WorldWideScience

Sample records for hydraulically driven crack

  1. Elasticity-Driven Backflow of Fluid-Driven Cracks

    Science.gov (United States)

    Lai, Ching-Yao; Zheng, Zhong; Dressaire, Emilie; Ramon, Guy; Huppert, Herbert E.; Stone, Howard A.

    2016-11-01

    Fluid-driven cracks are generated by the injection of pressurized fluid into an elastic medium. Once the injection pressure is released, the crack closes up due to elasticity and the fluid in the crack drains out of the crack through an outlet, which we refer to as backflow. We experimentally study the effects of crack size, elasticity of the matrix, and fluid viscosity on the backflow dynamics. During backflow, the volume of liquid remaining in the crack as a function of time exhibits a transition from a fast decay at early times to a power law behavior at late times. Our results at late times can be explained by scaling arguments balancing elastic and viscous stresses in the crack. This work may relate to the environmental issue of flowback in hydraulic fracturing. This work is supported by National Science Foundation via Grant CBET-1509347 and partially supported by Andlinger Center for Energy and the Environment at Princeton University.

  2. Gravity-Driven Hydraulic Fractures

    Science.gov (United States)

    Germanovich, L. N.; Garagash, D.; Murdoch, L. C.; Robinowitz, M.

    2014-12-01

    This study is motived by a new method for disposing of nuclear waste by injecting it as a dense slurry into a hydraulic fracture that grows downward to great enough depth to permanently isolate the waste. Disposing of nuclear waste using gravity-driven hydraulic fractures is mechanically similar to the upward growth of dikes filled with low density magma. A fundamental question in both applications is how the injected fluid controls the propagation dynamics and fracture geometry (depth and breadth) in three dimensions. Analog experiments in gelatin [e.g., Heimpel and Olson, 1994; Taisne and Tait, 2009] show that fracture breadth (the short horizontal dimension) remains nearly stationary when the process in the fracture "head" (where breadth is controlled) is dominated by solid toughness, whereas viscous fluid dissipation is dominant in the fracture tail. We model propagation of the resulting gravity-driven (buoyant or sinking), finger-like fracture of stationary breadth with slowly varying opening along the crack length. The elastic response to fluid loading in a horizontal cross-section is local and can be treated similar to the classical Perkins-Kern-Nordgren (PKN) model of hydraulic fracturing. The propagation condition for a finger-like crack is based on balancing the global energy release rate due to a unit crack extension with the rock fracture toughness. It allows us to relate the net fluid pressure at the tip to the fracture breadth and rock toughness. Unlike the PKN fracture, where breadth is known a priori, the final breadth of a finger-like fracture is a result of processes in the fracture head. Because the head is much more open than the tail, viscous pressure drop in the head can be neglected leading to a 3D analog of Weertman's hydrostatic pulse. This requires relaxing the local elasticity assumption of the PKN model in the fracture head. As a result, we resolve the breadth, and then match the viscosity-dominated tail with the 3-D, toughness

  3. Investigating Reaction-Driven Cracking

    Science.gov (United States)

    Kelemen, P. B.; Hirth, G.; Savage, H. M.

    2013-12-01

    Many metamorphic reactions lead to large volume changes, and potentially to reaction-driven cracking [1,2]. Large-scale hydration of mantle peridotite to produce serpentine or talc is invoked to explain the rheology of plate boundaries, the nature of earthquakes, and the seismic properties of slow-spread ocean crust and the 'mantle wedge' above subduction zones. Carbonation of peridotite may be an important sink in the global carbon cycle. Zones of 100% magnesite + quartz replacing peridotite, up to 200 m thick, formed where oceanic mantle was thrust over carbonate-bearing metasediments in Oman. Talc + carbonate is an important component of the matrix in subduction mélanges at Santa Catalina Island , California, and the Sanbagawa metamorphic belt, Japan. Engineered systems to emulate natural mineral carbonation could provide relatively inexpensive CO2 capture and storage [3]. More generally, engineered reaction-driven cracking could supplement or replace hydraulic fracture in geothermal systems, solution mining, and extraction of tight oil and gas. The controls on reaction-driven cracking are poorly understood. Hydration and carbonation reactions can be self-limiting, since they potentially reduce permeability and armor reactive surfaces [4]. Also, in some cases, hydration or carbonation may take place at constant volume. Small changes in volume due to precipitation of solid products increases stress, destabilizing solid reactants, until precipitation and dissolution rates become equal at a steady state stress [5]. In a third case, volume change due to precipitation of solid products causes brittle failure. This has been invoked on qualitative grounds to explain, e.g., complete serpentinization of mantle peridotite [6]. Below ~ 300°C, the available potential energy for hydration and carbonation of olivine could produce stresses of 100's of MPa [2], sufficient to fracture rocks to 10 km depth or more, causing brittle failure below the steady state stress required

  4. Phenomenon of methane driven caused by hydraulic fracturing in methane-bearing coal seams

    Institute of Scientific and Technical Information of China (English)

    Huang Bingxiang; Cheng Qingying; Chen Shuliang

    2016-01-01

    The methane concentration of the return current will always be enhanced to a certain degree when hydraulic fracturing with bedding drilling is implemented to a gassy coal seam in an underground coal mine. The methane in coal seam is driven out by hydraulic fracturing. Thus, the phenomenon is named as methane driven effect of hydraulic fracturing. After deep-hole hydraulic fracturing at the tunneling face of the gassy coal seam, the coal methane content exhibits a‘low-high-low”distribution along exca-vation direction in the following advancing process, verifying the existence of methane driven caused by hydraulic fracturing in methane-bearing coal seam. Hydraulic fracturing causes the change of pore-water and methane pressure in surrounding coal. The uneven distribution of the pore pressure forms a pore pressure gradient. The free methane migrates from the position of high pore (methane) pressure to the position of low pore (methane) pressure. The methane pressure gradient is the fundamental driving force for methane-driven coal seam hydraulic fracturing. The uneven hydraulic crack propagation and the effect of time (as some processes need time to complete and are not completed instantaneously) will result in uneven methane driven. Therefore, an even hydraulic fracturing technique should be used to avoid the negative effects of methane driven; on the other hand, by taking fully advantage of methane driven, two technologies are presented.

  5. Analytic crack solutions for tilt fields around hydraulic fractures

    Energy Technology Data Exchange (ETDEWEB)

    Warpinski, N.R.

    2000-01-05

    The recent development of downhole tiltmeter arrays for monitoring hydraulic fractures has provided new information on fracture growth and geometry. These downhole arrays offer the significant advantages of being close to the fracture (large signal) and being unaffected by the free surface. As with surface tiltmeter data, analysis of these measurements requires the inversion of a crack or dislocation model. To supplement the dislocation models of Davis [1983], Okada [1992] and others, this work has extended several elastic crack solutions to provide tilt calculations. The solutions include constant-pressure 2D, penny-shaped, and 3D-elliptic cracks and a 2D-variable-pressure crack. Equations are developed for an arbitrary inclined fracture in an infinite elastic space. Effects of fracture height, fracture length, fracture dip, fracture azimuth, fracture width and monitoring distance on the tilt distribution are given, as well as comparisons with the dislocation model. The results show that the tilt measurements are very sensitive to the fracture dimensions, but also that it is difficult to separate the competing effects of the various parameters.

  6. Modeling of Propagation of Interacting Cracks Under Hydraulic Pressure Gradient

    Energy Technology Data Exchange (ETDEWEB)

    Huang, Hai [Idaho National Laboratory; Mattson, Earl Douglas [Idaho National Laboratory; Podgorney, Robert Karl [Idaho National Laboratory

    2015-04-01

    A robust and reliable numerical model for fracture initiation and propagation, which includes the interactions among propagating fractures and the coupling between deformation, fracturing and fluid flow in fracture apertures and in the permeable rock matrix, would be an important tool for developing a better understanding of fracturing behaviors of crystalline brittle rocks driven by thermal and (or) hydraulic pressure gradients. In this paper, we present a physics-based hydraulic fracturing simulator based on coupling a quasi-static discrete element model (DEM) for deformation and fracturing with conjugate lattice network flow model for fluid flow in both fractures and porous matrix. Fracturing is represented explicitly by removing broken bonds from the network to represent microcracks. Initiation of new microfractures and growth and coalescence of the microcracks leads to the formation of macroscopic fractures when external and/or internal loads are applied. The coupled DEM-network flow model reproduces realistic growth pattern of hydraulic fractures. In particular, simulation results of perforated horizontal wellbore clearly demonstrate that elastic interactions among multiple propagating fractures, fluid viscosity, strong coupling between fluid pressure fluctuations within fractures and fracturing, and lower length scale heterogeneities, collectively lead to complicated fracturing patterns.

  7. Impacts of bedding directions of shale gas reservoirs on hydraulically induced crack propagation

    Directory of Open Access Journals (Sweden)

    Keming Sun

    2016-03-01

    Full Text Available Shale gas reservoirs are different from conventional ones in terms of their bedding architectures, so their hydraulic fracturing rules are somewhat different. In this paper, shale hydraulic fracturing tests were carried out by using the triaxial hydraulic fracturing test system to identify the effects of natural bedding directions on the crack propagation in the process of hydraulic fracturing. Then, the fracture initiation criterion of hydraulic fracturing was prepared using the extended finite element method. On this basis, a 3D hydraulic fracturing computation model was established for shale gas reservoirs. And finally, a series of studies were performed about the effects of bedding directions on the crack propagation created by hydraulic fracturing in shale reservoirs. It is shown that the propagation rules of hydraulically induced fractures in shale gas reservoirs are jointly controlled by the in-situ stress and the bedding plane architecture and strength, with the bedding direction as the main factor controlling the crack propagation directions. If the normal tensile stress of bedding surface reaches its tensile strength after the fracturing, cracks will propagate along the bedding direction, and otherwise vertical to the minimum in-situ stress direction. With the propagating of cracks along bedding surfaces, the included angle between the bedding normal direction and the minimum in-situ stress direction increases, the fracture initiation and propagation pressures increase and the crack areas decrease. Generally, cracks propagate in the form of non-plane ellipsoids. With the injection of fracturing fluids, crack areas and total formation filtration increase and crack propagation velocity decreases. The test results agree well with the calculated crack propagation rules, which demonstrate the validity of the above-mentioned model.

  8. Hydraulically Driven Grips For Hot Tensile Specimens

    Science.gov (United States)

    Bird, R. Keith; Johnson, George W.

    1994-01-01

    Pair of grips for tensile and compressive test specimens operate at temperatures up to 1,500 degrees F. Grips include wedges holding specimen inside furnace, where heated to uniform temperature. Hydraulic pistons drive wedges, causing them to exert clamping force. Hydraulic pistons and hydraulic fluid remain outside furnace, at room temperature. Cooling water flows through parts of grips to reduce heat transferred to external components. Advantages over older devices for gripping specimens in high-temperature tests; no need to drill holes in specimens, maintains constant gripping force on specimens, and heated to same temperature as that of specimen without risk of heating hydraulic fluid and acuator components.

  9. Effects of leachate infiltration and desiccation cracks on hydraulic conductivity of compacted clay

    Directory of Open Access Journals (Sweden)

    Jun HE

    2015-04-01

    Full Text Available Both cracks in clay liner and the complex composition of landfill leachate might have effects on the hydraulic conductivity of a compacted clay liner. In this study, the hydraulic conductivities of natural clay and bentonite-modified clay with and without desiccation cracks were measured, respectively, using three types of liquids as permeating liquid: 2 500 mg/L acetic acid solution, 0.5 mol/L CaCl2 solution, and tap water. When tap water was adopted as the permeating liquid, desiccation cracks resulted in increases in the average value of hydraulic conductivity: a 25-fold increase for the natural clay and a 5.7-fold increase for the bentonite-modified clay. It was also found out that the strong self-healing capability of bentonite helped to reduce the adverse impact of cracks on hydraulic performance. In contrast to tap water, simulated leachates (acetic acid and CaCl2 solutions show no adverse effect on the hydraulic conductivities of natural and bentonite-modified clays. It is concluded that desiccation cracks and bentonite have more significant effects on hydraulic performance than simulated leachates.

  10. Robust control of a hydraulically driven flexible arm

    Institute of Scientific and Technical Information of China (English)

    Guang LI; Khajepour AMIR

    2004-01-01

    A new robust controller is proposed to regulate both flexural vibrations and rigid body motion of a hydraulically driven flexible arm. The controller combines backstepping control and sliding mode to arrive at a controller capable of dealing with a nonlinear system with uncertainties. The sliding mode technique is used to achieve an asymptotic joint angle and vibration regulation in the presence of payload uncertainty by providing a virtual torque input at the joint while the backstepping technique is used to regulate the spool position of a hydraulic valve to provide the required torque. It is shown that there is no chatter in the hydraulic valve, which results in smoother operation of the system.

  11. Growth model for large branched three-dimensional hydraulic crack system in gas or oil shale.

    Science.gov (United States)

    Chau, Viet T; Bažant, Zdeněk P; Su, Yewang

    2016-10-13

    Recent analysis of gas outflow histories at wellheads shows that the hydraulic crack spacing must be of the order of 0.1 m (rather than 1 m or 10 m). Consequently, the existing models, limited to one or several cracks, are unrealistic. The reality is 10(5)-10(6) almost vertical hydraulic cracks per fracking stage. Here, we study the growth of two intersecting near-orthogonal systems of parallel hydraulic cracks spaced at 0.1 m, preferably following pre-existing rock joints. One key idea is that, to model lateral cracks branching from a primary crack wall, crack pressurization, by viscous Poiseuille-type flow, of compressible (proppant-laden) frac water must be complemented with the pressurization of a sufficient volume of micropores and microcracks by Darcy-type water diffusion into the shale, to generate tension along existing crack walls, overcoming the strength limit of the cohesive-crack or crack-band model. A second key idea is that enforcing the equilibrium of stresses in cracks, pores and water, with the generation of tension in the solid phase, requires a new three-phase medium concept, which is transitional between Biot's two-phase medium and Terzaghi's effective stress and introduces the loading of the solid by pressure gradients of diffusing pore water. A computer program, combining finite elements for deformation and fracture with volume elements for water flow, is developed to validate the new model.This article is part of the themed issue 'Energy and the subsurface'.

  12. Blade-shaped (PKN) Hydraulic Fracture Driven By A Turbulent Fluid In An Impermeable Rock

    CERN Document Server

    Zolfaghari, Navid; Bunger, Andrew P

    2016-01-01

    High flow rate, water-driven hydraulic fractures are more common now than ever in the oil and gas industry. Although the fractures are small, the high injection rate and low viscosity of the water, lead to high Reynolds numbers and potentially turbulence in the fracture. Here we present a semi-analytical solution for a blade-shaped (PKN) geometry hydraulic fracture driven by a turbulent fluid in the limit of zero fluid leak-off to the formation. We model the turbulence in the PKN fracture using the Gaukler-Manning-Strickler parametrization, which relates the the flow rate of the water to the pressure gradient along the fracture. The key parameter in this relation is the Darcy-Weisbach friction factor for the roughness of the crack wall. Coupling this turbulence parametrization with conservation of mass allows us to write a nonlinear pde for the crack width as a function of space and time. By way of a similarity ansatz, we obtain a semi-analytical solution using an orthogonal polynomial series. Embedding the a...

  13. Bench-mark solution for a penny-shaped hydraulic fracture driven by a thinning fluid

    CERN Document Server

    Linkov, Aleksandr

    2015-01-01

    The paper presents a solution for axisymmetric propagation of a penny-shaped crack driven by a thinning fluid. The solution to the accuracy of four significant digits, at least, is obtained on the basis of the modified formulation of hydraulic fracture problem by employing the particle velocity, rather than conventionally used flux. This serves to properly organize iterations in the opening after reducing the problem to the self-similar form. Numerical results obtained show relatively small dependence of self-similar quantities (fracture radius, propagation speed, opening, particle velocity, pressure, flux) on the behavior index of a thinning fluid. The results provide bench marks for the accuracy control of truly 3D simulators and they serve for assigning an apparent viscosity when simulating the action of a thinning fluid by replacing it with an equivalent Newtonian fluid.

  14. Thermal hydraulics of accelerator driven system windowless targets

    Directory of Open Access Journals (Sweden)

    Bruno ePanella

    2015-07-01

    Full Text Available The study of the fluid dynamics of the windowless spallation target of an Accelerator Driven System (ADS is presented. Several target mockup configurations have been investigated: the first one was a symmetrical target, that was made by two concentric cylinders, the other configurations are not symmetrical. In the experiments water has been used as hydraulic equivalent to lead-bismuth eutectic fluid. The experiments have been carried out at room temperature and flow rate up to 24 kg/s. The fluid velocity components have been measured by an ultrasound technique. The velocity field of the liquid within the target region either for the approximately axial-symmetrical configuration or for the not symmetrical ones as a function of the flow rate and the initial liquid level is presented. A comparison of experimental data with the prediction of the finite volume FLUENT code is also presented. Moreover the results of a 2D-3D numerical analysis that investigates the effect on the steady state thermal and flow fields due to the insertion of guide vanes in the windowless target unit of the EFIT project ADS nuclear reactor are presented, by analysing both the cold flow case (absence of power generation and the hot flow case (nominal power generation inside the target unit.

  15. Statistical investigation of hydraulic driven circular interpolation motions

    Indian Academy of Sciences (India)

    Ahmet Murat Pinar; Abdulkadir Gullu; Sezai Taskin

    2012-10-01

    In this study, a twin-axis gantry has been structured to examine hydraulic driven positioning skills of the curvilinear motions based on ISO 230-4 standard entitled ‘Circular tests for numerically controlled machine tools’. The system is controlled by a path and position control module of a PLC device. As a result of the experiments conducted based on the full factorial design, the effects of piston diameter, feed rate, radius and their two-way interactions on the circularity error are determined through analysis of variance. Accordingly, minimum circularity error is obtained with the piston diameter of 63 mm, inertia load of 12.5 kg, radius of 5 mm and feed rate of 50 mm/min as 0.345 mm. Circularity error increases with the increase of inertia load, radius and feed rate, and declines with the increase of piston diameter. Lastly, piston diameter has the greatest effect on the circularity error change and followed by radius, feed rate, piston diameter–radius, radius–feed rate, piston diameter-feed-rate, inertia load, piston diameter–inertia load, and inertia load–radius factors and interactions.

  16. Singular perturbation approach for control of hydraulically driven flexible manipulator

    Institute of Scientific and Technical Information of China (English)

    LI Guang; WU Min

    2005-01-01

    The hydraulic flexible manipulator system is divided into two parts: flexible arm dynamics and hydraulic servomechanism, a driving Jacobian is derived to connect these two parts. Taking hydraulic actuator force as virtual input, a singular perturbed composite model is formulated and used to design composite controllers for the flexible link, in which the slow subsystem controller dominates the trajectory tracking, and then a fast controller is designed to damp out the vibration of the flexible structure. Moreover, the backstepping technique is applied to regulate the spool position of a hydraulic valve to provide the required force. Simulation results are provided to show the effectiveness of the presented approach.

  17. Hydraulics.

    Science.gov (United States)

    Decker, Robert L.; Kirby, Klane

    This curriculum guide contains a course in hydraulics to train entry-level workers for automotive mechanics and other fields that utilize hydraulics. The module contains 14 instructional units that cover the following topics: (1) introduction to hydraulics; (2) fundamentals of hydraulics; (3) reservoirs; (4) lines, fittings, and couplers; (5)…

  18. An evaluation of a hubless inducer and a full flow hydraulic turbine driven inducer boost pump

    Science.gov (United States)

    Lindley, B. K.; Martinson, A. R.

    1971-01-01

    The purpose of the study was to compare the performance of several configurations of hubless inducers with a hydrodynamically similar conventional inducer and to demonstrate the performance of a full flow hydraulic turbine driven inducer boost pump using these inducers. A boost pump of this type consists of an inducer connected to a hydraulic turbine with a high speed rotor located in between. All the flow passes through the inducer, rotor, and hydraulic turbine, then into the main pump. The rotor, which is attached to the main pump shaft, provides the input power to drive the hydraulic turbine which, in turn, drives the inducer. The inducer, rotating at a lower speed, develops the necessary head to prevent rotor cavitation. The rotor speed is consistent with present main engine liquid hydrogen pump designs and the overall boost pump head rise is sufficient to provide adequate main pump suction head. This system would have the potential for operating at lower liquid hydrogen tank pressures.

  19. Mixing and entrainment in hydraulically driven stratified sill flows

    DEFF Research Database (Denmark)

    Nielsen, Morten Holtegaard; Pratt, Larry; Helfrich, Karl

    2004-01-01

    that the reduced gravity model systematically underestimates inertia and overestimates buoyancy. These differences are quantified by shape coefficients that measure the vertical non-uniformities of the density and horizontal velocity that arise, in part, by incomplete mixing of entrained mass and momentum over...... model. Self-similarity is not observed in the numerically generated flow, but the observed critical section continues to lie upstream of the location predicted by the reduced gravity model. The factors influencing this result are explored.......The investigation involves the hydraulic behaviour of a dense layer of fluid flowing over an obstacle and subject to entrainment of mass and momentum from a dynamically inactive (but possibly moving) overlying fluid. An approach based on the use of reduced gravity, shallow-water theory with a cross...

  20. Mixing and entrainment in hydraulically driven stratified sill flows

    Science.gov (United States)

    Holtegaard Nielsen, Morten; Pratt, Larry; Helfrich, Karl

    2004-09-01

    The investigation involves the hydraulic behaviour of a dense layer of fluid flowing over an obstacle and subject to entrainment of mass and momentum from a dynamically inactive (but possibly moving) overlying fluid. An approach based on the use of reduced gravity, shallow-water theory with a cross-interface entrainment velocity is compared with numerical simulations based on a model with continuously varying stratification and velocity. The locations of critical flow (hydraulic control) in the continuous model are estimated by observing the direction of propagation of small-amplitude long-wave disturbances introduced into the flow field. Although some of the trends predicted by the shallow-water model are observed in the continuous model, the agreement between the interface profiles and the position of critical flow is quantitatively poor. A reformulation of the equations governing the continuous flow suggests that the reduced gravity model systematically underestimates inertia and overestimates buoyancy. These differences are quantified by shape coefficients that measure the vertical non-uniformities of the density and horizontal velocity that arise, in part, by incomplete mixing of entrained mass and momentum over the lower-layer depth. Under conditions of self-similarity (as in Wood's similarity solution) the shape coefficients are constant and the formulation determines a new criterion for and location of critical flow. This location generally lies upstream of the critical section predicted by the reduced-gravity model. Self-similarity is not observed in the numerically generated flow, but the observed critical section continues to lie upstream of the location predicted by the reduced gravity model. The factors influencing this result are explored.

  1. Experimental Study of Crack Initiation and Extension Induced by Hydraulic Fracturing in a Tree-Type Borehole Array

    Directory of Open Access Journals (Sweden)

    Yiyu Lu

    2016-06-01

    Full Text Available High-pressure hydraulic fracturing technology in coal and coal bed methane mines can lead to roof and floor damage, and fracture initiation disorder that leads to a “blank area”, and other issues. A new method of hydraulic fracturing is proposed to increase the homogeneous permeability of coal in underground coalmines. Numerical and other simulation tests for different forms of a tree-type, branched borehole model are presented. The results show that the branched array causes cracks to initiate from the bottom of the array, and these extend along the direction of the adjacent boreholes. Generally, as the number of branched boreholes increases, the coal seam fracture network also increase, improving the distribution of the fracture network, making the fracturing effect better. The branched boreholes appear to reduce initiation pressure and, with increasing branches, the initiation pressure decreases. A model with four tree-type, branched boreholes leads to a reduction in initiation pressure of 69%. In terms of permeability improvement technology in underground coalmines, a branched hydraulic fracturing borehole array has the advantages of reducing initiation pressure, controlling crack initiation and extension, enhancing the fracturing effect and reducing the destruction of the roof and floor.

  2. Fluid driven fracture mechanics in highly anisotropic shale: a laboratory study with application to hydraulic fracturing

    Science.gov (United States)

    Gehne, Stephan; Benson, Philip; Koor, Nick; Enfield, Mark

    2017-04-01

    The finding of considerable volumes of hydrocarbon resources within tight sedimentary rock formations in the UK led to focused attention on the fundamental fracture properties of low permeability rock types and hydraulic fracturing. Despite much research in these fields, there remains a scarcity of available experimental data concerning the fracture mechanics of fluid driven fracturing and the fracture properties of anisotropic, low permeability rock types. In this study, hydraulic fracturing is simulated in a controlled laboratory environment to track fracture nucleation (location) and propagation (velocity) in space and time and assess how environmental factors and rock properties influence the fracture process and the developing fracture network. Here we report data on employing fluid overpressure to generate a permeable network of micro tensile fractures in a highly anisotropic shale ( 50% P-wave velocity anisotropy). Experiments are carried out in a triaxial deformation apparatus using cylindrical samples. The bedding planes are orientated either parallel or normal to the major principal stress direction (σ1). A newly developed technique, using a steel guide arrangement to direct pressurised fluid into a sealed section of an axially drilled conduit, allows the pore fluid to contact the rock directly and to initiate tensile fractures from the pre-defined zone inside the sample. Acoustic Emission location is used to record and map the nucleation and development of the micro-fracture network. Indirect tensile strength measurements at atmospheric pressure show a high tensile strength anisotropy ( 60%) of the shale. Depending on the relative bedding orientation within the stress field, we find that fluid induced fractures in the sample propagate in two of the three principal fracture orientations: Divider and Short-Transverse. The fracture progresses parallel to the bedding plane (Short-Transverse orientation) if the bedding plane is aligned (parallel) with the

  3. Top-down cracking of rigid pavements constructed with fast setting hydraulic cement concrete

    CSIR Research Space (South Africa)

    Heath, AC

    2009-01-29

    Full Text Available Jointed plain concrete pavement (JPCP) test sections were constructed using fast setting hydrualic cement concrete (FSHCC) as part of the California accelerated pavement testing program (CAL/APT). Many of the longer slabs cracked under environmental...

  4. Crack deflection in brittle media with heterogeneous interfaces and its application in shale fracking

    Science.gov (United States)

    Zeng, Xiaguang; Wei, Yujie

    Driven by the rapid progress in exploiting unconventional energy resources such as shale gas, there is growing interest in hydraulic fracture of brittle yet heterogeneous shales. In particular, how hydraulic cracks interact with natural weak zones in sedimentary rocks to form permeable cracking networks is of significance in engineering practice. Such a process is typically influenced by crack deflection, material anisotropy, crack-surface friction, crustal stresses, and so on. In this work, we extend the He-Hutchinson theory (He and Hutchinson, 1989) to give the closed-form formulae of the strain energy release rate of a hydraulic crack with arbitrary angles with respect to the crustal stress. The critical conditions in which the hydraulic crack deflects into weak interfaces and exhibits a dependence on crack-surface friction and crustal stress anisotropy are given in explicit formulae. We reveal analytically that, with increasing pressure, hydraulic fracture in shales may sequentially undergo friction locking, mode II fracture, and mixed mode fracture. Mode II fracture dominates the hydraulic fracturing process and the impinging angle between the hydraulic crack and the weak interface is the determining factor that accounts for crack deflection; the lower friction coefficient between cracked planes and the greater crustal stress difference favor hydraulic fracturing. In addition to shale fracking, the analytical solution of crack deflection could be used in failure analysis of other brittle media.

  5. Selection of finite-element mesh parameters in modeling the growth of hydraulic fracturing cracks

    Science.gov (United States)

    Kurguzov, V. D.

    2016-12-01

    The effect of the mesh geometry on the accuracy of solutions obtained by the finite-element method for problems of linear fracture mechanics is investigated. The guidelines have been formulated for constructing an optimum mesh for several routine problems involving elements with linear and quadratic approximation of displacements. The accuracy of finite-element solutions is estimated based on the degree of the difference between the calculated stress-intensity factor (SIF) and its value obtained analytically. In problems of hydrofracturing of oil-bearing formation, the pump-in pressure of injected water produces a distributed load on crack flanks as opposed to standard fracture mechanics problems that have analytical solutions, where a load is applied to the external boundaries of the computational region and the cracks themselves are kept free from stresses. Some model pressure profiles, as well as pressure profiles taken from real hydrodynamic computations, have been considered. Computer models of cracks with allowance for the pre-stressed state, fracture toughness, and elastic properties of materials are developed in the MSC.Marc 2012 finite-element analysis software. The Irwin force criterion is used as a criterion of brittle fracture and the SIFs are computed using the Cherepanov-Rice invariant J-integral. The process of crack propagation in a linearly elastic isotropic body is described in terms of the elastic energy release rate G and modeled using the VCCT (Virtual Crack Closure Technique) approach. It has been found that the solution accuracy is sensitive to the mesh configuration. Several parameters that are decisive in constructing effective finite-element meshes, namely, the minimum element size, the distance between mesh nodes in the vicinity of a crack tip, and the ratio of the height of an element to its length, have been established. It has been shown that a mesh that consists of only small elements does not improve the accuracy of the solution.

  6. Model predictive control of servo motor driven constant pump hydraulic system in injection molding process based on neurodynamic optimization

    Institute of Scientific and Technical Information of China (English)

    Yong-gang PENG; Jun WANG; Wei WEI

    2014-01-01

    In view of the high energy consumption and low response speed of the traditional hydraulic system for an injection molding machine, a servo motor driven constant pump hydraulic system is designed for a precision injection molding process, which uses a servo motor, a constant pump, and a pressure sensor, instead of a common motor, a constant pump, a pressure pro-portion valve, and a flow proportion valve. A model predictive control strategy based on neurodynamic optimization is proposed to control this new hydraulic system in the injection molding process. Simulation results showed that this control method has good control precision and quick response.

  7. Differential profiles of crack users in respondent-driven and institutional samples: a three-site comparison

    NARCIS (Netherlands)

    Oteo Pérez, A.; Benschop, A.; Korf, D.J.

    2012-01-01

    Background/Aim: Respondent-driven sampling (RDS) is increasingly applied in social epidemiological surveys among ‘hidden populations’ of hard drug users. The objective of the present study was to assess whether the profile of frequent crack users recruited through RDS differed from those surveyed in

  8. Forming-Precision-Driven Structure Design of Hydraulic Press:Methodology and Case Study

    Institute of Scientific and Technical Information of China (English)

    李艳聪; 张连洪; 何柏岩; 陈永亮; 张淳

    2015-01-01

    The structure stiffness of presses has great effects on the forming precision of workpieces, especially in near-net or net shape forming. Conventionally the stiffness specification of presses is empirically determined, re-sulting in poor designs with insufficient or over sufficient stiffness of press structures. In this paper, an approach for the structure design of hydraulic presses is proposed, which is forming-precision-driven and can make presses cost-effective by lightweight optimization. The approach consists of five steps:(1)the determination of the press stiff-ness specification in terms of the forming precision requirement of workpieces;(2)the conceptual design of the press structures according to the stiffness and workspace specifications, and the structure configuration of the press;(3)the prototype design of the press structures by equivalently converting the conceptual design to proto-types;(4)the selection of key structure parameters by sensitivity analysis of the prototype design; and(5)the opti-mization of the prototype design. The approach is demonstrated and validated through a case study of the structure design of a 100 MN hydraulic press.

  9. Elastic Relaxation of Fluid-Driven Cracks and the Resulting Backflow

    Science.gov (United States)

    Lai, Ching-Yao; Zheng, Zhong; Dressaire, Emilie; Ramon, Guy Z.; Huppert, Herbert E.; Stone, Howard A.

    2016-12-01

    Cracks filled with fluid propagation when the pressurized fluid is injected into the crack. Subsequently, when the fluid inlet is exposed to a lower pressure, the fluid flows backwards (backflow) and the crack closes due to the elastic relaxation of the solid. Here we study the dynamics of the crack closure during the backflow. We find that the crack radius remains constant and the fluid volume in the crack decreases with time in a power-law manner at late times. The balance between the viscous stresses in the fluid and elastic stresses in the fluid and the elastic stresses in the solid yields a scaling law that agrees with the experimental results for different fluid viscosities, Young's moduli of the solid, and initial radii of the cracks. Furthermore, we visualize the time-dependent crack shapes, and the convergence to a universal dimensionless shape demonstrates the self-similarity of the crack shapes during the backflow process.

  10. Crack Features and Shear-Wave Splitting Associated with Fracture Extension during Hydraulic Stimulation of the Geothermal Reservoir in Soultz-sous-Forêts

    Directory of Open Access Journals (Sweden)

    Adelinet M.

    2016-05-01

    Full Text Available The recent tomography results obtained within the scope of the Enhanced Geothermal System (EGS European Soultz project led us to revisit the meso-fracturing properties of Soultz test site. In this paper, we develop a novel approach coupling effective medium modeling and shear-wave splitting to characterize the evolution of crack properties throughout the hydraulic stimulation process. The stimulation experiment performed in 2000 consisted of 3 successive injection steps spanning over 6 days. An accurate 4-D tomographic image was first carried out based upon the travel-times measured for the induced seismicity [Calò M., Dorbath C., Cornet F.H., Cuenot N. (2011 Large-scale aseismic motion identified through 4-D P-wave tomography, Geophys. J. Int. 186, 1295-1314]. The current study shows how to take advantage of the resulting compressional wave (Calò et al., 2011 and shear-wave velocity models. These are given as input data to an anisotropic effective medium model and converted into crack properties. In short, the effective medium model aims to estimate the impact of cracks on velocities. It refers to a crack-free matrix and 2 families of penny-shaped cracks with orientations in agreement with the main observed geological features: North-South strike and dip of 65°East and 65°West [Genter A., Traineau H. (1996 Analysis of macroscopic fractures in granite in the HDR geothermal well EPS-1, Soultz-sous-Forêts, France, J. Vol. Geoth. Res. 72, 121-141], respectively. The resulting output data are the spatial distributions of crack features (lengths and apertures within the 3-D geological formation. We point out that a flow rate increase results in a crack shortening in the area imaged by both compressional and shear waves, especially in the upper part of the reservoir. Conversely, the crack length, estimated during continuous injection rate phases, is higher than during the increasing injection rate phases. A possible explanation for this is that

  11. Spacing of crack patterns driven by steady-state cooling or drying and influenced by a solidification boundary

    Science.gov (United States)

    Hofmann, Martin; Bahr, Hans-Achim; Weiss, Hans-Jürgen; Bahr, Ute; Balke, Herbert

    2011-03-01

    Regular columnar joints that originate from networklike crack patterns can be observed in basalt and, on a much smaller scale, in dried starch slurry. Here, the basalt columns are idealized by a periodic array of parallel cracks driven by steady-state cooling. By means of a bifurcation analysis, the minimal possible crack spacing for sustained propagation of the crack array is calculated. It can be shown qualitatively that the minimal possible crack spacing for sustained propagation increases with decreasing velocity. This is confirmed by numerical calculations. The latent heat released at the solidification front is taken into account in the thermomechanical linear-elastic model of propagating shrinkage. Our calculations show that the solidification front is positioned not far ahead of the crack tips, which influences the result considerably. The results agree reasonably well with new measured data of basalt columns. By use of the analogy between contraction due to cooling and that due to drying the model is applied for columns in dried cornstarch, too, showing good agreement with recent experimental data.

  12. Crack propagation through adhesive interface in glass driven by dynamic loading

    Science.gov (United States)

    Park, Hwun

    Dynamic crack behaviors at glass interfaces were investigated to understand dynamic failure mechanisms of glass. To produce highly intensive and rapidly increasing loading, glass specimens jointed with epoxy adhesive in edge-to-edge configurations were impacted on their notched edges with plastic projectiles. Cracks developed from the notch and propagated into the interfaces between glass plates at the maximum speed. The patterns of crack propagation through the interfaces were observed to depend on the interface's conditions. Crack propagation stops at the interface where no adhesive was applied. The crack penetrates through the interface where two glass plates were bonded directly without any space. If the interface has finite thickness of an adhesive layer, a crack passing through the interface branches into multiple cracks immediately when it extends to the second glass plate. Both of the slow crack speed in the epoxy adhesive and resistance for crack initiation in the second glass account for the delay in crack propagation at the interface. The surface conditions of glass at the interface affect the resistance for crack initiation. Mirror-like polished surfaces have better resistance than rough surfaces trimmed by a water jet. If the polished surface is etched with hydrofluoric acid to remove surface flaws, the glass surfaces have higher strength and resistance for damage. This etched glass even ceases crack propagation completely with a sufficiently thick adhesive layer. Crack branching has been an open topic. Exact explanation has not been given yet. As the consistent shape of crack branching are created with the proposed method, diagnostics experiments were conducted to reveal the nature of crack branching. To investigate interaction between stress propagation and crack branching, stress histories synchronizing with high speed images were measured. Two types of specimen were used to vary stress distribution during crack propagation. The apex angle of

  13. Mode III crack propagation in a bimaterial plane driven by a channel of small line defects

    CERN Document Server

    Piccolroaz, A; Movchan, A; Movchan, N

    2011-01-01

    We consider the quasi-static propagation of a Mode III crack along the interface in a bimaterial plane containing a finite array of small line defects (microcracks and rigid line inclusions). The microdefects are arranged to form a channel around the interface that can facilitate (or prevent) the crack propagation. The two dissimilar elastic materials are assumed to be weakly bonded, so that there is no kinking of the main crack from the straight path. On the basis of asymptotic formulae obtained by the authors, the propagation is analysed as a perturbation problem and the incremental crack advance is analytically derived at each position of the crack tip along the interface relative to the position of the defects. Numerical examples are provided showing potential applications of the proposed approach in the analysis of failure of composite materials. Extension to the case of infinite number of defects is discussed.

  14. Magnetic-field-driven crack formation in an evaporated anisotropic colloidal assembly

    Science.gov (United States)

    Lama, Hisay; Dugyala, Venkateshwar Rao; Basavaraj, Madivala G.; Satapathy, Dillip K.

    2016-07-01

    We report the effect of applied magnetic field on the morphology of cracks formed after evaporation of a colloidal suspension consisting of shape-anisotropic ellipsoidal particles on a glass substrate. The evaporation experiments are performed in sessile drop configuration, which usually leads to accumulation of particles at the drop boundaries, commonly known as the "coffee-ring effect." The coffee-ring-like deposits that accompany cracks are formed in the presence as well as in the absence of magnetic field. However, the crack patterns formed in both cases are found to differ markedly. The direction of cracks in the presence of the magnetic field is found to be governed by the orientation of particles and not solely by the magnetic field direction. Our experimental results show that at the vicinity of cracks the particles are ordered and oriented with their long-axis parallel to crack direction. In addition, we observe that the crack spacing in general increases with the height of the particulate film.

  15. Effect of leaching-driven flow on the alteration kinetics of an ideal crack in SON68 glass

    Energy Technology Data Exchange (ETDEWEB)

    Chomat, Laure [CEA, DEN, DPC, SECR, Laboratoire d' Etude du Comportement des Betons et des Argiles, F-91191 Gif-sur-Yvette (France); Bouyer, Frederic, E-mail: frederic.bouyer@cea.fr [CEA, DEN, DTCD/SECM/LCLT, Marcoule, F-30207 Bagnols-sur-Ceze (France); Gin, Stephane [CEA, DEN, DTCD/SECM/LCLT, Marcoule, F-30207 Bagnols-sur-Ceze (France); Roux, Stephane [LMT-Cachan, ENS de Cachan/CNRS UMR 8535/Universite Paris 6/PRES UniverSud Paris, 61 Avenue du President-Wilson, 94235 Cachan Cedex (France)

    2012-07-15

    The kinetics of glass alteration is studied in a reactor cell containing parallel glass plates with a small gap, representing an ideal crack geometry. The calibrated aperture of the crack is varied from a few tens to a few hundred micrometers. The glass coupons are immersed in a highly alkaline solution to obtain fast alteration. Although the cell is closed and isothermal, it is observed that vertical or horizontal configurations lead to very different alteration gel thickness profiles. This effect results from gravity-driven flow taking place in the vertical geometry due to glass leaching as opposed to essentially diffusive transport in the horizontal case. The advection velocity is estimated from a one-dimensional model of the coupled reaction/transport mechanism, based on a zero or first order reaction. The coupling between reaction and transport has a clear influence on the apparent alteration kinetics, a phenomenon generally ignored.

  16. A comparative analysis of reticular crack on ceramic plate driven by thermal shock

    Science.gov (United States)

    Xu, XiangHong; Sheng, ShiLong; Tian, Cheng; Yuan, WenJun

    2016-07-01

    Reticular crack is generally found on the surface of ceramic material that has been subjected to a thermal-shock condition. In the present study, a quantitative effect of thermal shock and quench temperature has been studied and investigated. Experimental tests were carried out to characterize the reticular crack that has been found in the Ge Kiln, which is a famous art of the ancient Chinese culture. After comparative analysis between thermal-shock cracks and the glaze crack patterns of the Ge Kiln porcelain, it is found that this study is expected to provide a powerful tool for recurrence of the long-lost firing and cooling process of the Ge Kiln porcelain.

  17. Development of a data-driven forecasting tool for hydraulically fractured, horizontal wells in tight-gas sands

    Science.gov (United States)

    Kulga, B.; Artun, E.; Ertekin, T.

    2017-06-01

    Tight-gas sand reservoirs are considered to be one of the major unconventional resources. Due to the strong heterogeneity and very low permeability of the formation, and the complexity of well trajectories with multiple hydraulic fractures; there are challenges associated with performance forecasting and optimum exploitation of these resources using conventional modeling approaches. In this study, it is aimed to develop a data-driven forecasting tool for tight-gas sands, which are based on artificial neural networks that can complement the physics-driven modeling approach, namely numerical-simulation models. The tool is designed to predict the horizontal-well performance as a proxy to the numerical model, once the initial conditions, operational parameters, reservoir/hydraulic-fracture characteristics are provided. The data-driven model, that the forecasting tool is based on, is validated with blind cases by estimating the cumulative gas production after 10 years with an average error of 3.2%. A graphical-user-interface application is developed that allows the practicing engineer to use the developed tool in a practical manner by visualizing estimated performance for a given reservoir within a fraction of a second. Practicality of the tool is demonstrated with a case study for the Williams Fork Formation by assessing the performance of various well designs and by incorporating known uncertainties through Monte Carlo simulation. P10, P50 and P90 estimates of the horizontal-well performance are quickly obtained within acceptable accuracy levels.

  18. Using Program Theory-Driven Evaluation Science to Crack the Da Vinci Code

    Science.gov (United States)

    Donaldson, Stewart I.

    2005-01-01

    Program theory-driven evaluation science uses substantive knowledge, as opposed to method proclivities, to guide program evaluations. It aspires to update, clarify, simplify, and make more accessible the evolving theory of evaluation practice commonly referred to as theory-driven or theory-based evaluation. The evaluator in this chapter provides a…

  19. Seismological investigation of crack formation in hydraulic rock fracturing experiments and in natural geothermal environments. Progress report, September 1, 1979-August 31, 1980

    Energy Technology Data Exchange (ETDEWEB)

    Aki, K.

    1980-09-01

    Progress is reported in the following research areas: a synthesis of seismic experiments at the Fenton Hill Hot-Dry-Rock System; attenuation of high-frequency shear waves in the lithosphere; a new kinematic source model for deep volcanic tremors; ground motion in the near-field of a fluid-driven crack and its interpretation in the study of shallow volcanic tremor; low-velocity bodies under geothermal areas; and operation of event recorders in Mt. St. Helens and Newberry Peak with preliminary results from them. (MHR)

  20. Reaction-driven cracking in the TAG deep-sea hydrothermal field: Implications for serpentinization and carbonation of peridotite

    Science.gov (United States)

    Sohn, R. A.

    2013-12-01

    Tens of thousands of very small (-1.5 ≤ ML ≤ 0.5) microearthquakes were detected by a small-aperture (200 m) network of 5 ocean bottom seismometers during a 9-month deployment at the TAG active hydrothermal mound on the Mid-Atlantic Ridge (26°N). The earthquakes exhibit purely compressional phase arrivals, are clustered within a narrow depth interval extending from ~50 - 150 m below the seafloor, and are located just beyond the perimeter of the surface expression of the hydrothermal mound. Analyses of these events indicates that they are most likely generated by crack opening resulting from the deposition of anhydrite in the secondary circulation system of the active mound. This reaction-driven cracking is analogous to that expected from serpentinization and/or carbonation of peridotite, and suggests that a properly designed seismic experiment may be able to provide in-situ monitoring of these processes either on land or in the oceans. A straightforward test of this hypothesis could be obtained by deploying a borehole seismic network in a subaerial region, such as the ophiolite terrains of Oman, where serpentinization and carbonation of peridotite are active processes

  1. FOUR WHEELS DRIVEN INDEPENDENTLY BY ONE PUMP DRIVING FOUR HYDRAULIC MOTORS

    Institute of Scientific and Technical Information of China (English)

    Wu Baolin; Qiu Lihua; Wang Zhanlin

    2005-01-01

    An improved Narendra model reference adaptive control (MRAC) scheme is proposed to research one variable displacement pump driving four hydraulic variable displacement motors. This approach not only ensures the underdamped and unstable system be global uniform asymptotic stability, but also has good robustness in these aspects of modeling uncertainty, pressure fluctuation of constant pressure network, and disturbance from external load, which also upgrades the rapidity of system response so as to make controlled system with nicer dynamic quality. The scheme of one pump driving four motors can meet the demand on off-road mobility of engineering vehicles and armored cars. A proof of stability about improved Narendra MRAC scheme is also given.

  2. Hydraulic conductance of Acacia phyllodes (foliage) is driven by primary nerve (vein) conductance and density.

    Science.gov (United States)

    Sommerville, Katy E; Sack, Lawren; Ball, Marilyn C

    2012-01-01

    We determined effects of venation traits on hydraulic conductance of phyllodes (foliage), using an array of Acacia s.str. species with diverse phyllode morphologies as the source of variation. Measurements were made on phyllodes from 44 species, grown in common gardens but originating from different positions along a precipitation gradient. K(phyllode) varied 18-fold and was positively correlated with primary nerve hydraulic conductance, and with primary nerve (vein) density but not with minor nerve density, in contrast with previous studies of true leaves in other dicotyledons. Phyllodes with higher primary nerve density also had greater mass per area (PMA) and larger bundle sheath extensions (BSEs) from their minor nerves. We suggest that higher primary nerve conductivity and density may decrease the distance travelled in the high-resistance extra-xylem pathways of the phyllode. Further, larger BSEs may increase the area available for dispersion of water from the xylem to the extra-xylem tissue. High PMA phyllodes were more common in acacias from areas receiving lower annual precipitation. Maximizing efficient water movement through phyllodes may be more important where rainfall is meagre and infrequent, explaining relationships between nerve patterns and the climates of origin in Australian phyllodinous Acacia.

  3. Dynamically balanced, hydraulically driven compressor/pump apparatus for resonant free piston Stirling engines

    Science.gov (United States)

    Corey, John A.

    1984-05-29

    A compressor, pump, or alternator apparatus is designed for use with a resonant free piston Stirling engine so as to isolate apparatus fluid from the periodically pressurized working fluid of the Stirling engine. The apparatus housing has a first side closed by a power coupling flexible diaphragm (the engine working member) and a second side closed by a flexible diaphragm gas spring. A reciprocally movable piston is disposed in a transverse cylinder in the housing and moves substantially at right angles relative to the flexible diaphragms. An incompressible fluid fills the housing which is divided into two separate chambers by suitable ports. One chamber provides fluid coupling between the power diaphragm of the RFPSE and the piston and the second chamber provides fluid coupling between the gas spring diaphragm and the opposite side of the piston. The working members of a gas compressor, pump, or alternator are driven by the piston. Sealing and wearing parts of the apparatus are mounted at the external ends of the transverse cylinder in a double acting arrangement for accessibility. An annular counterweight is mounted externally of the reciprocally movable piston and is driven by incompressible fluid coupling in a direction opposite to the piston so as to damp out transverse vibrations.

  4. Waterfall formation driven by interacting flow hydraulics, sediment cover, and erosion in an experimental bedrock canyon

    Science.gov (United States)

    Scheingross, Joel; Lamb, Michael; Fuller, Brian

    2016-04-01

    Waterfalls are ubiquitous in steep landscapes and have been documented to retreat upstream at rates far outpacing standard fluvial incision into bedrock. While the formation of waterfalls following changes in climate and base-level lowering have been well-documented, little work has explored the formation of waterfalls via the internal dynamics from interacting flow hydraulics, sediment flux, and evolving channel morphology. Distinguishing between waterfalls formed via external versus internal forcing is important, as waterfall formation and retreat rate is often applied in inverse to determine the timing of external forcing. Here, we present results from a laboratory experiment designed to explore channel incision and waterfall formation. We fed water and sediment at constant rates over an initially planar surface tilted to 19.5% slope. A channel rapidly incised into the artificial bedrock substrate, and small-wavelength variations in erosion rate created steps and pools which grew in amplitude. As pools deepened, sediment cover at the downstream portion of pools locally limited erosion, while erosion in the upstream portion of the pool created steep faces. At the topographic breaks between these steep segments and their upstream treads, water detached from the bed forming ventilated waterfall jets which impacted the plunge pools below. Individual waterfalls were short-lived as pool-deepening promoted alluviation which prevented further pool-incision, while amplified erosion at the waterfall lip incised a new pool into the bedrock previously composing the waterfall face. Repetition of this process in our experiment suggests that interactions between bedrock erosion and sediment cover can result in the formation of a series of plunge pools which retreat upstream.

  5. Brief introduction of servo-driven hydraulic press%伺服驱动液压机浅析

    Institute of Scientific and Technical Information of China (English)

    李贵闪

    2011-01-01

    文章介绍了伺服驱动液压机液压结构原理,与普通液压机比较,伺服控制液压机具有诸多优点,可以取代现有的大多数普通液压机,具有广泛的市场前景.%The principle of hydraulic structure for servo hydraulic press has been introduced in the text. Comparing with the common hydraulic press, the servo hydraulic press has lots of advantages, which makes it possible to take place of the many common hydraulic presses. It shows a broad marking prospect.

  6. Thermal-hydraulic analysis of LBE spallation target for accelerator-driven systems

    Indian Academy of Sciences (India)

    Aniseh Ahmed Atef Abdalla; Jiyang Yu; Yongwel Yang

    2013-01-01

    In an accelerator-driven subcritical system (ADS), a high-performance spallation neutron source is used to feed the subcritical reactor. Neutron generation depends on the proton beam intensity. If the beam intensity is increased by a given factor, the number of generated neutrons will increase. The mechanism yielding a high rate of neutron production per energy is the spallation process, and this mechanism produces very high-energy deposition in the spallation target material. Producing a high rate of neutrons is accompanied by creation of problems of decay heat cooling and radiological protection. As a first step in designing a full-scale industrial ADS, a small-scale experimental ADS, which is similar to the European experimental ADS (XADS) is analysed. The analysis presented in this paper is based on lead–bismuth eutectic (LBE) cooled XADS-type experimental reactors, designed during the European experimental (PDS-XADS) project. Computational fluid dynamics analysis has been carried out for the spallation target. Steady-state behaviour and shear stress transport turbulence model with the automatic wall treatment were applied in the present analysis.

  7. Simulating Plant Water Stress and Phenology in Seasonally Dry Tropical Forests: Plant Hydraulics and Trait-Driven Trade-Offs

    Science.gov (United States)

    Xu, X.; Medvigy, D.; Powers, J. S.; Becknell, J. M.

    2014-12-01

    Seasonally dry tropical forests account for over 40% of the forested area in tropical and subtropical regions. Previous studies suggest that seasonal water stress is one main driver of phenology and related vegetation dynamics in seasonally dry tropical forests. Species that coexist in seasonally dry tropical forests have different plant traits, experience different degrees of plant water stress and show distinctive phenological patterns. However, the observed diversity in plant phenology and related vegetation dynamics is poorly represented in current dynamic vegetation models. In this study, we employ a new modeling approach to enhance our model skills in seasonally dry tropical forests. First, we implement a new plant hydraulic module under the framework of a state-of-the-art dynamic vegetation model, Ecosystem Demography 2 (ED2). Second, we link plant water stress with several key coordinated plant traits. Unlike previous models, the updated ED2 does not prescribe leaf phenology (deciduous or evergreen) and plant water stress is not determined by empirical water stress factors or by soil moisture alone. Instead, the model tracks more mechanistic indicators of plant water stress like leaf water potential, accounts for different abilities to tolerate water stress among plant functional types and predicts dry season leaf deciduousness and related vegetation dynamics. The updated model is then tested with in-situ meteorological data and long-term ecological observations. We also perform numerical experiments to explore the possible biases of ignoring the observed diversity in seasonally dry tropical forests. We find that (i) variations of several key plant traits (specific leaf area, wood density, turgor loss point and rooting depth) can account for the observed distinctive phenological patterns as well as inter-annual variations in vegetation growth among species. (ii) Ignoring the trait-driven trade-offs and diversity in seasonality would introduce significant

  8. Hydraulic redistribution in dwarf Rhizophora mangle trees driven by interstitial soil water salinity gradients: impacts on hydraulic architecture and gas exchange.

    Science.gov (United States)

    Hao, Guang-You; Jones, Tim J; Luton, Corene; Zhang, Yong-Jiang; Manzane, Eric; Scholz, Fabian G; Bucci, Sandra J; Cao, Kun-Fang; Goldstein, Guillermo

    2009-05-01

    Rhizophora mangle L. trees of Biscayne National Park (Florida, USA) have two distinct growth forms: tall trees (5-10 m) growing along the coast and dwarf trees (1 m or less) growing in the adjacent inland zone. Sharp decreases in salinity and thus increases in soil water potential from surface soil to about a depth of 1 m were found at the dwarf mangrove site but not at the tall mangrove site. Consistent with our prediction, hydraulic redistribution detected by reverse sap flow in shallow prop roots was observed during nighttime, early morning and late afternoon in dwarf trees, but not in tall trees. In addition, hydraulic redistribution was observed throughout the 24-h period during a low temperature spell. Dwarf trees had significantly lower sapwood-specific hydraulic conductivity, smaller stem vessel diameter, lower leaf area to sapwood area ratio (LA/SA), smaller leaf size and higher leaf mass per area. Leaves of dwarf trees had lower CO(2) assimilation rate and lower stomatal conductance compared to tall trees. Leaf water potentials at midday were more negative in tall trees that are consistent with their substantially higher stomatal conductance and LA/SA. The substantially lower water transport efficiency and the more conservative water use of dwarf trees may be due to a combination of factors such as high salinity in the surface soil, particularly during dry periods, and substantial reverse sap flow in shallow roots that make upper soil layers with high salinity a competing sink of water to the transpiring leaves. There may also be a benefit for the dwarf trees in having hydraulic redistribution because the reverse flow and the release of water to upper soil layers should lead to dilution of the high salinity in the rhizosphere and thus relieve its potential harm to dwarf R. mangle trees.

  9. Hydraulic-driven Based the Design of the Transmission Assemblies%基于液压驱动的传动组合装置的设计

    Institute of Scientific and Technical Information of China (English)

    黄象珊; 谢颂京

    2013-01-01

    To meet the needs of the basic course teaching of the task-driven automotive major, a kind of hydraulic-driven transmission assemblies is designed. The device mainly consists of hydraulic-driven systems, transmission systems and test systems. It is free to mix different driven programs and collect data. It is proved through practice that the device is flexible for package and with strong function. The device is easy for operation and for secondary development. The students' practical abilities can be improved greatly.%为满足当前基于任务驱动的汽车专业基础类课程教学需要,设计了一种基于液压驱动的传动组合装置.该装置主要由液压驱动系统、传动系统和测试系统组成,能自由组合实现不同的传动方案并进行数据采集,通过实践证明,该组合装置组装灵活、功能强,具有较好的可操作性和二次开发性,能够提高学生综合实践能力和创新能力.

  10. Constant-Pressure Hydraulic Pump

    Science.gov (United States)

    Galloway, C. W.

    1982-01-01

    Constant output pressure in gas-driven hydraulic pump would be assured in new design for gas-to-hydraulic power converter. With a force-multiplying ring attached to gas piston, expanding gas would apply constant force on hydraulic piston even though gas pressure drops. As a result, pressure of hydraulic fluid remains steady, and power output of the pump does not vary.

  11. The Initial Cracking Point of Multi-Branch Hydraulic Fracture Temporary Plugging%多分支缝水力压裂暂堵起裂点位置研究

    Institute of Scientific and Technical Information of China (English)

    夏冲; 廖旋; 刘荆成

    2016-01-01

    针对多分支缝压裂成缝起裂点不明确的问题,基于多孔介质流固耦合理论模型,通过 Comsol Multiphysics 软件进行有限元模拟分支缝压裂过程,分析不同应力差条件下缝内起裂点和井筒起裂点的集中应力变化规律,随着缝内净压力的增加,存在一个差别点,区分起裂点起裂的优先顺序。通过控制缝内净压力变化,调整起裂优先顺序,控制分支缝延伸条数,保证了多分支缝水力压裂缝网的复杂性。对海拉尔油田现场实例计算分析,调整缝内净压力,施工结果与模拟结果相同,可以指导现场施工,提高多分支缝水力压裂的成功率。%The seam crack point of multiple branch seam fracturing is not clear.Based on the theory of porous media of fluid-solid coupling mode,Comsol software was used to simulate branch seam fracturing process using finite element simulation.The changing law of stress concentration of seam crack point and shaft crack point was analysized under the condition of different stress difference it was found that with the increase of net pressure on the seam,there was a difference which distinguished between crack priorities.By controlling the net pressure change within joint,the crack priorities was adjusted,the number of multi-branch fracture was controlled,and the multi-branch seam hydraulic pressure of the complexity of the fracture network was ensured.Calculation analysis of hailaer oil field on the spot was used to adjust the net pressure inside seam.The result of construction was same with simulation,and can be used to guide the construction to improve the success rate of multi-branch seam hydraulic fracturing.

  12. Plant root-driven hydraulic redistribution, root nutrient uptake and carbon exudation interact with soil properties to generate rhizosphere resource hotspots that vary in space and time

    Science.gov (United States)

    Espeleta, J. F.; Neumann, R. B.; Cardon, Z. G.; Mayer, K. U.; Rastetter, E. B.

    2014-12-01

    Hydraulic redistribution (HR) of soil water by plants occurs in seasonally dry ecosystems worldwide. During drought, water flows from deep moist soil, through plant roots, into dry (often litter-rich) upper soil layers. Using modeling, we explored how physical transport processes driven by transpiration and hydraulic redistribution interact with root physiology (nutrient uptake and carbon exudation) and soil properties (soil texture and cation exchange) to influence nitrogen and carbon concentrations in the rhizosphere. At the single root scale, we modeled a 10-cm radial soil domain, and simulated solute transport, soil cation exchange, and root exudation and nutrient uptake under two water flow patterns: daytime transpiration without nighttime HR, and daytime transpiration with nighttime HR. During HR, water efflux flushed solutes away from the root, diluting the concentrations of key nutrients like nitrate. The transport of cations by transpiration in the day and their accumulation near the root led to competitive desorption of ammonium from soil further from the root and generation of hotspots of ammonium availability at night. HR influenced the spatial and temporal patterns of these hotspots and their intensity. They were also influenced by soil properties of texture and cation exchange capacity. This dynamic resource landscape caused by diel cycling between transpiration and hydraulic redistribution presents a stage for greater complexity of microbial interactions. We are currently embedding a microbial community and small food web into this rhizosphere model in order to explore how organisms responsible for nutrient and soil carbon cycling respond to these fluctuating resource regimes.

  13. Numerical design and optimization of hydraulic resistance and wall shear stress inside pressure-driven microfluidic networks.

