Search

One main challenge for prediction of gas permeability in shale is the geometrical complexity at pore scale of shale. Shale structure is highly anisotropic and heterogeneous, which cannot be well described by packing of spheres or bundle of tubes. Besides, there are abundant nanoscale pores in shale so that the Knudsen number of gas flow is high, leading to failure of the conventional Darcy's law. Aiming at these challenges, we have studied the influences from pore-scale anisotropy and heterogeneity of shale microstructures on gas permeability including the high Knudsen number effect (or Klinkenberg effect for Darcy scale). First, a geometry-based method is proposed to quantify the pore-scale anisotropy and heterogeneity of shale. Then we reconstruct three-dimensional shale structures by the random generation-growth algorithm and use the lattice Boltzmann method to predict its permeability. To reveal the high Knudsen number effect, both intrinsic permeability and apparent permeability are evaluated. Our results suggest that the intrinsic permeability increases with the anisotropy of pore geometry in parallel direction to the bed, while decreases in perpendicular direction. The slip factor for Klinkenberg correction also exhibits anisotropy when high Knudsen effect is considered. On the other hand, the heterogeneity of pore distribution may have positive influences on intrinsic permeability for given porosities. [ABSTRACT FROM AUTHOR]

The geometry effect on energy transfer rate in a coupled cylindrical quantum wires system is investigated. The corrected random phase approximation by the zero-temperature static Hubbard correction is employed to calculate dielectric function of the system. The geometry effect on energy transfer rate is studied for statically and dynamically screened electron–electron interaction. Both the linear and nonlinear regimes correspond respectively to weak and strong external field are considered. The calculations show that increasing wire radius increases energy transfer rate in both the static and dynamic screening approximations for electron–electron interactions. Moreover, the same trend is predicted by the calculations for both the linear and nonlinear regimes. [ABSTRACT FROM AUTHOR]

Effect of geometry on the atherosclerosis is a significant issue, so the 3D s-shape and 2D axisymmetric stenosis tube as a blood vessel have been analyzed in this work. This paper has focused on the most important parameters in the LSC uptake, inlet Re number and infiltration velocity in the presence of non-uniform magnetic field. The magnetic field is arising from the thin wire with electric current placed vertically to the arterial blood vessel. According to the results of this study, applying magnetic field can be a treatment for atherosclerosis by reducing LSC along the vessel wall. It is observed that, application of magnetic field leads to production of a vortex in the flow, high strain rate, increment of WSS, and also reduction in LSC. For solving the mass transport equation, Lumen-wall model has been used. Blood flow has been considered laminar and incompressible containing Ferro fluid (blood and 4 vol% Fe 3 O 4 ) under steady state conditions. Numerical solution of governing equations was obtained by using the single-phase model and control volume technique for flow field. [ABSTRACT FROM AUTHOR]

This study presents a Single Channel Method using Urban Exitance Model (UEM-SCM) to retrieve land surface temperature (LST) from satellite data in an urbanized city, and evaluates the geometry effect on land surface temperature retrieval using single channel method and split-window algorithm. The UEM-SCM incorporates the effect of urban geometry and considers both reflection caused by the target pixel and its neighboring pixels. In order to evaluate the geometry effect, the retrieved LSTs with and without geometry effect were studied. Results show that the LSTs without geometry effect are generally higher than the LSTs with geometry effect. The temperature difference occurs because the material emissivity is always lower than the effective emissivity caused by multiple scattering and reflection in urban areas (cavity effect). The LST without geometry effect also cannot fully capture the variability and complexity of urban thermal patterns. The temperature difference between with and without the geometry effect can reach 2 K in built-up areas. A comparison was also conducted between LST retrieved by split-window algorithm with and without geometry effect. Results show that the LST retrieved by split-window algorithm without geometry effect has generally higher values than the one with the geometry effect, e.g. 1.1 K on average and 1.5–2 K in built-up areas. The geometry effect will be removed and mis-deemed as atmospheric effect when the split-window algorithm without geometry effect is applied in urban areas. The split-window algorithm with the geometry effect can be used to distinguish between geometry and atmospheric effect in further study. [ABSTRACT FROM AUTHOR]

