Shear Stress Concentration Research Articles

혈관 유연성을 고려한 경동맥 분기부 모델 혈류역학 해석

Blood flow simulations in an realistic carotid bifurcation model with considering wall compliance were carried out to investigate the effect of wall elasticity on the wall shear stress and wall solid stress. Canonical waveforms of flow rates and pressure in carotid arteries were imposed for boundary conditions. Compared to a rigid wall model, we found an increased recirculation region at the carotid bulb and an overall reduction of wall shear stress in a compliant model. Additionally, there was appreciable change of flow rate and pressure wave in longitudinal direction. Both solid and wall shear stress concentration occur at the bifurcation apex.

Augmentation of classical failure criteria for comprehensive applicability to interfacially deficient woven-roving composites

The dominant mode of failure in the fiber-reinforced composite materials of poor fiber-matrix adhesion is the interfacial shear failure. The main objective of the current study is to modify the classical failure criteria to comprise this mode of failure as they ignore the actual failure mechanisms, which are emerging microscopic deficiencies. An interfacial shear correction factor is proposed to augment the local shear component ( σ6) in the investigated failure criteria. Thus, the shear stress concentration at fiber-matrix interface in the boundary of the deficient zone is considered. To conduct the experimental part, thin-walled cylindrical specimens are fabricated from two layers of woven-roving E-glass fabrics of [±45°] and [0°, 90°] fiber directions. The fabrics are reinforced with polyester. For each fiber orientation, the specimens are divided into four groups: the first group includes the pristine specimens and the other three groups having circular inclusions of 5, 7, or 9 mm radii, respectively. Each specimen is subjected to fully reversed bending loading using a strain-controlled testing machine. The S-N curves and the relative damage vs. number of cycles to failure (N) curves are plotted for each group. The relative damage values are used to examine the theories applicability to the studied material and to calculate the values of the proposed interfacial shear correction factor.

Survey of Active Structural Control and Repair Using Piezoelectric Patches

The piezoelectric actuator has gained popularity over the last few years. Attention has been directed towards the study of their electromechanical response in active repair and the control of damaged structures. This has been made possible through the development of various numerical and analytical techniques for such studies. The shift of focus towards the piezoelectric based approaches has been due to their advantages, which include strategic cost benefits in maintenance, as well as an increase in the life cycle of the repaired structures. Furthermore, adhesively bonded joints are widely used in the manufacturing and repairing of structures in many industries, especially automotive and aerospace engineering. This is due to the requirement for lightweight materials as well as the potential adhesive used to join materials with different characteristics. The piezoelectric actuator has also shown the capacity in controlling and lowering the shear stress concentration and joint edge peel in adhesively bonded joint systems. The structure’s control of stress and repair can generally be viewed as a reinforcement that influences the structure’s damage tolerance. Therefore, the interest of this review is on the applications of the piezoelectric actuators in both structural damage and the bonded adhesive joint system. The specific goal is to recognize the contemporary scientific challenges, including future opportunities.

Energy Dissipation Due to Interfacial Slip in Nanocomposites Reinforced with Aligned Carbon Nanotubes

Interfacial slip mechanisms of strain energy dissipation and vibration damping of highly aligned carbon nanotube (CNT) reinforced polymer composites were studied through experimentation and complementary micromechanics modeling. Experimentally, we have developed CNT-polystyrene (PS) composites with a high degree of CNT alignment via a combination of twin-screw extrusion and hot-drawing. The aligned nanocomposites enabled a focused study of the interfacial slip mechanics associated with shear stress concentrations along the CNT-PS interface induced by the elastic mismatch between the filler and matrix. The variation of storage and loss modulus suggests the initiation of the interfacial slip occurs at axial strains as low as 0.028%, primarily due to shear stress concentration along the CNT-PS interface. Through micromechanics modeling and by matching the model with the experimental results at the onset of slip, the interfacial shear strength was evaluated. The model was then used to provide additional insight into the experimental observations by showing that the nonlinear variation of damping with dynamic strain can be attributed to slip-stick behavior. The dependence of the interfacial load-transfer reversibility on the dynamic strain history and characteristic time scale was experimentally investigated to demonstrate the relative contribution of van der Waals (vdW) interactions, mechanical interlocking, and covalent bonding to shear interactions.

