Maximum Shear Stress Values Research Articles

Mining data from hemodynamic simulations via Bayesian emulation

Background:Arterial geometry variability is inevitable both within and across individuals. To ensure realistic prediction of cardiovascular flows, there is a need for efficient numerical methods that can systematically account for geometric uncertainty.Methods and results:A statistical framework based on Bayesian Gaussian process modeling was proposed for mining data generated from computer simulations. The proposed approach was applied to analyze the influence of geometric parameters on hemodynamics in the human carotid artery bifurcation. A parametric model in conjunction with a design of computer experiments strategy was used for generating a set of observational data that contains the maximum wall shear stress values for a range of probable arterial geometries. The dataset was mined via a Bayesian Gaussian process emulator to estimate: (a) the influence of key parameters on the output via sensitivity analysis, (b) uncertainty in output as a function of uncertainty in input, and (c) which settings of the input parameters result in maximum and minimum values of the output. Finally, potential diagnostic indicators were proposed that can be used to aid the assessment of stroke risk for a given patient's geometry.

In Vivo/Ex Vivo MRI-Based 3D Non-Newtonian FSI Models for Human Atherosclerotic Plaques Compared with Fluid/Wall-Only Models.

It has been recognized that fluid-structure interactions (FSI) play an important role in cardiovascular disease initiation and development. However, in vivo MRI multi-component FSI models for human carotid atherosclerotic plaques with bifurcation and quantitative comparisons of FSI models with fluid-only or structure-only models are currently lacking in the literature. A 3D non-Newtonian multi-component FSI model based on in vivo/ex vivo MRI images for human atherosclerotic plaques was introduced to investigate flow and plaque stress/strain behaviors which may be related to plaque progression and rupture. Both artery wall and plaque components were assumed to be hyperelastic, isotropic, incompressible and homogeneous. Blood flow was assumed to be laminar, non-Newtonian, viscous and incompressible. In vivo/ex vivo MRI images were acquired using histologically-validated multi-spectral MRI protocols. The 3D FSI models were solved and results were compared with those from a Newtonian FSI model and wall-only/fluid-only models. A 145% difference in maximum principal stresses (Stress-P(1)) between the FSI and wall-only models and 40% difference in flow maximum shear stress (MSS) between the FSI and fluid-only models were found at the throat of the plaque using a severe plaque sample (70% severity by diameter). Flow maximum shear stress (MSS) from the rigid wall model is much higher (20-40% in maximum MSS values, 100-150% in stagnation region) than those from FSI models.

Limit strength and reeling effects of sandwich pipes with bonded layers

Sandwich pipes composed of two steel layers separated by a polypropylene annular can be used for deepwater oil and gas transportation, combining high structural resistance with thermal insulation in order to prevent paraffin and hydrates formation. In this work, sandwich pipes with typical inner diameters of those employed in the offshore production are analyzed numerically regarding to the influence of the inter-layer adhesion between steel and polymer on the ultimate strength under external pressure and longitudinal bending. The effect of the reeling method of installation is also simulated. The maximum shear stress of the metal–polymer interface is obtained by experimental tests. Numerical simulation of the adhesion is modeled by contact surfaces adopting a maximum shear stress value to allow the relative displacement between the layers. It was observed that the ultimate strength of the sandwich pipe is strongly dependent on the shear stress acting at the interface.

Analysis of the interface between a thermoplastic fiber and a thermosetting matrix using photoelasticity

Abstract The photoelastic images of the isochromatic fringes for a pull-out specimen were used to measure and to analyze the maximum interfacial shear strength for a thermoplastic–thermoset interface (PET/Epoxy). The photoelastic technique allows the loading process to be followed in-situ, as well as the determination of the shear stress distribution on a tested sample. A description of the stress transfer process and the measurement of the shear stress level along the embedded fiber were done. The maximum shear strength was located along the fiber surface at a distance of 2.5 times the diameter from the specimen border. The maximum shear stress values obtained from the photoelastic analysis were corrected to include the tri-dimensional axisymmetric distribution of the shear stress around the fiber. The corrected shear stress measured τcMax ranged from 0.27 to 1.17 MPa.