The characteristics of break flows of small break loss of coolant accident (SBLOCA) tests in the ATLAS (Advanced thermal–hydraulic Test Loop for Accident Simulation) facility were investigated. For an investigation of the characteristics of break flows for SBLOCA tests, cold leg (CL) pipe break and direct vessel injection (DVI) line break tests were compared with respect to several kinds of viewpoints, e.g., pressurizer (PZR) pressure vs. accumulated break mass; comparison of accumulated break masses; occurrence of choking at the break nozzle; comparison of upstream conditions; and comparison of the discharge coefficient. In the comparison of PZR pressure vs. accumulated break mass, the overall trends were similar between CL pipe and DVI line breaks. In the comparison of accumulated break masses, the accumulated break mass of the CL pipe break was larger than that of the DVI line break for four different break sizes. In the comparison of the occurrence of choking at the break nozzle, it was found that there should be choking at the break nozzle in the CL pipe and DVI line SBLOCA tests. For a comparison of the upstream conditions, upstream fluid temperatures showed effects of downcomer wall temperature in a DVI line break. For a comparison of the C d values, the geometry effect, e.g., the L / D ratio, was discussed, especially regarding the two smallest break tests. [ABSTRACT FROM AUTHOR]

Solder joint integrity has long been recognized as a key issue affecting the reliability of integrated circuit packages. In this study, both experimental and finite element simulation methods were used to characterize the mechanical performance and fracture behavior of micro-scale ball grid array (BGA) structure Cu/Sn–3.0Ag–0.5Cu/Cu solder joints with different standoff heights ( h , varying from 500 to 100 μm) and constant pad diameter ( d , d = 480 μm) and contact angle under shear loading. With decreasing h (or the ratio of h / d ), results show that the stiffness of BGA solder joints clearly increases with decreasing coefficient of stress state and torque. The stress triaxiality reflects the mechanical constraint effect on the mechanical strength of the solder joints and it is dependent on the loading mode and increases dramatically with decreasing h under tensile loading, while the change of h has very limited influence on the stress triaxiality under shear loading. Moreover, when h is decreased, the concentration of stress and plastic strain energy along the interface of solder and pad decreases, and the fracture location of BGA solder joints changes from near the interface to the middle of the solder. Both geometry and microstructure greatly affect the shear behavior of joints, the average shear strength shows a parabolic trend with decreasing standoff height. Furthermore, the brittle fracture of BGA solder joints after long-time isothermal aging was investigated. Results obtained show that, under the same shear force, the stress intensity factors, K I and K II , and the strain energy release rate, G I , at the Sn–3.0Ag–0.5Cu/Cu 6 Sn 5 interface and in the Cu 6 Sn 5 layer obviously decrease with decreasing h, hence brittle fracture is more prone to occur in the joint with a large standoff height. [ABSTRACT FROM AUTHOR]

Adhesion molecules, often thought to be acting by a 'lock and key' mechanism, have been thought to control the adhesion of cells. While there is no doubt that a coating of adhesion molecules such as fibronectin on a surface affects cell adhesion, this paper aims to show that such surface contamination is only one factor in the equation. Starting from the baseline idea that van der Waals force is a ubiquitous attraction between all molecules, and thereby must contribute to cell adhesion, it is clear that effects from geometry, elasticity and surface molecules must all add on to the basic cell attractive force. These effects of geometry, elasticity and surface molecules are analysed. The adhesion force measured between macroscopic polymer spheres was found to be strongest when the surfaces were absolutely smooth and clean, with no projecting protruberances. Values of the measured surface energy were then about 35 mJ m-2, as expected for van der Waals attractions between the non-polar molecules. Surface projections such as abrasion roughness or dust reduced the molecular adhesion substantially. Water cut the measured surface energy to 3.4 mJ m-2. Surface active molecules lowered the adhesion still further to less than 0.3 mJ m-2. These observations do not support the lock and key concept. [ABSTRACT FROM AUTHOR]

The fracture behavior of Neyriz marble is investigated both experimentally and theoretically by using two different test configurations: (1) the center cracked circular disk specimen subjected to mode I loading, and (2) the edge cracked triangular samples under mixed mode loading. The experimental results show that there is a noticeable difference between the values of mode I fracture resistance obtained from these two test configurations. The aim of this paper is to justify this difference by using a modified maximum tangential stress criterion which takes into account the effects of non-singular stress terms ( T -stress, A 3 and B 3 ) in addition to the singular terms. The same criterion is then extended to estimate the mixed mode fracture resistance of triangular specimen from the mode I fracture resistance obtained from the circular specimen. It is also shown that the criterion provides better estimates for the experimental data when uses A 3 in the calculation of the fracture process zone length. [ABSTRACT FROM AUTHOR]

