High Shear Stress Zone Research Articles

Influence of bottom protection structures group on the hydraulic characteristics in sharp bends

Bottom protection (BP) is a commonly used engineering measure in river training. A 3D hydrodynamic numerical model is established to study the influence of the overall arrangements of BP structures on the hydraulic characteristics of the sharp bends. Under the action of the BP structures group, the maximum longitudinal flow velocity is closer to the water surface vertically and closer to the concave bank laterally compared with no BP. The high shear stress zones on the riverbed at the exit straight section of the bend do not occur. The so-called primary circulation after the apex of the bend gradually weakens and disappears. If the coverage rate of BP is increased to 1.5 times that of the sequential BP, the average longitudinal flow velocity near the bottom of BP decreases by 10% and the average bed shear stress at the outlet section of the bend decreases by 35%. In the staggered BP condition, the average bed shear stress at the outlet section of the bend is reduced by 23% compared with the sequential BP. Moreover, the results show that the protection effects of the dense BP and the staggered BP are better than that of sequential BP.

Shear‐Responsive Drug Delivery Systems in Medical Devices: Focus on Thrombosis and Bleeding

AbstractCardiovascular disease is the leading cause of death worldwide. Blood‐contacting medical devices provide critical support for patients with severe respiratory and/or cardiac failure. High shear stress zones and non‐biocompatible circuit can increase the risk of thrombus formation in patients. These thrombi restrict blood flow through the circuits and travel to the lungs and brain, creating significant consequences. Antithrombotic drugs are used to lower this risk, but they also raise the incidence of bleeding problems. This article explores the delicate balance between thrombosis and bleeding in medical devices by examining platelet activation and thrombosis formation under shear stress. The feasibility of a shear‐responsive nanomedicine‐based drug delivery system has been explored as a potential approach for targeted administration of antithrombotic medications to lower systemic drug levels and reduce the bleeding risk. Furthermore, the lack of in vitro platforms to investigate the biological behavior of antithrombotic nanoparticles is impeding their clinical translation. As a result, microfluidic technology offers a platform for investigating nanoparticle behavior in vitro and linking it to their performance in vivo. Finally, the challenges and factors that affect the functionality, stability, and circulation time of liposomal drugs are investigated to improve their efficacy for targeted drug administration in medical devices.

Influence of growth plate morphology on bone trabecular groups, a framework computational approach.

The morpholog of the growth plate undergoes various transformations during each stage of development, affecting its shape, width, density, and other characteristics. This significantly impacts the distribution of stress in the epiphysis of long bones. To the best of our knowledge, this study represents the first attempt to examine the relationship between growth plate morphology and trabecular bone patterns. Our analysis was conducted using a finite element model and we analyzed two medical cases: trabecular patterns in the femoral epiphysis and the calcaneus bone. Our findings revealed a correlation between the formation of main trabecular groups and growth plate morphology. We investigated how an increased density in high-shear stress zones, which are typically located at the periphery of the growth plate, may occur to prevent failure by shear. This is evident in cases such as slipped capital femoral epiphysis or sever's disease, different simulations align with the clinical data available in the literature from a qualitative and quantitative point of view. Our results suggest that further research should focus on understanding the impact of growth plate morphology on bone remodeling and exploring potential preventive measures for different bone disorders.

Correlating the HWTT laboratory test data to field rutting performance of in-service highway sections