Magnetocrystalline Anisotropy and Twinning Stress of 10M and 2M Martensites in Ni-Mn-Ga System

Ni2MnGa alloy with 10M martensite exhibits rearrangement of martensite variants (RMV) by magnetic field, but Ni2.14Mn0.92Ga0.94 with 2M martensite does not. In order to explain the difference, we measured uniaxial magnetocrystalline anisotropy constant Ku and the stress required for twinning plane movement τreq in these alloys. Concerning the former alloy, the maximum value of magnetic shear stress acting across twinning plane τmag, which is evaluated as |Ku| divided by twinning shear, becomes larger than τr eq. On the other hand, concerning the latter alloy, the maximum of τmag is only one-tenth of τreq at any temperature examined. Obviously, the relation, τmag> τr eq, is satisfied when RMV occurs by magnetic field and vice versa. In this martensite, the large twinning shear of 2M martensite is responsible for small τmag and large τreq.

Valley cross‐profile morphology and glaciation in Park Valley, Tararua Range, New Zealand

Previous anecdotal research by G. L. Adkin over 90 years ago suggested that Park Valley in the Tararua Range was glaciated during the Late Quaternary, on the basis of the “U‐shaped” cross‐profile character of the uppermost parts of the valley. We quantitatively describe the cross‐profile morphology of the upper parts of Park Valley in the Tararua Range, using the power‐law model (y = axb ) and the form ratio model (FR = D/2W). Comparison of these results with morphological data published in global studies of glaciated landscapes suggests the upper parts of Park Valley have indeed been glaciated. Palaeoglacier reconstruction of this area gives a surface area of c. 1.41 km2, a maximum thickness of 130 m and a maximum basal shear stress value of 99 kPa. The equilibrium‐line altitude of the former glacier has been calculated as c. 1210 m, and with the absence of any dated moraines, the glacier is assumed to have formed during the Otira Glaciation.

Effects of insulated rail joint on the wheel/rail contact stresses under the condition of partial slip

The effect of insulated rail joint (IRJ) on the wheel–rail normal and tangential contact stress distribution is studied using the finite element method. In this investigation, contact elements are used to simulate the interaction between wheel and rail. Numerical simulations are used to explore the effects of contact distances and materials of IRJ on the contact stress and the maximum shear stress distributions. Numerical results show that the presence of IRJ might significantly affect the wheel–rail contact stress distributions. The results also indicate that Carter's theory is no longer effective in predicting the tangential stress distribution of the wheel–rail contact near an IRJ. The tangential stress causes the location of maximum shear stress shifted toward the rail surface as the wheel–rail contact point moves closer to the IRJ. The maximum shear stress value is more sensitive to a braked force than to a tractive force as the wheel–rail contact point is within the IRJ region.

Low-volume wet-process sprayed concrete: pumping and spraying

This paper, which reports on part of a three-year research project into wet-process sprayed concrete for repair, examines the influence of rheology on the pumping and spraying of fine concretes. The performance of ten laboratory-designed fine concretes were examined using a rotational viscometer, the slump test, a build test and a vane shear strength test. Visual grading and a sorptivity test were used to quantify the degree of reinforcement encasement which is a crucial factor in long term performance. Taken together, these tests form a rheological audit of each concrete which can help guide the design of sprayable, but also durable concretes. The two-point apparatus was successful for determining the flow resistance and torque viscosity of fine aggregate concretes, including those with air entrainment. The vane shear strength test was successful in providing an instantaneous reading of the shear strength of the concretes and is compared with their slump. The concretes were pumped and sprayed through a piston pump to assess their suitability and to measure their adhesion to a substrate by build thickness. This value is a measure of sprayability and is converted into values of maximum shear and tensile stress which are then compared with the workability parameters in order to determine their inter-relationship. These relationships are also compared with those obtained from a separated study of mortars. On its own, the sorptivity test did not accurately assess the encapsulation of the reinforcement. However, when considered with a visual grading of the cores, a more reliable indication can be obtained of the potential durability of the finished concrete, as well as the degree of encapsulation of the reinforcement. We demonstrate the conflict in selecting mix proportions that satisfy requirements for both installation and product quality.

