent cloth layers. The structures observed include two-dimensional networks of open pipes linking adjacent holes, arrays of parallel one-dimensional pipes linking holes, and relatively closed channels exhibiting little structure, and these different structures would appear to offer very different resistances to gas flow through the preform. These measurements, and future measurements for different fiber architectures, will yield improved understanding of the role of preform structure on processing.

FEM analysis on elastic-plastic deformation of perforated sheets

The influence of distribution and growth of voids on macroscopic mechanical properties are important issues in the ductile fracture of metals. In the present paper, we consider perforated sheets with regularly distributed holes as a simple model for void containg materials. Elastic-Plastic deformation of perforated sheet, where circular holes are distributed regularly, was analyzed numerically under the plane stress condition by means of finite element method introducing the periodic boundary conditions. It is shown that the deformation behavior depends highly on the distribution and arrangement of holes. This results in anisotropy of yield stresses of perforated sheets, which is related to the stress concentration near the holes. It is also shown that the plastic region in perforated sheets does not develop simply in the direction to adjacent holes.

Crack growth arresting property of a hole and Brinell-type dimple : Goto, M. Miyagawa, H. and Nisitani, H. Fatigue Fract. Eng. Mater. Struct. (1996) 19 (1), 39–49

In rock excavating and mining, blasting a row of circular holes is a common practice. It is often observed that cracks emanating from two adjacent holes tend to avoid each other when closely approached and form a hooked or butterfly-shaped loops. Five crack models were designed in this paper to study the propensity of forming the hook pattern. The five models are to simulate geometric imperfection in the field or laboratory for the two borehole case. Using the T-stress at the crack tip, the incremental crack growth method is adopted to simulate the crack propagation paths. The results showed that: (1) the T-stress values calculated from the first two models are negative, indicating curving (or hooking) cannot occur, (2) the T-stress at the crack tip is positive in the third model, and therefore crack curving (or hooking) may occur, (3) unlike the first three models, the fourth and fifth models are mixed mode I/II crack geometries and the mode II stress intensity factor dictates the crack curving direction, (4) the hook pattern would indeed happen under certain conditions.

Generation of diffraction-free beams for applications in optical microlithography

A new concept based on a Fabry–Pérot interferometer for the generation of nondiffracting Bessel beams is described and proposed for potential applications in microlithography such as the fabrication of small isolated patterns. It was experimentally demonstrated that the depth of focus can be increased by a factor of about 2, and simultaneously the transverse resolution improved by a factor of 1.6, when using this technique to image contact holes. The properties of simultaneous imaging of two contact holes were also investigated. It was shown experimentally that, even in the most critical case (when the first diffraction rings overlap), undesirable interference effects between the adjacent contact holes can be eliminated by means of a phase shifting technique.