scholarly journals Study of Flow-Assisted Corrosion of AZ91D Magnesium Alloy in Loop System Based on Array Electrode Technology

2015 ◽  
Vol 2015 ◽  
pp. 1-8
Author(s):  
Hualiang Huang ◽  
Guoan Zhang ◽  
Jiakuan Yang ◽  
Zhiquan Pan ◽  
Xingpeng Guo
Keyword(s):  
Shear Stress ◽  
Magnesium Alloy ◽  
Corrosion Rate ◽  
Flow Velocity ◽  
Maximum Flow ◽  
Outer Wall ◽  
Loop System ◽  
Dynamics Simulation ◽  
Az91d Magnesium Alloy ◽  
Array Electrode

A loop system was used to investigate flow-assisted corrosion (FAC) of AZ91D magnesium alloy at an elbow based on array electrode technology by potentiodynamic polarization, computational fluid dynamics, simulation and surface analysis. The experimental results demonstrate the fluid hydrodynamics plays a significant role in the FAC of AZ91D magnesium alloy. The corrosion rate increases from the outer wall to the inner wall of the elbow, with the higher corrosion rate corresponding to the higher flow velocity and larger shear stress at the elbow. The maximum corrosion rate appears at the innermost wall of the elbow, the location with the maximum flow velocity and shear stress.

Study on Static Shear-Rheologic Characteristics of Semi-Solid AZ91D Magnesium Alloy by Reheating

2006 ◽  
Vol 116-117 ◽  
pp. 738-741
Author(s):  
Ze Sheng Ji ◽  
Mao Liang Hu ◽  
Xiao Ping Zheng
Keyword(s):  
Shear Stress ◽  
Magnesium Alloy ◽  
Critical Shear Stress ◽  
Critical Value ◽  
Holding Time ◽  
Az91d Magnesium Alloy ◽  
Coarse Grains ◽  
Small Grains ◽  
Semi Solid ◽  
Static Shear

Static shear-rheology for self-made semi-solid AZ91D magnesium alloy slurry was studied by using the tester and a universal electronic machine. Shear-stress along with cylindrical surface in the sample was produced by using the tester and then shear-rheologic deformation happened. It showed that on the condition of the same loading, the longer the loading time and holding time were, the larger the deforming rate was. When the holding time attained a certain value, small grains acquired enough energy to grow up or amalgamate with prolonging the holding time and coarse grains started to melt from intergranular or grain boundaries, but the critical shear-stress kept a constant. The sample didn’t flow but appeared to instantaneous shear-strains with starting to load. When the loading exceeded the critical value, the sample started to flow and had the phenomena of elastic after-working, elastic before-working and remained deformation. The rheologic characteristics of semi-solid AZ91D magnesium alloy were expressed by the five element mechanical model: H1—(N1/H2)—(N2/S).

scholarly journals Modelling the Wave Overtopping Flow over the Crest and the Landward Slope of Grass-Covered Flood Defences

2020 ◽  
Vol 8 (7) ◽  
pp. 489
Author(s):  
Vera M. van Bergeijk ◽  
Jord J. Warmink ◽  
Suzanne J. M. H. Hulscher
Keyword(s):  
Shear Stress ◽  
Numerical Model ◽  
Flow Velocity ◽  
Normal Stress ◽  
High Pressures ◽  
Maximum Shear Stress ◽  
Maximum Flow ◽  
Maximum Pressure ◽  
Grass Cover ◽  
Wave Overtopping