Cold-lamination-bending of glass: Sinusoidal is better than circular

Cold-lamination-bending (CLB) of glass consists, first, in constraining the unbonded glass-interlayer package in the desired curved shape and, second, in performing the lamination process in autoclave. Releasing the laminate, the curvature is only partially maintained through the interlayer bond, due to an initial spring-back followed by the relaxation of the polymeric interlayer. Here, the whole process of single-curvature CLB, including the phase of release and the consequent contact problem with the constraining mould, is analyzed using sandwich beam theory. Comparisons are made between “stiff” interlayers (like Ionoplastic Polymers) and “soft” interlayers (like PVB). The time-dependent redistribution of stresses due to the interlayer viscosity is found for any assigned initial shape of the mould. Remarkably, the constant-curvature shape, indeed the most used, provokes shear stress concentrations in the interlayer with consequent risks of delamination. The sinusoidal shape, which for typical values of the deformation inappreciably differs from the circular one, provides a much smoother distribution of the shear stresses. A properly-designed gradual release of the laminated glass from the mould can substantially contribute to mitigate the peak stresses.

Optimal cold bending of laminated glass

Cold-bending of laminated glass panels, by forcing their contact with a constraining frame, is a promising technique for free-form glazed surfaces. Their static state varies in time due to the viscosity of the polymeric interlayer, which causes the decay of the shear-coupling of the constituent glass plies. The direct problem consists in calculating the spatial and temporal evolution of stress after cold-bending. Considering an equivalent secant elastic shear-modulus for the interlayer to account for its viscoelasticity, various conditions for cylindrical deformations are analyzed in detail. A “conjugate-beam analogy” is proposed for the inverse problem, i.e., to determine the deformed shape that, at a prescribed time, provides the desired state of stress. Remarkably, the simplest constant-curvature deformation, often used for cold bending, produces high shear stress concentrations in the interlayer with consequent risks of delamination. For the same sag, better linear or cubic distribution of shear stress are attained with slightly different deformations, compatibly with glass strength. Among the considered cases, the optimal configuration is sinusoidal, because it provides the smoothest distribution of shear stress with inappreciable geometric differences with respect to the circular shape.

Effects of hydrodynamic conditions on the sorption behaviors of aniline on sediment with coexistence of nitrobenzene.

The sorption behaviors of pollutants affected by hydrodynamic conditions were confirmed in natural water environment. The effects of hydrodynamic conditions on the sorption behaviors of aniline on sediment with coexistence of nitrobenzene were investigated. The particle entrainment simulator (PES) was used to simulate varied bottom shear stresses. The batch equilibrium method was applied to the experiments with the stress levels and the action time controlled at 0.2-0.5 N/m(2) and 24 h, respectively. The findings indicated that apparent partition coefficient of aniline on sediment increased with the shear stress significantly, while decreased with nitrobenzene concentration. On the contrary, both the sorption amount of aniline on suspended particulate matter (Q s) and the effect of nitrobenzene concentration on Q s declined as the shear stress increased. The sorption kinetic results showed that the sorption process followed the pseudo-second-order kinetics equation, and the process included two stages: fast sorption stage and slow sorption stage, among which the average sorption rate of fast stage was 7.5-9.5 times that of slow one. The effect of shear stress on the average sorption rate of aniline was enhanced with the increase of nitrobenzene concentration. And shear stress weakened the disturbance of cosolute on main solute sorption process. In addition, experiment results of sorption kinetic show that only the initial sorption rate was affected by shear stress and cosolute concentration. In the first 5 min, shear stress had positive effects on the sorption rate. After that, the sorption rate barely changed with shear stress and cosolute concentration.

Mesoscopic deformation features of shocked porous ceramic: Polycrystalline modeling and experimental observations