This article presents numerical results of detonation in a two-dimensional curved channel in order to discuss its propagation behavior and the stable propagation limit. We simulated the detonation with various channel widths in two types of the ratios of inner and outer radii (Rout/Rin), which are 1.5 and 2. Two propagation modes, named as marginal and stable modes, were observed. In marginal mode, curved detonation propagates with repetition of decay, re-ignition, and propagation. Its velocity varies from underdriven to overdriven in one cycle. In a stable mode, the detonation propagates steadily while keeping a curved shock front structure and a constant detonation velocity in the circumferential direction. The idea of quasi-steady solution to the numerical results is applied for stable detonation limit. We confirmed that the detonation propagates steadily in the case that a shock radius of the detonation front is larger than the critical value of quasi-steady solution. [ABSTRACT FROM PUBLISHER]

In this paper, the effects of specimen size and geometry on the apparent mode I fracture toughness ( K) of an Iranian white marble (Neyriz) are studied. A number of fracture tests were conducted on center-cracked circular disk (CCCD) specimens with different radii to investigate the size effects on K. The experimental results demonstrate that the apparent fracture toughness increases in bigger specimens. In order to explain the experimental results, the modified maximum tangential stress (MMTS) criterion is used, where higher order terms of the Williams' series expansion are included in the maximum tangential stress criterion. It is shown that the MMTS criterion provides good estimates for the apparent fracture toughness of Neyriz marble, obtained from fracture tests of edge-cracked triangular specimens. It is, therefore, concluded that the proposed criterion is able to account for the size and geometry effects on the fracture resistance of rocks simultaneously. [ABSTRACT FROM AUTHOR]

SUMMARY Modelling failure in geomaterials, concrete or other quasi-brittle materials and proper accounting for size effect, geometry and boundary effects are still pending issues. Regularised failure models are capable of describing size effect on specimens with a specific geometry, but extrapolations to other geometries are rare, mostly because experimental data presenting size effect for different geometries and for the same material are lacking. Three-point bending fracture tests of geometrically similar notched and unnotched specimens are presented. The experimental results are compared with numerical simulations performed with an integral-type non-local model. Comparisons illustrate the shortcomings of this classical formulation, which fails to describe size effect over the investigated range of geometries and sizes. Finally, experimental results are also compared with the universal size effect law. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: Understanding the role of geometry, inertia, and dynamic contact angle on wetting and dewetting of capillary tubes has theoretical and practical aspects alike. The specific and synergistic effects of these factors were studied theoretically using a mathematical model that includes inertial and dynamic contact angle terms. After validating the model for capillaries of uniform cross section, the model was extended to capillaries with sinusoidal modulations of the radius, since in practice, capillaries rarely have uniform cross-sections. The height of the meniscus during wetting and dewetting was significantly affected by the relations between the local slope of the capillary surface and the Young contact angle. Non-dimensional variables were defined using viscous effects and gravity as the scaling parameters. Simulations using the dimensionless model showed that the inertial and dynamic contact angle terms can be neglected for narrow capillaries of uniform cross-section but not for uniform, wide cross-section capillaries. Moreover, nonuniformity in cross-sectional area induced hysteresis, deceleration, blocking, and metastable equilibrium locations. An increase in contact angle further amplified the effect of geometry on wetting and dewetting processes. These results enable characterization and modeling of fluid retention and flow in porous structures that inherently consist of capillaries of varying cross section. [Copyright &y& Elsevier]

Abstract: Characterization of Mode-I fracture toughness of ductile polymeric thin films is nontrivial. Proper specimen preparation and experimental procedures are required to ensure in-plane tensile loading. In this study, a custom-built double-edge notched tensile test fixture was employed to characterize the Mode-I essential work of fracture (EWF) toughness of metallocene linear low-density polyethylene (m-LLDPE) films. Effects of specimen geometry, strain rate and film orientation on the specific essential work of fracture, we, and the specific non-essential work of fracture, wp, were investigated. Results indicate both EWF parameters are independent of the crosshead speed, gauge length (distance between upper and lower clamps) and specimen width within the ranges tested. we is significantly higher for thinner films and for crack propagation perpendicular to the blown film machine direction (MD). The usefulness of EWF for evaluating m-LLDPE fracture toughness is discussed. [Copyright &y& Elsevier]