The wave overtopping flow can exert high hydraulic loads on the grass cover of dikes leading to failure of the cover layer on the crest and the landward slope. Hydraulic variables such as the near bed velocity, pressure, shear stress and normal stress are important to describe the forces that may lead to cover erosion. This paper presents a numerical model in the open source software OpenFOAM® to simulate the overtopping flow on the grass-covered crest and slope of individual overtopping waves for a range of landward slope angles. The model provides insights on how the hydraulic forces change along the profile and how irregularities in the profile affect these forces. The effect of irregularities in the grass cover on the overtopping flow are captured in the Nikuradse roughness height calibrated in this study. The model was validated with two datasets of overtopping tests on existing grass-covered dikes in the Netherlands. The model results show good agreement with measurements of the flow velocity in the top layer of the wave, as well as the near bed velocity. The model application shows that the pressure, shear stress and normal stress are maximal at the wave front. High pressures occur at geometrical transitions such as the start and end of the dike crest and at the inner toe. The shear stress is maximal on the lower slope, and the normal stress is maximal halfway of the slope, making these locations vulnerable to cover failure due to high loads. The exact location of the maximum forces depends on the overtopping volume. Furthermore, the model shows that the maximum pressure and maximum normal stress are largely affected by the steepness of the landward slope, but the slope steepness only has a small effect on the maximum flow velocity and maximum shear stress compared to the overtopping volume. This new numerical model is a useful tool to determine the hydraulic forces along the profile to find vulnerable points for cover failure and improve the design of grass-covered flood defences.

Thixotropic Behavior of Semi-Solid Magnesium Alloy

2006 ◽  
Vol 116-117 ◽  
pp. 648-651 ◽  
Author(s):  
Hsueh I Chen ◽  
Jyh Chen Chen
Keyword(s):  
Shear Stress ◽  
High Temperature ◽  
Magnesium Alloy ◽  
Shear Rate ◽  
Experiment Data ◽  
Az91d Magnesium Alloy ◽  
Thixotropic Behavior ◽  
Semi Solid ◽  
Rising Time ◽  
Shear Thinning Fluid

By a high-temperature Couette type viscometer, we studied the thixotropic behavior of the semi-solid AZ91D magnesium alloy slurry. According to different variable conditions, we could measure the change of the shear stress. The results showed that the shear stress of semi-solid AZ91D magnesium alloy slurry increased at starting shearing, and the shear stress fell down at the maintained shear rate shearing. In our experiment data, we found that the semi-solid AZ91D magnesium alloy slurry had the behavior of shear thinning fluid. As the maximum shear rate increased, the measured shear stress increased at a dissimilar level. When the rising time was shorter, the increasing range of shear stress was larger. As the shearing time of the maintained shear rate increased, the falling down degree of the shear stress increased and it can be presented as a function of shearing time, such as: e 0.0159t min 11331 τ = − . At the same shear rate, the area of hysteresis loop was bigger and the thixotropic behavior was more obvious.

Comparative Analyses of Blood Flow Through Mechanical Trileaflet and Bileaflet Aortic Valves

2021 ◽  
Author(s):  
Marek Pawlikowski ◽  
Anna Nieroda
Keyword(s):  
Blood Flow ◽  
Shear Stress ◽  
Flow Velocity ◽  
Circulatory System ◽  
Maximum Flow ◽  
Von Mises Stress ◽  
Effective Orifice Area ◽  
Aortic Valves ◽  
Orifice Area ◽  
Flow Through

Abstract The paper describes one of many issues concerning the human circulatory system. The simulation of blood flow through an artificial aortic heart valve using the finite element method (FEM) is the main subject of the paper. The studies aim to verify the performance of mechanical aortic valves of two types, i.e. bileaflet (BIL) and trileaflet (TRI) valves. The blood was modelled as Newtonian and non-Newtonian. Although the design of our TRI valve is preliminary and needs to be optimised, our results highlight some advances of such a valve geometry. This is manifested mainly by a central blood jet, contributing to more physiological blood flow and decreasing the risk of haemolysis. The central flow minimises the risk of leaflet dislocation. In addition, lower stresses extend the durability of the valve. However, the TRI valve geometry has also disadvantages, for instance, the occurrence of small peripheral streams or relatively low effective orifice area. The valves' performance was assessed by means of the reduced stress in the valves, the shear stress in the aortic wall, flow velocity field, and the effective orifice area. The maximum von Mises stress for the BIL valve leaflets is 0.3 MPa, and for the TRI valve: 0.06 MPa. The maximum flow velocity for the BIL valve is 4.52 m/s for 40° and for the TRI valve is 5.74 m/s. Higher shear stress is present in the BIL (151.5 Pa) than for the TRI valve (49.64 Pa).

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