    Science.gov (United States)

    Damiri, Hazem Salim; Bardaweel, Hamzeh Khalid

    2015-11-07

    Microfluidic networks represent the milestone of microfluidic devices. Recent advancements in microfluidic technologies mandate complex designs where both hydraulic resistance and pressure drop across the microfluidic network are minimized, while wall shear stress is precisely mapped throughout the network. In this work, a combination of theoretical and modeling techniques is used to construct a microfluidic network that operates under minimum hydraulic resistance and minimum pressure drop while constraining wall shear stress throughout the network. The results show that in order to minimize the hydraulic resistance and pressure drop throughout the network while maintaining constant wall shear stress throughout the network, geometric and shape conditions related to the compactness and aspect ratio of the parent and daughter branches must be followed. Also, results suggest that while a "local" minimum hydraulic resistance can be achieved for a geometry with an arbitrary aspect ratio, a "global" minimum hydraulic resistance occurs only when the aspect ratio of that geometry is set to unity. Thus, it is concluded that square and equilateral triangular cross-sectional area microfluidic networks have the least resistance compared to all rectangular and isosceles triangular cross-sectional microfluidic networks, respectively. Precise control over wall shear stress through the bifurcations of the microfluidic network is demonstrated in this work. Three multi-generation microfluidic network designs are considered. In these three designs, wall shear stress in the microfluidic network is successfully kept constant, increased in the daughter-branch direction, or decreased in the daughter-branch direction, respectively. For the multi-generation microfluidic network with constant wall shear stress, the design guidelines presented in this work result in identical profiles of wall shear stresses not only within a single generation but also through all the generations of the

  14. Robust H(∞) positional control of 2-DOF robotic arm driven by electro-hydraulic servo system.

    Science.gov (United States)

    Guo, Qing; Yu, Tian; Jiang, Dan

    2015-11-01

    In this paper an H∞ positional feedback controller is developed to improve the robust performance under structural and parametric uncertainty disturbance in electro-hydraulic servo system (EHSS). The robust control model is described as the linear state-space equation by upper linear fractional transformation. According to the solution of H∞ sub-optimal control problem, the robust controller is designed and simplified to lower order linear model which is easily realized in EHSS. The simulation and experimental results can validate the robustness of this proposed method. The comparison result with PI control shows that the robust controller is suitable for this EHSS under the critical condition where the desired system bandwidth is higher and the external load of the hydraulic actuator is closed to its limited capability. Copyright © 2015 ISA. Published by Elsevier Ltd. All rights reserved.

  15. Transient radon signals driven by fluid pressure pulse, micro-crack closure, and failure during granite deformation experiments

    Science.gov (United States)

    Girault, Frédéric; Schubnel, Alexandre; Pili, Éric

    2017-09-01

    In seismically active fault zones, various crustal fluids including gases are released at the surface. Radon-222, a radioactive gas naturally produced in rocks, is used in volcanic and tectonic contexts to illuminate crustal deformation or earthquake mechanisms. At some locations, intriguing radon signals have been recorded before, during, or after tectonic events, but such observations remain controversial, mainly because physical characterization of potential radon anomalies from the upper crust is lacking. Here we conducted several month-long deformation experiments under controlled dry upper crustal conditions with a triaxial cell to continuously monitor radon emission from crustal rocks affected by three main effects: a fluid pressure pulse, micro-crack closure, and differential stress increase to macroscopic failure. We found that these effects are systematically associated with a variety of radon signals that can be explained using a first-order advective model of radon transport. First, connection to a source of deep fluid pressure (a fluid pressure pulse) is associated with a large transient radon emission increase (factor of 3-7) compared with the background level. We reason that peak amplitude is governed by the accumulation time and the radon source term, and that peak duration is controlled by radioactive decay, permeability, and advective losses of radon. Second, increasing isostatic compression is first accompanied by an increase in radon emission followed by a decrease beyond a critical pressure representing the depth below which crack closure hampers radon emission (150-250 MPa, ca. 5.5-9.5 km depth in our experiments). Third, the increase of differential stress, and associated shear and volumetric deformation, systematically triggers significant radon peaks (ca. 25-350% above background level) before macroscopic failure, by connecting isolated cracks, which dramatically enhances permeability. The detection of transient radon signals before rupture

  16. Subcritical growth of natural hydraulic fractures

    Science.gov (United States)

    Garagash, D.

    2014-12-01

    Joints are the most common example of brittle tensile failure in the crust. Their genesis at depth is linked to the natural hydraulic fracturing, which requires pore fluid pressure in excess of the minimum in situ stress [Pollard and Aidyn, JSG1988]. Depending on the geological setting, high pore pressure can result form burial compaction of interbedded strata, diagenesis, or tectonics. Common to these loading scenarios is slow build-up of pore pressure over a geological timescale, until conditions for initiation of crack growth are met on favorably oriented/sized flaws. The flaws can vary in size from grain-size cracks in igneous rocks to a fossil-size flaws in clastic rock, and once activated, are inferred to propagate mostly subcritically [Segall JGR 1984; Olson JGR 1993]. Despite many observational studies of natural hydraulic fractures, the modeling attempts appear to be few [Renshaw and Harvey JGR 1994]. Here, we use boundary integral formulation for the pore fluid inflow from the permeable rock into a propagating joint [Berchenko et al. IJRMMS 1997] coupled with the criteria for subcritical propagation assisted by the environmental effects of pore fluid at the crack tip to solve for the evolution of a penny-shape joint, which, in interbedded rock, may eventually evolve to short-blade geometry (propagation confined to a bed). Initial growth is exceedingly slow, paced by the stress corrosion reaction kinetics at the crack tip. During this stage the crack is fully-drained (i.e. the fluid pressure in the crack is equilibrated with the ambient pore pressure). This "slow" stage is followed by a rapid acceleration, driven by the increase of the mechanical stress intensity factor with the crack length, towards the terminal joint velocity. We provide an analytical expression for the latter as a function of the rock diffusivity, net pressure loading at the initiation (or flaw lengthscale), and parameters describing resistance to fracture growth. Due to a much slower

  17. Seismological investigation of crack formation in hydraulic rock fracturing experiments and in natural geothermal environments. Progress report, September 1, 1978-August 31, 1979

    Energy Technology Data Exchange (ETDEWEB)

    Aki, K.

    1979-09-01

    An interpretation theory based on the fluid-filled crack model of geothermal systems is being developed and tested against a variety of data from various geothermal areas. Progress is reported on the following subjects: (1) analysis and interpretation of seismic data obtained from the bore holes at the LASL Hot Dry Rock geothermal site. (2) Collection, analysis and interpretation of data on deep volcanic tremors at the USGS Hawaii Volcano Observatory. (3) Development of a new method for determining seismic attenuation at frequencies higher than 1HZ, and initiation of a cooperative work with Mexican seismologists on the attenuation measurements at various geothermal areas in Baja, California using the method. (4) Installation of 3-component digital event-recorders at four stations in the Newberry Peak volcano, Oregon. (5) Developing a computer program for calculating seismic motion generated by the vibration of fluid-filled crack in a layered medium.

  18. 混凝土灌注桩裂缝处理应用技术研究%Research on the application technology of cracking treatment for concrete driven cast-in-place pile

    Institute of Scientific and Technical Information of China (English)

    郁孟龙

    2011-01-01

    介绍温州市城区防洪堤工程混凝土灌注桩裂缝产生经过.混凝土灌注桩为防洪堤基础结构,对出现裂缝的灌注桩进行全面的裂缝特性以及桩身完整性检测.裂缝处理采用注射法以低黏度、高强度的YZJ-5裂缝修补胶液进行修补,并在裂缝处用4层高强度的Ⅱ级碳纤维布进行包覆处理,外层再用4层玻璃纤维布包覆进行防护,能有效封闭裂缝、防止海水侵蚀钢筋,又能对桩身进行补强,取得了较好的工程处理效果.%The occurrence process of crack in concrete driven cast-in-situ pile in anti-flood dike engineering of Wenzhou City is introduced. The concrete driven cast-in-situ pile is the foundation structure of anti-flood dike,an overall check of crack characteristic and pile integrity to those driven cast-in-place piles with cracks are carried out. Crack-repairing glue with low viscosity and high strength is used to inject into cracks,on which 4 layers of grade Ⅱ carbon fibre and 4 layers of glass fibre are applied successively,with effective closure of cracks,preventing erosion from sea water into reinforcement,and strengthening of pile, better treatment results are obtained from above.

  19. Seismological investigation of crack formation in hydraulic rock fracturing experiments and in natural geothermal environments. Progress report, September 1, 1980-August 31, 1981

    Energy Technology Data Exchange (ETDEWEB)

    Aki, K.

    1981-09-01

    Progress is reported on the following: interpretation of seismic data from hydraulic fracturing experiments at the Fenton Hill Hot Dry Rock Geothermal Site, interpretation of 3-D velocity anomalies in the western US with special attention to geothermal areas, theoretical and observational studies of scattering and attenuation of high-frequency seismic waves, theoretical and observational studies of volcanic tremors in relation to magma transport mechanisms, and deployment and maintenance of 9 event-recorders around Mt. St. Helens. Abstracts of papers submitted for publication are included. (MHR)

  20. Fluid-driven fractures in brittle hydrogels

    Science.gov (United States)

    O'Keeffe, Niall; Linden, Paul

    2016-11-01

    Hydraulic fracturing is a process in which fluid is injected deep underground at high pressures that can overcome the strength of the surrounding matrix. This results in an increase of surface area connected to the well bore and thus allows extraction of natural gas previously trapped in a rock formation. We experimentally study the physical mechanisms of these fluid-driven fractures in low permeability reservoirs where the leak-off of fracturing fluid is considered negligible. This is done through the use of small scale experiments on transparent and brittle, heavily cross-linked hydrogels. The propagation of these fractures can be split into two distinct regimes depending on whether the dominant energy dissipation mechanism is viscous flow or material toughness. We will analyse crack growth rates, crack thickness and tip shape in both regimes. Moreover, PIV techniques allow us to explore the flow dynamics within the fracture, which is crucial in predicting transport of proppants designed to prevent localisation of cracks.

  1. Experimental investigation of the thermal hydraulics in lead bismuth eutectic-helium experimental loop of an accelerator-driven system

    Energy Technology Data Exchange (ETDEWEB)

    Xi, Wenxuan; Wang, Yong Wei; Li, Xun Feng; Huai, Xiulan; Cal, Jun [Institute of Engineering Thermophysics, Chinese Academy of Sciences, Beijing (China)

    2016-10-15

    The heat transfer characteristics between liquid lead bismuth eutectic (LBE) and helium are of great significance for the two-loop cooling system based on an accelerator-driven system (ADS). This paper presents an experimental study on the resistance characteristics and heat transfer performance in a LBE-helium experimental loop of ADS. Pressure drops in the LBE loop, the main heat transfer, and the coupled heat transfer characteristics between LBE and helium are investigated experimentally. The temperature of LBE has a significant effect on the LBE thermo-physical properties, and is therefore considered in the prediction of pressure drops. The results show that the overall heat transfer coefficient increases with the increasing helium flow rate and the decreasing inlet temperature of helium. Increasing the LBE Reynolds number and LBE inlet temperature promotes the heat transfer performance of main heat transfer and thus the overall heat transfer coefficient. The experimental results give an insight into the flow and heat transfer properties in a LBE-helium heat exchanger and are helpful for the optimization of an ADS system design.

  2. Linking hydraulic traits to tropical forest function in a size-structured and trait-driven model (TFS v.1-Hydro)

    Science.gov (United States)

    Christoffersen, Bradley O.; Gloor, Manuel; Fauset, Sophie; Fyllas, Nikolaos M.; Galbraith, David R.; Baker, Timothy R.; Kruijt, Bart; Rowland, Lucy; Fisher, Rosie A.; Binks, Oliver J.; Sevanto, Sanna; Xu, Chonggang; Jansen, Steven; Choat, Brendan; Mencuccini, Maurizio; McDowell, Nate G.; Meir, Patrick

    2016-11-01

    Forest ecosystem models based on heuristic water stress functions poorly predict tropical forest response to drought partly because they do not capture the diversity of hydraulic traits (including variation in tree size) observed in tropical forests. We developed a continuous porous media approach to modeling plant hydraulics in which all parameters of the constitutive equations are biologically interpretable and measurable plant hydraulic traits (e.g., turgor loss point πtlp, bulk elastic modulus ɛ, hydraulic capacitance Cft, xylem hydraulic conductivity ks,max, water potential at 50 % loss of conductivity for both xylem (P50,x) and stomata (P50,gs), and the leaf : sapwood area ratio Al : As). We embedded this plant hydraulics model within a trait forest simulator (TFS) that models light environments of individual trees and their upper boundary conditions (transpiration), as well as providing a means for parameterizing variation in hydraulic traits among individuals. We synthesized literature and existing databases to parameterize all hydraulic traits as a function of stem and leaf traits, including wood density (WD), leaf mass per area (LMA), and photosynthetic capacity (Amax), and evaluated the coupled model (called TFS v.1-Hydro) predictions, against observed diurnal and seasonal variability in stem and leaf water potential as well as stand-scaled sap flux. Our hydraulic trait synthesis revealed coordination among leaf and xylem hydraulic traits and statistically significant relationships of most hydraulic traits with more easily measured plant traits. Using the most informative empirical trait-trait relationships derived from this synthesis, TFS v.1-Hydro successfully captured individual variation in leaf and stem water potential due to increasing tree size and light environment, with model representation of hydraulic architecture and plant traits exerting primary and secondary controls, respectively, on the fidelity of model predictions. The plant

  3. Hydraulic fracture during epithelial stretching

    Science.gov (United States)

    Casares, Laura; Vincent, Romaric; Zalvidea, Dobryna; Campillo, Noelia; Navajas, Daniel; Arroyo, Marino; Trepat, Xavier

    2015-03-01

    The origin of fracture in epithelial cell sheets subject to stretch is commonly attributed to excess tension in the cells’ cytoskeleton, in the plasma membrane, or in cell-cell contacts. Here, we demonstrate that for a variety of synthetic and physiological hydrogel substrates the formation of epithelial cracks is caused by tissue stretching independently of epithelial tension. We show that the origin of the cracks is hydraulic; they result from a transient pressure build-up in the substrate during stretch and compression manoeuvres. After pressure equilibration, cracks heal readily through actomyosin-dependent mechanisms. The observed phenomenology is captured by the theory of poroelasticity, which predicts the size and healing dynamics of epithelial cracks as a function of the stiffness, geometry and composition of the hydrogel substrate. Our findings demonstrate that epithelial integrity is determined in a tension-independent manner by the coupling between tissue stretching and matrix hydraulics.

  4. Hydraulic System Design of Hydraulic-Driven Load Exoskeleton Robot%液压驱动型负重外骨骼机器人液压系统设计

    Institute of Scientific and Technical Information of China (English)

    周加永; 张昂; 莫新民; 赵浩; 纪平鑫

    2016-01-01

    Started from human motion characteristics, the hydraulic drive overall load exoskeleton robot skeleton structure was an-alyzed. According to the characteristics of the load exoskeleton robot, a complete hydraulic drive system was designed, and the main el-ements of the selection calculation were carried out as hydraulic system, hydraulic pumps, servo valves and hydraulic cylinders, and etc. Simhydraulics software was used to establish the simulation schematics for hydraulic system of load exoskeleton robot, study and simulation analysis were carried out for the hydraulic system, and simulation results were proved of the rational design of the hydraulic system. In the last, technology challenges faced by the hydraulic drive load exoskeleton robot are analyzed, which provide reference for further design of the hydraulic system.%从人体运动特征出发,分析了液压驱动负重外骨骼机器人的整体骨架结构。根据负重外骨骼机器人的特点要求设计了一套完整的液压传动系统,对液压系统中液压泵、伺服阀和液压缸等主要元件进行了选型计算。利用Simhydraulics软件建立了负重外骨骼机器人液压系统仿真原理图,并对液压系统进行了仿真分析研究,由仿真结果证明了所设计液压系统的合理性。最后对液压驱动型负重外骨骼机器人技术面临的挑战进行了分析,为该液压系统的深化设计提供了参考。

  5. Simulation of Hydraulic Fracturing Crack Propagating of Horizontal Shale Well Based on Extended Finite Element Method%基于扩展有限元的页岩水平井压裂裂缝扩展模拟

    Institute of Scientific and Technical Information of China (English)

    魏波; 陈军斌; 谢青; 张杰; 王汉青; 赵逸然

    2016-01-01

    考虑裂缝内流体流动和岩石受力变形,建立页岩水平井水力压裂裂缝扩展数学模型,采用扩展有限元方法求解该模型。分析水平主应力、岩石力学特征参数及注入速度对裂缝扩展长度的影响,并研究多条裂缝的扩展及转向规律。结果表明:岩石弹性模量越大,泊松比越小,形成的裂缝越长;最小主应力越小,压裂液注入速度越大,裂缝扩展长度越长。同时扩展的2条裂缝之间存在应力干扰使裂缝向外转,裂缝间距越近,转向越明显。3条裂缝同时扩展,中间裂缝受到左右两边裂缝的制约作用,起裂较晚,扩展受到限制;随着压裂时间的延长,中间裂缝会摆脱两边裂缝的影响,冲出应力干扰区。%The mathematical model for the hydraulic fracturing crack propagating of horizontal well in shale reservoir was established under considering the flow of fluid in cracks and the deformation of rock,and it was solved using the extended finite element method. The influences of horizontal principal stress,the mechanics parameters of rock and the injection rate of fracturing fluid on the propaga-tion length of cracks were analyzed,and the propagation and steering law of multiple fractures was researched. The results show that the greater the elasticity modulus of reservoir rock and the less the Poissonˊs ratio of it,the longer the fractures;the lower the minimum prin-cipal stress and the greater the injection rate,the longer the fractures. There is stress interference between two simultaneously propaga-ting fractures,which makes two fractures turning to the outside. The closer the fractures are,the more obvious the steering is. When the three fractures simultaneously propagate,the fracture in middle is restricted,and its initiation is later than on both sides. With the fractu-ring time increasing,the middle fracture breaks away from the stress interference of the cracks on both sides and

  6. Thermally Actuated Hydraulic Pumps

    Science.gov (United States)

    Jones, Jack; Ross, Ronald; Chao, Yi

    2008-01-01

    Thermally actuated hydraulic pumps have been proposed for diverse applications in which direct electrical or mechanical actuation is undesirable and the relative slowness of thermal actuation can be tolerated. The proposed pumps would not contain any sliding (wearing) parts in their compressors and, hence, could have long operational lifetimes. The basic principle of a pump according to the proposal is to utilize the thermal expansion and contraction of a wax or other phase-change material in contact with a hydraulic fluid in a rigid chamber. Heating the chamber and its contents from below to above the melting temperature of the phase-change material would cause the material to expand significantly, thus causing a substantial increase in hydraulic pressure and/or a substantial displacement of hydraulic fluid out of the chamber. Similarly, cooling the chamber and its contents from above to below the melting temperature of the phase-change material would cause the material to contract significantly, thus causing a substantial decrease in hydraulic pressure and/or a substantial displacement of hydraulic fluid into the chamber. The displacement of the hydraulic fluid could be used to drive a piston. The figure illustrates a simple example of a hydraulic jack driven by a thermally actuated hydraulic pump. The pump chamber would be a cylinder containing encapsulated wax pellets and containing radial fins to facilitate transfer of heat to and from the wax. The plastic encapsulation would serve as an oil/wax barrier and the remaining interior space could be filled with hydraulic oil. A filter would retain the encapsulated wax particles in the pump chamber while allowing the hydraulic oil to flow into and out of the chamber. In one important class of potential applications, thermally actuated hydraulic pumps, exploiting vertical ocean temperature gradients for heating and cooling as needed, would be used to vary hydraulic pressures to control buoyancy in undersea research

  7. Experimental Investigation on the Basic Law of Hydraulic Fracturing After Water Pressure Control Blasting

    Science.gov (United States)

    Huang, Bingxiang; Li, Pengfeng; Ma, Jian; Chen, Shuliang

    2014-07-01

    Because of the advantages of integrating water pressure blasting and hydraulic fracturing, the use of hydraulic fracturing after water pressure control blasting is a method that is used to fully transform the structure of a coal-rock mass by increasing the number and range of hydraulic cracks. An experiment to study hydraulic fracturing after water pressure blasting on cement mortar samples (300 × 300 × 300 mm3) was conducted using a large-sized true triaxial hydraulic fracturing experimental system. A traditional hydraulic fracturing experiment was also performed for comparison. The experimental results show that water pressure blasting produces many blasting cracks, and follow-up hydraulic fracturing forces blasting cracks to propagate further and to form numerous multidirectional hydraulic cracks. Four macroscopic main hydraulic cracks in total were noted along the borehole axial and radial directions on the sample surfaces. Axial and radial main failure planes induced by macroscopic main hydraulic cracks split the sample into three big parts. Meanwhile, numerous local hydraulic cracks were formed on the main failure planes, in different directions and of different types. Local hydraulic cracks are mainly of three types: local hydraulic crack bands, local branched hydraulic cracks, and axial layered cracks. Because local hydraulic cracks produce multiple local layered failure planes and lamellar ruptures inside the sample, the integrity of the sample decreases greatly. The formation and propagation process of many multidirectional hydraulic cracks is affected by a combination of water pressure blasting, water pressure of fracturing, and the stress field of the surrounding rock. To a certain degree, the stress field of surrounding rock guides the formation and propagation process of the blasting crack and the follow-up hydraulic crack. Following hydraulic fracturing that has been conducted after water pressure blasting, the integrity of the sample is found to

  8. Effects of hydraulic retention time and [Formula: see text] ratio on thiosulfate-driven autotrophic denitrification for nitrate removal from micro-polluted surface water.

    Science.gov (United States)

    Wang, Zheng; Fei, Xiang; He, Sheng-Bing; Huang, Jung-Chen; Zhou, Wei-Li

    2017-01-18

    This study was carried out to investigate the possibility of a thiosulfate-driven autotrophic denitrification for nitrate-N removal from micro-polluted surface water. The aim was to study the effects of [Formula: see text] ratio (S/N molar ratio) and hydraulic retention time (HRT) on the autotrophic denitrification performance. Besides, utilization efficiencies of [Formula: see text] along the biofilter and the restart-up of the bioreactor were also investigated. Autotrophic denitrification using thiosulfate as an electron donor for treating micro-polluted surface water without the addition of external alkalinity proved to be feasible and the biofilter could be readied in two weeks. Average nitrate-N removal efficiencies at HRTs of 0.5, 1 and 2 h were 78.7%, 87.8% and 97.4%, respectively, and corresponding removal rates were 186.24, 103.92 and 58.56 g [Formula: see text], respectively. When water temperature was in the range of 8-12°C and HRT was 1 h, average nitrate-N removal efficiencies of 41.9%, 97.1% and 97.0%, nitrite accumulation concentrations of 1.45, 0.46 and 0.22 mg/L and thiosulfate utilization efficiencies of 100%, 98.8% and 92.1% were obtained at S/N ratios of 1.0, 1.2 and 1.5, respectively. Besides, the autotrophic denitrification rate in the filtration media layer was the highest along the biofilter at an S/N ratio of 1.5. Finally, after a one-month period of starvation, the biofilter could be restarted successfully in three weeks without inoculation of seed sludge.

  9. Unsaturated Seepage Analysis of Cracked Soil including Development Process of Cracks

    Directory of Open Access Journals (Sweden)

    Ling Cao

    2016-01-01

    Full Text Available Cracks in soil provide preferential pathways for water flow and their morphological parameters significantly affect the hydraulic conductivity of the soil. To study the hydraulic properties of cracks, the dynamic development of cracks in the expansive soil during drying and wetting has been measured in the laboratory. The test results enable the development of the relationships between the cracks morphological parameters and the water content. In this study, the fractal model has been used to predict the soil-water characteristic curve (SWCC of the cracked soil, including the developmental process of the cracks. The cracked expansive soil has been considered as a crack-pore medium. A dual media flow model has been developed to simulate the seepage characteristics of the cracked expansive soil. The variations in pore water pressure at different part of the model are quite different due to the impact of the cracks. This study proves that seepage characteristics can be better predicted if the impact of cracks is taken into account.

  10. Hydraulics and pneumatics

    CERN Document Server

    Parr, Andrew

    2006-01-01

    Nearly all industrial processes require objects to be moved, manipulated or subjected to some sort of force. This is frequently accomplished by means of electrical equipment (such as motors or solenoids), or via devices driven by air (pneumatics) or liquids (hydraulics).This book has been written by a process control engineer as a guide to the operation of hydraulic and pneumatic systems for all engineers and technicians who wish to have an insight into the components and operation of such a system.This second edition has been fully updated to include all recent developments su

  11. 46 CFR 112.50-3 - Hydraulic starting.

    Science.gov (United States)

    2010-10-01

    ... 46 Shipping 4 2010-10-01 2010-10-01 false Hydraulic starting. 112.50-3 Section 112.50-3 Shipping... POWER SYSTEMS Emergency Diesel and Gas Turbine Engine Driven Generator Sets § 112.50-3 Hydraulic starting. A hydraulic starting system must meet the following: (a) The hydraulic starting system must be...

  12. Hydraulic structures

    CERN Document Server

    Chen, Sheng-Hong

    2015-01-01

    This book discusses in detail the planning, design, construction and management of hydraulic structures, covering dams, spillways, tunnels, cut slopes, sluices, water intake and measuring works, ship locks and lifts, as well as fish ways. Particular attention is paid to considerations concerning the environment, hydrology, geology and materials etc. in the planning and design of hydraulic projects. It also considers the type selection, profile configuration, stress/stability calibration and engineering countermeasures, flood releasing arrangements and scouring protection, operation and maintenance etc. for a variety of specific hydraulic structures. The book is primarily intended for engineers, undergraduate and graduate students in the field of civil and hydraulic engineering who are faced with the challenges of extending our understanding of hydraulic structures ranging from traditional to groundbreaking, as well as designing, constructing and managing safe, durable hydraulic structures that are economical ...

  13. HYDRAULIC SERVO

    Science.gov (United States)

    Wiegand, D.E.

    1962-05-01

    A hydraulic servo is designed in which a small pressure difference produced at two orifices by an electrically operated flapper arm in a constantly flowing hydraulic loop is hydraulically amplified by two constant flow pumps, two additional orifices, and three unconnected ball pistons. Two of the pistons are of one size and operate against the additional orifices, and the third piston is of a different size and operates between and against the first two pistons. (AEC)

  14. 超磁致伸缩电液伺服阀驱动机构控制系统设计%Design of Control System of Giant Magnetostrictive Electro-hydraulic Servo Valve Driven Machine

    Institute of Scientific and Technical Information of China (English)

    杨朝舒; 何忠波; 李冬伟; 薛光明

    2014-01-01

    为了实现超磁致伸缩电液伺服阀的快速、准确控制,论述了基于PWM控制的超磁致伸缩电液伺服阀的基本结构和工作原理,设计了基于PicoScope2203数字示波器和STC89C51单片机的超磁致伸缩材料电液伺服阀驱动机构的控制系统。结果表明:该控制系统具有控制精度高、控制迅速、集成度高、操作便捷等特点。%In order to achieve the speedy and precision control of electro⁃hydraulic servo valve based on giant magnetostrictive material, the basic structure and working principle of a kind of Electro⁃hydraulic Servo Valve based on giant magnetostrictive material with PWM control was discussed. A control system for the giant magnetostrictive electro⁃hydraulic servo valve driven machine based on PicoScope2203 Digital Oscilloscope and STC89C51 series MCU was designed. The results show that the control system has properties of high speed and precision, highly integrated and convenient for operation, and etc.

  15. Crack Growth in Concrete Gravity Dams Based on Discrete Crack Method

    Directory of Open Access Journals (Sweden)

    A. R. Lohrasbi

    2008-01-01

    Full Text Available Seepage is the most parameter in water management safety and in stable agricultural. This seepage is passed through the cracks that are present to some degree in hydraulic structures. They may exist as basic defects in the constituent materials or may be induced in construction or during service life. To avoid such failure in concrete dams, safety would be an important factor. Over-design carries heavy penalty in terms of excess weight. So the fracture mechanics theory is a principal necessity of evaluating the stability of such crack propagation. For the process of crack propagation analysis in concrete structures, there are two general models: discrete crack and smeared crack. This study surveys the crack propagation in concrete gravity dams based on discrete crack methods. Moreover, we use a program provided specifically for this purpose.

  16. Resolving discrepancies between hydraulic and chemical calibration data for seawater intrusion groundwater flow models by considering climate-driven sea level change.

    Energy Technology Data Exchange (ETDEWEB)

    J. Chapman; A. Hassan; K. Pohlmann

    2001-10-18

    Groundwater models of seawater intrusion environments can be calibrated using both hydraulic and chemical information. The possible impact of the long-term transient process of sea level change is difficult to identify, but important to accurate simulation of present conditions. The response times of the pressure and chemical fields to major fluctuations in sea level change are investigated

  17. Knuckle Cracking

    Science.gov (United States)

    ... Ask The Expert Ask a Question Physician Corner Rheumatology Conference Rheumatology Rounds Case Rounds Radiology Rounds Pathophysiology of the ... Appointment Information Contact Us Our Faculty Our Staff Rheumatology Specialty Centers Knuckle Cracking Q & A September 10, ...

  18. Basic hydraulics

    CERN Document Server

    Smith, P D

    1982-01-01

    BASIC Hydraulics aims to help students both to become proficient in the BASIC programming language by actually using the language in an important field of engineering and to use computing as a means of mastering the subject of hydraulics. The book begins with a summary of the technique of computing in BASIC together with comments and listing of the main commands and statements. Subsequent chapters introduce the fundamental concepts and appropriate governing equations. Topics covered include principles of fluid mechanics; flow in pipes, pipe networks and open channels; hydraulic machinery;

  19. 新型涡轮驱动水力振荡器设计与实验研究%Design and experimental study on a new type of turbine driven hydraulic oscillator

    Institute of Scientific and Technical Information of China (English)

    王杰; 夏成宇; 冯定; 于长柏

    2016-01-01

    提出了一种新型的石油钻井用水力振荡器,可有效降低管柱摩阻,提高钻井效率.该水力振荡器采用涡轮驱动,并使用双偏心动定阀作为压力脉冲发生机构.通过建立双偏心动定阀的运动特性方程,结合实际工况得出阀盘的最优尺寸.通过选定阀型的水力振荡器性能测试实验,得出在模拟钻压为30 kN ,流量为28 L/s ,工作介质为清水时的振动冲击力约为15859 N ,振动位移约为4.1 mm ,振动频率约为11.4 Hz .该分析与实验结果对水力振荡器的设计与应用具有指导意义.%A new type of hydraulic oscillator for oil drilling is presented ,w hich can effectively re‐duce the frictional resistance and increase the drilling efficiency . The hydraulic oscillator was driven by a turbine ,and double eccentric valve was used as the pressure pulse generating mecha‐nism .By establishing the motion characteristic equation of the double eccentric valve ,the optimal size of the valve disc was obtained based on the actual working conditions .The performance test experiment of the hydraulic oscillator with selected valve was carried out ,the experimental re‐sults showed that the vibration impact force of the hydraulic oscillator was about 15 859 N ,the vibration displacement was about 4.1 mm ,and the vibration frequency was about 11.4 Hz when the drilling pressure was 30 kN ,the flow rate was 28 L/s ,and the working medium was water . The analysis and experimental results have guiding significance for the design and application of the hydraulic oscillator .

  20. Application of Phase-Field Techniques to Hydraulically- and Deformation-Induced Fracture.

    Energy Technology Data Exchange (ETDEWEB)

    Culp, David [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Miller, Nathan [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Schweizer, Laura [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

    2017-08-01

    Phase-field techniques provide an alternative approach to fracture problems which mitigate some of the computational expense associated with tracking the crack interface and the coalescence of individual fractures. The technique is extended to apply to hydraulically driven fracture such as would occur during fracking or CO2 sequestration. Additionally, the technique is applied to a stainless steel specimen used in the Sandia Fracture Challenge. It was found that the phase-field model performs very well, at least qualitatively, in both deformation-induced fracture and hydraulically-induced fracture, though spurious hourglassing modes were observed during coupled hydralically-induced fracture. Future work would include performing additional quantitative benchmark tests and updating the model as needed.

  1. Hydraulic Structures

    Data.gov (United States)

    Department of Homeland Security — This table is required whenever hydraulic structures are shown in the flood profile. It is also required if levees are shown on the FIRM, channels containing the...

  2. Slow crack growth in spinel in water

    Science.gov (United States)

    Schwantes, S.; Elber, W.

    1983-01-01

    Magnesium aluminate spinel was tested in a water environment at room temperature to establish its slow crack-growth behavior. Ring specimens with artificial flaws on the outside surface were loaded hydraulically on the inside surface. The time to failure was measured. Various precracking techniques were evaluated and multiple precracks were used to minimize the scatter in the static fatigue tests. Statistical analysis techniques were developed to determine the strength and crack velocities for a single flaw. Slow crack-growth rupture was observed at stress intensities as low as 70 percent of K sub c. A strengthening effect was observed in specimens that had survived long-time static fatigue tests.

  3. Hydraulic conductivity of GCLs in MSW landfills

    Institute of Scientific and Technical Information of China (English)

    LI Guo-cheng; YANG Wu-chao; DAN Tang-hui

    2008-01-01

    The state of the art of the study on the hydraulic conductivity of GCLs is presented in terms of the in-fluence of the effective stress, chemical interactions, freeze - thaw cycles and temperature gradients. The chan-ges of void ratio caused by changes of effective stress have a direct linear effect on the hydraulic conductivity, regardless of the cation concentration or the thickness of the adsorbed layer. The hydraulic conductivity is relat-ed to the relative abundance of monovalent and divalent cation(RMD), and RMD has a great effect on the hy-draulic conductivity in weak solution. The long-term susceptibility of GCLs to increased hydraulic conductivity as a response to repeated freeze-thaw cycling is minimal, which has been proved after 150 freeze-thaw cycles. The potential of desiccation cracking increases with the increasing temperature gradient and is related to the ini-tial subsoil water content, the applied overburden stress, etc.

  4. A time step criterion for the stable numerical simulation of hydraulic fracturing

    Science.gov (United States)

    Juan-Lien Ramirez, Alina; Löhnert, Stefan; Neuweiler, Insa

    2017-04-01

    within the crack rises. The fluid flow within the crack and in the porous medium are simulated using the mass balance for water and Darcy's law for flow. The equations for flow and deformation in the rock and that for flow in the fracture are solved in a staggered manner. The two sets of equations are coupled via Lagrange multipliers. We present a time step criterion for the stability of the scheme and illustrate this criterion with test examples of crack propagation. [1] T. Boone and A. Ingraffea. A numerical procedure for simulation of hydraulically-driven fracture propagation in poroelastic media. Int. J. Numer. Anal. Met. 14, 27-47, (1990) [2] T. Mohammadnejad and A. Khoei. An extended finite element method for hydraulic fracture propagation in deformable porous media with the cohesive crack model. Finite Elements in Analysis and Design. 73, 77-95, (2013) [3] E.W. Remij, J.J.C. Remmers, J.M. Huyghe, D.M.J. Smeulders. The enhanced local pressure model for the accurate analysis of fluid pressure driven fracture in porous materials. Comput. Methods Appl. Mech. Engrg. 286, 293-312, (2015)

  5. Parallel Rolling Robot with Hydraulic Driven Expandable Chain%液压驱动缩放支链的并联式滚动机器人

    Institute of Scientific and Technical Information of China (English)

    沈海阔; 丁万; 仝龙飞; 黄齐来; 姚燕安

    2015-01-01

    A novel three degrees of freedom (DOF) parallel rolling robot is proposed. The main consideration for proposing the robot aims at acquiring large deformation capability, powerful strength output, rapid response and flexible locomotion. The robot adopts the parallel mechanism as its architecture to guarantee the stiffness of the robot. The large deformation capability is obtained by taking advantage of the planar expandable mechanism as the extension ratio enlarging mechanism. The usage of the hydraulic actuation as the telescopic input increases the locomotion flexibility and the strength output of the robot. The robot rolls by properly planning and controlling the relations between the center of mass (CM) of the robot and the supporting region. The mechanical construction and configuration of the robot is described, the rolling gaits are planned, and the optimal locomotion rule is given. Based on the rule, the kinematic model of the robot is built. The correctness of the kinematic model is verified by the given numerical example. The locomotion feasibility of the two locomotion periods is analysed. A set of experimental system including the hydraulic system and robotic system is built. Four rolling experiments are carried out accordingly. The experimental results demonstrate that the experimental system is reliable and possesses the rapid response capability, and verify that the validity and feasibility of the theoretical analysis and the rolling locomotion.%提出一种新型三自由度并联式滚动机器人。该机器人以大变形、强力输出、快速响应和运动灵活为目标,构型上采用提出的新型并联机构为本体以保证机构整体刚度,设计上应用平面缩放支链作为伸缩比放大机构以获得大变形能力,驱动上利用液压执行元件作为伸缩驱动输入以增强滚动机器人运动的灵活性与力量输出。其翻滚运动是通过合理规划与控制机器人质心与支撑区域之间关系而

  6. Towards a Model of Reactive-Cracking: the Role of Reactions, Elasticity and Surface Energy Driven Flow in Poro-elastic Media

    Science.gov (United States)

    Evans, O.; Spiegelman, M. W.; Wilson, C. R.; Kelemen, P. B.

    2016-12-01

    Many critical processes can be described by reactive fluid flow in brittle media, including hydration/alteration of oceanic plates near spreading ridges, chemical weathering, and dehydration/decarbonation of subducting plates. Such hydration reactions can produce volume changes that may induce stresses large enough to drive fracture in the rock, in turn exposing new reactive surface and modifying the permeability. A better understanding of this potentially rich feedback could also be critical in the design of engineered systems for geologic carbon sequestration. To aid understanding of these processes we have developed a macroscopic continuum description of reactive fluid flow in an elastically deformable porous media. We explore the behaviour of this model by considering a simplified hydration reaction (e.g. olivine + H20 -> serpentine + brucite). In a closed system, these hydration reactions will continue to consume available fluids until the permeability reaches zero, leaving behind it a highly stressed residuum. Our model demonstrates this limiting behaviour, and that the elastic stresses generated are large enough to cause failure/fracture of the host rock. Whilst it is understood that `reactive fracture' is an important mechanism for the continued evolution of this process, it is also proposed that imbibition/surface energy driven flow may play a role. Through a simplified set of computational experiments, we investigate the relative roles of elasticity and surface energy in both a non-reactive purely poro-elastic framework, and then in the presence of reaction. We demonstrate that surface energy can drive rapid diffusion of porosity, thus allowing the reaction to propagate over larger areas. As we expect both surface energy and fracture/failure to be of importance in these processes, we plan to integrate the current model into one that allows for fracture once critical stresses are exceeded.

  7. 46 CFR 111.97-5 - Electric and hydraulic power supply.

    Science.gov (United States)

    2010-10-01

    ... by one or more motor-driven hydraulic pumps that can operate from the final source of the emergency lighting and power system. (d) The motor-driven hydraulic pumps must automatically maintain the accumulator... 46 Shipping 4 2010-10-01 2010-10-01 false Electric and hydraulic power supply. 111.97-5...

  8. Two-axis hydraulic joint for high speed, heavy lift robotic operations

    Energy Technology Data Exchange (ETDEWEB)

    Vaughn, M.R.; Robinett, R.D.; Phelan, J.R.; VanZuiden, D.M.

    1994-04-01

    A hydraulically driven universal joint was developed for a heavy lift, high speed nuclear waste remediation application. Each axis is driven by a simple hydraulic cylinder controlled by a jet pipe servovalve. Servovalve behavior is controlled by a force feedback control system, which damps the hydraulic resonance. A prototype single joint robot was built and tested. A two joint robot is under construction.

  9. Matrix Crack Detection by an Embedded Polarimetric Sensor

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    Polarimetric optical fibre sensors have been embedded within the 0° ply and close to the 0/90 interface of transparent cross-ply GFRP coupons. The laminate ply cracks may initiate and propagate across the coupon when the coupons were subjected to an increasing quasi-static load in a servo-hydraulic testing machine.Crack accumulation have been monitored using a long gauge-length extensometer. The response of the strain signal, the optical signal and the load signal to cracks at different positions in the coupon in relation to the extensometer and optical sensor positions have been acquired and compared by means of video images of the crack growth. The relationship between crack growth and sensor response was demonstrated. The displacement induced by a new transverse crack has been predicted and compared with experimental data.

  10. Self-potential observations during hydraulic fracturing

    Energy Technology Data Exchange (ETDEWEB)

    Moore, Jeffrey R.; Glaser, Steven D.

    2007-09-13

    The self-potential (SP) response during hydraulic fracturing of intact Sierra granite was investigated in the laboratory. Excellent correlation of pressure drop and SP suggests that the SP response is created primarily by electrokinetic coupling. For low pressures, the variation of SP with pressure drop is linear, indicating a constant coupling coefficient (Cc) of -200 mV/MPa. However for pressure drops >2 MPa, the magnitude of the Cc increases by 80% in an exponential trend. This increasing Cc is related to increasing permeability at high pore pressures caused by dilatancy of micro-cracks, and is explained by a decrease in the hydraulic tortuosity. Resistivity measurements reveal a decrease of 2% prior to hydraulic fracturing and a decrease of {approx}35% after fracturing. An asymmetric spatial SP response created by injectate diffusion into dilatant zones is observed prior to hydraulic fracturing, and in most cases this SP variation revealed the impending crack geometry seconds before failure. At rupture, injectate rushes into the new fracture area where the zeta potential is different than in the rock porosity, and an anomalous SP spike is observed. After fracturing, the spatial SP distribution reveals the direction of fracture propagation. Finally, during tensile cracking in a point load device with no water flow, a SP spike is observed that is caused by contact electrification. However, the time constant of this event is much less than that for transients observed during hydraulic fracturing, suggesting that SP created solely from material fracture does not contribute to the SP response during hydraulic fracturing.

  11. Numerical modelling of desiccation cracking of clayey soil

    Directory of Open Access Journals (Sweden)

    Vo Thi Dong

    2016-01-01

    Full Text Available The formation and propagation of desiccation cracks in soil is an extremely complex phenomenon because of the coupling between hydraulic and mechanical behaviour of soil, which are constituted here by the presence of capillary forces and discontinuities. The formation of a cracks network strongly influences the mechanical and hydraulic properties of soil. The main objective of this research is to study the evolution of suction and strain fields, the initiation and propagation of cracks under the effect of drying, using the finite element method. A simulation of a soil sample with four cohesive joints shows the results similar to experimental data. In addition, a simulation of multijoints shows that cracks does not open in all potentials positions and it gives similar spacing.

  12. FEEDBACK LINEARISATION APPLIED ON A HYDRAULIC

    DEFF Research Database (Denmark)

    Andersen, Torben Ole; Hansen, Michael Rygaard; Pedersen, Henrik C.;

    2005-01-01

    Generally most hydraulic systems are intrensically non-linear, why applying linear control techniques typically results in conservatively dimensioned controllers to obtain stable performance. Non-linear control techniques have the potential of overcoming these problems, and in this paper the focus...... is on developing and applying several different feedback linearisation (FL) controllers to the individual servo actuators in a hydraulically driven servo robot to evaluate and compare their possiblities and limitations. This is done based on both simulation and experimental results....

  13. DESIGN AND CONSTRUCTION OF A HYDRAULIC PISTON

    OpenAIRE

    Santos De La Cruz, Eulogio; Universidad Nacional Mayor de San Marcos; Rojas Lazo, Oswaldo; Universidad Nacional Mayor de San Marcos; Yenque Dedios, Julio; Universidad Nacional Mayor de San Marcos; Lavado Soto, Aurelio; Universidad Nacional Mayor de San Marcos

    2014-01-01

    A hydraulic system project includes the design, materials selection and construction of the hydraulic piston, hydraulic circuit and the joint with the pump and its accesories. This equiment will be driven by the force of moving fluid, whose application is in the devices of machines, tools, printing, perforation, packing and others. El proyecto de un sistema hidráulico, comprende el diseño, selección de materiales y construcción del pistón hidráulico, circuito hidráulico y el ensamble con l...

  14. Gear Crack Propagation Investigation

    Science.gov (United States)

    1995-01-01

    Reduced weight is a major design goal in aircraft power transmissions. Some gear designs incorporate thin rims to help meet this goal. Thin rims, however, may lead to bending fatigue cracks. These cracks may propagate through a gear tooth or into the gear rim. A crack that propagates through a tooth would probably not be catastrophic, and ample warning of a failure could be possible. On the other hand, a crack that propagates through the rim would be catastrophic. Such cracks could lead to disengagement of a rotor or propeller from an engine, loss of an aircraft, and fatalities. To help create and validate tools for the gear designer, the NASA Lewis Research Center performed in-house analytical and experimental studies to investigate the effect of rim thickness on gear-tooth crack propagation. Our goal was to determine whether cracks grew through gear teeth (benign failure mode) or through gear rims (catastrophic failure mode) for various rim thicknesses. In addition, we investigated the effect of rim thickness on crack propagation life. A finite-element-based computer program simulated gear-tooth crack propagation. The analysis used principles of linear elastic fracture mechanics, and quarter-point, triangular elements were used at the crack tip to represent the stress singularity. The program had an automated crack propagation option in which cracks were grown numerically via an automated remeshing scheme. Crack-tip stress-intensity factors were estimated to determine crack-propagation direction. Also, various fatigue crack growth models were used to estimate crack-propagation life. Experiments were performed in Lewis' Spur Gear Fatigue Rig to validate predicted crack propagation results. Gears with various backup ratios were tested to validate crack-path predictions. Also, test gears were installed with special crack-propagation gages in the tooth fillet region to measure bending-fatigue crack growth. From both predictions and tests, gears with backup ratios

  15. Simulation of Hydraulic Fracture in Unsaturated Soils with High Degree of Saturation

    Directory of Open Access Journals (Sweden)

    Tielin Chen

    2014-01-01

    Full Text Available A numerical simulation approach of hydraulic fracture process, considering the couplings of the stress distribution, the fluid flow of the water-air mixture, the compression and dissolution of air, and the element damage evolution, has been developed to investigate the mechanisms of crack initiation and propagation in porous media during hydraulic fracturing. The concept of homogenized pore fluid has been adopted to represent the water air mixture. A large number of numerical analysis on hydraulic fracturing in clay with incipient injection slot have been carried out to study the mechanism of hydraulic fracturing in unsaturated soil with the characteristic of critical model I type of crack loading using stress intensity factor KIc. The results provide a numerical picture depicting the mechanisms of crack initiation and propagation during hydraulic fracturing. The numerical results are in good agreement with the experimental results, which confirms the adequacy and the power of the numerical approach.

  16. Research for different crack width calculation methods of concrete-lined steel pressure pipe

    Science.gov (United States)

    Xu, Chuang; Li, Yang

    2017-08-01

    Based on a certain threshold to ensure the durability of structure, the concrete-lined steel pressure pipes used in the structure of large hydropower station widely are allowed to exist in concrete cracking under the action of a certain hydraulic pressure. According to the 1:2 large scale experiment model and the measured data of Three Gorges Hydro-power Station, the existing different methods for calculating crack width were compared and improvements and crack control measures were raised.

  17. Hydraulic drive and control system of the cone collecting robot

    Institute of Scientific and Technical Information of China (English)

    Kong Qinghua; Liu Jinhao; Lu Huaimin

    1999-01-01

    This paper describes the basic structure and design and operation principle of the hydraulic drive and control system with two pumps and two circuits. The manipulator of the cone collecting robot designed is full driven by hydraulic, which has five freedoms. The computer and electrohydraulic proportion velocity regulating valve were installed to realize open loop serve control for reducing cost and easy application.

  18. Modified Dugdale cracks and Fictitious cracks

    DEFF Research Database (Denmark)

    Nielsen, Lauge Fuglsang

    1998-01-01

    (displacement) respectively of material considered. The practical applicability of the two models is limited such that predicted strength sigma_CR must be less than sigma_L/3, which corresponds to an assumption that fictitious cracks are much smaller than real crack lengths considered. The reason......A number of theories are presented in the literature on crack mechanics by which the strength of damaged materials can be predicted. Among these are theories based on the well-known Dugdale model of a crack prevented from spreading by self-created constant cohesive flow stressed acting in local...... Dugdale crack is the same as if it has been weakened by the well-known Griffith crack, namely sigma_CR = (EG_CR/phi)^1/2 where E and 1 are Young's modulus and crack half-length respectively, and G_CR is the so-called critical energy release rate. The physical significance of G_CR, however, is different...

  19. HYDRAULICS, LOUISA COUNTY, USA

    Data.gov (United States)

    Federal Emergency Management Agency, Department of Homeland Security — Hydraulic data include spatial datasets and data tables necessary for documenting the hydraulic analysis for estimating flood stages for a flood insurance study. It...

  20. Hydraulic Hybrid Vehicles

    Science.gov (United States)

    EPA and the United Parcel Service (UPS) have developed a hydraulic hybrid delivery vehicle to explore and demonstrate the environmental benefits of the hydraulic hybrid for urban pick-up and delivery fleets.

  1. Field investigation into directional hydraulic fracturing for hard roof in Tashan Coal Mine

    Institute of Scientific and Technical Information of China (English)

    Bing-Xiang HUANG; Bin YU; Feng FENG; Zhao LI; You-Zhuang WANG; Jin-Rong LIU

    2013-01-01

    Research and development of safe and effective control technology of hard roof is an inevitable trend at present.Directional hydraulic fracturing technology is expected to become a safe and effective way to control and manage hard roof.In order to make hard roof fracture in a directional way,a hydraulic fracture field test has been conducted in the third panel district of Tashan Coal Mine in Datong.First,two hydraulic fracturing drilling holes and four observing drilling holes were arranged in the roof,followed by a wedge-shaped ring slot in each hydraulic fracturing drilling hole.The hydraulic fracturing holes were then sealed and,hydraulic fracturing was conducted.The results show that the hard roof is fractured directionally by the hydraulic fracturing function of the two fracturing drilling holes; the sudden drop,or the overall downward trend of hydraulic pressure from hydraulic monitoring is the proof that the rock in the hard roof has been fractured.The required hydraulic pressure to fracture the hard roof in Tashan coal mine,consisting of carboniferous sandstone layer,is 50.09 MPa,and the fracturing radius of a single drilling hole is not less than 10.5 m.The wedge-shaped ring slot made in the bottom of the hydraulic fracturing drilling hole plays a guiding role for crack propagation.After the hydraulic fracturing drill hole is cracked,the propagation of the resulting hydraulic crack,affected mainly by the regional stress field,will turn to other directions.

  2. Experimental Investigation of Moisture Driven Fracture in Solid Wood

    DEFF Research Database (Denmark)

    Larsen, Finn; Ormarsson, Sigurdur; Olesen, John Forbes

    2010-01-01

    Solid timber products, containing both heartwood and sapwood, often have a high tendency to crack during the drying process. This can cause severe loss of material for the saw-mills, especially for products with large cross sectional dimensions. The cracks (e.g. end-cracks) arise, in some cases, ...... of a finite element model to evaluate the various couplings in the hygro-mechanical problem that govern moisture driven cracking in wood....

  3. Crack layer theory

    Science.gov (United States)

    Chudnovsky, A.

    1984-01-01

    A damage parameter is introduced in addition to conventional parameters of continuum mechanics and consider a crack surrounded by an array of microdefects within the continuum mechanics framework. A system consisting of the main crack and surrounding damage is called crack layer (CL). Crack layer propagation is an irreversible process. The general framework of the thermodynamics of irreversible processes are employed to identify the driving forces (causes) and to derive the constitutive equation of CL propagation, that is, the relationship between the rates of the crack growth and damage dissemination from one side and the conjugated thermodynamic forces from another. The proposed law of CL propagation is in good agreement with the experimental data on fatigue CL propagation in various materials. The theory also elaborates material toughness characterization.

  4. Effect of crack propagation on crack tip fields

    Directory of Open Access Journals (Sweden)

    F.V. Antunes

    2013-07-01

    Full Text Available Crack closure influences fatigue crack growth rate and must be included in the design of components. Plasticity induced crack closure is intimately linked with the crack tip plastic deformation, which becomes residual as the crack propagates. The objective here is to study numerically the effect of crack propagation on crack tip fields. The transient effect observed at the beginning of crack propagation is linked to the hardening behavior of material. The effect of mesh refinement is studied, and a singular behavior is evident, which is explained by the sharp crack associated with mesh topology, composed of a regular pattern of square elements. The plastic zone size measured perpendicularly to crack flank in the residual plastic wake is quantified and compared with literature models. Finally, the removal of material at the first node behind crack tip with load cycling was observed for plane strain state and some hardening models in plane stress state.

  5. Numerical modeling of concrete hydraulic fracturing with extended finite element method

    Institute of Scientific and Technical Information of China (English)

    REN QingWen; DONG YuWen; YU TianTang

    2009-01-01

    The extended finite element method (XFEM) is a new numerical method for modeling discontinuity.Research about numerical modeling for concrete hydraulic fracturing by XFEM is explored. By building the virtual work principle of the fracture problem considering water pressure on the crack surface, the governing equations of XFEM for hydraulic fracture modeling are derived. Implementation of the XFEM for hydraulic fracturing is presented. Finally, the method is verified by two examples and the advan-tages of the XFEM for hydraulic fracturing analysis are displayed.

  6. Numerical modeling of concrete hydraulic fracturing with extended finite element method

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    The extended finite element method (XFEM) is a new numerical method for modeling discontinuity. Research about numerical modeling for concrete hydraulic fracturing by XFEM is explored. By building the virtual work principle of the fracture problem considering water pressure on the crack surface, the governing equations of XFEM for hydraulic fracture modeling are derived. Implementation of the XFEM for hydraulic fracturing is presented. Finally, the method is verified by two examples and the advan- tages of the XFEM for hydraulic fracturing analysis are displayed.

  7. Small-crack test methods

    Science.gov (United States)

    Larsen, James M.; Allison, John E.

    This book contains chapters on fracture mechanics parameters for small fatigue cracks, monitoring small-crack growth by the replication method, measurement of small cracks by photomicroscopy (experiments and analysis), and experimental mechanics of microcracks. Other topics discussed are the real-time measurement of small-crack-opening behavior using an interferometric strain/displacement gage; direct current electrical potential measurement of the growth of small cracks; an ultrasonic method for the measurement of the size and opening behavior of small fatigue cracks; and the simulation of short crack and other low closure loading conditions, utilizing constant K(max) Delta-K-decreasing fatigue crack growth procedures.

  8. Subcooled choked flow through steam generator tube cracks

    Science.gov (United States)

    Wolf, Brian J.

    The work presented here describes an experimental investigation into the choked flow of initially subcooled water through simulated steam generator tube cracks at pressures up to 6.9 MPa. The study of such flow is relevant to the prediction of leak flow rates from a nuclear reactor primary side to secondary side through cracks in steam generator tubes. An experimental approach to measuring such flow is de- scribed. Experimental results from data found in literature as well as the data collected in this work are compared with predictions from presented models as well as predictions from the thermal-hydraulic system code RELAP5. It is found that the homogeneous equilibrium model underpredicts choked flow rates of subcooled water through slits and artificial steam generator tube cracks. Additional modeling of thermal non-equilibrium improves the predictibility of choking mass flux for homogeneous models, however they fail to account for the characteristics of the two-phase pressure drop. An integral modeling approach is enhanced using a correlation developed from the data herein. Also, an assessment of the thermal-hydraulics code RELAP5 is performed and it’s applicability to predict choking flow rates through steam generator tube cracks is addressed. This assessment determined that the Henry & Fauske model, as coded in RELAP5, is best suited for modeling choked flow through steam generator tube cracks. Finally, an approach to applying choked flow data that is not at the same thermo-dynamic conditions as a prototype is developed.

  9. Effect of crack surface geometry on fatigue crack closure

    Energy Technology Data Exchange (ETDEWEB)

    Drury, W.J. [P and L Technologies, Inc., Atlanta, GA (United States); Gokhale, A.M. [Georgia Inst. of Tech., Atlanta, GA (United States). School of Materials Science and Engineering; Antolovich, S.D. [Washington State Univ., Pullman, WA (United States). School of Mechanical and Materials Engineering

    1995-10-01

    The geometry of crack faces often plays a critical role in reducing crack extension forces when crack closure occurs during fatigue crack growth. Most previous studies of fatigue crack closure are concerned with mechanical measure of closure as related to the crack growth rate; very little attention has been given to the geometry of the crack surfaces. The objective is to identify those aspects of crack surface geometry that are important in the closure process, to develop quantitative fractographic techniques to estimate such attributes in a statistically significant and robust manner, and to correlate them to the physical process of crack closure. For this purpose, fatigue crack propagation experiments were performed on a Ni-base superalloy and crack growth rates and crack closure loads were measured. Digital image profilometry and software-based analysis techniques were used for statistically reliable and detailed quantitative characterization of fatigue crack profiles. It is shown that the dimensionless, scale-independent attributes, such a height-to-width ratio of asperities, fractal dimensions, dimensionless roughness parameters, etc., do not represent the aspects of crack geometry that are of primary importance in the crack closure phenomena. Furthermore, it is shown that the scale-dependent characteristics, such as average asperity height, do represent the aspects of crack geometry that play an interactive role in the closure process. These observations have implications concerning the validity of geometry-dependent, closure-based models for fatigue crack growth.

  10. Hydraulic Redistribution: A Modeling Perspective

    Science.gov (United States)

    Daly, E.; Verma, P.; Loheide, S. P., III

    2014-12-01

    Roots play a key role in the soil water balance. They extract and transport water for transpiration, which usually represents the most important soil water loss in vegetated areas, and can redistribute soil water, thereby increasing transpiration rates and enhancing root nutrient uptake. We present here a two-dimensional model capable of describing two key aspects of root water uptake: root water compensation and hydraulic redistribution. Root water compensation is the ability of root systems to respond to the reduction of water uptake from areas of the soil with low soil water potential by increasing the water uptake from the roots in soil parts with higher water potential. Hydraulic redistribution is a passive transfer of water through the root system from areas of the soil with greater water potential to areas with lower water potential. Both mechanisms are driven by gradients of water potential in the soil and the roots. The inclusion of root water compensation and hydraulic redistribution in models can be achieved by describing root water uptake as a function of the difference in water potential between soil and root xylem. We use a model comprising the Richards equation for the water flow in variably saturated soils and the Darcy's equation for the water flow in the xylem. The two equations are coupled via a sink term, which is assumed to be proportional to the difference between soil and xylem water potentials. The model is applied in two case studies to describe vertical and horizontal hydraulic redistribution and the interaction between vegetation with different root depths. In the case of horizontal redistribution, the model is used to reproduce the fluxes of water across the root system of a tree subjected to uneven irrigation. This example can be extended to situations when only part of the root system has access to water, such as vegetation near creeks, trees at the edge of forests, and street trees in urban areas. The second case is inspired by recent

  11. Quantity effect of radial cracks on the cracking propagation behavior and the crack morphology.

    Directory of Open Access Journals (Sweden)

    Jingjing Chen

    Full Text Available In this letter, the quantity effect of radial cracks on the cracking propagation behavior as well as the circular crack generation on the impacted glass plate within the sandwiched glass sheets are experimentally investigated via high-speed photography system. Results show that the radial crack velocity on the backing glass layer decreases with the crack number under the same impact conditions during large quantities of repeated experiments. Thus, the "energy conversion factor" is suggested to elucidate the physical relation between the cracking number and the crack propagation speed. Besides, the number of radial crack also takes the determinative effect in the crack morphology of the impacted glass plate. This study may shed lights on understanding the cracking and propagation mechanism in laminated glass structures and provide useful tool to explore the impact information on the cracking debris.

  12. Pulsating hydraulic fracturing technology in low permeability coal seams

    Institute of Scientific and Technical Information of China (English)

    Wang Wenchao; Li Xianzhong; Lin Baiquan; Zhai Cheng

    2015-01-01

    Based on the difficult situation of gas drainage in a single coal bed of high gas content and low perme-ability, we investigate the technology of pulsating hydraulic pressure relief, the process of crank plunger movement and the mechanism of pulsating pressure formation using theoretical research, mathematical modeling and field testing. We analyze the effect of pulsating pressure on the formation and growth of fractures in coal by using the pulsating hydraulic theory in hydraulics. The research results show that the amplitude of fluctuating pressure tends to increase in the case where the exit is blocked, caused by pulsating pressure reflection and frictional resistance superposition, and it contributes to the growth of fractures in coal. The crack initiation pressure of pulsating hydraulic fracturing is 8 MPa, which is half than that of normal hydraulic fracturing;the pulsating hydraulic fracturing influence radius reaches 8 m. The total amount of gas extraction is increased by 3.6 times, and reaches 50 L/min at the highest point. The extraction flow increases greatly, and is 4 times larger than that of drilling without fracturing and 1.2 times larger than that of normal hydraulic fracturing. The technology provides a technical measure for gas drainage of high gas content and low permeability in the single coal bed.

