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Due to various architectural requirements the structures are subjected to large shear stresses and hence the study of shear performance of structural materials is essential. Push-off test is a simple test which can be performed to determine the in-plane shear strength (IPSS) of materials effectively. Geopolymer concrete is a recent construction material which is a suitable alternative cement concretes especially in precast construction due to the non-requirement of cement, the manufacture of which is energy intensive and involves the liberation of CO2 which is a known pollutant and leads to global warming. Concrete has good performance under compressive loads and fails generally due to crack propagation, bridging of these cracks can improve the load carrying capacity of the concrete, addition of fibre is one such method available where the fibres act as crack arrestors. The present experimental investigation has made an effort to understand the influence of fibres over shear strength of Geo Polymer Concrete (GPC) adopting push-off specimen. From the experimental studies it was observed that shear strength and resistance against cracking increased with increase in fibre volume and the effectiveness of GPC reinforced by fibres were higher than that of NSC specimen. [ABSTRACT FROM AUTHOR]

In recent years, the ocean development in our country urgently needs to be accelerated. The construction of artificial coral reefs has become an important development direction. In this paper, experimental studies of simple shear and cyclic simple shear of coral sand are carried out, and the shear properties and particle breakage of coral sand are analyzed. The results show that the coral sand samples show an overall shear failure in the simple shear test, which is more accurate and effective for studying the particle breakage. The shear displacement corresponding to the peak shear stress of the simple shear test is significantly larger than that corresponding to the peak shear stress of the direct shear test. The degree of particle breakage caused by the simple shear test is significantly related to the normal stress level. The particle breakage of coral sand after the cyclic simple shear test obviously increases compared with that of the simple shear test, and universal particle breakage occurs within the whole particle size range. The increasing of the cycle-index under cyclic simple shear test results in continuous compacting of the sample, so that the envelope curve of peak shearing force increases with the accumulated shear displacement. [ABSTRACT FROM AUTHOR]

Asphaltenes are identified as the main cause of crude oil fouling in preheat trains. The understanding of individual trajectory of asphaltenes particles, transportation behavior of the fouling precursors in the domain and the effect of various attractive and/or repulsive forces acting on the asphaltenes particles, which lead to an increase/decrease in the deposition, have been impeded by a shortage of information. In the present work, an attempt has been made to understand the transportation and adhesion behavior of asphaltenes in a heat exchanger tube through Computational Fluid Dynamics approach. A Lagrangian based discrete-phase model has been implemented to understand the hydrodynamics of asphaltenes particles and the effect of various forces on the asphaltenes particles deposition on the heat transfer surfaces. The effect of wall shear stress, surface roughness, and temperature difference on asphaltenes deposition is also reported. From the CFD analysis, the net mass deposition of the asphaltenes particles is minimized with an increase in wall shear stress and surface roughness. The asphaltenes particles in the region where the temperature difference between the bulk and wall is lower at a constant wall temperature are carried forward with the flow and particles with higher temperature difference between the bulk and wall at constant wall temperature are attracted towards the heat transfer surface and deposited on the wall of the heat exchanger tube. [ABSTRACT FROM AUTHOR]

Asphaltenes are identified as the main cause of crude oil fouling in the shell and tube exchangers. There are occasions where the crude oil flows through the shell side of the heat exchangers and some fouling is reported in the shell side of those heat exchangers. Understanding the fouling phenomena in the shell sides requires the knowledge on the irregular fluid flow paths and most susceptible locations of particles deposition. In the present work, an attempt has been made to investigate the effect of shear stress and surface roughness on shell-side asphaltenes deposition in a shell and tube heat exchanger through Computational Fluid Dynamics approach. The hydrodynamics of asphaltenes particles and the effect of various forces on the asphaltenes deposition on the heat transfer surfaces has been investigated through a Lagrangian based discrete-phase model. From the CFD analysis, the net mass deposition of the asphaltenes particles reduces with an increase in surface roughness from 0 to 0.04 mm and wall shear stress from 0 to 0.04 Pa for flow velocity 1 m/s, respectively. The asphaltenes mass deposition becomes constant with further increase in wall shear stress and surface roughness. [ABSTRACT FROM AUTHOR]

