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Guedda, H. Z., T. Ouahrani, A. Morales-García, R. Franco, M. A. Salvadó, P. Pertierra y J. M. Recio. "Computer simulations of 3C-SiC under hydrostatic and non-hydrostatic stresses". Physical Chemistry Chemical Physics 18, n.º 11 (2016): 8132–39. http://dx.doi.org/10.1039/c6cp00081a.
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Doe, T. W. y G. Boyce. "Orientation of hydraulic fractures in salt under hydrostatic and non-hydrostatic stresses". International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts 26, n.º 6 (diciembre de 1989): 605–11. http://dx.doi.org/10.1016/0148-9062(89)91441-1.
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Wang, Xu y Peter Schiavone. "Coated non-elliptical harmonic inclusions with internal uniform hydrostatic stresses". International Journal of Engineering Science 63 (febrero de 2013): 30–39. http://dx.doi.org/10.1016/j.ijengsci.2012.11.003.
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Wang, Xu y Peter Schiavone. "Two non-elliptical decagonal quasicrystalline inclusions with internal uniform hydrostatic phonon stresses". ZAMM - Journal of Applied Mathematics and Mechanics / Zeitschrift für Angewandte Mathematik und Mechanik 98, n.º 11 (17 de septiembre de 2018): 2027–34. http://dx.doi.org/10.1002/zamm.201800106.
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Korotaev, Pavel, Pavel Pokatashkin y Aleksey Yanilkin. "The role of non-hydrostatic stresses in phase transitions in boron carbide". Computational Materials Science 121 (agosto de 2016): 106–12. http://dx.doi.org/10.1016/j.commatsci.2016.04.041.
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Wang, Xu y Peter Schiavone. "Internal uniform hydrostatic stresses in a three-phase non-elliptical inclusion subjected to a nearby concentrated couple". Mathematics and Mechanics of Solids 24, n.º 9 (29 de enero de 2019): 2931–43. http://dx.doi.org/10.1177/1081286519827059.
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We apply conformal mapping techniques with analytic continuation to study the existence of a uniform hydrostatic stress field inside a non-elliptical inclusion bonded to an infinite matrix via a finite thickness interphase layer when the matrix is simultaneously subjected to a concentrated couple as well as uniform remote in-plane stresses. We show that the desired internal uniform hydrostatic stress field is possible for given material and geometric parameters provided a certain constraint is placed on the remote loading. Subsequently, when the single loading parameter, five material parameters and three geometric parameters are prescribed, all of the unknown complex coefficients appearing in the series representing the corresponding conformal mapping function can be uniquely determined from a set of nonlinear recurrence relations. We find that the internal uniform hydrostatic stress field, the constant mean stress in the interphase layer and the hoop stress along the inner interface on the interphase layer side are all unaffected by the existence of the concentrated couple whereas the non-elliptical shape of the (three-phase) inclusion is attributed solely to the influence of the nearby concentrated couple.
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Zerihun, Yebegaeshet T. "A Numerical Study of Non-hydrostatic Shallow Flows in Open Channels". Archives of Hydro-Engineering and Environmental Mechanics 64, n.º 1 (27 de junio de 2017): 17–35. http://dx.doi.org/10.1515/heem-2017-0002.
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AbstractThe flow field of many practical open channel flow problems, e.g. flow over natural bed forms or hydraulic structures, is characterised by curved streamlines that result in a non-hydrostatic pressure distribution. The essential vertical details of such a flow field need to be accounted for, so as to be able to treat the complex transition between hydrostatic and non-hydrostatic flow regimes. Apparently, the shallow-water equations, which assume a mild longitudinal slope and negligible vertical acceleration, are inappropriate to analyse these types of problems. Besides, most of the current Boussinesq-type models do not consider the effects of turbulence. A novel approach, stemming from the vertical integration of the Reynolds-averaged Navier-Stokes equations, is applied herein to develop a non-hydrostatic model which includes terms accounting for the effective stresses arising from the turbulent characteristics of the flow. The feasibility of the proposed model is examined by simulating flow situations that involve non-hydrostatic pressure and/or nonuniform velocity distributions. The computational results for free-surface and bed pressure profiles exhibit good correlations with experimental data, demonstrating that the present model is capable of simulating the salient features of free-surface flows over sharply-curved overflow structures and rigid-bed dunes.
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Lazemi, Hossein Ali, Mohammad Fatehi Marji, Ali Reza Yarahmadi Bafghi y Kamran Goshtasbi. "Rock Failure Analysis of the Broken Zone Around a Circular Opening / Analiza pęknięcia skały w strefie naruszonej wokół otworu kolistego". Archives of Mining Sciences 58, n.º 1 (1 de marzo de 2013): 165–88. http://dx.doi.org/10.2478/amsc-2013-0012.
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In this paper, considering the non-linear Hoek-Brown failure criterion, a new theoretical model is presented to predict the stress components and estimate the plastic zone radius around a circular tunnel. The tunnel is excavated in an elasto-plastic rock mass subjected to plane hydrostatic and axial in situ stresses. Effects of the axial in situ stress on the plastic zone radius and stress components are studied. Based on the combination of plane hydrostatic and axial in situ stresses with the equilibrium equation and a suitable failure criterion (Hoek & Brown failure criterion), several cases are considered. For each case, the stress components, the plastic zone radius and the necessary conditions for its occurrence are determined. The results obtained by the present method are compared with those using Mohr-Coulomb criterion and with the experimental data, illustrating the validity of the present model in predicting the failure zone radius.