  13. Vibration of hydraulic machinery

    CERN Document Server

    Wu, Yulin; Liu, Shuhong; Dou, Hua-Shu; Qian, Zhongdong

    2013-01-01

    Vibration of Hydraulic Machinery deals with the vibration problem which has significant influence on the safety and reliable operation of hydraulic machinery. It provides new achievements and the latest developments in these areas, even in the basic areas of this subject. The present book covers the fundamentals of mechanical vibration and rotordynamics as well as their main numerical models and analysis methods for the vibration prediction. The mechanical and hydraulic excitations to the vibration are analyzed, and the pressure fluctuations induced by the unsteady turbulent flow is predicted in order to obtain the unsteady loads. This book also discusses the loads, constraint conditions and the elastic and damping characters of the mechanical system, the structure dynamic analysis, the rotor dynamic analysis and the system instability of hydraulic machines, including the illustration of monitoring system for the instability and the vibration in hydraulic units. All the problems are necessary for vibration pr...

  14. Handbook of hydraulic fluid technology

    CERN Document Server

    Totten, George E

    2011-01-01

    ""The Handbook of Hydraulic Fluid Technology"" serves as the foremost resource for designing hydraulic systems and for selecting hydraulic fluids used in engineering applications. Featuring new illustrations, data tables, as well as practical examples, this second edition is updated with essential information on the latest hydraulic fluids and testing methods. The detailed text facilitates unparalleled understanding of the total hydraulic system, including important hardware, fluid properties, and hydraulic lubricants. Written by worldwide experts, the book also offers a rigorous overview of h

  15. Characteristics of Crack Growth in High Performance Concrete Subjected to Fire

    Institute of Scientific and Technical Information of China (English)

    Gaifei PENG; Sammy Yin Nin CHAN; Jianhua YAN; Yefeng LIU; Quanxin YI

    2005-01-01

    An experimental investigation was conducted to identify the characteristics of crack growth in high performance concrete (HPC) subjected to fire, including two parts of work, I.e. Crack growth resistance determinations and cracking observations, using concrete of three strength grades 40 Mpa, 70 Mpa, and 110 Mpa. The crack growth resistance curves (R-curves) of HPC subjected to high temperatures were determined using notched three-point bend beam specimens of 100 mm×100 mm×300 mm. The R-curve (crack growth resistance curve) flattening shows that the crack growth resistance has been significantly reduced by elevated temperature. Concrete with a higher strength grade has a steeper R-curve, with a higher fracture toughness but a shorter critical crack growth. The shorter critical crack growth means that concrete of a higher strength grade has a more brittle behavior. The concrete cracking observations reveal that the consequences of rapid heating are quite different from those of slow heating. For slow heating at a rate of 0.5℃/min, HPC suffered no obvious cracking below 600℃ even if it had a high moisture content. Explosive spalling is an extreme case of the internal cracking driven mainly by vapor pressure. All these results confirmed the vapor pressure mechanism for spalling behavior which should be more significant for denser concrete. The crack growth ranges obtained from the R-curve determination results are in good agreement with those measured in the concrete cracking observations.

  16. Modelling of Corrosion Cracks

    DEFF Research Database (Denmark)

    Thoft-Christensen, Palle

    Modelling of corrosion cracking of reinforced concrete structures is complicated as a great number of uncertain factors are involved. To get a reliable modelling a physical and mechanical understanding of the process behind corrosion in needed.......Modelling of corrosion cracking of reinforced concrete structures is complicated as a great number of uncertain factors are involved. To get a reliable modelling a physical and mechanical understanding of the process behind corrosion in needed....

  17. Hydraulics and pneumatics a technician's and engineer's guide

    CERN Document Server

    Parr, Andrew

    2011-01-01

    Nearly all industrial processes require objects to be moved, manipulated or subjected to some sort of force. Such movements and manipulations are frequently accomplished by means of devices driven by liquids (hydraulics) or air (pneumatics), the subject of this book. Hydraulics and Pneumatics is written by a practicing process control engineer as a guide to the successful operation of hydraulic and pneumatic systems for all engineers and technicians working with them. Keeping mathematics and theory to a minimum, this practical guide is thorough but accessible to technicians without a

  18. Natural hydraulic fractures and the mechanical stratigraphy of shale-dominated strata

    Science.gov (United States)

    Imber, Jonathan; Armstrong, Howard; Atar, Elizabeth; Clancy, Sarah; Daniels, Susan; Grattage, Joshua; Herringshaw, Liam; Trabucho-Alexandre, João; Warren, Cassandra; Wille, Jascha; Yahaya, Liyana

    2016-04-01

    .2-4.3 fractures per m, consistent with field observations that this formation is more highly fractured than the Cleveland Ironstone Formation. Semi-quantitative estimates of the mineralogical "brittleness index" suggest the highly fractured, clay-rich Mulgrave Shale Member of the Whitby Mudstone Formation has a low brittleness. Our results are therefore inconsistent with the widely held assumption that natural fracture density is greatest within units characterised by a high brittleness index. We propose that stratigraphic variations in fracture densities are more likely to result from the different distributions of crack driving stresses; formations containing decimetre-scale, and most likely stiff, carbonate layers (such as the Cleveland Ironstone Formation) will have differing crack driving stresses compared with silt- and mudstone dominated successions (such as the Whitby Mudstone Formation). The high fracture density observed within the Mulgrave Shale Member is also consistent with propagation of natural hydraulic fractures driven by fluid overpressure caused by maturation of organic matter concentrated within this unit. The next step is to investigate the relative importance of maturation-driven overpressure v. mechanical heterogeneity by analysing the stratigraphic variations in fracture density within the underlying, organic-matter lean Redcar Mudstone Formation.

  19. Predicting Future Deterioration of Hydraulic Steel Structures with Markov Chain and Multivariate Samples of Statistical Distributions

    Directory of Open Access Journals (Sweden)

    Guillermo A. Riveros

    2014-01-01

    Full Text Available Combined effects of several complex phenomena cause the deterioration of elements of steel hydraulic structures on the nation’s lock systems: loss of protective systems, corrosion, cracking and fatigue, impacts, and overloads. This paper presents examples of deterioration of steel hydraulic structures. A method for predicting future deterioration based on current conditions is also presented. This paper also includes a procedure for developing deterioration curves when condition state data is available.

  20. FEMA DFIRM Hydraulic Structures

    Data.gov (United States)

    Minnesota Department of Natural Resources — This layer and accompanying attribute table is required whenever hydraulic structures are shown in the flood profile. It is also required if levees are shown on the...

  1. Water Hydraulic Systems

    DEFF Research Database (Denmark)

    Conrad, Finn

    2005-01-01

    The paper presents research results using IT-Tools for CAD and dynamic modelling, simulation, analysis, and design of water hydraulic actuators for motion control of machines, lifts, cranes and robots. Matlab/Simulink and CATIA are used as IT-Tools. The contributions include results from on......-going research projects on fluid power and mechatronics based on tap water hydraulic servovalves and linear servo actuators and rotary vane actuators for motion control and power transmission. Development and design a novel water hydraulic rotary vane actuator for robot manipulators. Proposed mathematical...... modelling, control and simulation of a water hydraulic rotary vane actuator applied to power and control a two-links manipulator and evaluate performance. The results include engineering design and test of the proposed simulation models compared with IHA Tampere University’s presentation of research...

  2. Modeling multidomain hydraulic properties of shrink-swell soils

    Science.gov (United States)

    Stewart, Ryan D.; Abou Najm, Majdi R.; Rupp, David E.; Selker, John S.

    2016-10-01

    Shrink-swell soils crack and become compacted as they dry, changing properties such as bulk density and hydraulic conductivity. Multidomain models divide soil into independent realms that allow soil cracks to be incorporated into classical flow and transport models. Incongruously, most applications of multidomain models assume that the porosity distributions, bulk density, and effective saturated hydraulic conductivity of the soil are constant. This study builds on a recently derived soil shrinkage model to develop a new multidomain, dual-permeability model that can accurately predict variations in soil hydraulic properties due to dynamic changes in crack size and connectivity. The model only requires estimates of soil gravimetric water content and a minimal set of parameters, all of which can be determined using laboratory and/or field measurements. We apply the model to eight clayey soils, and demonstrate its ability to quantify variations in volumetric water content (as can be determined during measurement of a soil water characteristic curve) and transient saturated hydraulic conductivity, Ks (as can be measured using infiltration tests). The proposed model is able to capture observed variations in Ks of one to more than two orders of magnitude. In contrast, other dual-permeability models assume that Ks is constant, resulting in the potential for large error when predicting water movement through shrink-swell soils. Overall, the multidomain model presented here successfully quantifies fluctuations in the hydraulic properties of shrink-swell soil matrices, and are suitable for use in physical flow and transport models based on Darcy's Law, the Richards Equation, and the advection-dispersion equation.

  3. Creating new life for hydraulic turbines by upgrading and rehabilitation

    Energy Technology Data Exchange (ETDEWEB)

    Wachter, G.F.

    1998-12-01

    Methods by which to extend the life of aging hydraulic turbines which are still in operation today are discussed. Upgrading some of these turbines which were built as far back as 80 years ago may be feasible with current rehabilitation technology and advanced computer aided hydraulic mechanical design analysis techniques. The benefits achieved with many hydraulic turbine upgrade and rehabilitation programs include: (1) increased performance, (2) extended service life, (3) stopping accelerated deterioration due to cavitation, (4) reducing detrimental symptoms such as unit vibration, component cracking and excessive wearing ring clearances, (5) reducing the possibility of major failures, and (6) reducing unscheduled forced outages. Increased usage of a non-polluting, renewable energy source is an additional benefit of rehabilitation and upgrading of hydro power generating units.2 refs., 2 tabs., 7 figs.

  4. Mechanical behavior and failure mechanism of pre-cracked specimen under uniaxial compression

    Science.gov (United States)

    Liu, Ting; Lin, Baiquan; Yang, Wei

    2017-08-01

    As a desirable permeability enhancement method, hydraulic slotting has been widely used for enhanced coal bed methane (ECBM) recovery in China. Aiming at the problem that the action mechanism of the slot on the mechanical properties of the slotted coal is still unclear, this paper investigates the effects of flaw inclination on the strength, deformation and cracking process of the pre-cracked specimens. The result shows that the stress-strain curves can be divided into three categories based on the stress behaviors, dropping step by step or dropping sharply, after the peak. With an increase of the flaw inclination, the strength and elastic modulus of the pre-cracked specimen increases gradually, which is verified by the numerical simulation and theoretical results. Analysis of the cracking processes indicates that the initiation position of the first crack in specimens with various flaw inclinations is different, which is caused by the various distributions of tensile and compressive stress concentration zones. The distribution of the stress field controls the cracking process which will in turn affect the stress field distribution. With the propagation of the cracks, the tensile stress concentration zones expand and the concentration degree lowers gradually, while the compressive stress concentration zones show the opposite variation trend. Based on the above results, an optimized slot arrangement method has been proposed for the field application of hydraulic slotting.

  5. Trend of hydraulic units

    Energy Technology Data Exchange (ETDEWEB)

    Deshimaru, Jun' ichi

    1988-11-01

    The gear, vane and piston pumps occupy a more then 90% share in the hydraulic pumps. Comparatively large pumps are mainly variable delivery piston pumps. The piston pumps are comparatively high in output density (output per unit weight), indicating the hydraulic pump in performance, and tend to become higher and higher in it. Though they are mainly 210 to 350kgf/cm/sup 2/ in rated pressure, some of them come to surpass 400kgf/cm/sup 3/ in it. While the progress in computation also requires the high speed operation, high accuracy and other severe conditions for the hydraulic units, which accordingly and increasingly intensify the requirement for hydraulic oil in abrasion resistibility, oxidation stability and response characteristics. While cavitation comes to easily occur, which considerably and disadvantageously influences hydraulic oil in life through degradation, noise level and respondingness. From now on, the development of high performance oil and study of mechanical structure are important. 19 references, 9 figures, 2 tables.

  6. Cavitation in Hydraulic Machinery

    Energy Technology Data Exchange (ETDEWEB)

    Kjeldsen, M.

    1996-11-01

    The main purpose of this doctoral thesis on cavitation in hydraulic machinery is to change focus towards the coupling of non-stationary flow phenomena and cavitation. It is argued that, in addition to turbulence, superimposed sound pressure fluctuations can have a major impact on cavitation and lead to particularly severe erosion. For the design of hydraulic devices this finding may indicate how to further limit the cavitation problems. Chapter 1 reviews cavitation in general in the context of hydraulic machinery, emphasizing the initial cavitation event and the role of the water quality. Chapter 2 discusses the existence of pressure fluctuations for situations common in such machinery. Chapter 3 on cavitation dynamics presents an algorithm for calculating the nucleation of a cavity cluster. Chapter 4 describes the equipment used in this work. 53 refs., 55 figs.,10 tabs.

  7. Review on hidden trouble detection and health diagnosis of hydraulic concrete structures

    Institute of Scientific and Technical Information of China (English)

    WU; ZhongRu; LI; Ji; GU; ChongShi; SU; HuaiZhi

    2007-01-01

    A large number of hydraulic concrete structures have hidden defects such as cracks,erosion,freeze and thaw,thermal fatigue,carbonization.These hidden defects seriously affect the strength,stability and durability of structures.These problems are studied mainly by single monitoring or diagnosis methods at present.The integration of multiple monitoring and diagnosis methods is not applied widely.Besides,the analysis theory on these problems is not developed very well.The systemic study on the aging mechanism of hydraulic concrete structures,timevariation model and health diagnosis is still not enough.The support for engineering practice is limited.Aimed at these major scientific and technological problems and combined with specific projects,study on detection of hidden defects and health diagnosis of hydraulic concrete structure has been carried out.This study includes the following content: field non-destructive examination of hidden defects of hydraulic concrete structures,seepage detection,the construction of in-situ sensing system,the combination of field detection and in-situ monitoring,the mechanism of crack,freeze and thaw,erosion and carbonization of hydraulic concrete structure,mechanism of combination aging; time-variation model of hydraulic concrete structure,theories and methods for health diagnosis of hydraulic concrete structures.

  8. Popeye Project: Hydraulic umbilical

    Energy Technology Data Exchange (ETDEWEB)

    Jordan, K.G.; Williams, V.T.

    1996-12-31

    For the Popeye Project, the longest super-duplex hydraulic umbilical in the world was installed in the Gulf of Mexico. This paper reports on its selection and project implementation. Material selection addresses corrosion in seawater, water-based hydraulic fluid, and methanol. Five alternatives were considered: (1) carbon-steel with traditional coating and anodes, (2) carbon-steel coated with thermally sprayed aluminum, (3) carbon-steel sheathed in aluminum, (4) super-duplex, and (5) titanium. The merits and risks associated with each alternative are discussed. The manufacture and installation of the selected umbilical are also reported.

  9. Three-dimensional Space Mechanics Analysis of Hexapod Robot with Electro-hydraulic Driven%电液驱动六足机器人三维空间力学分析

    Institute of Scientific and Technical Information of China (English)

    程乾; 蒋刚

    2015-01-01

    A 3D model of hexapod robot leg mechanism is built,and the optimization problems of hydraulic design are discussed.Then its mechanics model is established.The output torque characteristics of robot each joint at steady state are obtained through the statics analysis,and the output torque characteristics of robot each joint in the process of movement are obtained by Lagrange method as an approach for the dynamics analysis.Finally,based on the dynamics analysis results,the foot trajectory and leg posture simulations of single leg mechanism are carried out by using ADAMS,and through the results,the smooth movement of the leg mechanism is verified and the theoretical support for the follow-up research is provided.%建立了六足机器人的腿部机构三维空间模型,对其关节液压缸设计优化问题进行了讨论.接着进一步建立了腿部机构力学模型,通过对静力学分析得到了机器人稳定状态时各关节的输出力矩特性,同时采用拉格朗日方法对机器人单腿机构进行了动力学分析,得到了单腿结构在运动过程中各关节的输出力矩特性.最后根据动力学分析结果用ADAMS软件对单腿机构进行了足端轨迹和腿部位姿仿真,仿真结果验证了腿部结构的运动平稳性,为后续研究工作提供了理论支撑.

  10. Internal hydraulics of an agricultural drainage denitrification bioreactor

    Science.gov (United States)

    Denitrification bioreactors to reduce the amount of nitrate-nitrogen in agricultural drainage are now being deployed across the U.S. Midwest. However, there are still many unknowns regarding internal hydraulic-driven processes in these "black box" engineered treatment systems. To improve this unders...

  11. Hydraulic Arm Modeling via Matlab SimHydraulics

    OpenAIRE

    Věchet, Stanislav; Krejsa, Jiří

    2009-01-01

    System modeling is a vital tool for cost reduction and design process speed up in most engineering fields. The paper is focused on modeling of hydraulic arm as a part of intelligent prosthesis project, in the form of 2DOF open kinematic chain. The arm model combines mechanical, hydraulic and electric subsystems and uses Matlab as modeling tool. SimMechanics Matlab extension is used for mechanical part modeling, SimHydraulics toolbox is used for modeling of hydraulic circuit used for actuating...

  12. Primary factors governing hydraulic fractures in heterogeneous stratified porous formations

    Energy Technology Data Exchange (ETDEWEB)

    Cleary, M.P.

    1978-08-24

    Some primary material, macrostructural and tectonic features of typical geological formations are identified, insofar as they affect the hydraulic fracturing operation whereby suitably treated fluid is pumped into massive crack(s) underground: the retardation or channeling due to strata interfaces, discontinuities and other heterogeneities is roughly characterized, in the context of fully three-dimensional crack shape evolution, and the initiation from oriented boreholes is discussed in detail. A general-purpose numerical scheme is described, efficiently based on a physically transparent distribution of discontinuity multipoles (or dislocations) and the solution of resulting singular integral equations, which permits precise quantification of these effects: in particular, the barriers provided by adjacent stiffer and tougher strata are properly rationalized and the roles of inelastic slippage, blunting, branching, arrest, and re-initiation are placed in more transparent perspective. Stabilization effects due to alterations of pore-fluid pressure (and hence effective decohering stress), or the flux of formation fluid into the open region near to the crack tip, are described as potentially unfavorable for hydrofrac containment. However, the dominant time-dependent mechanism of frac fluid penetration into the narrow crack aperture attracts most attention: this process is very naturally and tractably incorporated in our comprehensive numerical formulation so that realistic simulation of actual field operations should be feasible in the near future.

  13. Concrete decontamination by electro-hydraulic scabbling

    Energy Technology Data Exchange (ETDEWEB)

    Goldfarb, V.; Gannon, R. [Textron Defense System, Everett, MA (United States)

    1995-10-01

    Textron Defense Systems (TDS) is developing an electro-hydraulic device that has the potential for faster, safer, and less expensive scabbling of contaminated concrete surfaces. In the device, shock waves and cavitating bubbles are produced in water by the electric pulses, and the direct and reflected shock waves impinging on the concrete surface result in the crushing and cracking of the concrete. Pulse energy, frequency, and traverse speed control the depth of the scabbling action. Performance thus far has demonstrated the capability of a prototype unit to process a swath 24 inches wide, up to 3/4 inch deep at a linear velocity of up to 6 feet per hour, i.e., at a scabbling rate of 12 sq. ft. per hour.

  14. Valorization of phosphogypsum as hydraulic binder.

    Science.gov (United States)

    Kuryatnyk, T; Angulski da Luz, C; Ambroise, J; Pera, J

    2008-12-30

    Phosphogypsum (calcium sulfate) is a naturally occurring part of the process of creating phosphoric acid (H(3)PO(4)), an essential component of many modern fertilizers. For every tonne of phosphoric acid made, from the reaction of phosphate rock with acid, commonly sulfuric acid, about 3t of phosphogypsum are created. There are three options for managing phosphogypsum: (i) disposal or dumping, (ii) stacking, (iii) use-in, for example, agriculture, construction, or landfill. This paper presents the valorization of two Tunisian phosphogypsums (referred as G and S) in calcium sulfoaluminate cement in the following proportions: 70% phosphogypsum-30% calcium sulfoaluminate clinker. The use of sample G leads to the production of a hydraulic binder which means that it is not destroyed when immersed in water. The binder including sample S performs very well when cured in air but is not resistant in water. Formation of massive ettringite in a rigid body leads to cracking and strength loss.

  15. Dissolution Condensation Mechanism of Stress Corrosion Cracking in Liquid Metals: Driving Force and Crack Kinetics

    Science.gov (United States)

    Glickman, Evgeny E.

    2011-02-01

    Stress corrosion cracking (SCC) in aqueous solution is driven by exothermic reactions of metal oxidation. This stimulus, as well as classical mechanisms of SCC, does not apply to SCC in liquid metals (LMs). In the framework of the dissolution-condensation mechanism (DCM), we analyzed the driving force and crack kinetics for this nonelectrochemical mode of SCC that is loosely called "liquid metal embrittlement" (LME). According to DCM, a stress-induced increase in chemical potential at the crack tip acts as the driving force for out-of-the-tip diffusion mass transfer that is fast because diffusion in LMs is very fast and surface energy at the solid-liquid interface is small. In this article, we review two versions of DCM mechanism, discuss the major physics behind them, and develop DCM further. The refined mechanism is applied then to the experimental data on crack velocity V vs stress intensity factor, the activation energy of LME, and alloying effects. It is concluded that DCM provides a good conceptual framework for analysis of a unified kinetic mechanism of LME and may also contribute to SCC in aqueous solutions.

  16. HYDRAULICS, TUSCARAWAS COUNTY, OHIO, USA

    Data.gov (United States)

    Federal Emergency Management Agency, Department of Homeland Security — Hydraulic data include spatial datasets and data tables necessary for documenting the hydraulic procedures for estimating flood discharges for a flood insurance...

  17. Fatigue Crack Topography.

    Science.gov (United States)

    1984-01-01

    evaluating ciack initiation time and crack propagation, prgram I was used for performing the major fatigue test with the aircraft structure. In...advantage to begin with the end of the fracture, this is especially so in the case of the quantitative evaluation of striations. The overload fracture...Select the Measuring Line for Quantitative Evaluation Actually, the fatigue fracture should be inspected completely from the point of origin to the

  18. Cracking in desiccating soils

    OpenAIRE

    Ledesma Alberto

    2016-01-01

    Soil shrinkage is produced typically under desiccating conditions. Eventually shrinkage may generate cracks in the soil mass, a phenomenon that is being studied by several researchers, because its prediction is far from being a routine in Soil Mechanics. Within this context, Unsaturated Soil Mechanics provides a promising framework to understand the mechanisms involved. In addition to that, physical modelling of desiccating soils constitutes a good tool to explore the nature of this problem. ...

  19. Utopia Cracks and Polygons

    Science.gov (United States)

    2003-01-01

    MGS MOC Release No. MOC2-339, 23 April 2003This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a pattern of polygonal cracks and aligned, elliptical pits in western Utopia Planitia. The picture covers an area about 3 km (about 1.9 mi) wide near 44.9oN, 274.7oW. Sunlight illuminates the scene from the left.

  20. Hydraulic hoist-press

    Energy Technology Data Exchange (ETDEWEB)

    Babayev, Z.B.; Abashev, Z.V.

    1982-01-01

    The efficiency expert of the Angrenskiy production-technological administration of the production association Sredazugol A. V. Bubnov has suggested a hydraulic hoist-press for repairing road equipment which is a device consisting of lifting mechanism, press and test stand for verifying the high pressure hoses and pumps.

  1. Modelling of Hydraulic Robot

    DEFF Research Database (Denmark)

    Madsen, Henrik; Zhou, Jianjun; Hansen, Lars Henrik

    1997-01-01

    This paper describes a case study of identifying the physical model (or the grey box model) of a hydraulic test robot. The obtained model is intended to provide a basis for model-based control of the robot. The physical model is formulated in continuous time and is derived by application...

  2. Water Treatment Technology - Hydraulics.

    Science.gov (United States)

    Ross-Harrington, Melinda; Kincaid, G. David

    One of twelve water treatment technology units, this student manual on hydraulics provides instructional materials for three competencies. (The twelve units are designed for a continuing education training course for public water supply operators.) The competencies focus on the following areas: head loss in pipes in series, function loss in…

  3. Water Hydraulic Systems

    DEFF Research Database (Denmark)

    Conrad, Finn

    2005-01-01

    The paper presents research results using IT-Tools for CAD and dynamic modelling, simulation, analysis, and design of water hydraulic actuators for motion control of machines, lifts, cranes and robots. Matlab/Simulink and CATIA are used as IT-Tools. The contributions include results from on-going...

  4. Fatigue crack propagation in self-assembling nanocomposites

    Science.gov (United States)

    Klingler, Andreas; Wetzel, Bernd

    2016-05-01

    Self-assembling block-copolymers allow the easy manufacturing of nanocomposites due to the thermodynamically driven in situ formation of nanosized phases in thermosetting resins during the curing process. Complex mechanical dispersion processes can be avoided. The current study investigates the effect of a block-copolymer on the fatigue crack propagation resistance of a cycloaliphatic amine cured epoxy resin. It was found that a small amount of MAM triblock-copolymer significantly increases the resistance to fatigue crack propagation of epoxy. Crack growth rate and the Paris law exponent for fatigue-crack growth were considerably reduced from m=15.5 of the neat epoxy to m=8.1 of the nanocomposite. To identify the related reinforcing and fracture mechanisms structural analyses of the fractured surfaces were performed by scanning electron microscope. Characteristic features were identified to be deformation, debonding and fracture of the nano-phases as well as crack pinning. However, the highest resistance against fatigue crack propagation was achieved in a bi-continuous microstructure that consisted of an epoxy-rich phase with embedded submicron sized MAM inclusions, and which was surrounded by a block-copolymer-rich phase that showed rupture and plastic deformation.

  5. Evaluating Pavement Cracks with Bidimensional Empirical Mode Decomposition

    Directory of Open Access Journals (Sweden)

    Nii Attoh-Okine

    2008-05-01

    Full Text Available Crack evaluation is essential for effective classification of pavement cracks. Digital images of pavement cracks have been analyzed using techniques such as fuzzy set theory and neural networks. Bidimensional empirical mode decomposition (BEMD, a new image analysis method recently developed, can potentially be used for pavement crack evaluation. BEMD is an extension of the empirical mode decomposition (EMD, which can decompose nonlinear and nonstationary signals into basis functions called intrinsic mode functions (IMFs. IMFs are monocomponent functions that have well-defined instantaneous frequencies. EMD is a sifting process that is nonparametric and data driven; it does not depend on an a priori basis set. It is able to remove noise from signals without complicated convolution processes. BEMD decomposes an image into two-dimensional IMFs. The present paper explores pavement crack detection using BEMD together with the Sobel edge detector. A number of images are filtered with BEMD to remove noise, and the residual image analyzed with the Sobel edge detector for crack detection. The results are compared with results from the Canny edge detector, which uses a Gaussian filter for image smoothing before performing edge detection. The objective is to qualitatively explore how well BEMD is able to smooth an image for more effective edge detection with the Sobel method.

  6. Effect of wetting-drying cycles on soil desiccation cracking behaviour

    Directory of Open Access Journals (Sweden)

    Tang Chao-Sheng

    2016-01-01

    Full Text Available Better understanding the desiccation cracking process is essential in analysing drought effects on soil hydraulic and mechanical properties through consideration of the atmosphere-ground interaction. Laboratory tests were conducted to investigate the consequence of wetting-drying cycles on the initiation and propagation characteristics of desiccation cracks on soil surface. Initially saturated slurry specimens were prepared and subjected to five subsequent wetting-drying cycles. Image processing technique was employed to quantitatively analyze the morphology characteristics of crack patterns formed during each drying path. The results show that the desiccation cracking behaviour of soil is significantly affected by the wetting-drying cycles. Before the third wetting-drying cycle is reached, the surface crack ratio and the average crack width increases while the average clod area decreases with increasing the number of wetting-drying cycles. The number of intersections and crack segments per unit area reaches the peak values after the second wetting-drying cycle. After the third wetting-drying cycle is reached, the effect of increasing wetting-drying cycles on crack patterns is insignificant. Moreover, it is observed that the applied wetting-drying cycles are accompanied by a continual reconstruction of soil structure. The initial homogenous slurry structure is completely replaced with aggregated structure after the third cycles, and a significant increase in the inter-aggregate porosity can be observed.

  7. Crack Tip Parameters for Growing Cracks in Linear Viscoelastic Materials

    DEFF Research Database (Denmark)

    Brincker, Rune

    intensity factors. In the special case of a constant Poisson ratio only 2 deformation intensity factors are needed. Closed form solutions are given both for a slowly growing crack and for a crack that is suddenly arrested at a point at the crack extension path. Two examples are studied; a stress boundary...... value problem, and a displacement boundary value problem. The results show that the stress intensity factors and the displacement intensity factors do not depend explicitly upon the velocity of the crack tip....

  8. Effect of Concrete Cracks on Dynamic Characteristics of Powerhouse for Giant-Scale Hydrostation

    Institute of Scientific and Technical Information of China (English)

    TIAN Ziain; ZHANG Yunliang; MA Zhenvue; CHEN Jing

    2008-01-01

    With the increase of capacity and size of the hydro-generator unit, the spiral case be-comes a more super-giant hydraulic structure with very high hid value, where H and D denote water head and maximum intake diameter of spiral case, respectively. Due to the induced lower stiffness by the more giant size and adverse operation conditions, dynamic performances of the powerhouse and the supporting structure for the giant units have become more important and attracted much attention. If the manner of steel spiral case embedded directly in concrete is adopted, on some locations of the concrete surrounding the spiral case, distributed and concentrated cracks will emerge due to high tensile stress. Although the concrete is reinforced well to control the maximum crack width, definitely these cracks will reduce the local and entire stiffness of the powerhouse.Under dynamic loads such as hydraulic forces including water pressure pulsation in flow passage acting on the structure, effect of the cracks on the dynamic characteristics of the local members and entire structure needs to be evaluated. However, research on this subject is few in hydroelectric engineering. In this paper, Three-Gorge Project was taken as an example to evaluate effect of such cracks on natural frequencies and the vibration responses of the powerhouse under hydraulic and earthquake forces in detail. Results show that cracks only reduce the local structural stiffness greatly but have little effect on the entire powerhouse especially the superstructure; vibrations of powerhouse with cracks in concrete surrounding the spiral case are still under the design limits.Results in this paper have been verified by practice of Three-Gorge Project.

  9. Hydraulic manipulator research at ORNL

    Energy Technology Data Exchange (ETDEWEB)

    Kress, R.L.; Jansen, J.F. [Oak Ridge National Lab., TN (United States); Love, L.J. [Oak Ridge Inst. for Science and Education, TN (United States)

    1997-03-01

    Recently, task requirements have dictated that manipulator payload capacity increase to accommodate greater payloads, greater manipulator length, and larger environmental interaction forces. General tasks such as waste storage tank cleanup and facility dismantlement and decommissioning require manipulator life capacities in the range of hundreds of pounds rather than tens of pounds. To meet the increased payload capacities demanded by present-day tasks, manipulator designers have turned once again to hydraulics as a means of actuation. In order to successfully design, build, and deploy a new hydraulic manipulator (or subsystem), sophisticated modeling, analysis, and control experiments are usually needed. Oak Ridge National Laboratory (ORNL) has a history of projects that incorporate hydraulics technology, including mobile robots, teleoperated manipulators, and full-scale construction equipment. In addition, to support the development and deployment of new hydraulic manipulators, ORNL has outfitted a significant experimental laboratory and has developed the software capability for research into hydraulic manipulators, hydraulic actuators, hydraulic systems, modeling of hydraulic systems, and hydraulic controls. The purpose of this article is to describe the past hydraulic manipulator developments and current hydraulic manipulator research capabilities at ORNL. Included are example experimental results from ORNL`s flexible/prismatic test stand.

  10. Cryptography cracking codes

    CERN Document Server

    2014-01-01

    While cracking a code might seem like something few of us would encounter in our daily lives, it is actually far more prevalent than we may realize. Anyone who has had personal information taken because of a hacked email account can understand the need for cryptography and the importance of encryption-essentially the need to code information to keep it safe. This detailed volume examines the logic and science behind various ciphers, their real world uses, how codes can be broken, and the use of technology in this oft-overlooked field.

  11. Remotely Adjustable Hydraulic Pump

    Science.gov (United States)

    Kouns, H. H.; Gardner, L. D.

    1987-01-01

    Outlet pressure adjusted to match varying loads. Electrohydraulic servo has positioned sleeve in leftmost position, adjusting outlet pressure to maximum value. Sleeve in equilibrium position, with control land covering control port. For lowest pressure setting, sleeve shifted toward right by increased pressure on sleeve shoulder from servovalve. Pump used in aircraft and robots, where hydraulic actuators repeatedly turned on and off, changing pump load frequently and over wide range.

  12. Undular Hydraulic Jump

    Directory of Open Access Journals (Sweden)

    Oscar Castro-Orgaz

    2015-04-01

    Full Text Available The transition from subcritical to supercritical flow when the inflow Froude number Fo is close to unity appears in the form of steady state waves called undular hydraulic jump. The characterization of the undular hydraulic jump is complex due to the existence of a non-hydrostatic pressure distribution that invalidates the gradually-varied flow theory, and supercritical shock waves. The objective of this work is to present a mathematical model for the undular hydraulic jump obtained from an approximate integration of the Reynolds equations for turbulent flow assuming that the Reynolds number R is high. Simple analytical solutions are presented to reveal the physics of the theory, and a numerical model is used to integrate the complete equations. The limit of application of the theory is discussed using a wave breaking condition for the inception of a surface roller. The validity of the mathematical predictions is critically assessed using physical data, thereby revealing aspects on which more research is needed

  13. Research on a Lamb Wave and Particle Filter-Based On-Line Crack Propagation Prognosis Method.

    Science.gov (United States)

    Chen, Jian; Yuan, Shenfang; Qiu, Lei; Cai, Jian; Yang, Weibo

    2016-03-03

    Prognostics and health management techniques have drawn widespread attention due to their ability to facilitate maintenance activities based on need. On-line prognosis of fatigue crack propagation can offer information for optimizing operation and maintenance strategies in real-time. This paper proposes a Lamb wave-particle filter (LW-PF)-based method for on-line prognosis of fatigue crack propagation which takes advantages of the possibility of on-line monitoring to evaluate the actual crack length and uses a particle filter to deal with the crack evolution and monitoring uncertainties. The piezoelectric transducers (PZTs)-based active Lamb wave method is adopted for on-line crack monitoring. The state space model relating to crack propagation is established by the data-driven and finite element methods. Fatigue experiments performed on hole-edge crack specimens have validated the advantages of the proposed method.

  14. Research on a Lamb Wave and Particle Filter-Based On-Line Crack Propagation Prognosis Method

    Directory of Open Access Journals (Sweden)

    Jian Chen

    2016-03-01

    Full Text Available Prognostics and health management techniques have drawn widespread attention due to their ability to facilitate maintenance activities based on need. On-line prognosis of fatigue crack propagation can offer information for optimizing operation and maintenance strategies in real-time. This paper proposes a Lamb wave-particle filter (LW-PF-based method for on-line prognosis of fatigue crack propagation which takes advantages of the possibility of on-line monitoring to evaluate the actual crack length and uses a particle filter to deal with the crack evolution and monitoring uncertainties. The piezoelectric transducers (PZTs-based active Lamb wave method is adopted for on-line crack monitoring. The state space model relating to crack propagation is established by the data-driven and finite element methods. Fatigue experiments performed on hole-edge crack specimens have validated the advantages of the proposed method.

  15. Multiaxial mixed-mode cracking - small crack initiation and propagation

    Energy Technology Data Exchange (ETDEWEB)

    Freitas, M. de; Reis, L.; Li Bin [Lisbon Univ. (Portugal). ICEMS - Inst. of Material and Surface Science and Engineering

    2006-07-01

    Both the fatigue crack path and fatigue life of CK45 steel and 42CrMo4 steel under various multiaxial loading paths are studied in this paper. The replica method was applied to monitor the crack initiation and small crack growth, the fractographic analyses were carried out on the fracture surface and the crack initiation angle was measured. The effects of non-proportional loading on both the crack path and fatigue life were studied, and the flattening of asperities on the crack surface due to compressive normal stress was also observed. An improved model is proposed based on correcting the strain range parameter of the ASME code approach, taking into account the additional hardening caused by the non-proportional loading path, which can improve the predictions of the fatigue lives for various non-proportional loading paths and provide an easy way to overcome the drawbacks of the current ASME code approach for non-proportional fatigue. Based on these corrected strain range parameters, a strain intensity factor range is used to correlate with the experimental results of small crack growth rates. It is concluded that the orientation of the early crack growth can be predicted well by the critical damage plane, but the fatigue life can not be predicted accurately using only the parameters on the critical plane, since the damage on all the planes contributes to fatigue damage as stated by the integral approaches. (orig.)

  16. Experimental evaluation of control strategies for hydraulic servo robot

    DEFF Research Database (Denmark)

    Bech, Michael Møller; Andersen, Torben Ole; Pedersen, Henrik C.

    2013-01-01

    In this paper different linear and non-linear controllers applied to a hydraulically driven servo robot are evaluated and validated. The task is to make the actuators of the manipulator track a position reference with minimum error. Hydraulic systems are intrinsically non-linear and using linear...... control techniques typically results in conservatively dimensioned controllers to obtain stable performance. Non-linear control techniques have the potential of overcoming these problems and in this paper the focus is on applying simple nonlinear robust and adaptive controllers feasible for implementation...... in industrial servo drives. The different controllers are compared and evaluated from simulation and experimental results....

  17. Catalytic cracking of lignites

    Energy Technology Data Exchange (ETDEWEB)

    Seitz, M.; Nowak, S.; Naegler, T.; Zimmermann, J. [Hochschule Merseburg (Germany); Welscher, J.; Schwieger, W. [Erlangen-Nuernberg Univ. (Germany); Hahn, T. [Halle-Wittenberg Univ., Halle (Germany)

    2013-11-01

    A most important factor for the chemical industry is the availability of cheap raw materials. As the oil price of crude oil is rising alternative feedstocks like coal are coming into focus. This work, the catalytic cracking of lignite is part of the alliance ibi (innovative Braunkohlenintegration) to use lignite as a raw material to produce chemicals. With this new one step process without an input of external hydrogen, mostly propylene, butenes and aromatics and char are formed. The product yield depends on manifold process parameters. The use of acid catalysts (zeolites like MFI) shows the highest amount of the desired products. Hydrogen rich lignites with a molar H/C ratio of > 1 are to be favoured. Due to primary cracking and secondary reactions the ratio between catalyst and lignite, temperature and residence time are the most important parameter to control the product distribution. Experiments at 500 C in a discontinuous rotary kiln reactor show yields up to 32 wt-% of hydrocarbons per lignite (maf - moisture and ash free) and 43 wt-% char, which can be gasified. Particularly, the yields of propylene and butenes as main products can be enhanced four times to about 8 wt-% by the use of catalysts while the tar yield decreases. In order to develop this innovative process catalyst systems fixed on beads were developed for an easy separation and regeneration of the used catalyst from the formed char. (orig.)

  18. Hydraulic System Design of Hydraulic Actuators for Large Butterfly Valves

    OpenAIRE

    HUANG, Ye; Liu, Changsheng; Shiongur Bamed

    2014-01-01

    Hydraulic control systems of butterfly valves are presently valve-controlled and pump-controlled. Valve-controlled hydraulic systems have serious power loss and generate much heat during throttling. Pump-controlled hydraulic systems have no overflow or throttling losses but are limited in the speed adjustment of the variable-displacement pump, generate much noise, pollute the environment, and have motor power that does not match load requirements, resulting in low efficiency under...

  19. Hydraulic System Design of Hydraulic Actuators for Large Butterfly Valves

    Directory of Open Access Journals (Sweden)

    Ye HUANG

    2014-09-01

    Full Text Available Hydraulic control systems of butterfly valves are presently valve-controlled and pump-controlled. Valve-controlled hydraulic systems have serious power loss and generate much heat during throttling. Pump-controlled hydraulic systems have no overflow or throttling losses but are limited in the speed adjustment of the variable-displacement pump, generate much noise, pollute the environment, and have motor power that does not match load requirements, resulting in low efficiency under light loads and wearing of the variable-displacement pump. To overcome these shortcomings, this article designs a closed hydraulic control system in which an AC servo motor drives a quantitative pump that controls a spiral swinging hydraulic cylinder, and analyzes and calculates the structure and parameters of a spiral swinging hydraulic cylinder. The hydraulic system adjusts the servo motor’s speed according to the requirements of the control system, and the motor power matches the power provided to components, thus eliminating the throttling loss of hydraulic circuits. The system is compact, produces a large output force, provides stable transmission, has a quick response, and is suitable as a hydraulic control system of a large butterfly valve.

  20. Experiences on IGSCC crack manufacturing

    Energy Technology Data Exchange (ETDEWEB)

    Veron, P. [Equipos Nucleares, S.A., Maliano (Spain)

    1997-02-01

    The author presents his experience in manufacturing IGSCC realistic defects, mainly in INCONEL 600 MA Steam Generator Tubes. From that experience he extracts some knowledge about this cracking (influence of chemistry in the environment, stress state, crack growth rate, and occurrence in laboratory condition of break before leak).

  1. HYDROGEN TRANSFER IN CATALYTIC CRACKING

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Hydrogen transfer is an important secondary reaction of catalytic cracking reactions, which affects product yield distribution and product quality. It is an exothermic reaction with low activation energy around 43.3 kJ/mol. Catalyst properties and operation parameters in catalytic cracking greatly influence the hydrogen transfer reaction. Satisfactory results are expected through careful selection of proper catalysts and operation conditions.

  2. HYDRAULIC CONDUCTIVITY OF GCL WITH BENTONITE – SILICA FUME MATRIX

    Directory of Open Access Journals (Sweden)

    Mudimby Andal

    2012-12-01

    Full Text Available This paper presents the influence of partial replacement of bentonite by silica fume which is used in the manufacture of Geosynthetic Clay Liner (GCL. Geosynthetic Clay Liners consist bentonite (Sodium Based sandwiched between two geotextile. Benotinite, having low permeability imparts better hydraulic performance to the GCL to act as liner. In this investigation, an attempt has been made to study the hydraulic conductivity of GCL with modified Bentonite. The bentonite is partially replaced by silica fume, a waste product of ferroalloy industries. Silica fume reduces the cracking characteristics of bentonite on desiccation. The replacement levels varied from 0% to 50% at a gradual increment of 5%. The test results indicated that partial replacement of bentonite by silica fume did not affected the permeability of bentonite even at 30%. Beyond 45% replacement levels the bentonite- silica fume mixtures showed increased permeability. This increased permeability also well within permeability limits of liners 1×10-9 m/sec.

  3. HYDRAULIC CONDUCTIVITY OF GCL WITH BENTONITE - SILICA FUME MATRIX

    Directory of Open Access Journals (Sweden)

    M. Andal

    2012-01-01

    Full Text Available This paper presents the influence of partial replacement of bentonite by silica fume which is used in the manufacture of Geosynthetic Clay Liner (GCL. Geosynthetic Clay Liners consist bentonite (Sodium Based sandwiched between two geotextile. Benotinite, having low permeability imparts better hydraulic performance to the GCL to act as liner. In this investigation, an attempt has been made to study the hydraulic conductivity of GCL with modified Bentonite. The bentonite is partially replaced by silica fume, a waste product of ferroalloy industries. Silica fume reduces the cracking characteristics of bentonite on desiccation. The replacement levels varied from 0% to 50% at a gradual increment of 5%. The test results indicated that partial replacement of bentonite by silica fume did not affected the permeability of bentonite even at 30%. Beyond 45% replacement levels the bentonite- silica fume mixtures showed increased permeability. This increased permeability also well within permeability limits of liners 1×10-9m/sec.

  4. Micromechanical Aspects of Hydraulic Fracturing Processes

    Science.gov (United States)

    Galindo-torres, S. A.; Behraftar, S.; Scheuermann, A.; Li, L.; Williams, D.

    2014-12-01

    A micromechanical model is developed to simulate the hydraulic fracturing process. The model comprises two key components. Firstly, the solid matrix, assumed as a rock mass with pre-fabricated cracks, is represented by an array of bonded particles simulated by the Discrete Element Model (DEM)[1]. The interaction is ruled by the spheropolyhedra method, which was introduced by the authors previously and has been shown to realistically represent many of the features found in fracturing and communition processes. The second component is the fluid, which is modelled by the Lattice Boltzmann Method (LBM). It was recently coupled with the spheropolyhedra by the authors and validated. An advantage of this coupled LBM-DEM model is the control of many of the parameters of the fracturing fluid, such as its viscosity and the injection rate. To the best of the authors' knowledge this is the first application of such a coupled scheme for studying hydraulic fracturing[2]. In this first implementation, results are presented for a two-dimensional situation. Fig. 1 shows one snapshot of the LBM-DEM coupled simulation for the hydraulic fracturing where the elements with broken bonds can be identified and the fracture geometry quantified. The simulation involves a variation of the underground stress, particularly the difference between the two principal components of the stress tensor, to explore the effect on the fracture path. A second study focuses on the fluid viscosity to examine the effect of the time scales of different injection plans on the fracture geometry. The developed tool and the presented results have important implications for future studies of the hydraulic fracturing process and technology. references 1. Galindo-Torres, S.A., et al., Breaking processes in three-dimensional bonded granular materials with general shapes. Computer Physics Communications, 2012. 183(2): p. 266-277. 2. Galindo-Torres, S.A., A coupled Discrete Element Lattice Boltzmann Method for the

  5. Modelling of Hydraulic Robot

    DEFF Research Database (Denmark)

    Madsen, Henrik; Zhou, Jianjun; Hansen, Lars Henrik

    1997-01-01

    This paper describes a case study of identifying the physical model (or the grey box model) of a hydraulic test robot. The obtained model is intended to provide a basis for model-based control of the robot. The physical model is formulated in continuous time and is derived by application...... of the laws of physics on the system. The unknown (or uncertain) parameters are estimated with Maximum Likelihood (ML) parameter estimation. The identified model has been evaluated by comparing the measurements with simulation of the model. The identified model was much more capable of describing the dynamics...... of the system than the deterministic model....

  6. Hydraulic mining method

    Science.gov (United States)

    Huffman, Lester H.; Knoke, Gerald S.

    1985-08-20

    A method of hydraulically mining an underground pitched mineral vein comprising drilling a vertical borehole through the earth's lithosphere into the vein and drilling a slant borehole along the footwall of the vein to intersect the vertical borehole. Material is removed from the mineral vein by directing a high pressure water jet thereagainst. The resulting slurry of mineral fragments and water flows along the slant borehole into the lower end of the vertical borehole from where it is pumped upwardly through the vertical borehole to the surface.

  7. Spinning hydraulic jump

    Science.gov (United States)

    Abderrahmane, Hamid; Kasimov, Aslan

    2013-11-01

    We report an experimental observation of a new symmetry breaking of circular hydraulic jump into a self-organized structure that consists of a spinning polygonal jump and logarithmic-spiral waves of fluid elevation downstream. The waves are strikingly similar to spiral density waves in galaxies. The fluid flow exhibits counterparts of salient morphological features of galactic flows, in particular the outflow from the center, jets, circum-nuclear rings, gas inflows toward the galactic center, and vortices. The hydrodynamic instability revealed here may have a counterpart that plays a role in the formation and sustainability of spiral arms in galaxies.

  8. Energy Release Rate in hydraulic fracture: can we neglect an impact of the hydraulically induced shear stress?

    CERN Document Server

    Wrobel, Michal; Piccolroaz, Andrea

    2016-01-01

    A novel hydraulic fracture (HF) formulation is introduced which accounts for the hydraulically induced shear stress at the crack faces. It utilizes a general form of the elasticity operator alongside a revised fracture propagation condition based on the critical value of the energy release rate. It is shown that the revised formulation describes the underlying physics of HF in a more accurate way and is in agreement with the asymptotic behaviour of the linear elastic fracture mechanics. A number of numerical simulations by means of the universal HF algorithm previously developed in Wrobel & Mishuris (2015) are performed in order to: i) compare the modified HF formulation with its classic counterpart and ii) investigate the peculiarities of the former. Computational advantages of the revised HF model are demonstrated. Asymptotic estimations of the main solution elements are provided for the cases of small and large toughness. The modified formulation opens new ways to analyse the physical phenomenon of HF ...

  9. A consistent partly cracked XFEM element for cohesive crack growth

    DEFF Research Database (Denmark)

    Asferg, Jesper L.; Poulsen, Peter Noe; Nielsen, Leif Otto

    2007-01-01

    capable of modelling variations in the discontinuous displacement field on both sides of the crack and hence also capable of modelling the case where equal stresses are present on each side of the crack. The enrichment was implemented for the 3-node constant strain triangle (CST) and a standard algorithm...... was used to solve the non-linear equations. The performance of the element is illustrated by modelling fracture mechanical benchmark tests. Investigations were carried out on the performance of the element for different crack lengths within one element. The results are compared with previously obtained...

  10. 46 CFR 28.880 - Hydraulic equipment.

    Science.gov (United States)

    2010-10-01

    ... hydraulic equipment and the adjacent work area. Protection shall be afforded to the operator of hydraulic... 46 Shipping 1 2010-10-01 2010-10-01 false Hydraulic equipment. 28.880 Section 28.880 Shipping... INDUSTRY VESSELS Aleutian Trade Act Vessels § 28.880 Hydraulic equipment. (a) Each hydraulic system must...

  11. The concept of the average stress in the fracture process zone for the search of the crack path

    Directory of Open Access Journals (Sweden)

    Yu.G. Matvienko

    2015-10-01

    Full Text Available The concept of the average stress has been employed to propose the maximum average tangential stress (MATS criterion for predicting the direction of fracture angle. This criterion states that a crack grows when the maximum average tangential stress in the fracture process zone ahead of the crack tip reaches its critical value and the crack growth direction coincides with the direction of the maximum average tangential stress along a constant radius around the crack tip. The tangential stress is described by the singular and nonsingular (T-stress terms in the Williams series solution. To demonstrate the validity of the proposed MATS criterion, this criterion is directly applied to experiments reported in the literature for the mixed mode I/II crack growth behavior of Guiting limestone. The predicted directions of fracture angle are consistent with the experimental data. The concept of the average stress has been also employed to predict the surface crack path under rolling-sliding contact loading. The proposed model considers the size and orientation of the initial crack, normal and tangential loading due to rolling–sliding contact as well as the influence of fluid trapped inside the crack by a hydraulic pressure mechanism. The MATS criterion is directly applied to equivalent contact model for surface crack growth on a gear tooth flank.

  12. Dynamic Analysis & Characterization of Conventional Hydraulic Power Supply Units

    DEFF Research Database (Denmark)

    Schmidt, Lasse; Liedhegener, Michael; Bech, Michael Møller

    2016-01-01

    Hydraulic power units operated as constant supply pres-sure systems remain to be widely used in the industry, to supply valve controlled hydraulic drives etc., where the hydraulic power units are constituted by variable pumps with mechanical outlet pressure control, driven by induction motors...... and drives will reduce the flow-to-pressure gain of the supply system, and hence increase the time constant of the sup-ply pressure dynamics. A consequence of this may be large vari-ations in the supply pressure, hence large variations in the pump shaft torque, and thereby the induction motor load torque......, with possible excitation of the induction motor dynamics as a result. In such cases, the coupled dynamics of the pressure controlled pump and induction motor may influence the supply pressure sig-nificantly, possibly affecting the dynamics of the supplied drives, especially in cases where pilot operated valves...

  13. Continuum theory of memory effect in crack patterns of drying pastes

    OpenAIRE

    OOSHIDA, Takeshi

    2008-01-01

    A possible clarification of memory effect observed in crack patterns of drying pastes [A. Nakahara and Y. Matsuo, J. Phys. Soc. Japan 74, 1362 (2005)] is presented in terms of a macroscopic elastoplastic model of isotropic pastes. We study flows driven by steady gravitational force instead of external oscillation. The model predicts creation of residual tension in favor of cracks perpendicular to the flow direction, thus causing the same type of memory effect as that reported by Nakahara and ...

  14. Peak Stress Intensity Factor Governs Crack Propagation Velocity In Crosslinked UHMWPE

    Science.gov (United States)

    Sirimamilla, P. Abhiram; Furmanski, Jevan; Rimnac, Clare

    2013-01-01

    Ultra high molecular weight polyethylene (UHMWPE) has been successfully used as a bearing material in total joint replacement components. However, these bearing materials can fail as a result of in vivo static and cyclic loads. Crack propagation behavior in this material has been considered using the Paris relationship which relates fatigue crack growth rate, da/dN (mm/cycle) versus the stress intensity factor range, ΔK (Kmax-Kmin, MPa√m). However, recent work suggests that the crack propagation velocity of conventional UHMWPE is driven by the peak stress intensity (Kmax), not ΔK. The hypothesis of this study is that the crack propagation velocity of highly crosslinked and remelted UHMWPE is also driven by the peak stress intensity, Kmax, during cyclic loading, rather than by ΔK. To test this hypothesis, two highly crosslinked (65 kGy and 100 kGy) and remelted UHMWPE materials were examined. Frequency, waveform and R-ratio were varied between test conditions to determine the governing factor for fatigue crack propagation. It was found that the crack propagation velocity in crosslinked UHMWPE is also driven by Kmax and not ΔK, and is dependent on loading waveform and frequency in a predictable quasi-static manner. The current study supports that crack growth in crosslinked UHMWPE materials, even under cyclic loading conditions, can be described by a relationship between the velocity of crack growth, da/dt and the peak stress intensity, Kmax. The findings suggest that stable crack propagation can occur as a result of static loading only and this should be taken into consideration in design of UHMWPE total joint replacement components. PMID:23165898

  15. Peak stress intensity factor governs crack propagation velocity in crosslinked ultrahigh-molecular-weight polyethylene.

    Science.gov (United States)

    Sirimamilla, Abhiram; Furmanski, Jevan; Rimnac, Clare

    2013-04-01

    Ultrahigh-molecular-weight polyethylene (UHMWPE) has been successfully used as a bearing material in total joint replacement components. However, these bearing materials can fail as a result of in vivo static and cyclic loads. Crack propagation behavior in this material has been considered using the Paris relationship which relates fatigue crack growth rate, da/dN (mm/cycle) versus the stress intensity factor range, ΔK (Kmax - Kmin , MPa√m). However, recent work suggests that the crack propagation velocity of conventional UHMWPE is driven by the peak stress intensity (Kmax ), not ΔK. The hypothesis of this study is that the crack propagation velocity of highly crosslinked and remelted UHMWPE is also driven by the peak stress intensity, Kmax , during cyclic loading. To test this hypothesis, two highly crosslinked (65 kGy and 100 kGy) and remelted UHMWPE materials were examined. Frequency, waveform, and R-ratio were varied between test conditions to determine the governing factor for fatigue crack propagation. It was found that the crack propagation velocity in crosslinked UHMWPE is also driven by Kmax and not ΔK, and is dependent on loading waveform and frequency in a predictable quasistatic manner. This study supports that crack growth in crosslinked UHMWPE materials, even under cyclic loading conditions, can be described by a relationship between the velocity of crack growth, da/dt and the peak stress intensity, Kmax . The findings suggest that stable crack propagation can occur as a result of static loading only and this should be taken into consideration in design of UHMWPE total joint replacement components.

  16. Development of Efficient Finite Element Software of Crack Propagation Simulation using Adaptive Mesh Strategy

    Directory of Open Access Journals (Sweden)

    Abdulnaser M. Alshoaibi

    2009-01-01

    Full Text Available The purpose of this study is on the determination of 2D crack paths and surfaces as well as on the evaluation of the stress intensity factors as a part of the damage tolerant assessment. Problem statement: The evaluation of SIFs and crack tip singular stresses for arbitrary fracture structure are a challenging problem, involving the calculation of the crack path and the crack propagation rates at each step especially under mixed mode loading. Approach: This study was provided a finite element code which produces results comparable to the current available commercial software. Throughout the simulation of crack propagation an automatic adaptive mesh was carried out in the vicinity of the crack front nodes and in the elements which represent the higher stresses distribution. The finite element mesh was generated using the advancing front method. The adaptive remising process carried out based on the posteriori stress error norm scheme to obtain an optimal mesh. The onset criterion of crack propagation was based on the stress intensity factors which provide as the most important parameter that must be accurately estimated. Facilitated by the singular elements, the displacement extrapolation technique is employed to calculate the stress intensity factor. Crack direction is predicted using the maximum circumferential stress theory. The fracture was modeled by the splitting node approach and the trajectory follows the successive linear extensions of each crack increment. The propagation process is driven by Linear Elastic Fracture Mechanics (LEFM approach with minimum user interaction. Results: In evaluating the accuracy of the estimated stress intensity factors and the crack path predictions, the results were compared with sets of experimental data, benchmark analytical solutions as well as numerical results of other researchers. Conclusion/Recommendations: The assessment indicated that the program was highly reliable to evaluate the stress intensity

  17. Applied hydraulic transients

    CERN Document Server

    Chaudhry, M Hanif

    2014-01-01

    This book covers hydraulic transients in a comprehensive and systematic manner from introduction to advanced level and presents various methods of analysis for computer solution. The field of application of the book is very broad and diverse and covers areas such as hydroelectric projects, pumped storage schemes, water-supply systems, cooling-water systems, oil pipelines and industrial piping systems. Strong emphasis is given to practical applications, including several case studies, problems of applied nature, and design criteria. This will help design engineers and introduce students to real-life projects. This book also: ·         Presents modern methods of analysis suitable for computer analysis, such as the method of characteristics, explicit and implicit finite-difference methods and matrix methods ·         Includes case studies of actual projects ·         Provides extensive and complete treatment of governed hydraulic turbines ·         Presents design charts, desi...

  18. Dynamic Evolution of Microscopic Wet Cracking Noises

    CERN Document Server

    Ghaffari, H O; Benson, P M

    2015-01-01

    Characterizing the interaction between water and microscopic defects is one of the long-standing challenges in understanding a broad range of cracking processes. Different physical aspects of microscopic events, driven or influenced by water, have been extensively discussed in atomistic calculations but have not been accessible in microscale experiments. Through the analysis of the emitted noises during the evolution of individual, dynamic microcracking events, we show that the onset of a secondary instability known as hybrid events occurs during the fast healing phase of microcracking, which leads to (local) sudden increase of pore water pressure in the process zone, inducing a secondary instability, which is followed by a fast-locking phase on the microscopic faults (pulse-like rupture).

  19. Probabilistic Analysis of Crack Width

    Directory of Open Access Journals (Sweden)

    J. Marková

    2000-01-01

    Full Text Available Probabilistic analysis of crack width of a reinforced concrete element is based on the formulas accepted in Eurocode 2 and European Model Code 90. Obtained values of reliability index b seem to be satisfactory for the reinforced concrete slab that fulfils requirements for the crack width specified in Eurocode 2. However, the reliability of the slab seems to be insufficient when the European Model Code 90 is considered; reliability index is less than recommended value 1.5 for serviceability limit states indicated in Eurocode 1. Analysis of sensitivity factors of basic variables enables to find out variables significantly affecting the total crack width.

  20. Analysis of Crack Arrest Toughness.

    Science.gov (United States)

    1988-01-15

    vload(m) vp tn(m) Vertical Source Load (kN) on wedge HY80 Finite Element 0.0122 0.0099 3.81x10 -4 144 Steel Calculations Experiment 0.0122 --- 3.74x10-4...curve, are bona fide measures of the fracture arrest capability of tough ductile steels . The second is that the J-values represent the crack driving...fibrous mode of crack extension. (b) A new test method for studying fast fracture and arrest in tough steels . (c) Measurements of fast fracture and crack

  1. A computational algorithm for crack determination: The multiple crack case

    Science.gov (United States)

    Bryan, Kurt; Vogelius, Michael

    1992-01-01

    An algorithm for recovering a collection of linear cracks in a homogeneous electrical conductor from boundary measurements of voltages induced by specified current fluxes is developed. The technique is a variation of Newton's method and is based on taking weighted averages of the boundary data. The method also adaptively changes the applied current flux at each iteration to maintain maximum sensitivity to the estimated locations of the cracks.

  2. Hydraulic rams; a comparative investigation

    NARCIS (Netherlands)

    Tacke, J.H.P.M.

