High Stress Zone Research Articles

Stability analysis of composite plates under localized in-plane load

Stability characteristics of isotropic and composite plates subjected to partial or concentrated compressive edge loads are investigated here using a four-noded shear-flexible quadrilateral high-precision plate-bending element. A complete cubic polynomial shape function is used to interpolate the in-plane displacements for better accuracy in capturing the high-stress zone near the locally distributed edge load. The influences of location and distribution of in-plane edge compression on the buckling load of composite plates are studied. The nonlinear governing equations based on von Kármán's assumptions are solved by Newton–Raphson technique to get the hitherto unreported postbuckling equilibrium paths of partially loaded plates made of isotropic, symmetric, and unsymmetric laminates. Marguerre's shallow-shell theory is employed to study the effect of sinusoidal imperfection on the nonlinear behavior of composite plates under partial in-plane load.

Lithospheric gravitational instability beneath the Southeast Carpathians

The Southeast corner of the Carpathians, known as the Vrancea region, is characterised by a cluster of strong seismicity to depths of about 200 km. The peculiar features of this seismicity make it a region of high geophysical interest. In this study we calculate the seismic strain-rate tensors for the period 1967–2007, and describe the variation of strain-rate with depth. The observed results are compared with strain-rates predicted by numerical experiments. We explore a new dynamical model for this region based on the idea of viscous flow of the lithospheric mantle permitting the development of local continental mantle downwelling beneath Vrancea, due to a Rayleigh–Taylor instability that has developed since the cessation of subduction at 11 Ma. The model simulations use a Lagrangean frame 3D finite-element algorithm solving the equations of conservation of mass and momentum for a spatially varying viscous creeping flow. The finite deformation calculations of the gravitational instability of the continental lithosphere demonstrate that the Rayleigh–Taylor mechanism can explain the present distribution of deformation within the downwelling lithosphere, both in terms of stress localisation and amplitude of strain-rates. The spatial extent of the high stress zone that corresponds to the seismically active zone is realistically represented when we assume that viscosity decreases by at least an order of magnitude across the lithosphere. The mantle downwelling is balanced by lithospheric thinning in an adjacent area which would correspond to the Transylvanian Basin. Crustal thickening is predicted above the downwelling structure and thinning beneath the basin.

Simulation of the relationship between roadway dynamic destruction and hypocenter parameters

Abstract Many factors can induce rock burst. Shock energy and shock distance are two key factors affecting rock burst. The 32101 roadway of the Xingcun coal mine, which has a tendency for rock burst, was used as an example. The dynamic module of Itasca's FLAC (Fast Lagrangian Analysis of Continua) 2D explicit finite-difference software was used to simulate the roadway's destruction. The vibration velocity and displacements of the rock surrounding the roadway were modeled for different shock energies and hypocenter distances. The simulation results indicate that the vibration velocity and displacement of rock surrounding the roadway have a quadratic relationship to the shock energy and a power law relationship to the distance of the hypocenter from the roadway. A dynamic view of the process was obtained from a series of “snap-shots” collected at 100 different time steps. This shows an isolating “river” is first formed at the hypocenter. The region above the “river” is a low stress zone while below the “river” a high stress zone exists. This high stress zone surrounds the ribs of the roadway in a “double ear” pattern. Continuous and repeated action of the high stress in the “double ear” shaped zone destroys the roadway.

ＣＯ２炭層固定化技術開発予備実験の成果

The feasibility of extracting gas from the coal seam while storing carbon dioxide underground in Japan was evaluated. A CO2-ECBM project had begun near the town of Yubari on the island of Hokkaido in northern Japan. The primary coal seam of interest was 5-6m thick Yubari coal seam located at the depth of 900m. A micro-pilot and two multi-wells CO2 injection tests, involving an injection and production wells, were carried out in the period between May 2004 and October 2007. There were a variety of tests conducted in the injection well, including an initial water-injection falloff test and series of CO2 injection and falloff tests. Although gas production was obviously enhanced by CO2 njection, water production was not clearly affected by CO2 injection. Several injection tests suggested that injectivity of CO2 into the virgin coal seam saturated with water was eventually increased as the water saturation near the injector was decreased with the injected CO2 . It was believed that low injectivity of CO2 was caused by the reduction in permeability that swelling in coal matrix induced. So N2 flooding test was performed in 2006 to evaluate the effectiveness of N2 flooding on improving well injectivity. The N2 flooding test showed that daily CO2 injection rate was boosted, but only temporary. On the top of that, the permeability might not return after CO2 and N2 were repeatedly injected. It is likely that the matrix swelling might create a high stress zone near to the injection well.