Rigid polygons in shear

Abstract Clasts, inclusions and intrusions in shear are potential recorders of strain, stress, rheology and metamorphism. In order to extract the recorded information, it is essential to have analytical and numerical theories that describe the deformation mechanics of such bodies. To overcome the simplifications of the commonly employed ellipsoid-based shape approximation, a combination of Muskhelishvili-type analytical solutions and finite-element method calculations is used to study the behaviour of (quasi) rigid polygons in shear. The results confirm that the polygon rotation and the pressure perturbation outside rigid polygonal clasts are well approximated by ellipse-based theories. However, this observation does not hold for the inside of these polygons, which show strongly varying values of pressure perturbation and maximum shear stress. For example, pressure perturbations inside the polygons are usually the opposite of the neighbouring matrix values across the polygon-matrix interface. This complex behaviour is summarized in the ellipse decomposition rule that allows for the qualitative understanding of the pressure perturbation in and around a wide range of polygons in shear. Other quantities studied include maximum values of over-pressure relative to the shortening stress, and the area that undergoes overpressure with respect to the clast size. The results demonstrate that overpressure can be twice as large as the rock strength.

Rolling Contact Fatigue of Alumina Ceramics Sprayed Roller

The rolling contact fatigue of a sprayed alumina ceramics with a nominal composition of Al2O3-2.3 mass%TiO2 was studied with a two-roller test apparatus under pure rolling contact condition with oil lubricant. The alumina ceramics was prepared by plasma spray process. The influence of undercoating of sprayed Ni based alloy and surface sealing on the rolling contact fatigue was investigated. The failure mode of all sprayed rollers was spalling caused by subsurface cracking. Neither undercoating nor surface sealing contributed to the improvement of the rolling contact fatigue. The elastic modulus of the alumina sprayed layer evaluated with the nano-indentation method was around 85 GPa. The subsurface shear stresses were calculated with two-dimensional FEM analyses. The maximum values of orthogonal shear stress and maximum shear stress occurred within the sprayed layer. The depths of observed subsurface cracks were generally deeper than those of the maxima of shear stresses.

Time-Resolved Analysis of Turbulent Mixing Flow Characteristics of Intermittent Multi-Hole Diesel Spray Using 2-D PDPA

The turbulent mixing flow characteristics of an intermittent diesel spray were investigated. A 5-hole diesel nozzle (dn=0.32mm) with a 2-spring nozzle holder, which is widely used in heavy-duty diesel engines, was tested. Time-resolved analysis of the turbulent mixing flow characteristics of the spray, injected intermittently into the still ambient air, was made under room temperature by using a 2-D PDPA system. The mean and the fluctuation velocities of the spray were measured. The axial velocity distribution shows similar to that of the free air jets at the downstream of the spray, and the distribution well coincides with the result proposed by Hinze at R/b<1.5. The turbulent intensity of the axial velocity component is high near the spray axis, and it decreases gradually with the increase in the radial distance. The turbulent shear stress increases with proceeding to the trailing edge as well as the downstream of the spray. The maximum value of the turbulent shear stress is observed near R/b≈1.0, regardless of the evolution time. The turbulent shear stress in the central parts of the spray is lower than that of the continuous free air jets, whereas that in the trailing edge is considerably higher.

脳血管の流体シミュレーション

The paper aims to investigate the relationship between cerebrovascular morphology and hemodynmaics in order to predict rupture and creation of cerebral aneurysms. The authors have been developing an image-based simulation system together with a database system. Using 19 cases of the middle cerebral artery (MCA) analysis from the database system, the multiple regression analysis is performed to estimate a maximum value of wall shear stress. The results are compared and show good agreement with those of numerical analyses.