    1988-01-01

    A mathematical model describing the essential features of hydraulic ram operation is developed in order to clarify the possibilities and limitations of the ram relative to its site and its adjustments. The model distinguishes three different periods in the pumping cycle of the hydraulic ram: acceler

  3. Hydraulics. FOS: Fundamentals of Service.

    Science.gov (United States)

    John Deere Co., Moline, IL.

    This manual on hydraulics is one of a series of power mechanics texts and visual aids for training in the servicing of agricultural and industrial machinery. Focus is on oil hydraulics. Materials provide basic information and illustrations for use by vocational students and teachers as well as shop servicemen and laymen. The twelve chapters focus…

  4. Discuss on Concrete Cracks%混凝土裂缝的探讨

    Institute of Scientific and Technical Information of China (English)

    甘努力

    2015-01-01

    To investigate the cause of concrete cracks of concrete, control methods and approaches produce cracks after concrete cracks to avoid an impact on the structure of the building and service life. Concrete Crack is one of the more serious problems in hydraulic architecture, too wide cracks can cause severe corrosion of steel, thereby enabling to reduce the structural strength. In practical engineering, more than because of concrete cracks and failure, scrapped precedent. In addition, to withstand water pressure of hydraulic concrete buildings, cracks will reduce its impermeability and frost resistance, thereby shortening the life of the building.%主要探讨了混凝土砼裂缝产生的原因、控制方法和产生裂缝后的处理办法,以免砼裂缝对建筑物的结构和使用寿命等造成影响。砼裂缝在水工建筑中是较为严重的问题之一,过宽的裂缝会引起钢筋严重锈蚀,进而使结构强度降低。在实际工程中,已有多个因砼裂缝而失效、报废的先例。此外,在承受水压力的水工砼建筑中,裂缝还会降低其抗渗性和抗冻性,进而缩短建筑物的使用寿命。

  5. Hydraulic Stability of Accropode Armour

    DEFF Research Database (Denmark)

    Jensen, T.; Burcharth, H. F.; Frigaard, Peter

    , and to assess the influence of core permeability on the hydraulic stability of Accropodes. Two structures were examined, one with a relatively permeable core and one with a relatively impermeable core. In November/December 1995, Ph.D.-student Marten Christensen carried out the model tests on the structure...... with permeable core (crushed granite with a gradation of 5-8 mm). The outcome of this study is described in "Hydraulic Stability of Single-Layer Dolos and Accropode Armour Layers" by Christensen & Burcharth (1995). In January/February 1996, Research Assistant Thomas Jensen carried out a similar study......The present report describes the hydraulic model tests of Accropode armour layers carried out at the Hydraulics Laboratory at Aalborg University from November 1995 through March 1996. The objective of the model tests was to investigate the hydraulic stability of Accropode armour layers...

  6. Hydraulic Stability of Accropode Armour

    DEFF Research Database (Denmark)

    Jensen, T.; Burcharth, H. F.; Frigaard, Peter

    , and to assess the influence of core permeability on the hydraulic stability of Accropodes. Two structures were examined, one with a relatively permeable core and one with a relatively impermeable core. In November/December 1995, Ph.D.-student Marten Christensen carried out the model tests on the structure...... with permeable core (crushed granite with a gradation of 5-8 mm). The outcome of this study is described in "Hydraulic Stability of Single-Layer Dolos and Accropode Armour Layers" by Christensen & Burcharth (1995). In January/February 1996, Research Assistant Thomas Jensen carried out a similar study......The present report describes the hydraulic model tests of Accropode armour layers carried out at the Hydraulics Laboratory at Aalborg University from November 1995 through March 1996. The objective of the model tests was to investigate the hydraulic stability of Accropode armour layers...

  7. Cracks in Utopia

    Science.gov (United States)

    1999-01-01

    Many of the craters found on the northern plains of Mars have been partly filled or buried by some material (possibly sediment). The Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image presented here (MOC2-136b, above left) shows a high-resolution view of a tiny portion of the floor of one of these northern plains craters. The crater, located in Utopia Planitia at 44oN, 258oW, is shown on the right (MOC2-136a)with a small white box to indicate the location of the MOC image. The MOC image reveals that the material covering the floor of this crater is cracked and pitted. The origin and source of material that has been deposited in this crater is unknown.The MOC image was acquired in June 1999 and covers an area only 1.1 kilometers (0.7 miles) wide at a resolution of 1.8 meters (6 feet) per pixel. The context picture is a mosaic of Viking 2 orbiter images 010B53 and 010B55, taken in 1976. Both images are illuminated from the left. Malin Space Science Systems and the California Institute of Technology built the MOC using spare hardware from the Mars Observer mission. MSSS operates the camera from its facilities in San Diego, CA. The Jet Propulsion Laboratory's Mars Surveyor Operations Project operates the Mars Global Surveyor spacecraft with its industrial partner, Lockheed Martin Astronautics, from facilities in Pasadena, CA and Denver, CO.

  8. Peridynamic model for fatigue cracking.

    Energy Technology Data Exchange (ETDEWEB)

    Silling, Stewart Andrew; Abe Askari (Boeing)

    2014-10-01

    The peridynamic theory is an extension of traditional solid mechanics in which the field equations can be applied on discontinuities, such as growing cracks. This paper proposes a bond damage model within peridynamics to treat the nucleation and growth of cracks due to cyclic loading. Bond damage occurs according to the evolution of a variable called the "remaining life" of each bond that changes over time according to the cyclic strain in the bond. It is shown that the model reproduces the main features of S-N data for typical materials and also reproduces the Paris law for fatigue crack growth. Extensions of the model account for the effects of loading spectrum, fatigue limit, and variable load ratio. A three-dimensional example illustrates the nucleation and growth of a helical fatigue crack in the torsion of an aluminum alloy rod.

  9. 21 CFR 137.190 - Cracked wheat.

    Science.gov (United States)

    2010-04-01

    ... 21 Food and Drugs 2 2010-04-01 2010-04-01 false Cracked wheat. 137.190 Section 137.190 Food and... Related Products § 137.190 Cracked wheat. Cracked wheat is the food prepared by so cracking or cutting into angular fragments cleaned wheat other than durum wheat and red durum wheat that, when tested by...

  10. The crack growth mechanism in asphaltic mixes

    NARCIS (Netherlands)

    Jacobs, .M.M.J.; Hopman, P.C.; Molenaar, A.A.A.

    1995-01-01

    The crack growth mechanism in asphalt concrete (Ac) mixes is studied. In cyclic tests on several asphaltic mixes crack growth is measured, both with crack foils and with cOD-gauges. It is found that crack growth in asphaltic mixes is described by three processes which are parallel in time: cohesive

  11. Hydraulic Yaw System

    DEFF Research Database (Denmark)

    Stubkier, Søren; Pedersen, Henrik C.; Mørkholt, M.

    As wind turbines increase in size, combined with increased lifetime demands, new methods for load reduction needs to be examined. One method is to make the yaw system of the turbine soft/flexible and hereby dampen the loads to the system, which is the focus of the current paper. By utilizing...... the HAWC2 aeroelastic code and an extended model of the NREL 5MW turbine combined with a simplified linear model of the turbine, the parameters of the soft yaw system are optimized to reduce loading in critical components. Results shows that a significant reduction in fatigue and extreme loads to the yaw...... system and rotor shaft when utilizing the soft yaw drive concept compared to the original stiff yaw system. The physical demands of the hydraulic yaw system are furthermore examined for a life time of 20 years. Based on the extrapolated loads, the duty cycles show that it is possible to construct...

  12. Electro Hydraulic Hitch Control

    DEFF Research Database (Denmark)

    Hansen, M. R.; Andersen, T. O.; Nielsen, B.

    2003-01-01

    system for agricultural applications and driving for transportation. During tranport phases, the lack of suspension causes the vehicle to bounce and pitch, and makes it difficalt to control. Many systems have been proposed to cope with the oscillatory behavior, and different solutions exist. Common......This paper present and discusses R&D results on electro hydraulic hitch control for off-road vehicle, in particular active damping of oscillation occuring on tractors. The research deals with analysis and control of the oscillations occuring on tractors which are design without any susspection...... for most of the systems are that they operate on the hydrailc actuators generally providing the motive forces for moving the implement and/or attachment, typically a plough. The basic idea and physical working principle are to use the implement, moveable relative to the vehicle, as a damper mass. The paper...

  13. Linear Perturbation Adaptive Control of Hydraulically Driven Manipulators

    DEFF Research Database (Denmark)

    Andersen, T.O.; Hansen, M.R.; Conrad, Finn

    2004-01-01

    control.Using the Lyapunov approach, under slowly time-varying assumptions, it is shown that the tracking error and the parameter error remain bounded. This bound is a function of the ideal parameters and a bounded disturbance. The control algorithm decouples and linearizes the manipulator so that each...

  14. Fiber Sensing of Micro -Crack

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    Optical fiber sensors are used for sensing micro-cracking in composite and metal materials in aerospace applications. The sensing mechanism is based on the detection of acoustic emission signals, which are known to emanate from micro-cracks when they grow under further loading. The sensor head consists of a fiber Bragg grating that is capable of detecting acoustic emission signals generated by pencil lead breaking, of frequencies up to 200 kHz.

  15. Investigation of Possible Wellbore Cement Failures During Hydraulic Fracturing Operations

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Jihoon; Moridis, George

    2014-11-01

    We model and assess the possibility of shear failure, using the Mohr-Coulomb model ? along the vertical well by employing a rigorous coupled flow-geomechanic analysis. To this end, we vary the values of cohesion between the well casing and the surrounding cement to representing different quality levels of the cementing operation (low cohesion corresponds to low-quality cement and/or incomplete cementing). The simulation results show that there is very little fracturing when the cement is of high quality.. Conversely, incomplete cementing and/or weak cement can causes significant shear failure and the evolution of long fractures/cracks along the vertical well. Specifically, low cohesion between the well and cemented areas can cause significant shear failure along the well, but the same cohesion as the cemented zone does not cause shear failure. When the hydraulic fracturing pressure is high, low cohesion of the cement can causes fast propagation of shear failure and of the resulting fracture/crack, but a high-quality cement with no weak zones exhibits limited shear failure that is concentrated near the bottom of the vertical part of the well. Thus, high-quality cement and complete cementing along the vertical well appears to be the strongest protection against shear failure of the wellbore cement and, consequently, against contamination hazards to drinking water aquifers during hydraulic fracturing operations.

  16. Hydraulic conductivity of compacted zeolites.

    Science.gov (United States)

    Oren, A Hakan; Ozdamar, Tuğçe

    2013-06-01

    Hydraulic conductivities of compacted zeolites were investigated as a function of compaction water content and zeolite particle size. Initially, the compaction characteristics of zeolites were determined. The compaction test results showed that maximum dry unit weight (γ(dmax)) of fine zeolite was greater than that of granular zeolites. The γ(dmax) of compacted zeolites was between 1.01 and 1.17 Mg m(-3) and optimum water content (w(opt)) was between 38% and 53%. Regardless of zeolite particle size, compacted zeolites had low γ(dmax) and high w(opt) when compared with compacted natural soils. Then, hydraulic conductivity tests were run on compacted zeolites. The hydraulic conductivity values were within the range of 2.0 × 10(-3) cm s(-1) to 1.1 × 10(-7) cm s(-1). Hydraulic conductivity of all compacted zeolites decreased almost 50 times as the water content increased. It is noteworthy that hydraulic conductivity of compacted zeolite was strongly dependent on the zeolite particle size. The hydraulic conductivity decreased almost three orders of magnitude up to 39% fine content; then, it remained almost unchanged beyond 39%. Only one report was found in the literature on the hydraulic conductivity of compacted zeolite, which is in agreement with the findings of this study.

  17. Computational and physical consequences of interaction of closely located simultaneous hydraulic fractures

    CERN Document Server

    Rejwer, Ewa

    2015-01-01

    Strong interaction of closely located, nearly parallel hydraulic fractures and its influence on their propagation are studied. Both computational and physical aspects of the problem are considered. It is shown that from the computational point of view, when a distance between cracks is small as compared with their sizes, the system becomes ill-conditioned and numerical results deteriorate. The physical consequence of the interaction consists in decreasing of the crack opening and even greater decrease of conductivity. Then the resistance to fluid flow grows what results in the propagation of only those fractures, the distance between which is large enough. The research aims to suggests a means to overcome the computational difficulty and to improve numerical simulation of hydraulic fractures in shales. Numerical experiments are carried out for a 2D problem by using the complex variable hypersingular boundary element method of higher order accuracy. The condition number of the main matrix of a system, the open...

  18. Testing study of subcritical crack growth rate and fracture toughness in different rocks

    Institute of Scientific and Technical Information of China (English)

    CAO Ping; LI Jiang-teng; YUAN Hai-ping

    2006-01-01

    Subcritical crack growth of double torsion specimens made of ore, lherzolite, marble and granite was studied using Instron1342 type electro hydraulic servo test machine. The relations of the mode-Ⅰ stress intensity factor KI versus the subcritical crack growth velocity v and the fracture toughness KIC were obtained by the double torsion constant displacement load relaxation method. The behavior of subcritical crack growth was analyzed for different rocks. The results show that lgKI-lgv relations of four kinds of rocks measured by this method accord with linear rule, i.e. the relations between subcritical crack growth velocity and stress intensity factor have a power law, which is in good agreement with CHARLES theory. lgKI-lgv curves move to top left corner with the decrease of the elastic modulus, which implies that the subcritical crack growth velocity speeds up. The maximum subcritical crack growth velocity exhibits negative exponential increase, and mode-Ⅰ fracture toughness KIC decreases with the decrease of elastic modulus. The testing results provide a basis for time-dependence of rock engineering stability.

  19. Hydraulic Actuators with Autonomous Hydraulic Supply for the Mainline Aircrafts

    Directory of Open Access Journals (Sweden)

    I. S. Shumilov

    2014-01-01

    Full Text Available Applied in the aircraft control systems, hydraulic servo actuators with autonomous hydraulic supply, so-called, hydraulic actuators of integrated configuration, i.e. combination of a source of hydraulic power and its load in the single unit, are aimed at increasing control system reliability both owing to elimination of the pipelines connecting the actuator to the hydraulic supply source, and owing to avoidance of influence of other loads failure on the actuator operability. Their purpose is also to raise control system survivability by eliminating the long pipeline communications and their replacing for the electro-conductive power supply system, thus reducing the vulnerability of systems. The main reason for a delayed application of the hydraulic actuators in the cutting-edge aircrafts was that such aircrafts require hydraulic actuators of considerably higher power with considerable heat releases, which caused an unacceptable overheat of the hydraulic actuators. Positive and negative sides of the hydraulic actuators, their alternative options of increased reliability and survivability, local hydraulic systems as an advanced alternative to independent hydraulic actuators are considered.Now to use hydraulic actuators in mainline aircrafts is inexpedient since there are the unfairly large number of the problems reducing, first and last, safety of flights, with no essential weight and operational advantages. Still works to create competitive hydraulic actuators ought to be continued.Application of local hydraulic systems (LHS will allow us to reduce length of pressure head and drain pipelines and mass of pipelines, as well as to raise their general fail-safety and survivability. Application of the LHS principle will allow us to use a majority of steering drive advantages. It is necessary to allocate especially the following:- ease of meeting requirements for the non-local spread of the engine weight;- essentially reducing length and weight of

  20. Polypropylene Fiber Amendments to Alleviate Initiation and Evolution of Desiccation Cracks in Bentonite Liners

    Science.gov (United States)

    Tuller, M.; Gebrenegus, T. B.

    2009-12-01

    Sodium saturated bentonite is a major constituent of compacted and geosynthetic liners and covers for hydraulic isolation of hazardous waste, playing a crucial role in protecting groundwater and other environmental resources from harmful landfill leachates. Due to favorable hydraulic properties (i.e., low permeability), large surface area and associated adsorption capacity for particular contaminants, and relative abundance and low cost, bentonite is the material of choice in many modern waste containment systems. However, long-term interactions between bentonite and waste leachate and exposure of bentonite to desiccative conditions may significantly deteriorate liner or cover performance and ultimately lead to failure of containment systems. In the presented study, the potential usefulness of polypropylene fiber amendments for preventing initiation and evolution of desiccation cracks, while maintaining acceptably low permeability under saturated conditions was investigated. Well-controlled desiccation experiments were conducted using initially saturated bentonite-sand mixtures that contained varying amounts of polypropylene fibers. Initiation and evolution of surface cracks were observed by means of X-Ray Computed Tomography (CT). Advanced image analysis techniques were employed to characterize and quantify 2-D and 3-D features of the evolving crack networks. Potential negative effects of employed additives on saturated hydraulic conductivity were determined with fully-automated Flexible Wall Permeametry (FWP).

  1. Hydraulic conductivity of organomodified soil

    Energy Technology Data Exchange (ETDEWEB)

    Wallace, R.B.; Grant, J.M.; Voice, T.C.; Rakhshandehroo, G.; Xu, S.; Boyd, S.A. [Michigan State Univ., East Lansing, MI (United States)

    1995-11-01

    The effects of organomodification on soil hydraulic conductivity were investigated. Hydraulic conductivity and porosity of treated and untreated samples of a sandy loam were measured as a function of effective stress. Batch treatment with hexadecyltrimethyl ammonium (HDTMA) and dry packing produced organomodified samples that were 79% less conducive than untreated samples prior to loading. Treated samples lost less hydraulic conductivity as a result of loading than untreated samples so that treated samples had higher conductivity at high loads. Observed differences in conductivity are explained in terms of the role of the treated and untreated clay in controlling initial effective pore size and its change during consolidation.

  2. Fatigue reliability of cracked engineering structures

    Science.gov (United States)

    Lanning, David Bruce, Jr.

    1997-12-01

    This study investigates the reliability of engineering structures containing fatigue cracks. Stress concentrations and welded joints are probable locations for the initiation and propagation of fatigue cracks. Due to the many unknowns of loading, materials properties, crack sizes and crack shapes present at these locations, a statistics-based reliability analysis is valuable in the careful consideration of these many different random factors involved in a fatigue life analysis, several of which are expanded upon in this study. The basic problem of a crack near a stress concentration is first considered. A formulation for the aspect ratio (a/c) of a propagating semi-elliptical fatigue crack located at the toe of a welded T-joint is developed using Newman and Raju's stress intensity factor for a cracked flat plate with a weld magnification factor and compared to that of a cracked flat plate, and the reliability in terms of fatigue lifetime is calculated with the aid of Paris' crack propagation equation for membrane and bending loadings. Crack closure effects are then introduced in the consideration of short crack effects, where crack growth rates typically may exceed those found using traditional linear elastic fracture mechanics solutions for long cracks. The probability of a very small, microstructurally influenced crack growing to a size influenced by local plastic conditions is calculated utilizing the probability of a crack continuing to grow past an obstacle, such as a grain boundary. The result is then combined with the probability for failure defined using the crack closure-modified Paris equation to find an overall reliability for the structure. Last, the probability of fracture is determined when a crack front encounters regions of non-uniform toughness, such as typical in the heat affected zone of a welded joint. An expression for the effective crack lengths of the dissimilar regions is derived, and used in a weakest-link fracture model in the evaluation

  3. Hydraulic fracturing - an attempt of DEM simulation

    Science.gov (United States)

    Kosmala, Alicja; Foltyn, Natalia; Klejment, Piotr; Dębski, Wojciech

    2017-04-01

    Hydraulic fracturing is a technique widely used in oil, gas and unconventional reservoirs exploitation in order to enable the oil/gas to flow more easily and enhance the production. It relays on pumping into a rock a special fluid under a high pressure which creates a set of microcracks which enhance porosity of the reservoir rock. In this research, attempt of simulation of such hydrofracturing process using the Discrete Element Method approach is presented. The basic assumption of this approach is that the rock can be represented as an assembly of discrete particles cemented into a rigid sample (Potyondy 2004). An existence of voids among particles simulates then a pore system which can be filled out by fracturing fluid, numerically represented by much smaller particles. Following this microscopic point of view and its numerical representation by DEM method we present primary results of numerical analysis of hydrofracturing phenomena, using the ESyS-Particle Software. In particular, we consider what is happening in distinct vicinity of the border between rock sample and fracking particles, how cracks are creating and evolving by breaking bonds between particles, how acoustic/seismic energy is releasing and so on. D.O. Potyondy, P.A. Cundall. A bonded-particle model for rock. International Journal of Rock Mechanics and Mining Sciences, 41 (2004), pp. 1329-1364.

  4. Soil desiccation cracks as a suction–contraction process

    KAUST Repository

    Cordero, J. A.

    2017-10-05

    Recent macro- and particle-scale advances in unsaturated soil behaviour have led to an enhanced understanding of the effects of moisture changes on soil response. This research examines desiccation cracks as a suction–contraction-coupled process using sand–clay mixtures. Suction–moisture measurements highlight the role of fines on suction potential even at low fines content; on the other hand, oedometer tests exhibit a marked transition from sand-controlled to clay-controlled compressibility. Time-lapse photography of desiccation tests in flat trays show the onset of crack initiation and the subsequent evolution in horizontal strains; concurrent gravimetric water content measurements relate crack nucleation to suction at air entry. Suction and compressibility increase with the soil-specific surface and have a compounded effect on desiccation-driven lateral contraction. Both layer thickness and its lateral extent affect the development of desiccation cracks. The recently proposed revised soil classification system properly anticipates the transitions in compressibility and capillary phenomena observed in this study (between 15 and 35% fines content).

  5. Cracking Process and Stress Field Evolution in Specimen Containing Combined Flaw Under Uniaxial Compression

    Science.gov (United States)

    Liu, Ting; Lin, Baiquan; Yang, Wei; Zou, Quanle; Kong, Jia; Yan, Fazhi

    2016-08-01

    Hydraulic slotting, an efficient technique for underground enhanced coal bed methane (ECBM) recovery, has been widely used in China. However, its pressure relief mechanism is unclear. Thus far, only limited research has been conducted on the relationships among the mechanical properties, flaw parameters, and crack propagation patterns of coal after hydraulic slotting. In addition, because of the limitations of test methods, an in-depth information is not available for this purpose. In this work, numerical models of specimens containing combined flaws are established based on particle flow code method. Our results provide insights into the effects of flaw inclination angle on the mechanical properties, crack propagation patterns, and temporal and spatial evolution rules of stress field in specimens containing combined flaws during the loading process. Besides, based on the initiation position and underlying mechanism, three types of crack initiation modes are identified from the failure processes of specimens. Finally, the crack propagation pattern is quantitatively described by the fractal dimension, which is found to be inversely proportional to the uniaxial compressive strength and elastic modulus of the specimen. To verify the rationality of the numerical simulation results, laboratory tests were conducted and their results match well with those obtained from the numerical simulation.

  6. HYDRAULICS, ATHENS COUNTY, OHIO, USA

    Data.gov (United States)

    Federal Emergency Management Agency, Department of Homeland Security — Hydraulic data include spatial datasets and data tables necessary for documenting the hydrologic procedures for estimating flood discharges for a flood insurance...

  7. HYDRAULICS, JACKSON COUNTY, KENTUCKY, USA

    Data.gov (United States)

    Federal Emergency Management Agency, Department of Homeland Security — Hydraulic data include spatial datasets and data tables necessary for documenting the hydrologic procedures for estimating flood discharges for a flood insurance...

  8. HYDRAULICS, MADISON COUNTY, ALABAMA, USA

    Data.gov (United States)

    Federal Emergency Management Agency, Department of Homeland Security — This Hydraulic data was reviewed and approved by FEMA during the initial MT-2 processing. Recent developments in digital terrain and geospatial database management...

  9. HYDRAULICS, HAMPDEN COUNTY, MA, USA

    Data.gov (United States)

    Federal Emergency Management Agency, Department of Homeland Security — Hydraulic data in this submittal include spatial datasets and model outputs necessary for computation of the 1-percent flooding extent. The minimum requirement for...

  10. Hydraulic wind energy conversion system

    Energy Technology Data Exchange (ETDEWEB)

    1981-07-01

    The purpose of this research was to design, build and test a hydraulic wind energy system. This design used a three bladed turbine, which drove a hydraulic pump. The energy is transmitted from the pump through a long hose and into a hydraulic motor, where the energy is used. This wind system was built and tested during the winter of 1980-1981. The power train included a five meter, three bladed wind turbine, a 9.8:1 ratio gearbox, a 1.44 cubic inch displacement pump with a small supercharge gear pump attached. The hydraulic fluid was pumped through a 70', 3/4'' I-D-high pressure flexhose, then through a volume control valve and into a 1.44 cubic inch displacement motor. The fluid was returned through a 70', 1'' I-D-flexhose.

  11. 14 CFR 29.1435 - Hydraulic systems.

    Science.gov (United States)

    2010-01-01

    ... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Hydraulic systems. 29.1435 Section 29.1435... STANDARDS: TRANSPORT CATEGORY ROTORCRAFT Equipment Miscellaneous Equipment § 29.1435 Hydraulic systems. (a) Design. Each hydraulic system must be designed as follows: (1) Each element of the hydraulic system...

  12. 14 CFR 23.1435 - Hydraulic systems.

    Science.gov (United States)

    2010-01-01

    ... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Hydraulic systems. 23.1435 Section 23.1435... § 23.1435 Hydraulic systems. (a) Design. Each hydraulic system must be designed as follows: (1) Each hydraulic system and its elements must withstand, without yielding, the structural loads expected...

  13. 46 CFR 28.405 - Hydraulic equipment.

    Science.gov (United States)

    2010-10-01

    ... 46 Shipping 1 2010-10-01 2010-10-01 false Hydraulic equipment. 28.405 Section 28.405 Shipping... Operate With More Than 16 Individuals on Board § 28.405 Hydraulic equipment. (a) Each hydraulic system... than four times the system maximum operating pressure. (c) Each hydraulic system must be equipped...

  14. SHORT FATIGUE CRACK PARAMETER BASED ON THE TOTAL CRACK AREA

    Institute of Scientific and Technical Information of China (English)

    Z.X.Wu; X.C.Wu

    2001-01-01

    The progressive fatigue damage of a material is closely related to the whole populationof cracks on the surface of an un-notched specimen.In order to understand whichparameter is a more useful indicator of fatigue damage,rotatory bending fatigue testswere carried out using smooth specimens of medium-carbon steel.The behavior ofshort crack propagation during fatigue was examined and a new parameter "totalcrack area" was suggested.The aim of this paper is to extend the research on fatiguedamage in the already studied steel and to study how these damage parameters arecorrelated with the process of fatigue damage in order to evaluate the effectiveness ofdamage detection methods.

  15. Advanced Performance Hydraulic Wind Energy

    Science.gov (United States)

    Jones, Jack A.; Bruce, Allan; Lam, Adrienne S.

    2013-01-01

    The Jet Propulsion Laboratory, California Institute of Technology, has developed a novel advanced hydraulic wind energy design, which has up to 23% performance improvement over conventional wind turbine and conventional hydraulic wind energy systems with 5 m/sec winds. It also has significant cost advantages with levelized costs equal to coal (after carbon tax rebate). The design is equally applicable to tidal energy systems and has passed preliminary laboratory proof-of-performance tests, as funded by the Department of Energy.

  16. Study on magnetic memory signals of medium carbon steel specimens with surface crack precut during loading process

    Institute of Scientific and Technical Information of China (English)

    DONG Lihong; XU Binshi; DONG Shiyun; YE Minghui; CHEN Qunzhi

    2006-01-01

    Static tensile test and tensile-tensile fatigue test of medium carbon steel sheet specimens with surface crack precut were performed on MTS810 hydraulic testing machine to clear the meaning of the point of Hp( y ) value zero. Magnetic memory signals were measured during the test process. The results show that only one point of Hp( y ) zero value exists in all measured magnetic signal curves during the loading process, which should be a sign of intersection of positive-negative magnetic poles after magnetic ordered state appears and does not indicate the position of surface crack precut. The analysis shows that the surface crack precut can not interrupt the magnetic ordered state occurred during the test completely, hence its Hp( y ) value is not zero. However, the crack extending to a penetrated defect at the instant of specimen's fracture leads to the discontinuance of magnetic ordered state.

  17. IDENTIFICATION OF CRACKED ROTOR BY WAVELET TRANSFORM

    Institute of Scientific and Technical Information of China (English)

    邹剑; 陈进; 蒲亚鹏

    2002-01-01

    The dynamic equation of cracked rotor in rotational frame was modelled, the numerical simulation solutions of the cracked rotor and the uncracked rotor were obtained. By the wavelet transform, the time-frequency properties of the cracked rotor and the uncracked rotor were discussed, the difference of the time-frequency properties between the cracked rotor and the uncracked rotor was compared. A new detection algorithm using wavelet transform to identify crack was proposed. The experiments verify the availability and validity of the wavelet transform in identification of crack.

  18. Technologies and Innovations for Hydraulic Pumps

    OpenAIRE

    Ivantysynova, Monika

    2016-01-01

    Positive displacement machines working as hydraulic pumps or hydraulic motors have always been, are and will be an essential part of any hydraulic system. Current trends and future demands on energy efficient systems will not only drastically increase the number of positive displacement machines needed for modern efficient hydraulic circuits but will significantly change the performance requirements of pumps and motors. Throttleless system configurations will change the landscape of hydraulic...

  19. Review of Environmentally Assisted Cracking

    Science.gov (United States)

    Sadananda, K.; Vasudevan, A. K.

    2011-02-01

    Many efforts have been made in the past by several researchers to arrive at some unifying principles governing the embrittlement phenomena. An inescapable conclusion reached by all these efforts was that the behavior is very complex. Hence, recognizing the complexity of material/environment behavior, we focus our attention here only in extracting some similarities in the experimental trends to arrive at some generic principles of behavior. Crack nucleation and growth are examined under static load in the presence of internal and external environments. Stress concentration, either pre-existing or in-situ generated, appears to be a requirement for embrittlement. A chemical stress concentration factor is defined for a given material/environment system as the ratio of failure stress with and without the damaging chemical environment. All factors that affect the buildup of the required stress concentration, such as planarity of slip, stacking fault energy, etc., also affect the stress-corrosion behavior. The chemical stress concentration factor is coupled with the mechanical stress concentration factor. In addition, generic features for all systems appear to be (a) an existence of a threshold stress as a function of concentration of the damaging environment and flow properties of the material, and (b) an existence of a limiting threshold as a function of concentration, indicative of a damage saturation for that environment. Kinetics of crack growth also depends on concentration and the mode of crack growth. In general, environment appears to enhance crack tip ductility on one side by the reduction of energy for dislocation nucleation and glide, and to reduce cohesive energy for cleavage, on the other. These two opposing factors are coupled to provide environmentally induced crack nucleation and growth. The relative ratio of these two opposing factors depends on concentration and flow properties, thereby affecting limiting thresholds. The limiting concentration or

  20. Cracking and corrosion recovery boiler

    Energy Technology Data Exchange (ETDEWEB)

    Suik, H. [Tallinn Technical University, Horizon Pulp and Paper, Tallinn (Estonia)

    1998-12-31

    The corrosion of heat surfaces and the cracking the drums are the main problems of the recovery boiler. These phenomena have been appeared during long-term operation of boiler `Mitsubishi - 315` erected at 1964. Depth of the crack is depending on the number of shutdowns and on operation time. Corrosion intensity of different heat surfaces is varying depend on the metal temperature and the conditions at place of positioning of tube. The lowest intensity of corrosion is on the bank tubes and the greatest is on the tubes of the second stage superheater and on the tubes at the openings of air ports. (orig.) 5 refs.

  1. Theory and application of rock burst prevention using deep hole high pressure hydraulic fracturing

    Institute of Scientific and Technical Information of China (English)

    Shan-Kun ZHAO; Jun LIU; Xiang-Zhi WEI; Chuan-Hong DING; Yu-Lei LV; Gang-Feng LI

    2013-01-01

    In order to analyze the mechanism of deep hole high pressure hydraulic fracturing,nonlinear dynamic theory,damage mechanics,elastic-plastic mechanics are used,and the law of crack propagation and stress transfer under two deep hole hydraulic fracturing in tectonic stress areas is studied using seepage-stress coupling models with RFPA simulation software.In addition,the effects of rock burst control are tested using multiple methods,either in the stress field or in the energy field.The research findings show that with two deep holes hydraulic fracturing in tectonic stress areas,the direction of the main crack propagation under shear-tensile stress is parallel to the greatest principal stress direction.High-pressure hydraulic fracturing water seepage can result in the destruction of the coal structure,while also weakening the physical and mechanical properties of coal and rock.Therefore the impact of high stress concentration in hazardous areas will level off,which has an effect on rock burst prevention and control in the region.

  2. Modified Dugdale crack models - some easy crack relations

    DEFF Research Database (Denmark)

    Nielsen, Lauge Fuglsang

    1997-01-01

    are assumed to be self created by local materials flow. The strength sigma_CR predictid by the Dugdale model is sigma_CR =(E Gamma_CR/phi1)^½ where E and 1 are Young’s modulus and crack half-length respectively of the material considered. The so-called critical strain energy rate is Gamma_CR = sigma......_Ldelta_CR where sigma_L is strength, and at the same time constant flow stress, of the uncracked material while delta_CR is flow limit (displacement).Obviously predictions by the Dugdale model are most reliable for materials with stress-strain relations where flow can actually be described (or well approximated......) by a constant flow stress (sigma_L). A number of materials, however, do not at all exhibit this kind of flow. Such materials are considered in this paper by Modified Dugdale crack models which apply for any cohesive stress distribution in crack front areas. Formally modified Dugdale crack models exhibit...

  3. Fatigue crack growth study of SCS6/Ti-15-3 composite

    Science.gov (United States)

    Kantzos, P.; Telesman, J.

    1990-01-01

    A study was performed to determine the fatigue crack growth (FCG) behavior and the associated fatigue damage processes in a (0)8- and (90)8-oriented SCS6/Ti-15-3 composite. Companion testing was also done on identically processed Ti-15-3 unreinforced material. The active fatigue crack growth failure processes were very similar for both composite orientations tested. For both orientations, fatigue crack growth was along the fiber direction. It was found that the composite constituent most susceptible to fatigue damage was the interface region and, in particular, the carbon coating surrounding the fiber. The failure of the interface region led to crack initiation and also strongly influenced the FCG behavior in this composite. The failure of the interface region was apparently driven by normal stresses perpendicular to the fiber direction. The FCG rates were considerably higher for the (90)8-oriented CT specimens in comparison to the unreinforced material.

  4. Fatigue Crack Growth Prediction for generalized fiber metal laminates and hybrid materials

    NARCIS (Netherlands)

    Wilson, G.S.

    2013-01-01

    The excellent durability performance of Glare, a thin fiber metal laminate (FML) material system, is now being proven in service. This has motivated work towards the application of FMLs to thicker structures driven by damage tolerance. In order to fully characterize the crack growth life of such mat

  5. FRACTAL KINEMATICS OF CRACK PROPAGATION IN GEOMATERIALS

    Institute of Scientific and Technical Information of China (English)

    谢和平

    1995-01-01

    Experimental results indicate that propagation paths of cracks in geomaterials are often irregular, producing rough fracture surfaces which are fractal. A formula is derived for the fractal kinematics of crack propagation in geomaterials. The formula correlates the dynamic and static fracture toughnesses with crack velocity, crack length and a microstructural parameter, and allows the fractal dimension to be obtained. From the equations for estimating crack velocity and fractal dimension it can be shown that the measured crack velocity, Vo , should be much smaller than the fractal crack velocity, V. It can also be shown that the fractal dimension of the crack propagation path can be calculated directly from Vo and from the fracture toughness.

  6. Interacting Cracks in an Environmentally Assisted Fracture

    Science.gov (United States)

    Levandovsky, Artem; Balazs, Anna

    2006-03-01

    We perform the study of environmentally assisted fracture within the framework of a lattice model. Formation of an ensemble of environmentally assisted microcracks, their coalescence and formation of crack ``avalanches'' lead to a very rich dynamical picture. Under specific condition crack healing can occur due to cohesive forces, which hold material together and tend to pull atoms together even if they are separated by a crack over several lattice units. We investigate the dynamical interplay between crack formation, arrest, healing and re-cracking. The goal here is to provide an understanding of the conditions leading to the phenomena of crack healing that happens along with the crack formation. We study the morphology of crack patterns with the intentions to establish a way to enhance the healing property of a material sample.

  7. On multiple crack detection in beam structures

    Energy Technology Data Exchange (ETDEWEB)

    Moradi, Shapour; Kargozarfard, Mohammad [Shahid Chamran University, Ahvaz (Iran, Islamic Republic of)

    2013-01-15

    This study presents an inverse procedure to identify multiple cracks in beams using an evolutionary algorithm. By considering the crack detection procedure as an optimization problem, an objective function can be constructed based on the change of the eigenfrequencies and some strain energy parameters. Each crack is modeled by a rotational spring. The changes in natural frequencies due to the presence of the cracks are related to a damage index vector. Then, the bees algorithm, a swarm-based evolutionary optimization technique, is used to optimize the objective function and find the damage index vector, whose positive components show the number and position of the cracks. A second objective function is also optimized to find the crack depths. Several experimental studies on cracked cantilever beams are conducted to ensure the integrity of the proposed method. The results show that the number of cracks as well as their sizes and locations can be predicted well through this method.

  8. Crack and flip phacoemulsification technique.

    Science.gov (United States)

    Fine, I H; Maloney, W F; Dillman, D M

    1993-11-01

    The crack and flip phacoemulsification technique combines the advantages of circumferential division of the nucleus and nucleofactis techniques. As such, it adds safety and control to the procedure. We describe each of the surgical maneuvers, including machine settings, and explain the rationale for maneuvers and machine settings.

  9. China Cracks Down Internet Piracy

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

      National Copyright Administration of China carried out a special operation to crack down on behaviors involving network infringement and piracy from September to December in 2005 ,according to the speech of Yan Xiaohong,Deputy Commissioner of National Copyright Administration on the Press Conference of the State Council.Now the relevant conditions are as follows:……

  10. China Cracks Down Internet Piracy

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    @@ National Copyright Administration of China carried out a special operation to crack down on behaviors involving network infringement and piracy from September to December in 2005 ,according to the speech of Yan Xiaohong,Deputy Commissioner of National Copyright Administration on the Press Conference of the State Council.Now the relevant conditions are as follows:

  11. HYDROTHERMAL CRACKING OF RESIDUAL OILS

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The hydrothermal cracking of heavy oils, such as Canadian oil sand bitumen and Arabian heavy vacuum residue, as well as their model compound were performed over sulfided Ni/Al2O3 and NiMo/Al2O3 catalysts under 663~703 K and 6.0~8.0 MPa of hydrogen pressure in a batch autoclave reactor. According to the reaction mechanism of hydrothermal cracking, a small amount of free redical initiators, such as di-tert-peroxide, sulfur, etc., was added into the feed to generate free redicals at lower temperature, and obviously showed promotional effect on the conversion of hydrocarbons. The reaction mechanisms of hydrothermal cracking as well as the enhancing effect of initiators were studied by a probe reaction with 1-phenyldodecane as a model compound. The hydrothermal cracking of hydrocarbon proceeded via free redical mechanism and hydrogenating quench. The initiators might easily generate free redicals under reaction temperature, these redicals might abstract H from hydrocarbon molecule and reasonably initiate the chain reactions, therefore, promote the conversion of hydrocarbon even at lower reaction temperature.

  12. Confining crack propagation in defective graphene.

    Science.gov (United States)

    López-Polín, Guillermo; Gómez-Herrero, Julio; Gómez-Navarro, Cristina

    2015-03-11

    Crack propagation in graphene is essential to understand mechanical failure in 2D materials. We report a systematic study of crack propagation in graphene as a function of defect content. Nanoindentations and subsequent images of graphene membranes with controlled induced defects show that while tears in pristine graphene span microns length, crack propagation is strongly reduced in the presence of defects. Accordingly, graphene oxide exhibits minor crack propagation. Our work suggests controlled defect creation as an approach to avoid catastrophic failure in graphene.

  13. Correction to the crack extension direction in numerical modelling of mixed mode crack paths

    DEFF Research Database (Denmark)

    Lucht, Tore; Aliabadi, M.H.

    2007-01-01

    In order to avoid introduction of an error when a local crack-growth criterion is used in an incremental crack growth formulation, each straight crack extension would have to be infinitesimal or have its direction corrected. In this paper a new procedure to correct the crack extension direction i...

  14. Mesh sensitivity effects on fatigue crack growth by crack-tip blunting and re-sharpening

    DEFF Research Database (Denmark)

    Tvergaard, Viggo

    2007-01-01

    Crack-tip blunting under tensile loads and re-sharpening of the crack-tip during unloading is one of the basic mechanisms for fatigue crack growth in ductile metals. Based on an elastic–perfectly plastic material model, crack growth computations have been continued up to 700 full cycles by using...

  15. Fatigue crack growth from a cracked elastic particle into a ductile matrix

    NARCIS (Netherlands)

    Groh, S.; Olarnrithinun, S.; Curtin, W. A.; Needleman, A.; Deshpande, V. S.; Van der Giessen, E.

    2008-01-01

    The monotonic and cyclic crack growth rate of cracks is strongly influenced by the microstructure. Here, the growth of cracks emanating from pre-cracked micron-scale elastic particles and growing into single crystals is investigated, with a focus on the effects of (i) plastic confinement due to the

  16. Twisting cracks in Bouligand structures.

    Science.gov (United States)

    Suksangpanya, Nobphadon; Yaraghi, Nicholas A; Kisailus, David; Zavattieri, Pablo

    2017-06-10

    The Bouligand structure, which is found in many biological materials, is a hierarchical architecture that features uniaxial fiber layers assembled periodically into a helicoidal pattern. Many studies have highlighted the high damage-resistant performance of natural and biomimetic Bouligand structures. One particular species that utilizes the Bouligand structure to achieve outstanding mechanical performance is the smashing Mantis Shrimp, Odontodactylus Scyllarus (or stomatopod). The mantis shrimp generates high speed, high acceleration blows using its raptorial appendage to defeat highly armored preys. The load-bearing part of this appendage, the dactyl club, contains an interior region [16] that consists of a Bouligand structure. This region is capable of developing a significant amount of nested twisting microcracks without exhibiting catastrophic failure. The development and propagation of these microcracks are a source of energy dissipation and stress relaxation that ultimately contributes to the remarkable damage tolerance properties of the dactyl club. We develop a theoretical model to provide additional insights into the local stress intensity factors at the crack front of twisting cracks formed within the Bouligand structure. Our results reveal that changes in the local fracture mode at the crack front leads to a reduction of the local strain energy release rate, hence, increasing the necessary applied energy release rate to propagate the crack, which is quantified by the local toughening factor. Ancillary 3D simulations of the asymptotic crack front field were carried out using a J-integral to validate the theoretical values of the energy release rate and the local stress intensity factors. Copyright © 2017 Elsevier Ltd. All rights reserved.

  17. Fatigue crack growth simulations of 3-D linear elastic cracks under thermal load by XFEM

    Institute of Scientific and Technical Information of China (English)

    Himanshu PATHAK[1; Akhilendra SINGH[2; I.V. SINGH[3; S. K. YADAV[3

    2015-01-01

    This paper deals with the fatigue crack growth simulations of three-dimensional linear elastic cracks by XFEM under cyclic thermal load. Both temperature and displacement approximations are extrinsically enriched by Heaviside and crack front enrichment functions. Crack growth is modelled by successive linear extensions, and the end points of these linear extensions are joined by cubic spline segments to obtain a modified crack front. Different crack geometries such as planer, non-planer and arbitrary spline shape cracks are simulated under thermal shock, adiabatic and isothermal loads to reveal the sturdiness and versatility of the XFEM approach.

  18. Variation of crack intensity factor in three compacted clay liners exposed to annual cycle of atmospheric conditions with and without geotextile cover.

    Science.gov (United States)

    Safari, E; Jalili Ghazizade, M; Abduli, M A; Gatmiri, B

    2014-08-01

    Performance of compacted clay liners commonly used as landfill barrier systems can be subject to decline in terms of hydraulic conductivity if left exposed to atmospheric conditions for an extended period of time prior to placement of overlaying layers. The resulting desiccation cracking can lead to increased hydraulic conductivity. Desiccation crack intensity was studied for three clayey soils commonly used for construction of landfill barrier system in a relatively large scale test setup exposed to real time atmospheric conditions over a complete annual cycle. A white separator geotextile cover was presumed to be capable of reducing the intensity of desiccation cracking through absorbing and maintaining higher amounts of moisture and reducing the temperature of the soil surface in comparison to a directly exposed soil surface. Desiccation cracking was monitored using a digital imaging technique for three compacted clay liners in two sets, one open to air and the second covered with the white geotextile. Crack intensity factor approached a relatively stable phase after certain cycles corresponding to atmospheric dry wet cycles. The results indicated that the white separator geotextile was capable of reducing the crack intensity factor by 37.4-45.9% throughout the experiment including the cyclic phase of desiccation cracking. During the stable phase, the maximum reduction in crack intensity factor of 90.4% as a result of applying geotextile cover was observed for the soil with the lowest plastic index and clay content and therefore the lowest magnitude of crack intensity factor. The other two soils with similar clay content but different plastic index showed 23.6% and 52.2% reductions in crack intensity factor after cyclic phase when covered with geotextile.

  19. System for nucleation and propagation of fatigue cracks on SE(B) specimens

    Energy Technology Data Exchange (ETDEWEB)

    Rocha, Nirlando Antonio; Gomes Junyor, Jose Onesimo; Reis, Emil; Vilela, Jefferson Jose, E-mail: nar@cdtn.br, E-mail: ze_onezo@hotmail.com, E-mail: emilr@cdtn.br, E-mail: jjv@cdtn.br [Centro de Desenvolvimento da Tecnologia Nuclear (CDTN/CNEN-MG), Belo Horizonte, MG (Brazil); Moura, Cassio Melo, E-mail: cassio.moura@gerdau.com.br [Gerdau S.A., Ouro Branco, MG (Brazil)

    2015-07-01

    The degree of safety that a structural component has against catastrophic fracture in service can be obtained from fracture mechanics parameters. The master curve could be used for integrity evaluation in pressure vessel of nuclear power plant. The pre-crack specimens are used in this evaluation. The tests based on ASTM E 8M and ASTM E 647 standards to determination of material properties related to fracture mechanics, most often performed in a servo-hydraulic drive equipment, are time consuming and costly. This paper presents the development of a system for nucleation and propagation of fatigue cracks on SE(B) specimens. The operating principle consists of a cyclic loading, concentrated in the center of the specimen, transmitted and controlled by an eccentric mechanism. The main contribution of this work is the low-cost technology in the production of fatigue pre-crack, and the possibility of performing the nucleation and propagation of the pre-crack required for obtaining the J{sub IC} and CTOD parameters. The experimental results satisfied expectations with respect to the plastic deformation in the crack tip and met the requirements of the standards. (author)

  20. Case Study and Numerical Analysis of Vibration and Runner Cracks for the Lipno I Hydroelectric Project

    Science.gov (United States)

    Zouhar, J.; Obrovsky, J.; Feilhauer, M.; Skotak, A.

    2016-11-01

    The refurbishment of the Lipno I TG2 Francis turbine, situated on River Vltava, with maximum net head of 165 m and required operational range from 0 to 67MW of turbine power was performed in 2014. The new hydraulic design of the spiral case, distributor and runner was developed for this project. After about 1000 hours of operation the site inspection was performed and the cracks were found on 8 runner blades of 17 blades altogether. The all cracks were found near runner hub beginning from the trailing edge. The dimensions of the cracks were different with maximum length of 123 mm and minimum length of 3 mm. The runner was repaired and the intensive investigation was started to define the main cause of the cracks creation and to determine the measures for their elimination. This paper presents the program of this investigation which consists of static and dynamic blade strain measurement, CFD and FEM analysis, discusses the crack causes and overview the solution how to return the turbine successfully to operation.

  1. Complex Fluids and Hydraulic Fracturing.

    Science.gov (United States)

    Barbati, Alexander C; Desroches, Jean; Robisson, Agathe; McKinley, Gareth H

    2016-06-07

    Nearly 70 years old, hydraulic fracturing is a core technique for stimulating hydrocarbon production in a majority of oil and gas reservoirs. Complex fluids are implemented in nearly every step of the fracturing process, most significantly to generate and sustain fractures and transport and distribute proppant particles during and following fluid injection. An extremely wide range of complex fluids are used: naturally occurring polysaccharide and synthetic polymer solutions, aqueous physical and chemical gels, organic gels, micellar surfactant solutions, emulsions, and foams. These fluids are loaded over a wide range of concentrations with particles of varying sizes and aspect ratios and are subjected to extreme mechanical and environmental conditions. We describe the settings of hydraulic fracturing (framed by geology), fracturing mechanics and physics, and the critical role that non-Newtonian fluid dynamics and complex fluids play in the hydraulic fracturing process.

  2. Hydraulic properties of ladle slags

    Directory of Open Access Journals (Sweden)

    J. Vlček

    2016-07-01

    Full Text Available The article presents results of examining of hydraulic properties of ladle slags formed during production of steel. The studied ladle slags were subjected to different cooling mode from the molten state. Based on the ability of the slag react with the water was assessed their hydraulic activity. The hydraulic properties are caused by the presence of minerals dicalcium silicate, tricalcium aluminate, mayenite, brownmillerite and dicalcium ferite. The emergence of required hydrating phases in the ladle slags is conditioned by a sufficient CaO content and their cooling rate. The contact the slag with water during processing and their ageing has a negative effect. The experiment has shown that the phase transformation of the mineral dicalcium silicate which occurs during cooling of the ladle slags cause their volume instability.

  3. Hydraulic resistance of biofilms

    KAUST Repository

    Dreszer, C.

    2013-02-01

    Biofilms may interfere with membrane performance in at least three ways: (i) increase of the transmembrane pressure drop, (ii) increase of feed channel (feed-concentrate) pressure drop, and (iii) increase of transmembrane passage. Given the relevance of biofouling, it is surprising how few data exist about the hydraulic resistance of biofilms that may affect the transmembrane pressure drop and membrane passage. In this study, biofilms were generated in a lab scale cross flow microfiltration system at two fluxes (20 and 100Lm-2h-1) and constant cross flow (0.1ms-1). As a nutrient source, acetate was added (1.0mgL-1 acetate C) besides a control without nutrient supply. A microfiltration (MF) membrane was chosen because the MF membrane resistance is very low compared to the expected biofilm resistance and, thus, biofilm resistance can be determined accurately. Transmembrane pressure drop was monitored. As biofilm parameters, thickness, total cell number, TOC, and extracellular polymeric substances (EPS) were determined, it was demonstrated that no internal membrane fouling occurred and that the fouling layer actually consisted of a grown biofilm and was not a filter cake of accumulated bacterial cells. At 20Lm-2h-1 flux with a nutrient dosage of 1mgL-1 acetate C, the resistance after 4 days reached a value of 6×1012m-1. At 100Lm-2h-1 flux under the same conditions, the resistance was 5×1013m-1. No correlation of biofilm resistance to biofilm thickness was found; Biofilms with similar thickness could have different resistance depending on the applied flux. The cell number in biofilms was between 4×107 and 5×108 cellscm-2. At this number, bacterial cells make up less than a half percent of the overall biofilm volume and therefore did not hamper the water flow through the biofilm significantly. A flux of 100Lm-2h-1 with nutrient supply caused higher cell numbers, more biomass, and higher biofilm resistance than a flux of 20Lm-2h-1. However, the biofilm thickness

  4. Photoelastic studies of crack propagation and crack arrest. [Homalite 100

    Energy Technology Data Exchange (ETDEWEB)

    Irwin, G.R.; Dally, J.W.; Kobayashi, T.; Fourney, W.L.; Etheridge, J.M.

    1977-09-01

    This report describes the third year effort on research programs dealing with the characterization of dynamic aspects of fracture. The results included in this report are (1) verification of the BCL one-dimensional computer code; (2) determination of a-dot--K relationship from modified compact-tension specimen of Homalite 100; (3) verification of the MRL procedure for K/sub Ia/ measurement with machine-loaded C-DCB specimen of Homalite 100; (4) influence of adhesive toughness, adhesive thickness, and toughness of the arrest section on crack behavior in duplex specimens of both the M-CT and R-DCB types; (5) crack propagation in a thermally stressed ring specimen; and (6) development of a two-dimensional finite-difference code to predict fracture behavior in specimens of rectangular geometry under various a-dot vs K relationships. 118 figures, 53 tables.

  5. Controls of Hydraulic Wind Turbine

    Directory of Open Access Journals (Sweden)

    Zhang Yin

    2016-01-01

    Full Text Available In this paper a hydraulic wind turbine generator system was proposed based on analysis the current wind turbines technologies. The construction and principles were introduced. The mathematical model was verified using MATLAB and AMsim. A displacement closed loop of swash plate of motor and a speed closed loop of generator were setup, a PID control is introduced to maintain a constant speed and fixed frequency at wind turbine generator. Simulation and experiment demonstrated that the system can connect grid to generate electric and enhance reliability. The control system demonstrates a high performance speed regulation and effectiveness. The results are great significant to design a new type hydraulic wind turbine system.

  6. Inhibiting Corrosion Cracking: Crack Tip Chemistry and Physics.

    Science.gov (United States)

    1986-03-14

    5 5. Swuzary 113 Rferences 114 wl NO 4L iv . List of Figuring 1. Microipette pulling machine . 29 2. Anodic polarization of 7075-T6 Al alloy in dilute...environment has a strong effect on microplastic behavior at the tip of a fatigue crack. Stolz and Pelloux suggest that nitrate ion competes with chloride...Crystalline Na2 N 20 29H20 precipitates when the filtrate is placed in a vacunm desiccator over sulfuric acid. The filtered precipitate is washed

  7. Crack branching in carbon steel. Fracture mechanisms

    Science.gov (United States)

    Syromyatnikova, A. S.; Alekseev, A. A.; Levin, A. I.; Lyglaev, A. V.

    2010-04-01

    The fracture surfaces of pressure vessels made of carbon steel that form during crack branching propagation are examined by fractography. Crack branching is found to occur at a crack velocity higher than a certain critical value V > V c . In this case, the material volume that is involved in fracture and depends on the elastoplastic properties of the material and the sample width has no time to dissipate the energy released upon crack motion via the damage mechanisms intrinsic in the material under given deformation conditions (in our case, via cracking according to intragranular cleavage).

  8. Strength of Cracked Reinforced Concrete Disks

    DEFF Research Database (Denmark)

    Hoang, Cao Linh; Nielsen, Mogens Peter

    1999-01-01

    The paper deals with models, based on the theory of plasticity, to be used in strength assessments of reinforced concrete disks suffering from different kinds of cracking. Based on the assumption that the sliding strength of concrete is reduced in sections where cracks are located, solutions...... for the shear strength of disks with initial cracks and disks suffering from isotropic cracking are presented. Furthermore, in the case of isotropicly cracked disks subjected to arbitrary in-plane loading, a general yield condition is derived....

  9. CRACK REASON ANALYSIS OF DAMAGED CARBONITRIDED PART

    Directory of Open Access Journals (Sweden)

    Karin Kocúrová

    2010-03-01

    Full Text Available The article deals with the analysis of a damaged part, which was designed for use in a mechanical clutch of a car. The crack in the part was found during the production inspection. The aim of metallographic and fractography analyses of the fracture surfaces was to discover the reasons for the crack. The reason for creating the crack was the formation of smaller cracks in the production during pressing process of the semiproduct. These cracks even grew after the following thermochemical treatment. The fracture was initiated during the straightening process of quenched part.

  10. Integrating hydraulic equivalent sections into a hydraulic geometry study

    Science.gov (United States)

    Jia, Yanhong; Yi, Yujun; Li, Zhiwei; Wang, Zhaoyin; Zheng, Xiangmin

    2017-09-01

    Hydraulic geometry (HG) is an important geomorphic concept that has played an indispensable role in hydrological analyses, physical studies of streams, ecosystem and aquatic habitat studies, and sedimentology research. More than 60 years after Leopold and Maddock (1953) first introduced the concept of HG, researchers have still not uncovered the physical principles underlying HG behavior. One impediment is the complexity of the natural river cross section. The current study presents a new way to simplify the cross section, namely, the hydraulic equivalent section, which is generalized from the cross section in the ;gradually varied flow of an alluvial river; (GVFAR) and features hydrodynamic properties and bed-building laws similar to those of the GVFAR. Energy balance was used to derive the stage Z-discharge Q relationship in the GVFAR. The GVFAR in the Songhua River and the Yangtze River were selected as examples. The data, including measured discharge, river width, water stage, water depth, wet area, and cross section, were collected from the hydrological yearbooks of typical hydrological stations on the Songhua River and the Yangtze River from 1955 to 1987. The relationships between stage Z-discharge Q and cross-sectional area A-stage Z at various stations were analyzed, and ;at-a-station hydraulic geometry; (AHG) relationships were obtained in power-law forms. Based on derived results and observational data analysis, the Z-Q and Z-A relationships of AHG were similar to rectangular weir flows, thus the cross section of the GVFAR was generalized as a compound rectangular, hydraulic equivalent cross section. As to bed-building characteristics, the bankfull discharge method and the stage-discharge-relation method were used to calculate the dominant variables of the alluvial river. This hydraulic equivalent section has the same Z-Q relation, Z-A relation, dominant discharge, dominant river width, and dominant water depth as the cross section in the GVFAR. With the

  11. Numerical Investigation into the Effect of Natural Fracture Density on Hydraulic Fracture Network Propagation

    Directory of Open Access Journals (Sweden)

    Zhaohui Chong

    2017-07-01

    Full Text Available Hydraulic fracturing is an important method to enhance permeability in oil and gas exploitation projects and weaken hard roofs of coal seams to reduce dynamic disasters, for example, rock burst. It is necessary to fully understand the mechanism of the initiation, propagation, and coalescence of hydraulic fracture network (HFN caused by fluid flow in rock formations. In this study, a coupled hydro-mechanical model was built based on synthetic rock mass (SRM method to investigate the effects of natural fracture (NF density on HFN propagation. Firstly, the geometrical structures of NF obtained from borehole images at the field scale were applied to the model. Secondly, the micro-parameters of the proposed model were validated against the interaction between NF and hydraulic fracture (HF in physical experiments. Finally, a series of numerical simulations were performed to study the mechanism of HFN propagation. In addition, confining pressure ratio (CPR and injection rate were also taken into consideration. The results suggested that the increase of NF density drives the growth of stimulated reservoir volume (SRV, concentration area of injection pressure (CAIP, and the number of cracks caused by NF. The number of tensile cracks caused by rock matrix decrease gradually with the increase of NF density, and the number of shear cracks caused by rock matrix are almost immune to the change of NF density. The propagation orientation of HFN and the breakdown pressure in rock formations are mainly controlled by CPR. Different injection rates would result in a relatively big difference in the gradient of injection pressure, but this difference would be gradually narrowed with the increase of NF density. Natural fracture density is the key factor that influences the percentages of different crack types in HFN, regardless of the value of CPR and injection rate. The proposed model may help predict HFN propagation and optimize fracturing treatment designs in

  12. A study on the effect of crack in concrete structure in the point of radiation shielding

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Chang-Min; Lee, Yoon-Hee; Lee, Kun-Jai [KAIST, Daejeon (Korea, Republic of); Cho, Cheon-Hyung; Choi, Byung-Il; Lee, Heung-Young [Nuclear Environment Technology Institute, Daejeon (Korea, Republic of)

    2005-11-15

    The saturation of South Korea's at-reactor (AR) spent fuel storage pools has created a necessity for additional spent fuel storage capacity. Because the South Korean government has a plan to increase the number of nuclear power plants to 27 units by 2016, the increase of spent nuclear fuel generation will be accelerated. Because there is no concrete plan for spent unclear fuel permanent disposal, the Korea hydraulic nuclear power company is planning to construct dry storage facility. Spent nuclear fuel from CANDU type nuclear power plant will be stored in MACSTOR-400 composed by reinforced concrete. Because it is new model, it has to be licensed. Life time estimation is needed for licensing. Deterioration of reinforced concrete structure is currently of great concern for life time estimation. The most significant form of deterioration is reinforcement corrosion that gives rise to crack the concrete structure. In this study, in order to estimate the life time of MACSTOR, the tendency of crack creation, propagation and the effect of crack in concrete structure against radiation shielding are investigated. Crack creation and propagation depends on concrete cover thickness and c/d ratio. The surface dose rate at the concrete shield in MACSTOR is simulated by MCNP code about several cases. Generally in the case of point source, surface dose rate depends on shape, width and length of crack. In the case of MACSTOR-400, It is estimated that crack is not dominant factor in the point of radiation shielding in less than 0.4mm of crack width. Above results will be helpful to estimate the life time of concrete structure as radiation shield.

