Average Shear Stress Research Articles

Seismic Behaviour of Beris Dam Under Six Earthquake Excitations by using Finite Element Method

This paper focused on the behavior of the dam when exposed to seismic loading and ability of the dam to withstand the applied loads from various seismic events. The chosen concrete dam to be referred to in the two- dimensional analysis is Beris Dam located in Kedah, Malaysia. A nonlinear dynamic analysis is chosen to analyse the behavior of Beris Dam under selected ground motion. Analysis of the dam is performed using the finite element method by utilizing ABAQUS software. From the cracking analysis pattern, a crack appeared at the upstream face of the dam caused mainly by the excessive tensile stress. Based on the results, the displacement of the dam is increased with the increasing of ground motion data where the displacement occurred in the horizontal direction. The maximum stresses exerted by the dam structure do not exceed the allowable capacity of concrete dams. The stress behaviour of the dam was satisfactorily acceptable as the maximum normal stress and shear stress of the dam when numerous seismic loadings are applied do not exceed the allowable stress capacity which is 800 kN/m2.

Fluid flow and heat transfer in carotid sinuses of different sizes and locations in an open surgery: CFD vs FSI

PurposeAtherosclerosis tends to occur in the distinctive carotid sinus, leading to vascular stenosis and then causing death. The purpose of this paper is to investigate the effect of sinus sizes, positions and hematocrit on blood flow dynamics and heat transfer by different numerical approaches.Design/methodology/approachThe fluid flow and heat transfer in the carotid artery with three different sinus sizes, three different sinus locations and four different hematocrits are studied by both computational fluid dynamics (CFD) and fluid-structure interaction (FSI) methods. An ideal geometric model and temperature-dependent non-Newtonian viscosity are adopted, while the wall heat flux concerning convection, radiation and evaporation is used.FindingsWith increasing sinus size, the average velocity and temperature of the blood fluid decrease, and the area of time average wall shear stress (TAWSS)with small values decreases. As the distances between sinuses and bifurcation points increase, the average temperature and the maximum TAWSS decrease. Atherosclerosis is more likely to develop when the sinuses are enlarged, when the sinuses are far from bifurcation points, or when the hematocrit is relatively large or small. The probability of thrombosis forming and developing becomes larger when the sinus becomes larger and the hematocrit is small enough. The movement of the arterial wall obviously reduces the velocity of blood flow, blood temperature and WSS. This study also suggests that the elastic role of arterial walls cannot be ignored.Originality/valueThe hemodynamics of the internal carotid artery sinus in a carotid artery with a bifurcation structure have been investigated thoroughly, on which the impacts of many factors have been considered, including the non-Newtonian behavior of blood and empirical boundary conditions. The results when the FSI is considered and absent are compared.

Selection of vortex ripple dimensions in sinusoidal oscillatory flows. Part 1. Ripple dimensions and fluid kinematics

Subaqueous vortex ripples in equilibrium are characterized by their unique geometry and dimensions. Motivated by the recent direct numerical simulation study of oscillatory turbulent flow over a wavy bottom by Önder & Yuan (J. Fluid Mech., vol. 858, 2019, pp. 264–314), the objective of this study is to further investigate the fluid dynamical controls that determine the distinctive equilibrium dimensions of vortex ripples. We use direct numerical simulations to investigate the differences in flow kinetics between sinusoidal oscillatory flow over equilibrium and out-of-equilibrium vortex ripples. In comparison with the equilibrium case, the spanwise coherent vortices, the averaged bottom shear stress on overlying flow and the shear stress distribution on the ripple surface are identified as the key fluid dynamical controls on equilibrium dimensions. Based on these controls, we propose mechanisms in the selection of vortex ripple dimensions. We observe that the flow adjusts in such a way that the interaction between overlying flow and vortex ripples tends to generate the strongest coherent vortices while the ripple surface (or overlying flow) experiences the smallest shear stress averaged over ripple wavelength during the selection process. Through a triple decomposition of the flow, the component of the ripple-induced fluctuation is found to dictate these fluid dynamical controls, which implies that this component plays an important role in the evolution of vortex ripples.