Abstract: This computational study investigates three-dimensional, finite deformation of four common shapes – rod, disc, cube, and sphere – for fast-response, thermo-sensitive hydrogels. These hydrogels have an inherent advantage in their fast-response to stimuli, making them attractive components for a wide range of applications. Here, two basic hydrogels with varying compositions are considered: semi-interpenetrating-networked and macroporous poly(N-isopropylacrylamide). The predicted equilibrium swelling and deformation kinetics are calibrated and validated with their experimental counterparts. In short, the results suggest that the deformation kinetics of a hydrogel is significantly influenced by its geometry; however, the equilibrium swelling ratio of the hydrogels is found to be independent of their geometries. Within the mathematical framework one can also explore the stress distribution within the hydrogels as well as other related parameters. In addition, the model can be extended to account for other stimuli, such as glucose and alcohol. [Copyright &y& Elsevier]

Abstract: Thermoelectric generators (TEG) convert heat energy to electrical power by means of semiconductor charge carriers serving as working fluid. In this work, a TEG is applied to a parallel microchannel heat sink. The effect of the inlet plenum arrangement on the laminar flow distribution in the channels is considered at a wide range of the pressure drop along the heat sink. The particular focus of this study is geometrical effect of the TEG on the heat transfer characteristics in the micro-heat sink. The hydraulic diameter of the microchannels is 270 μm, and three heat fluxes are applied on the hot surface of the TEG. By considering the maximum temperature limitation for Bi2Te3 material and using the microchannel heat sink for cooling down the TEG system, an optimum pumping power is achieved. The results are in a good agreement with the previous experimental and theoretical studies. [Copyright &y& Elsevier]

Mixed mode fracture experiments were conducted on Harsin marble using two disc-shape samples namely the Brazilian disc (BD) and the semi-circular bend (SCB) specimens. For each specimen, a complete fracture toughness envelope ranging from pure mode I to pure mode II was obtained. The experimental results indicate that the mixed mode fracture toughness depends on the geometry and loading conditions such that for any similar mode mixture, the BD test data were significantly greater than the SCB fracture toughness results. Therefore, the conventional fracture criteria which present a unique mixed mode fracture curve, fail to predict the test results. It is shown that a generalized criterion, which takes into account the effects of geometry and loading conditions, is able to provide individual fracture curves for theses specimens with very good estimates for the test results obtained from both BD and SCB specimens. The BD and SCB specimens can be suggested as appropriate specimens for obtaining typical upper bound and lower bound envelopes for mixed mode fracture toughness of rocks. [ABSTRACT FROM AUTHOR]

Abstract: A method using finite element method (FEM) is proposed to evaluate the geometry effect of indenter tip on indentation behavior of film/substrate system. For the nanoindentation of film/substrate system, the power function relationship is proposed to describe the loading curve of the thin film indentation process due to substrate effect. The exponent of the power function and the maximum indentation load can reflect the geometry effect of indenter and substrate effect. In the forward analysis, FEM is used to simulate the indentation behavior of thin film with different apex angles of numerical conical indenter tip, and maximum indentation load and loading curve exponent are obtained from the numerical loading curves. Meanwhile, the dimensionless equations between the loading curve exponent, the maximum load, elastic properties of film/substrate system and apex angle of indenter are established considering substrate effect. In the reverse analysis, a nanoindentation test was performed on thin film to obtain the maximum indentation load and the loading curve exponent, and then the experimental data is substituted into the dimensionless equations. The elastic modulus of thin film and the real apex angle of indenter can be obtained by solving the dimensionless equations. The results can be helpful to the measurement of the mechanical properties of thin films by means of nanoindentation. [Copyright &y& Elsevier]

Abstract: Natural convection experiments inside a vertical cylindrical cavity were performed for Rayleigh numbers of 1.08×1010–2.11×1013 and for four different geometrical arrangements: both-open (pipe-shape), bottom-closed (cup-shape), top-closed (cap), and both-closed (cavity) cylinders. A copper electroplating system was employed for the measurements of heat transfer rates using analogy concept. The lids used to close top or bottom were adiabatic; i.e. inactive surfaces in the electrodeposition experiments. The bottom-closed cavity showed the highest heat transfer rates and then followed both-closed, both-open, top-closed ones in both laminar and turbulent flows. The results were in satisfactory agreements with the existing correlations developed for similar geometrical configurations and the empirical correlations were derived. The numerical simulations were carried out using the FLUENT 6.2 to explain the measured results. The analysis of the streamline and the local Nusselt number gave explanations for the observation. [ABSTRACT FROM AUTHOR]