Rutting is one of the common distresses occurring in hot-mix asphalt (HMA) pavements that can be mitigated through adequate laboratory testing during the HMA mix-design screening stage. The Hamburg Wheel Tracking Tester (HWTT) is one of the test methods widely used in the routine HMA mix-design screening and quantification of the HMA rutting resistance potential in the laboratory. However, the occurrence of premature field rutting failures have been reported for some surface HMA mixes (even after being satisfactorily screened with the HWTT test in the laboratory), mostly in high-temperature environments, heavy truck-trafficked areas, and high shear-stress zones such as intersections, curves, etc. In an effort to improve the HWTT’s screening and performance predictive capabilities, new models and HMA rutting parameters such as the rutting area, normalized rutting area, shape factor, rut-depth ratio, rutting resistance index, and the equivalent remaining laboratory rutting life were evaluated to supplement the traditional rut depth and number of load passes criteria. The fundamental theory for formulating these new models and HMA rutting parameters is to better account for the currently prevailing traffic loading and climatic conditions. However, one key challenge associated with such enhancements and new model developments prior to industry implementation is correlations and validation with field performance data. Using the Texas flexible pavements and overlays database, namely the Texas Data Storage System (DSS) as the data source, this study was conducted to correlate and validate the HWTT laboratory test data to field rutting performance of in-service highways. As extracted from the DSS, three Texas commonly used HMA mixes (ranging from fine to coarse-graded) and five in-service highways were used for the study. Overall, the laboratory HWTT yielded good correlations with field rutting performance data with a coefficient of determination generally exceeding 60% for most of the HMA rutting parameters evaluated. In particular, the rutting area and normalized rutting area parameters exhibited statistical superiority in terms of correlations with all the field rutting performance data, with coefficient of determination values averaging 69.9%. Nonetheless, more field correlations and validation studies of this nature are strongly recommended, among others, to aid in defining and establishing the pass-fail screening criteria/thresholds for the proposed HMA rutting parameters.

The prediction of the operating conditions on the permeate flux and on protein aggregation during membrane processing of monoclonal antibodies

The lack of available material during early stage bioprocess development poses numerous processing challenges such as limiting the number of full-scale experiments. Extended fundamental process understanding could be gained with the use of an ultra scale-down (USD) device using as little as 1.7 mL per experimental run. The USD system is used to predict diafiltration and ultrafiltration/diafiltration (UF/DF) performance of a pilot-scale tangential flow filtration (TFF) system, fitted with a flat-sheet cassette, operating at 500-fold larger scale. Both systems were designed by maintaining a volumetric loading of 8.1 L of feed per m2. Permeate flux was predicted for monoclonal antibody solutions with the USD system across a range of transmembrane pressure drops, feed concentrations and flow conditions during diafiltration, and desired retentate concentrations during UF/DF operations. The resulting USD data were in good agreement with the pilot-scale TFF when scaled based on similar shear rates over the membrane surface. Little change in soluble aggregates was observed in both systems but there were significantly higher increases in product turbidity in the USD system. A correlation was established to relate turbidity increase based on the volume fraction of high shear stress zone for USD systems and various pilot-scale TFF systems. The correlation was extended to encompass the processing time and concentration for a wide range of membrane processing challenges in both scales.

Identification of Potential Location and Extent of Localized Interface Debonding in the Wheelpath of Asphalt Pavements

Debonding between asphalt layers is usually modeled as a global or “smeared” phenomenon across the entire lane. However, field evidence indicates debonding may be limited to a portion of the interface. The objective of this study was to determine the potential location and extent of localized interface debonding in asphalt pavements so that more realistic interface conditions and pavement responses can be employed in future performance predictions. A parametric study was conducted to locate stress states potentially conducive to interface debonding. Factors considered included asphalt concrete (AC) layer thickness, AC-to-base stiffness ratio, interface compliance, tire size, and traffic wander. The parametric study showed existence of a zone of high shear stress coupled with low confinement for a broad range of depths (1–3 in. below the surface) and extending to 2 in. from the tire edge. Given the drop in confinement immediately outside the tire edge and that shear stress magnitude in this zone was similar to shear strength values reported in the literature, it was concluded that the repetition of these critical stress state conditions can cause localized debonding of an interface located about 2 in. below the pavement surface. Existence of a potential zone of localized interface debonding around the edge of a tire can promote a debonded strip below the wheelpath, which is consistent with field observations. The width of the debonded strip can extend to 42 in. Future research efforts should examine the stress redistribution associated with the presence of a debonded strip below the wheelpath.

Influence of External Forces during Supercooling on Dispersion Stability during Melt Emulsification

AbstractA special high‐pressure homogenization process – simultaneous homogenization and mixing (SHM) – was applied to produce hexadecane (C16H34), octadecane (C18H38), eicosane (C20H42), and docosane (C22H46) in water dispersions. Additionally, a high‐shear stress zone (HSSZ) was connected to the SHM unit to investigate the influence of external forces during supercooling on dispersion stability. The HSSZ did not affect the droplet disruption efficiency but induced aggregation behavior of the dispersed phase with increasing alkane chain length and dispersed‐phase content. High‐shear treatment during crystallization led to a change in particle shape, which was more favorable to aggregation.