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Wu, Bisheng, Xi Zhang, Robert G. Jeffrey y Bailin Wu. "A semi-analytic solution of a wellbore in a non-isothermal low-permeability porous medium under non-hydrostatic stresses". International Journal of Solids and Structures 49, n.º 13 (junio de 2012): 1472–84. http://dx.doi.org/10.1016/j.ijsolstr.2012.02.035.
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Wang, Xu y Peter Schiavone. "Uniform hydrostatic stresses inside a coated non-parabolic inhomogeneity in the vicinity of a concentrated couple". International Journal of Solids and Structures 206 (diciembre de 2020): 23–29. http://dx.doi.org/10.1016/j.ijsolstr.2020.09.001.
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Rizza, Giancarlo, Yaasiin Ramjauny, Marc Hayoun, Sandrine Perruchas, Thierry Gacoin, Patrick Kluth y Mark C. Ridgway. "Saturation of the ion-hammering effect for large non-hydrostatic capillarity stresses in colloidal silica nanoparticles". Nanotechnology 22, n.º 47 (2 de noviembre de 2011): 475302. http://dx.doi.org/10.1088/0957-4484/22/47/475302.
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Gudkova, T. V., A. V. Batov y V. N. Zharkov. "Model Estimates of Non-Hydrostatic Stresses in the Martian Crust and Mantle: 1—Two-Level Model". Solar System Research 51, n.º 6 (noviembre de 2017): 457–78. http://dx.doi.org/10.1134/s003809461706003x.
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Batov, A. V., T. V. Gudkova y V. N. Zharkov. "Model Estimates of Non-Hydrostatic Stresses in the Martian Crust and Mantle: 2−Three-Level Model". Solar System Research 52, n.º 3 (mayo de 2018): 234–40. http://dx.doi.org/10.1134/s0038094618030012.
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Moayyedian, Farzad y Mehran Kadkhodayan. "Non-linear influence of hydrostatic pressure on the yielding of asymmetric anisotropic sheet metals". Mathematics and Mechanics of Solids 23, n.º 2 (14 de noviembre de 2016): 159–80. http://dx.doi.org/10.1177/1081286516675662.
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The objective of the current research is the investigation into possible non-linear influence of hydrostatic pressure on yielding of asymmetric (exhibiting the so-called “strength-differential effect”) anisotropic sheet metals. To reach this aim, two yield functions are developed, called here “non-linear pressure sensitive criteria I and II,” (NPC-1 and NPC-2). In addition, the non-associated flow rules are employed for these new criteria. The yield functions are defined as non-linearly dependent on hydrostatic pressure, while the plastic potential functions are introduced to be pressure insensitive. To calibrate these criteria, the yield functions need 10 directional experimental yield stresses and the plastic potential functions need eight Lankford coefficients data points. Four well-known anisotropic sheet metals with different structures, namely AA 2008-T4, a Face Centered Cubic material (FCC), AA 2090-T3, a Face Centered Cubic material (FCC), AZ31, a hexagonal closed packed material (HCP) and high-purity [Formula: see text]-titanium (HCP) are considered as case studies. Finally, it is observed that NPC-1 and NPC-2 are more successful than previous criteria in anticipating directional strength and mechanical properties.
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Wang, Xu, Liang Chen y Peter Schiavone. "An elastic harmonic inclusion near a rigid harmonic inclusion loaded by a couple". IMA Journal of Applied Mathematics 84, n.º 3 (7 de febrero de 2019): 555–66. http://dx.doi.org/10.1093/imamat/hxz005.
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AbstractWe use conformal mapping techniques to solve the inverse problem concerned with an elastic non-elliptical harmonic inclusion in the vicinity of a rigid non-elliptical harmonic inclusion loaded by a couple when the surrounding matrix is subjected to remote uniform stresses. Both a size-independent complex loading parameter and a size-dependent real loading parameter are introduced as part of the solution procedure. The stress field inside the elastic inclusion is uniform and hydrostatic; the interfacial normal and tangential stresses as well as the hoop stress on the matrix side are uniform along each one of the two inclusion–matrix interfaces. The tangential stress along the interface of the elastic inclusion (free of external loading) vanishes, whereas that along the interface of the rigid inclusion (loaded by the couple) does not. A novel method is proposed to determine the area of the rigid inclusion.
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Lennon, R. F. "The Effects of Cold Forming and Welding Residual Stress States on the Buckling Resistance of Orthogonally Stiffened Cylinders". Applied Mechanics and Materials 5-6 (octubre de 2006): 509–18. http://dx.doi.org/10.4028/www.scientific.net/amm.5-6.509.
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The buckling resistance of orthogonally stiffened cylinders is investigated for elastic critical buckling and non-linear elasto-plastic buckling tests. The effects of residual stresses arising from cold forming the cylinder and welding frame components are considered in the analysis of two stiffened cylinder models with similar material weights and different geometric spacings. A static axial load is applied to the models to represent loading from the supported structure followed by a non-linear elasto-plastic buckling step representing a wave loading combined with hydrostatic pressure, producing large displacement compartment buckling. Residual stress is shown to cause a reduction in buckling resistance of approximately 25% in the stiffened cylinder segments.
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Angel, Ross J., Maciej Bujak, Jing Zhao, G. Diego Gatta y Steven D. Jacobsen. "Effective hydrostatic limits of pressure media for high-pressure crystallographic studies". Journal of Applied Crystallography 40, n.º 1 (12 de enero de 2007): 26–32. http://dx.doi.org/10.1107/s0021889806045523.