To prevent functional failure, the macroscopic shock response of ceramics needs to be understood. We explored the mesoscopic deformation features of porous ceramics, which are responsible for the measured macroscopic “plastic” wave profiles, using polycrystalline modeling and experiments. A polycrystalline model is established that considers the influence of two major microstructures (multi-voids and grain boundaries) in the porous ceramics. Shock experiments with the recovery of shocked porous lead zirconate titanate ceramics were conducted. The computational results show that shear cracks nucleate around voids under shock because of severe shear stress concentrations. Broken fragments fill the voids and lead to void collapse. Representative long-distance extended cracks and thick crevices are observed in the recovered sample subjected to 3.3 GPa compression. These representative features are reproduced by the polycrystalline model. An initial transgranular crack translates into an intergranular crack after a certain propagation range to form a long-distance extended crack. Intergranular cracks branch from the main transgranular crack during main crack propagation to form a thick crevice. The simultaneous propagation of main and branching cracks results in a more effective shock energy dissipation. Slippage and rotation deformation induced by multi-cracks allows the shocked porous ceramic to deform even after all the voids have collapsed. Mesoscopic deformations of porous ceramics induce significant stress relaxations and lead to macroscopic “plastic” wave profiles. The polycrystalline model will aid microstructures design and provide guidance for preventing the shock failure of functional ceramics.

Study and characterization of the crest module design: A 3D finite element analysis

Statement of problemThe importance of the crest module design in the cortical bone region triggered a need to understand its geometry and its influence on stress management and bone stimulation. PurposeThe purpose of this study was to determine the effect of different crest module designs in the cortical bone region in terms of critical stress distribution and bone stimulation. Material and methodsSeveral 3-dimensional finite element analyses were conducted of a mandibular cross section with osseointegrated dental implants. For the numerical models, different crest module designs (cylindrical, divergent, convergent, and cup shaped) were analyzed. An average value of a maximum occlusal load of 250 N was applied to each dental implant design, 30 degrees from the top surface. The concentration and distribution patterns of principal and maximum shear stresses and strains were obtained and analyzed. ResultsAccording to the comparative finite element analyses, the most pathologic stress and strain peaks around the implant collar in the cortical bone region were found in divergent crest modules with angles 14 degrees or larger. Nevertheless, the highest physiologic peaks of passive bone stimulation through compression, and the lowest tensile and shear stresses and strains in the cortical bone region were promoted by extended divergent crest module designs. ConclusionsA slightly divergent and smooth crest module design extended to the cancellous bone increases the surface area available. This results in the dissipation of critical stresses expressed around the collar of the cortical bone region, not only promoting a higher bone-implant contact area and a physiologic bone stimulation but also boosting a healthy and strong bone-implant interface.

Strength of Wall-Slab Junction with New Form of Shear Reinforcement in a Laterally Loaded Tall Shear Wall Building

Very high concentration of flexural, shear and torsional stresses occurs at the wall-slab junctions in a laterally loaded tall building consisting of planar walls and coupling slabs. Due to this concentration of stresses and their interaction, there are great chances of failure to occur at the junction. Also the flexural stresses are not uniformly distributed and have the highest intensity near the periphery of inner walls but are reduced drastically as we move away from the wall-slab junction. Numerous attempts have been made to strengthen the wall-slab junction by using various types of shear reinforcement to ensure that shear failure should not occur. Various methods including fibre reinforcement consisting of twins of twisted steel couplets have already been used. This paper describes a new method of placing 2 inch wide flange I-sections at appropriate locations to improve the shear strength of the wall-slab junctions. Based on systematic research, a new procedure has also been developed to assess the strength of wall-slab junction using the new reinforcement method. Test results showed that a substantial increase, up to 57%, in the shear strength of specimens was obtained by using the new method of shear reinforcement in a laterally loaded tall building.

Three-dimensional modeling of pavement with dual load using finite element

The model developed tries to predict the stresses and strains of the structure of the pavement in a more real way, doing a lineal elastic structural analysis in three dimensions with capacity to model loads of double axes, that which constitutes an advance regarding twodimensional axisymmetrical models that only represent the state tense-deformational of the pavement under loads of simple axes. Earlier stages of this research showed two-dimensional models under different load scenarios, league between layers and nonlinear constitutive models, however the purpose is to move towards analysis methodology stress-strain state under standard loads. The model was implemented in the Algor © program and a comparison with the Elsym5 multilayer freeware was performed. The results warn the existence of shear stress concentrations that can be causing major flaws that are not considered in traditional design methods which could lead to the possibility of reassessed.