Analysis of the Shear Stresses in a Filling Line of Parenteral Products: The Role of Tubing

Parenteral products appear to be sensitive to process conditions in bioprocessing steps, such as interfacial stress and shear stress. The combination of these elements is widely believed and proven to influence product stability, but the defined roles of these players in the product damage process have not yet been identified. The present work addresses a current industrial problem, by focusing on the analysis of shear stress on protein-based therapeutics flowing in tubing by means of Computational Fluid Dynamics simulations. The purpose of this article is not to pinpoint the mechanism triggering the damage of the product, but it represents the first step towards wider experimental investigations and introduces a new strategy to quantify the average shear stress. The field of scale-down approaches, used to scale the commercial process down to the laboratory level, is also explored. Since quality control is critical in the pharmaceutical realm, it is essential that the scale-down approach preserves the same stress exposure as the commercial scale, which in the present work is considered to be that resulting from shear effects. Therefore, a new approach for scaling down the commercial process is proposed, which has been compared with traditional approaches and shown to provide greater representativeness between the two scales.

An analytical formulation of unidirectional composite curved beam with out-of-plane fiber waviness under bending

A closed-form analytical solution is developed for analyzing laminated composite curved beam with out-of-plane fiber waviness under bending. Timoshenko beam theory was adopted in derivation where the effects of shear deformation was considered for moderately thick beam. Explicit expressions for evaluating equivalent axial and bending stiffness are formulated based upon the modified lamination theory and taking the structural deformation characteristics of narrow section beam into consideration. Stress distribution at any given location calculated by the proposed method is investigated. Significant increase of radial normal stress and shear stresses are observed when out-of-plane fiber waviness is introduced. The comparisons between present analytical results and numerical data indicate that the present methodology have ability to capture radial normal, circumferential normal, and shear stress distributions of composite curved beam with out-of-plane fiber waviness and the level of stress predicted is satisfactory with numerical results.

Scaling of pressure fluctuations in compressible turbulent plane channel flow

The purpose of the paper is to identify Mach-number effects on pressure fluctuations$p'$in compressible turbulent plane channel flow. We use data from a specifically constructed$(Re_{\tau ^\star },\bar {M}_{{CL}_x})$-matrix direct numerical simulation (DNS) database, with systematic variation of the centreline streamwise Mach number$0.32\leqslant \bar {M}_{{CL}_x}\leqslant 2.49$and of the HCB (Huanget al.,J. Fluid Mech., vol. 305, 1995, pp. 185–218) friction Reynolds number$66\leqslant Re_{\tau ^\star }\lessapprox 1000$. Strong$\bar {M}_{{CL}_x}$effects (enhanced by the increasingly cold-wall condition) appear for$\bar {M}_{{CL}_x}\gtrapprox 2$, for all$Re_{\tau ^\star }$, very close to the wall ($y^\star \lessapprox 15$). Compared with incompressible flow at the same$Re_{\tau ^\star }$, the wall root-mean-square$[p'_{rms}]^+_w$(in wall-units, i.e. scaled by the average wall shear stress$\bar {\tau }_w$) strongly increases with$\bar {M}_{{CL}_x}$. In contrast, the peak level across the channel,$[p'_{rms}]^+_{PEAK}$, slightly decreases with increasing$\bar {M}_{{CL}_x}$. In order to study the near-wall coherent structures we introduce a new wall-distance-independent non-local system of units, based for all$y$on wall friction and the extreme values of density and dynamic viscosity, namely, for cold walls$\{\bar {\tau }_w,\min _y\bar {\rho },\max _y\bar {\mu }\}$. The average spanwise distance between streaks, scaled by this length-unit, is nearly independent of$\bar {M}_{{CL}_x}$at constant$Re_{\tau ^\star }$. Using the in-plane (parallel to the wall) Laplacian$\nabla ^2_{xz}p'$we find that the$(+/-)\text {-}p'$wave-packet-like structures appearing inside the low-speed streaks ($y^\star \lessapprox 15$) with increasing$\bar {M}_{{CL}_x}\gtrapprox 2$are part of a more complex wave system with spanwise extent over several streaks, whose spatial density decreases rapidly with decreasing$\bar {M}_{{CL}_x}$or increasing$y^\star$. These$p'$wave packets appear to be collocated with strong$(+/-)$-$v'$events and could be responsible for compensating towards 0 the negative incompressible-flow correlation coefficient$c_{p'v'}$, with increasing$\bar {M}_{{CL}_x}$very near the wall.