Ternary IrO-SbO-SnO anode has shown its superiorities over IrO and many other electrocatalysts for O evolution, in terms of electrochemical stability, activity and cost. The performance of IrO-SbO-SnO anodes is affected by its electrochemical properties and operating conditions. In this paper, the electrochemical stability and activity of the Ti/IrO-SbO-SnO anodes prepared with three different geometries were investigated under different operating conditions. It was found that anodes with large mean curvature have high electrochemical stability. Although increasing temperature results in a decrease in the stability of Ti/IrO-SbO-SnO, the anode with a mean curvature of 200 m still shows acceptable service life even at 70 °C. This tolerance of high temperature was attributed to the thermal expansion difference between the substrate and the coating layer, the redox window for Ir(V)/Ir(IV) conversion, and the redox reversibility of Sb and Sn species in the coating layer. [ABSTRACT FROM AUTHOR]

Effects of solder ball geometry on lap shear creep deformation were investigated using the three-dimensional (3-D) finite element method (FEM). The meridian of the solder ball before creep, calculated using the energy principle, was very close to the circular arc which was assumed for subsequent calculations. As solder with a given volume and pad area was varied in geometry from convex to concave, lap shear strain rates increased by two to three orders of magnitude, implying that the solder geometry effect must be taken into account for accurate assessment of lap shear results. Finally, a simple method which can handle the solder geometry effect is proposed. [ABSTRACT FROM AUTHOR]

Shielded Active Gas Forge Welding is a robust and efficient solid state welding method applicable to offshore and oilfield applications. The mechanical or fracture performance of the welded connection may be influenced by the forge weld shape. In this paper the main focus is on the geometry effect of weld shape and defects on forge weld mechanical performance and fracture behavior. The potential impact of variables on the undercut description is parametrically analyzed by finite element calculation. As for the undercut located in the transition region between weld and base material, our studies show that the outer undercut of more than 0.3 mm has a significant impact on mechanical behaviour of welded pipe. When the undercut is located in the fusion plane, its impact on mechanical performance of welded pipe is negligible. Weld caps are beneficial since they contribute to weakening the driving forces for crack propagation. Even if the effect of undercut is considered, the beneficial contribution of weld cap still exists. [ABSTRACT FROM AUTHOR]

Abstract: The mixed mode I/II fracture resistance of polymethylmethacrylate (PMMA) is studied using four different test samples namely the Brazilian disc (BD), semi-circular bend (SCB), four-point bend (FPB) and diagonally loaded square plate (DLSP) specimens. The noticeable discrepancy observed between the different sets of fracture toughness data reveals the influence of specimen geometry and loading condition on the crack growth behaviour. It is shown that the upper and lower bound mixed mode fracture toughness data obtained from the BD and SCB specimens, respectively are mainly due to the effects of negative T-stress in the BD and positive T-stress in the SCB samples. The FPB and DLSP test data are also close to each other and lie between the BD and SCB test results because the T-stress is nearly zero in both FPB and DLSP specimens. [Copyright &y& Elsevier]

This paper uses both two-dimensional (2D) and three-dimensional (3D) finite element (FE) analyses to examine three cases involving the construction of full-scale test embankments to failure on soft clay deposits. By comparing the calculated fill thickness at failure from 2D and 3D analyses, it is shown that 3D effects are significant for all test fills, despite the dramatically different locations, fill thicknesses, and underlying clay deposits. In addition, the calculated undrained displacement and extent of failure from 3D analysis agree well with those measured in each case. The risk of neglecting 3D effects is highlighted by the analyses, where it is shown that failure to account for 3D effects while interpreting the response of a test embankment can lead to unsatisfactory performance of the actual long embankment. Finally, by comparing FE analysis results with well-known bearing capacity factors, it is shown that test embankments with a base length to width ratio less than 2 are more strongly influenced by 3D effects than spread footings on similar soil profiles. The analyses presented in this paper provide practical insight into some factors that should be taken into account for the design and construction of embankments and test fills on soft clay deposits. [ABSTRACT FROM AUTHOR]

Polyetheretherketone (PEEK)-matrix nanocomposites filled with copper nanowires (Cu NWs) and copper nanoparticles (Cu NPs) were prepared by hot compaction method. The effects of Cu NWs and Cu NPs on the thermal conductivity, dynamic mechanical performance, and tribological property of PEEK-matrix nanocomposites were investigated. Results indicate that Cu NPs and Cu NWs with different geometry exhibit different influences on the crystallization behavior, melting behavior, dynamic mechanical properties, and friction and wear behavior of PEEK matrix. Namely, Compared to Cu NPs, Cu NWs can more efficiently better dissipate heat and transfer stress at PEEK/nanofiller interface. Moreover, the friction and wear behavior of the PEEK-matrix nanocomposites is also related to the geometry of the Cu nanofillers to some extent. This is because Cu NPs can act as roll bearings to reduce friction; and Cu NWs with a high thermal conductivity can prevent softening of PEEK matrix and increase the wear resistance via well dissipating friction heat away from the sliding interface. In one word, the comprehensive properties of PEEK-matrix nanocomposites are closely related to the geometry effect of Cu NPs and Cu NWs, which could be of significance for revealing the relation between the micro morphology and the macro application of inorganic nanofillers. [Display omitted] • The two morphologies of copper nanofillers are well distributed in the PEEK. • Cu NWs are superior in enhancing the thermal conductivity in comparison with Cu NPs. • Cu nanofillers (0.5 vol%) enhance the crystallization performance of neat PEEK. • Cu NWs can better dissipate heat and transfer stress at PEEK/nanofiller interface. • Cu NWs can effectively improve the wear resistance of PEEK matrix. [ABSTRACT FROM AUTHOR]