Mechanical properties of wood are an important aspect in its processing. Wood is traditionally used for construction and technical purposes. Recently, its importance has grown in energy use. For energy use, it is necessary to modify the wood dimensionally into the desired shape. Therefore, the disintegration is an important operation in wood processing. Its difficulty depends on the properties of the wood. The authors have determined the parameters of energy-using wood species on a water content in the range of 0-50%. The observed properties were wood shear stress. With decreasing water content, the shear stress of wood decreases. The shear strength limit of poplar wood increased from 22.3 MPa to 30.2 MPa. Poplar samples had a higher shear strength than willow samples. [ABSTRACT FROM AUTHOR]

The article presents the results of research on basic parameters of screw-type device designed to lift off, mix, and re-suspend sediments which build up on the bottom of the oil tank. When crude oil is stored in tanks, invariably solid particles and heavy paraffin sediments are deposited. To prevent any sediment from building up on the bottom of the storage tank and to ensure all oil requirements are met, screw-type devices or propellers which are installed at the first horizontal ring of a tank are basically used to lift off, mix, and re-suspend sediments. The rotating blades of the propeller produce collimated turbulent flow in crude oil. The collimated flow is strong enough to mix oil in the tank lifting solids off the floor. 60° rotation of the propeller shaft ensures faster blending. Correct position in the tank creates cross tank and bottom-to-top-to-bottom circular mixing action in oil. The current simulation study has revealed the dependence of sediment resuspension velocity on the distance from the rotating blades at various temperatures and corresponding oil viscosity. The conditions to re-suspend oil tank bottom sediments were defined for the given propeller geometry. It has been proved that the use of screw-type devices is an effective method to lift solids off the floor of the storage tank and ensure required characteristics of tank oil. [ABSTRACT FROM AUTHOR]

Three-dimensional flow of anisotropic plastic layer compressed by parallel rough flat dies is considered. Ideal plastic material model with Hill anisotropic yield criterion modification of Mises isotropic model is used with associated plastic flow rule. General solution of a thin layer plastic flow problem with Prandtl linear velocity and shear stress variation in layer thickness direction is presented. Effects of contact friction force vector module and direction on the layer pressure on the dies and the layer plastic flow are considered. [ABSTRACT FROM AUTHOR]

Most materials in mining and civil engineering construction are not only viscoplastic, but also cohesive frictional. Fresh concrete, fly ash and mining slurries are all granular-frictional-visco-plastic fluids, although solid concrete is normally considered as a cohesive frictional material. Presented here is both a formulation of the pipe and disc flow rates as a function of pressure and pressure gradient and the CFD application to fresh concrete flow in L-Box tests. [ABSTRACT FROM AUTHOR]

Sea-level rise, the increasing number and intensity of storms, oil and groundwater extraction, and coastal land subsidence are putting people and property at risk along Louisiana's coast, with major implications for human safety and economic health of coastal areas. A major goal towards re-establishing a healthy and sustainable coastal ecosystem has been to rebuild Louisiana's disappearing wetlands with fine grained sediments that are dredged or diverted from nearby rivers, channels and lakes to build land in open water areas. A thorough geo-hydrodynamic characterization of the deposited sediments is important in the correct design and a more realistic outcome assessment of the long-term performance measures for ongoing coastal restoration projects. This paper evaluates the effects of salinity and solid particle concentration on the re-suspension characteristics of fine-grained dredged sediments obtained from multiple geographic locations along the Gulf coast. The critical bed-shear-stress for erosion has been evaluated as a function of sedimentation time. The sediment hydrodynamic properties obtained from the laboratory testing were used in a numerical coastal sediment distribution model to aid in evaluating sediment diversions from the Mississippi River into Breton Sound and Barataria Bay. [ABSTRACT FROM AUTHOR]