Classification of Blood Rheological Models through an Idealized Symmetrical Bifurcation

The assumed rheological behavior of blood influences the hemodynamic characteristics of numerical blood flow simulations. Until now, alternative rheological specifications have been utilized, with uncertain implications for the results obtained. This work aims to group sixteen blood rheological models in homogeneous clusters, by exploiting data generated from numerical simulations on an idealized symmetrical arterial bifurcation. Blood flow is assumed to be pulsatile and is simulated using a commercial finite volume solver. An appropriate mesh convergence study is performed, and all results are collected at three different time instants throughout the cardiac cycle: at peak systole, early diastole, and late diastole. Six hemodynamic variables are computed: the time average wall shear stress, oscillatory shear index, relative residence time, global and local non-Newtonian importance factor, and non-Newtonian effect factor. The resulting data are analyzed using hierarchical agglomerative clustering algorithms, which constitute typical unsupervised classification methods. Interestingly, the rheological models can be partitioned into three homogeneous groups, whereas three specifications appear as outliers which do not belong in any partition. Our findings suggest that models which are defined in a similar manner from a mathematical perspective may behave substantially differently in terms of the data they produce. On the other hand, models characterized by different mathematical formulations may belong to the same statistical group (cluster) and can thus be considered interchangeably.

Effect of Sac Asymmetry, Neck and Iliac Angle on the Hemodynamic Behavior of Idealized Abdominal Aortic Aneurysm Geometries

Abdominal Aortic Aneurysms (AAAs) are currently treated based on the universal maximum diameter criterion, but other geometric variables may play a role in the risk of rupture. The hemodynamic environment inside the AAA sac has been shown to interact with several biologic processes which can affect prognosis. AAA geometric configuration has a significant impact in the hemodynamic conditions that develop, which has only been recently realized, with implications for rupture risk estimations. We aim to perform a parametric study to evaluate the effect of aortic neck angulation, angle between the iliac arteries and sac asymmetry on the hemodynamic variables of AAAs. This study uses idealized AAA models and it is parametrized in terms of three quantities: the neck angle, φ(o), iliac angle, θ(o), and sac asymmetry, SA(%), each of which accepts three different values, specifically φ=(0o,30o,60o),θ=(40o,60o,80o), and SA=(S,SS,OS) where the sac asymmetry can either be on the same side with respect to neck (SS) or on the opposite side (OS). Time Average Wall Shear Stress (TAWSS), Oscillatory Shear Index (OSI), Relative Residence Time (RRT) and the velocity profile are calculated for different geometric configurations while the percentage of the total surface area under thrombogenic conditions, using thresholds previously reported in the literature, is also recorded. In case of an angulated neck and a higher angle between iliac arteries, favorable hemodynamic conditions are predicted with higher TAWSS and lower OSI and RRT values. The area under thrombogenic conditions reduces by 16%-46% as the neck angle increases from 0o to 60o, depending on the hemodynamic variable under consideration. The effect of iliac angulation is present but less pronounced with 2.5%-7.5% change between the lower and the higher angle. The effect of sac asymmetry seems to be significant for OSI with a non-symmetrical configuration being hemodynamically favorable, which in the presence of an angulated neck is more pronounced for the OS outline. Favorable hemodynamic conditions develop inside the sac of idealized AAAs with increasing neck and iliac angles. Regarding the sac asymmetry parameter, asymmetrical configurations most often appear advantageous. Concerning the velocity profile the triplet (φ,θ,SA) may affect outcomes under certain conditions and thus should be taken into account when parametrizing the geometric characteristics of AAAs.