The relationship between rainfall and human density and its implications for future water stress in Sub-Saharan Africa

This paper estimates the relationship between average rainfall and population density in Sub-Saharan Africa in order to assess the consequences of climate and demographic changes in terms of future water stress in that region. Geographic Information System (GIS) data on density and rainfall and climate change scenarios are combined in order to identify areas which will be subject to increased pressures stemming from excessive population, given their precipitation levels. We first describe the empirical relationship existing between average yearly rainfall and density over sub-Saharan Africa. The limit of 900 mm of annual rainfall appears to define the threshold below which water constitutes a binding constraint to higher densities. Above that threshold, density and rainfall are not spatially correlated. In a second stage, we identify areas subject to water stress. In our framework, those are defined as zones belonging to the right end of the distribution of densities conditional on average rainfall. In a last step, localized population projections and changes in rainfall predicted by two mainstream climate change scenarios are utilized to assess the respective impacts of those two factors on the changes in extent and distribution of high-stress zones over the continent between 2000 and 2050. If population growth follows projected trends, density increases across the continent should lead to a significant increase in the extent of such zones, especially around the Sahel belt and in Eastern Africa. The impact of changes in rainfall is more difficult to assess, because climate models differ locally as regards projections of yearly rainfall, especially in intermediate zones such as the Sahel. If, according to the predictions of most climate models, the Sahel were to experience average rainfall increases, these would ease, though not offset totally, the pressure stemming from demographic growth in that region. In contrast, in most of Eastern Africa, predicted drops in average rainfall would work in the same direction as demographic changes to increase the pressure on significant parts of the territory. In Southern Africa, demographic stagnation is likely to mitigate significantly the impact of climate change.

Metallurgical studies on a failed EN 19 steel shear pin

The presence of inclusion at or close to the surface of components are detrimental for their performance, especially when they are subjected to fatigue loading. Role of inclusion in fatigue performance of a shear pin, fabricated out of EN 19 steel has been studied. The shear pin was used in a chemical mixer as an overload protection, attached to agitators, rotating at different revolution per minutes (rpm) depending on the power transmitted to it through gear system. The shear pin located in the power transmission system had a notch throughout the periphery and fractured incidentally at notch, after use for a cumulative period of approximately 100 h. Extensive metallurgical investigations revealed that inclusions, present in the steel and located near the notch, a region of high stress zone, caused fatigue crack to initiate. Once the crack was initiated under fatigue, de-bonding and fragmentation of non-metallic inclusion facilitated its propagation. This paper highlights the details of investigation carried out on the fractured shear pin and established the deleterious effect of inclusion in steel, especially for fatigue performance.

Evaluation of Cracked Beam-to-Column Connection from Brittle Failure Using Finite Element Method

The bolted end-plate composite beam-CCSHRC column connection was validated to be ductile and offered an alternative to pre-Northridge connection. This study aims at the beam lower flange fracture in the connection test, and applies the J-integral criteria to examine the connection’s nonlinear fracture behavior. Advanced 3-D connection models containing initial crack in the high stress zone at lower flange are created, and the J values at the crack tip are calculated with considering the influences of certain parameters. The results demonstrate that the J values are strongly affected by the initial crack length and interstory drift. For 0.94, 1.35, 1.86 and 2.50 mm long crack, the J values sharply increase during loading history. The crack with a length of 2.50 mm propagates at a 66 mm drift, while the 1.35 mm long crack grows at a 120 mm drift. For 0.94 or 0.61 mm long crack, it keeps stable without growing upon loading. Besides, the J values exhibit a weak sensitivity to the beam concrete strength and tensile reinforcement ratio for beam. Under the same drift, the J-integral increases by about 3.5% when concrete strength changes from 15 to 24 MPa, and the J values at 0.6% tensile reinforcement ratio for beam are 1.5% larger than those at 0.3% or 1% reinforcement ratio.

Comparison of Stress Zones in Finite Element Models of Deformed Bovine Claw Capsules

Pathological claw formations occur subsequent to irregular or prolonged claw trimming periods and as a result of improper flooring. Clinical experience and material testing finds horn of minor quality to be associated with the malformations. Finite element models (FEM) of a flat claw (FC), a contracted claw (CC), and a laminitic claw (LC) were designed from native claw specimens to combine material properties and altered claw geometry for stress analysis. The FEM were created by digitizing the typically deformed exungulated claw capsule by means of computed tomography or digital photography. The derived geometry data were meshed with finite elements and the material properties were attributed. Loading was performed via vertical load vectors according to the suspensory and support apparatus of the bovine digit. All FEM were loaded on soft floors. Loading of the FEM of the FC with 756 N exhibited maximum stress values of 3.32 MPa in the dorsal wall, that of the CC exhibited comparably lower stress of 1.33 MPa in the distal abaxial wall, and the model of the LC showed maximum stress of 4.51 MPa in the region of the dorsal border, all at the same loading. The solar surfaces and the corresponding imprints showed stress concentrations in the palmar aspect of the bulb in the FC, a highly stressed bearing margin of the abaxial wall in the CC, and a diffusely stressed sole and bulb in the LC in contrast to the sound claw models. The FEM of the selected pathological claw forms (FC, CC, LC) calculated high stress zones exactly at locations in the claw wall and sole where clinical experts expect the typical claw lesions for these pathologies. These results were obtained simply by exchanging the outer form of the claw capsules; the method of loading and type of flooring for these pathological models were equivalent to those of the sound FEM. It is highly possible that the stress zones derived from these calculations represent corium compression in reality, and these data support the pathophysiological theory that claw lesions may arise as a consequence thereof.