Study of stress distribution and stress concentration factor in notched wood pieces with cohesive surfaces

In this study, the stress distribution and stress concentration factor (SCF) of a generic notched wood piece and ASTM D 143:14 notched shear block specimen were analysed. A 2D plane stress finite element model with linear elastic behaviour was assumed for the bulk material and a predefined potential crack path and cohesive behaviour of the crack surfaces were considered. Wood was considered an orthotropic material with transversal isotropy. In the notched wood pieces, the shear stress distribution along the shear plane and the SCF when varying the ratio l/t (length of the heel/depth of the notch) was obtained. The shear stress distribution is not uniform in any situation, approaching a slightly triangular shape. The shear stress concentration increases when l/t is greater and for l/t > 8 failure occurs due to crack progression. The SCF can be brought fairly close to the natural logarithm of l/t. In the ASTM D 143:14 notched shear block specimen, shear stress distribution only remains a constant value in the central part of the shear plane, while the SCF is greater than 2.

Shear Stress Discontinuities in Adhesive Joints

This paper deals with the stress discontinuities in shear stress distribution of adhesive joints. The three-dimensional finite element analysis (FEA) software was used to model the joints and predict the shear stress distribution along the whole beam. The FEA results indicated that there are stress discontinuities existing in the shear stress distribution within adhesive layer and adherends at the lower interface and the upper interface of the boded section. The numerical values of the shear stress concentration at key locations of the joints and the stress concentration ratio are discussed.

Hemodynamics in growing and stable cerebral aneurysms

ObjectiveThe detailed mechanisms of cerebral aneurysm evolution are poorly understood but are important for objective aneurysm evaluation and improved patient management. The purpose of this study was to identify hemodynamic...

Experimental and theoretical study of the anisotropic properties of shale

The effect of bedding plane orientations on shear strength and failure mechanisms of shale is investigated, with an emphasis on the shear parameters of the bedding planes. This study is based on direct shear tests conducted on directional shale samples obtained from formations which exhibit well-developed stratification. The tested cylindrical specimens were prepared by coring at 30° intervals from the direction of the bedding planes. The results indicate that the anisotropy of the shear strength of shale can be readily observed due to the anisotropic effects of bedding plane orientation and normal stress. The shear parameters, such as strength, cohesion and internal friction angle reach their maximum and the minimum values at β=60° and β=0°, respectively, where β is the angle between the bedding planes and the coring orientation, which is also the direction of normal stress during the laboratory tests. It is demonstrated that the bedding planes are weak not only with regards to cementing strength, but also with regards to friction. Three different shear failure modes were built up depending on the shearing angle β: (1) sliding failure across the bedding planes, (2) sliding failure along the bedding planes and (3) sliding failure across the bedding planes combined with tensile splitting along the bedding planes. An expression of the shear stress concentration factor of the direct shear model is derived to evaluate the anisotropy of shear strength.

Modeling of TRPV₄-C₁ -mediated calcium signaling in vascular endothelial cells induced by fluid shear stress and ATP.

The calcium signaling plays a vital role in flow-dependent vascular endothelial cell (VEC) physiology. Variations in fluid shear stress and ATP concentration in blood vessels can activate dynamic responses of cytosolic-free [Formula: see text] through various calcium channels on the plasma membrane. In this paper, a novel dynamic model has been proposed for transient receptor potential vanilloid 4 [Formula: see text]-mediated intracellular calcium dynamics in VECs induced by fluid shear stress and ATP. Our model includes [Formula: see text] signaling pathways through P2Y receptors and [Formula: see text] channels (indirect mechanism) and captures the roles of the [Formula: see text] compound channels in VEC [Formula: see text] signaling in response to fluid shear stress (direct mechanism). In particular, it takes into account that the [Formula: see text] compound channels are regulated by intracellular [Formula: see text] and [Formula: see text] concentrations. The simulation studies have demonstrated that the dynamic responses of calcium concentration produced by the proposed model correlate well with the existing experimental observations. We also conclude from the simulation studies that endogenously released ATP may play an insignificant role in the process of intracellular [Formula: see text] response to shear stress.