Numerical Simulation of Thrombotic Occlusion in Tortuous Arterioles

Tortuous microvessels alter blood flow and stimulate thrombosis but the physical mechanisms are poorly understood. Both tortuous microvessels and abnormally large platelets are seen in diabetic patients. Thus, the objective of this study was to determine the physical effects of arteriole tortuosity and platelet size on the microscale processes of thrombotic occlusion in microvessels. A new lattice-Boltzmann method-based discrete element model was developed to simulate the fluid flow field with fluid-platelet coupling, platelet interactions, thrombus formation, and thrombotic occlusion in tortuous arterioles. Our results show that vessel tortuosity creates high shear stress zones that activate platelets and stimulate thrombus formation. The growth rate depends on the level of tortuosity and the pressure and flow boundary conditions. Once thrombi began to form, platelet collisions with thrombi and subsequent activations were more important than tortuosity level. Thrombus growth narrowed the channel and reduced the flow rate. Larger platelet size leads to quicker decrease of flow rate due to larger thrombi that occluded the arteriole. This study elucidated the important roles that tortuosity and platelet size play in thrombus formation and occlusion in arterioles.

Supershear transition mechanism induced by step over geometry

AbstractFew studies have focused on the supershear transition mechanism induced by fault step overs, although seismic observations suggest that rupture speed transitions occur at geometrical complexities on faults. Based on dynamic rupture simulations on fault systems with step overs in a 3‐D full space where the initial stresses preclude a supershear transition on a single buried fault according to the Burridge‐Andrews mechanism, we show that rupture speeds can transit from subshear on the primary fault to supershear on the secondary fault. The low normal stress zone and the high shear stress zone beyond the fault step, which radiate from the end of the primary fault if its rupture arrest is sudden, determine the supershear rupture occurrence on the secondary fault. However, a low shear stress zone traveling at the shear wave speed is also radiated, making the rupture speed return to subshear in most cases. Sustained supershear ruptures are also possible on compressional step overs under certain conditions. Self‐arresting ruptures are observed in the overlap area on the secondary fault. In a half‐space model where supershear rupture is induced by the free surface on the primary fault, the rupture speed on the secondary fault rapidly transits to subshear near the fault step if its width exceeds a critical value.

CFRP shear strengthening of reinforced concrete beams in zones of combined shear and normal stresses

Strengthening RC beams using FRP laminate becomes one of the main strengthening techniques. Failure of these beams is usually controlled by the bond strength between the laminate and the concrete surface. As such, ACI 440.2-08 limits the bond strength via a bond reduction factor, which is adopted to reduce the effective strain in the FRP laminate. Equations characterizing the shear strength of such beams, which explicitly include the said bond reduction factor, has been verified for region of high shear stress and negligible normal stress. Such conditions simulate the high shear stress zone in a simply supported beam in the vicinity of the support; however, they fail to mimic the high shear and normal stresses zones in continuous beams existing in the vicinity of any intermediate support. Allegedly, the ACI 440.2-08 adopts the bond reduction factor for zones of combined high shear and normal stresses because “it is sufficiently conservative”. Consequently, this paper presents an experimental investigation performed on continuous RC beams strengthened with CFRP sheets: sheets were U-wrapped around the intermediate support of eight two-span beams. The investigation serves to confirm whether or not the currently adopted bond reduction factor is conservative for regions of combined normal and shear stresses.

A microfluidic shear device that accommodates parallel high and low stress zones within the same culturing chamber.

Fluid shear stress (FSS) plays a critical role in regulating endothelium function and maintaining vascular homeostasis. Current microfluidic devices for studying FSS effects on cells either separate high shear stress zone and low shear stress zone into different culturing chambers, or arranging the zones serially along the flow direction, which complicates subsequent data interpretation. In this paper, we report a diamond shaped microfluidic shear device where the high shear stress zone and the low shear stress zone are arranged in parallel within one culturing chamber. Since the zones with different shear stress magnitudes are aligned normal to the flow direction, the cells in one stress group are not substantially affected by the flow-induced cytokine/chemokine releases by cells in the other group. Cell loading experiments using human umbilical vein endothelial cells show that the device is able to reveal stress magnitude-dependent and loading duration-dependent cell responses. The co-existence of shear stress zones with varied magnitudes within the same culturing chamber not only ensures that all the cells are subject to the identical culturing conditions, but also allows the resemblance of the differential shear stress pattern in natural arterial conditions. The device is expected to provide a new solution for studying the effects of heterogeneous hemodynamic patterns in the onset and progression of various vascular diseases.