Numerical fatigue analysis of the turbine components under low cycle fatigue (LCF) conditions

This paper presents results of the stress and fatigue analysis of the turbine disc and blade. A non-linear finite element method was utilized to determine the stress state of the turbine components under operational condition. A critical, high stress zones were found at the several region of turbine. Results obtained from the preliminary static calculation were next used into total fatigue life (S-N) analysis performed for the load time history equivalents to 1-hours work of engine under operating flight. In this analysis, the number of hours to the total damage of the critical components of turbine subjected to low cycle fatigue was estimated.

Stress and Fatigue Analysis of Modified Wing-Fuselage Connector for the Agricultural Aircraft

This paper presents numerical stress and fatigue analyses of a main wing-fuselage connector for agricultural aircraft. A nonlinear finite-element method was utilized to determine the stress states of both standard and modified connectors under operating conditions. High-stress zones were found at the region of the standard wing lug, where the failure occurred. Obtained results were next put into total fatigue life (S-N) and crack initiation (e-N) analyses performed for load time history equivalent to 10 min operating flight. In these analyses, the number of flight hours to the first fatigue crack and also to total damage of the wing lug were estimated. Moreover, the influence of many factors such as overload, corrosion, heat treatment, and surface treatment on the fatigue lives of the standard and modified connectors were analyzed.

Failure analysis of turbine disc of an aero engine

This paper presents the failure analysis of the turbine disc of an aero engine, installed in a certain type of aircraft. From the visual examination of the fractured surface, it was possible to observe beach marks, typical of fatigue failure. A non-linear finite element method was utilized to determine the stress state of the disc/blade segment under operating conditions. High stress zones were found at the region of the lower fir-tree slot, where the failure occurred. A computation were also performed with excessive rotational speed. Attention of this study is devoted to the mechanisms of damage of the turbine disc and also the critical high stress areas.

Failure analysis of the wing-fuselage connector of an agricultural aircraft

This paper presents an analysis of failure of the wing-fuselage connector for the agricultural aircraft. From the visual examination of the fractured surface, it was possible to observe beach marks, typical for fatigue failure. Careful observation showed that the crack origin surface was covered by corrosion products, therefore the failure had a character of fatigue combined with corrosion. A nonlinear finite element method was utilized to determine the stress state of the connector under operating condition. High stress zones were found at the region of the wing lug, where the failure occurred. Obtained results were next put into total fatigue life (S–N) and crack initiation ( ε–N) analyses performed for the load time history equivalent to 10-minute operating flight. In these analyses, the number of flight hours to the first fatigue crack and also to total damage of the wing lug were estimated. Moreover the influence of many factors such as: heat treatment, surface treatment, corrosion and overload on the fatigue life of the connector were analyzed.

炭素繊維の引張応力による電気抵抗の変化

To develop high temperature sensor, the change in an electrical resistivity of carbon fiber according to the stress increasing was measured as basic research. It was confirmed that the stress in the low stress zone decreased electrical resistivity, whereas the excess stress increased the electrical resistivity in the high stress zone.

Stress analysis of turbine components under spin rig thermomechanical condition

Abstract This paper presents the stress analysis of a second stage turbine disc, subjected to spin rig test. To solve the problem, the finite element analysis of complex geometrical model of the disc/blade segment with much physical nonlinearity such as contact and plasticity was carried out. The adequate mechanical and thermal conditions for the spin rig test were next defined to determine the stress state of the disc/blade segment. High stress zones were found at the regions of the turbine where the first fatigue cracks are expected to appear. The results of this study are useful during the laboratory spin rig test of turbine. The zones of maximum stress indicated in this analysis will be in detail inspected under laboratory crack initiation and crack growth tests of turbine. For better understanding the phenomena occurring in spin rig test of turbine, the test details were also described.