  13. Robust Force Control of a 6-Link Electro-Hydraulic Manipulator

    Science.gov (United States)

    Ahn, Kyoungkwan; Yokota, Shinichi

    Uninterrupted power supply has become indispensable during the maintenance task of active electric power lines as a result of today's highly information-oriented society and increasing demand of electric utilities. This maintenance task has the risk of electric shock and the danger of falling from high place. Therefore it is necessary to realize an autonomous robot system using electro-hydraulic manipulator because hydraulic manipulators have the advantage of electric insulation and power/mass density. Meanwhile an electro-hydraulic manipulator using hydraulic actuators has many nonlinear elements, and its parameter fluctuations are greater than those of an electrically driven manipulator. So it is relatively difficult to realize not only stable contact work but also accurate force control for the autonomous assembly tasks using hydraulic manipulators. In this paper, the robust force control of a 6-link electro-hydraulic manipulator system used in the real maintenance task of active electic line is examined in detail. A nominal model for the system is obtained from experimental frequency responses of the system, and the deviation of the manipulator system from the nominal model is derived by a multiplicative uncertainty. Robust disturbance observers for force control are designed using this information in an H∞ framework, and implemented on the two different setups. Experimental results show that highly robust force tracking by a 6-link electro-hydraulic manipulator could be achieved even if the stiffness of environment and the shape of wall change.

  14. Fundamental characteristics of oil hydraulic servo system; Yuatsu servo kei no kihonteki tokusei

    Energy Technology Data Exchange (ETDEWEB)

    Suzuki, K. [Musashi Instsitute of Technology, Tokyo (Japan)

    1999-05-15

    Since a hydraulic servo generates a great force very quickly upon receiving a small force or electric power, it is widely used in machine tools, construction machinery, and vehicles. The basics are that a high pressure fluid generated by a hydraulic pump is controlled by a valve and forwarded to a hydraulic cylinder or rotary hydraulic motor for the generation of a parallel motion or rotation. For the control of the valve, there are the mechanical-hydraulic servo mechanism in which the valve is operated by mechanical linkage and the electrical-hydraulic servo system in which the valve is driven by electric signals. It is difficult to perform sophisticated control such as optimum control by use of the mechanical method while the electrical method may be applied to such sophisticated control. In the former, a hydraulic servo system is constructed using mechanical feedback. It is simpler and more reliable than the other, and is used for the control of aircraft wings and for the steering of ships and vehicles. Using the latter, electric signals low in power are amplified in a servo amplifier before being sent to the servo valve. For the driving of the spool in a servo valve, the nozzle and flapper system is widely in use. (NEDO)

  15. 任务驱动教学模式在高职理论教学中的实践研究--以水利工程类专业“水利工程CAD与识读”课程为例%Study on the Practice of Task-driven Teaching Mode In Higher Vocational Teaching of Theory---Taking Water Conservancy Class Professional"Hydraulic CAD and Literacy"Courses as an example

    Institute of Scientific and Technical Information of China (English)

    黄梦琪

    2014-01-01

    水利工程类专业“水利工程CAD与识读”课程课堂理论教学中采用任务驱动教学模式,强调学生在完成任务或解决问题的过程中,通过自主协作、讨论、会话等方式,在轻松愉快的氛围中开展并完成学习活动,不仅能培养学生主观能动性、创新精神,完成课堂角色转换,对提高教师教学水平也很有帮助。%In the teaching of classroom theory, Water Conservancy Class Professional "Hydraulic CAD and Literacy" Courses adopt the task-driven teaching mode and emphasize the importance of the ways of autonomous collaboration, discussion and conversation, etc,to develop and finish the study activities in the telexing and pleasant atmosphere during the process of finishing the tasks or solving problems. In this way, it can not only develop students' subjective initiative and cultivation, and complete the role reversal in the classroom, but also be helpful to improve teachers' teaching levels.

  16. Alternating grain orientation and weld solidification cracking

    Science.gov (United States)

    Kou, S.; Le, Y.

    1985-10-01

    A new mechanism for reducing weld solidification cracking was proposed, based on the concept of the crack path and resistance to crack propagation, and its effectiveness was verified in magnetically oscillated GTA welds of a rather crack susceptible material 2014 aluminum alloy. This mechanism, i.e., alternating grain orientation, was most pronounced in welds made with transverse arc oscillation of low frequency and high amplitude, and solidification cracking was dramatically reduced in these welds. The effect of the arc oscillation pattern, amplitude, and frequency on the formation of alternating columnar grains and the reduction of solidification cracking in GTA welds of 2014 aluminum alloy was examined and explained. The present study demonstrated for the first time that columnar grains can, in fact, be very effective in reducing solidification cracking, provided that they are oriented favorably.

  17. A New Type of Hydraulic Actuator Using Electrorheological Fluids

    Science.gov (United States)

    Wendt, Eckhard; Büsing, Klaus W.

    Electrorheological Fluids (ERF) are usually used in semi active damping elements, e.g. shock absorbers or engine mounts because of their continuously controllable shear stress. A totally new field of application may be achieved, if an ERF is used as a hydraulic fluid and not only as a control medium. In this case a fundamental need is the capability to produce a volume flow by using normal hydraulic pumps, e.g. gear pumps. The ERF and the hydraulic components both must have a long lifetime without unusual wear. Bayer AG has developed an ERF based on soft crosslinked PU-particles dispersed in silicone oil. These ERF are characterised by a low basic viscosity, a high ER-effect and a moderate conductivity. Compared with previous ERF where hard inorganic particles were used, the new fluid is not abrasive. It is foremostly this characteristic which gives the possibility of using the ERF in hydraulic systems with high shear rates and high shear stresses. The usage of ERF as hydraulic fluid allows the construction of proportional valves without mechanically driven parts. The control of the pressure drop over the valves is realised directly by an electrical signal. It is possible to realise actuators with very fast response times since the reaction time of ERF is within milliseconds. For demonstration purpose Bayer AG has built an actuator which is controlled by an electrorheological valve-block. The calculation of the dimension of this actuator and the valves will be shown and the realised response time will be demonstrated.

  18. CRITICALITY CURVES FOR PLUTONIUM HYDRAULIC FLUID MIXTURES

    Energy Technology Data Exchange (ETDEWEB)

    WITTEKIND WD

    2007-10-03

    This Calculation Note performs and documents MCNP criticality calculations for plutonium (100% {sup 239}Pu) hydraulic fluid mixtures. Spherical geometry was used for these generalized criticality safety calculations and three geometries of neutron reflection are: {sm_bullet}bare, {sm_bullet}1 inch of hydraulic fluid, or {sm_bullet}12 inches of hydraulic fluid. This document shows the critical volume and critical mass for various concentrations of plutonium in hydraulic fluid. Between 1 and 2 gallons of hydraulic fluid were discovered in the bottom of HA-23S. This HA-23S hydraulic fluid was reported by engineering to be Fyrquel 220. The hydraulic fluid in GLovebox HA-23S is Fyrquel 220 which contains phosphorus. Critical spherical geometry in air is calculated with 0 in., 1 in., or 12 inches hydraulic fluid reflection.

  19. DCS Hydraulics Submittal, Butler County, Alabama, USA

    Data.gov (United States)

    Federal Emergency Management Agency, Department of Homeland Security — Hydraulics data includes spatial datasets and data tables necessary for documenting the hydraulic procedures for computing flood elevations for a flood insurance...

  20. DCS Hydraulics Submittal, Bullock County, Alabama, USA

    Data.gov (United States)

    Federal Emergency Management Agency, Department of Homeland Security — Hydraulics data includes spatial datasets and data tables necessary for documenting the hydraulic procedures for computing flood elevations for a flood insurance...

  1. DCS Hydraulics Submittal, Covington County, Alabama, USA

    Data.gov (United States)

    Federal Emergency Management Agency, Department of Homeland Security — Hydraulics data includes spatial datasets and data tables necessary for documenting the hydraulic procedures for computing flood elevations for a flood insurance...

  2. High Pressure Hydraulic Distribution System

    Science.gov (United States)

    1991-05-20

    to 500 0 F. 5 cycles. 5000 F room temperature to 50001F; 45 ______________ Icycles The tesis planned for the distribution system demonstrator were...American Society for Testing and Materials ASTM D412 - Tension Testing of Vulcanized Rubber ASTM D571 - Testing Automotive Hydraulic Brake Hose Society of

  3. Hydraulic fracturing system and method

    Energy Technology Data Exchange (ETDEWEB)

    Ciezobka, Jordan; Salehi, Iraj

    2017-02-28

    A hydraulic fracturing system and method for enhancing effective permeability of earth formations to increase hydrocarbon production, enhance operation efficiency by reducing fluid entry friction due to tortuosity and perforation, and to open perforations that are either unopened or not effective using traditional techniques, by varying a pump rate and/or a flow rate to a wellbore.

  4. Hydraulic jumps in a channel

    DEFF Research Database (Denmark)

    Bonn, D.; Andersen, Anders Peter; Bohr, Tomas

    2009-01-01

    We present a study of hydraulic jumps with flow predominantly in one direction, created either by confining the flow to a narrow channel with parallel walls or by providing an inflow in the form of a narrow sheet. In the channel flow, we find a linear height profile upstream of the jump as expected...

  5. Hydraulic Fracture Containment in Sand

    NARCIS (Netherlands)

    Dong, Y.

    2010-01-01

    The mechanism of hydraulic fracturing in soft, high permeability material is considered fundamentally different from that in hard, low permeability rock, where a tensile fracture is created and conventional linear elastic fracture mechanics (LEFM) applies. The fracturing and associated modeling work

  6. Design of hydraulic recuperation unit

    Directory of Open Access Journals (Sweden)

    Jandourek Pavel

    2016-01-01

    Full Text Available This article deals with design and measurement of hydraulic recuperation unit. Recuperation unit consist of radial turbine and axial pump, which are coupled on the same shaft. Speed of shaft with impellers are 6000 1/min. For economic reasons, is design of recuperation unit performed using commercially manufactured propellers.

  7. Tree Hydraulics: How Sap Rises

    Science.gov (United States)

    Denny, Mark

    2012-01-01

    Trees transport water from roots to crown--a height that can exceed 100 m. The physics of tree hydraulics can be conveyed with simple fluid dynamics based upon the Hagen-Poiseuille equation and Murray's law. Here the conduit structure is modelled as conical pipes and as branching pipes. The force required to lift sap is generated mostly by…

  8. Tree Hydraulics: How Sap Rises

    Science.gov (United States)

    Denny, Mark

    2012-01-01

    Trees transport water from roots to crown--a height that can exceed 100 m. The physics of tree hydraulics can be conveyed with simple fluid dynamics based upon the Hagen-Poiseuille equation and Murray's law. Here the conduit structure is modelled as conical pipes and as branching pipes. The force required to lift sap is generated mostly by…

  9. Hydraulic conductivity study of compacted clay soils used as landfill liners for an acidic waste.

    Science.gov (United States)

    Hamdi, Noureddine; Srasra, Ezzeddine

    2013-01-01

    Three natural clayey soils from Tunisia were studied to assess their suitability for use as a liner for an acid waste disposal site. An investigation of the effect of the mineral composition and mechanical compaction on the hydraulic conductivity and fluoride and phosphate removal of three different soils is presented. The hydraulic conductivity of these three natural soils are 8.5 × 10(-10), 2.08 × 10(-9) and 6.8 × 10(-10)m/s for soil-1, soil-2 and soil-3, respectively. Soil specimens were compacted under various compaction strains in order to obtain three wet densities (1850, 1950 and 2050 kg/m(3)). In this condition, the hydraulic conductivity (k) was reduced with increasing density of sample for all soils. The test results of hydraulic conductivity at long-term (>200 days) using acidic waste solution (pH=2.7, charged with fluoride and phosphate ions) shows a decrease in k with time only for natural soil-1 and soil-2. However, the specimens of soil-2 compressed to the two highest densities (1950 and 2050 kg/m(3)) are cracked after 60 and 20 days, respectively, of hydraulic conductivity testing. This damage is the result of a continued increase in the internal stress due to the swelling and to the effect of aggressive wastewater. The analysis of anions shows that the retention of fluoride is higher compared to phosphate and soil-1 has the highest sorption capacity.

  10. Biaxial Fatigue Cracking from Notch

    Science.gov (United States)

    2013-03-04

    Leevers (reference 11) noticed that the variation in  from 0 to 2 has little effect on the da/dN in PVC ( polyvinyl - chloride ), but reduces the da/dN...under biaxial rotating and bending. Ahmad (reference 2) formulated a model for the biaxial fatigue crack growth in aggressive environment, outlined by...1962, Vol. 90, pp. 238-239. 20. ASM Handbook , Vol. 12 Fractography: 1992, p. 430, 438. 21. Metals Handbook , Vol. 9 Fractography and Atlas of

  11. A new linear type hydraulic motor

    Science.gov (United States)

    Jiang, Dong; Zhang, Tong; Li, Wenhua; Chen, Xinyang

    2017-08-01

    This paper proposes the design of liner type hydraulic motor on the base of inner curved radial piston hydraulic motor. The hydraulic cylinders of the new type motor are in the straight line which will improve the utilization of the axial space and different out power can be supplied by changes the number of cylinders. In this paper, the structure and working principle of the liner type hydraulic motor is introduced.

  12. The Growth of Small Corrosion Fatigue Cracks in Alloy 7075

    Science.gov (United States)

    Piascik, Robert S.

    2015-01-01

    The corrosion fatigue crack growth characteristics of small (greater than 35 micrometers) surface and corner cracks in aluminum alloy 7075 is established. The early stage of crack growth is studied by performing in situ long focal length microscope (500×) crack length measurements in laboratory air and 1% sodium chloride (NaCl) environments. To quantify the "small crack effect" in the corrosive environment, the corrosion fatigue crack propagation behavior of small cracks is compared to long through-the-thickness cracks grown under identical experimental conditions. In salt water, long crack constant K(sub max) growth rates are similar to small crack da/dN.

  13. Fatigue cracks in Eurofer 97 steel: Part II. Comparison of small and long fatigue crack growth

    Science.gov (United States)

    Kruml, T.; Hutař, P.; Náhlík, L.; Seitl, S.; Polák, J.

    2011-05-01

    The fatigue crack growth rate in the Eurofer 97 steel at room temperature was measured by two different methodologies. Small crack growth data were obtained using cylindrical specimens with a shallow notch and no artificial crack starters. The growth of semicircular cracks of length between 10-2000 μm was followed in symmetrical cycling with constant strain amplitude ( R ɛ = -1). Long crack data were measured using standard CT specimen and ASTM methodology, i.e. R = 0.1. The growth of cracks having the length in the range of 10-30 mm was measured. It is shown that the crack growth rates of both types of cracks are in a very good agreement if J-integral representation is used and usual assumptions of the crack closure effects are taken into account.

  14. Fatigue cracks in Eurofer 97 steel: Part II. Comparison of small and long fatigue crack growth

    Energy Technology Data Exchange (ETDEWEB)

    Kruml, T., E-mail: kruml@ipm.cz [Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Zizkova 22, CZ 61662 Brno (Czech Republic); Hutar, P.; Nahlik, L.; Seitl, S.; Polak, J. [Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Zizkova 22, CZ 61662 Brno (Czech Republic)

    2011-05-01

    The fatigue crack growth rate in the Eurofer 97 steel at room temperature was measured by two different methodologies. Small crack growth data were obtained using cylindrical specimens with a shallow notch and no artificial crack starters. The growth of semicircular cracks of length between 10-2000 {mu}m was followed in symmetrical cycling with constant strain amplitude (R{sub {epsilon}} = -1). Long crack data were measured using standard CT specimen and ASTM methodology, i.e. R = 0.1. The growth of cracks having the length in the range of 10-30 mm was measured. It is shown that the crack growth rates of both types of cracks are in a very good agreement if J-integral representation is used and usual assumptions of the crack closure effects are taken into account.

  15. Hydraulic characterization of " Furcraea andina

    Science.gov (United States)

    Rivera-Velasquez, M. F.; Fallico, C.; Molinari, A.; Santillan, P.; Salazar, M.

    2012-04-01

    The present level of pollution, increasingly involving groundwaters, constitutes a serious risk for environment and human health. Therefore the remediation of saturated and unsaturated soils, removing pollutant materials through innovative and economic bio-remediation techniques is more frequently required. Recent studies on natural fiber development have shown the effectiveness of these fibers for removal of some heavy metals, due to the lignin content in the natural fibers which plays an important role in the adsorption of metal cations (Lee et al., 2004; Troisi et al., 2008; C. Fallico, 2010). In the context of remediation techniques for unsaturated and/or saturated zone, an experimental approach for the hydraulic characterization of the "Furcraea andina" (i.e., Cabuya Blanca) fiber was carried out. This fiber is native to Andean regions and grows easily in wild or cultivated form in the valleys and hillsides of Colombia, Ecuador, and Peru. Fibers of "Furcraea andina" were characterized by experimental tests to determine their hydraulic conductivity or permeability and porosity in order to use this medium for bioremediation of contaminated aquifer exploiting the physical, chemical and microbial capacity of natural fiber in heavy metal adsorption. To evaluate empirically the hydraulic conductivity, laboratory tests were carried out at constant head specifically on the fibers manually extracted. For these tests we used a flow cell (used as permeameter), containing the "Furcraea andina" fibers to be characterized, suitably connected by a tygon pipe to a Marriott's bottle, which had a plastic tube that allow the adjustment of the hydraulic head for different tests to a constant value. By this experiment it was also possible to identify relationships that enable the estimation of permeability as a function of density, i.e. of the compaction degree of the fibers. Our study was carried out for three values of hydraulic head (H), namely 10, 18, and 25 cm and for each

  16. 14 CFR 25.1435 - Hydraulic systems.

    Science.gov (United States)

    2010-01-01

    ... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Hydraulic systems. 25.1435 Section 25.1435... STANDARDS: TRANSPORT CATEGORY AIRPLANES Equipment Miscellaneous Equipment § 25.1435 Hydraulic systems. (a) Element design. Each element of the hydraulic system must be designed to: (1) Withstand the proof...

  17. 14 CFR 27.1435 - Hydraulic systems.

    Science.gov (United States)

    2010-01-01

    ... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Hydraulic systems. 27.1435 Section 27.1435... STANDARDS: NORMAL CATEGORY ROTORCRAFT Equipment Safety Equipment § 27.1435 Hydraulic systems. (a) Design. Each hydraulic system and its elements must withstand, without yielding, any structural loads...

  18. Linear hydraulic drive system for a Stirling engine

    Science.gov (United States)

    Walsh, Michael M.

    1984-02-21

    A hydraulic drive system operating from the periodic pressure wave produced by a Stirling engine along a first axis thereof and effecting transfer of power from the Stirling engine to a load apparatus therefor and wherein the movable, or working member of the load apparatus is reciprocatingly driven along an axis substantially at right angles to the first axis to achieve an arrangement of a Stirling engine and load apparatus assembly which is much shorter and the components of the load apparatus more readily accessible.

  19. Subsidence crack closure: rate, magnitude and sequence

    Energy Technology Data Exchange (ETDEWEB)

    De Graff, J.V.; Romesburg, H.C.

    1981-06-01

    Tension cracks are a major surface disturbance resulting from subsidence and differential settlement above underground coal mines. Recent engineering studies of subsidence indicate that cracks may close where tensile stresses causing the cracks are reduced or relaxed. This stress reduction occurs as mining in the area is completed. Crack closure was confirmed by a study in the Wasatch Plateau coal field of central Utah. Cracks occurred in both exposed bedrock and regolith in an area with maximum subsidence of 3 m. Mean closure rate was 0.3 cm per week with individual crack closure rates between 0.2 cm and 1.0 cm per week. The mean crack closure magnitude was 80% with closure magnitudes varying between 31% and 100%. Actual magnitude values ranged from 0.6 cm to 6.5 cm with a mean value of 3.8 cm. Statistical analysis compared width change status among cracks over time. It was found that: 1) a 41% probability existed that a crack would exhibit decreasing width per weekly measurement, 2) closure state sequences seem random over time, and 3) real differences in closure state sequence existed among different cracks. (6 refs.) (In English)

  20. Crack propagation in fracture mechanical graded structures

    Directory of Open Access Journals (Sweden)

    B. Schramm

    2015-10-01

    Full Text Available The focus of manufacturing is more and more on innovative and application-oriented products considering lightweight construction. Hence, especially functional graded materials come to the fore. Due to the application-matched functional material gradation different local demands such as absorbability, abrasion and fatigue of structures are met. However, the material gradation can also have a remarkable influence on the crack propagation behavior. Therefore, this paper examines how the crack propagation behavior changes when a crack grows through regions which are characterized by different fracture mechanical material properties (e.g. different threshold values KI,th, different fracture toughness KIC. In particular, the emphasis of this paper is on the beginning of stable crack propagation, the crack velocity, the crack propagation direction as well as on the occurrence of unstable crack growth under static as well as cyclic loading. In this context, the developed TSSR-concept is presented which allows the prediction of crack propagation in fracture mechanical graded structures considering the loading situation (Mode I, Mode II and plane Mixed Mode and the material gradation. In addition, results of experimental investigations for a mode I loading situation and numerical simulations of crack growth in such graded structures confirm the theoretical findings and clarify the influence of the material gradation on the crack propagation behavior.

  1. Understanding hydraulic fracturing: a multi-scale problem.

    Science.gov (United States)

    Hyman, J D; Jiménez-Martínez, J; Viswanathan, H S; Carey, J W; Porter, M L; Rougier, E; Karra, S; Kang, Q; Frash, L; Chen, L; Lei, Z; O'Malley, D; Makedonska, N

    2016-10-13

    Despite the impact that hydraulic fracturing has had on the energy sector, the physical mechanisms that control its efficiency and environmental impacts remain poorly understood in part because the length scales involved range from nanometres to kilometres. We characterize flow and transport in shale formations across and between these scales using integrated computational, theoretical and experimental efforts/methods. At the field scale, we use discrete fracture network modelling to simulate production of a hydraulically fractured well from a fracture network that is based on the site characterization of a shale gas reservoir. At the core scale, we use triaxial fracture experiments and a finite-discrete element model to study dynamic fracture/crack propagation in low permeability shale. We use lattice Boltzmann pore-scale simulations and microfluidic experiments in both synthetic and shale rock micromodels to study pore-scale flow and transport phenomena, including multi-phase flow and fluids mixing. A mechanistic description and integration of these multiple scales is required for accurate predictions of production and the eventual optimization of hydrocarbon extraction from unconventional reservoirs. Finally, we discuss the potential of CO2 as an alternative working fluid, both in fracturing and re-stimulating activities, beyond its environmental advantages.This article is part of the themed issue 'Energy and the subsurface'.

  2. Determining the spatial altitude of the hydraulic fractures.

    Science.gov (United States)

    Khamiev, Marsel; Kosarev, Victor; Goncharova, Galina

    2016-04-01

    Mathematical modeling and numerical simulation are the most widely used approaches for the solving geological problems. They imply software tools which are based on Monte Carlo method. The results of this project presents shows the possibility of using PNL tool to determine fracturing location. The modeled media is a homogeneous rock (limestone) cut by a vertical borehole (d=216 mm) with metal casing 9 mm thick. The cement sheath is 35 mm thick. The borehole is filled with fresh water. The rock mass is cut by crack, filled with a mixture of doped (gadolinium oxide Gd2O3) proppant (75%) and water (25%). A pulse neutron logging (PNL) tool is used for quality control in hydraulic fracturing operations. It includes a fast neutron source (so-called "neutron generator") and a set of thermal (or epithermal) neutron-sensing devices, forming the so-called near (ND) and far (FD) detectors. To evaluate neutron properties various segments (sectors) of the rock mass, the detector must register only neutrons that come from this very formation. It's possible if detecting block includes some (6 for example) thermal neutron detectors arranged circumferentially inside the tool. As a result we get few independent well logs, each accords with define rock sector. Afterwards synthetic logs processing we can determine spatial position of the hydraulic fracture.

  3. Thermal Hydraulic Performance of Tight Lattice Bundle

    Science.gov (United States)

    Yamamoto, Yasushi; Akiba, Miyuki; Morooka, Shinichi; Shirakawa, Kenetsu; Abe, Nobuaki

    Recently, the reduced moderation spectrum BWR has been studied. The fast neutron spectrum is obtained through triangular tight lattice fuel. However, there are few thermal hydraulic test data and thermal hydraulic correlation applicable to critical power prediction in such a tight lattice bundle. This study aims to enhance the database of the thermal hydraulic performance of the tight lattice bundle whose rod gap is about 1mm. Therefore, thermal hydraulic performance measurement tests of tight lattice bundles for the critical power, the pressure drop and the counter current flow limiting were performed. Moreover, the correlations to evaluate the thermal-hydraulic performance of the tight lattice bundle were developed.

  4. Design of hydraulic output Stirling engine

    Science.gov (United States)

    Toscano, W. M.; Harvey, A. C.; Lee, K.

    1983-01-01

    A hydraulic output system for the RE-1000 free piston stirling engine (FPSE) was designed. The hydraulic output system can be readily integrated with the existing hot section of RE-1000 FPSE. The system has two simply supported diaphragms which separate the engine gas from the hydraulic fluid, a dynamic balance mechanism, and a novel, null center band hydraulic pump. The diaphragms are designed to endure more than 10 billion cycles, and to withstand the differential pressure load as high as 14 MPa. The projected thermodynamic performance of the hydraulic output version of RE-1000 FPSE is 1.87 kW at 29/7 percent brake efficiency.

  5. Controlling fatigue crack paths for crack surface marking and growth investigations

    Directory of Open Access Journals (Sweden)

    S. Barter

    2016-01-01

    Full Text Available While it is well known that fatigue crack growth in metals that display confined slip, such as high strength aluminium alloys, develop crack paths that are responsive to the loading direction and the local microstructural orientation, it is less well known that such paths are also responsive to the loading history. In these materials, certain loading sequences can produce highly directional slip bands ahead of the crack tip and by adjusting the sequence of loads, distinct fracture surface features or progression marks, even at very small crack depths can result. Investigating the path a crack selects in fatigue testing when particular combinations of constant and variable amplitude load sequences are applied is providing insight into crack growth. Further, it is possible to design load sequences that allow very small amounts of crack growth to be measured, at very small crack sizes, well below the conventional crack growth threshold in the aluminium alloy discussed here. This paper reports on observations of the crack path phenomenon and a novel test loading method for measuring crack growth rates for very small crack depths in aluminium alloy 7050-T7451 (an important aircraft primary structural material. The aim of this work was to firstly generate short- crack constant amplitude growth data and secondly, through the careful manipulation of the applied loading, to achieve a greater understanding of the mechanisms of fatigue crack growth in the material being investigated. A particular focus of this work is the identification of the possible sources of crack growth retardation and closure in these small cracks. Interpreting these results suggests a possible mechanism for why small fatigue crack growth through this material under variable amplitude loading is faster than predicted from models based on constant amplitude data alone.

  6. Online Bridge Crack Monitoring with Smart Film

    Directory of Open Access Journals (Sweden)

    Benniu Zhang

    2013-01-01

    Full Text Available Smart film crack monitoring method, which can be used for detecting initiation, length, width, shape, location, and propagation of cracks on real bridges, is proposed. Firstly, the fabrication of the smart film is developed. Then the feasibility of the method is analyzed and verified by the mechanical sensing character of the smart film under the two conditions of normal strain and crack initiation. Meanwhile, the coupling interference between parallel enameled wires of the smart film is discussed, and then low-frequency detecting signal and the custom communication protocol are used to decrease interference. On this basis, crack monitoring system with smart film is designed, where the collected crack data is sent to the remote monitoring center and the cracks are simulated and recurred. Finally, the monitoring system is applied to six bridges, and the effects are discussed.

  7. Crack Propagation in Bamboo's Hierarchical Cellular Structure

    Science.gov (United States)

    Habibi, Meisam K.; Lu, Yang

    2014-07-01

    Bamboo, as a natural hierarchical cellular material, exhibits remarkable mechanical properties including excellent flexibility and fracture toughness. As far as bamboo as a functionally graded bio-composite is concerned, the interactions of different constituents (bamboo fibers; parenchyma cells; and vessels.) alongside their corresponding interfacial areas with a developed crack should be of high significance. Here, by using multi-scale mechanical characterizations coupled with advanced environmental electron microscopy (ESEM), we unambiguously show that fibers' interfacial areas along with parenchyma cells' boundaries were preferred routes for crack growth in both radial and longitudinal directions. Irrespective of the honeycomb structure of fibers along with cellular configuration of parenchyma ground, the hollow vessels within bamboo culm affected the crack propagation too, by crack deflection or crack-tip energy dissipation. It is expected that the tortuous crack propagation mode exhibited in the present study could be applicable to other cellular natural materials as well.

  8. Air flow through smooth and rough cracks

    Energy Technology Data Exchange (ETDEWEB)

    Kula, H.-G.; Sharples, S. [Sheffield Univ. (United Kingdom). Dept. of Building Science

    1994-12-31

    A series of laboratory experiments are described which investigated the effect of surface roughness on the air flow characteristics of simple, straight-through, no-bend cracks with smooth and rough internal surfaces. The crack thicknesses used in the study were 1.0, 1.5 and 2.0mm. The crack lengths, in the direction of flow, were 50.8mm and 76.2mm. For the rough cracks the roughness was simulated with two different grades of commercially available energy-cloth (grade 60 and 100). The experimental results were satisfactorily fitted to a quadratic relationship between {Delta}p and Q of the form {Delta}p = AQ + BQ{sup 2} for both the smooth and rough crack data. The effect of roughness on the reduction of air flowing through a crack is also discussed. (author)

  9. Crack problem in a long cylindrical superconductor

    Science.gov (United States)

    Yong, Hua-Dong; Zhou, You-He; Zeng, Jun

    2008-12-01

    In this work, the general problem of a center crack in a long cylindrical superconductor is studied. The dependence of the stress intensity factor on the parameters, including the crack length and the applied field, is investigated. We presented a simple model in which the effect of the crack on the critical current is taken into account. It is assumed that the crack forms a perfect barrier to the flow of current. The Bean model and the Kim model are considered for the critical state. Based on the complex potential and boundary collocation methods, the stress intensity factor under the magnetic field is obtained for a long cylindrical superconductor containing a central crack. The results show that the crack length and the applied field have significant effects on the fracture behavior of the superconductor.

  10. Numerical Study of Corrosion Crack Opening

    DEFF Research Database (Denmark)

    Thoft-Christensen, Palle; Frandsen, Henrik Lund; Svensson, Staffan

    2008-01-01

    for the corrosion crack opening. Experiments and theoretical analysis by a numerical method, FEM, support that the relation between the reduction of the reinforcement bar diameter due to corrosion and the corresponding increase in crack width for a given time interval, measured on the surface of a concrete specimen...... is proportional. More recently, the constant of proportionality, the so-called crack-corrosion index, has been studied further with respect to its dependence on the diameter of the reinforcement and the concrete cover. In the present paper the above-mentioned work is presented and extended with more realistic 3D......-models of the cracked concrete beam. The crack-corrosion index is evaluated for a variation of different parameters, i.e. bar diameter, concrete cover, crack length and type of corrosion product. This paper is an extended version of a paper by Thoft-Christensen et al. (2005) presented at the IFIP WG 7.5 Conference...

  11. DBEM crack propagation for nonlinear fracture problems

    Directory of Open Access Journals (Sweden)

    R. Citarella

    2015-10-01

    Full Text Available A three-dimensional crack propagation simulation is performed by the Dual Boundary Element Method (DBEM. The Stress Intensity Factors (SIFs along the front of a semi elliptical crack, initiated from the external surface of a hollow axle, are calculated for bending and press fit loading separately and for a combination of them. In correspondence of the latter loading condition, a crack propagation is also simulated, with the crack growth rates calculated using the NASGRO3 formula, calibrated for the material under analysis (steel ASTM A469. The J-integral and COD approaches are selected for SIFs calculation in DBEM environment, where the crack path is assessed by the minimum strain energy density criterion (MSED. In correspondence of the initial crack scenario, SIFs along the crack front are also calculated by the Finite Element (FE code ZENCRACK, using COD, in order to provide, by a cross comparison with DBEM, an assessment on the level of accuracy obtained. Due to the symmetry of the bending problem a pure mode I crack propagation is realised with no kinking of the propagating crack whereas for press fit loading the crack propagation becomes mixed mode. The crack growth analysis is nonlinear because of normal gap elements used to model the press fit condition with added friction, and is developed in an iterative-incremental procedure. From the analysis of the SIFs results related to the initial cracked configuration, it is possible to assess the impact of the press fit condition when superimposed to the bending load case.

  12. Transition from Multiple Macro-Cracking to Multiple Micro-Cracking in Cementitious Composites

    Institute of Scientific and Technical Information of China (English)

    ZHANG Jun; LENG Bing

    2008-01-01

    This paper presents an experimental study of the possibility of transition from multiple macro-cracking to multiple micro-cracking in cementitious composites.Conventional polyvinyl alcohol fiber reinforced cementitious composites normally exhibit macroscopic strain-hardening and multiple cracking after the first cracks appear.However,the individual crack width at the saturated stage is normally 60 to 80 μm.In the current study,the effect of fine aggregate size on the cracking performance,especially the individual crack width in the strain-hardening stage was studied by bending tests.The results show that the individual crack widths can be reduced from 60-80 μm to 10-30 μm by modifying the particle size of the fine aggregates used in the composites.

  13. Bio-based Hydraulic Fluids

    Science.gov (United States)

    2008-04-17

    currently formulated with vegetable oils (i.e., rapeseed , sun flower, corn, soybean, canola, coconut, etc.) and synthetic ester, such as polyol ester...2008 Vegetable Oil • Excellent lubrication • Nontoxic • Biodegradable • Derived from renewable resources such as rapeseed , sunflower, corn...Mineral Oil 100 SAE 15W-40 G Rapeseed 32 Commercial HF H Polyol ester 22 MIL-PRF-32073 Grade 2 I Canola - Cooking Oil *Hydraulic fluid 3717 April

  14. Fire Resistant Aircraft Hydraulic System.

    Science.gov (United States)

    1982-07-01

    and compounds based on new experimental elastomers as well as most commercially available elastomers were screened in seeking seals that were both...for hydraulic component testing. All of the available E6.5 stock was purchased for the screening tests. However, DuPont stated that other homologs of...with the lubricity and anti-wear additive olyvan A (molybdenum oxysulphide dithiocarbamate ) added in the quantity of less than one percent by weight

  15. Fatigue Crack Closure Analysis Using Digital Image Correlation

    Science.gov (United States)

    Leser, William P.; Newman, John A.; Johnston, William M.

    2010-01-01

    Fatigue crack closure during crack growth testing is analyzed in order to evaluate the critieria of ASTM Standard E647 for measurement of fatigue crack growth rates. Of specific concern is remote closure, which occurs away from the crack tip and is a product of the load history during crack-driving-force-reduction fatigue crack growth testing. Crack closure behavior is characterized using relative displacements determined from a series of high-magnification digital images acquired as the crack is loaded. Changes in the relative displacements of features on opposite sides of the crack are used to generate crack closure data as a function of crack wake position. For the results presented in this paper, remote closure did not affect fatigue crack growth rate measurements when ASTM Standard E647 was strictly followed and only became a problem when testing parameters (e.g., load shed rate, initial crack driving force, etc.) greatly exceeded the guidelines of the accepted standard.

  16. Crack

    Science.gov (United States)

    ... rate, breathing rate, blood pressure , and body temperature decreased appetite and less need for sleep feelings of restlessness, ... effects include: gangrene in the bowels resulting from decreased blood ... chest pain reduced appetite, plus health problems associated with not eating a ...

  17. SPIRALING CRACKS IN THIN SHEETS

    OpenAIRE

    2010-01-01

    En este trabajo de tesis presentamos dos experimentos en que trayectorias de fracturas sumamente reproducibles son obtenidas en láminas delgadas frágiles. En ambos casos, a partir de configuraciones iniciales sumamente simples y pequeñas, las trayectorias obtenidas son espirales logarítmicas de gran tamao. Nuestro primer experimento consiste en un crack que se inicia desde un corte recto hecho en una lámina delgada y que es forzado a propagarse por medio de empujar con un objeto sólido....

  18. Fatigue Crack Closure - A Review

    Science.gov (United States)

    1990-09-01

    gauge along the crack line. They used CCT speci- mens of high tensile strength steel ( HY80 ). The measured value of U was found to be a minimum at the...ultrasonic surface wave technique on 12.5mm thick specimens of 2024-T851, 2024-T351, Al 2219, Ti-6AI-4V and 17-4 PH steel . Most of the results were...medium and high strength steels . Exami- nation of the fracture surfaces suggested that raising the mean stress in low fracture toughness steels could

  19. Expansive Soil Crack Depth under Cumulative Damage

    Directory of Open Access Journals (Sweden)

    Bei-xiao Shi

    2014-01-01

    Full Text Available The crack developing depth is a key problem to slope stability of the expansive soil and its project governance and the crack appears under the roles of dry-wet cycle and gradually develops. It is believed from the analysis that, because of its own cohesion, the expansive soil will have a certain amount of deformation under pulling stress but without cracks. The soil body will crack only when the deformation exceeds the ultimate tensile strain that causes cracks. And it is also believed that, due to the combined effect of various environmental factors, particularly changes of the internal water content, the inherent basic physical properties of expansive soil are weakened, and irreversible cumulative damages are eventually formed, resulting in the development of expansive soil cracks in depth. Starting from the perspective of volumetric strain that is caused by water loss, considering the influences of water loss rate and dry-wet cycle on crack developing depth, the crack developing depth calculation model which considers the water loss rate and the cumulative damages is established. Both the proposal of water loss rate and the application of cumulative damage theory to the expansive soil crack development problems try to avoid difficulties in matrix suction measurement, which will surely play a good role in promoting and improving the research of unsaturated expansive soil.

  20. Nonlinear modal method of crack localization

    Science.gov (United States)

    Ostrovsky, Lev; Sutin, Alexander; Lebedev, Andrey

    2004-05-01

    A simple scheme for crack localization is discussed that is relevant to nonlinear modal tomography based on the cross-modulation of two signals at different frequencies. The scheme is illustrated by a theoretical model, in which a thin plate or bar with a single crack is excited by a strong low-frequency wave and a high-frequency probing wave (ultrasound). The crack is assumed to be small relative to all wavelengths. Nonlinear scattering from the crack is studied using a general matrix approach as well as simplified models allowing one to find the nonlinear part of crack volume variations under the given stress and then the combinational wave components in the tested material. The nonlinear response strongly depends on the crack position with respect to the peaks or nodes of the corresponding interacting signals which can be used for determination of the crack position. Juxtaposing various resonant modes interacting at the crack it is possible to retrieve both crack location and orientation. Some aspects of inverse problem solutions are also discussed, and preliminary experimental results are presented.

  1. Wettability Induced Crack Dynamics and Morphology

    CERN Document Server

    Ghosh, Udita Uday; Bhandari, Aditya Bikram; Chakraborty, Suman; DasGupta, Sunando

    2014-01-01

    Substrate wettability alteration induced control over crack formation process in thin colloidal films has been addressed in the present study. Colloidal nanosuspension (53nm, mean particle diameter) droplets have been subjected to natural drying to outline the effects of substrate surface energies over the dry-out characteristics with emphasis on crack dynamics, crack morphology and underlying particle arrangements. Experimental findings indicate that number of cracks formed decreases with increase in substrate hydrophobicity. These physical phenomena have been explained based on the magnitude of stress dissipation incurred by the substrate. DLVO predictions are also found to be in tune with the reported experimental investigations.

  2. Crack depth determination with inductive thermography

    Science.gov (United States)

    Oswald-Tranta, B.; Schmidt, R.

    2015-05-01

    Castings, forgings and other steel products are nowadays usually tested with magnetic particle inspection, in order to detect surface cracks. An alternative method is active thermography with inductive heating, which is quicker, it can be well automated and as in this paper presented, even the depth of a crack can be estimated. The induced eddy current, due to its very small penetration depth in ferro-magnetic materials, flows around a surface crack, heating this selectively. The surface temperature is recorded during and after the short inductive heating pulse with an infrared camera. Using Fourier transformation the whole IR image sequence is evaluated and the phase image is processed to detect surface cracks. The level and the local distribution of the phase around a crack correspond to its depth. Analytical calculations were used to model the signal distribution around cracks with different depth and a relationship has been derived between the depth of a crack and its phase value. Additionally, also the influence of the heating pulse duration has been investigated. Samples with artificial and with natural cracks have been tested. Results are presented comparing the calculated and measured phase values depending on the crack depth. Keywords: inductive heating, eddy current, infrared

  3. Fatigue crack growth detect, assess, avoid

    CERN Document Server

    Richard, Hans Albert

    2016-01-01

    This book offers a concise introduction to fatigue crack growth, based on practical examples. It discusses the essential concepts of fracture mechanics, fatigue crack growth under constant and variable amplitude loading and the determination of the fracture-mechanical material parameters. The book also introduces the analytical and numerical simulation of fatigue crack growth as well as crack initiation. It concludes with a detailed description of several practical case studies and some exercises. The target group includes graduate students, researchers at universities and practicing engineers.

  4. Investigations of Low Temperature Time Dependent Cracking

    Energy Technology Data Exchange (ETDEWEB)

    Van der Sluys, W A; Robitz, E S; Young, B A; Bloom, J

    2002-09-30

    The objective of this project was to investigate metallurgical and mechanical phenomena associated with time dependent cracking of cold bent carbon steel piping at temperatures between 327 C and 360 C. Boiler piping failures have demonstrated that understanding the fundamental metallurgical and mechanical parameters controlling these failures is insufficient to eliminate it from the field. The results of the project consisted of the development of a testing methodology to reproduce low temperature time dependent cracking in laboratory specimens. This methodology was used to evaluate the cracking resistance of candidate heats in order to identify the factors that enhance cracking sensitivity. The resultant data was integrated into current available life prediction tools.

  5. Cracking of open traffic rigid pavement

    Directory of Open Access Journals (Sweden)

    Niken Chatarina

    2017-01-01

    Full Text Available The research is done by observing the growth of real structure cracking in Natar, Lampung, Indonesia compared to C. Niken’s et al research and literature study. The rigid pavement was done with open traffic system. There are two main crack types on Natar rigid pavement: cracks cross the road, and cracks spreads on rigid pavement surface. The observation of cracks was analyzed by analyzing material, casting, curing, loading and shrinkage mechanism. The relationship between these analysis and shrinkage mechanism was studied in concrete micro structure. Open traffic make hydration process occur under vibration; therefore, fresh concrete was compressed and tensioned alternately since beginning. High temperature together with compression, cement dissociation, the growth of Ca2+ at very early age leads abnormal swelling. No prevention from outside water movement leads hydration process occur with limited water which caused spreads fine cracks. Limited water improves shrinkage and plastic phase becomes shorter; therefore, rigid pavement can’t accommodate the abnormal swelling and shrinking alternately and creates the spread of cracks. Discontinuing casting the concrete makes both mix under different condition, the first is shrink and the second is swell and creates weak line on the border; so, the cracks appear as cracks across the road.

  6. Crack spacing of unsaturated soils in the critical state

    Institute of Scientific and Technical Information of China (English)

    SUN JiChao; WANG GuangQian; SUN QiCheng

    2009-01-01

    The cracking mechanism of unsaturated soils due to evaporation is poorly understood, and the magnitude of crack spacing is usually hard to estimate. In this work, cracks were postulated to occur suc-cedently rather than simultaneously, that is, secondary cracks appear after primary cracks as evaporation continues. Formulae of the secondary crack spacing and secondary trend crack spacing were then derived after stress analysis. The calculated spacing values were consistent with the published experimental data. Meanwhile, the effect of the Poisson ratio on the crack spacing was analyzed, which showed that the magnitude of crack spacing was proportional to the Poisson ratio in the range of [0.30,0.35].

  7. On the application of cohesive crack modeling in cementitious materials

    DEFF Research Database (Denmark)

    Stang, Henrik; Olesen, John Forbes; Poulsen, Peter Noe;

    2007-01-01

    Cohesive crack models-in particular the Fictitious Crack Model - are applied routinely in the analysis of crack propagation in concrete and mortar. Bridged crack models-where cohesive stresses are assumed to exist together with a stress singularity at the crack tip-on the other hand, are used....... Further, a quantitative condition is established indicating when a bridged crack model can be approximated with a cohesive crack model with smooth crack closure in terms of the ratio between the energy dissipation associated with the crack tip and the process zone....

  8. Effect of Crack Closure on Ultrasonic Detection of Fatigue Cracks at Fastener Holes

    Science.gov (United States)

    Bowles, S. J.; Harding, C. A.; Hugo, G. R.

    2009-03-01

    The ultrasonic response from closed fatigue cracks grown in aluminium alloy specimens using a representative aircraft spectrum loading has been characterised as a function of tensile applied load using pulse-echo 45° shear-wave ultrasonic C-scans with focused immersion transducers. Observed trends with crack size and applied load are described and compared to results for artificial machined defects. The results demonstrate that crack closure significantly reduces the ultrasonic response compared to open cracks or machined defects.

  9. Mode Ⅰ Plane Crack Interacting with an Interfacial Crack Along a Circular Inhomogeneity

    Institute of Scientific and Technical Information of China (English)

    WANG Rui; MA Jian-jun; LIU Zheng-guang

    2006-01-01

    The elastic interaction of the mode Ⅰ plane crack with an interfacial crack along a circular inhomogeneity is dealt with. The dislocation density and the stress intensity factors (SIFs) of the mode I plane crack are obtained numerically. A new kind of dislocation equilibrium equation about the plane crack is applied. The influence of some material parameters on the dislocation density and SIFs are analyzed.

  10. Extended propagation model for interfacial crack in composite material structure

    Institute of Scientific and Technical Information of China (English)

    闫相桥; 冯希金

    2002-01-01

    An interfacial crack is a common damage in a composite material structure . An extended propaga-tion model has been established for an interfacial crack to study the dependence of crack growth on the relativesizes of energy release rates at left and right crack tips and the properties of interfacial material characterize thegrowth of interfacial crack better.

  11. Research and Application of Influences of Lateral Pressure Coefficients on the Extension Angle of Coal Cracks

    Directory of Open Access Journals (Sweden)

    Cheng Liu

    2016-01-01

    Full Text Available Fluid-solid coupling seepage fields are ubiquitous in engineering practices. However, few investigations have been carried out on the rules of crack extension of solids under the effect of fluids. By using the RFPA2D (realistic failure process analysis in 2 dimensions, this research studied the influences of different lateral pressure coefficients on the extension direction and length of coal cracks. Also the result can be proved by fracture mechanics, stress intensity factor theory, and sliding crack theory. On this basis, aiming at a coal mine with the mining depth being over 700 m, the reliability of the above conclusion was further proved by testing the crustal stress at the positions with the buried depth varying from 750 m to 1,300 m. At the same time, in condition of meeting the water pressure required by the crack extension, permeability-increasing radius is selected preferably through AE energy index by simulation of hydraulic fracturing for coal seams under different lateral pressure coefficients, and the gas drainage achieves good effect in engineering practice.

  12. Chloride Penetration through Cracks in High-Performance Concrete and Surface Treatment System for Crack Healing

    Directory of Open Access Journals (Sweden)

    In-Seok Yoon

    2012-01-01

    Full Text Available For enhancing the service life of concrete structures, it is very important to minimize crack at surface. Even if these cracks are very small, the problem is to which extend these cracks may jeopardize the durability of these decks. It was proposed that crack depth corresponding with critical crack width from the surface is a crucial factor in view of durability design of concrete structures. It was necessary to deal with chloride penetration through microcracks characterized with the mixing features of concrete. This study is devoted to examine the effect of high strength concrete and reinforcement of steel fiber on chloride penetration through cracks. High strength concrete is regarded as an excellent barrier to resist chloride penetration. However, durability performance of cracked high strength concrete was reduced seriously up to that of ordinary cracked concrete. Steel fiber reinforcement is effective to reduce chloride penetration through cracks because steel fiber reinforcement can lead to reduce crack depth significantly. Meanwhile, surface treatment systems are put on the surface of the concrete in order to seal the concrete. The key-issue is to which extend a sealing is able to ensure that chloride-induced corrosion can be prevented. As a result, penetrant cannot cure cracks, however, coating and combined treatment can prevent chloride from flowing in concrete with maximum crack width of 0.06 mm and 0.08 mm, respectively.

  13. On fatigue crack growth in ductile materials by crack-tip blunting

    DEFF Research Database (Denmark)

    Tvergaard, Viggo

    2004-01-01

    One of the basic mechanisms for fatigue crack growth in ductile metals is that depending on crack-tip blunting under tensile loads and re-sharpening of the crack-tip during unloading. In a standard numerical analysis accounting for finite strains it is not possible to follow this process during...

  14. A Creaking and Cracking Comet

    Science.gov (United States)

    Faurschou Hviid, Stubbe; Hüttig, Christian; Groussin, Olivier; Mottola, Stefano; Keller, Horst Uwe; OSIRIS Team

    2016-10-01

    Since the middle of 2014 the OSIRIS cameras on the ESA Rosetta mission have been monitoring the evolution of the comet 67P/Churyumov-Gerasimenko as it passed through perihelion. During the perihelion passage several change events have been observed on the nucleus surface. For example existing large scale cracks have expanded and new large scale cracks have been created. Also several large scale "wave pattern" like change events have been observed in the Imhotep and Hapi regions. These are events not directly correlated with any normal visible cometary activity. One interpretation is that these are events likely caused by "seismic" activity. The seismic activity is created by the self-gravity stress of the non-spherical comet nucleus and stress created by the non-gravitational forces acting on the comet. The non-gravitational forces are changing the rotation period of the comet (~20min/perihelion passage) which induces a changing mechanical stress pattern through the perihelion passage. Also the diurnal cycle with its changing activity pattern is causing a periodic wobble in the stress pattern that can act as a trigger for a comet quake. The stress pattern has been modeled using a finite element model that includes self-gravity, the comet spin and the non-gravitational forces based on a cometary activity model. This paper will discuss what can be learned about the comet nucleus structure and about the cometary material properties from these events and from the FEM model.

  15. What can cracked polymer do

    Science.gov (United States)

    Jiao, Kexin; Zhou, Chuanhong; Kohli, Punit; Poudel, Anish; Chu, Tsuchin

    2015-03-01

    Buckling, delamination, and cracking are very well known phenomenon observed in most thin films. They were theoretically explained by the existence of mechanical instability due to the residue stress generated when a thin film is deposited on substrates or undergoing environmental stimulus. Buckled structures at micro- or nano-scale have been of great interests and have been used extensively in many applications including particles self-assembling, surface wettability modification, and micro-electronic device fabrication. However, peeling of a layer from a substrate due to delamination or fractures on a thin film due to cracking is mostly taken as an undesirable result. Therefore, strategies are inspired for preventing or removing these often undesired structures. We found that after being heated above its decomposition temperature and then cooled to room temperature, a PDMS thin film showed micro-fibers of 100 μm width and up to 1.5 cm in length. By studying the formation mechanism, control of the dimensions and of the growth pattern on a substrate for PDMS micro-fibers were realized. Giving credit to their high flexibility and optical transparency, a PDMS micro-fiber were utilized in high resolution near field imaging achieved by attaching a micro-lens on the fiber. Interestingly, a surface covered by PDMS micro-fibers will turn from superhydrophobic into superhydrophilic by further heating providing potential applications in surface wettability modification. In future, we will investigate and simulate the growth of PDMS micro-fiber and look for more possible applications.

  16. Hydraulic jumps within pyroclastic density currents and their sedimentary record

    Science.gov (United States)

    Douillet, G.; Mueller, S.; Kueppers, U.; Dingwell, D. B.

    2013-12-01

    This contribution presents a complete and comprehensive formulation of the hydraulic jump phenomenon and reviews sedimentary structures that may be associated with them. Beginning from the general fluid phenomenon, we then focus on examples from pyroclastic density currents in order to infer dynamic parameters on the parent flows. A hydraulic jump is a fluid dynamics phenomenon that corresponds to the sudden increase of the thickness of a flow accompanied by a decrease of its velocity and/or density. A hydraulic jump is the expression of the transition of the flow from two different flow regimes: supercritical to subcritical. This entrains a change in the energy balance between kinetic energy and gravity potential energy. Recently, the terms of 'pneumatic jumps' have been used for similar phenomenon driven within a gas phase, and granular jumps for dense granular flows. It is thought that such strong changes in the flow conditions may leave characteristic structures in the sedimentary record. Indeed, the main variables influencing the sedimentation rate are the flow velocity, particle concentration and turbulence level, all of them strongly affected by a hydraulic jump. Structures deposited by hydraulic/pneumatic jumps have been called cyclic steps and chute and pool structures. Chute and pools represent the record of a single supercritical to subcritical transition, whereas cyclic steps are produced by stable trains of hydraulic jumps and subsequent re-accelerations. Pyroclastic density currents (PDCs) are gas and pyroclasts flows. As such, they can be subjected to granular and pneumatic jumps and their deposit have often been interpreted as containing records of jumps. Steep sided truncations covered by lensoidal layers have been interpreted as the record of internal jumps within density stratified flows. Fines-depleted breccias at breaks in slope are thought to result from the enhanced turbulence at a jump of the entire flow. Sudden increases in thickness of

  17. Development of crack shape: LBB methodology for cracked pipes

    Energy Technology Data Exchange (ETDEWEB)

    Moulin, D.; Chapuliot, S.; Drubay, B. [Commissariat a l Energie Atomique, Gif sur Yvette (France)

    1997-04-01

    For structures like vessels or pipes containing a fluid, the Leak-Before-Break (LBB) assessment requires to demonstrate that it is possible, during the lifetime of the component, to detect a rate of leakage due to a possible defect, the growth of which would result in a leak before-break of the component. This LBB assessment could be an important contribution to the overall structural integrity argument for many components. The aim of this paper is to review some practices used for LBB assessment and to describe how some new R & D results have been used to provide a simplified approach of fracture mechanics analysis and especially the evaluation of crack shape and size during the lifetime of the component.

  18. Variation of Eddy Current Density Distribution and its Effect on Crack Signal in Eddy Current Non-Destructive of Testing

    Directory of Open Access Journals (Sweden)

    Ladislav Janousek

    2006-01-01

    Full Text Available The paper deals with variation of eddy current density distribution along material depth and investigates an effect of the variation on a crack signal in eddy current non-destructive testing. Four coaxial rectangular tangential coils are used to induce eddy currents in a tested conductive object. The exciting coils are driven independently by phase-shifted AC currents; a ratio of amplitudes of the exciting currents is continuously changed to vary the distribution of eddy current density along material depth under a circular pick-up coil positioned in centre between the exciting coils. Dependences of a crack signal amplitude and its phase on the ratio are evaluated and special features are extracted. It is revealed that the dependences are strongly influenced by depth of a crack, and thus the extracted features can enhance evaluation of a detected crack.

  19. Characterization of crack growth under combined loading

    Science.gov (United States)

    Feldman, A.; Smith, F. W.; Holston, A., Jr.

    1977-01-01

    Room-temperature static and cyclic tests were made on 21 aluminum plates in the shape of a 91.4x91.4-cm Maltese cross with 45 deg flaws to develop crack growth and fracture toughness data under mixed-mode conditions. During cyclic testing, it was impossible to maintain a high proportion of shear-mode deformation on the crack tips. Cracks either branched or turned. Under static loading, cracks remained straight if shear stress intensity exceeded normal stress intensity. Mixed-mode crack growth rate data compared reasonably well with published single-mode data, and measured crack displacements agreed with the straight and branched crack analyses. Values of critical strain energy release rate at fracture for pure shear were approximately 50% higher than for pure normal opening, and there was a large reduction in normal stress intensity at fracture in the presence of high shear stress intensity. Net section stresses were well into the inelastic range when fracture occurred under high shear on the cracks.

  20. Locating a leaking crack by safe stimulation

    Energy Technology Data Exchange (ETDEWEB)

    Coleman, C.E.; Sagat, S. (Atomic Energy of Canada Ltd., Chalk River, ON (Canada). Chalk River Nuclear Labs.); Shek, G.K.; Graham, D.B.; Durand, M.A. (Ontario Hydro, Toronto, ON (Canada))

    1990-01-01

    A few Zr-2.5 Nb alloy pressure tubes in CANDU nuclear reactors have leaked through cracks that have grown by delayed hydride cracking (DHC). In some instances, tubes contained confirmed leaks that were leaking at a rate too low for precise identification of the leaking channel. Controlled stimulation of DHC can be used to help locate these leaks by extending the crack and increasing the leak rate without approaching crack instability. In the event of a leak being detected, a plant operator can gain time for leak location by a heating and unloading manoeuvre that will arrest crack growth and increase the critical crack length. This manoeuvre increases the safety margin against tube rupture. If required, the operator can then stimulate cracking in a controlled manner to aid in leak identification. Sequences of temperature and load manoeuvres for safe crack stimulation have been found by laboratory tests on dry specimens and the efficacy of the process has been demonstrated, partly in a power reactor, and partly in a full-scale simulation of a leaking pressure tube. (author).

  1. Entering a Crack: An Encounter with Gossip

    Science.gov (United States)

    Henderson, Linda

    2014-01-01

    In this paper, I enter a crack to think otherwise about the concept "gossip". Drawing on previous scholarship engaging with Deleuzian concepts to inform research methodologies, this paper builds on this body of work. Following Deleuze and Guattari, the paper undertakes a mapping of gossip, subsequent to an encounter with a crack.…

  2. Crack propagation directions in unfilled resins.

    Science.gov (United States)

    Baran, G; Sadeghipour, K; Jayaraman, S; Silage, D; Paul, D; Boberick, K

    1998-11-01

    Posterior composite restorative materials undergo accelerated wear in the occlusal contact area, primarily through a fatigue mechanism. To facilitate the timely development of new and improved materials, a predictive wear model is desirable. The objective of this study was to develop a finite element model enabling investigators to predict crack propagation directions in resins used as the matrix material in composites, and to verify these predictions by observing cracks formed during the pin-on-disc wear of a 60:40 BISGMA:TEGDMA resin and an EBPADMA resin. Laser confocal scanning microscopy was used to measure crack locations. Finite element studies were done by means of ABAQUS software, modeling a cylinder sliding on a material with pre-existing surface-breaking cracks. Variables included modulus, cylinder/material friction coefficient, crack face friction, and yield behavior. Experimental results were surprising, since most crack directions were opposite previously published observations. The majority of surface cracks, though initially orthogonal to the surface, changed direction to run 20 to 30 degrees from the horizontal in the direction of indenter movement. Finite element modeling established the importance of subsurface shear stresses, since calculations provided evidence that cracks propagate in the direction of maximum K(II)(theta), in the same direction as the motion of the indenter, and at an angle of approximately 20 degrees. These findings provide the foundation for a predictive model of sliding wear in unfilled glassy resins.

  3. Uncertainty Quantification in Fatigue Crack Growth Prognosis

    Directory of Open Access Journals (Sweden)

    Shankar Sankararaman

    2011-01-01

    Full Text Available This paper presents a methodology to quantify the uncertainty in fatigue crack growth prognosis, applied to structures with complicated geometry and subjected to variable amplitude multi-axial loading. Finite element analysis is used to address the complicated geometry and calculate the stress intensity factors. Multi-modal stress intensity factors due to multi-axial loading are combined to calculate an equivalent stress intensity factor using a characteristic plane approach. Crack growth under variable amplitude loading is modeled using a modified Paris law that includes retardation effects. During cycle-by-cycle integration of the crack growth law, a Gaussian process surrogate model is used to replace the expensive finite element analysis. The effect of different types of uncertainty – physical variability, data uncertainty and modeling errors – on crack growth prediction is investigated. The various sources of uncertainty include, but not limited to, variability in loading conditions, material parameters, experimental data, model uncertainty, etc. Three different types of modeling errors – crack growth model error, discretization error and surrogate model error – are included in analysis. The different types of uncertainty are incorporated into the crack growth prediction methodology to predict the probability distribution of crack size as a function of number of load cycles. The proposed method is illustrated using an application problem, surface cracking in a cylindrical structure.