Determination of the ground anchors ultimate carrying capacity is mostly conducted using various empirical and semi-empirical methods. These procedures are usually successful but highly simplified. Wide range of empirical factors is required, which knowledge is limited only for certain types of soils. One of the major simplifications of these methods is an assumption that the bond stress on the soil--grout interface is mobilized uniformly along the whole fixed length. The result of these methods is mostly only ultimate carrying capacity with no additional information about the displacement required to mobilize this ultimate force. An innovative approach incorporating load transfer functions [2] is therefore proposed. A load transfer function (t-z curve) is the dependence of shear stress mobilized on the surface of a member on the vertical displacement of a corresponding member. The load transfer function is frequently adopted for determination of the load--settlement curve of vertically loaded piles; however its use for ground anchors is rare. The important feature of the proposed approach is the possibility to determine t-z curves as a combination of standard laboratory tests results (e. g. direct shear test) and certain assumption of shear stress mobilization in radial direction [4]. Employing load transfer functions with shear strength envelope determined from series of direct shear tests is demonstrated on the back analysis of prestressing tests carried out on ground anchors fabricated on the construction site "Optimization of the railway section Krasíkov--Česká Třebová". [ABSTRACT FROM AUTHOR]

The article discusses research which assessed the occurrence condition of sediment resuspension in Osaka Bay in Japan by a tsunami caused by the Nankai Trough Earthquake. Topics discussed include the average elevation and flow velocity of a tsunami, non-dimensional bed shear stress and the resuspension of sediment to trigger red tide and water pollution through advection after the tsunami.

A simple mechanical technique for polyethylene (LDPE) film coating by a thin graphene layer is here described. This technique is based on the exfoliation of nanocrystalline graphite (few-layer graphene, FLG) by application of shear-stress, and it leads to a thin graphene layer on the plastic substrate with characteristics of good electrical conductivity and perfect transparency in the visible spectral region. These transparent-conductive films are suitable for ITO replacement in optoelectronics and photovoltaics. [ABSTRACT FROM AUTHOR]

This paper focuses on the evaluation of critical stresses of biomaterials of spherical shape under radial and axial compression employing Hertz contact theory and finite element method. The mechanical properties of UTC tomatoes were determined with a compression test rig for radial and axial compression contacts with metal plate. The maximum contact pressure Pmax was evaluated as 0.063MPa while the maximum shear stress was 0.022MPa. The finite element analysis gave the von mises stresses for axial and radial contacts as 0.001699MPa and 0.012271MPa. The design yield stress was predicted for UTC tomatoes and specified as 0.0012MPa for UTC containers design for transportation. The results of this study will therefore be relevant in the design of transportation for fruits of spherical shape. [ABSTRACT FROM AUTHOR]

Precise determination of elastic and mechanical characteristics of materials is essential in engineering. A simple method for finding both shear strength and shear modulus is proposed, based on modified Iosipescu or Hawong shear test that uses a notched beam probe loaded by forces applied on the median line via four pins. The probe presents two V notches and the effect of geometrical parameters is studied using finite element analysis. For the modified probe, it is found that a notch angle of 110° is preferable in achieving an uniform shear stress state and the deeper the notch - the reduced stress concentrator effect. An advantage of the method is highlighted by the observation that the shear stress field in the studied region of the probe is symmetrical. [ABSTRACT FROM AUTHOR]

The shear stress state in a rectangular plate can be practically obtained only on limited area, because the plate loading is made by concentrated forces and therefore in the vicinity of points of load application, the stress field is strongly disturbed. But at great distance from the force application points, a stress state closed to ideal pure shear is generated. There are two theoretical ways in obtaining the pure shear stress state. The paper presents a proposed method for qualitative evaluation the degree of reaching pure shear state in a rectangular plate and for predicted loading case. The method considers a rectangular plate with two circular holes, loaded. The finite element method analysis of the stress state is made and afterwards compared to the theoretical and experimental (photoelastic) analysis made by the authors in previous papers. A very good agreement of the results is obtained. [ABSTRACT FROM AUTHOR]

Stent implantation alters coronary artery hemodynamic and wall shear stress during cardiac cycles. In this study, three dimensional models were used to analyze the effects of different stent designs and strut thicknesses on the hemodynamic of the artery. The flow was assumed to be pulsatile and stent models were expanded in the artery the same as angioplasty procedure that uses balloon. The data was applied to Fluent-ANSYS package as a UDF MATLAB code. A non-slip condition was applied to the artery walls. The pressure variation in different stents and the wall shear stress distribution were studied. Furthermore, the hemodynamic effects on the flow were investigated for two different thickness values of the same stent design. These results showed that stent implanting is one of the main parameters of pressure drop in the artery. Moreover, the surface of the stent is the location of maximum wall shear stress and the thicker stent strut did not vary this stress much. Our study implies that some design parameters such as thickness affect the hemodynamic factors of blood after stent implantation. Even, stent implanting cause re stenosis in the coronary artery. Using new real models is suggested to investigate the new aspects of stent design and related effects on the hemodynamic of coronary arteries. [ABSTRACT FROM PUBLISHER]