Characterization and damaging law of CFC for high heat flux actively cooled plasma facing components

The carbon fiber reinforced carbon composite (CFC) Sepcarb N11 has been used in the Tore Supra (TS) tokamak (Cadarache, France) as armour material for the plasma facing components. For the fabrication of the Wendelstein 7-X (W7-X) divertor (Greifswald, Germany), the NB31 material was chosen. For the fabrication of the ITER divertor, two potential CFC candidates are the NB31 and NB41 materials. In the case of Tore Supra, defects such as microcracks or debonding were found at the interface between CFC tile and copper heat sink. A mechanical characterization of the behaviour of N11 and NB31 was undertaken, allowing the identification of a damage model and finite element calculations both for flat tiles (TS and W7-X) and monoblock (ITER) armours. The mechanical responses of these CFC materials were found almost linear under on-axis tensile tests but highly nonlinear under shear tests or off-axis tensile tests. As a consequence, damage develops within the high shear-stress zones.

Stability Evaluation of Chenmenshan Open-Pit by SURPAC and MIDAS

Chengmenshan open pit has been constructed to be the biggest copper pit in China. The slope designed with empirical rock mass rating and engineering analogy needs reinvestigation and evaluation for its overall stability. With help of SURPAC, the topographic contour of the mine was converted into surface model. Then the geological information of the mine was embedded into the numerical solid model by NURBS treatment of the core loggings. Through overall stability analysis with MIDAS, it was found that there was no obvious failure in the pit with the current design. But the major principal stress at the north especially the north-east corner of the pit tended to be high, so the width of the bench below the high stress region is suggested to be widened for possible collapse in this region. And field observation should be carried out in the region. Once evident slip or collapse happens, anchor and netting structures should be used. At the same time, high shear stress zones were revealed at the south-east of the outside limit of the pit. More planting is suggested to avoid soil creep or even landslides in heavy rain.

Damage prediction of carbon fibre composite armoured actively cooled plasma-facing components under cycling heat loads

In order to predict the lifetime of carbon fibre composite (CFC) armoured plasma-facing components in magnetic fusion devices, it is necessary to analyse the damage mechanisms and to model the damage propagation under cycling heat loads. At Tore Supra studies have been launched to better understand the damage process of the armoured flat tile elements of the actively cooled toroidal pump limiter, leading to the characterization of the damageable mechanical behaviour of the used N11 CFC material and of the CFC/Cu bond. Up until now the calculations have shown damage developing in the CFC (within the zone submitted to high shear stress) and in the bond (from the free edge of the CFC/Cu interface). Damage is due to manufacturing shear stresses and does not evolve under heat due to stress relaxation.For the ITER divertor, NB31 material has been characterized and the characterization of NB41 is in progress. Finite element calculations show again the development of CFC damage in the high shear stress zones after manufacturing. Stresses also decrease under heat flux so the damage does not evolve. The characterization of the CFC/Cu bond is more complex due to the monoblock geometry, which leads to more scattered stresses.These calculations allow the fabrication difficulties to be better understood and will help to analyse future high heat flux tests on various mock-ups.

Numerical simulation of blood flow in a curved textile vascular prosthesis

Woven and knitted cardiovascular prostheses are tubular structures made of polyester filaments. They present particular mechanical properties linked to the wavy form of their walls, allowing them to be used in curved configurations. Pulsatile blood flows have been studied in bent textile prosthesis. The results obtained showed velocity peaks involving high-shear stress zones and turbulence phenomenon inside the graft. The flow velocity distribution near a prosthetic surface is strongly influenced by the crimping morphology. A local flow analysis is imperative in understanding pathologies implying hemodynamic factors and in optimizing the prosthesis design.