STRESS ANALYSIS OF TURBINE COMPONENTS UNDER SPIN RIG THERMOMECHANICAL CONDITION

This paper presents the stress analysis of a second stage turbine disc, subjected to spin rig test. To solve the problem, the finite element analysis of complex geometrical model of the disc/blade segment with much physical nonlinearity such as contact and plasticity was carried out. The adequate mechanical and thermal conditions for the spin rig test were next defined to determine the stress state of the disc/blade segment. High stress zones were found at the regions of the turbine where the first fatigue cracks are expected to appear. The results of this study are useful during the laboratory spin rig test of turbine. The zones of maximum stress indicated in this analysis will be in detail inspected under laboratory crack initiation and crack growth tests of turbine. For better understanding the phenomena occurring in spin rig test of turbine, the test details were also described.

Finite element simulation of the electromagnetic piercing of sheet metal

In the paper, the sheet electromagnetic piercing process is analyzed from a dynamic view. 3D non-linear simulation is undertaken by means of a dynamic explicit finite element method. Patterns of stress distribution, deformation, kinetic energy, and equivalent rigid velocity have been obtained. According to the different characteristics of deformation and using the von Mises stress distribution condition, the forming of the workpiece can be divided into four phases. In phase I, stress extends to the center of the workpiece gradually, showing a distinct circular wave. In phase II, the drawing of the workpiece increases gradually and the workpiece zone near to the die blade becomes highly stressed and high radial elongation occurs. In phase III, rupture occurs. The high stress zone changes to the center of the waste sheet with little displacement, but there is great bending deformation. In phase IV, inertial emission of waste sheet starts and bending deformation of the waste sheet continues to extend to its center. It is established that the method has substantial feasibility. The present work affords a sound theoretical basis for further work.

Comparative analysis of limit displacements for tunnels at the unlined and primary support stages

This paper presents an investigation of the development of excavation damaged zones (EDZs) around a rectangular coal roadway under mining-induced pressure in a longwall mining process. Field stress monitoring at a coal mine in Shaanxi Province, China was carried out to obtain stress distribution induced by mining in the surrounding rock mass. During longwall mining, a high-stress zone with a limited scope is distributed in front of longwall face, and a relatively low-stress increment occurs near the roadway wall due to the failure of rock mass. A borehole camera was employed to clearly observe the development state of cracks in the damaged zones around the roadway to capture the characteristics of the EDZ. To investigate the rock failure process and development patterns of the EDZ under mining-induced loading conditions, three numerical simulation cases considering the heterogeneity of rock were conducted with a proposed loading mode similar to the mining-induced pressure. The results of the simulations show that the complexity of EDZ development under the proposed loading conditions involves tensile and shear failures, the development of remote cracks, and the effect of roadway geometry. The development patterns of the EDZ around the rectangular roadway show agreement with field observations.

Effect of LVAD outflow conduit insertion angle on flow through the native aorta

Background and aim: The goal of this study was to evaluate the effect of surgical anastomosis configuration of the aortic outflow conduit (AOC) from a continuous flow left ventricular assist device (LVAD) on the flow fields in the aorta using CFD simulations. The geometry of the surgical integration of the LVAD is an important factor in the flow pattern that develops both in series (aortic valve closed, all flow through LVAD) and in parallel (heart pumping in addition to LVAD).Methods: CFD models of the AOC junctions simulate geometry as cylindrical tubes that intersect at angles ranging from 30° to 90°. Velocity fields are computed over a range of cardiac output for both series and parallel flow.Results: Our results demonstrate that the flow patterns are significantly affected by the angle of insertion of the AOC into the native aorta, both during series and parallel flow conditions. Zones of flow recirculation and high shear stress on the aortic wall can be observed at the highest angle, gradually decreasing in size until disappearing at the lowest angle of 30°. The highest velocity and shear stress values were associated with series flow.Conclusions: The results suggest that connecting the LVAD outflow conduit to the proximal aorta at a shallower angle produces fewer secondary flow patterns in the native cardiovascular system.

Adaptive Finite-element Analysis of Plastic Deformation of Plates under Projectile Impact

This paper deals with the finite-element analysis of plastic deformation of plates during normal impact of projectile on plates, The finite element method implemented here is based on the flow formulation of plasticity. During projectile impact the geometrical configuration of domain is progressively altered that generally causes distortion of mesh. It affects the accuracy of finite-element solution, Hence, a posteriori error estimation for the computed finite-element solution has been incorporated to capture the zones of high stress and strain gradients. The h-refinement of the mesh is carried out over such domain to limit the solution error, Two projectile impact problems on a circular aluminium plate-one by a blunt-end projectile and another by a hemi-spherical-headed projectile-are analysed to illustrate the proposed method.

PIV를 이용한 인공심장용 폴리우레탄 인공판막 하류의 유동 측정 : 맥동유동실험

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.