Since the original derivation of human embryonic stem cells (hESC) in 1998, development of efficient culture systems to produce and expand clinical-grade human pluripotent stem cells (hPSC) has been an extremely active research field. Despite the significant progress over the last decade, however, the pathways and signaling cues associated with survival, self-renewal and differentiation of hPSC have not been fully understood yet. Recent development in 2D adherent culture methods has given a wealth of information in hPSC regulations, but limitations in scalability, reproducibility and control in culture parameters and chemical gradients still represent a daunting task to improve the cell expansion rate. Advancing from 2D cultures, cultivating hPSC in 3D culture systems sets a more promising standard for large-scale production and establishing a good manufacturing practice (GMP). Here we will first discuss the potential of 3D culture systems, such as suspended cells in a bioreactor. We will then review mechanisms that help the cells to grow under suspension. Moreover, an advantage of using 3D system, besides scalability, is the enhanced control in culture conditions and reproducibility. In light of these advantages, we will discuss our strategy to minimize unknown variables by setting consistent conditions. Further, we will discuss how these variations may be instituted to optimize the parameters to meet the best condition for survival, self-renewal and differentiation. [ABSTRACT FROM PUBLISHER]

The majority of acute ischemic events are caused by plaque rupture and ensuing thrombosis. Early evaluation and continuous monitoring of a plaque's vulnerability are critical for reducing the risk of catastrophic cardio-cerebral events and mortality and morbidity of atherosclerotic cardiovascular diseases. Many studies have suggested that increased stress in the fibrous cap of atherosclerotic plaque is the key factor triggers a plaque rupture directly. In this study, we investigate the influence of the blood viscosity and bulk modulus of plaque compositions on the stress distribution in the fibrous cap, by simulating the fluid-structure interaction using COMSOL Multiphysics 3.5a. Our results indicated that, when the thickness of fibrous cap, the degree of luminal stenosis, and the other conditions were fixed, an increase of blood viscosity and a decrease of bulk modulus of lipid core caused shear stresses in all directions and normal stress along the inflow direction to increase. It can be inferred that the increase of blood viscosity and decrease of bulk modulus of lipid core may increase the risk of plaque rupture and then may lead to acute CV events. The simulation results agreed with the previous clinical/experimental studies that indicate that blood viscosity was a major risk factor for ischemic heart disease and soft lipid core was more susceptible to plaque rupture. [ABSTRACT FROM PUBLISHER]

Right-circular (ϕ 15 mm x 26 mm) and spherical (ϕ 10mm) projectiles were fired vertically-downward (300-1,000 m/s) into acrylic containers (ϕ 100-190 mm) containing either quartz Eglin sand or solid, amorphous glass beads. A variety of shearing conditions were observed; allowing estimation of stresses along the various shearing surfaces. Under certain conditions a false nose was formed of partially-crushed particles on the front of the projectile and the particulate media sheared along the false nose surface. The included angle of the false nose varies with impact velocity (up to a velocity of 375 m/s) and appears to be a residual artifact of initial impact conditions. An analytical model is presented to explain the false nose formation and stability during the projectile deceleration. Other impact conditions (especially on the front face of the spherical projectiles) resulted in shearing along the surface or surface abrasion. [ABSTRACT FROM AUTHOR]

This article presents a study on the structural responses for a typical location of RoRo passenger ferry using the beam analysis and the three-dimensional FE analysis. The purpose of the study is to examine the structural strength of primary members under the internal loads with vertical acceleration and racking phenomenon. The study concludes that it is important that the guideline using the correction factor might be applied to the scantling of structural design with the simple method.