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In-vitro flow characteristics downstream of a polyurethane artificial heart valve and a Bj??rk-Shiley Monostrut mechanical valve have been comparatively investigated in pulsatile flow using particle image velocimetry (PIY). With a triggering system and a time-delayed circuit the velocity distributions on the two perpendicular measurement planes downstream of the valves are evaluated at any given instant in conjunction with the opening behaviors of valve leaflets during a cardiac cycle. The regions of stasis and high shear stress can be found simultaneously by examining the entire view of the instantaneous velocity and Reynolds shear stress fields. It is known that high shear stress regions exist at the interface between strong axial jet flows along the wall and vortical flows in the central area distal to the valves. In addition. there are large stagnation or recirculation regions in the vicinity of the valve leaflet. where thrombus formation can be induced by accumulation of blood elements damaged in the high shear stress zones. A correlation between the unsteady flow patterns downstream of the valve and the corresponding opening postures of the polyurethane valve membrane gives useful data necessary for improved design of the frame structure and leaflet geometry of the polyurethane valve.

Finite element analysis of construction stability of Thika Dam

Abstract High pore water pressures were measured in the fill material of the Thika Dam embankment early in its construction. These caused concern about the subsequent short term stability. Therefore construction was stopped. Stability reassessment and drainage design was performed using finite element analyses before construction was allowed to continue. Different methods of modelling the pore water pressure allowed efficient analysis of various drainage options. The analyses highlighted zones of high shear stress and shear strain, and formation of failure surfaces. They established the necessary level of drainage required to ensure stability, control movement and reduce the risk of residual shear surfaces. Large toe movement was predicted immediately after construction recommences. ©

ON HIGH-FREQUENCY SEISMIC MOTIONS OF REINFORCED CONCRETE STRUCTURES

In relation to disastrous damage of reinforced concrete (RC) columns due to recent Hanshin-Awaji Earthquake, high-frequency behavior of RC beams subjected to impact loading is reexamined. Thus, the effect of high-frequency horizontal motions on the columns is inclusively studied, solving RC beams in the elastic range by BEM. From the dimensional analysis, it is suggested that the local failure mode of the columns due to horizontal motions could result from high-frequency earthquakes over 10Hz. The stress analysis suggests spalling failure of cover concrete due to high-frequency bending motions and the high shear stress zone localized at one end due to the higher frequency motions.

Indentation stress-strain curves for “quasi-ductile” ceramics

A micromechanical model describing “quasi-ductile” Hertzian contacts in otherwise brittle ceramics is developed. The elemental basis of the model is a discrete “fault” along an internal weak interface, constrained at its ends by an elastic matrix and subject to frictional sliding, in the subsurface zone of high shear stress in the Hertzian field. By summation over a prescribed density of shear faults within the active plastic zone, the analysis leads to a constitutive identation stress-strain function, with special provision for the incorporation of microstructural variables. Experimental data from a series of mica-containing glass-ceramics with contiguous platelet microstructures are used to confirm the essential predictions of the model. It is demonstrated that plasticity increases with volume fraction and aspect ratio, but not size, of the platelets. Parametric evaluations by curve fitting the indentation stress-strain data allow for predictions of intrinsic stress-strain responses for the glass-ceramics in conventional uniform stressing states.

Investigation into the impact wear behaviour of ceramic coatings

Ceramic coatings with good impact wear resistance, hardness, toughness and adhesion are required in many applications. Coatings deposited by physical vapor deposition processes (CrN over an ENiP interlayer, TiC x N y , TiN and Ti x% -diamond-like carbon) have been evaluated using a specially designed cyclic impact tester. The test allows the modelling of wear under repetitive high local loads, as encountered by machine parts subjected to impact or tools used in interrupted cutting or cold forming. To adjust the test conditions for different applications, the impact force and frequency are variable and each impact can be monitored using a piezo-force transducer. A comparison of the results of the tests on the coatings studied shows differences in the characteristics of the impact wear in each case. Scanning electron microscopy and optical inspections of the wear regions allowed the creation of a model to describe hard coating degradation under repeated impact loading. Three different zones were identified: a central zone of cohesive failure; an intermediate zone of cohesive-adhesive failure; and a peripheral zone with circular cracks. Furthermore, it was found that the wear increased at the macrocracks, depending on the number of impacts, before coating delamination or spallation started to occur. The TiC x N y coatings and, in particular, the TiC 0.75N 0.25 coatings were found to have better resistance to this kind of dynamic impact wear than was the case for the coatings with an ENiP interlayer. The Ti x%-diamond-like carbon coatings showed good wear resistance in the cavity of the indentation area until a high number of impacts was reached, but coating delamination at the high shear stress zones (at the edges and centre of the cavity) took place after a lower number of impacts.