We experimentally discussed the effects of airflow geometries in an air suction gun on the suction characteristics of running yarn. Geometry parameters focused on were 1) compressed-air inflow angle of nozzle, 2) diverging angle of nozzle, 3) throat diameter of de Laval tube, 4) converging angle of de Laval tube and 5) yarn propulsion tube length. As a result, effects of the geometry parameters on the yarn suction force, the mass flow rate of compressed-air and the yarn suction efficiency, which is defined as the yarn suction force divided by the mass flow rate of compressed-air, were made clear and the optimum geometry of an air suction gun was obtained on the basis of the energy efficiency. In addition, the yarn suction force showed two types of time dependency because of different yarn motion on some experimental conditions. [ABSTRACT FROM AUTHOR]

Monolayers comprised of banana-shaped achiral molecules are modeled taking into account the hard-core repulsive force and electrostatic interaction between constituent molecules and the water surface. The model predicts the achiral-chiral transition of orientational structure along with in-plane nematic ordering during a monolayer compression due to the 2D geometry of monolayers. This model further reveals that in-plane nematic order is established beforehand of the chiral transition since banana-shaped molecules behave as rod-shaped molecules with variable aspect ratio in 2D geometry. It indicates the importance of in-plane nematic order in the achiral-chiral phase transition of monolayers comprised of banana-shaped achiral molecules. [ABSTRACT FROM AUTHOR]

Abstract: A cross-check analysis of the plasma wall interaction in RFX-mod is presented. Different methods to determine the footprint of the interaction are compared. The issue is particularly important for the plasma performances, due to the presence of a quasi-stationary distortion of the plasma surface related to the phase locking of the dynamo modes. We show a good agreement between the different analysis and an important reduction of the phenomenon in the discharges with active feedback control of the magnetic boundary. [Copyright &y& Elsevier]

Abstract: This paper quantifies the effect of geometry (planar or cylindrical) and crack location (internal or edge cracks; weld center or interface cracks) on crack driving force for welded joints, via systematic elastic–creep and elastic–plastic finite element (FE) analyses for welded joints. For engineering estimates of crack driving forces for mismatched welded joints, the equivalent material approach is employed. It is found that the equivalent material concept works very well only for a planar geometry with an internal crack, such as the middle cracked tension specimen. For a planar geometry with an edge crack, it works reasonably well, but tends to provide conservative results for under-matching and for interface cracks. For a cylindrical geometry with an edge crack, the results are similar to those for a planar geometry with an edge crack, but caution should be exercised for over-matching, as non-conservative estimates are possible due to gross-section yielding. For a cylindrical geometry with an internal crack, excessively conservative estimates for under-matching are found, and thus an improved estimation method is desired. [Copyright &y& Elsevier]

Abstract: The challenges in evaluating the fatigue strength of the web-flange weld of corrugated web girders are the complexity of the stress field and uncertainty regarding the appropriate fatigue strength category. In this paper, using finite element analysis and crack propagation analysis, the fatigue strength of this web-flange weld is analytically examined. The main conclusions are that the fatigue strength is negatively affected by the existence of the longitudinal folds of the corrugated web and that it is necessary to have a large bend radius so that the fatigue critical point on the inclined folds are far from the longitudinal folds to eliminate the influence of the longitudinal folds. In addition, simple methods to estimate the predict fatigue life of the web-flange welds of corrugated web girders are proposed. [Copyright &y& Elsevier]

Abstract: The fatigue performance of the web-flange weld of steel girders with trapezoidal corrugated webs was examined experimentally, using large-scale girder specimens, and analytically. The focus was on a region of constant bending moment. Fatigue cracks initiated at many points along the inclined folds, and then propagated perpendicular to the principal stress direction. Propagation of cracks initiating near the end of the inclined folds led to failure. Parametric FEM analyses indicated that the corrugation angle and the bend radius at the fold lines of the corrugations are the parameters that most influence the stress at the web-flange weld toe. [Copyright &y& Elsevier]