In order to understand the complex with the intermediate asphalt pavement rubble shear properties, used the method of elastic-plastic finite element to analysis the impact of graded broken stone's modulus, high temperature, Horizontal load, and heavy load on the shear stress of graded gravel layer. Draw out the key factors. To obtain the distribution and the maximum shear stress of Graded gravel layer in composite of asphalt pavement. And to determine the impossibility of shear failure occurrence in Graded gravel layer. [ABSTRACT FROM PUBLISHER]

It is hypothesized that microstreaming might play a role in the sonoporation process, inducing shear stresses which create tension and stretching over the cell membrane and thus lead to its transient permeabilization. In this study, the results of microscopic particle-image velocimetry (PIV) for large bubbles are presented and compared to those obtained using a numerical model. Air bubbles were created in a water solution and then attached to a wall. For each bubble, the microstreaming was measured over a plane located at a distance of 50 µm from the bubble wall. Bubbles were excited using a single element transducer at 28 kHz and 7 kPa. The acoustic microstreaming generated by the air bubble was calculated for the same excitation signal by using a theoretical model based on an analytical solution of the time-averaged Navier-Stokes equation. This approach was also applied to estimate the flow around an encapsulated contrast microbubble using an excitation signal centered at 2.87 MHz with a pressure amplitude of 50 kPa. PIV measurements show that a maximal average velocity of 0.25 mm/s occurs near the bubble resonant size (244 µm diameter bubble). For this bubble, the shear stress is also maximal. Theoretical data are in good qualitative agreement with PIV measurements. Using the contrast agent microbubble model, a maximal flow velocity and shear stress of 4 mm/s and 19 Pa respectively are obtained for a 2.5 µm diameter bubble. The shear stresses are much higher than those produced by normal blood flow (0.5 – 2 Pa). These results suggest that bubbles are capable of exerting significant shear stresses on the cell membrane, affecting likely the sonoporation process. [ABSTRACT FROM PUBLISHER]

From infrared spectra of absorption of pure and magnetized water we discover exceptionally that its infrared absorptions have an irreversible effect during the processes of increasing and decreasing temperature. Then we infer that water is not a fluid conforming to Newtonian laws. Hence we collected the rheology features of pure and magnetized water, and discover that their viscosities decreases with increasing shear stress, speed of shear distortion, intensity of magnetic-field and magnetized time, the speed of shear distortion versus shear stress are some straight lines without passaging the origin of coordinate, their obliquity rates increase with increasing magnetized time and intensity of magnetic-field. Hence we affirm that water, in especial, magnetized water is not a Newtonian fluid, but a plastic fluid. Also, we discovered that there are plenty of hydrogen-bonded chains or clusters of molecules in water, which result directly in its plastic flowing. This alters our traditional understanding to water. [ABSTRACT FROM PUBLISHER]

Martinsons Träbroar produces currently around 40-50 timber bridges each year where more than half of them are transversally prestressed (stress laminated) decks. A semi-empirical beam theory model is and has been used to determine the height of the decks and the prestress levels. An alternative modelling technique using finite element methods is described in this paper. The purpose for investigating this alternative method is to increase the understanding of behaviour and load bearing capacity of prestressed timber decks. Also to increase the accuracy and efficiency of the design process. The alternative simulation model is an elastic-plastic three-dimensional finite element model. It handles all stress components and is well suited for stress design of timber bridges. The plastic material behaviour of the model makes it possible to model slip between glulam beams in a bridge deck of a prestressed timber bridge. Examples of simulation and experimental results for bridge decks are shown. The results are especially interesting when judging the behaviour of bridge decks for low levels of prestress. An important question is how these results can be interpreted when it comes to design of timber bridges and also the long-time behaviour of real timber bridges. [ABSTRACT FROM AUTHOR]

The purpose of present investigation is to obtain knowledge for developments of momentum transfer in the entrance region of a gravity driven liquid film flow. Experimental research of turbulent film flow in the entrance region was performed. A brief description of experimental set-up is presented in the study. The method for measurement of shear stress on outside surface of vertical tube is proposed. The results of experiments are discussed with respect to shear stress variation dependence on initial velocity and Reynolds number of the liquid film. The film flow stabilization length is determined experimentally. [ABSTRACT FROM AUTHOR]