Earth pressure distribution on laterally loaded offshore monopiles

Unlike conventional pile foundations, a monopile is a large diameter open-ended steel tube driven into the seabed. Accurate quantification of the earth pressure distribution along a monopile due to lateral loads plays a pivotal role in the design of offshore wind turbines and remains a problem of great interest. This paper presents an attempt to address the problem by means of three-dimensional (3D) finite element modeling, with focus on the effect of pile slenderness on earth pressure distribution and the associated soil deformation mechanisms. The study shows that as pile diameter increases, the deformation mode of the pile will change from flexural to rotational deflection while the deformation pattern of the surrounding soil varies from being the wedge-type to a combination of the wedge-type and the rotation-type. The magnitude of either normal contact stress or shear stress at a pile section decreases with increasing pile diameter, but the distribution pattern of the normalized contact stress (either normal or shear stress) is nearly the same. The implications of these findings for engineering practice are two-fold: (a) Use of the p-y relationship established from field tests on piles of reduced scales in the design of large-diameter piles may still result in a potential risk of overestimating the lateral bearing capacity if the test pile diameter is not large; and (b) a unified factor independent of pile diameter can be introduced to average the contact stress across the pile section in the development of simplified methods.

An MHD Casson fluid flow past a porous stretching sheet with threshold Non-Fourier heat flux model

The present paper investigates the magnetohydrodynamics Casson fluid flow with porous medium. The Cu-water nanofluid is used to investigate further analytical results. Thermal radiation is considered along with the Cattaneo-Christov heat flux model and then solved analytically, then expresses the closed forms analytical solution in terms of two variables of hypergeometric function. The special form of Appell hypergeometric solutions are closed form of analytical solutions. The results of normalized shear stress at the wall and temperature profile, and rate of heat flux can be analyzed with suitable parameters, Viz., relaxation time parameter, Prandtl number, Radiation parameter, Magnetic parameter, and so on. The newness of the current work's novelty is to explain a solution to issues with stretching sheets on the basis of Appell hypergeometric form and also investigation takes place on a time relaxation parameter. The shear stress fηη0 is also calculated analytically. This problem has many industrial applications and engineering processes, namely glass-fiber production, extrusion of rubber sheets and so on. Finding that an increase in the thermal relaxation parameter and Prandtl number keeps the fluid temperature constant is the primary physical application.

Hydrodynamic effects of non-uniform feed spacer structures on energy loss and mass transfer in spiral wound module

To find a balance between feed flow rate and energy penalty, the hydrodynamic effects of non-uniform feed spacer structures on energy loss and mass transfer in spiral wound reverse osmosis (RO) module were numerically simulated by the CFD method through adopting dumbbell-shaped filament. The user-defined function (UDF) was employed to satisfy the permeability boundary conditions of membrane surfaces. The hydrodynamic effects of different filament diameter ratios (DR, d2/d1) as well as the spacer mesh angle α were studied. The simulation results showed that the spacer configuration greatly affected the energy loss and mass transfer in the spiral wound module. The pressure drop rate increased with increasing space mesh angle and a mesh angle between 60° and 120° was recommended for bearable pressure drop. The specific helicity was introduced to measure the vorticity transported with the flow. The negative region of specific helicity can be used to represent the wake size easily. The feed spacer with varied cross-section has the potential to reduce the specific energy consumption. When DR decreases from 1.0 to 0.45, the wake length becomes longer, and the pressure drop rate decreases significantly by about 58.1%. By increasing the Reynolds number from 50 to 200, the averaged wall shear stress increases by more than 5.6 times, and the averaged permeate water flux increases by 18.2%. Thus, the recommended value of feed flow Re was about 200. This detailed numerical study is of great significance to improve the understanding of concentration polarization and energy loss suppression by the optimized feed spacer configuration.