Shock plasticity design of brittle material

The mechanical properties of a material are closely related to its internal micro-structure. Enhancing shock plasticity by designing appropriate micro-structure will help to slow down or delay shock failure of brittle material. In this paper, we put forward a method of designing and improving shock plasticity of brittle material by implanting specific micro-voids. A lattice-spring model is adopted, which can represent mechanical properties of brittle materials quantitatively. Simulations reveal how the arrangement modes of micro-voids can affect the shock response of brittle material. By implanting randomly arranged voids, porous brittle material has significantly higher shock plasticity than dense brittle material and the design of the regular arrangement mode of voids will help to enhance the shock plasticity further. The dominant mechanism corresponding to the void collapse in the shocked brittle material is shear slip caused by shear stress concentration, which features the occurrence of shear cracks around the voids. Features of mesoscopic deformation in the sample with 5% porosity indicate that the shock plasticity of porous brittle material comes from the volume shrinkage deformation caused by void collapse and the slippage and rotation deformation caused by extension of shear cracks. The inter-permeation of voids and volume shrinkage deformation play a leading role in the sample with regularly arranged voids. While the shear cracks extends over long distance, slippage and rotation deformation take place dominantly in the sample with randomly arranged voids. The two samples with different arrangement modes of voids both have three stages of response in the Hugoniot stress-strain curves in this paper, i. e., linear elasticity stage, collapse deformation stage, and slippage and rotation deformation stage. The sample with higher porosity has a higher shock plasticity than the sample with lower porosity. When the samples have the same porosity, the collapse deformation stage makes greater contribution to the overall shock plasticity if voids are regularly arranged, while the slippage and rotation deformation stage make greater contribution to the overall shock plasticity if the voids are randomly arranged. The principle of enhancing shock plasticity of brittle material by arranging voids regularly in this paper provides physical knowledge for the designing and preparing new types of brittle materials, thereby helping to prevent the function failure induced by shock in brittle material.

Stress Distribution of CF/EP Laminated Composites under Supercritical Conditions

Enormous amounts of wastes have been produced due to extensive use of carbon fiber/epoxy resin (CF/EP) composites. The fact that the supercritical fluid can be used to recycle these composites efficiently has attracted widespread concerns. A three-dimensional model of CF/EP laminates considering the interfacial layers was established. The internal stress distribution of laminates was simulated based on a heat transfer model; and the change of shear stress with supercritical temperature and pressure was investigated. The results show that the shear stress concentration was located in the interfacial layers; the maximum shear stress can be expressed by a curve of convex parabola to the temperature; and the most serious damage occurred in interfacial layers when temperature approached the glass-transition temperature of resin.

Numerical simulation on the effects of drug eluting stents at different Reynolds numbers on hemodynamic and drug concentration distribution.

BackgroundThe changes of hemodynamics and drug concentration distribution caused by the implantation of drug eluting stents (DESs) in curved vessels have significant effects on In-Stent Restenosis.MethodsA 3D virtual stent with 90°curvature was modelled and the distribution of wall shear stress (WSS) and drug concentration in this model were numerically studied at Reynolds numbers of 200, 400, 600, 800.ResultsThe results showed that (1) the intensity of secondary flow at the 45° cross-section was stronger than that at the 90° cross-section; (2) As the Reynolds number increases, the WSS decreases. When the Reynolds number reaches 600, the low-WSS region only accounts for 3% of the total area. (3) The effects of Reynolds number on drug concentration in the vascular wall decreases in proportionally and then the blood velocity increased 4 times, the drug concentration in the vascular wall decreased by about 30%. (4) The size of the high drug concentration region is inversely proportional to the Reynolds number. As the blood velocity increases, the drug concentration in the DES decreases, especially at the outer bend.ConclusionsIt is beneficial for the patient to decrease vigorous activities and keep calm at the beginning of the stent implantation, because a substantial amount of the drug is released in the first two months of stent implantation, thus a calm status is conducive to drug release and absorption; Subsequently, appropriate exercise which increases the blood velocity is helpful in decreasing regions of low-WSS.

Gravity-induced shear force in reinforced concrete walls above transfer structures

In this study, the gravity loads in reinforced concrete shear walls supported on transfer structures are investigated. Emphasis is placed on the shear-stress concentration effects on the supported shear walls owing to the distortion of the transfer structure. A simplified model is proposed to illustrate the fundamental physical interactions. Finite-element analysis is also conducted to study the influences of the symmetric and asymmetric shear-wall arrangements, positioning of supporting columns and span-to-depth ratio of the transfer structure. Non-linear behaviours encompassing the use of yielded stiffness at ultimate limit state, sequential construction and the creep of reinforced concrete under gravity loads are addressed. Various effects of modelling assumptions and simplifications on the stress redistribution of the transfer structure are investigated. Remedial measures are proposed, such as increasing the depth of the transfer girders using late-cast slabs, segmented upper shear walls and concrete of higher grade for critical regions.