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The behavior of a number of commonly used pressure media, including nitrogen, argon, 2-propanol, a 4:1 methanol–ethanol mixture, glycerol and various grades of silicone oil, has been examined by measuring the X-ray diffraction maxima from quartz single crystals loaded in a diamond-anvil cell with each of these pressure media in turn. In all cases, the onset of non-hydrostatic stresses within the medium is detectable as the broadening of the rocking curves of X-ray diffraction peaks from the single crystals. The onset of broadening of the rocking curves of quartz is detected at ∼9.8 GPa in a 4:1 mixture of methanol and ethanol and at ∼4.2 GPa in 2-propanol, essentially at the same pressures as the previously reported hydrostatic limits determined by other techniques. Gigahertz ultrasonic interferometry was also used to detect the onset of the glass transition in 4:1 methanol–ethanol and 16:3:1 methanol–ethanol–water, which were observed to support shear waves above ∼9.2 and ∼10.5 GPa, respectively, at 0.8–1.2 GHz. By contrast, peak broadening is first detected at ∼3 GPa in nitrogen, ∼1.9 GPa in argon, ∼1.4 GPa in glycerol and ∼0.9 GPa in various grades of silicone oil. These pressures, which are significantly lower than hydrostatic limits quoted in the literature, should be considered as the practical maximum limits to the hydrostatic behavior of these pressure media at room temperature.
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Ahmad, Mohd Hilton, Jamaloddin Noorzaie y Fayda Al Qbadi. "PRINCIPAL STRESSES IN NON-LINEAR ANALYSIS OF BAKUN CONCRETE FACED ROCKFILL DAM". ASEAN Journal on Science and Technology for Development 25, n.º 2 (22 de noviembre de 2017): 469–97. http://dx.doi.org/10.29037/ajstd.277.
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With rapid population growth and accelerating economic development, much of the world’s WATER which requires urgent attention to ensure sustainable use. Nowadays, Concrete Faced Rockfill Dam (CFRD) is preferred among dam consultant due to its advantages. They are designed to withstand all applied loads; namely gravity load due to its massive weight and hydrostatic load due to water thrust from the reservoir. Bakun CFRD, which ranks as the second highest CFRD in the world when completed, is analyzed to its safety due to both loads mentioned earlier by using Finite Element Method. 2-D plane strain finite element analysis of non-linear Duncan-Chang hyperbolic Model which formulated by Duncan and Chang is used to study the structural response of the dam in respect to the deformation and stresses of Main dam of Bakun’s CFRD project. Dead-Birth-Ghost element technique was used to simulate sequences of construction of the dam as well as during reservoir fillings. The comparison of rigid and flexible foundation on the behaviour of the dam was discussed. The maximum and minimum principal stresses are the maximum and minimum possible values of the normal stresses. The maximum principal stress controls brittle fracture. In the finite element modeling the concrete slab on the upstream was represented through six-noded element, while the interface characteristic between dam body and concrete slab was modeled using interface element. The maximum settlement and stresses of the cross section was founded and the distribution of them were discussed and tabulated in form of contours.
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Taqieddin, Ziad N. y George Z. Voyiadjis. "Studying the effect of a hydrostatic stress/strain reduction factor on damage mechanics of concrete materials". Journal of the Mechanical Behavior of Materials 22, n.º 5-6 (1 de diciembre de 2013): 149–59. http://dx.doi.org/10.1515/jmbm-2013-0022.
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AbstractIn the non-linear finite element analysis (NFEA) of concrete materials, continuum damage mechanics (CDM) provides a powerful framework for the derivation of constitutive models capable of describing the mechanical behavior of such materials. The internal state variables of CDM can be introduced to the elastic analysis of concrete to form elastic-damage models (no inelastic strains), or to the elastic-plastic analysis in order to form coupled/uncoupled elastic-plastic-damage models. Experimental evidence that is well documented in literature shows that the susceptibility of concrete to damage and failure is distinguished under deviatoric loading from that corresponding to hydrostatic loading. A reduction factor is usually introduced into a CDM model to reduce the susceptibility of concrete to hydrostatic stresses/strains. In this work, the effect of a hydrostatic stress/strain reduction factor on the performances of two NFEA concrete models will be studied. These two (independently published) models did not provide any results showing such effect. One of these two models is an elastic-damage model, whereas the other is an uncoupled elastic-plastic-damage model. Simulations and comparisons are carried out between the performances of the two models under uniaxial tensile and compressive loading conditions. Simulations are also provided for the uncoupled elastic-plastic-damage model under the following additional loading conditions: biaxial tension and biaxial compression, uniaxial cyclic loading, and varying ratios of triaxial compressive loadings. These simulations clearly show the effect of the reduction factor on the numerically depicted behaviors of concrete materials. To have rational comparisons, the hydrostatic stress reduction factor applied to each model is chosen to be a function of the internal state variables common to both models. Therefore, once the two models are calibrated to simulate the experimental behaviors, their corresponding reduction factors are readily available at every increment of the iterative NFEA procedures.
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Meir, A., D. S. McNally, J. C. Fairbank, D. Jones y J. P. Urban. "The internal pressure and stress environment of the scoliotic intervertebral disc — a review". Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine 222, n.º 2 (1 de febrero de 2008): 209–19. http://dx.doi.org/10.1243/09544119jeim303.