  4. Entering a Crack: An Encounter with Gossip

    Science.gov (United States)

    Henderson, Linda

    2014-01-01

    In this paper, I enter a crack to think otherwise about the concept "gossip". Drawing on previous scholarship engaging with Deleuzian concepts to inform research methodologies, this paper builds on this body of work. Following Deleuze and Guattari, the paper undertakes a mapping of gossip, subsequent to an encounter with a crack.…

  5. Investigation of Cracked Lithium Hydride Reactor Vessels

    Energy Technology Data Exchange (ETDEWEB)

    bird, e.l.; mustaleski, t.m.

    1999-06-01

    Visual examination of lithium hydride reactor vessels revealed cracks that were adjacent to welds, most of which were circumferentially located in the bottom portion of the vessels. Sections were cut from the vessels containing these cracks and examined by use of the metallograph, scanning electron microscope, and microprobe to determine the cause of cracking. Most of the cracks originated on the outer surface just outside the weld fusion line in the base material and propagated along grain boundaries. Crack depths of those examined sections ranged from {approximately}300 to 500 {micro}m. Other cracks were reported to have reached a maximum depth of 1/8 in. The primary cause of cracking was the creation of high tensile stresses associated with the differences in the coefficients of thermal expansion between the filler metal and the base metal during operation of the vessel in a thermally cyclic environment. This failure mechanism could be described as creep-type fatigue, whereby crack propagation may have been aided by the presence of brittle chromium carbides along the grain boundaries, which indicates a slightly sensitized microstructure.

  6. Fracture Mechanical Markov Chain Crack Growth Model

    DEFF Research Database (Denmark)

    Gansted, L.; Brincker, Rune; Hansen, Lars Pilegaard

    1991-01-01

    On the basis of the B-model developed in [J. L. Bogdanoff and F. Kozin, Probabilistic Models of Cumulative Damage. John Wiley, New York (1985)] a new numerical model incorporating the physical knowledge of fatigue crack propagation is developed. The model is based on the assumption that the crack...

  7. Solute transport in cracking clay soils

    NARCIS (Netherlands)

    Bronswijk, J.J.B.; Ritsema, C.J.; Oostindie, K.; Hamminga, P.

    1996-01-01

    A bromide tracer applied to a cracked clay soil was adsorbed in the soil matrix close to the soil surface. Upon subsequent precipitation, a small part of the bromide dissolved and flowed rapidly through cracks to the subsoil and the groundwater. As a result, the groundwater and the drain discharge

  8. Strength of Cracked Reinforced Concrete Disks

    DEFF Research Database (Denmark)

    Hoang, Cao Linh; Nielsen, Mogens Peter

    1999-01-01

    The paper deals with models, based on the theory of plasticity, to be used in strength assessments of reinforced concrete disks suffering from different kinds of cracking. Based on the assumption that the sliding strength of concrete is reduced in sections where cracks are located, solutions...

  9. Corrosion and Cracking of Reinforced Concrete

    DEFF Research Database (Denmark)

    Thoft-Christensen, Palle

    Modelling of the deterioration of reinforced concrete has in recent years changed from being a deterministic modelling based on experience to be stochastic modelling based on sound and consistent physical, chemical and mechanical principles. In this paper is presented a brief review of modern mod...... for time to initial corrosion, time to initial cracking, and time to a given crack width may be obtained....

  10. Numerical study of rotor-stator interactions in a hydraulic turbine with Foam-extend

    Science.gov (United States)

    Romain, Cappato; Guibault, François; Devals, Christophe; Nennemann, Bernd

    2016-11-01

    In the development of high head hydraulic turbines, vibrations are one of the critical problems. In Francis turbines, pressure fluctuations occur at the interface between the blades of the runner and guide vanes. This rotor-stator interaction can be responsible for fatigue failures and cracks. Although the flow inside the turbomachinery is complex, and the unsteadiness makes it difficult to model, the choice of an appropriate setup enables the study of this phenomenon. This study validates a numerical setup of the Foam-extend open source software for rotor-stator simulations. Pressure fluctuations results show a good correspondence with data from experiments.

  11. Crack spacing threshold of double cracks propagation for large-module rack

    Institute of Scientific and Technical Information of China (English)

    赵铁柱; 石端伟; 姚哲皓; 毛宏勇; 程术潇; 彭惠

    2015-01-01

    Large-module rack of the Three Gorges shiplift is manufactured by casting and machining, which is unable to avoid slag inclusions and surface cracks. To ensure its safety in the future service, studying on crack propagation rule and the residual life estimation method of large-module rack is of great significance. The possible crack distribution forms of the rack in the Three Gorges shiplift were studied. By applying moving load on the model in FRANC3D and ANSYS, quantitative analyses of interference effects on double cracks in both collinear and offset conditions were conducted. The variation rule of the stress intensity factor (SIF) influence factor,RK, of double collinear cracks changing with crack spacing ratio,RS, was researched. The horizontal and vertical crack spacing threshold of double cracks within the design life of the shiplift were obtained, which are 24 and 4 times as large as half of initial crack length,c0, respectively. The crack growth rates along the length and depth directions in the process of coalescence on double collinear cracks were also studied.

  12. Probabilistic analysis of linear elastic cracked structures

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    This paper presents a probabilistic methodology for linear fracture mechanics analysis of cracked structures. The main focus is on probabilistic aspect related to the nature of crack in material. The methodology involves finite element analysis; statistical models for uncertainty in material properties, crack size, fracture toughness and loads; and standard reliability methods for evaluating probabilistic characteristics of linear elastic fracture parameter. The uncertainty in the crack size can have a significant effect on the probability of failure, particularly when the crack size has a large coefficient of variation. Numerical example is presented to show that probabilistic methodology based on Monte Carlo simulation provides accurate estimates of failure probability for use in linear elastic fracture mechanics.

  13. Strain rate effects in stress corrosion cracking

    Energy Technology Data Exchange (ETDEWEB)

    Parkins, R.N. (Newcastle upon Tyne Univ. (UK). Dept. of Metallurgy and Engineering Materials)

    1990-03-01

    Slow strain rate testing (SSRT) was initially developed as a rapid, ad hoc laboratory method for assessing the propensity for metals an environments to promote stress corrosion cracking. It is now clear, however, that there are good theoretical reasons why strain rate, as opposed to stress per se, will often be the controlling parameter in determining whether or not cracks are nucleated and, if so, are propagated. The synergistic effects of the time dependence of corrosion-related reactions and microplastic strain provide the basis for mechanistic understanding of stress corrosion cracking in high-pressure pipelines and other structures. However, while this may be readily comprehended in the context of laboratory slow strain tests, its extension to service situations may be less apparent. Laboratory work involving realistic stressing conditions, including low-frequency cyclic loading, shows that strain or creep rates give good correlation with thresholds for cracking and with crack growth kinetics.

  14. Crack front propagation by kink formation

    Energy Technology Data Exchange (ETDEWEB)

    Roesch, Frohmut; Trebin, Hans-Rainer [Universitaet Stuttgart, Institut fuer Theoretische und Angewandte Physik, 70550 Stuttgart (Germany)

    2010-07-01

    In a brittle material a travelling crack generates an upper and a lower fracture surface, which meet at a one-dimensional crack front. From a macroscopic point of view there is no reason why this curve should deviate from a straight line, contrary to the atomistic point of view, where a crack propagates by successive rupture of cohesive bonds. We investigate fracture of the C15 NbCr{sub 2} Friauf-laves phase on an atomic level by means of molecular dynamics simulations. The numerical experiments highlight that crack fronts in general do not form a straight line and propagate by kink-pair formation at low loads (EPL 87 (2009) 66004). This mechanism should be relevant for crack propagation in any ordered brittle solid.

  15. XFEM for Thermal Crack of Massive Concrete

    Directory of Open Access Journals (Sweden)

    Guowei Liu

    2013-01-01

    Full Text Available Thermal cracking of massive concrete structures occurs as a result of stresses caused by hydration in real environment conditions. The extended finite element method that combines thermal fields and creep is used in this study to analyze the thermal cracking of massive concrete structures. The temperature field is accurately simulated through an equivalent equation of heat conduction that considers the effect of a cooling pipe system. The time-dependent creep behavior of massive concrete is determined by the viscoelastic constitutive model with Prony series. Based on the degree of hydration, we consider the main properties related to cracking evolving with time. Numerical simulations of a real massive concrete structure are conducted. Results show that the developed method is efficient for numerical calculations of thermal cracks on massive concrete. Further analyses indicate that a cooling system and appropriate heat preservation measures can efficiently prevent the occurrence of thermal cracks.

  16. The geometry of soil crack networks

    CERN Document Server

    Chertkov, V Y

    2014-01-01

    The subject of this work is the modification and specification of an approach to detail the estimation of soil crack network characteristics. The modification aims at accounting for the corrected soil crack volume based on the corrected shrinkage geometry factor compared to known estimates of crack volume and shrinkage geometry factor. The mode of the correction relies on recent results of the soil reference shrinkage curve. The main exposition follows the preliminary brief review of available approaches to dealing with the geometry of soil crack networks and gives a preliminary brief summary of the approach to be modified and specified. To validate and illustrate the modified approach the latter is used in the analysis of available data on soil cracking in a lysimeter.

  17. Field cracking performance of airfield rigid pavements

    Directory of Open Access Journals (Sweden)

    Yusuf Mehta

    2017-08-01

    Full Text Available This paper discusses cracking in airport pavements as studied in Construction Cycle 6 of testing carried out at the National Airport Pavement Testing Facility by the Federal Aviation Administration. Pavements of three different flexural strengths as well as two different subgrades, a soft bituminous layer and a more rigid layer known as econocrete, were tested. In addition to this, cracking near two types of isolated transition joints, a reinforced edge joint and a thickened edge joint, was considered. The pavement sections were tested using a moving load simulating that of an aircraft. It has been determined that the degree of cracking was reduced as the flexural strength of the pavement was increased and that fewer cracks formed over the econocrete base than over the bituminous base. In addition, the thickened edge transition joint was more effective in preventing cracking at the edges compared to the reinforced edge joint.

  18. Vibrations of hydraulic pump and their solution

    OpenAIRE

    Dobšáková Lenka; Nováková Naděžda; Habán Vladimír; Hudec Martin; Jandourek Pavel

    2017-01-01

    The vibrations of hydraulic pump and connected pipeline system are very problematic and often hardly soluble. The high pressure pulsations of hydraulic pump with the double suction inlet are investigated. For that reason the static pressure and accelerations are measured. The numerical simulations are carried out in order to correlate computed data with experimental ones and assess the main source of vibrations. Consequently the design optimization of the inner hydraulic part of pump is done ...

  19. Crack shape developments and leak rates for circumferential complex-cracked pipes

    Energy Technology Data Exchange (ETDEWEB)

    Brickstad, B.; Bergman, M. [SAQ Inspection Ltd., Stockholm (Sweden)

    1997-04-01

    A computerized procedure has been developed that predicts the growth of an initial circumferential surface crack through a pipe and further on to failure. The crack growth mechanism can either be fatigue or stress corrosion. Consideration is taken to complex crack shapes and for the through-wall cracks, crack opening areas and leak rates are also calculated. The procedure is based on a large number of three-dimensional finite element calculations of cracked pipes. The results from these calculations are stored in a database from which the PC-program, denoted LBBPIPE, reads all necessary information. In this paper, a sensitivity analysis is presented for cracked pipes subjected to both stress corrosion and vibration fatigue.

  20. Fully plastic crack opening analyses of complex-cracked pipes for Ramberg-Osgood materials

    Energy Technology Data Exchange (ETDEWEB)

    Jeong, Jae Uk; Choi, Jae Boong [Sungkyunkwan University, Suwon (Korea, Republic of); Huh, Nam Su [Seoul National University, Seoul (Korea, Republic of); Kim, Yun Jae [Korea University, Seoul (Korea, Republic of)

    2016-04-15

    The plastic influence functions for calculating fully plastic Crack opening displacement (COD) of complex-cracked pipes were newly proposed based on systematic 3-dimensional (3-D) elastic-plastic Finite element (FE) analyses using Ramberg-Osgood (R-O) relation, where global bending moment, axial tension and internal pressure are considered separately as a loading condition. Then, crack opening analyses were performed based on GE/EPRI concept by using the new plastic influence functions for complex-cracked pipes made of SA376 TP304 stainless steel, and the predicted CODs were compared with FE results based on deformation plasticity theory of tensile material behavior. From the comparison, the confidence of the proposed fully plastic crack opening solutions for complex-cracked pipes was gained. Therefore, the proposed engineering scheme for COD estimation using the new plastic influence functions can be utilized to estimate leak rate of a complex-cracked pipe for R-O material.

  1. General forms of elastic-plastic matching equations for mode-Ⅲ cracks near crack line

    Institute of Scientific and Technical Information of China (English)

    Zhi-jian YI; Chao-hua ZHAO; Qing-guo YANG; Kai PENG; Zong-ming HUANG

    2009-01-01

    Crack line analysis is an effective way to solve elastic-plastic crack problems.Application of the method does not need the traditional small-scale yielding conditions and can obtain sufficiently accurate solutions near the crack line. To address mode-Ⅲ crack problems under the perfect elastic-plastic condition,matching procedures of the crack line analysis method are summarized and refined to give general forms and formulation steps of plastic field,elastic-plastic boundary,and elastic-plastic matching equations near the crack line. The research unifies mode-Ⅲ crack problems under different conditions into a problem of determining four integral constants with four matching equations.An example is given to verify correctness,conciseness,and generality of the procedure.

  2. Cracks assessment using ultrasonic technology

    Energy Technology Data Exchange (ETDEWEB)

    Martinez, Maria Pia; Tomasella, Marcelo [OLDELVAL S.A. Oleoductos del Valle, Rio Negro (Argentina). Pipeline Integrity Dept.

    2005-07-01

    The goal of Oldelval Integrity Program is to prevent ruptures and leaks, developing strategies for a better handling of the integrity of our pipelines. In order to achieve it we have studied and modeled each process that involved in the integrity pipeline. Those processes are mainly based on defects reported by an internal inspection tool and supplied with field inspection and monitoring data. Years of evaluation, study and the continuous effort overturned towards a phenomenon that worries to the industry, as it is the SCC. Since 1998 up to 2004 SCC was included in the integrity program with some preventive maintenance programs. The accomplishment of the inspection based on ultrasound tools, is the culmination of years of evaluation and investigations supported by field digs and materials susceptibility. This paper describes Oldelval's results with ultrasonic crack detection tool, and how it can be reliably to detect SCC. (author)

  3. Initiation and growth kinetics of solidification cracking during welding of steel

    Science.gov (United States)

    Aucott, L.; Huang, D.; Dong, H. B.; Wen, S. W.; Marsden, J. A.; Rack, A.; Cocks, A. C. F.

    2017-01-01

    Solidification cracking is a key phenomenon associated with defect formation during welding. To elucidate the failure mechanisms, solidification cracking during arc welding of steel are investigated in situ with high-speed, high-energy synchrotron X-ray radiography. Damage initiates at relatively low true strain of about 3.1% in the form of micro-cavities at the weld subsurface where peak volumetric strain and triaxiality are localised. The initial micro-cavities, with sizes from 10 × 10−6 m to 27 × 10−6 m, are mostly formed in isolation as revealed by synchrotron X-ray micro-tomography. The growth of micro-cavities is driven by increasing strain induced to the solidifying steel. Cavities grow through coalescence of micro-cavities to form micro-cracks first and then through the propagation of micro-cracks. Cracks propagate from the core of the weld towards the free surface along the solidifying grain boundaries at a speed of 2–3 × 10−3 m s−1. PMID:28074852

  4. Initiation and growth kinetics of solidification cracking during welding of steel

    Science.gov (United States)

    Aucott, L.; Huang, D.; Dong, H. B.; Wen, S. W.; Marsden, J. A.; Rack, A.; Cocks, A. C. F.

    2017-01-01

    Solidification cracking is a key phenomenon associated with defect formation during welding. To elucidate the failure mechanisms, solidification cracking during arc welding of steel are investigated in situ with high-speed, high-energy synchrotron X-ray radiography. Damage initiates at relatively low true strain of about 3.1% in the form of micro-cavities at the weld subsurface where peak volumetric strain and triaxiality are localised. The initial micro-cavities, with sizes from 10 × 10‑6 m to 27 × 10‑6 m, are mostly formed in isolation as revealed by synchrotron X-ray micro-tomography. The growth of micro-cavities is driven by increasing strain induced to the solidifying steel. Cavities grow through coalescence of micro-cavities to form micro-cracks first and then through the propagation of micro-cracks. Cracks propagate from the core of the weld towards the free surface along the solidifying grain boundaries at a speed of 2–3 × 10‑3 m s‑1.

  5. Diversity in plant hydraulic traits explains seasonal and inter-annual variations of vegetation dynamics in seasonally dry tropical forests.

    Science.gov (United States)

    Xu, Xiangtao; Medvigy, David; Powers, Jennifer S; Becknell, Justin M; Guan, Kaiyu

    2016-10-01

    We assessed whether diversity in plant hydraulic traits can explain the observed diversity in plant responses to water stress in seasonally dry tropical forests (SDTFs). The Ecosystem Demography model 2 (ED2) was updated with a trait-driven mechanistic plant hydraulic module, as well as novel drought-phenology and plant water stress schemes. Four plant functional types were parameterized on the basis of meta-analysis of plant hydraulic traits. Simulations from both the original and the updated ED2 were evaluated against 5 yr of field data from a Costa Rican SDTF site and remote-sensing data over Central America. The updated model generated realistic plant hydraulic dynamics, such as leaf water potential and stem sap flow. Compared with the original ED2, predictions from our novel trait-driven model matched better with observed growth, phenology and their variations among functional groups. Most notably, the original ED2 produced unrealistically small leaf area index (LAI) and underestimated cumulative leaf litter. Both of these biases were corrected by the updated model. The updated model was also better able to simulate spatial patterns of LAI dynamics in Central America. Plant hydraulic traits are intercorrelated in SDTFs. Mechanistic incorporation of plant hydraulic traits is necessary for the simulation of spatiotemporal patterns of vegetation dynamics in SDTFs in vegetation models.

  6. Design and Analysis of Hydraulic Chassis with Obstacle Avoidance Function

    Science.gov (United States)

    Hong, Yingjie; Zhang, Xiang

    2017-07-01

    This article mainly expounds the design of hydraulic system for the hydraulic chassis with obstacle avoidance function. Including the selection of hydraulic motor wheels, hydraulic pump, digital hydraulic cylinder and the matching of engine power. And briefly introduces the principle of obstacle avoidance.

  7. Three-Dimensional Gear Crack Propagation Studied

    Science.gov (United States)

    Lewicki, David G.

    1999-01-01

    Gears used in current helicopters and turboprops are designed for light weight, high margins of safety, and high reliability. However, unexpected gear failures may occur even with adequate tooth design. To design an extremely safe system, the designer must ask and address the question, "What happens when a failure occurs?" With gear-tooth bending fatigue, tooth or rim fractures may occur. A crack that propagates through a rim will be catastrophic, leading to disengagement of the rotor or propeller, loss of an aircraft, and possible fatalities. This failure mode should be avoided. A crack that propagates through a tooth may or may not be catastrophic, depending on the design and operating conditions. Also, early warning of this failure mode may be possible because of advances in modern diagnostic systems. One concept proposed to address bending fatigue fracture from a safety aspect is a splittooth gear design. The prime objective of this design would be to control crack propagation in a desired direction such that at least half of the tooth would remain operational should a bending failure occur. A study at the NASA Lewis Research Center analytically validated the crack-propagation failsafe characteristics of a split-tooth gear. It used a specially developed three-dimensional crack analysis program that was based on boundary element modeling and principles of linear elastic fracture mechanics. Crack shapes as well as the crack-propagation life were predicted on the basis of the calculated stress intensity factors, mixed-mode crack-propagation trajectory theories, and fatigue crack-growth theories. The preceding figures show the effect of the location of initial cracks on crack propagation. Initial cracks in the fillet of the teeth produced stress intensity factors of greater magnitude (and thus, greater crack growth rates) than those in the root or groove areas of the teeth. Crack growth was simulated in a case study to evaluate crack-propagation paths. Tooth

  8. Position Control of an Over‐Actuated Direct Hydraulic Cylinder Drive

    DEFF Research Database (Denmark)

    Schmidt, Lasse; Grønkjær, Morten; Pedersen, Henrik Clemmensen

    2017-01-01

    This paper considers the analysis and control strategy for a novel direct hydraulic cylinder drive, that is overactuated in the sense that it has more inputs than sensible outputs. Efforts to overcome the inherent loss of energy due to th+rottling in valve driven hydraulic drives are many......, and various approaches have been proposed by research communities as well as the industry. Recently, a so-called Speed-variable Switched Differential Pump was proposed for direct drive of hydraulic differential cylinders. The main idea with this drive is to utilize an electric rotary drive with the shaft...... the ability to bleed off flow from the transmission lines to achieve reasonable pressure levels. This design renders the drive over-actuated as the line pressures and the cylinder piston motion cannot be controlled independently, due to the pressure difference being motion generating. In order to achieve...

  9. Hydraulic vs. Electric: A Review of Actuation Systems in Offshore Drilling Equipment

    Directory of Open Access Journals (Sweden)

    Witold Pawlus

    2016-01-01

    Full Text Available This article presents a survey on actuation systems encountered in offshore drilling applications. Specifically, it focuses on giving a comparison of hydraulic and electric drivetrains along with detailed explanations of their advantages and drawbacks. A significant number of industrial case studies is examined in addition to the collection of academic publications, in order to accurately describe the current market situation. Some key directions of research and development required to satisfy increasing demands on powertrains operating offshore are identified. The impact of the literature and application surveys is further strengthened by benchmarking two designs of a full-scale pipe handling machine. Apart from other benefits, the electrically actuated machine reduces the total power consumption by 70% compared to its hydraulically driven counterpart. It is concluded that electric actuation systems, among other advantages, in general offer higher efficiency and flexibility, however, in some specific applications (such as energy accumulation or translational motion control hydraulic powertrains are favorable.

  10. Helical coil thermal hydraulic model

    Science.gov (United States)

    Caramello, M.; Bertani, C.; De Salve, M.; Panella, B.

    2014-11-01

    A model has been developed in Matlab environment for the thermal hydraulic analysis of helical coil and shell steam generators. The model considers the internal flow inside one helix and its associated control volume of water on the external side, both characterized by their inlet thermodynamic conditions and the characteristic geometry data. The model evaluates the behaviour of the thermal-hydraulic parameters of the two fluids, such as temperature, pressure, heat transfer coefficients, flow quality, void fraction and heat flux. The evaluation of the heat transfer coefficients as well as the pressure drops has been performed by means of the most validated literature correlations. The model has been applied to one of the steam generators of the IRIS modular reactor and a comparison has been performed with the RELAP5/Mod.3.3 code applied to an inclined straight pipe that has the same length and the same elevation change between inlet and outlet of the real helix. The predictions of the developed model and RELAP5/Mod.3.3 code are in fairly good agreement before the dryout region, while the dryout front inside the helical pipes is predicted at a lower distance from inlet by the model.

  11. A Simulation Method for High-Cycle Fatigue-Driven Delamination using a Cohesive Zone Model

    DEFF Research Database (Denmark)

    Bak, Brian Lau Verndal; Turon, A.; Lindgaard, Esben;

    2016-01-01

    on parameter fitting of any kind. The method has been implemented as a zero-thickness eight-node interface element for Abaqus and as a spring element for a simple finite element model in MATLAB. The method has been validated in simulations of mode I, mode II, and mixed-mode crack loading for both self......A novel computational method for simulating fatigue-driven mixed-mode delamination cracks in laminated structures under cyclic loading is presented. The proposed fatigue method is based on linking a cohesive zone model for quasi-static crack growth and a Paris' law-like model described......-similar and non-self-similar crack propagation. The method produces highly accurate results compared with currently available methods and is capable of simulating general mixed-mode non-self-similar crack growth problems....

  12. WATER ENERGY IN HYDROAMELIORATIVE SYSTEMS USING THE HYDRAULIC TRANSFORMER TYPE A. BARGLAZAN AND THE HYDRAULIC HAMMER (HYDRAULIC PUMP

    Directory of Open Access Journals (Sweden)

    Teodor Eugen Man

    2010-01-01

    Full Text Available This paper presents two examples of exploitation of water energy that can be used in the irrigation field. First of theseexamples is the hydraulic transformer type A. Barglazan used for irrigation, pumped water is taken directly from theriver’s well, using a hydraulic pump which simultaneously carried out a double transformation in this way: hydraulicenergy into mechanic energy and mechanical energy into hydraulic energy. Technology preparation and devices designwas done in record time, seeing that this constructive solution is more robust, reliable and with improved energyperformance versus the laboratory prototype. The experimental research which was made at 1:1 scale proved theirgood function over time. Another example is the hydraulic hammer (hydraulic pump that uses low-head energy topump water, with a global efficiency of about 10 - 50%. Currently, the new situation of private ownership of landprovides conditions for new pumping microstations to be made where irrigation is necessary and optimal hydrauliclocations exist.

  13. Production of hydrogen by thermocatalytic cracking of natural gas

    Energy Technology Data Exchange (ETDEWEB)

    Muradov, N.Z. [Univ. of Central Florida, Cape Canaveral, FL (United States)

    1995-09-01

    It is universally accepted that in the next few decades hydrogen production will continue to rely on fossil fuels (primarily, natural gas). On the other hand, the conventional methods of hydrogen production from natural gas (for example, steam reforming) are complex multi-step processes. These processes also result in the emission of large quantities of CO{sub 2} into the atmosphere that produce adverse ecological effects. One alternative is the one-step thermocatalytic cracking (TCC) (or decomposition) of natural gas into hydrogen and carbon. Preliminary analysis indicates that the cost of hydrogen produced by thermal decomposition of natural gas is somewhat lower than the conventional processes after by-product carbon credit is taken. In the short term, this process can be used for on-site production of hydrogen-methane mixtures in gas-filling stations and for CO{sub x}-free production of hydrogen for fuel cell driven prime movers. The experimental data on the thermocatalytic cracking of methane over various catalysts and supports in a wide range of temperatures (500-900{degrees}C) are presented in this paper. Two types of reactors were designed and built at FSEC: continuous flow and pulse fix bed catalytic reactors. The temperature dependence of the hydrogen production yield using oxide type catalysts was studied. Alumina-supported Ni- and Fe-catalysts demonstrated relatively high efficiency in the methane cracking reaction at moderate temperatures (600-800{degrees}C). Kinetic curves of hydrogen production over metal and metal oxide catalysts at different temperatures are presented in the paper. Fe-catalyst demonstrated good stability (for several hours), whereas alumina-supported Pt-catalyst rapidly lost its catalytic activity.

  14. Crack detection in a beam with an arbitrary number of transverse cracks using genetic algorithms

    Energy Technology Data Exchange (ETDEWEB)

    Khaji, N. [Tarbiat Modares University, Tehran (Iran, Islamic Republic of); Mehrjoo, M. [Islamic Azad University, Tehran (Iran, Islamic Republic of)

    2014-03-15

    In this paper, a crack detection approach is presented for detecting depth and location of cracks in beam-like structures. For this purpose, a new beam element with an arbitrary number of embedded transverse edge cracks, in arbitrary positions of beam element with any depth, is derived. The components of the stiffness matrix for the cracked element are computed using the conjugate beam concept and Betti's theorem, and finally represented in closed-form expressions. The proposed beam element is efficiently employed for solving forward problem (i.e., to gain precise natural frequencies and mode shapes of the beam knowing the cracks' characteristics). To validate the proposed element, results obtained by new element are compared with two-dimensional (2D) finite element results and available experimental measurements. Moreover, by knowing the natural frequencies and mode shapes, an inverse problem is established in which the location and depth of cracks are determined. In the inverse approach, an optimization problem based on the new finite element and genetic algorithms (GAs) is solved to search the solution. It is shown that the present algorithm is able to identify various crack configurations in a cracked beam. The proposed approach is verified through a cracked beam containing various cracks with different depths.

  15. Identification of cracks in thick beams with a cracked beam element model

    Science.gov (United States)

    Hou, Chuanchuan; Lu, Yong

    2016-12-01

    The effect of a crack on the vibration of a beam is a classical problem, and various models have been proposed, ranging from the basic stiffness reduction method to the more sophisticated model involving formulation based on the additional flexibility due to a crack. However, in the damage identification or finite element model updating applications, it is still common practice to employ a simple stiffness reduction factor to represent a crack in the identification process, whereas the use of a more realistic crack model is rather limited. In this paper, the issues with the simple stiffness reduction method, particularly concerning thick beams, are highlighted along with a review of several other crack models. A robust finite element model updating procedure is then presented for the detection of cracks in beams. The description of the crack parameters is based on the cracked beam flexibility formulated by means of the fracture mechanics, and it takes into consideration of shear deformation and coupling between translational and longitudinal vibrations, and thus is particularly suitable for thick beams. The identification procedure employs a global searching technique using Genetic Algorithms, and there is no restriction on the location, severity and the number of cracks to be identified. The procedure is verified to yield satisfactory identification for practically any configurations of cracks in a beam.

  16. Subcritical crack growth in two titanium alloys.

    Science.gov (United States)

    Williams, D. N.

    1973-01-01

    Measurement of subcritical crack growth during static loading of precracked titanium alloys in salt water using samples too thin for plane strain loading to predominate was examined as a method for determining the critical stress intensity for crack propagation in salt water. Significant internal crack growth followed by arrest was found at quite low stress intensities, but crack growth rates were relatively low. Assuming these techniques provided a reliable measurement of the critical stress intensity, the value for annealed Ti-4Al-1.5Mo-0.5V alloy was apparently about 35 ksi-in. to the 1/2 power, while that for annealed Ti-4Al-3Mo-1V was below 45 ksi-in. to the 1/2 power. Crack growth was also observed in tests conducted in both alloys in an air environment. At 65 ksi-in. to the 1/2 power, the extent of crack growth was greater in air than in salt water. Ti-4Al-3Mo-1V showed arrested crack growth in air at a stress intensity of 45 ksi-in. to the 1/2 power.

  17. A mini slug test method for determination of a local hydraulic conductivity of an unconfined sandy aquifer

    DEFF Research Database (Denmark)

    Hinsby, Klaus; Bjerg, Poul Løgstrup; Andersen, Lars J.;

    1992-01-01

    from level to level and thereby establish vertical profiles of the hydraulic conductivity. The head data from the test well are recorded with a 10 mm pressure transducer, and the initial head difference required is established by a small vacuum pump. The method described has provided 274 spatially......A new and efficient mini slug test method for the determination of local hydraulic conductivities in unconfined sandy aquifers is developed. The slug test is performed in a small-diameter (1 inch) driven well with a 0.25 m screen just above the drive point. The screened drive point can be driven...... distributed measurements of a local hydraulic conductivity at a tracer test site at Vejen, Denmark. The mini slug test results calculated by a modified Dax slug test analysing method, applying the elastic storativity in the Dax equations instead of the specific yield, are in good accordance with the results...

  18. HYDRAULIC CHARACTERISTICS OF VERTICAL VORTEX AT HYDRAULIC INTAKES

    Institute of Scientific and Technical Information of China (English)

    CHEN Yun-liang; WU Chao; YE Mao; JU Xiao-ming

    2007-01-01

    The trace of vertical vortex flow at hydraulic intakes is of the shape of spiral lines, which was observed in the presented experiments with the tracer technique. It represents the fluid particles flow spirally from the water surface to the underwater and rotate around the vortex-axis multi-cycle. This process is similar to the movement of screw. To describe the multi-circle spiral characteristics under the axisymmetric condition, the vertical vortex would change not only in the radial direction but also in the axial direction. The improved formulae for three velocity components for the vertical vortex flow were deduced by using the method of separation of variables in this article. In the improved formulae, the velocity components are the functions of the radial and axial coordinates, so the multi-circle spiral flow of vertical vortex could be simulated. The calculated and measured results for the vertical vortex flow were compared and the causes of errors were analyzed.

  19. Crack growth monitoring at CFRP bond lines

    Science.gov (United States)

    Rahammer, M.; Adebahr, W.; Sachse, R.; Gröninger, S.; Kreutzbruck, M.

    2016-02-01

    With the growing need for lightweight technologies in aerospace and automotive industries, fibre-reinforced plastics, especially carbon-fibre (CFRP), are used with a continuously increasing annual growth rate. A promising joining technique for composites is adhesive bonding. While rivet holes destroy the fibres and cause stress concentration, adhesive bond lines distribute the load evenly. Today bonding is only used in secondary structures due to a lack of knowledge with regard to long-term predictability. In all industries, numerical simulation plays a critical part in the development process of new materials and structures, while it plays a vital role when it comes to CFRP adhesive bondings conducing the predictability of life time and damage tolerance. The critical issue with adhesive bondings is crack growth. In a dynamic tensile stress testing machine we dynamically load bonded CFRP coupon specimen and measure the growth rate of an artificially started crack in order to feed the models with the results. We also investigate the effect of mechanical crack stopping features. For observation of the bond line, we apply two non-contact NDT techniques: Air-coupled ultrasound in slanted transmission mode and active lockin-thermography evaluated at load frequencies. Both methods give promising results for detecting the current crack front location. While the ultrasonic technique provides a slightly higher accuracy, thermography has the advantage of true online monitoring, because the measurements are made while the cyclic load is being applied. The NDT methods are compared to visual inspection of the crack front at the specimen flanks and show high congruence. Furthermore, the effect of crack stopping features within the specimen on the crack growth is investigated. The results show, that not all crack fronts are perfectly horizontal, but all of them eventually come to a halt in the crack stopping feature vicinity.

  20. Hydraulic Transport Across Hydrophilic and Hydrophobic Nanopores: Flow Experiments with Water and n-Hexane

    CERN Document Server

    Gruener, Simon; Greulich, Stefanie; Busch, Mark; Huber, Patrick

    2015-01-01

    We experimentally explore pressure-driven flow of water and n-hexane across nanoporous silica (Vycor glass monoliths with 7 or 10 nm pore diameters, respectively) as a function of temperature and surface functionalization (native and silanized glass surfaces). Hydraulic flow rates are measured by applying hydrostatic pressures via inert gases (argon and helium, pressurized up to 70 bar) on the upstream side in a capacitor-based membrane permeability setup. For the native, hydrophilic silica walls, the measured hydraulic permeabilities can be quantitatively accounted for by bulk fluidity provided we assume a sticking boundary layer, i.e. a negative velocity slip length of molecular dimensions. The thickness of this boundary layer is discussed with regard to previous capillarity-driven flow experiments (spontaneous imbibition) and with regard to velocity slippage at the pore walls resulting from dissolved gas. Water flow across the silanized, hydrophobic nanopores is blocked up to a hydrostatic pressure of at l...

  1. Mitigation strategies for autogenous shrinkage cracking

    DEFF Research Database (Denmark)

    Bentz, Dale P.; Jensen, Ole Mejlhede

    2004-01-01

    , the fundamental parameters contributing to the autogenous shrinkage and resultant early-age cracking of concrete are presented. Basic characteristics of the cement paste that contribute to or control the autogenous shrinkage response include the surface tension of the pore solution, the geometry of the pore...... of early-age cracking due to autogenous shrinkage. Mitigation strategies discussed in this paper include: the addition of shrinkage-reducing admixtures more commonly used to control drying shrinkage, control of the cement particle size distribution, modification of the mineralogical composition......, it should be possible to minimize cracking due to autogenous shrinkage via some combination of the presented approaches....

  2. Prediction of Crack Growth in Aqueous Environments.

    Science.gov (United States)

    1986-07-01

    Impedance for the Propagation of a Crack Through HY80 Steel in 3.5Z NaCl Solution at 25*C Under Sinusoidal Loading Condi t ions...THE PROPAGATION OF A CRACK THROUGH HY80 STEEL IN 3.5% NaCI SOLUTION AT 25°C UNDER SINUSOIDAL LOADING CONDITIONS 49 and the properties of greatest...VELOCITY AS A FUNCTION OF TIME FOR A CRACK GROWN AT CONSTANT CURRENT IN HY80 STEEL Initial conditions CI in Table 5. 66 400 UJ x v> l/> L. 0

  3. Design of Pumps for Water Hydraulic Systems

    DEFF Research Database (Denmark)

    Klit, Peder; Olsen, Stefan; Bech, Thomas Nørgaard

    1999-01-01

    This paper considers the development of two pumps for water hydraulic applications. The pumps are based on two different working principles: The Vane-type pump and the Gear-type pump. Emphasis is put on the considerations that should be made to account for water as the hydraulic fluid.......KEYWORDS: water, pump, design, vane, gear....

  4. Hydraulic fracturing with distinct element method

    NARCIS (Netherlands)

    Pruiksma, J.P.; Bezuijen, A.

    2002-01-01

    In this report, hydraulic fracturing is investigated using the distinct element code PFC2D from Itasca. Special routines were written to be able to model hydraulic fracturing. These include adding fluid flow to PFC2D and updating the fluid flow domains when fractures appear. A brief description of t

  5. Hydraulic Actuator for Ganged Control Rods

    Science.gov (United States)

    Thompson, D. C.; Robey, R. M.

    1986-01-01

    Hydraulic actuator moves several nuclear-reactor control rods in unison. Electromagnetic pump pushes liquid lithium against ends of control rods, forcing them out of or into nuclear reactor. Color arrows show lithium flow for reactor startup and operation. Flow reversed for shutdown. Conceived for use aboard spacecraft, actuator principle applied to terrestrial hydraulic machinery involving motion of ganged rods.

  6. Control arrangement for the actuation of hydraulic consumers

    Energy Technology Data Exchange (ETDEWEB)

    Kussel, W.; Dettmers, M.; Weirich, W.

    1988-11-09

    An arrangement for controlling the actuation of hydraulic consumers, by selectively connecting the consumers to hydraulic pressure and return lines; the control arrangement comprising a respective hydraulically operated directional control valve associated with each of the hydraulic consumers, a respective electro-magnetically operated pre-control valve associated with each of the hydraulic directional control valves, and further electro-magnetically operated directional control valve means associated with the pre-control valves, each of the hydraulic consumers being connectible to the hydraulic pressure or return lines via the associated hydraulically operated directional control valve which is actuatable by a hydraulic control line leading from the output of the associated pre-control valve, wherein the inputs of the pre-control valves are connected directly to the hydraulic return line and indirectly, via the further control valve means, to the hydraulic return line or to a hydraulic control pressure line.

  7. Scaling hydraulic properties of a macroporous soil

    Science.gov (United States)

    Mohanty, Binayak P.

    1999-06-01

    Macroporous soils exhibit significant differences in their hydraulic properties for different pore domains. Multimodal hydraulic functions may be used to describe the characteristics of multiporosity media. I investigated the usefulness of scaling to describe the spatial variability of hydraulic conductivity (K(-h)) functions of a macroporous soil in Las Nutrias, New Mexico. Piecewise-continuous hydraulic conductivity functions suitable for macroporous soils in conjunction with a hybrid similar media-functional normalization scaling approach were used. Results showed that gravity-dominated flow and the related hydraulic conductivity (K(minus;h) functions of the macropore region are more readily scalable than capillary-dominated flow properties of the mesopore and micropore regions. A possible reason for this behavior is that gravity-dominated flow in the larger pores is mostly influenced by the pore diameter which remains more uniform as compared to tortuous mesopores and micropores with variable neck and body sizes along the pore length.

  8. Modeling and Simulation of Hydraulic Engine Mounts

    Institute of Scientific and Technical Information of China (English)

    DUAN Shanzhong; Marshall McNea

    2012-01-01

    Hydraulic engine mounts are widely used in automotive powertrains for vibration isolation.A lumped mechanical parameter model is a traditional approach to model and simulate such mounts.This paper presents a dynamical model of a passive hydraulic engine mount with a double-chamber,an inertia track,a decoupler,and a plunger.The model is developed based on analogy between electrical systems and mechanical-hydraulic systems.The model is established to capture both low and high frequency dynatmic behaviors of the hydraulic mount.The model will be further used to find the approximate pulse responses of the mounts in terms of the force transmission and top chamber pressure.The close form solution from the simplifiod linear model may provide some insight into the highly nonlinear behavior of the mounts.Based on the model,computer simulation has been carried out to study dynamic performance of the hydraulic mount.

  9. Hydraulic design of a low-specific speed Francis runner for a hydraulic cooling tower

    Science.gov (United States)

    Ruan, H.; Luo, X. Q.; Liao, W. L.; Zhao, Y. P.

    2012-11-01

    The air blower in a cooling tower is normally driven by an electromotor, and the electric energy consumed by the electromotor is tremendous. The remaining energy at the outlet of the cooling cycle is considerable. This energy can be utilized to drive a hydraulic turbine and consequently to rotate the air blower. The purpose of this project is to recycle energy, lower energy consumption and reduce pollutant discharge. Firstly, a two-order polynomial is proposed to describe the blade setting angle distribution law along the meridional streamline in the streamline equation. The runner is designed by the point-to-point integration method with a specific blade setting angle distribution. Three different ultra-low-specificspeed Francis runners with different wrap angles are obtained in this method. Secondly, based on CFD numerical simulations, the effects of blade setting angle distribution on pressure coefficient distribution and relative efficiency have been analyzed. Finally, blade angles of inlet and outlet and control coefficients of blade setting angle distribution law are optimal variables, efficiency and minimum pressure are objective functions, adopting NSGA-II algorithm, a multi-objective optimization for ultra-low-specific speed Francis runner is carried out. The obtained results show that the optimal runner has higher efficiency and better cavitation performance.

  10. The Analysis Regarding the Building of a Hydraulic Power Plant on the Black Sea Shore

    Directory of Open Access Journals (Sweden)

    Gheorghe Samoilescu

    2013-09-01

    Full Text Available The present paper represents the result of a research project regarding the construction of a wave driven hydraulic plant that is going to be installed on the Black Sea shore in the area of the city of Constanta. Several phases were analyzed: numerical simulations for the micro plant – wave energy theory; finite element simulation – results and conclusions; generating the blueprint for the construction of the plant.

  11. Interfacial Crack Arrest in Sandwich Panels with Embedded Crack Stoppers Subjected to Fatigue Loading

    Science.gov (United States)

    Martakos, G.; Andreasen, J. H.; Berggreen, C.; Thomsen, O. T.

    2017-02-01

    A novel crack arresting device has been implemented in sandwich panels and tested using a special rig to apply out-of-plane loading on the sandwich panel face-sheets. Fatigue crack propagation was induced in the face-core interface of the sandwich panels which met the crack arrester. The effect of the embedded crack arresters was evaluated in terms of the achieved enhancement of the damage tolerance of the tested sandwich panels. A finite element (FE) model of the experimental setup was used for predicting propagation rates and direction of the crack growth. The FE simulation was based on the adoption of linear fracture mechanics and a fatigue propagation law (i.e. Paris law) to predict the residual fatigue life-time and behaviour of the test specimens. Finally, a comparison between the experimental results and the numerical simulations was made to validate the numerical predictions as well as the overall performance of the crack arresters.

  12. Interfacial Crack Arrest in Sandwich Panels with Embedded Crack Stoppers Subjected to Fatigue Loading

    Science.gov (United States)

    Martakos, G.; Andreasen, J. H.; Berggreen, C.; Thomsen, O. T.

    2016-08-01

    A novel crack arresting device has been implemented in sandwich panels and tested using a special rig to apply out-of-plane loading on the sandwich panel face-sheets. Fatigue crack propagation was induced in the face-core interface of the sandwich panels which met the crack arrester. The effect of the embedded crack arresters was evaluated in terms of the achieved enhancement of the damage tolerance of the tested sandwich panels. A finite element (FE) model of the experimental setup was used for predicting propagation rates and direction of the crack growth. The FE simulation was based on the adoption of linear fracture mechanics and a fatigue propagation law (i.e. Paris law) to predict the residual fatigue life-time and behaviour of the test specimens. Finally, a comparison between the experimental results and the numerical simulations was made to validate the numerical predictions as well as the overall performance of the crack arresters.

  13. The Hydraulic Mission and the Mexican Hydrocracy: Regulating and Reforming the Flows of Water and Power

    Directory of Open Access Journals (Sweden)

    Philippus Wester

    2009-10-01

    Full Text Available In Mexico, the hydraulic mission, the centralisation of water control, and the growth of the federal hydraulic bureaucracy (hydrocracy recursively shaped and reinforced each other during the 20th century. The hydraulic mission entails that the state, embodied in an autonomous hydrocracy, takes the lead in water resources development to capture as much water as possible for human uses. The hydraulic mission was central to the formation of Mexico’s hydrocracy, which highly prized its autonomy. Bureaucratic rivals, political transitions, and economic developments recurrently challenged the hydrocracy’s degree of autonomy. However, driven by the argument that a single water authority should regulate and control the nation’s waters, the hydrocracy consistently managed to renew its, always precarious, autonomy at different political moments in the country’s history. The legacy of the hydraulic mission continues to inform water reforms in Mexico, and largely explains the strong resilience of the Mexican hydrocracy to 'deep' institutional change and political transitions. While the emphasis on infrastructure has lessened, the hydrocracy has actively renewed its control over water decisions and budgets and has played a remarkably constant, hegemonic role in defining and shaping Mexico’s water laws, policies and institutions.

  14. Hydraulic test for evaluation of hydrophone VSP

    Energy Technology Data Exchange (ETDEWEB)

    Yabuuchi, Satoshi; Koide, Kaoru [Power Reactor and Nuclear Fuel Development Corp., Toki, Gifu (Japan). Tono Geoscience Center

    1997-12-01

    This hydraulic test was carried out at the test site of Tono Geoscience Center, Mizunami-shi, Gifu Pref. in order to evaluate the reliability of the hydraulic conductivity estimated from hydrophone VSP experiment. From March to April 1997, we carried out measurements of pore-water pressure at five depths and permeability tests at seven depths down to G.L.-300m, within a borehole drilled in granitic rock. We compared the results of hydraulic test with hydrophone VSP experiment on condition that a single open fracture existed, and we obtained two notable results. First, for the granitic rock at which a single open fracture was found by BTV and also detected by hydrophone VSP experiment, the hydraulic conductivity was 1.54 x 10{sup -7} cm/sec, while for the same granitic rock at which another single open fracture was found by BTV but not detected by hydrophone VSP experiment, the hydraulic conductivity was less than 6 x 10{sup -10} cm/sec. Second, we converted the hydraulic conductivity of 1.54 x 10{sup -7} cm/sec which was obtained in a hydraulic test section of length 2.5 m into an equivalent value for a single open fracture of width 1 mm. The converted value (3.8 x 10{sup -4} cm/sec) was similar to the hydraulic conductivity estimated from hydrophone VSP experiment. In conclusion, the hydraulic test result shows that hydrophone VSP is useful to estimate an approximate hydraulic conductivity of a single open fracture. (author)

  15. Hydraulic assessment of the Buda Thermal Karst area and its vulnerability (Budapest, Hungary)

    Science.gov (United States)

    Czauner, Brigitta; Erőss, Anita; Erhardt, Ildikó; Ötvös, Viktória; Simon, Szilvia; Mádl-Szőnyi, Judit

    2017-04-01

    Thermal and medicinal water resources of Budapest (Hungary), the "City of Spas", are provided by the Buda Thermal Karst area. Assessment of its vulnerability requires the understanding of the discharge phenomena and thus the groundwater flow conditions in the area. Accordingly, BTK has already been the objective of several hydrogeological investigations, including numerical simulations as well, which led to conceptual models. The aim of the present study was the hydraulic evaluation of the flow systems based on the complex analysis of real, i.e. measured, archival hydraulic data of wells in order to i) get acquainted with the real flow systems, and ii) hydraulically confirm or disprove the previous conceptual models, in particular the applicability of gravity-driven regional groundwater flow concept and hydraulic continuity, separation of the natural discharge zones, and hypogenic karstification. Considering the data distribution, pressure vs. elevation profiles, tomographic fluid-potential maps, and hydraulic cross-sections were constructed for the first time in this area. As a result, gravitational flow systems and the modifying effects of aquitard units and faults were identified. Consequently, the differences in temperature, hydrochemistry, discharge distribution (one and two-components), and related cave forming processes between the Central (Rózsadomb) and Southern (Gellért Hill) natural discharge areas could be explained, as well as the hydraulic behaviour of the Northeastern Margin-fault of the Buda Hills could be determined. Regarding the on-going hypogenic karstification processes, regional upward flow conditions were confirmed along the main discharge zone of the Danube. Identification of gravity as the main fluid flow driving force, as well as the hydraulic effects of heterogeneities can significantly contribute to the recognition of the risk factors regarding the vulnerability of the Buda Thermal Karst area. The research was supported by the

  16. The composition and compression of biofilms developed on ultrafiltration membranes determine hydraulic biofilm resistance.

    Science.gov (United States)

    Derlon, Nicolas; Grütter, Alexander; Brandenberger, Fabienne; Sutter, Anja; Kuhlicke, Ute; Neu, Thomas R; Morgenroth, Eberhard

    2016-10-01

    This study aimed at identifying how to improve the level of permeate flux stabilisation during gravity-driven membrane filtration without control of biofilm formation. The focus was therefore on understanding (i) how the different fractions of the biofilms (inorganics particles, bacterial cells, EPS matrix) influence its hydraulic resistance and (ii) how the compression of biofilms impacts its hydraulic resistance, i.e., can water head be increased to increase the level of permeate flux stabilisation. Biofilms were developed on ultrafiltration membranes at 88 and 284 cm water heads with dead-end filtration for around 50 days. A larger water head resulted in a smaller biofilm permeability (150 and 50 L m(-2) h(-1) bar(-1) for biofilms grown at 88 cm and 284 cm water head, respectively). Biofilms were mainly composed of EPS (>90% in volume). The comparison of the hydraulic resistances of biofilms to model fouling layers indicated that most of the hydraulic resistance is due to the EPS matrix. The compressibility of the biofilm was also evaluated by subjecting the biofilms to short-term (few minutes) and long-term variations of transmembrane pressures (TMP). A sudden change of TMP resulted in an instantaneous and reversible change of biofilm hydraulic resistance. A long-term change of TMP induced a slow change in the biofilm hydraulic resistance. Our results demonstrate that the response of biofilms to a TMP change has two components: an immediate variation of resistance (due to compression/relaxation) and a long-term response (linked to biofilm adaptation/growth). Our results provide relevant information about the relationship between the operating conditions in terms of TMP, the biofilm structure and composition and the resulting biofilm hydraulic resistance. These findings have practical implications for a broad range of membrane systems. Copyright © 2016 Elsevier Ltd. All rights reserved.

  17. DLC coatings for hydraulic applications

    Institute of Scientific and Technical Information of China (English)

    Luca NOBILI; Luca MAGAGNIN

    2009-01-01

    Replacement of lubricating oils with water or low-viscosity fluids is highly desirable in many industrial fields, on account of the environmental and economical advantages. Low lubricity of water might be insufficient for proper operation of hydraulic components, and diamond-like carbon(DLC) coatings are very attractive as solid lubricant films. A remote-plasma PACVD process was utilized to deposit hydrogenated DLC coatings (a-C:H) on different substrates. Microindentation measurements show that the coating hardness is around 35 GPa. Tribological behavior was evaluated by block-on-ring tests performed in water and water with alumina. The wear rate was calculated after measuring the wear volume by a laser profilemeter. Morphological and compositional analysis of the wear tracks reveal that coating failure may occur by abrasive wear or delamination, depending on the substrate properties. Hard and smooth substrates give the best results and dispersed alumina particles increase the wear rate.

  18. Aircraft Hydraulic Systems Dynamic Analysis

    Science.gov (United States)

    1978-10-01

    4400 PSIG OUTLET PRESSURE ~’f UM5 S1 l .( FIF ~0RV lR 1 .I. AP (c R (V) IFWM) APPROX C ASE !VPý :iI S ReUN N•;MRF.. r p kN i t, isI A! f IN, I:E • ’l...and 1F.GI pump modelo were assumed from data supplied by CECO. 165 _ -- --- - SECTION V HYDRAULIC MOTOR MODEL DEVELOPMENT AND VERIFICATION A fixed...3 70 P.,0 601 ~4 M24.0 3 1p ’, 4 r I 1 1 ISIS 2411 APPENDIX E (CONT.) HSFR TECHNICAL MANUAL (AFAPL-TR-76-43, VOL. IV) 4.15 VANE PU`MP SUBROUTINE 4.15A

  19. On Cracking of Charged Anisotropic Polytropes

    CERN Document Server

    Azam, M

    2016-01-01

    Recently in \\cite{34}, the role of electromagnetic field on the cracking of spherical polytropes has been investigated without perturbing charge parameter explicitly. In this study, we have examined the occurrence of cracking of anisotropic spherical polytropes through perturbing parameters like anisotropic pressure, energy density and charge. We consider two different types of polytropes in this study. We discuss the occurrence of cracking in two different ways $(i)$ by perturbing polytropic constant, anisotropy and charge parameter $(ii)$ by perturbing polytropic index, anisotropy and charge parameter for each case. We conclude that cracking appears for a wide range of parameters in both cases. Also, our results are reduced to \\cite{33} in the absence of charge.

  20. Struggling with Fitzgerald's "Crack-Up" Essays.

    Science.gov (United States)

    Fulcher, James

    1998-01-01

    Ponders F. Scott Fitzgerald's essays about his "crack-up" and relates them to the many complex aspects of the struggles of a teacher using post-structural literary theory and teaching two-year college students. (SR)

  1. The Effect of Water on Crack Interaction

    Science.gov (United States)

    Gaede, O.; Regenauer-Lieb, K.

    2009-04-01

    While the mechanical coupling between pore fluid and solid phase is relatively well understood, quantitative studies dealing with chemical-mechanical weakening in geological materials are rare. Many classical poroelastic problems can be addressed with the simple law of effective stress. Experimental studies show that the presence of a chemically active fluid can have effects that exceed the predictions of the law of effective stress. These chemical fluid-rock interactions alter the mechanical properties of the solid phase. Especially chemical-mechanical weakening has important ramifications for many areas of applied geosciences ranging from nuclear waste disposal over reservoir enhancement to fault stability. In this study, we model chemically induced changes of the size of the process zone around a crack tip. The knowledge of the process zone size is used to extend existing effective medium approximations of cracked solids. The stress distribution around a crack leads to a chemical potential gradient. This gradient will be a driver for mass diffusion through the solid phase. As an example, mass diffusion is towards the crack tip for a mode I crack. In this case a chemical reaction, that weakens the solid phase, will increase the size of the process zone around the crack tip. We apply our model to the prominent hydrolytic weakening effect observed in the quartz-water system (Griggs and Blacic, 1965). Hydrolytic weakening is generally attributed to water hydrolyzing the strong Si-O bonds of the quartz crystal. The hydrolysis replaces a Si-O-Si bridge with a relatively weak hydrogen bridge between two silanol groups. This enhances dislocation mobility and hence the yield stress is reduced. The plastic process zone around a crack tip is therefore larger in a wet crystal than in a dry crystal. We calculate the size of the process zone by solving this coupled mechanical-chemical problem with the Finite Element code ABAQUS. We consider single crack, collinear crack and

  2. Inner Crack Detection Method for Cantilever Beams

    Science.gov (United States)

    Li, Zheng; Zhang, Wei; Li, Yixuan; Su, Xianyue

    2008-02-01

    In this paper, continuous wavelet transform has been performed to extract the inner crack information from the guided waves in cantilever beams, and the location and size of crack can be detected exactly. Considering its best time-frequency property, Gabor continuous wavelet transform is employed to analyze the complicated flexible wave signals in cantilever beam, which is inspirited by an impact on the free end. Otherwise, in order to enhance the sensitivity of detection for some small cracks, an improved method is discussed. Here, both computational and experimental methods are carried out for comparing the influence of different crack location in beam. Therefore, the method proposed can be expected to expand to a powerful damage detection method in a broad engineering application.

  3. Initiating, growing and cracking of hydrogen blisters

    Institute of Scientific and Technical Information of China (English)

    REN Xuechong; SHAN Guangbin; CHU Wuyang; SU Yanjing; GAO Kewei; QIAO Lijie; JIANG Bo; CHEN Gang; CUI Yinhui

    2005-01-01

    The growing process of a hydrogen blister in a wheel steel was observed in situ with an optical microscope, and the fracture surfaces formed from broken blisters on a wheel steel and bulk metallic glass were investigated. The initiating, growing, cracking and breaking of hydrogen blisters are as follows. Supersaturated vacancies can increase greatly during charging and gather together into a vacancy cluster (small cavity). Hydrogen atoms become hydrogen molecules in the vacancy cluster and hydrogen molecules can stabilize the vacancy cluster. The small cavity becomes the nucleus of hydrogen blister. The blister will grow with entering of vacancies and hydrogen atoms. With increasing hydrogen pressure, plastic deformation occurs first, the hydrogen blister near the surface extrudes, and then cracks initiate along the wall of the blister with further increasing hydrogen pressure. A cracked blister can grow further through propagating of cracks until it breaks.

  4. Dynamic Strain and Crack Monitoring Sensor Project

    Data.gov (United States)

    National Aeronautics and Space Administration — Los Gatos Research proposes to develop a new automated vehicle health monitoring sensor system capable of measuring loads and detecting crack, corrosion, and...

  5. Finite Element Analysis of the Effect of Crack Depth and Crack Opening On the Girder

    Directory of Open Access Journals (Sweden)

    Md. Kamrul Hassan

    2011-01-01

    Full Text Available In order to identify the effect of crack depth and opening on the girder, finite element method (FEM has been used in this paper. In FE analysis, six nodded two dimensional plane elements (PLANE-2 are considered. Each node has two degree of freedom such as UX and UY. For the plane elements, a plane stress width/thickness option is chosen. For analytical model of crack of the concrete bridge girder, crack opening was increased from 0.2 mm to 1mm at an interval 0.2 mm and crack depth also increased from 30 mm to 150 mm at an interval 30 mm. The models were discreatized by a triangular mesh and convergence test was executed to obtain satisfactory results from the Plane-2 element. From the numerical result, it is seen that the principal stress become a higher with increased the crack depth and also crack opening with respect to load increasing. But the crack depth at 90 mm and crack opening at 0.6 mm, it has more effect on the girder because the stress concentration is higher than other crack depth and opening.

  6. Calculation of the crack tip opening displacement of a crack lying in a subsurface layer

    Science.gov (United States)

    Higashida, Y.; Kamada, K.

    1985-11-01

    Crack tip opening displacement of a crack lying parallel to a free surface is calculated by counting the number of dislocations emitted into the plastic zone from a crack tip. A discrete dislocation model was used to simulate the crack, while varying the strength of dislocations so as to satisfy the boundary condition. The result coincides numerically with the predictions made in a previous paper, in which the stress intensity factor appearing in a theory of bulk materials was replaced with the one which includes the surface correction.

  7. Crack Closure Effects on Fatigue Crack Propagation Rates: Application of a Proposed Theoretical Model

    Directory of Open Access Journals (Sweden)

    José A. F. O. Correia

    2016-01-01

    Full Text Available Structural design taking into account fatigue damage requires a thorough knowledge of the behaviour of materials. In addition to the monotonic behaviour of the materials, it is also important to assess their cyclic response and fatigue crack propagation behaviour under constant and variable amplitude loading. Materials whenever subjected to fatigue cracking may exhibit mean stress effects as well as crack closure effects. In this paper, a theoretical model based on the same initial assumptions of the analytical models proposed by Hudak and Davidson and Ellyin is proposed to estimate the influence of the crack closure effects. This proposal based further on Walker’s propagation law was applied to the P355NL1 steel using an inverse analysis (back-extrapolation of experimental fatigue crack propagation results. Based on this proposed model it is possible to estimate the crack opening stress intensity factor, Kop, the relationship between U=ΔKeff/ΔK quantity and the stress intensity factor, the crack length, and the stress ratio. This allows the evaluation of the influence of the crack closure effects for different stress ratio levels, in the fatigue crack propagation rates. Finally, a good agreement is found between the proposed theoretical model and the analytical models presented in the literature.