Stress Distributions in Brazed Single-Lap Joints Under Tensile Loading

The most common method for characterizing the strength of brazed joints is uniaxial tension testing of single lap joints (SLJs). Standard interpretations depend on the assumption that the average shear stress at failure is the key metric in determining joint strength. However, it is evident from the geometry that the stress distributions must be inhomogeneous with shear lag type stress concentrations at the ends of the overlap regions. Eccentric loading causes overlap rotation and bending stresses that amplify the stress concentrations and result in geometric nonlinearity. Unfortunately, details of the distributions of normal and shear stresses on the braze needed to understand failure have not been presented. Thus, finite element analysis was used to quantify these stress distributions using 2D elastic and elasto-plastic models of monolithic stainless steel SLJs. Bending stresses and normal and shear stresses acting on the braze were determined over a wide range of overlap ratios and applied stresses. For all conditions, stresses are highly concentrated in a narrow region at overlap ends with peak normal stresses exceeding peak shear stresses. Variations in peak stresses with applied stress and overlap ratio were found to fully explain experimental joint strength data. Common interpretations based on the average shear stress at failure are found to be incorrect. Implications for testing, interpretation, and joint design are discussed.

Study of biaxial stress in rectangular patch-reinforced composites with elastic and damage interface

A two-dimensional (2-D) shear-lag model with an elastic and damage interface was developed to investigate stress transfer in rectangular patch-reinforced composites subjected to uniaxial or biaxial loads. The semi-analytical solutions of bi-directional normal stress and interface shear stress of the composites were derived. The effect of Poisson's ratio of the substrate, aspect ratio, interface thickness and elastic modulus of the interface on the stress of the composites was investigated. The stress distribution solutions of the 2-D model agree well with the finite element (FE) results. It provides an effective model for solving the 2-D stress problem in rectangular patch-reinforced composites.

Shear stress control of vascular leaks and atheromas through Tie2 activation by VE‐PTP sequestration

Vascular endothelial protein tyrosine phosphatase (VE‐PTP) influences endothelial barrier function by regulating the activation of tyrosine kinase receptor Tie2. We determined whether this action is linked to the development of atherosclerosis by examining the influence of arterial shear stress on VE‐PTP, Tie2 activation, plasma leakage, and atherogenesis. We found that exposure to high average shear stress led to downstream polarization and endocytosis of VE‐PTP accompanied by Tie2 activation at cell junctions. In aortic regions with disturbed flow, VE‐PTP was not redistributed away from Tie2. Endothelial cells exposed to high shear stress had greater Tie2 activation and less macromolecular permeability than regions with disturbed flow. Deleting endothelial VE‐PTP in VE‐PTPiECKO mice increased Tie2 activation and reduced plasma leakage in atheroprone regions. ApoE−/− mice bred with VE‐PTPiECKO mice had less plasma leakage and fewer atheromas on a high‐fat diet. Pharmacologic inhibition of VE‐PTP by AKB‐9785 had similar anti‐atherogenic effects. Together, the findings identify VE‐PTP as a novel target for suppression of atherosclerosis.

A Dual DIC System for Analysis of Dynamic Mechanical Properties of Large Sandstone under Uniaxial Compression Load

In this paper, an experiment is carried out to acquire the dynamic mechanical properties of a simulated sandstone tunnel by a dual DIC system. The sandstone tunnel is simulated by large sandstone with a prefabricated hole in the center. The speckle size required by DIC system was evaluated, and the results showed that for large specimens a marker pen could be used to spot speckles and make sure that the diameters of speckle points in an image should be ranged from three to five pixels. The dual DIC system is composed of a low-speed camera and a high-speed camera. The low-speed camera is used to record the speckle patterns of the sandstone in one side during the whole process of compression load, and the high-speed camera is placed in the other side to record speckle patterns for 11.5 seconds before and after failure. It is realized that monitoring whole process of deformation and instantaneous failure in two directions is required. Measurement results are effectively analyzed. The results are shown as follows: At the initial stage of loading the sandstone is in an elastic stage without macroscopic cracks. With the increase in compression load the sandstone has several small stress releases and several obvious macroscopic cracks. In the final stage of loading, the distribution of normal stress and shear stress are almost the same, and cracks are subjected to the coupling effect of normal stress and shear stress. The two ends of the prefabricated hole perpendicular to the applied load direction are prone to cracks parallel to the applied load direction.