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The aetiology, in terms of both initiation and progression, of the deformity in idiopathic scoliosis is at present unclear. Even in neuromuscular cases, the mechanisms underlying progression are not fully elucidated. It is thought, however, that asymmetrical loading is involved in the progression of the disease, with evidence mainly from animal studies and modelling. There is, however, very little direct information as to the origin or mechanism of action of these forces in the scoliotic spine. This review describes the concept of intervertebral disc pressure or stress and examines possible measurement techniques. The biological and mechanical consequences of abnormalities in these parameters are described. Future possible studies and their clinical significance are also briefly discussed. Techniques of pressure measurement have culminated in the development of ‘pressure profilometry’, which provides stress profiles across the disc in mutually perpendicular axes. A hydrated intervertebral disc exhibits mainly hydrostatic behaviour. However, in pathological states such as degeneration and scoliosis, non-hydrostatic behaviour predominates and annular peaks of stress occur. Recent studies have shown that, in scoliosis, high hydrostatic pressures are seen with asymmetrical stresses from concave to convex sides. These abnormalities could influence both disc and endplate cellular activity directly, causing asymmetrical growth and matrix changes. In addition, disc cells could be influenced via nutritional changes consequent to end-plate calcification. Evidence suggests that the stress environment of the scoliotic disc is abnormal, probably generated by high and asymmetrical loading of non-muscular origin. If present in the scoliotic spine during daily activities, this could generate a positive feedback of cellular changes, resulting in curve progression. Future advances in understanding may rely on the development of computer models owing to the difficulties of in-vivo invasive measurements.
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Sibiryakov, Boris P., Lourenildo W. B. Leite y Wildney W. S. Vieira. "BEHAVIOR OF STRESSES AND HYDRODYNAMICS FROM MULTICOMPONENT SEISMIC DATA". Revista Brasileira de Geofísica 33, n.º 1 (19 de noviembre de 2015): 57. http://dx.doi.org/10.22564/rbgf.v33i1.601.
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ABSTRACT. A method for fluid-stress modeling of 3D seismic, and drilling data, provided new information on the stress conditions, and on the hydrodynamics of the U11 layer of the Upper Jurassic sandstone reservoir in the Arigol field, Western Siberia, Russia. It is proposed to detect and outline oil fields, and divide them into isolated traps, marked by low sedimentary overburden pressure, and fluid-trapping properties based on correlation between the structural pattern and mapped stress. A different systematic approach was adopted, considering: the use of 3D component seismic data of Vp and Vs velocities; the density ρ, and the stress models of the reservoirs to detect the areas of low overburden pressure P(x, y, z); and the vertical inclination of fractures (faults), ϕ(x, y, z), caused by the non-hydrostatic behavior of stress.Keywords: seismic structured media, porous media, fractured media.RESUMO. Um novo método para a modelagem de tensão e fluidos em sísmica 3D, além de dados de perfuração, forneceram nova informação para as condições de tensão e para a hidrodinâmica da camada U11 do arenito reservatório do Jurássico Superior no Campo Arigol, Oeste da Sibéria, Rússia. São propostos métodos para a detecção e delimitação de campos de petróleo, e segmentá-los em trapas isoladas, marcadas por baixa pressão da sobrecarga sedimentar, e por propriedades de trapeamento de fluidos baseado na correlação entre os padrões estruturais e o mapeamento de tensões. Uma metodologia alternativa e sistemática foi adotada, considerando-se o uso de: dados sísmicos das componentes 3D para as velocidades Vp e Vs; a densidade ρ, e a modelagem dos reservatórios para detectar as áreas de baixa pressão da sobrecarga P(x, y, z); e a inclinação vertical de fraturas (falhas), ϕ(x, y, z), causadas pelo comportamento não-hidrostático das tensões.Palavras-chave: meios sísmicos estruturados, meios porosos, meios fraturados.
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Cho, J. R., C. Y. Park y D. Y. Yang. "Investigation of the Cogging Process by Three-Dimensional Thermo-Viscoplastic Finite Element Analysis". Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture 206, n.º 4 (noviembre de 1992): 277–86. http://dx.doi.org/10.1243/pime_proc_1992_206_084_02.
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The purpose of cogging in open-die press forging is to maximize the internal deformation for better structural homogeneity and centre-line consolidation in the core of the ingot. A three-dimensional thermo-viscoplastic finite element analysis is carried out for the non-isothermal cogging process in order to study the distribution of hydrostatic stresses, effective strains and temperature of the ingot and the die during the process. In the simulation, V-die and flat-die are employed for computation. A circular ingot of body weight 160 ton is subjected to cogging simulation and the effects of cogging parameters, such as die configuration, die width, temperature gradient, height reduction and draft design, are compared between two types of dies. Thus favourable working conditions are suggested for better and more desirable product quality.
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Rousselot, Marie y Urs H. Fischer. "A laboratory study of ploughing". Journal of Glaciology 53, n.º 181 (2007): 225–31. http://dx.doi.org/10.3189/172756507782202775.