This paper describes the influence of some geometric parameters on aerodynamics performance of a low-aspect-ratio turbine blading designed by a novel method developed at the Institute of Engineering Thermophysics, Chinese Academy of Sciences. This is a part of the study on aerodynamics optimization of turbomachinery. It follows the development of the basic ideas in the turbomachinery aerodynamics research project at the institute. The present paper concentrates mainly on the effects of geometry, such as stagger angle, leading and trailing edge thickness, maximum thickness and its location on adiabatic efficiency, total pressure ratio and mass flow rate. The study was performed and assessed for a low-aspect ratio turbine nozzle using 3D steady Reynolds-averaged N.S. solver. Using the knowledge of the flow physics analysis an optimized turbine nozzle was obtained. [ABSTRACT FROM AUTHOR]

A chromium doped amorphous carbon (a-C) film was deposited by an unbalanced magnetron sputtering. A special designed double-V shaped stainless steel model in simulating a plastic injection mold gateway was used as the substrate to investigate the geometric effect on the uniformity of the film. It was found that, on both the side wall and bottom plane of the double-V shaped substrate, the film properties strongly depended on a geometric parameter, geometric aspect ratio, defined as the depth over width of the simulated gateway at the points under measurement. With the increase of the aspect ratio, i.e. approaching to the narrow end and/or closer to the bottom plane of the gateway, the film thickness and hardness decreased and the intensity ratio of the Raman sub-bands D over G increased. With the increase of the aspect ratio, the micro hardness of the a-C film decreased far more significantly on the side wall than that on the bottom plane. With increasing working gas pressure, the film thickness decreased consistently, and the hardness uniformity on both the side wall and bottom plane was improved. When the substrate negative bias voltage was changed from -70 to -100 V, the film uniformity (for both the thickness and hardness) was improved on the bottom plane, but degraded on the side wall. [Copyright &y& Elsevier]

• Helical-structured Ag microcoils can be used as a SERS substrate. • Surface-enhanced Raman scattering (SERS) effect in Ag microcoils is anisotropic. • SERS effect is dominated by geometry of Ag microcoils. • Sharp corners or bends act as hot spots in Ag microcoils. Ag nanostructure-based surface-enhanced Raman scattering (SERS) substrates tend to be oxidized and corroded by sulfides owing to their large specific surface area, resulting in severe deterioration. Contrastingly, micrometer-sized Ag structures are more chemically stable. Nevertheless, no reports exist on the utilization of Ag microstructures as SERS substrates, as they lack hot spots. Herein, for the first time, SERS is observed in helical Ag structures with coil diameters and pitches of the micrometer order. The geometry-dominated anisotropic SERS effect is investigated by controlling the shape of Ag microcoils. A new model is proposed to elucidate the mechanism of hot spot formation in Ag microcoils. The results of this study should aid efforts to develop improved SERS substrates. [ABSTRACT FROM AUTHOR]

• A double-slope method was proposed to calculate the critical distance. • An elastic geometrical feature factor was defined to account for stress concentration. • A stress sensitivity factor was proposed to assess the plasticity effect. • A fatigue life estimation approach was proposed with a good accuracy. This paper proposes a notch fatigue life prediction model to account for the effect of geometry and applied stress. A double-slope method was proposed to calculate the critical distance, which was utilized to determine the damage zone of geometrically complex structures. An elastic geometrical feature factor was defined to characterize the stress concentration. Considering the effect of applied stress on low cycle fatigue (LCF) life, a stress factor was proposed. A fatigue life estimation approach was established by introducing the elastic geometrical feature factor, the stress factor and an improved critical distance method. This model was validated by the experimental results of notched specimens with various geometries and loadings. Compared with the existing models, the proposed model provides a better accuracy. [ABSTRACT FROM AUTHOR]