Pullout Behavior of Connections Using Self-Drilling Screws for Pultruded Fiber-Reinforced Polymer Composites in Construction

Self-drilling screws provide an efficient and cost-effective way of joining lightweight structural members. In this work, the performance of self-drilling screw connections for fiber-reinforced polymer (FRP) structural members is investigated, for use in joining panels or plates to square hollow sections (SHSs). To investigate the resistance to pullout loads, tensile tests were conducted on connection specimens consisting of an FRP plate joined to an FRP SHS at a right angle. The specimens were prepared in five configurations, with differences in pultrusion directions of the FRP plate, screw gauge size, and coarseness of the screw threads. The specimens having fibers oriented transversely in the FRP plate exhibited a flexural failure of the plate and the lowest connection strength. The specimens having fibers oriented longitudinally in the FRP plate failed by the screw being pulled out from the FRP SHS profiles; shearing out of the thread in the screw hole. An increase in screw gauge size and thread coarseness was found to be beneficial to the connection strength. Further analysis was carried out to estimate the initial stiffness and the connection strength, by finite-element and analytical modeling, respectively. In addition, these analyses are able to correlate the average shear stress at failure of the connection specimens to the screw gauge size, thread coarseness, and effective contact area of the screws.

Numerical simulation of vortex shedding from rectangular cylinders with different elongation ratios

RANS simulations are performed for flow past rectangular cylinders with different elongation ratios (L/D= 1, 2, 4, 6, 8, 10, 12, 14 and 16) at Re= 22 000 using the k-ω SST turbulence model. As L/D increases from 1 to 6, stepwise increase of Strouhal number (St) exists, whereas an almost linear variation of St with respect to L/D can be found (St= 0.1618*L/D) at L/D⩾ 8. In the flow, two small secondary vortices beneath the shear layers are identified and the trailing-edge secondary vortex presents opposite rotational direction comparing with the leading-edge main vortex. Analysis of the shear layer and vortex characteristics is carried out to correlate with the wall normal stress and shear stress on the rectangular cylinder surfaces. Further, four coupling modes between leading-edge vortex (L-vortex) and trailing-edge vortex (T-vortex) among cylinders with different L/D are observed, named L-Vortex Mode (i.e. L/D= 1–2), L-T-Vortex Mode (i.e. L/D= 4–8), T-L-Vortex Mode (i.e. L/D= 10–14), and T-Vortex Mode (i.e. L/D ⩾ 16). When L/D > 4, the convective velocity of the L- and T-vortex is not sensitive to the L/D.

The effect of building arrangement on the flow characteristics in meandering compound channels

Due to the fact that most of the cities and villages are built on the banks of the rivers, the hydraulic characteristics of water flow always undergo changes during floods, so it is necessary to study the interaction of the flood flows of meandering compound channel in these areas. In this paper, the effect of building arrangement on the flow characteristics in meandering compound channels was investigated by using laboratory models. For this purpose, a smooth floodplain (without building) and three different types of building arrangement on the floodplain including structural obstacles perpendicular and parallel to the floodplain flow and checkered structural obstacles have been used. The tests have been conducted at three relative depths of 0.29, 0.39 and 0.49 and the corresponding discharges. All experiments were performed under a quasi-uniform and fully developed flow condition. The measurement data were recorded at different sections along the meandering main channel. Stage-discharge curves, Manning's n, velocity distribution, boundary shear stress and Darcy-Weisbach friction factor are determined over 12 test runs. The results of this research show that the arrangement of buildings has a great effect on the longitudinal velocity of the main channel. At a relative depth of 0.49, in a meandering compound channel with the arrangement of structural obstacles perpendicular to the floodplain flow, the dimensionless longitudinal velocity of the main channel compared to the smooth floodplain increases by 113%, but with the arrangement of structural obstacles parallel to the floodplain flow, the dimensionless longitudinal velocity increases by 27%. Also, the building arrangement is effective in reducing the discharge capacity of the meandering compound channel, so that in a building density of 18.5%, structural obstacles perpendicular to the floodplain flow reduce the discharge capacity of the channel by 50% compared to the smooth floodplain. In the channel with structural obstacles arranged perpendicular to the floodplain flow, Manning's roughness coefficient increases sharply with increasing the relative depth, but in the channel with the structural obstacles parallel to the floodplain flow, Manning's roughness coefficient decreases with increasing the relative depth. In the channel with the arrangement of structural obstacles perpendicular to the floodplain flow, the bed shear stress of the main channel is higher than the other building arrangements, so that at the relative depth of 0.49, the average maximum bed shear stress in all sections increases by 42% compared to the smooth floodplain.