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AbstractA new laboratory device is used to investigate the resistance to clast ploughing at the base of glaciers. In experiments in which a ploughing tip is dragged at different velocities and effective normal stresses through water-saturated sediment from Unteraargletscher, Switzerland, pore pressures above and below the hydrostatic level develop around the tip. The absolute magnitude of these nonhydrostatic pore pressures increases with the ploughing velocity but remains small compared to the sediment yield strength, so that the pore pressures do not significantly weaken the sediment. The shear stress on the tip is independent of the velocity but scales with the applied effective normal stress, in agreement with a Coulomb-plastic behavior of the sediment. The results indicate that, depending upon position close to the object, both sediment compaction and dilation can influence the pore-pressure distribution and thus the sediment yield strength. Comparison with other studies of clast ploughing suggests that the significance of sediment weakening in front of ploughing clasts may depend on the relative magnitudes of the non-hydrostatic pore pressures. Therefore, depending on the dominant pore-pressure response of the deforming sediment, clast ploughing may have the potential to either trigger ice-flow instabilities or stabilize glacier motion.
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Ma, Yaocai, Aizhong Lu y Hui Cai. "An analytical method for determining the non-enclosed elastoplastic interface of a circular hole". Mathematics and Mechanics of Solids 25, n.º 5 (26 de febrero de 2020): 1199–213. http://dx.doi.org/10.1177/1081286520909489.
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Based on the Mohr–Coulomb yield criterion, an analytical method is presented to determine the plastic zone in an infinite plate weakened by a circular hole and subjected to non-hydrostatic stresses at infinity. It is worth noting that this paper considers the more complicated case that the plastic zone cannot completely surround the hole, namely the elastoplastic interface is non-enclosed. Initially, the non-circular elastic zone in the physical plane is mapped onto the outer region of a unit circle in the image plane by the conformal transformation in the complex variable method. Thereby, determining the elastoplastic interface is equivalent to solving the mapping function coefficients. The nonlinear equations for solving the coefficients are established by considering both the stress continuity conditions along the elastoplastic interface and the stress boundary conditions along the elastic part of the hole. Naturally, the problem can be further transformed into an optimization problem, which is ultimately achieved by the differential-evolution algorithm; what is more, an analytical solution with high accuracy is obtained. Based on the programmed computing, the influences of various parameters on the shape and size of the plastic zone are given.
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Lynch, Elliot M. y Gordon I. Ogilvie. "Dynamical structure of highly eccentric discs with applications to tidal disruption events". Monthly Notices of the Royal Astronomical Society 500, n.º 3 (7 de noviembre de 2020): 4110–25. http://dx.doi.org/10.1093/mnras/staa3459.
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ABSTRACT Whether tidal disruption events circularize or accrete directly as highly eccentric discs is the subject of current research and appears to depend sensitively on the disc thermodynamics. One aspect of this problem that has not received much attention is that a highly eccentric disc must have a strong, non-hydrostatic variation of the disc scale height around each orbit. As a complement to numerical simulations carried out by other groups, we investigate the dynamical structure of TDE discs using the non-linear theory of eccentric accretion discs. In particular, we study the variation of physical quantities around each elliptical orbit, taking into account the dynamical vertical structure, as well as viscous dissipation and radiative cooling. The solutions include a structure similar to the nozzle-like structure seen in simulations. We find evidence for the existence of the thermal instability in highly eccentric discs dominated by radiation pressure. For thermally stable solutions many of our models indicate a failure of the α-prescription for turbulent stresses. We discuss the consequences of our results for the structure of eccentric TDE discs.
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Klaus, Manuela y Christoph Genzel. "Nondestructive separation of residual stress and composition gradients in thin films by angle- and energy-dispersive X-ray diffraction. I. Theoretical concepts". Journal of Applied Crystallography 50, n.º 1 (1 de febrero de 2017): 252–64. http://dx.doi.org/10.1107/s1600576716020598.
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Different X-ray measurement and data evaluation concepts are presented, which allow for residual stress analysis in thin films with pronounced gradients in chemical composition. These gradients lead to a variation in the strain-free lattice parameter a 0 with respect to the film thickness and superimpose the lattice strain induced by the film's inherent stresses. Non-consideration of a 0(z) gradients is shown to lead to considerable errors (`ghost stresses') in the residual stress depth profiles. With the simulated example of a TiC x N1−x film with a pronounced carbon gradient, the first part of this series introduces four approaches, which permit the separation of residual stress and composition depth distributions at different levels of approximation. They are based on lattice spacing depth profile measurements performed in either the sin2ψ mode or the scattering vector mode, or in combinations of these two scanning modes. Depending on the approach used for separating the residual stress and composition gradients, angle- or energy-dispersive diffraction has to be applied, employing monochromatic X-ray sources available in the laboratory or either white high-energy synchrotron radiation or the Bremsstrahlung of conventional X-ray tubes, respectively. The methods introduced here assume a biaxial residual stress state within the film. For a triaxial residual stress state with σ33 ≠ 0, a separation of stress and composition gradients is not straightforward, because an a 0(z) gradient cannot be distinguished from the hydrostatic part of the stress tensor.
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Yavari, Arash y Alain Goriely. "Weyl geometry and the nonlinear mechanics of distributed point defects". Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 468, n.º 2148 (5 de septiembre de 2012): 3902–22. http://dx.doi.org/10.1098/rspa.2012.0342.