Comparative assessment of stress transfer efficiency in tension and compression

Raman spectroscopy is used to get an insight into the microstructural aspects of the compressional behaviour of carbon fibre composites. This is done by a comparative assessment of the stress transfer efficiency in tension and compression in single-fibre discontinuous model geometries. It was found that the axial stress is transferred in the fibre through the generation of shear stresses at the interface. The mechanism of stress transfer is independent of the loading mode. Furthermore, the values of maximum interfacial shear stress are a function of the applied strain for both tension and compression loading. Significant differences were found, however, in the mode of failure of the two systems. In tension, interfacial failure initiates from the fibre ends at relatively high applied strains and the stress transfer efficiency is affected by the onset of matrix plasticity. On the other hand, in compression, deterioration of the stress transfer efficiency occurs prior to any noticeable interfacial failure at the fibre ends due to fibre collapse at low strains. Finally, it is worth noting that in compression, the fibre fragments remain in contact, and thus can still bear load.

Finite element analysis of forces created by root separation and resection modelling.

Natural teeth with a healthy periodontal support exhibit stress transfer when functional forces are applied to them. These stress patterns show considerable variations during differing treatment modalities, which may influence both the tooth and supporting alveolar bone. The purpose of this study was to evaluate variations in the stress transfer under functional loads on first molars with periodontal furcation involvement, which were treated either with by root resection or root separation. This study used a two dimensional mathematical model of a mandibular first molar that was subjected to either a root separation or a root resection procedure. An evenly distributed dynamic load (600 N) was applied on two buccal cusps and distal fossae of the molar in centric occlusion. The analysis was performed using an IBM-compatible computer running standard analysis software. It was found that in the root resection model the stress values were maximum on the centre of rotation, and compressive stresses increased towards the middle of the cervical line. For the root separation model, the maximum shear stress values were observed in the distal portion, and a uniform stress distribution was observed in the mesial portion. Shear stress values for bone increased towards the centre in the bifurcation area. The outcomes of this study may be useful as a guide in clinical restorative procedures.

Thermal stress analysis and design optimization of direct chip attach (DCA) and chip scale package (CSP) in flip chip technology

Underfill encapsulation is a technique used to reinforce the solder bumps between the chip and the substrate in flip chip technology. To determine the optimal geometrical parameters and material properties for the package and candidate underfill materials is an important strategy for improving the thermo-mechanical reliability of flip chip packages. In this study, a stress-function-based energy method was developed to evaluate the interfacial peel and shear stress distributions in multilayered packaging structures. The stress functions were expressed in terms of sine and cosine trigonometric series. Simple programming and short CPU time lead to accurate stress distributions. After comparisons with other proposed numerical methods and results, the developed model was then coupled with a Genetic Algorithm to optimize the design of the direct chip attach (DCA) and chip scale package (CSP) in order to diminish the interfacial stresses and the possibility of crack initiation. The results revealed that the maximum peel and shear stress values were productively decreased and their peaks moved toward the center after conducting the optimizations in both cases. Improved geometrical and material parameters of the flip chip package were determined.

Numerical simulation of the turbulent flow field distal to an aortic heart valve.

A numerical technique is described which simulates the turbulent flow through a aortic Jellyfish valve, for two volumetric flow rates of 15 and 26 l/min representing peak systole flow. The steady incompressible Navier-Stokes equations written in three-dimensional (3-D) format are solved iteratively using a computational fluid dynamics code (Bio-FL). The numerical results show that the flow at the edge of the membrane of the valve splits into two nearly symmetrical jets with similar phenomenological features. Moreover, the 3-D flow simulations indicate the existence of two vortices in the immediate vicinity of the valve ring. Although these vortices are attenuated rapidly downstream by diffusion, they can have an adverse effect on erythrocytes and active platelets. It is also shown that elevated shear stresses occur in the vicinity of the upstream surface of the open occluder. In general. the numerical predictions compare well with the experimental measurements made at various locations downstream of the valve. The locations and the values of maximum velocity and shear stress, as well as width and length of re-circulation regions, are correctly predicted.

Indentation failure behavior of honeycomb sandwich panels

The failure behavior of simply supported honeycomb sandwich panels subjected to indentation loading on the top skin has been studied. A plate-on-elastic-foundation approach based on distributed load and panel-specific considerations (finite thickness and transverse shear) is developed to analyze the panel stress distribution. Panels with various glass-fibre/epoxy skins and aramid cores are analyzed by using this approach together with the finite-element analysis. Surprisingly good agreement is found between the theoretical and FEA solutions, suggesting that the model satisfactorily describes the panel indentation behavior. Indentation-induced stresses in the core relevant to the onset of indentation failure are found to depend on skin bending stiffness, core stiffness and indenter size. The calculated maximum shear and normal stress values are compared with the experimental data to assess the core failure mechanisms involved. The comparisons clearly show that core shear failure dominates the onset of indentation failure.