  8. Hydration Process and Crack Tendency of Concrete Based on Resistivity and Restrained Shrinkage Crack

    Institute of Scientific and Technical Information of China (English)

    MUAZU Bawa Samaila; WEI Xiaosheng; WANG Lei

    2016-01-01

    Hydration process, crack potential and setting time of concrete grade C30, C40 and C50 were monitored by using a non-contact electrical resistivity apparatus, a novel plastic ring mould and penetration resistance methods, respectively. The results show the highest resistivity of C30 at the early stage until a point when C50 accelerated and overtook the others. It has been experimentally conifrmed that the crossing point of C30 and C50 corresponds to the ifnal setting time of C50. From resistivity derivative curve, four different stages were observed upon which the hydration process is classiifed; these are dissolution, induction, acceleration and deceleration periods. Consequently, restrained shrinkage crack and setting time results demonstrated that C50 set and cracked the earliest. The cracking time of all the samples occurred within a reasonable experimental period thus the novel plastic ring is a convenient method for predicting concrete’s crack potential. The highest inlfection time (ti) obtained from resistivity curve and the ifnal setting time (tf) were used with crack time (tc) in coming up with mathematical models for the prediction of concrete’s cracking age for the range of concrete grade considered. Finally, an ANSYS numerical simulation supports the experimental ifndings in terms of the earliest crack age of C50 and the crack location.

  9. Impact of hydraulic perforation on fracture initiation and propagation in shale rocks

    Institute of Scientific and Technical Information of China (English)

    ZHAO Xi; JU Yang; YANG Yong; SU Sun; GONG WenBo

    2016-01-01

    To enhance the oil and gas recovery rate,hydraulic fracturing techniques have been widely adopted for stimulation of low-permeability reservoirs.Pioneering work indicates that hydraulic perforation and layout could significantly affect fracture initiation and propagation in low-permeability reservoir rocks subjected to complex in-situ stresses.This paper reports on a novel numerical method that incorporates fracture mechanics principles and the numerical tools FRANC3D and ANSYS to investigate the three-dimensional initiation and propagation behavior of hydro-fracturing cracks in shale rock.Considering the transverse isotropic property of shale rocks,the mechanical parameters of reservoir rocks attained from laboratory tests were adopted in the simulation.The influence of perforation layouts on the 3D initiation of hydro-fracturing fractures in reservoir rocks under geo-stresses was quantitatively illuminated.The propagation and growth of fractures in three dimensions in different perforating azimuth values were illustrated.The results indicate that:1) the optimal perforation direction should be parallel to the maximum horizontal principal stress,2) the crack plane gradually turns toward the direction of the maximum horizontal principal stress when they are not in parallel,3) compared with the linear and symmetric pattern,the staggered perforation is the optimal one,4) the proper perforation density is four to six holes per meter,5) the optimal perforation diameter in this model is 30 mm,and 6) the influence of the perforation depth on the fracture initiation pressure is low.

  10. Molecular dynamics simulation of propagating cracks

    Science.gov (United States)

    Mullins, M.

    1982-01-01

    Steady state crack propagation is investigated numerically using a model consisting of 236 free atoms in two (010) planes of bcc alpha iron. The continuum region is modeled using the finite element method with 175 nodes and 288 elements. The model shows clear (010) plane fracture to the edge of the discrete region at moderate loads. Analysis of the results obtained indicates that models of this type can provide realistic simulation of steady state crack propagation.

  11. Fatigue Crack Initiation Analysis in 1060 Steel

    Directory of Open Access Journals (Sweden)

    L. Gyansah

    2010-07-01

    Full Text Available This study investigates initiation of small cracks on dumble-shaped plate type specimens of 1060steel at the load ratio of R = 0 under varied cyclic stress amplitudes between 0.6 and 1.0 of yield stress usingthe Instron machine (model: 8501. Sinusoidal wave of a frequency of 10 Hz was used in the experiment. Theexperiment was conducted at a room temperature of 23ºC. Each test for different applied stress ranges wascarried out for 2×104 cycles. Microstructure and fractography of the fractured specimen were also analyzed.Nucleations of cracks were observed at Ferrite-Ferrite G rain Boundary (FFGB as well as inside Ferrite GrainBody (FGB, but the FFGB location was preferred. Results show that the average length of FFGB cracks isfound larger than that of the average length of cracks initiated inside FGB at the same cyclic loading conditions.The formation of slip band inside grain body, slip band impingement at grain boundary and elastic-plasticincompatibility synergistically have significant influence on fatigue crack initiation in 1060 steel. Additionally,the formation of irregular voids inside slip bands, initiation and growth of small voids at grain boundary andthe subsequent joining of these with other voids were seen as specific characteristics of 1060 steel. It was alsoestablished that cracks nucleate both at grain boundary and inside grain body in 1060 steel in the investigateddomain of 0.6 to 1.0Fy.It was further established that the orientation of the grain body cracks at low stress levelis greater than 45º and the average angle of orientation of these cracks increases like that of grain boundarycracks with increased magnitude of stress range.

  12. Molecular dynamics simulation of propagating cracks

    Science.gov (United States)

    Mullins, M.

    1982-01-01

    Steady state crack propagation is investigated numerically using a model consisting of 236 free atoms in two (010) planes of bcc alpha iron. The continuum region is modeled using the finite element method with 175 nodes and 288 elements. The model shows clear (010) plane fracture to the edge of the discrete region at moderate loads. Analysis of the results obtained indicates that models of this type can provide realistic simulation of steady state crack propagation.

  13. Atomistic observation of a crack tip approaching coherent twin boundaries.

    Science.gov (United States)

    Liu, L; Wang, J; Gong, S K; Mao, S X

    2014-03-18

    Coherent twin boundaries (CTBs) in nano-twinned materials could improve crack resistance. However, the role of the CTBs during crack penetration has never been explored at atomic scale. Our in situ observation on nano-twinned Ag under a high resolution transmission electron microscope (HRTEM) reveals the dynamic processes of a crack penetration across the CTBs, which involve alternated crack tip blunting, crack deflection, twinning/detwinning and slip transmission across the CTBs. The alternated blunting processes are related to the emission of different types of dislocations at the crack tip and vary with the distance of the crack tip from the CTBs.

  14. Crack shape analysis of PWSCC in S/G tubings

    Energy Technology Data Exchange (ETDEWEB)

    Park, I. K. [Sunmon Univ., Chonan (Korea, Republic of)

    2000-10-01

    Crack shape of PWSCC was analyzed, based on the fractured pulled-out S/G tubings of Ulchin-1 steam generator. The shape of the cracks in kiss roll transitions was elliptical shape for short cracks, and car shape for long cracks with flat crack front. The bulging was observed under the inner wall after shot-peening. Crack shape change after shot-peening was resulted from the crack growth restraint in axial direction due to compressive residual stresses on the primary side surface.

  15. Thermally activated processes of fatigue crack growth in steels

    Science.gov (United States)

    Tanaka, Masaki; Fujii, Atsushi; Noguchi, Hiroshi; Higashida, Kenji

    2014-02-01

    Fatigue crack growth rates in steels at high and low temperatures have been investigated using Paris curves. The fatigue crack growth rates at high temperatures are quite different from those at low temperatures. Arrhenius plots between fatigue crack growth rate (da/dN) and test temperatures at constant stress intensity factor range (ΔKI) indicate a difference of the rate-controlling process for fatigue crack growth with temperature. Slip deformation at the crack tip governs fatigue crack growth at high temperatures, while hydrogen diffusion is associated with crack growth at low temperatures.

  16. Subcritical crack growth and mechanical weathering: a new consideration of how moisture influences rock erosion rates.

    Science.gov (United States)

    Eppes, Martha-Cary; Keanini, Russell; Hancock, Gregory S.

    2016-04-01

    The contributions of moisture to the mechanical aspects of rock weathering and regolith production are poorly quantified. In particular, geomorphologists have largely overlooked the role of subcritical crack growth processes in physical weathering and the fact that moisture strongly influences the rates of those processes. This influence is irrespective of the function that moisture plays in stress loading mechanisms like freezing or hydration. Here we present a simple numerical model that explores the efficacy of subcritical crack growth in granite rock subaerially exposed under a range of moisture conditions. Because most weathering-related stress loading for rocks found at, or near, Earth's surface (hereafter surface rocks) is cyclic, we modeled crack growth using a novel combination of Paris' Law and Charles' Law. This combination allowed us to apply existing empirically-derived data for the stress corrosion index of Charles' Law to fatigue cracking. For stress, we focused on the relatively straightforward case of intergranular stresses that arise during solar-induced thermal cycling by conductive heat transfer, making the assumption that such stresses represent a universal minimum weathering stress experienced by all surface rocks. Because all other tensile weathering-related stresses would be additive in the context of crack growth, however, our model can be adapted to include other stress loading mechanisms. We validated our calculations using recently published thermal-stress-induced cracking rates. Our results demonstrate that 1) weathering-induced stresses as modeled herein, and as published by others, are sufficient to propagate fractures subcritically over long timescales with or without the presence of water 2) fracture propagation rates increase exponentially with respect to moisture, specifically relative humidity 3) fracture propagation rates driven by thermal cycling are strongly dependent on the magnitude of diurnal temperature ranges and the

  17. Hierarchical Formation of Intrasplat Cracks in Thermal Spray Ceramic Coatings

    Science.gov (United States)

    Chen, Lin; Yang, Guan-Jun; Li, Cheng-Xin; Li, Chang-Jiu

    2016-06-01

    Intrasplat cracks, an essential feature of thermally sprayed ceramic coatings, play important roles in determining coating properties. However, final intrasplat crack patterns are always considered to be disordered and irregular, resulting from random cracking during splat cooling, since the detailed formation process of intrasplat cracks has scarcely been considered. In the present study, the primary formation mechanism for intrasplat cracking was explored based on both experimental observations and mechanical analysis. The results show that the intrasplat crack pattern in thermally sprayed ceramic splats presents a hierarchical structure with four sides and six neighbors, indicating that intrasplat crack patterns arise from successive domain divisions due to sequential cracking during splat cooling. The driving forces for intrasplat cracking are discussed, and the experimental data quantitatively agree well with theoretical results. This will provide insight for further coating structure designs and tailoring by tuning of intrasplat cracks.

  18. Electromagnetic pulsed thermography for natural cracks inspection

    Science.gov (United States)

    Gao, Yunlai; Tian, Gui Yun; Wang, Ping; Wang, Haitao; Gao, Bin; Woo, Wai Lok; Li, Kongjing

    2017-02-01

    Emerging integrated sensing and monitoring of material degradation and cracks are increasingly required for characterizing the structural integrity and safety of infrastructure. However, most conventional nondestructive evaluation (NDE) methods are based on single modality sensing which is not adequate to evaluate structural integrity and natural cracks. This paper proposed electromagnetic pulsed thermography for fast and comprehensive defect characterization. It hybrids multiple physical phenomena i.e. magnetic flux leakage, induced eddy current and induction heating linking to physics as well as signal processing algorithms to provide abundant information of material properties and defects. New features are proposed using 1st derivation that reflects multiphysics spatial and temporal behaviors to enhance the detection of cracks with different orientations. Promising results that robust to lift-off changes and invariant features for artificial and natural cracks detection have been demonstrated that the proposed method significantly improves defect detectability. It opens up multiphysics sensing and integrated NDE with potential impact for natural understanding and better quantitative evaluation of natural cracks including stress corrosion crack (SCC) and rolling contact fatigue (RCF).

  19. Nonlinear modal methods for crack localization

    Science.gov (United States)

    Sutin, Alexander; Ostrovsky, Lev; Lebedev, Andrey

    2003-10-01

    A nonlinear method for locating defects in solid materials is discussed that is relevant to nonlinear modal tomography based on the signal cross-modulation. The scheme is illustrated by a theoretical model in which a thin plate or bar with a single crack is excited by a strong low-frequency wave and a high-frequency probing wave (ultrasound). A crack is considered as a small contact-type defect which does not perturb the modal structure of sound in linear approximation but creates combinational-frequency components whose amplitudes depend on their closeness to a resonance and crack position. Using different crack models, including the hysteretic ones, the nonlinear part of its volume variations under the given stress and then the combinational wave components in the bar can be determined. Evidently, their amplitude depends strongly on the crack position with respect to the peaks or nodes of the corresponding linear signals which can be used for localization of the crack position. Exciting the sample by sweeping ultrasound frequencies through several resonances (modes) reduces the ambiguity in the localization. Some aspects of inverse problem solution are also discussed, and preliminary experimental results are presented.

  20. Electromagnetic pulsed thermography for natural cracks inspection

    Science.gov (United States)

    Gao, Yunlai; Tian, Gui Yun; Wang, Ping; Wang, Haitao; Gao, Bin; Woo, Wai Lok; Li, Kongjing

    2017-01-01

    Emerging integrated sensing and monitoring of material degradation and cracks are increasingly required for characterizing the structural integrity and safety of infrastructure. However, most conventional nondestructive evaluation (NDE) methods are based on single modality sensing which is not adequate to evaluate structural integrity and natural cracks. This paper proposed electromagnetic pulsed thermography for fast and comprehensive defect characterization. It hybrids multiple physical phenomena i.e. magnetic flux leakage, induced eddy current and induction heating linking to physics as well as signal processing algorithms to provide abundant information of material properties and defects. New features are proposed using 1st derivation that reflects multiphysics spatial and temporal behaviors to enhance the detection of cracks with different orientations. Promising results that robust to lift-off changes and invariant features for artificial and natural cracks detection have been demonstrated that the proposed method significantly improves defect detectability. It opens up multiphysics sensing and integrated NDE with potential impact for natural understanding and better quantitative evaluation of natural cracks including stress corrosion crack (SCC) and rolling contact fatigue (RCF). PMID:28169361

  1. Dynamic behaviour of a rotating cracked beam

    Science.gov (United States)

    Yashar, Ahmed; Ghandchi-Tehrani, Maryam; Ferguson, Neil

    2016-09-01

    This paper presents a new approach to investigate and analyse the vibrational behaviour of cracked rotating cantilever beams, which can for example represent helicopter or wind turbine blades. The analytical Hamiltonian method is used in modelling the rotating beam and two numerical methods, the Rayleigh-Ritz and FEM, are used to study the natural frequencies and the mode shapes of the intact rotating beams. Subsequently, a crack is introduced into the FE model and simulations are performed to identify the modal characteristics for an open cracked rotating beam. The effect of various parameters such as non-dimensional rotating speed, hub ratio and slenderness ratio are investigated for both the intact and the cracked rotating beam, and in both directions of chordwise and flapwise motion. The veering phenomena in the natural frequencies as a function of the rotational speed and the buckling speed are considered with respect to the slenderness ratio. In addition, the mode shapes obtained for the flapwise vibration are compared using the modal assurance criterion (MAC). Finally, a new three dimensional design chart is produced, showing the effect of crack location and depth on the natural frequencies of the rotating beam. This chart will be subsequently important in identifying crack defects in rotating blades.

  2. Protection of brittle film against cracking

    Science.gov (United States)

    Musil, J.; Sklenka, J.; Čerstvý, R.

    2016-05-01

    This article reports on the protection of the brittle Zrsbnd Sisbnd O film against cracking in bending by the highly elastic top film (over-layer). In experiments the Zrsbnd Sisbnd O films with different elemental composition and structure were used. Both the brittle and highly elastic films were prepared by magnetron sputtering using a dual magnetron. The brittle film easily cracks in bending. On the other hand, the highly elastic film exhibits enhanced resistance to cracking in bending. Main characteristic parameters of both the brittle and highly elastic films are given. Special attention is devoted to the effect of the structure (crystalline, amorphous) of both the brittle and highly elastic top film on the resistance of cracking of the brittle film. It was found that (1) both the X-ray amorphous and crystalline brittle films easily crack in bending, (2) the highly elastic film can have either X-ray amorphous or crystalline structure and (3) both the X-ray amorphous and crystalline, highly elastic top films perfectly protect the brittle films against cracking in bending. The structure, mechanical properties and optical transparency of the brittle and highly elastic sputtered Zrsbnd Sisbnd O films are described in detail. At the end of this article, the principle of the low-temperature formation of the highly elastic films is also explained.

  3. Fatigue crack propagation analysis of plaque rupture.

    Science.gov (United States)

    Pei, Xuan; Wu, Baijian; Li, Zhi-Yong

    2013-10-01

    Rupture of atheromatous plaque is the major cause of stroke or heart attack. Considering that the cardiovascular system is a classic fatigue environment, plaque rupture was treated as a chronic fatigue crack growth process in this study. Fracture mechanics theory was introduced to describe the stress status at the crack tip and Paris' law was used to calculate the crack growth rate. The effect of anatomical variation of an idealized plaque cross-section model was investigated. The crack initiation was considered to be either at the maximum circumferential stress location or at any other possible locations around the lumen. Although the crack automatically initialized at the maximum circumferential stress location usually propagated faster than others, it was not necessarily the most critical location where the fatigue life reached its minimum. We found that the fatigue life was minimum for cracks initialized in the following three regions: the midcap zone, the shoulder zone, and the backside zone. The anatomical variation has a significant influence on the fatigue life. Either a decrease in cap thickness or an increase in lipid pool size resulted in a significant decrease in fatigue life. Comparing to the previously used stress analysis, this fatigue model provides some possible explanations of plaque rupture at a low stress level in a pulsatile cardiovascular environment, and the method proposed here may be useful for further investigation of the mechanism of plaque rupture based on in vivo patient data.

  4. Permeability, storage and hydraulic diffusivity controlled by earthquakes

    Science.gov (United States)

    Brodsky, E. E.; Fulton, P. M.; Xue, L.

    2016-12-01

    Earthquakes can increase permeability in fractured rocks. In the farfield, such permeability increases are attributed to seismic waves and can last for months after the initial earthquake. Laboratory studies suggest that unclogging of fractures by the transient flow driven by seismic waves is a viable mechanism. These dynamic permeability increases may contribute to permeability enhancement in the seismic clouds accompanying hydraulic fracking. Permeability enhancement by seismic waves could potentially be engineered and the experiments suggest the process will be most effective at a preferred frequency. We have recently observed similar processes inside active fault zones after major earthquakes. A borehole observatory in the fault that generated the M9.0 2011 Tohoku earthquake reveals a sequence of temperature pulses during the secondary aftershock sequence of an M7.3 aftershock. The pulses are attributed to fluid advection by a flow through a zone of transiently increased permeability. Directly after the M7.3 earthquake, the newly damaged fault zone is highly susceptible to further permeability enhancement, but ultimately heals within a month and becomes no longer as sensitive. The observation suggests that the newly damaged fault zone is more prone to fluid pulsing than would be expected based on the long-term permeability structure. Even longer term healing is seen inside the fault zone of the 2008 M7.9 Wenchuan earthquake. The competition between damage and healing (or clogging and unclogging) results in dynamically controlled permeability, storage and hydraulic diffusivity. Recent measurements of in situ fault zone architecture at the 1-10 meter scale suggest that active fault zones often have hydraulic diffusivities near 10-2 m2/s. This uniformity is true even within the damage zone of the San Andreas fault where permeability and storage increases balance each other to achieve this value of diffusivity over a 400 m wide region. We speculate that fault zones

  5. Evolution of neural networks for the prediction of hydraulic conductivity as a function of borehole geophysical logs: Shobasama site, Japan.

    Energy Technology Data Exchange (ETDEWEB)

    Reeves, Paul C.; McKenna, Sean Andrew

    2004-06-01

    This report describes the methodology and results of a project to develop a neural network for the prediction of the measured hydraulic conductivity or transmissivity in a series of boreholes at the Tono, Japan study site. Geophysical measurements were used as the input to EL feed-forward neural network. A simple genetic algorithm was used to evolve the architecture and parameters of the neural network in conjunction with an optimal subset of geophysical measurements for the prediction of hydraulic conductivity. The first attempt was focused on the estimation of the class of the hydraulic conductivity, high, medium or low, from the geophysical logs. This estimation was done while using the genetic algorithm to simultaneously determine which geophysical logs were the most important and optimizing the architecture of the neural network. Initial results showed that certain geophysical logs provided more information than others- most notably the 'short-normal', micro-resistivity, porosity and sonic logs provided the most information on hydraulic conductivity. The neural network produced excellent training results with accuracy of 90 percent or greater, but was unable to produce accurate predictions of the hydraulic conductivity class. The second attempt at prediction was done using a new methodology and a modified data set. The new methodology builds on the results of the first attempts at prediction by limiting the choices of geophysical logs to only those that provide significant information. Additionally, this second attempt uses a modified data set and predicts transmissivity instead of hydraulic conductivity. Results of these simulations indicate that the most informative geophysical measurements for the prediction of transmissivity are depth and sonic log. The long normal resistivity and self potential borehole logs are moderately informative. In addition, it was found that porosity and crack counts (clear, open, or hairline) do not inform predictions

  6. Stress corrosion cracking of copper canisters

    Energy Technology Data Exchange (ETDEWEB)

    King, Fraser (Integrity Corrosion Consulting Limited (Canada)); Newman, Roger (Univ. of Toronto (Canada))

    2010-12-15

    A critical review is presented of the possibility of stress corrosion cracking (SCC) of copper canisters in a deep geological repository in the Fennoscandian Shield. Each of the four main mechanisms proposed for the SCC of pure copper are reviewed and the required conditions for cracking compared with the expected environmental and mechanical loading conditions within the repository. Other possible mechanisms are also considered, as are recent studies specifically directed towards the SCC of copper canisters. The aim of the review is to determine if and when during the evolution of the repository environment copper canisters might be susceptible to SCC. Mechanisms that require a degree of oxidation or dissolution are only possible whilst oxidant is present in the repository and then only if other environmental and mechanical loading conditions are satisfied. These constraints are found to limit the period during which the canisters could be susceptible to cracking via film rupture (slip dissolution) or tarnish rupture mechanisms to the first few years after deposition of the canisters, at which time there will be insufficient SCC agent (ammonia, acetate, or nitrite) to support cracking. During the anaerobic phase, the supply of sulphide ions to the free surface will be transport limited by diffusion through the highly compacted bentonite. Therefore, no HS. will enter the crack and cracking by either of these mechanisms during the long term anaerobic phase is not feasible. Cracking via the film-induced cleavage mechanism requires a surface film of specific properties, most often associated with a nano porous structure. Slow rates of dissolution characteristic of processes in the repository will tend to coarsen any nano porous layer. Under some circumstances, a cuprous oxide film could support film-induced cleavage, but there is no evidence that this mechanism would operate in the presence of sulphide during the long-term anaerobic period because copper sulphide

  7. Experimental and analytical study of creep cracks damage in high temperature sodium plant branch connections

    Energy Technology Data Exchange (ETDEWEB)

    Corsi, F.; Fabi, A.; Di Giamberardino, P.; Botti, G.; Pasquale, G.; Dapor, V.

    1989-05-01

    A brief description of the operating conditions of the ESPRESSO sodium plant is given. The structural integrity problems of some ''T'' branch connections in the sodium plant are then presented. During a thermal cycling test a hydraulic packing loss is pointed out by a small amount of sodium leakage. Radiographic examinations revealed both a crack in the entire thickness and second partial crack in another branch connection. A series of technological tests was executed in which the presence of the cracks clearly indicated creep damage. To clarify the structural reliability of the most critical components a theoretical analysis of creep damage for the two branch connections was performed in detail. For this aim both elastic and inelastic analyses were carried out, with the general purpose CASTEM system developed at CEA Saclay, to determine the stress fields of the two components. The study tried to take into account the effects of the residual welding stresses in the creep regime. The main conclusions concerning the applications of the different existing rules are presented and compared. (orig./HP).

  8. FINITE ELEMENT ANALYSIS OF CENTRIFUGAL PUMP CASINGS TO DETECT THE CRACK AT THE TONGUE REGION.

    Directory of Open Access Journals (Sweden)

    Ramana Podugu

    2011-09-01

    Full Text Available The objective of this paper is to identify one of the reasons for the crack to initiate at the tongue region. The design of the tongue region of the centrifugal pump casing plays an important role in influencing the pump performance and cavitation. Tongue region should have enough strength to withstand against repeated loads imparted by the impeller. Crack at the tongue region is examined under hydrostatic pressure conditions .Practically, at the site location it was observed that the crack was formed at the tongue region when the casing was tested under hydrostatic pressure. Static linear analysis is performed to identify the critical zone where the maximum stress occurs that causes failure. Maximum stress is observed at the tongue region. To reduce the maximum stress, ribs thickness was increased in addition to increasing the portion of the volute thickness. Geometrical modifications are suggested in such a way that there is no effect on the hydraulic performance and to avoid increase in manufacturing cost. Stress distribution of the centrifugal pump casing volute is simulated using finite element software like Ansys. In this paper an attempt was made to validate finite element analysisresults with test conditions and found good concurrence between FEA results and theoretical results.

  9. A discontinuous finite element approach to cracking in coupled poro-elastic fluid flow models

    Science.gov (United States)

    Wilson, C. R.; Spiegelman, M. W.; Evans, O.; Ulven, O. I.; Sun, W.

    2016-12-01

    Reaction-driven cracking is a coupled process whereby fluid-induced reactions drive large volume changes in the host rock which produce stresses leading to crack propagation and failure. This in turn generates new surface area and fluid-flow pathways for subsequent reaction in a potentially self-sustaining system. This mechanism has has been proposed for the pervasive serpentinization and carbonation of peridotite, as well as applications to mineral carbon sequestration and hydrocarbon extraction. The key computational issue in this problem is implementing algorithms that adequately model the formation of discrete fractures. Here we present models using a discontinuous finite element method for modeling fracture formation (Radovitsky et al., 2011). Cracks are introduced along facets of the mesh by the relaxation of penalty parameters once a failure criterion is met. It is fully described in the weak form of the equations, requiring no modification of the underlying mesh structure and allowing fluid properties to be easily adjusted along cracked facets. To develop and test the method, we start by implementing the algorithm for the simplified Biot equations for poro-elasticity using the finite element model assembler TerraFERMA. We consider hydro-fracking around a borehole (Grassl et al., 2015), where elevated fluid pressure in the poro-elastic solid causes it to fail radially in tension. We investigate the effects of varying the Biot coefficient and adjusting the fluid transport properties in the vicinity of the crack and compare our results to related dual-graph models (Ulven & Sun, submitted). We discuss issues arising from this method, including the formation of null spaces and appropriate preconditioning and solution strategies. Initial results suggest that this method provides a promising way to incorporate cracking into our reactive fluid flow models and future work aims to integrate the mechanical and chemical aspects of this process.

  10. Mobile platform for hydraulic turbine blade repair robot

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    The wall-climbing mobile platform (MP) of a robot for repairing a hydraulic turbine blade onsite is developed.The MP is equipped with ferromagnetic adhesive devices and can work on a spatial curved surface.The contradiction between mobility and load-bearing ability is analyzed,and the problem of self-adaptation to the curved face is solved using differential-driven wheeled locomotion with ferromagnetic adhesive devices.The platform adheres to the blade surface through the force provided by the ferromagnetic devices,and a certain gap exists between the magnetic devices and the blade's surface.A mechanism of three revolution degrees of freedom,which connects the magnetic devices with the platform's chassis,is developed to make the platform self-adapt to the complex curved surface of the turbine blade.A proofof-principle prototype has been manufactured,and experiments prove the success of the MP.The payload of the zero-turn-radius MP with excellent maneuverability exceeds 80 kg.The platform can automatically adapt to complex spatial surfaces,which satisfy the requirements of a hydraulic turbine blade in-situ repair robot.

  11. In-Plant Testing of High-Efficiency Hydraulic Separators

    Energy Technology Data Exchange (ETDEWEB)

    G. H. Luttrell; R. Q. Honaker; R. C. Bratton; T. C. Westerfield; J. N. Kohmuench

    2006-06-30

    Hydraulic separators are commonly used for particle size classification and gravity concentration of minerals and coal. Unfortunately, the efficiency of these processes can be quite low due to poor equipment design and variations in feed consistency. To help alleviate these problems, an industry-driven R&D program has been undertaken to develop a new generation of hydraulic separators that are more efficient and less costly to operate and maintain. These units, which are commercially called the CrossFlow separator and HydroFloat separator, have the potential to improve performance (separation efficiency and throughput) and reduce operating costs (power consumption, water and reagent usage). In Phase I of this project, laboratory and pilot-scale test units were evaluated at various industrial sites in both the coal and mineral industries. Based on promising results obtained from Phase I, full-scale prototypes were purchased and installed by a major U.S. phosphate producer and a large eastern U.S. coal company. The test data obtained from these sites demonstrate that significant performance improvements can be realized through the application of these high-efficiency separators.

  12. IN-PLANT TESTING OF HIGH-EFFICIENCY HYDRAULIC SEPARATORS

    Energy Technology Data Exchange (ETDEWEB)

    G.H. Luttrell; R.Q. Honaker; R.C. Bratton; T.C. Westerfield; J.N. Kohmuench

    2006-05-22

    Hydraulic separators are commonly used for particle size classification and gravity concentration of minerals and coal. Unfortunately, the efficiency of these processes can be quite low due to poor equipment design and variations in feed consistency. To help alleviate these problems, an industry-driven R&D program has been undertaken to develop a new generation of hydraulic separators that are more efficient and less costly to operate and maintain. These units, which are commercially called the CrossFlow separator and HydroFloat separator, have the potential to improve performance (separation efficiency and throughput) and reduce operating costs (power consumption, water and reagent usage). In Phase I of this project, laboratory and pilot-scale test units were evaluated at various industrial sites in both the coal and mineral industries. Based on promising results obtained from Phase I, full-scale prototypes were purchased and installed by a major U.S. phosphate producer and a large eastern U.S. coal company. The test data obtained from these sites demonstrate that significant performance improvements can be realized through the application of these high-efficiency separators.

  13. Thermal-hydraulic modeling needs for passive reactors

    Energy Technology Data Exchange (ETDEWEB)

    Kelly, J.M. [Nuclear Regulatory Commission, Washington, DC (United States)

    1997-07-01

    The U.S. Nuclear Regulatory Commission has received an application for design certification from the Westinghouse Electric Corporation for an Advanced Light Water Reactor design known as the AP600. As part of the design certification process, the USNRC uses its thermal-hydraulic system analysis codes to independently audit the vendor calculations. The focus of this effort has been the small break LOCA transients that rely upon the passive safety features of the design to depressurize the primary system sufficiently so that gravity driven injection can provide a stable source for long term cooling. Of course, large break LOCAs have also been considered, but as the involved phenomena do not appear to be appreciably different from those of current plants, they were not discussed in this paper. Although the SBLOCA scenario does not appear to threaten core coolability - indeed, heatup is not even expected to occur - there have been concerns as to the performance of the passive safety systems. For example, the passive systems drive flows with small heads, consequently requiring more precision in the analysis compared to active systems methods for passive plants as compared to current plants with active systems. For the analysis of SBLOCAs and operating transients, the USNRC uses the RELAP5 thermal-hydraulic system analysis code. To assure the applicability of RELAP5 to the analysis of these transients for the AP600 design, a four year long program of code development and assessment has been undertaken.

  14. A Thermoelastic Hydraulic Fracture Design Tool for Geothermal Reservoir Development

    Energy Technology Data Exchange (ETDEWEB)

    Ahmad Ghassemi

    2003-06-30

    Geothermal energy is recovered by circulating water through heat exchange areas within a hot rock mass. Geothermal reservoir rock masses generally consist of igneous and metamorphic rocks that have low matrix permeability. Therefore, cracks and fractures play a significant role in extraction of geothermal energy by providing the major pathways for fluid flow and heat exchange. Thus, knowledge of conditions leading to formation of fractures and fracture networks is of paramount importance. Furthermore, in the absence of natural fractures or adequate connectivity, artificial fracture are created in the reservoir using hydraulic fracturing. At times, the practice aims to create a number of parallel fractures connecting a pair of wells. Multiple fractures are preferred because of the large size necessary when using only a single fracture. Although the basic idea is rather simple, hydraulic fracturing is a complex process involving interactions of high pressure fluid injections with a stressed hot rock mass, mechanical interaction of induced fractures with existing natural fractures, and the spatial and temporal variations of in-situ stress. As a result it is necessary to develop tools that can be used to study these interactions as an integral part of a comprehensive approach to geothermal reservoir development, particularly enhanced geothermal systems. In response to this need we have set out to develop advanced thermo-mechanical models for design of artificial fractures and rock fracture research in geothermal reservoirs. These models consider the significant hydraulic and thermo-mechanical processes and their interaction with the in-situ stress state. Wellbore failure and fracture initiation is studied using a model that fully couples poro-mechanical and thermo-mechanical effects. The fracture propagation model is based on a complex variable and regular displacement discontinuity formulations. In the complex variable approach the displacement discontinuities are

  15. Biogenic Cracks in Porous Rock

    Science.gov (United States)

    Hemmerle, A.; Hartung, J.; Hallatschek, O.; Goehring, L.; Herminghaus, S.

    2014-12-01

    Microorganisms growing on and inside porous rock may fracture it by various processes. Some of the mechanisms of biofouling and bioweathering are today identified and partially understood but most emphasis is on chemical weathering, while mechanical contributions have been neglected. However, as demonstrated by the perseverance of a seed germinating and cracking up a concrete block, the turgor pressure of living organisms can be very significant. Here, we present results of a systematic study of the effects of the mechanical forces of growing microbial populations on the weathering of porous media. We designed a model porous medium made of glass beads held together by polydimethylsiloxane (PDMS), a curable polymer. The rheological properties of the porous medium, whose shape and size are tunable, can be controlled by the ratio of crosslinker to base used in the PDMS (see Fig. 1). Glass and PDMS being inert to most chemicals, we are able to focus on the mechanical processes of biodeterioration, excluding any chemical weathering. Inspired by recent measurements of the high pressure (~0.5 Mpa) exerted by a growing population of yeasts trapped in a microfluidic device, we show that yeast cells can be cultured homogeneously within porous medium until saturation of the porous space. We investigate then the effects of such an inner pressure on the mechanical properties of the sample. Using the same model system, we study also the complex interplay between biofilms and porous media. We focus in particular on the effects of pore size on the penetration of the biofilm within the porous sample, and on the resulting deformations of the matrix, opening new perspectives into the understanding of life in complex geometry. Figure 1. Left : cell culture growing in a model porous medium. The white spheres represent the grains, bonds are displayed in grey, and microbes in green. Right: microscopy picture of glass beads linked by PDMS bridges, scale bar: 100 μm.

  16. Environmentally assisted cracking in light water reactors.

    Energy Technology Data Exchange (ETDEWEB)

    Chopra, O. K.; Chung, H. M.; Clark, R. W.; Gruber, E. E.; Shack, W. J.; Soppet, W. K.; Strain, R. V.

    2007-11-06

    This report summarizes work performed by Argonne National Laboratory on fatigue and environmentally assisted cracking (EAC) in light water reactors (LWRs) from January to December 2002. Topics that have been investigated include: (a) environmental effects on fatigue crack initiation in carbon and low-alloy steels and austenitic stainless steels (SSs), (b) irradiation-assisted stress corrosion cracking (IASCC) of austenitic SSs in BWRs, (c) evaluation of causes and mechanisms of irradiation-assisted cracking of austenitic SS in PWRs, and (d) cracking in Ni-alloys and welds. A critical review of the ASME Code fatigue design margins and an assessment of the conservation in the current choice of design margins are presented. The existing fatigue {var_epsilon}-N data have been evaluated to define the effects of key material, loading, and environmental parameters on the fatigue lives of carbon and low-alloy steels and austenitic SSs. Experimental data are presented on the effects of surface roughness on fatigue crack initiation in these materials in air and LWR environments. Crack growth tests were performed in BWR environments on SSs irradiated to 0.9 and 2.0 x 10{sup 21} n x cm{sup -2}. The crack growth rates (CGRs) of the irradiated steels are a factor of {approx}5 higher than the disposition curve proposed in NUREG-0313 for thermally sensitized materials. The CGRs decreased by an order of magnitude in low-dissolved oxygen (DO) environments. Slow-strain-rate tensile (SSRT) tests were conducted in high-purity 289 C water on steels irradiated to {approx}3 dpa. The bulk S content correlated well with the susceptibility to intergranular SCC in 289 C water. The IASCC susceptibility of SSs that contain >0.003 wt. % S increased drastically. bend tests in inert environments at 23 C were conducted on broken pieces of SSRT specimens and on unirradiated specimens of the same materials after hydrogen charging. The results of the tests and a review of other data in the literature

  17. Evaluation method of cracking resistance of lightweight aggregate concrete

    Institute of Scientific and Technical Information of China (English)

    季韬; 张彬彬; 陈永波; 庄一舟

    2014-01-01

    The cracking behavior of lightweight aggregate concrete (LWAC) was investigated by mechanical analysis, SEM and cracking-resistant test where a shrinkage-restrained ring with a clapboard was used. The relationship between the ceramsite type and the cracking resistance of LWAC was built up and compared with that of normal-weight coarse aggregate concrete (NWAC). A new method was proposed to evaluate the cracking resistance of concrete, where the concepts of cracking coefficient ζt(t) and the evaluation index Acr(t) were proposed, and the development of micro-cracks and damage accumulation were recognized. For the concrete with an ascending cracking coefficient curve, the larger Acr(t) is, the lower cracking resistance of concrete is. For the concrete with a descending cracking coefficient curve, the larger Acr(t) is, the stronger the cracking resistance of concrete is. The evaluation results show that in the case of that all the three types of coarse aggregates in concrete are pre-soaked for 24 h, NWAC has the lowest cracking resistance, followed by the LWAC with lower water absorption capacity ceramsite and the LWAC with higher water absorption capacity ceramsite has the strongest cracking resistance. The proposed method has obvious advantages over the cracking age method, because it can evaluate the cracking behavior of concrete even if the concrete has not an observable crack.

  18. Bubble visualization in a simulated hydraulic jump

    CERN Document Server

    Witt, Adam; Shen, Lian

    2013-01-01

    This is a fluid dynamics video of two- and three-dimensional computational fluid dynamics simulations carried out at St. Anthony Falls Laboratory. A transient hydraulic jump is simulated using OpenFOAM, an open source numerical solver. A Volume of Fluid numerical method is employed with a realizable k-epsilon turbulence model. The goal of this research is to model the void fraction and bubble size in a transient hydraulic jump. This fluid dynamics video depicts the air entrainment characteristics and bubble behavior within a hydraulic jump of Froude number 4.82.

  19. Hierarchically-Driven Approach for Quantifying Fatigue Crack Initiation and Short Crack Growth Behavior in Aerospace Materials

    Science.gov (United States)

    2016-08-31

    activated than prismatic and basal slip systems(pyramidal stress -intensity factor for slip transfer revealed a range of...and Bacon [19], initially in LAMMPS [20]. The edge dislocation structure obtained using the EAM potential was further relaxed using the QM/MM method...oxygen concentration; the slip direction is along 1210 . The oxygen atom was free to relax in all directions; whereas, Ti atoms were free to move

  20. Hydraulic Fracturing and the Environment

    Science.gov (United States)

    Ayatollahy Tafti, T.; Aminzadeh, F.; Jafarpour, B.; de Barros, F.

    2013-12-01

    In this presentation, we highlight two key environmental concerns of hydraulic fracturing (HF), namely induced seismicity and groundwater contamination (GC). We examine the induced seismicity (IS) associated with different subsurface fluid injection and production (SFIP) operations and the key operational parameters of SFIP impacting it. In addition we review the key potential sources for possible water contamination. Both in the case of IS and GC we propose modeling and data analysis methods to quantify the risk factors to be used for monitoring and risk reduction. SFIP include presents a risk in hydraulic fracturing, waste water injection, enhanced oil recovery as well as geothermal energy operations. Although a recent report (NRC 2012) documents that HF is not responsible for most of the induced seismicities, we primarily focus on HF here. We look into vaious operational parameters such as volume and rate of water injection, the direction of the well versus the natural fracture network, the depth of the target and the local stress field and fault system, as well as other geological features. The latter would determine the potential for triggering tectonic related events by small induced seismicity events. We provide the building blocks for IS risk assessment and monitoring. The system we propose will involve adequate layers of complexity based on mapped seismic attributes as well as results from ANN and probabilistic predictive modeling workflows. This leads to a set of guidelines which further defines 'safe operating conditions' and 'safe operating zones' which will be a valuable reference for future SFIP operations. We also illustrate how HF can lead to groundwater aquifer contamination. The source of aquifer contamination can be the hydrocarbon gas or the chemicals used in the injected liquid in the formation. We explore possible pathways of contamination within and discuss the likelihood of contamination from each source. Many of the chemical compounds used

  1. Study on Characteristics of Hydraulic Servo System for Force Control of Hydraulic Robots

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Hyo-gon; Han, Changsoo [Hanyang University, Seoul (Korea, Republic of); Lee, Jong-won [Korea University of Science and Technology, Seoul (Korea, Republic of); Park, Sangdeok [Korea Institute of Industrial Technology, Seoul (Korea, Republic of)

    2015-02-15

    Because a hydraulic actuator has high power and force densities, this allows the weight of the robot's limbs to be reduced. This allows for good dynamic characteristics and high energy efficiency. Thus, hydraulic actuators are used in some exoskeleton robots and quadrupedal robots that require high torque. Force control is useful for robot compliance with a user or environment. However, force control of a hydraulic robot is difficult because a hydraulic servo system is highly nonlinear from a control perspective. In this study, a nonlinear model was used to develop a simulation program for a hydraulic servo system consisting of a servo valve, transmission lines, and a cylinder. The problems and considerations with regard to the force control performance for a hydraulic servo system were investigated. A force control method using the nonlinear model was proposed, and its effect was evaluated with the simulation program.

  2. Firebox modeling of SRT cracking heaters

    Energy Technology Data Exchange (ETDEWEB)

    Sundaram, K.M.; Albano, J.V. [ABB Lummus Crest Inc., Bloomfield, NJ (United States)

    1994-12-31

    Thermal cracking of hydrocarbons remains the most economically attractive route for the production of ethylene. The heat for the endothermic cracking reaction is supplied in high capacity fired heaters which are designed specifically to have high selectivity to olefins. In the cracking process, coke is deposited within the tubes of the radiant coil. The rate of coke deposition in a cracking furnace is a function not only of process conditions but of other factors as well. High tube metal temperatures in certain areas of the coil or hot spots can cause locally high coking rate leading to partial blockage of the tubes and consequently, short runs. The small diameter tubes used in modern high selectivity heaters are more sensitive than older large tube designs. The occurrence of these hot zones is a strong function of fireside conditions. For satisfactory performance, the heat flux profile in a cracking heater must be maintained as uniform as possible. In addition, it is important to minimize the variation of process temperatures entering the various cracking coils. These fireside variables are not only a function of the type of burners, excess air, type of fuel(s) and distribution of air and fuel but depend significantly on the air and flue gas flow patterns associated with the firebox, i.e., the firebox aerodynamics. Poor aerodynamics can adversely affect firing patterns and hence heat flux profiles in commercial furnaces. A variety of modeling techniques have been used to evaluate the firebox aerodynamics of Lummus, Short Residence Time, cracking heaters. These include flow visualization, physical cold flow modeling, and computational techniques. These approaches are discussed in this paper.

  3. Crack propagation modeling using Peridynamic theory

    Science.gov (United States)

    Hafezi, M. H.; Alebrahim, R.; Kundu, T.

    2016-04-01

    Crack propagation and branching are modeled using nonlocal peridynamic theory. One major advantage of this nonlocal theory based analysis tool is the unifying approach towards material behavior modeling - irrespective of whether the crack is formed in the material or not. No separate damage law is needed for crack initiation and propagation. This theory overcomes the weaknesses of existing continuum mechanics based numerical tools (e.g. FEM, XFEM etc.) for identifying fracture modes and does not require any simplifying assumptions. Cracks grow autonomously and not necessarily along a prescribed path. However, in some special situations such as in case of ductile fracture, the damage evolution and failure depend on parameters characterizing the local stress state instead of peridynamic damage modeling technique developed for brittle fracture. For brittle fracture modeling the bond is simply broken when the failure criterion is satisfied. This simulation helps us to design more reliable modeling tool for crack propagation and branching in both brittle and ductile materials. Peridynamic analysis has been found to be very demanding computationally, particularly for real-world structures (e.g. vehicles, aircrafts, etc.). It also requires a very expensive visualization process. The goal of this paper is to bring awareness to researchers the impact of this cutting-edge simulation tool for a better understanding of the cracked material response. A computer code has been developed to implement the peridynamic theory based modeling tool for two-dimensional analysis. A good agreement between our predictions and previously published results is observed. Some interesting new results that have not been reported earlier by others are also obtained and presented in this paper. The final objective of this investigation is to increase the mechanics knowledge of self-similar and self-affine cracks.

  4. ENDOFEM INTEGRATED METHODOLOGY FOR FATIGUE CRACK GROWTH

    Institute of Scientific and Technical Information of China (English)

    C.F.Lee; L.T.Hsiao

    2002-01-01

    In this paper, the FEM with the incremental endochronic cyclic plasticity (EndoFEM) and the rc controlled node-released strategy are employed to study the fatigue crack opened/closed load (Pop) of A1 2024-T3 CCT specimens provided by Mageed and Pandey under several crack lengths and the constant amplitude with various load ratio (R). After statisfactory results are achieved by comparisons of computed Pop values and cited experimental data, the simulations will be extended to the crack lengths with significant bending effect due to short ligaments or high peak (Pmax) or high positive or very low negative R cyclic loads. Through these simulations, the complete map of Pop/Pmax vs. Kmax and R can be constructed and thereafter its correspondant empirical formulae can be proposed. Using these formulae and selecting the traditional fatigue crack growth parameter ΔKeff, the A1 2024-T3 fatigue crack growth rate da/dN vs. ΔK and R data, provided by Hiroshi and Schijve, can be employed to proposed empirical formulae of da/dN vs. ΔKeff and R. After integration, fatigue-crack-growth length a vs. N curves computed by EndoFEM can be obtained. The results are agreed very well with the existing experimental curves. According to the above procedures of simulation and steps of comparions with experiment, this paper may provides an integrate methodology of numerical simulation in the studies of fatigue crack growth for academic and industrial researches and design analysis.

  5. TRANSPORT THROUGH CRACKED CONCRETE: LITERATURE REVIEW

    Energy Technology Data Exchange (ETDEWEB)

    Langton, C.

    2012-05-11

    Concrete containment structures and cement-based fills and waste forms are used at the Savannah River Site to enhance the performance of shallow land disposal systems designed for containment of low-level radioactive waste. Understanding and measuring transport through cracked concrete is important for describing the initial condition of radioactive waste containment structures at the Savannah River Site (SRS) and for predicting performance of these structures over time. This report transmits the results of a literature review on transport through cracked concrete which was performed by Professor Jason Weiss, Purdue University per SRR0000678 (RFP-RQ00001029-WY). This review complements the NRC-sponsored literature review and assessment of factors relevant to performance of grouted systems for radioactive waste disposal. This review was performed by The Center for Nuclear Waste Regulatory Analyses, San Antonio, TX, and The University of Aberdeen, Aberdeen Scotland and was focused on tank closure. The objective of the literature review on transport through cracked concrete was to identify information in the open literature which can be applied to SRS transport models for cementitious containment structures, fills, and waste forms. In addition, the literature review was intended to: (1) Provide a framework for describing and classifying cracks in containment structures and cementitious materials used in radioactive waste disposal, (2) Document the state of knowledge and research related to transport through cracks in concrete for various exposure conditions, (3) Provide information or methodology for answering several specific questions related to cracking and transport in concrete, and (4) Provide information that can be used to design experiments on transport through cracked samples and actual structures.

  6. Recent evaluations of crack-opening-area in circumferentially cracked pipes

    Energy Technology Data Exchange (ETDEWEB)

    Rahman, S.; Brust, F.; Ghadiali, N.; Wilkowski, G.; Miura, N.

    1997-04-01

    Leak-before-break (LBB) analyses for circumferentially cracked pipes are currently being conducted in the nuclear industry to justify elimination of pipe whip restraints and jet shields which are present because of the expected dynamic effects from pipe rupture. The application of the LBB methodology frequently requires calculation of leak rates. The leak rates depend on the crack-opening area of the through-wall crack in the pipe. In addition to LBB analyses which assume a hypothetical flaw size, there is also interest in the integrity of actual leaking cracks corresponding to current leakage detection requirements in NRC Regulatory Guide 1.45, or for assessing temporary repair of Class 2 and 3 pipes that have leaks as are being evaluated in ASME Section XI. The objectives of this study were to review, evaluate, and refine current predictive models for performing crack-opening-area analyses of circumferentially cracked pipes. The results from twenty-five full-scale pipe fracture experiments, conducted in the Degraded Piping Program, the International Piping Integrity Research Group Program, and the Short Cracks in Piping and Piping Welds Program, were used to verify the analytical models. Standard statistical analyses were performed to assess used to verify the analytical models. Standard statistical analyses were performed to assess quantitatively the accuracy of the predictive models. The evaluation also involved finite element analyses for determining the crack-opening profile often needed to perform leak-rate calculations.

  7. Crack Growth Monitoring by Embedded Optical Fibre Bragg Grating Sensors: Fibre Reinforced Plastic Crack Growing Detection

    DEFF Research Database (Denmark)

    Pereira, Gilmar Ferreira; Mikkelsen, Lars Pilgaard; McGugan, Malcolm

    2015-01-01

    This article presents a novel method to asses a crack growing/damage event in fibre reinforced plastic, or adhesive using Fibre Bragg Grating (FBG) sensors embedded in a host material. Different features of the crack mechanism that induce a change in the FBG response were identified. Double Canti...

  8. Hydrocarbon cracking selectivities with a dual zeolite fluid cracking catalyst containing REY and ZSM-5

    Energy Technology Data Exchange (ETDEWEB)

    Rajagopalan, K.; Young, G.W. (W.R. Grace and Company, Columbia, MD (USA))

    1987-08-01

    Synthetic Y faujasite zeolites have been used commercially as cracking catalysts for the past two decades, and more recently dual zeolite fluid cracking catalysts, containing faujasite and ZSM-5 were discovered to increase the octane number of the gasoline during catalytic cracking of gas oil. This concept, where ZSM-5 constitutes only a small fraction (about 1 wt %) of the cracking catalyst, has been tested commercially in Europe and in the United States. Cracking of paraffinic and olefinic hydrocarbons by ZSM-5 catalysts has been studied by several investigators over a range of temperatures (350 to 540{degree}C) and using nearly pure ZSM-5 as the catalyst. The mechanism of octane number enhancement with the dual zeolite catalyst was investigated by examining the effect on product selectivity of addition of 1 wt % ZSM-5 to a cracking catalyst composition during catalytic cracking of a commercial gas oil at 500{degree}C. Changes in composition of the product gasoline (paraffins, olefins, naphthenes and aromatics) caused by ZSM-5 were measured. Since commercial cracking catalysts undergo continuous high temperature regeneration in the presence of steam, the effect of hydrothermal treatment of ZSM-5 was also investigated.

  9. Evolving fracture patterns: columnar joints, mud cracks, and polygonal terrain

    Science.gov (United States)

    Goehring, L.

    2012-12-01

    Contraction cracks can form captivating patterns, such as the artistic craquelure sometimes found in pottery glazes, to the cracks in dried mud, or the polygonal networks covering the polar regions of Earth and Mars. Two types are frequently encountered: those with irregular rectilinear patterns, such as that formed by an homogeneous slurry when dried (or cooled) uniformly, and more regular hexagonal patterns, such as those typified by columnar joints. Once cracks start to form in a thin contracting layer, they will sequentially break the layer into smaller and smaller pieces. A rectilinear crack pattern encodes information about the order of cracks, as later cracks tend to intersect with earlier cracks at right angles. In this manner they relieve the stresses perpendicular to the pre-existing crack. In a hexagonal pattern, in contrast, the angles between all cracks at a vertex are near 120°. In this presentation it will be shown how both types of pattern can arise from identical forces, and that a rectilinear, T-junction dominated pattern will develop into to a hexagonal pattern, with Y-junctions, if allowed to. Such an evolution can be explained as the result of three conditions: (1) if cracks advance through space, or heal and recur, that the previous positions of a crack tip acts as a line of weakness, guiding the next iteration of cracking; (2) that the order of opening of cracks can change in each iteration; and (3) that crack tips curve to maximise the local strain energy release rate. The ordering of crack patterns are seen in a number of systems: columnar joints in starch and lava; desiccation cracks in clays that are repeatedly wetted and dried; cracks in eroding gypsum-cemented sand layers; and the cracks in permafrost known as polygonal terrain. These patterns will each be briefly explored, in turn, and shown to obey the above principles of crack pattern evolution.

  10. Constraints on structural evolution from correlations between hydraulic properties and P-wave velocities during brittle faulting of rocks

    Science.gov (United States)

    Ahrens, Benedikt; Duda, Mandy; Renner, Jörg

    2017-04-01

    One of the key challenges in geophysics concerns the derivation of structure and state of rocks and rock formations from constraints on the spatial distribution of their physical properties, as gained from laboratory experiments, borehole logging, and surveys at the surface covering scales from centimeters to kilometers. The use of information from the propagation of elastic waves constitutes the most common approach to derive the structure and state of rocks, if direct information on in-situ properties is limited (e.g., through boreholes) or inaccessible. Furthermore, the determination of hydraulic rock properties serves the dual purpose of constraining structure and providing the basis for predictions of the behavior of a system of interest during continued fluid injection or production, as associated with, e.g., exploitation of hydrocarbon reservoirs, operation of subsurface liquid-waste repositories, or geothermal energy provision. In-situ, wave observations potentially provide better coverage of rock volumes (in space and time) than hydraulic investigations and thus constraints on correlations between elastic and hydraulic properties bear the potential to improve subsurface characterization. In our laboratory study, we continuously monitored hydraulic properties and elastic wave velocities of porous Wilkeson sandstone samples during conventional triaxial deformation. Confining pressures applied in the tests cover the range from below to above the critical pressure for crack closure to control the state of pre-existing cracks. Hydraulic properties were determined using the oscillatory pore-pressure method owing to its benefits regarding continuous and highly resolved monitoring of permeability and specific storage capacity during deformation and even imminent localized failure. The magnitude of the deformation-associated variations in the monitored physical properties strongly depends on initial microstructure and degree of hydrostatically induced crack closure

  11. Implicit level set algorithms for modelling hydraulic fracture propagation.

    Science.gov (United States)

    Peirce, A

    2016-10-13

    Hydraulic fractures are tensile cracks that propagate in pre-stressed solid media due to the injection of a viscous fluid. Developing numerical schemes to model the propagation of these fractures is particularly challenging due to the degenerate, hypersingular nature of the coupled integro-partial differential equations. These equations typically involve a singular free boundary whose velocity can only be determined by evaluating a distinguished limit. This review paper describes a class of numerical schemes that have been developed to use the multiscale asymptotic behaviour typically encountered near the fracture boundary as multiple physical processes compete to determine the evolution of the fracture. The fundamental concepts of locating the free boundary using the tip asymptotics and imposing the tip asymptotic behaviour in a weak form are illustrated in two quite different formulations of the governing equations. These formulations are the displacement discontinuity boundary integral method and the extended finite-element method. Practical issues are also discussed, including new models for proppant transport able to capture 'tip screen-out'; efficient numerical schemes to solve the coupled nonlinear equations; and fast methods to solve resulting linear systems. Numerical examples are provided to illustrate the performance of the numerical schemes. We conclude the paper with open questions for further research. This article is part of the themed issue 'Energy and the subsurface'.

  12. VALIDATION OF CRACK INTERACTION LIMIT MODEL FOR PARALLEL EDGE CRACKS USING TWO-DIMENSIONAL FINITE ELEMENT ANALYSIS

    Directory of Open Access Journals (Sweden)

    R. Daud

    2013-06-01

    Full Text Available Shielding interaction effects of two parallel edge cracks in finite thickness plates subjected to remote tension load is analyzed using a developed finite element analysis program. In the present study, the crack interaction limit is evaluated based on the fitness of service (FFS code, and focus is given to the weak crack interaction region as the crack interval exceeds the length of cracks (b > a. Crack interaction factors are evaluated based on stress intensity factors (SIFs for Mode I SIFs using a displacement extrapolation technique. Parametric studies involved a wide range of crack-to-width (0.05 ≤ a/W ≤ 0.5 and crack interval ratios (b/a > 1. For validation, crack interaction factors are compared with single edge crack SIFs as a state of zero interaction. Within the considered range of parameters, the proposed numerical evaluation used to predict the crack interaction factor reduces the error of existing analytical solution from 1.92% to 0.97% at higher a/W. In reference to FFS codes, the small discrepancy in the prediction of the crack interaction factor validates the reliability of the numerical model to predict crack interaction limits under shielding interaction effects. In conclusion, the numerical model gave a successful prediction in estimating the crack interaction limit, which can be used as a reference for the shielding orientation of other cracks.

  13. A model for hydraulic redistribution incorporating coupled soil-root moisture transport

    Directory of Open Access Journals (Sweden)

    G. G. Amenu

    2007-10-01

    Full Text Available One of the adaptive strategies of vegetation, particularly in water limited ecosystems, is the development of deep roots and the use of hydraulic redistribution which enables them to make optimal use of resources available throughout the soil column. Hydraulic redistribution refers to roots acting as a preferential pathway for the movement of water from wet to dry soil layers driven by the moisture gradient – be it from the shallow to deep layers or vice versa. This occurs during the nighttime while during the daytime moisture movement is driven to fulfill the transpiration demand at the canopy. In this study, we develop a model to investigate the effect of hydraulic redistribution by deep roots on the terrestrial climatology. Sierra Nevada eco-region is chosen as the study site which has wet winters and dry summers. Hydraulic redistribution enables the movement of moisture from the upper soil layers to deeper zones during the wet months and this moisture is then available to meet the transpiration demand during the late dry season. It results in significant alteration of the profiles of soil moisture and water uptake as well as increase in the canopy transpiration, carbon assimilation, and the associated water-use-efficiency during the dry summer season. This also makes the presence of roots in deeper soil layers much more important than their proportional abundance would otherwise dictate. Comparison with observations of latent heat from a flux tower demonstrates improved predictability and provides validation of the model results. Hydraulic redistribution serves as a mechanism for the interaction between the variability of deep layer soil-moisture and the land-surface climatology and could have significant implications for seasonal and sub-seasonal climate prediction.

  14. A model for hydraulic redistribution incorporating coupled soil-root moisture transport

    Directory of Open Access Journals (Sweden)

    G. G. Amenu

    2008-01-01

    Full Text Available One of the adaptive strategies of vegetation, particularly in water limited ecosystems, is the development of deep roots and the use of hydraulic redistribution which enables them to make optimal use of resources available throughout the soil column. Hydraulic redistribution refers to roots acting as a preferential pathway for the movement of water from wet to dry soil layers driven by the moisture gradient – be it from the shallow to deep layers or vice versa. This occurs during the nighttime while during the daytime moisture movement is driven to fulfill the transpiration demand at the canopy. In this study, we develop a model to investigate the effect of hydraulic redistribution by deep roots on the terrestrial climatology. Sierra Nevada eco-region is chosen as the study site which has wet winters and dry summers. Hydraulic redistribution enables the movement of moisture from the upper soil layers to deeper zones during the wet months and this moisture is then available to meet the transpiration demand during the late dry season. It results in significant alteration of the profiles of soil moisture and water uptake as well as increase in the canopy transpiration, carbon assimilation, and the associated water-use-efficiency during the dry summer season. This also makes the presence of roots in deeper soil layers much more important than their proportional abundance would otherwise dictate. Comparison with observations of latent heat from a flux tower demonstrates improved predictability and provides validation of the model results. Hydraulic redistribution serves as a mechanism for the interaction between the variability of deep layer soil-moisture and the land-surface climatology and could have significant implications for seasonal and sub-seasonal climate prediction.