The magneto-rheological fluid is a magnetic one. A magnetic fluid changes its properties (viscosity) under the influence of an external magnetic field. The viscosity of magneto-rheological fluid changes by magnetic field (from carrier fluid till like frozen butter). The ferromagnetic particles are single domains when magnetic field is off and the same particles are orientated and concentrated along of the magnetic field. First of all the magneto-rheological fluid were used in brakes and dampers. The rheological properties of MR fluids in particular the dynamic yield stress are based on a Bingham plastic model. This paper describes magneto-rheological brake operation principles and analysis of it. The design, optimal dimensions of MR brake, mathematical functions of shear stresses and torque are analyzed. The aim of this work is to develop a magneto-rheological brake system that has performance over conventional hydraulic brake system. The controllable yield stress is the reason of friction on the MR brake rotor. [ABSTRACT FROM AUTHOR]

The shock response of geological materials is of interest to many industries, in particular oil and gas exploration. The porous inhomogeneous composition of geological materials complicates characterisation under dynamic loading. The behaviour of dry limestone has been investigated under the condition of uniaxial strain using a plate impact facility. Manganin gauges were used to measure both longitudinal and lateral stresses within the limestone. The Hugoniot and shear data obtained are compared with that available in the open literature. [ABSTRACT FROM AUTHOR]

A series of plate impact experiments have been performed to assess the dynamic behaviour of dry and water saturated concrete under shock-loading. Information was obtained on the Hugoniot curve and dynamic shear properties using manganin gauges. This extends our previous data obtained on cement paste, mortar, and micro-concrete to full-size concrete. Despite the varying heterogeneous composition of concrete it has been found that all materials Hugoniot curves lie within a close range in Stress—Particle Velocity space (σ-up). [ABSTRACT FROM AUTHOR]

A series of plate impact experiments has been performed to assess the dynamic behaviour of micro-concrete (70% fine-grain dolerite powder and 30% cement paste by weight) in both longitudinal and lateral directions. Information was obtained for the Hugoniot curve and dynamic shear stress properties. Hugoniot results are compared with published data on cement paste, mortar and concrete from the UK, Germany, France and the US. When the shear strength of micro-concrete is compared to the cement paste very small differences are observed. Therefore, the shear strength of this system appears to be independent of the aggregates and mainly depends on the matrix material. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Spall strength of a hot-pressed silicon carbide marketed as SiC-N is determined to 16 GPa under both normal shock wave and under shock induced simultaneous compression-shear wave propagation. The preliminary results of this investigation suggest that shock induced shear under compression-shear wave propagation: (i) does bring about a decrease in the spall strength of SiC-N compared to under normal shock wave propagation and (ii) does seem to induce propagation of a failure front in SiC-N as evident from re-acceleration in the free surface velocity profiles in SiC-N prior to expected arrival of pull-back i.e., spall signal. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The dynamic response of pure nickel (Ni), and its alloy, Ni-60Co (by weight %), has been investigated during one-dimensional shock loading. Few materials’ properties are different and the only significantly altered feature is the reduced stacking fault energy (SFE) for the Ni-60Co. This paper considers the effect of this reduced SFE on the shear strength. Data (in terms of shock stress, particle velocity and shock velocity) are also presented. The influence on the shear stress, τ of cobalt additions in nickel are then investigated and presented. Results indicate that the lateral stress is increasing in both materials with the increasing impact stress. The shear stress was found to be higher in the nickel than in the Ni-60Co. The progressive decrease of the lateral stress noted during loading indicates a complex mechanism of deformation behind the shock front. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

In this study influence of leaflet calcification on Aortic Valve calcification was studied using fluid solid interactions approach. The leaflets of the aortic valve were modeled as flexible structure. The interaction between flexible leaflets and blood flow was modeled with an iterative implicit method. The time averaged wall shear stress and pressure drop parameters were calculated for different models with various Young Modulus of elasticity for leaflets. Results revealed that more calcified leaflets are imposed to more wall shear stress and higher levels of pressure drop. [ABSTRACT FROM AUTHOR]

In this study, we introduced an in vivo convective heat transfer-based micro-electromechanical system (MEMS) sensor that measured real-time experimental vascular shear stress values in the aortas of New Zealand White rabbits (n=4). Experiments were performed to measure flow profile changes in response to hyper-cholesterol diet and an irregular tachycardia condition. We have shown that these conditions induce shear stress changes indicative of pre-atherosclerosis regions by the MEMS thermal sensor. [ABSTRACT FROM PUBLISHER]