• The influence of test specimen geometry on made I fracture behavior of HMA mixture. • Effect of specimen thickness on mode I fracture toughness. • Effect of temperature and loading rate on KIc value of HMA mixtures. • Relation between the apparent mode I fracture toughness and critical T-stress. • Predicting the asphalt fracture data with modified maximum tangential strain criterion. Determination of fracture toughness (K Ic) for the asphalt mixture concrete requires employment of suitable testing methods and specimens. Disc-shape specimens are among the favorite test geometries for conducting the fracture toughness experiments on asphalt concrete materials since they can be manufactured easily from those samples obtained by the gyratory compactor machine. Semi-circular bend (SCB) and edge notch disc bend (ENDB) specimens are two suitable and well-known specimens in this regard, and both of them are tested using three-point bend setup. In order to compare the consistency of fracture toughness results obtained from these two specimens, an experimental study is performed herein on a typical asphalt concrete mixture. In the experiments, the thickness of SCB and ENDB specimens and also the loading rate and test temperature are considered as variable. It is found that the K Ic values obtained from both SCB and ENDB testing methods are in good agreement. The corresponding value of K Ic obtained from the SCB specimen being slightly smaller than the data obtained from the ENDB specimen. Using a two term K I + T strain-based fracture model, that the critical normal strain value for both specimens is shown to be nearly the same and constant for both SCB and ENDB specimens. In addition, it is found that the fracture toughness value and load carrying capacity of asphalt mixture increases by increasing the specimen thickness (from 30 to 70 mm) and the loading rate (from 1 to 6 mm/min), and by decreasing the test temperature (from −15 °C to −25 °C). [ABSTRACT FROM AUTHOR]

Previous studies have shown considerable discrepancies in the characteristics of pedestrian flow obtained in different experiments. So far, the origin of these discrepancies is not well understood. Here we test a possible mechanism by studying the possible influence of geometry on pedestrian traffic by controlled experiments in different set-ups. By combining instantaneous and improved local measurements we find strong indications for an influence of curvature on the flow properties comparing local flows and densities for an oval set-up, which includes a straight part, and a circular set-up. In the jamming phase, the most efficient flow appears in the straight passage (curvature K = 0) where the flow is about 20% higher than in the curved parts. We relate this reduction of flow in the curved part to the spatial distribution of pedestrians. Results for the headway distribution indicate that the curvature induces a more homogeneous distribution of pedestrians than the one observed for the straight part. The distribution on the straight part is more heterogeneous which seems to allow a more efficient use of the available space leading to larger flows. [ABSTRACT FROM AUTHOR]

• Experiments were carried out to investigate natural convection thermal characteristics in internally heated pool. • The effects of heating power density, pool height, crust solidification, cooling boundary were studied. • The geometry effect of 2D and 3D were investigated based on large-eddy simulation. The natural convection thermal behavior with high Rayleigh number was important in many industrial situations accompanied by internal heating, strong turbulence and solidification process. Experiments were carried out to investigate natural convection thermal characteristics in internally heated pool. Both water and nitrate were selected as simulant materials. The pool temperature along height, heat flux and crust thickness along polar angle were obtained from experiments. The effects of heating power density, pool height, crust solidification, cooling boundary were investigated. Moreover, the geometry effect of 2D and 3D were investigated based on the CFD simulation. The crust formation resulted in higher heat transfer on top with the largest heat flux ratio of 2.4 in nitrate cases and only 1.9 in water cases, indicating that the relationship without solidification applied in system codes may lead to lower peak heat flux at pool top. The Nu dn increased exponentially and the Nu dn from nitrate tests were higher than those from water tests with larger temperature gap T max - T int. The cooling effectiveness of 3D hemispherical pool was 1.5 times that of 2D slice pool. However, the Nu dn from hemispherical simulation was 24.06% higher than the COPRA relation prediction. The application of two-dimensional results needs consideration of geometry extrapolation for further application. [ABSTRACT FROM AUTHOR]

Stress concentration around nanosized defects such as cavities always leads to plastic deformation and failure of solids. We investigate the effects of depth, size, and shape of a lotus-type nanocavity on onset plasticity of single crystal Al during nanoindentation on a (001) surface using a quasicontinuum method. The results show that the presence of a nanocavity can greatly affect the contact stiffness (Sc) and yield stress (σy) of the matrix during nanoindentation. For a circular cavity, the Sc and σy gradually increase with the cavity depth. A critical depth can be identified, over which the Sc and σy are insensitive to the cavity depth and it is firstly observed that the nucleated dislocations extend into the matrix and form a y-shaped structure. Moreover, the critical depth varies approximately linearly with the indenter size, regarding the same cavity. The Sc almost linearly decreases with the cavity diameter, while the σy is slightly affected. For an ellipsoidal cavity, the Sc and σy increase with the aspect ratio (AR), while they are less affected when the AR is over 1. Our results shed light in the mechanical behavior of metals with cavities and could also be helpful in designing porous materials and structures. [ABSTRACT FROM AUTHOR]