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The residual stress field of a nonlinear elastic solid with a spherically symmetric distribution of point defects is obtained explicitly using methods from differential geometry. The material manifold of a solid with distributed point defects—where the body is stress-free—is a flat Weyl manifold, i.e. a manifold with an affine connection that has non-metricity with vanishing traceless part, but both its torsion and curvature tensors vanish. Given a spherically symmetric point defect distribution, we construct its Weyl material manifold using the method of Cartan's moving frames. Having the material manifold, the anelasticity problem is transformed to a nonlinear elasticity problem and reduces the problem of computing the residual stresses to finding an embedding into the Euclidean ambient space. In the case of incompressible neo-Hookean solids, we calculate explicitly this residual stress field. We consider the example of a finite ball and a point defect distribution uniform in a smaller ball and vanishing elsewhere. We show that the residual stress field inside the smaller ball is uniform and hydrostatic. We also prove a nonlinear analogue of Eshelby's celebrated inclusion problem for a spherical inclusion in an isotropic incompressible nonlinear solid.
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Baud, S. y P. Velex. "Static and Dynamic Tooth Loading in Spur and Helical Geared Systems-Experiments and Model Validation". Journal of Mechanical Design 124, n.º 2 (16 de mayo de 2002): 334–46. http://dx.doi.org/10.1115/1.1462044.
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The primary objective of this study is to validate a specific finite element code aimed at simulating dynamic tooth loading in geared rotor systems. Experiments have been conducted on a high-precision single stage spur and helical gear reducer with flexible shafts mounted on hydrostatic or hydrodynamic bearings. The numerical model is based on classical elements (shaft, lumped stiffnesses, …) and on a gear element which accounts for non-linear time-varying mesh stiffness, gear errors and tooth shape modifications. External and parametric excitations are derived from the instantaneous contact conditions between the mating flanks by using an iterative contact algorithm inserted in a time-step integration scheme. First, experimental and numerical results at low speeds are compared and confirmed that the proposed tooth mesh interface model is valid. Comparisons were then extended to dynamic fillet stresses on both spur and helical gears between 50–6000 rpm on pinion shaft. Despite a localized problem in the case of spur gears with one particular bearing arrangement, the broad agreement between the experimental and numerical response curves demonstrated that the model is representative of the dynamic behavior of geared systems.
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Russell, William D., Nicholas R. Bratton, YubRaj Paudel, Robert D. Moser, Zackery B. McClelland, Christopher D. Barrett, Andrew L. Oppedal et al. "In Situ Characterization of the Effect of Twin-Microstructure Interactions on {1 0 1 2} Tension and {1 0 1 1} Contraction Twin Nucleation, Growth and Damage in Magnesium". Metals 10, n.º 11 (22 de octubre de 2020): 1403. http://dx.doi.org/10.3390/met10111403.
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Through in situ electron backscatter diffraction (EBSD) experiments, this paper uncovers dominant damage mechanisms in traditional magnesium alloys exhibiting deformation twinning. The findings emphasize the level of deleterious strain incompatibility induced by twin interaction with other deformation modes and microstructural defects. A double fiber obtained by plane-strain extrusion as a starting texture of AM30 magnesium alloy offered the opportunity to track deformation by EBSD in neighboring grains where some undergo profuse {1 0 1 2} twinning and others do not. For a tensile loading applied along extrusion transverse (ET) direction, those experiencing profuse twinning reveal a major effect of grain boundaries on non-Schmid behavior affecting twin variant selection and growth. Similarly, a neighboring grain, with its ⟨c⟩-axis oriented nearly perpendicular to tensile loading, showed an abnormally early nucleation of {1 0 1 1} contraction twins (2% strain) while the same {1 0 1 1} twin mode triggering under ⟨c⟩-axis uniaxial compression have higher value of critical resolved shear stress exceeding the values for pyramidal ⟨c + a⟩ dislocations. The difference in nucleation behavior of contraction vs. compression {1 0 1 1} twins is attributed to the hydrostatic stresses that promote the required atomic shuffles at the core of twinning disconnections.
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Tota-Maharaj, Kiran, Ghassan Nounu y Navin Ramroop. "Modelling of Quadratic-Surface Sludge Digesters by Smoothed Particle Hydrodynamics (SPH) – Finite Element (FE) Methods". Archives of Hydro-Engineering and Environmental Mechanics 67, n.º 1-4 (1 de diciembre de 2020): 35–53. http://dx.doi.org/10.1515/heem-2020-0003.
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Abstract The quadric-surfaced sludge digester (QSD), also known as the egg-shaped sludge digester, has proven its advantages over traditional cylindrical digesters recently. A reduction in operational cost is the dominant factor. Its shell can be described as a revolution of a parabola with the apex and base being either tapered or spherical. This shape provides a surface free of discontinuities, which is advantageous regarding the efficiency during mixing. Since the shape does not produce areas of inactive fluid motion within the tank, sludge settlement and an eventual grit build-up are avoided. The stresses developed in the shell of the sludge digester, vary along the meridian and equatorial diameters. A non-dimensional parameter, ξ, defines the height-to-diameter aspect ratio which is used to delineate the parametric boundary conditions of the shell’s surface. Three groups of analyses were conducted to determine the orthogonal stresses in the shell of the QSD. The first-principles numerical models ran reasonably quickly, and many simulations were made during the study. The results showed that they were in within the range 5.34% to 7.2% to 2D FEA results. The 3D FEA simulation results were within the range of 8.3% to 9.2% to those from the MATLAB time-history models. This is a good indicator that the first principles numerical models are an excellent time-saving method to predict the behaviour of the QSD under seismic excitation. Upon examining the criteria for the design, analysing the results for the 2D FEA simulations showed that the fill height is not a significant variable with sloshing however the 3D FEA showed that the hydrostatic pressure is a significant variable. With the maximum tensile stress of the 3D-printed Acrylonitrile Butadiene Styrene (ABS)-a common thermoplastic polymer typically used for injection molding applications, being 24.4 MPa, the overall maximum stress of 5.45 MPa, the material can be a viable option for the use of QSD construction in small island developing states (SIDS).