A Novel Yield Criterion for Nickel-Based Superalloys

Abstract With the significant evolution of modern gas turbine engines, selection of high-temperature resistant alloys in the hot section is known to be the fundamental solution to enhance the capabilities of these engines. In general, the high-temperature components are mainly comprised of polycrystalline, directionally solidified, and single crystal superalloys. Single crystal (SX) superalloys were developed in the 1980s to achieve high fatigue resistance and substantial creep rupture strength by eliminating grain boundaries. Directional solidification methods enabled the solidification arrangement of the materials to be comprised of columnar grains which are aligned parallel to the 〈001〉 direction. These casting types have been frequently used with nickel-based superalloys (NBSAs) to develop modern gas turbine blades. In this work, the yield behavior of generic SX and directionally solidified (DS) NBSAs is studied. By observing various SX and DS alloys, it was concluded with need for a novel criterion that can present anisotropic and tensile/compressive asymmetric yield surfaces. This novel criterion is comprised of the criterion proposed by Hill for anisotropic materials and the method developed by Drucker and Prager for alloys that have different tensile and compressive yield strengths. Additional terms to Hill's criterion are introduced to capture the coupling effect of normal stress and shear stress when the applied loads are not in the direction of principal axes of the material coordinate system for single crystal alloys. The parameters for the criterion are obtained from simple uniaxial tension and compression experiments. Results are compared with various well-established yield criterions. Additionally, the novel criterion is utilized to capture the effective stress and strain of multi-axial loading of turbine blades under nonisothermal conditions

Comparison of the Haemodynamic Performance of Various Treatment Options for Aorto-Iliac Occlusive Disease

Several surgical and endovascular techniques are used during the treatment of aorto-iliac occlusive disease. Aortobifemoral bypass (AoBFB) is the standard of care, but other options such as axillobifemoral (AxBFB) bypass, aorto-iliac kissing stents (KS), and covered endovascular reconstruction of aortic bifurcation (CERAB) are also available. This study aimed to perform a computational comparison of these four modalities to investigate their haemodynamic performance. Eight patient specific anatomies were analysed, with each of the abovementioned techniques used to treat two anatomies. The CT angiograms were segmented from the renal (or axillary) to common femoral arteries and the 3D geometries were exported. A commercial finite volume solver was implemented for numerical simulations. Outcomes that were assessed were pressure drop (ΔP) between the inlet and the outlet for every configuration and haemodynamic indices of Time Average Wall Shear Stress (TAWSS), Oscillatory Shear Index (OSI), and Relative Residence Time (RRT) as markers of a thrombogenic environment. The results indicate that maximum ΔP was observed at peak systole for all models, with values ranging between 12mmHg and 21mmHg for the AoBFB, 64mmHg and 96mmHg for the AxBFB, 31mmHg and 46mmHg for the KS, and 43mmHg and 46mmHg for the CERAB configuration. TAWSS, OSI, and RRT varied among different configurations, mostly presenting values well above thrombogenic thresholds. Regarding RRT, the percentage of total surface area presenting such values is 2.5%, 3.2%, 2%, and 4.3% for the AoBFB, AxBFB, KS, and CERAB configurations, respectively. Computational modelling indicates a favourable haemodynamic performance of AoBFB compared with the other configurations. This leads to a smaller pressure drop and sconsequently a higher pressure in the outlet of the conduit, which is the perfusion pressure of the limb. Notably, lower patency rates of the latter modalities cannot be explained based on haemodynamic indices.