  15. Roof Weakening of Hydraulic Fracturing for Control of Hanging Roof in the Face End of High Gassy Coal Longwall Mining: A Case Study

    Science.gov (United States)

    Huang, Bingxiang; Wang, Youzhuang

    2016-09-01

    The occurence of hanging roof commonly arises in the face end of longwall coal mining under hard roof conditions. The sudden break and subsequent caving of a hanging roof could result in the extrusion of gas in the gob to the face, causing gas concentrations to rise sharply and to increase to over a safety-limited value. A series of linear fracturing-holes of 32 mm diameter were drilled into the roof of the entries with an anchor rig. According to the theory that the gob should be fully filled with the fragmentized falling roof rock, the drilling depth is determined as being 3 5 times the mining height if the broken expansion coefficient takes an empirical value. Considering the general extension range of cracks and the supporting form of the entryway, the spacing distance between two drilling holes is determined as being 1 2 times the crack's range of extension. Using a mounting pipe, a high pressure resistant sealing device of a small diameter-size was sent to the designated location for the high-pressure hydraulic fracturing of the roof rock. The hydraulic fracturing created the main hydro-fracturing crack and airfoil branch cracks in the interior of the roof-rock, transforming the roof structure and weakening the strength of the roof to form a weak plane which accelerated roof caving, and eventually induced the full caving in of the roof in time with the help of ground pressure. For holes deeper than 4 m, retreating hydraulic fracturing could ensure the uniformity of crack extension. Tested and applied at several mines in Shengdong Mining District, the highest ruptured water pressure was found to be 55 MPa, and the hanging roof at the face end was reduced in length from 12 m to less than 1 2 m. This technology has eliminated the risk of the extrusion of gas which has accumulated in the gob.

  16. Borehole Heat Exchanger Systems: Hydraulic Conductivity and Frost-Resistance of Backfill Materials

    Science.gov (United States)

    Anbergen, Hauke; Sass, Ingo

    2016-04-01

    constant radial stress boundary conditions (sigma 2 = sigma 3 = constant) • radial freezing from inside out, following the in-situ freezing direction The results differ substantially from prior test procedures (such as standardized frost tests for concrete or soft soils). Concentric frost-induced cracking was observed. The cracking pattern is in good agreement with cryostatic suction processes and frost heave in fine grained soils. The hydraulic conductivity of the system depends on the composition of the grout. With the developed testing device (and procedure) a unified and independent assessment and quality control becomes feasible. Adequate materials for advanced shallow geothermal systems can be clearly identified.

  17. Evaluation of Stress Intensity Factors for Multiple Cracked Circular Disks Under Crack Surface Tractions with SBFEM

    Institute of Scientific and Technical Information of China (English)

    LIU Jun-yu; LIN Gao; LI Xiao-chuan; XU Feng-lin

    2013-01-01

    Stress intensity factors (SIFs) for the cracked circular disks under different distributing surface tractions are evaluated with the scaled boundary finite element method (SBFEM).In the SBFEM,the analytical advantage of the solution in the radial direction allows SIFs to be directly determined from its definition,therefore no special crack-tip treatment is necessary.Furthermore anisotropic material behavior can be treated easily.Different distributions of surface tractions are considered for the center and double-edge-cracked disks.The benchmark examples are modeled and an excellent agreement between the results in the present study and those in published literature is found.It shows that SBFEM is effective and possesses high accuracy.The SIFs of the cracked orthotropic material circular disks subjected to different surface tractions are also evaluated.The technique of substructure is applied to handle the multiple cracks problem.

  18. Failure analysis of corrosion cracking and simulated testing for a fluid catalytic cracking unit

    Institute of Scientific and Technical Information of China (English)

    Hua Chen; Xiaogang Li; Chaofang Dong; Ming Li; Jinwen Yang

    2005-01-01

    The failure of a fluid catalysis and cracking unit (FCCU) in a Chinese refinery was investigated by using nondestructive detection methods, fracture surface examination, hardness measurement, chemical composition and corrosion products analysis. The results showed that the failure was caused by the dew point nitrate stress corrosion cracking. For a long operation period, the wall temperature of the regenerator in the FCCU was below the fume dew point. As a result, an acid fume NOx-SOx-H2O medium presented on the surface, resulting in stress corrosion cracking of the component with high residual stress. In order to confirm the relative conclusion, simulated testing was conducted in laboratory, and the results showed similar cracking characteristics. Finally, some suggestions have been made to prevent the stress corrosion cracking of an FCCU from re-occurring in the future.

  19. Parker Hybrid Hydraulic Drivetrain Demonstration

    Energy Technology Data Exchange (ETDEWEB)

    Collett, Raymond [Parker-Hannifin Corporation, Cleveland, OH (United States); Howland, James [Parker-Hannifin Corporation, Cleveland, OH (United States); Venkiteswaran, Prasad [National Energy Technology Lab. (NETL), Morgantown, WV (United States)

    2014-03-31

    This report examines the benefits of Parker Hannifin hydraulic hybrid brake energy recovery systems used in commercial applications for vocational purposes. A detailed background on the problem statement being addressed as well as the solution set specific for parcel delivery will be provided. Objectives of the demonstration performed in high start & stop applications included opportunities in fuel usage reduction, emissions reduction, vehicle productivity, and vehicle maintenance. Completed findings during the demonstration period and parallel investigations with NREL, CALSTART, along with a literature review will be provided herein on this research area. Lastly, results identified in the study by third parties validated the savings potential in fuel reduction of on average of 19% to 52% over the baseline in terms of mpg (Lammert, 2014, p11), Parker data for parcel delivery vehicles in the field parallels this at a range of 35% - 50%, emissions reduction of 17.4% lower CO2 per mile and 30.4% lower NOx per mile (Gallo, 2014, p15), with maintenance improvement in the areas of brake and starter replacement, while leaving room for further study in the area of productivity in terms of specific metrics that can be applied and studied.

  20. Thermal hydraulics development for CASL

    Energy Technology Data Exchange (ETDEWEB)

    Lowrie, Robert B [Los Alamos National Laboratory

    2010-12-07

    This talk will describe the technical direction of the Thermal-Hydraulics (T-H) Project within the Consortium for Advanced Simulation of Light Water Reactors (CASL) Department of Energy Innovation Hub. CASL is focused on developing a 'virtual reactor', that will simulate the physical processes that occur within a light-water reactor. These simulations will address several challenge problems, defined by laboratory, university, and industrial partners that make up CASL. CASL's T-H efforts are encompassed in two sub-projects: (1) Computational Fluid Dynamics (CFD), (2) Interface Treatment Methods (ITM). The CFD subproject will develop non-proprietary, scalable, verified and validated macroscale CFD simulation tools. These tools typically require closures for their turbulence and boiling models, which will be provided by the ITM sub-project, via experiments and microscale (such as DNS) simulation results. The near-term milestones and longer term plans of these two sub-projects will be discussed.

  1. Transputer Control of Hydraulic Actuators and Robots

    DEFF Research Database (Denmark)

    Conrad, Finn

    1996-01-01

    Results from a Danish mechatronics research program entitled IMCIA - Intelligent Control and Intelligent Actuators. The objective is development of intelligent actuators for intelligent motion control. A mechatronics test facility with a transputer controlled hydraulic robot suiteable for real...

  2. Concept Evaluation for Hydraulic Yaw System

    DEFF Research Database (Denmark)

    Stubkier, Søren; Pedersen, Henrik C.; Andersen, Torben Ole

    2013-01-01

    a suspension system on a car, leading the loads away from the turbine structure. However, to realize a soft hydraulic yaw system a new design concept must be found. As a part of the development of the new concept a preliminary concept evaluation has been conducted, evaluating seven different hydraulic yaw...... concepts, ranging from a one-to-one copy of the electrical drive (electrical drives replaced by hydraulic dittos), to floating suspension systems mounted on hydraulic cylinders. Rough calculations of size and consequences of the different systems are presented ending up with the final concept for further...... investigation. Loads and yaw demands are based on the IEC 61400-1 standard for wind turbine design, and the loads for this examination are extrapolated from the HAWC2 aeroelastic design code. The concepts are based on a 5 MW off-shore turbine....

  3. HYDRAULICS, Des Moines COUNTY, IOWA, USA

    Data.gov (United States)

    Federal Emergency Management Agency, Department of Homeland Security — Hydraulic data include spatial datasets and data tables necessary for documenting the hydrologic procedures for estimating flood discharges for a flood insurance...

  4. ON THE THEORIES OF HYDRAULIC GEOMETRY

    Institute of Scientific and Technical Information of China (English)

    Vijay P. SINGH

    2003-01-01

    Hydraulic geometry is of fundamental importance in planning, design, and management of river engineering and training works. Although some concepts of hydraulic geometry were proposed toward the end of the nineteenth century, the real impetus toward formulating a theory of hydraulic geometry was provided by the work of Leopold and Maddock (1953). A number of theories have since been proposed.Some of the theories are interrelated but others are based on quite different principles. All theories,however, assume that the river flow is steady and uniform and the river tends to attain a state of equilibrium or quasi-equilibrium. The differences are due to the differences in hydraulic mechanisms that the theories employ to explain the attainment of equilibrium by the river.

  5. Stream restoration hydraulic design course: lecture notes

    National Research Council Canada - National Science Library

    Newbury, R

    2002-01-01

    Steam restoration encompasses a broad range of activities and disciplines. This lecture series is designed for practitioners who must fit habitat improvement works in the hydraulics of degraded channels...

  6. Drawing a pictogram operator - hydraulic stowing assembly

    Energy Technology Data Exchange (ETDEWEB)

    Bukhgol' ts, V.P.; Dinershtein, V.A.

    1984-11-01

    Hydraulic stowing is widely used during the extraction of coal from seams prone to spontaneous ignition or from seams situated under preserved structures. Experience has shown that the presence of a considerable number of controlling and measuring devices on hydraulic stowing assemblies results in erratic operations. The authors, after examining the controls of the hydraulic stowing complexes, recommend that all functions which the operator might perform badly or not at all should be controlled automatically. The operator must, however, have access to manual controls which should be included in the system in order to achieve an effective and trouble free operation. The authors propose a pictogram to explain the relationship between the human operator and the hydraulic complex, based on structural diagrams. The system developed, which was tried out at the Koksovaya mine, increased the efficiency of the complex and reduced the work load of the operator. 3 references.

  7. HYDRAULICS, Des Moines COUNTY, IOWA, USA

    Data.gov (United States)

    Federal Emergency Management Agency, Department of Homeland Security — Hydraulic data include spatial datasets and data tables necessary for documenting the hydrologic procedures for estimating flood discharges for a flood insurance...

  8. Hydraulic fracturing chemicals and fluids technology

    CERN Document Server

    Fink, Johannes

    2013-01-01

    When classifying fracturing fluids and their additives, it is important that production, operation, and completion engineers understand which chemical should be utilized in different well environments. A user's guide to the many chemicals and chemical additives used in hydraulic fracturing operations, Hydraulic Fracturing Chemicals and Fluids Technology provides an easy-to-use manual to create fluid formulations that will meet project-specific needs while protecting the environment and the life of the well. Fink creates a concise and comprehensive reference that enables the engineer to logically select and use the appropriate chemicals on any hydraulic fracturing job. The first book devoted entirely to hydraulic fracturing chemicals, Fink eliminates the guesswork so the engineer can select the best chemicals needed on the job while providing the best protection for the well, workers and environment. Pinpoints the specific compounds used in any given fracturing operation Provides a systematic approach to class...

  9. Transputer Control of Hydraulic Actuators and Robots

    DEFF Research Database (Denmark)

    Conrad, Finn

    1996-01-01

    Results from a Danish mechatronics research program entitled IMCIA - Intelligent Control and Intelligent Actuators. The objective is development of intelligent actuators for intelligent motion control. A mechatronics test facility with a transputer controlled hydraulic robot suiteable for real...

  10. SIMULATION AND OPTIMIZATION OF THE HYDRAULIC FRACTURING OPERATION IN A HEAVY OIL RESERVOIR IN SOUTHERN IRAN

    Directory of Open Access Journals (Sweden)

    REZA MASOOMI

    2017-01-01

    Full Text Available Extraction of oil from some Iranian reservoirs due to high viscosity of their oil or reducing the formation permeability due to asphaltene precipitation or other problems is not satisfactory. Hydraulic fracturing method increases production in the viscous oil reservoirs that the production rate is low. So this is very important for some Iranian reservoirs that contain these characteristics. In this study, hydraulic fracturing method has been compositionally simulated in a heavy oil reservoir in southern Iran. In this study, the parameters of the fracture half length, the propagation direction of the cracks and the depth of fracturing have been considered in this oil reservoir. The aim of this study is to find the best scenario which has the highest recovery factor in this oil reservoir. For this purpose the parameters of the length, propagation direction and depth of fracturing have been optimized in this reservoir. Through this study the cumulative oil production has been evaluated with the compositional simulation for the next 10 years in this reservoir. Also at the end of this paper, increasing the final production of this oil reservoir caused by optimized hydraulic fracturing has been evaluated.

  11. 21 CFR 870.2780 - Hydraulic, pneumatic, or photoelectric plethysmographs.

    Science.gov (United States)

    2010-04-01

    ... 21 Food and Drugs 8 2010-04-01 2010-04-01 false Hydraulic, pneumatic, or photoelectric... § 870.2780 Hydraulic, pneumatic, or photoelectric plethysmographs. (a) Identification. A hydraulic... using hydraulic, pneumatic, or photoelectric measurement techniques. (b) Classification. Class...

  12. RESEARCH OF THE DYNAMIC CHARACTERISTICS ON A NEW HYDRAULIC SYSTEM OF ELECTRO-HYDRAULIC HAMMER

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    A new typed hydraulic system of electro-hydraulic hammer is researched and developed.By means of power bond graphs the modeling and simulation to the dynamic characteristics of the new hydraulic system are performed. The experimental research which is emphasized on the blowing stroke is also performed. It is proved from the result of simulation and experiment that this new hydraulic system possesses such advantages as simplification of structure,flexibleness of operation and reliability of working. Especially it possesses better dynamic characteristics.

  13. Design of a laboratory hydraulic device for testing of hydraulic pumps

    Directory of Open Access Journals (Sweden)

    Pavel Máchal

    2013-01-01

    Full Text Available The present contribution deals with solves problem of research of testing device to monitor of hydrostatic pumps durability about dynamic loading under laboratory conditions. When carrying out the design of testing device are based on load characteristics of tractor hydraulic circuit, the individual characteristics of hydraulic components and performed calculations. Load characteristics on the tractors CASE IH Magnum 310, JOHN DEERE 8100, ZETOR FORTERRA 114 41 and Fendt 926 Vario were measured. Design of a hydraulic laboratory device is based on the need for testing new types of hydraulic pumps or various types of hydraulic fluids. When creating of hydraulic device we focused on testing hydraulic pumps used in agricultural and forestry tractors. Proportional pressure control valve is an active member of the hydraulic device, which provides change of a continuous control signal into relative pressure of operating fluid. The advantage of a designed hydraulic system is possibility of simulation of dynamic operating loading, which is obtained by measurement under real conditions, and thereby creates laboratory conditions as close to real conditions as possible. The laboratory device is constructed at the Department of Transport and Handling, Faculty of Engineering, Slovak University of Agriculture in Nitra.

  14. Shaft Crack Identification Based on Vibration and AE Signals

    Directory of Open Access Journals (Sweden)

    Wenxiu Lu

    2011-01-01

    Full Text Available The shaft crack is one of the main serious malfunctions that often occur in rotating machinery. However, it is difficult to locate the crack and determine the depth of the crack. In this paper, the acoustic emission (AE signal and vibration response are used to diagnose the crack. The wavelet transform is applied to AE signal to decompose into a series of time-domain signals, each of which covers a specific octave frequency band. Then an improved union method based on threshold and cross-correlation method is applied to detect the location of the shaft crack. The finite element method is used to build the model of the cracked rotor, and the crack depth is identified by comparing the vibration response of experiment and simulation. The experimental results show that the AE signal is effective and convenient to locate the shaft crack, and the vibration signal is feasible to determine the depth of shaft crack.

  15. Virtual restoration of cracks in digitized image of paintings

    Energy Technology Data Exchange (ETDEWEB)

    Spagnolo, G Schirripa; Somma, F

    2010-11-01

    An integrated methodology for the detection and removal of cracks on digitized image is presented in this paper. Crack-like pattern detection have been a matter of high concern among researchers mostly for its useful contribution to a variety of applications. The results presented here regard the craquelure of old paintings, however, the same methodology can be used for a much wider set of application. Many images contain similar patterns: crack in protective coating for polymers and other surfaces; fatigue crack in MEMS/NEMS; crack in epoxies used for underfill and encapsulation microelectronics components; etc. In this paper the cracks are detected by thresholding the output of the morphological top-hat transform. Afterwards, the thin dark brush strokes which have been misidentified as cracks are removed using automatic procedure. Finally, crack filling using texture synthesis algorithms. The methodology has been shown to perform very well on digitized images suffering from cracks.

  16. Fracture mechanics of piezoelectric solids with interface cracks

    CERN Document Server

    Govorukha, Volodymyr; Loboda, Volodymyr; Lapusta, Yuri

    2017-01-01

    This book provides a comprehensive study of cracks situated at the interface of two piezoelectric materials. It discusses different electric boundary conditions along the crack faces, in particular the cases of electrically permeable, impermeable, partially permeable, and conducting cracks. The book also elaborates on a new technique for the determination of electromechanical fields at the tips of interface cracks in finite sized piezoceramic bodies of arbitrary shape under different load types. It solves scientific problems of solid mechanics in connection with the investigation of electromechanical fields in piezoceramic bodies with interface cracks, and develops calculation models and solution methods for plane fracture mechanical problems for piecewise homogeneous piezoceramic bodies with cracks at the interfaces. It discusses the “open” crack model, which leads to a physically unrealistic oscillating singularity at the crack tips, and the contact zone model for in-plane straight interface cracks betw...

  17. Characterization of a hydraulically induced bedrock fracture

    OpenAIRE

    2014-01-01

    Hydraulic fracturing is a controversial practice because of concerns about environmental impacts due to its widespread use in recovering unconventional petroleum and natural gas deposits. However, water-only hydraulic fracturing has been used safely and successfully for many years to increase the permeability of aquifers used for drinking and irrigation water supply. This process extends and widens existing bedrock fractures, allowing groundwater storage to increase. Researchers have studied ...

  18. Data Analytics of Hydraulic Fracturing Data

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Jovan Yang [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Viswanathan, Hari [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Hyman, Jeffery [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Middleton, Richard [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2016-08-11

    These are a set of slides on the data analytics of hydraulic fracturing data. The conclusions from this research are the following: they proposed a permeability evolution as a new mechanism to explain hydraulic fracturing trends; they created a model to include this mechanism and it showed promising results; the paper from this research is ready for submission; they devised a way to identify and sort refractures in order to study their effects, and this paper is currently being written.

  19. Automatic quantification of crack patterns by image processing

    Science.gov (United States)

    Liu, Chun; Tang, Chao-Sheng; Shi, Bin; Suo, Wen-Bin

    2013-08-01

    Image processing technologies are proposed to quantify crack patterns. On the basis of the technologies, a software "Crack Image Analysis System" (CIAS) has been developed. An image of soil crack network is used as an example to illustrate the image processing technologies and the operations of the CIAS. The quantification of the crack image involves the following three steps: image segmentation, crack identification and measurement. First, the image is converted to a binary image using a cluster analysis method; noise in the binary image is removed; and crack spaces are fused. Then, the medial axis of the crack network is extracted from the binary image, with which nodes and crack segments can be identified. Finally, various geometric parameters of the crack network can be calculated automatically, such as node number, crack number, clod area, clod perimeter, crack area, width, length, and direction. The thresholds used in the operations are specified by cluster analysis and other innovative methods. As a result, the objects (nodes, cracks and clods) in the crack network can be quantified automatically. The software may be used to study the generation and development of soil crack patterns and rock fractures.

  20. Crack Detection with Lamb Wave Wavenumber Analysis

    Science.gov (United States)

    Tian, Zhenhua; Leckey, Cara; Rogge, Matt; Yu, Lingyu

    2013-01-01

    In this work, we present our study of Lamb wave crack detection using wavenumber analysis. The aim is to demonstrate the application of wavenumber analysis to 3D Lamb wave data to enable damage detection. The 3D wavefields (including vx, vy and vz components) in time-space domain contain a wealth of information regarding the propagating waves in a damaged plate. For crack detection, three wavenumber analysis techniques are used: (i) two dimensional Fourier transform (2D-FT) which can transform the time-space wavefield into frequency-wavenumber representation while losing the spatial information; (ii) short space 2D-FT which can obtain the frequency-wavenumber spectra at various spatial locations, resulting in a space-frequency-wavenumber representation; (iii) local wavenumber analysis which can provide the distribution of the effective wavenumbers at different locations. All of these concepts are demonstrated through a numerical simulation example of an aluminum plate with a crack. The 3D elastodynamic finite integration technique (EFIT) was used to obtain the 3D wavefields, of which the vz (out-of-plane) wave component is compared with the experimental measurement obtained from a scanning laser Doppler vibrometer (SLDV) for verification purposes. The experimental and simulated results are found to be in close agreement. The application of wavenumber analysis on 3D EFIT simulation data shows the effectiveness of the analysis for crack detection. Keywords: : Lamb wave, crack detection, wavenumber analysis, EFIT modeling

  1. Applied Stress Affecting the Environmentally Assisted Cracking

    Science.gov (United States)

    Vasudevan, A. K.

    2013-03-01

    Stress corrosion cracking (SCC) is affected by the mode of applied stress, i.e., tension, compression, or torsion. The cracking is measured in terms of initiation time to nucleate a crack or time to failure. In a simple uniaxial loading under tension or compression, it is observed that the initiation time can vary in orders of magnitude depending on the alloy and the environment. Fracture can be intergranular or transgranular or mixed mode. Factors that affect SCC are solubility of the metal into surrounding chemical solution, and diffusion rate (like hydrogen into a tensile region) of an aggressive element into the metal and liquid metallic elements in the grain boundaries. Strain hardening exponent that affects the local internal stresses and their gradients can affect the diffusion kinetics. We examine two environments (Ga and 3.5 pct NaCl) for the same alloy 7075-T651, under constant uniaxial tension and compression load. These two cases provide us application to two different governing mechanisms namely liquid metal embrittlement (7075-Ga) and hydrogen-assisted cracking (7075-NaCl). We note that, in spite of the differences in their mechanisms, both systems show similar behavior in the applied K vs crack initiation time plots. One common theme among them is the transport mechanism of a solute element to a tensile-stress region to initiate fracture.

  2. Crack buckling in soft gels under compression

    Institute of Scientific and Technical Information of China (English)

    Rong Long; Chung-Yuen Hui

    2012-01-01

    Recent interest in designing soft gels with high fracture toughness has called for simple and robust methods to test fracture behavior.The conventional method of applying tension to a gel sample suffers from a difficulty of sample gripping.In this paper,we study a possible fracture mechanism of soft gels under uni-axial compression.We show that the surfaces of a pre-existing crack,oriented parallel to the loading axis,can buckle at a critical compressive stress.This buckling instability can open the crack surfaces and create highly concentrated stress fields near the crack tip,which can lead to crack growth.We show that the onset of crack buckling can be deduced by a dimensional argument combined with an analysis to determine the critical compression needed to induce surface instabilities of an elastic half space.The critical compression for buckling was verified for a neoHookean material model using finite element simulations.

  3. Imaging Cracks by Laser Excited Thermography

    Science.gov (United States)

    Schlichting, J.; Kervalishvili, G. N.; Maierhofer, Ch.; Kreutzbruck, M.

    2010-02-01

    During the last years active thermography is increasingly used in a number of NDT problems in production and maintenance. In this work we focus on the detection of vertical cracks starting at the surface, which is an important indication of structural failure. By using local thermal excitation it is possible to image anisotropies in the lateral diffusivity by recording the temporal temperature data with an infrared camera. The regional transient behaviour of temperature distribution then can provide quantitative information of the crack parameter. In doing so, we present an advanced technique for the determination of the crack depth. The experimental set-up is based on an Nd:YAG laser. The beam is focused on the test sample by using an optical scanner to create the required lateral heat flow. The time resolved temperature distribution is recorded with an infrared camera (InSb FPA, 3 to 5 μm) providing a frame rate of up to 500 Hz. In addition we report on numerical simulation to investigate the concept of local heat excitation for a quantitative estimation of crack parameters. The modeling also includes the influence of surface to surface radiation inside the crack. We obtained a good consistency between experimental and theoretical data.

  4. Hydraulic Motor Driving Variable-Pitch System for Wind Turbine

    Directory of Open Access Journals (Sweden)

    Ye HUANG

    2013-11-01

    Full Text Available The present hydraulic variable-pitch mechanism of wind turbine uses three hydraulic cylinders to drive three crank and connecting rod mechanisms respectively; the blades are moved with the cranks. The hydraulic variable-pitch mechanism has complex structure, occupies a lot of space and its maintenance is trouble. In order to make up for the shortcomings of hydraulic cylinder variable-pitch system, the present hydraulic variable-pitch mechanism should be changed as follows: hydraulic motors are used to drive gears; gears drive blades; the electro-hydraulic proportional valves are used to control hydraulic motors. The hydraulic control part and electrical control part of variable-pitch system is redesigned. The new variable-pitch system is called hydraulic motor driving variable-pitch system. The new variable-pitch system meets the control requirements of blade pitch, makes the structure simple and its application effect is perfect.    

  5. Propagation of stress corrosion cracks in alpha-brasses

    Energy Technology Data Exchange (ETDEWEB)

    Beggs, Dennis Vinton [Univ. of Illinois, Urbana-Champaign, IL (United States)

    1981-01-01

    Transgranular and intergranular stress corrosion cracks were investigated in alpha-brasses in a tarnishing ammoniacal solution. Surface observation indicated that the transgranular cracks propagated discontinuously by the sudden appearance of a fine crack extending several microns ahead of the previous crack tip, often associated with the detection of a discrete acoustic emission (AE). By periodically increasing the deflection, crack front markings were produced on the resulting fracture surfaces, showing that the discontinuous propagation of the crack trace was representative of the subsurface cracking. The intergranular crack trace appeared to propagate continuously at a relatively blunt crack tip and was not associated with discrete AE. Under load pulsing tests with a time between pulses, Δt greater than or equal to 3 s, the transgranular fracture surfaces always exhibited crack front markings which corresponded with the applied pulses. The spacing between crack front markings, Δx, decreased linearly with Δt. With Δt less than or equal to 1.5 s, the crack front markings were in a one-to-one correspondence with applied pulses only at relatively long crack lengths. In this case, Δx = Δx* which approached a limiting value of 1 μm. No crack front markings were observed on intergranular fracture surfaces produced during these tests. It is concluded that transgranular cracking occurs by discontinuous mechanical fracture of an embrittled region around the crack tip, while intergranular cracking results from a different mechanism with cracking occurring via the film-rupture mechanism.

  6. Engineering diagnostics for vortex-induced stay vanes cracks in a Francis turbine

    Science.gov (United States)

    D'Agostini Neto, Alexandre; Gissoni, Humberto, Dr.; Gonçalves, Manuel, Dr.; Cardoso, Rogério; Jung, Alexander, Dr.; Meneghini, Julio, Prof.

    2016-11-01

    Despite the fact that vortex-induced vibration (VIV) in hydraulic turbines components (especially in stay vanes) is a well-known phenomenon, it still remains challenging for operation and maintenance teams in several power plants around the world. Since the first publication of a similar problem in 1967, literature shows that at least 27 other turbines witnessed strong stay vane vibrations associated with vortex shedding. Recurrent stay vane cracks in a 250 MW Francis turbine in Brazil motivated an engineering study involving prototype measurements, structural and Computational Fluid Dynamics (CFD) analysis in order to determine a proper geometry modification that could eliminate the periodic vortex wake generated at the stay vanes trailing edge. First cracks appeared in 1978 just after the machine was put into operation. A study published in 1982 associated these cracks with dynamic excitations caused by the water flow at high flow conditions. New stay vane profiles were proposed and executed as well as improved welding recommendations. Cracks however, continued to appear requiring welding repairs roughly every two years. Although Voith Hydro was not the original equipment manufacturer for these units, the necessary information was available to study the issue and propose and execute new stay vane profiles. This paper details the approach taken for the study. First, indirect vibration measurements were used to determine vibration frequencies to help to characterize the affected mode shapes. These results were compared to finite element (FE) calculations. Strain gage measurements performed afterwards confirmed the conclusions of this analysis. Next, transient CFD calculations were run to reproduce the measured phenomenon and to serve as a basis for a new stay vane geometry. This modification was then implemented in the actual turbine stay vanes. A new set of indirect vibration measurements indicated the effectiveness of the proposed solution. Final confirmation

  7. Developer Driven and User Driven Usability Evaluations

    DEFF Research Database (Denmark)

    Bruun, Anders

    2013-01-01

    Usability evaluation provide software development teams with insights on the degree to which a software application enables a user to achieve his/her goals, how fast these goals can be achieved, how easy it is to learn and how satisfactory it is in use Although usability evaluations are crucial....... The four primary findings from my studies are: 1) The developer driven approach reveals a high level of thoroughness and downstream utility. 2) The user driven approach has higher performance regarding validity 3) The level of reliability is comparable between the two approaches. 4) The user driven...

  8. Crack tip shielding and anti-shielding effects of parallel cracks for a superconductor slab under an electromagnetic force

    Energy Technology Data Exchange (ETDEWEB)

    Gao, Zhi Wen; Zhou, You He [Ministry of Education, Singapore (China); Lee, Kang Yong [Yonsei University, Seoul (Korea, Republic of)

    2012-02-15

    In this letter, the shielding or anti-shielding effect is firstly applied to obtain the behavior of two parallel cracks in a two-dimensional type-II superconducting under electromagnetic force. Fracture analysis is performed by the finite element method and the magnetic behavior of superconductor is described by the critical state Bean model. The stress intensity factors at the crack tips can be obtained and discussed for decreasing field after zero-field cooling. The shielding or anti-shielding effect at the crack tips depend on the distance between two parallel cracks and the crack length. The results indicate that the shielding effects of the two parallel cracks increase when the distance between the two parallel cracks decreases. It can be also obtained that the superconductors with shorter cracks has more remarkable shielding effect than those with longer cracks.

  9. Effects of plastic anisotropy on crack-tip behaviour

    DEFF Research Database (Denmark)

    Legarth, Brian Nyvang; Tvergaard, Viggo; Kuroda, Mitsutoshi

    2002-01-01

    loading remote from the crack-tip. In cases where the principal axes of the anisotropy are inclined to the plane of the crack it is found that the plastic zones as well as the stress and strain fields just around the blunted tip of the crack become non-symmetric. In these cases the peak strain...... on the blunted tip occurs off the center line of the crack, thus indicating that the crack may want to grow in a different direction. When the anisotropic axes are parallel to the crack symmetry is retained, but the plastic zones and the near-tip fields still differ from those predicted by standard isotropic...

  10. Evaluation of a Small-Crack Monitoring System

    Science.gov (United States)

    Newman, John A.; Johnston, William M.

    2010-01-01

    A new system has been developed to obtain fatigue crack growth rate data from a series of images acquired during fatigue testing of specimens containing small surface cracks that initiate at highly-polished notches. The primary benefit associated with replica-based crack growth rate data methods is preserving a record of the crack configuration during the life of the specimen. Additionally, this system has the benefits of both reducing time and labor, and not requiring introduction of surface replica media into the crack. Fatigue crack growth rate data obtained using this new system are found to be in good agreement with similar results obtained from surface replicas.

  11. Fatigue design of hydraulic turbine runners

    Energy Technology Data Exchange (ETDEWEB)

    Huth, Hans-Joerg

    2005-07-01

    Turbine runners experience start-stop cycles and vibration cycles. Cracks initiated from service or manufacturing defects and propagated by start-stop cycles become critical when the stress intensity range due to vibrational loading exceeds the threshold for fatigue crack growth. In Francis turbine runners, semi-elliptical surface cracks tend to propagate from the quarter-circular transition of the welded T-joint transition between the blade and the band or crown. Assuming a crack to grow under a constant stress amplitude equal to that at the most highly loaded location at the welded joint between the blade and the band or crown of a Francis turbine runner yields a conservative estimate of the life of the runner. A more accurate prediction of fatigue life is obtained by considering the growth of a crack in the real, inhomogeneous stress field. For an idealised T-joint under pure bending, the stress field has been determined by means of plane strain finite element analysis. Finite element models of the entire Francis runner are built with respect to the calculation of fluid dynamic properties. Since in these models geometry transitions are modelled as a sharp notch, both a finite and a zero transition radius have been modelled, and the influence of the mesh size on the maximum stress has been investigated. For relatively small cracks, it is shown that the structural component geometry does not remarkably influence the stress intensity factor values, provided that the stress field in the vicinity of the crack is approximately the same. Therefore, in order to simplify the stress intensity factor retrieval and to generate a solution of extended applicability, a cracked finite-thickness plate is examined instead of the actual T-joint geometry. The stress intensity factors along the front of a semi-elliptical surface crack in such a plate are determined by means of an analysis using finite quarter-point wedge elements for different elementary loading conditions that can

  12. Sizing stress corrosion cracks using laser ultrasonics

    Energy Technology Data Exchange (ETDEWEB)

    Rehman, Hamood; McNealy, Rick; Fingerhut, Martin [Applus-RTD. Houston, TX (United States); Klein, Marvin; Ansari, Homayoon [Intelligent Optical Systems, Inc. Los Angeles, CA (United States); Kania Richard [TransCanada. Calgary, AB (Canada); Rapp, Steve [Spectra Energy, Houston, TX (United States)

    2010-07-01

    Despite various efforts, no reliable tools and techniques are available to enable an operator to quantify the impact of an SCC (Stress Corrosion Cracking) colony on the safety and integrity of a pipeline. Reliable non-destructive detection and measurement tools are not available either. There is therefore a large gap between current technology and the needs of the pipeline industry. Recent developments promise that with a concentrated effort, a comprehensive solution can be devised. This paper describes technical work performed to develop and validate both the inspection tool and the time of flight diffraction (TOFD) technique for sizing the depth of SCC. It also presents preliminary results of work on a closely related project that provides, on the basis of this technology, an integrated approach and tool for mapping, sizing, and evaluating SCC, through which significant cracks are filtered from more benign cracks within an SCC colony.

  13. Environmentally assisted cracking in LWR materials

    Energy Technology Data Exchange (ETDEWEB)

    Chopra, O.K.; Chung, H.M.; Kassner, T.F.; Park, J.H.; Shack, W.J. [Argonne National Lab., IL (United States); Zhang, J.; Brust, F.W.; Dong, P. [Battelle Columbus Labs., Columbus, OH (United States)

    1998-03-01

    The effect of dissolved oxygen level on fatigue life of austenitic stainless steels is discussed and the results of a detailed study of the effect of the environment on the growth of cracks during fatigue initiation are presented. Initial test results are given for specimens irradiated in the Halden reactor. Impurities introduced by shielded metal arc welding that may affect susceptibility to stress corrosion cracking are described. Results of calculations of residual stresses in core shroud weldments are summarized. Crack growth rates of high-nickel alloys under cyclic loading with R ratios from 0.2--0.95 in water that contains a wide range of dissolved oxygen and hydrogen concentrations at 289 and 320 C are summarized.

  14. Fatigue, Wear and Cracking of Dental Materials

    Directory of Open Access Journals (Sweden)

    Traian Eugen Bolfa

    2015-07-01

    Full Text Available Evaluation of the method of failure and crack propagation in dental metals, ceramics and polymer composite materials associated with occlusal activity are associated with contact, twisting and sliding modes. Such loads can result in various combinations of damage due to fatigue and wear. In order to increase sustainability and longevity the dental materials must demonstrate sufficient strength to dynamic stresses. In the case of masticatory forces associated with high contact tensions, the contact area of the superficial layer is under a state of specialcomplex voltage. Variations in the material or the structure, impurities, scratches and voids can directly influence the structural integrity of the material and result in microscopic cracks. These cracks propagate under repeated cyclic loading leading to dental restoration failure.

  15. Inverse Crack Problems in Piezoelectric Solids

    Science.gov (United States)

    Sladek, Jan; Sladek, Vladimir; Zhang, Chuanzeng

    2010-05-01

    In the present paper, the meshless local Petrov-Galerkin (MLPG) method is applied to cracked piezoelectric solids under a stationary or transient dynamic load and unspecified electrical conditions on the crack surfaces. On the outer surface of the cracked solid the electrical boundary conditions are over-specified. The coupled governing partial differential equations are satisfied in a weak-form on small fictitious sub-domains. Nodal points are introduced and spread on the analyzed domain and each node is surrounded by a small circle for simplicity, but without loss of generality. The spatial variations of the displacements and the electric potential are approximated by the Moving Least-Squares (MLS) scheme. After performing the spatial integrations, a system of linear algebraic equations for unknown nodal values is obtained. Singular value decomposition (SVD) is applied to solve the ill-conditioned linear system of algebraic equations obtained from the local integral equations (LIEs) after the MLS approximation.

  16. Computer Simulations of the Fatigue Crack Propagation

    Directory of Open Access Journals (Sweden)

    A. Materna

    2000-01-01

    Full Text Available The following hypothesis for design of structures based on the damage tolerance philosophy is laid down: the perpendicular fatigue crack growth rate v in a certain point of a curved crack front is given by the local value of stress intensity factor per unit of nominal stress K' and the local triaxiality T which describes the constraint. The relationship v = f (K', T is supposed to be typical for a given loading spectrum and material. Such relationship for a 2024 Al alloy and the flight-simulation spectrum was derived from the fatigue test of the rectangular panel with the central hole and used for three-dimensional simulation of the corner fatigue crack propagation in the model of the wing spar flangeplate. Finite element and boundary element methods were used for these computations. The results of the simulation are in good agreement with the experiment.

  17. Hydraulic Features of the Excavation Disturbed Zone - Laboratory investigations of samples taken from the Q- and S-tunnels at Aespoe HRL

    Energy Technology Data Exchange (ETDEWEB)

    Ericsson, Lars O.; Brinkhoff, Petra; Gustafson, Gunnar; Kvartsberg, Sara (Div. of GeoEngineering, Dept. of Civil and Environmental Engineering, Chalmers Univ. of Technology, Goeteborg (Sweden))

    2009-12-15

    The general aim of the project has been to contribute to the SKB safety and assessment analysis with realistic figures of hydraulic properties in an excavation disturbed zone. The project had the following more detailed objectives: - Develop a laboratory method to determine fracture transmissivity under water-saturated conditions. - Provide magnitudes for realistic values for fracture transmissivity in the disturbed or damaged zone due to excavation. - Map micro cracks radially from the tunnel wall. - Map the spread of matrix porosity radially from the tunnel wall. - Develop single-hole hydraulic testing methodology in tunnel wall for saturated conditions. - Integration of fracture geometries and transmissivity investigations for conceptual hydraulic modelling of the bedrock along a tunnel wall

  18. The mechanics of moisture-expansion cracking in fired-clay ceramics

    Science.gov (United States)

    Hamilton, Andrea; Hall, Christopher

    2013-03-01

    Samian ware (or terra sigillata) is a type of fired-clay ceramic produced at a number of sites in France in the period 50 BC to 200 AD and widely traded in Western Europe. It has a characteristic high-gloss surface, formed by application of a non-calcareous clay slip to the green body before firing. New SEM observations show that the slip layer is frequently crazed, although the cracks are not usually visible to the unaided eye. We discuss the mechanics of the crazing, and show that the cracking is driven by rehydroxylation (RHX) moisture expansion. Observations and analysis aid in understanding the RHX dating of archaeological pottery by showing that craze networks permit efficient transport of moisture through the slip layer.

  19. Crack initiation and crack growth behavior of carbon and low-alloy steels

    Energy Technology Data Exchange (ETDEWEB)

    Gavenda, D.J.; Luebbers, P.R.; Chopra, O.K. [Argonne National Lab., IL (United States). Energy Technology Div.

    1997-01-01

    Section III of the ASME Boiler and Pressure Vessel Code specifies fatigue design curves for structural materials. These curves were based on tests of smooth polished specimens at room temperature in air. The effects of reactor coolant environments are not explicitly addressed by the Code design curves, but recent test data illustrate potentially significant effects of LWR coolant environments on the fatigue resistance of carbon and low-alloy steels. Under certain loading and environmental conditions, fatigue lives of test specimens may be a factor of {approx}70 shorter than in air. Results of fatigue tests that examine the influence of reactor environment on crack imitation and crack growth of carbon and low-alloy steels are presented. Crack lengths as a function of fatigue cycles were determined in air by a surface replication technique, and in water by block loading that leaves marks on the fracture surface. Decreases in fatigue life of low-alloy steels in high-dissolved-oxygen (DO) water are primarily caused by the effects of environment during early stages of fatigue damage, i.e., growth of short cracks <100 {micro}m in depth. For crack sizes of >100 {micro}m, crack growth rates in high-DO water are higher than in air by one order of magnitude. The effects of LWR environments on growth of short cracks are discussed.

  20. Production of steam cracking feedstocks by mild cracking of plastic wastes

    Energy Technology Data Exchange (ETDEWEB)

    Angyal, Andras; Miskolczi, Norbert; Bartha, Laszlo; Tungler, Antal; Nagy, Lajos; Vida, Laszlo; Nagy, Gabor

    2010-11-15

    In this work the utility of new possible petrochemical feedstocks obtained by plastic waste cracking has been studied. The cracking process of polyethylene (PE), polyethylene-polypropylene (PEPP) and polyethylene-polystyrene (PEPS) has been carried out in a pilot scale tubular reactor. In this process mild reaction parameters has been applied, with the temperature of 530 C and the residence time of 15 min. The produced hydrocarbon fractions as light- and middle distillates were tested by using a laboratory steam cracking unit. It was concluded that the products of the mild cracking of plastic wastes could be applied as petrochemical feedstocks. Based on the analytical data it was determined that these liquid products contained in significant concentration (25-50 wt.%) of olefin hydrocarbons. Moreover the cracking of polystyrene containing raw material resulted in liquid products with significant amounts of aromatic hydrocarbons too. The steam cracking experiments proved that the products obtained by PE and PEPP cracking resulted in similar or better ethylene and propylene yields than the reference samples, however the aromatic content of PEPS products reduced the ethylene and propylene yields. (author)

  1. Thermographic characterization of stress during crack growth

    Science.gov (United States)

    Cramer, K. E.; Dawicke, David S.; Welch, Christopher S.

    1992-01-01

    A full-field-thermographic technique for imaging stress patterns in dynamically loaded structures using general purpose IR imaging and image processing hardware is described. The inspection technique is based on the thermoelastic effect. A simple geometry is examined, and the experimentally determined values for the stress invariant are shown to be consistent with theoretical and numerical calculations. The application of full-field-thermographic measurement would ensure that the observed stress field has a common sampling period, thus allowing the observation of rapidly occurring stress anomalies such as the propagation of a fatigue crack. Fatigue crack propagation in two consecutive thermoelastic stress images from an aluminum sample is shown.

  2. Fast electromigration crack in nanoscale aluminum film

    Science.gov (United States)

    Emelyanov, O. A.; Ivanov, I. O.

    2014-08-01

    The current-induced breakage of 20 nm thin aluminum layers deposited onto capacitor grade polypropylene (PP) films is experimentally studied. Biexponential current pulses of different amplitude (10-15 A) and duration (0.1-1 μs) were applied to the samples. Breakage occurred after fast development of electromigrating ˜200 nm-wide cracks with initial propagation velocity of ˜1 m/s under a high current density of ˜1012 A/m2. The cracks stopped when their lengths reached 250-450 μm. This behavior is explained by the balance of electromigration and stress-induced atomic fluxes.

  3. Crack Sensing Scheme in Rail Tracking System

    Directory of Open Access Journals (Sweden)

    Ch. Muneendra Rao,

    2014-01-01

    Full Text Available A major share to the Indian economy is contributed by the commercial transport railway network. So, any problems of crack detection in railway network when encountered, may be dealt with a robust and cost effective solution, else, there may be a proportionate decrease in the nations economy. This paper attempts to provide a viable solution by discussing the technical details and design aspects. The discussion continues with the explanation of different criteria involved in choosing simple components like GPS module,PC,IR-photo diode based crack detector module, modeled for effective implementation in India.

  4. Fatigue crack growth under variable amplitude loading

    Science.gov (United States)

    Sidawi, Jihad A.

    1994-01-01

    Fatigue crack growth tests were conducted on an Fe 510 E C-Mn steel and a submerged arc welded joint from the same material under constant, variable, and random loading amplitudes. Paris-Erdogan's crack growth rate law was tested for the evaluation of m and C using the stress intensity factor K, the J-integral, the effective stress intensity factor K(sub eff), and the root mean square stress intensity factor K(sub rms) fracture mechanics concepts. The effect of retardation and residual stresses resulting from welding was also considered. It was found that all concepts gave good life predictions in all cases.

  5. Multiple Gastrointestinal Complications of Crack Cocaine Abuse

    Directory of Open Access Journals (Sweden)

    Neal Carlin

    2014-01-01

    Full Text Available Cocaine and its alkaloid free base “crack-cocaine” have long since been substances of abuse. Drug abuse of cocaine via oral, inhalation, intravenous, and intranasal intake has famously been associated with a number of medical complications. Intestinal ischemia and perforation remain the most common manifestations of cocaine associated gastrointestinal disease and have historically been associated with oral intake of cocaine. Here we find a rare case of two relatively uncommon gastrointestinal complications of hemorrhage and pancreatitis presenting within a single admission in a chronic crack cocaine abuser.

  6. Matrix cracking of fiber-reinforced ceramic composites in shear

    Science.gov (United States)

    Rajan, Varun P.; Zok, Frank W.

    2014-12-01

    The mechanics of cracking in fiber-reinforced ceramic matrix composites (CMCs) under general loadings remains incomplete. The present paper addresses one outstanding aspect of this problem: the development of matrix cracks in unidirectional plies under shear loading. To this end, we develop a model based on potential energy differences upstream and downstream of a fully bridged steady-state matrix crack. Through a combination of analytical solutions and finite element simulations of the constituent stresses before and after cracking, we identify the dominant stress components that drive crack growth. We show that, when the axial slip lengths are much larger than the fiber diameter and when interfacial slip precedes cracking, the shear stresses in the constituents are largely unaffected by the presence of the crack; the changes that do occur are confined to a 'core' region within a distance of about one fiber diameter from the crack plane. Instead, the driving force for crack growth derives mainly from the axial stresses-tensile in the fibers and compressive in the matrix-that arise upon cracking. These stresses are well-approximated by solutions based on shear-lag analysis. Combining these solutions with the governing equation for crack growth yields an analytical estimate of the critical shear stress for matrix cracking. An analogous approach is used in deriving the critical stresses needed for matrix cracking under arbitrary in-plane loadings. The applicability of these results to cross-ply CMC laminates is briefly discussed.

  7. THERMAL FRACTURE OF FUNCTIONALLY GRADED PLATE WITH PARALLEL SURFACE CRACKS

    Institute of Scientific and Technical Information of China (English)

    Yuezhong Feng; Zhihe Jin

    2009-01-01

    This work examines the fracture behavior of a functionally graded material (FGM) plate containing parallel surface cracks with alternating lengths subjected to a thermal shock. The thermal stress intensity factors (TSIFs) at the tips of long and short cracks are calculated using a singular integral equation technique. The critical thermal shock △T_c that causes crack initiation is calculated using a stress intensity factor criterion. Numerical examples of TSIFs and △T_c for an Al_2O_3/Si_3N_4 FGM plate are presented to illustrate the effects of thermal property gradation, crack spacing and crack length ratio on the TSIFs and △T_c. It is found that for a given crack length ratio, the TSIFs at the tips of both long and short cracks can be reduced significantly and △T_c can be enhanced by introducing appropriate material gradation. The TSIFs also decrease dramatically with a decrease in crack spacing. The TSIF at the tips of short cracks may be higher than that for the long cracks under certain crack geometry conditions. Hence, the short cracks instead of long cracks may first start to grow under the thermal shock loading.

  8. Effects of variations in hydraulic conductivity and flow conditions on groundwater flow and solute transport in peatlands

    Energy Technology Data Exchange (ETDEWEB)

    Kellner, Erik [Dept. of Forest Ecology, Univ. of Helsinki (Finland)

    2007-02-15

    In this report it is examined to what extent the variation in hydraulic conductivity within a peatland and adjoining sediments would affect the flow patterns within it under some certain hydraulic-head gradients and other certain border conditions. The first part of the report contains a short review of organic and mineral-soil sediment types and characteristics and what we know about present peatlands and underlying sediments in the SKB investigation areas today. In the next part, a 2-dimensional model is used to simulate flows and transports in different settings of a peatland, with the objective of studying the effects of some particular factors: 1. The magnitude of the hydraulic conductivity of the peat and of underlying layers. 2. Presence and positions of cracks in underlying clay layers. 3. Anisotropy and heterogeneity in peat hydraulic conductivity. 4. The size of the water recharge at the peatland surface. 5. The seasonal variation of the water recharge. The modelling results show that the importance of flow direction decreases with decreasing hydraulic conductivity in the peatland. This occurs as the convective flux is slowed down and the transport is taken over by the diffusive flux. Because the lowest hydraulic conductivity layer to large extent determines the size of the flow, presence of a low-conductivity layer, such as a layer of clay, is an important factor. Presence of cracks in such tight layers can increase the transport of solutes into the peat. The highest inflow rates are reached when such cracks occur in discharge areas with strong upward flow. On the other hand, a conservative solute can spread efficiently if there is a crack in low-flow locations. The effect of anisotropy is found to be small, partly because the horizontal gradients become smaller as distances are larger. The effect of layers with high or low permeability varies depending on the location and the prevailing gradients. One tight layer has a strong effect on the flow pattern

  9. Bubble-Driven Inertial Micropump

    CERN Document Server

    Torniainen, Erik D; Markel, David P; Kornilovitch, Pavel E

    2012-01-01

    The fundamental action of the bubble-driven inertial micropump is investigated. The pump has no moving parts and consists of a thermal resistor placed asymmetrically within a straight channel connecting two reservoirs. Using numerical simulations, the net flow is studied as a function of channel geometry, resistor location, vapor bubble strength, fluid viscosity, and surface tension. Two major regimes of behavior are identified: axial and non-axial. In the axial regime, the drive bubble either remains inside the channel or continues to grow axially when it reaches the reservoir. In the non-axial regime the bubble grows out of the channel and in all three dimensions while inside the reservoir. The net flow in the axial regime is parabolic with respect to the hydraulic diameter of the channel cross-section but in the non-axial regime it is not. From numerical modeling, it is determined that the net flow is maximal when the axial regime crosses over to the non-axial regime. To elucidate the basic physical princi...

  10. Hydraulic Conductivity Anisotropy of Heterogeneous Unsaturated Soils

    Science.gov (United States)

    Sun, Dongmin; Zhu, Jianting

    2010-05-01

    The effects of saturation degree (or capillary pressure) on hydraulic conductivity anisotropy in unsaturated soils have not been fully understood. This study developed an approach based on a conceptualization of combining the neural network based pedo-transfer function (PTF) results with the thin layer concept to explore the capillary pressure-dependent anisotropy in relation to soil texture and soil bulk density. The main objective is to examine how anisotropy characteristics are related to the relationships between hydraulic parameters and the basic soil attributes such as texture and bulk density. The hydraulic parameters are correlated with the texture and bulk density based on the pedo-transfer function (PTF) results. It is demonstrated that non-monotonic behavior of the unsaturated soil anisotropy in relation to the capillary pressure is only observed when the saturated hydraulic conductivity and the shape parameter are both related to the mean particle diameter. When only one hydraulic parameter is related to the grain diameter or when both are not related to the same attribute simultaneously, the unsaturated soil anisotropy increases monotonically with the increasing capillary pressure head. Therefore, it is suggested that this behavior is mainly due to the coupled dependence of the layer saturated hydraulic conductivities and the shape factors on the texture and bulk density. The correlation between the soil grain diameter and bulk density decreases the anisotropy effects of the unsaturated layered soils. The study illustrates that the inter-relationships of soil texture, bulk density, and hydraulic properties may cause vastly different characteristics of anisotropic unsaturated soils.

  11. Hydraulic responses of whole vines and individual roots of kiwifruit (Actinidia chinensis) following root severance.

    Science.gov (United States)

    Black, Marykate Z; Patterson, Kevin J; Minchin, Peter E H; Gould, Kevin S; Clearwater, Michael J

    2011-05-01

    Whole vine (K(plant)) and individual root (K(root)) hydraulic conductances were measured in kiwifruit (Actinidia chinensis Planch. var. chinensis 'Hort16A') vines to observe hydraulic responses following partial root system excision. Heat dissipation and compensation heat pulse techniques were used to measure sap flow in trunks and individual roots, respectively. Sap flux and measurements of xylem pressure potential (Ψ) were used to calculate K(plant) and K(root) in vines with zero and ∼80% of roots severed. Whole vine transpiration (E), Ψ and K(plant) were significantly reduced within 24 h of root pruning, and did not recover within 6 weeks. Sap flux in intact roots increased within 24 h of root pruning, driven by an increase in the pressure gradient between the soil and canopy and without any change in root hydraulic conductance. Photosynthesis (A) and stomatal conductance (g(s)) were reduced, without significant effects on leaf internal CO(2) concentration (c(i)). Shoot growth rates were maintained; fruit growth and dry matter content were increased following pruning. The woody roots of kiwifruit did not demonstrate a rapid dynamic response to root system damage as has been observed previously in monocot seedlings. Increased sap flux in intact roots with no change in K(root) and only a moderate decline in shoot A suggests that under normal growing conditions root hydraulic conductance greatly exceeds requirements for adequate shoot hydration.

  12. Hydraulic leg extension is not necessarily the main drive in large spiders.

    Science.gov (United States)

    Weihmann, Tom; Günther, Michael; Blickhan, Reinhard

    2012-02-15

    Unlike most other arthropods, spiders have no extensor muscles in major leg joints. Therefore, hydraulic pressure generated in the prosoma provides leg extension. For decades, this mechanism was held responsible for the generation of the majority of the ground reaction forces, particularly in the hind legs. During propulsion, the front leg pairs must shorten whereas the hind legs have to be extended. Assuming that hind legs are essentially driven by hydraulics, their force vectors must pass the leg joints ventrally. However, at least in accelerated escape manoeuvres, we show here for the large cursorial spider species Ancylometes concolor that these force vectors, when projected into the leg plane, pass all leg joints dorsally. This indicates a reduced impact of the hydraulic mechanism on the generation of ground reaction forces. Although hydraulic leg extension still modulates their direction, the observed steep force vectors at the hind legs indicate a strong activity of flexors in the proximal joint complex that push the legs against the substrate. Consequently, the muscular mechanisms are dominant at least in the hind legs of large spiders.

  13. Coupled-disturbance-observer-based position tracking control for a cascade electro-hydraulic system.

    Science.gov (United States)

    Guo, Qing; Yin, Jing-Min; Yu, Tian; Jiang, Dan

    2017-05-01

    The disturbance suppression is one of the most common control problems in electro-hydraulic systems. especially largely an unknown disturbance often obviously degrades the dynamic performance by biasing the desired actuator outputs (e.g., load forces or torques). In order to reject the dynamic disturbances in some multi-degree-of-freedom manipulators driven by electro-hydraulic actuators, this paper proposes a state feedback control of the cascade electro-hydraulic system based on a coupled disturbance observer with backstepping. The coupled disturbance observer is designed to estimate both the independent element and the coupled element of the external loads on each electro-hydraulic actuator. The cascade controller has the ability to compensate for the disturbance estimating, as well as guarantees the system state error convergence to a prescribed steady state level. The effectiveness of the proposed controller for the suppression of largely unknown disturbances has been demonstrated by comparative study, which implies the proposed approach can achieve better dynamic performance on the motion control of Two-Degree-of-Freedom robotic arm. Copyright © 2017 ISA. Published by Elsevier Ltd. All rights reserved.

  14. Thermal-hydraulic modeling and analysis of hydraulic system by pseudo-bond graph

    Institute of Scientific and Technical Information of China (English)

    胡均平; 李科军

    2015-01-01

    To increase the efficiency and reliability of the thermodynamics analysis of the hydraulic system, the method based on pseudo-bond graph is introduced. According to the working mechanism of hydraulic components, they can be separated into two categories: capacitive components and resistive components. Then, the thermal-hydraulic pseudo-bond graphs of capacitive C element and resistance R element were developed, based on the conservation of mass and energy. Subsequently, the connection rule for the pseudo-bond graph elements and the method to construct the complete thermal-hydraulic system model were proposed. On the basis of heat transfer analysis of a typical hydraulic circuit containing a piston pump, the lumped parameter mathematical model of the system was given. The good agreement between the simulation results and experimental data demonstrates the validity of the modeling method.

  15. Crack Growth along Interfaces in Porous Ceramic Layers

    DEFF Research Database (Denmark)

    Sørensen, Bent F.; Horsewell, Andy

    2001-01-01

    Crack growth along porous ceramic layers was studied experimentally. Double cantilever beam sandwich specimens were loaded with pure bending moments to obtain stable crack growth. The experiments were conducted in an environmental scanning electron microscope enabling in situ observations...

  16. A MOVING CRACK IN A NONHOMOGENEOUS MATERIAL STRIP

    Institute of Scientific and Technical Information of China (English)

    Wang Baolin; Han Jiecai

    2006-01-01

    This paper considers an anti-plane moving crack in a nonhomogencous material strip of finite thickness. The shear modulus and the mass density of the strip are considered for a class of functional forms for which the equilibrium equation has analytical solutions. The problem is solved by means of the singular integral equation technique. The stress field near the crack tip is obtained. The results are plotted to show the effect of the material non-homogeneity and crack moving velocity on the crack tip field. Crack bifurcation behaviour is also discussed. The paper points out that use of an appropriate fracture criterion is essential for studying the stability of a moving crack in nonhomogeneous materials. The prediction whether the unstable crack growth will be enhanced or retarded is strongly dependent on the type of the fracture criterion used. is a suitable failure criterion for moving cracks in nonhomogeneous materials.

  17. Partial discharge-induced crack growth in dielectric materials

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    Partial discharge(PD) of an air-filled semi-permeable crack in a dielectric material is studied based on the streamer-type discharge mechanism to explore the effects of applied mechanical-electric fields on crack growth.Within the frame of two-dimensional deformation,the electric field inside the crack is first derived by taking the crack deformation into account.Then,the effects of electric field before PD are discussed through considering the contribution of the induced electric field inside the deformed crack space to the total energy release rate.Finally,PD and its effects on crack growth are investigated.It is found that:(1) before PD,the applied electric field always retards crack growth;(2) during PD,the applied electric field can induce crack growth in dielectric materials.

  18. Cracking the Genetic Code | NIH MedlinePlus the Magazine

    Science.gov (United States)

    ... this page please turn Javascript on. Cracking the Genetic Code, From NIH Director Dr. Francis S. Collins Past Issues / ... moment in science in 2000: Cracking of the genetic code raised the prospect of pinpointing the root causes ...

  19. Acoustic emission assessment of interface cracking in thermal barrier coatings

    Science.gov (United States)

    Yang, Li; Zhong, Zhi-Chun; Zhou, Yi-Chun; Zhu, Wang; Zhang, Zhi-Biao; Cai, Can-Ying; Lu, Chun-Sheng

    2016-04-01

    In this paper, acoustic emission (AE) and digital image correlation methods were applied to monitor interface cracking in thermal barrier coatings under compression. The interface failure process can be identified via its AE features, including buckling, delamination incubation and spallation. According to the Fourier transformation of AE signals, there are four different failure modes: surface vertical cracks, opening and sliding interface cracks, and substrate deformation. The characteristic frequency of AE signals from surface vertical cracks is 0.21 MHz, whilst that of the two types of interface cracks are 0.43 and 0.29 MHz, respectively. The energy released of the two types of interface cracks are 0.43 and 0.29 MHz, respectively. Based on the energy released from cracking and the AE signals, a relationship is established between the interface crack length and AE parameters, which is in good agreement with experimental results.

  20. A Parametric Study of Crack Propagation During Sonic IR Inspection

    Science.gov (United States)

    Chen, J. C.; Kephart, J.; Riddell, W. T.

    2006-03-01

    We have developed an experiment to study the propagation of synthetic cracks under various controlled conditions during sonic IR inspection. The experiment provides for good repeatability in testing. The parameters of interest include the initial crack length, load history (stress intensity and load ratio) during crack generation, geometry of the crack, material, and also the various conditions involving the ultrasonic source. In general, we find that under typical sonic IR inspection conditions, the initial crack will propagate when subjected to sonic IR testing. The crack growth after each inspection event varies and exhibits a distribution in length of propagation. The results show that the average crack propagation decreases with increasing initial crack length and increasing stress intensity.