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Herman, Agnieszka. "Wave-induced stress and breaking of sea ice in a coupled hydrodynamic discrete-element wave–ice model". Cryosphere 11, n.º 6 (24 de noviembre de 2017): 2711–25. http://dx.doi.org/10.5194/tc-11-2711-2017.
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Abstract. In this paper, a coupled sea ice–wave model is developed and used to analyze wave-induced stress and breaking in sea ice for a range of wave and ice conditions. The sea ice module is a discrete-element bonded-particle model, in which ice is represented as cuboid grains floating on the water surface that can be connected to their neighbors by elastic joints. The joints may break if instantaneous stresses acting on them exceed their strength. The wave module is based on an open-source version of the Non-Hydrostatic WAVE model (NHWAVE). The two modules are coupled with proper boundary conditions for pressure and velocity, exchanged at every wave model time step. In the present version, the model operates in two dimensions (one vertical and one horizontal) and is suitable for simulating compact ice in which heave and pitch motion dominates over surge. In a series of simulations with varying sea ice properties and incoming wavelength it is shown that wave-induced stress reaches maximum values at a certain distance from the ice edge. The value of maximum stress depends on both ice properties and characteristics of incoming waves, but, crucially for ice breaking, the location at which the maximum occurs does not change with the incoming wavelength. Consequently, both regular and random (Jonswap spectrum) waves break the ice into floes with almost identical sizes. The width of the zone of broken ice depends on ice strength and wave attenuation rates in the ice.
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WINTERS, KRAIG B. y HARVEY E. SEIM. "The role of dissipation and mixing in exchange flow through a contracting channel". Journal of Fluid Mechanics 407 (25 de marzo de 2000): 265–90. http://dx.doi.org/10.1017/s0022112099007727.
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We investigate the transport of mass and momentum between layers in idealized exchange flow through a contracting channel. Lock-exchange initial value problems are run to approximately steady state using a three-dimensional, non-hydrostatic numerical model. The numerical model resolves the large-scale exchange flow and shear instabilities that form at the interface, parameterizing the effects of subgrid-scale turbulence. The closure scheme is based on an assumed steady, local balance of turbulent production and dissipation in a density-stratified fluid.The simulated flows are analysed using a two-layer decomposition and compared with predictions from two-layer hydraulic theory. Inter-layer transport leads to a systematic deviation of the simulated maximal exchange flows from predictions. Relative to predictions, the observed flows exhibit lower Froude numbers, larger transports and wider regions of subcritical flow in the contraction. To describe entrainment and mixing between layers, the computed solutions are decomposed into a three-layer structure, with two bounding layers separated by an interfacial layer of finite thickness and variable properties. Both bounding layers lose fluid to the interfacial layer which carries a significant fraction of the horizontal transport. Entrainment is greatest from the faster moving layer, occurring preferentially downstream of the contraction.Bottom friction exerts a drag on the lower layer, fundamentally altering the overall dynamics of the exchange. An example where bed friction leads to a submaximal exchange is discussed. The external forcing required to sustain a net transport is significantly less than predicted in the absence of bottom stresses.
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KLEMP, JOSEPH B., RICHARD ROTUNNO y WILLIAM C. SKAMAROCK. "On the propagation of internal bores". Journal of Fluid Mechanics 331 (25 de enero de 1997): 81–106. http://dx.doi.org/10.1017/s0022112096003710.
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According to classical hydraulic theory, the energy losses within an external bore must occur within the expanding layer. However, the application of this theory to describe the propagation of internal bores leads to contradiction with accepted gravity-current behaviour in the limit as the depth of the expanding layer ahead of the bore becomes small. In seeking an improved expression for the propagation of internal bores, we have rederived the steady front condition for a bore in a two-layer Boussinesq fluid in a channel under the assumption that the energy loss occurs within the contracting layer. The resulting front condition is in good agreement with available laboratory data and numerical simulations, and has the appropriate behaviour in both the linear long-wave and gravity-current limits. Analysis of an idealized internal bore assuming localized turbulent stresses suggests that the energy within the expanding layer should, in fact, increase. Numerical simulations with a two-dimensional non-hydrostatic model also reveal a slight increase of energy within the expanding layer and suggest that the structure of internal bores is fundamentally different from classical external bores, having the opposite circulation and little turbulence in the vicinity of the leading edge. However, if there is strong shear near the interface between layers, the structure and propagation of internal jumps may become similar to their counterparts in classical hydraulic theory. The modified jump conditions for internal bores produce some significant alterations in the traditional Froude-number dependence of Boussinesq shallow-water flow over an obstacle owing to the altered behaviour of the upstream-propagating internal bore.
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Rutter, E. H. y K. H. Brodie. "Experimental approaches to the study of deformation/metamorphism relationships". Mineralogical Magazine 52, n.º 364 (marzo de 1988): 35–42. http://dx.doi.org/10.1180/minmag.1988.052.364.03.