The rheological performance of wet-process sprayed mortars

This paper, which reports on part of a three-year research project into wet process sprayed concrete for repair, examines the influence of rheology on the pumping and spraying of mortars. The performance of seven commercially available prepackaged repair mortars and six laboratory-designed fine mortars was examined using the Tattersall two-point and Viskomat rotational viscometers, the pressure bleed test, the slump test, a build test and a vane shear strength test. These tests were used to form a rheological audit of each mortars. The two-point apparatus was successful with low-workability mortars, and their flow resistance and torque viscosities were determine. These parameters were also obtained with the Viskomat, although problems were encountered owing to the low workability of the mortars. The pressure bleed test measured both the rate and the total volume of liquid emitted from the mixes, while the vane shear strength test provided an instantaneous reading of the shear strength of the mortars and is compared with their slump. The mortars were pumped and sprayed through a worm pump to assess their suitability and to measure their adhesion to a substrate by build thickness. This value is a measure of sprayability and is converted into values of maximum shear and bending stress, which are then compared with the workability parameters in order to determine their interrelationship.

Numerical study of effects of pulsatile amplitude for transitional turbulent pulsatile flow in pipes with ring-type constrictions

The effects of pulsatile amplitude on sinusoidal transitional turbulent flows through a rigid pipe in the vicinity of a sharp-edged mechanical ring-type constriction have been studied numerically. Pulsatile flows were studied for transitional turbulent flow with Reynolds number (Re) of the order of 104, Womersley number (Nw) of the order of 50 with a corresponding Strouhal number (St) of the order of 0.04. The pulsatile flow considered is a sinusoidal flow with dimensionless amplitudes varying from 0.0 to 1.0. Transitional laminar and turbulent flow characteristics in an alternative manner within the pulsatile flow fields were observed and studied numerically. The flow characteristics were studied through the pulsatile contours of streamlines, vorticity, shear stress and isobars. It was observed that fluid accelerations tend to suppress the development of flow disturbances. All the instantaneous maximum values of turbulent kinetic energy, turbulent viscosity, turbulent shear stress are smaller during the acceleration phase when compared with those during deceleration period. Various parametric equations within a pulsatile cycle have also been formulated through numerical experimentations with different pulsatile amplitudes. In the vicinity of constrictions, the empirical relationships were obtained for the instantaneous flow rate (Q), the pressure gradient (dp/dz), the pressure loss (Ploss), the maximum velocity (Vmax), the maximum vorticity (ζmax), the maximum wall vorticity (ζw,max), the maximum shear stress (τmax) and the maximum wall shear stress (τw,max). Elliptic relation was observed between flow rate and pressure gradient. Quadratic relations were observed between flow rate and the pressure loss, the maximum values of shear stress, wall shear stress, turbulent kinematic energy and the turbulent viscosity. Linear relationships exist between the instantaneous flow rate and the maximum values of vorticity, wall vorticity and velocity. The time-average axial pressure gradient and the time average pressure loss across the constriction were observed to increase linearly with the pulsatile amplitude. Copyright © 1999 John Wiley & Sons, Ltd.

The stress reducing capacity of unfilled resin in a Class V cavity.

This study examined the stress reducing capacity of varying thicknesses of unfilled resin in a Class V cavity. A two dimensional plane strain mesh of a Class V cavity, 3 mm in diameter and 2 mm deep, was produced and the thickness of the unfilled resin layer was varied from 0 to 80 microm. A polymerization shrinkage of 1.5% was applied to the composite resin and the interfacial forces examined. The maximum shear stresses were found to occur along the pulpal floor of the restoration at the unfilled resin-dentine interface. The maximum shear stress values varied from 11.1 to 22.4 MPa and the shear stresses decreased by up to 38% as the thickness of the unfilled resin increased to 80 microm.