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AbstractRock deformation and metamorphism can interact at the mechanistic level in the following ways: (a) facilitation of cataclasis through the release of high-pressure fluid during dehydration and decarbonation reactions; (b) facilitation of intracrystalline plasticity through the stresses induced during solid-state volume changes; (c) enhanced deformability through the transient existence of fine-grained reaction products; (d) modification of chemical potential gradients driving diffusion if a reaction can occur along the diffusion path; (f) changes in the resistance to intracrystalline plasticity through the effect of reaction-induced changes, pore fluid pressure and chemistry on point defect chemistry of the solid phases.Examples of experimental studies of each of these types of interaction are described. Special experimental problems arise through: (i) the effects of solid phase and pore space volume changes, and their effects on pore fluid pressure and measured strain; (ii) the effects of such microstructural changes on the determination of flow law parameters; and (iii) in many instances the need for very long duration deformation experiments if reaction kinetics are sluggish.There is an outstanding need for experimental studies of the effects of non-hydrostatic stress on the conditions for the onset of metamorphic reactions and phase transformations, as a basis for understanding some classes of deformation/metamorphism interaction. However, it is emphasized that the threefold classification of rock deformation mechanisms into cataclastic, crystal-plastic, and diffusive mass transfer processes, established from the study of deformation of monomineralic rocks, forms an essential framework for the understanding of deformation/metamorphism inter-relationships.
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Tao, Ming, Zhixian Hong, Kang Peng, Pengwei Sun, Mingyu Cao y Kun Du. "Evaluation of Excavation-Damaged Zone around Underground Tunnels by Theoretical Calculation and Field Test Methods". Energies 12, n.º 9 (3 de mayo de 2019): 1682. http://dx.doi.org/10.3390/en12091682.
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Excavation-damaged zones (EDZs) induced in underground mining and civil engineering potentially threaten tunnel safety and stability, and increase construction and support costs. In this paper, an investigation of the excavation damaged zone (EDZ) around roadways in Fankou lead-zinc mine in Guangzhou, China is performed by applying a seismic velocity method accompanied by SET-PLT-01 nonmetallic ultrasonic detector. Meanwhile, the in situ stress in the mining area was measured based on the stress relief method with the Swedish high-precision LUT system. The results indicate that the stress field is dominated by the maximum horizontal tectonic stress, and the extents of the EDZ on the roof-floor region are greater than that on the sidewall. In addition, both of the in situ stresses and EDZs show an increasing trend with an increase of depth. Analytical solutions of EDZ around circular openings in the brittle rock mass subjected to non-hydrostatic stress fields are presented in terms of the Mohr–Coulomb and generalized Hoek–Brown criteria, and validated by several cases mentioned above. The extents of EDZ solved by closed-form solutions were found to be in a great agreement with those obtained in the field. Finally, a series of parametric studies are conducted to investigate the effects of cohesion (c), friction angle (φ), geological strength index (GSI), mi, uniaxial compressive strength (σc), and disturbance factor (D) on EDZ. It is shown that the effects of c, φ, GSI, and σc are significant; however, more attention should be paid to consider the dynamic disturbances induced by mechanical drilling, blasting, and seismic waves in tunnel excavations or operations.
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Beuthe, Mikael. "Isostasy with Love: II Airy compensation arising from viscoelastic relaxation". Geophysical Journal International 227, n.º 1 (24 de junio de 2021): 693–716. http://dx.doi.org/10.1093/gji/ggab241.
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SUMMARY In modern geodynamics, isostasy can be viewed either as the static equilibrium of the crust that minimizes deviatoric stresses, or as a dynamic process resulting from the viscous relaxation of the non-hydrostatic crustal shape. Paper I gave a general formulation of Airy isostasy as an elastic loading problem solved with Love numbers, and applied it to the case of minimum stress isostasy. In this sequel, the same framework is used to study Airy isostasy as the long-time evolution of a viscoelastic shell submitted to surface and internal loads. Isostatic ratios are defined in terms of time-dependent deviatoric Love numbers. Dynamic isostasy depends on the loading history, two examples of which are the constant load applied on the surface in the far past and the constant shape maintained by addition or removal of material at the compensation depth. The former model results in a shape decreasing exponentially with time and has no elastic analogue, whereas the latter (stationary) model is equivalent to a form of elastic isostasy. Viscoelastic and viscous approaches are completely equivalent. If both load and shape vary slowly with time, isostatic ratios look like those of the stationary model. Isostatic models thus belong to two independent groups: the elastic/stationary approaches and the time-dependent approaches. If the shell is homogeneous, all models predict a similar compensation of large-scale gravity perturbations. If the shell rheology depends on depth, stationary models predict more compensation at long wavelengths, whereas time-dependent models result in negligible compensation. Mathematica and Fortran codes are available for computing the isostatic ratios of an incompressible body with three homogeneous layers.
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Correa, Diego, Dennis Cullinane y Juan Carlos Briceño. "INFLUENCE OF PRE-CONDITIONING LOADS ON BOVINE ARTICULAR CARTILAGE STRESS RELAXATION BEHAVIOR IN CONFINED COMPRESSION". Journal of Musculoskeletal Research 07, n.º 02 (junio de 2003): 145–50. http://dx.doi.org/10.1142/s0218957703001101.
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Articular Cartilage is a load bearing tissue whose microarchitecture, electrochemical composition, and fluid interactions afford it unique mechanical properties. It consists of an extracellular matrix (ECM) interspersed with a sparse population of chondrocytes, varying in density by depth. The structure and mechanical properties of this highly specialized tissue also vary depending on depth from the articular surface; with three specialized zones, each with unique material properties. Typically this tissue is mechanically modeled as a biphasic material, consisting of a solid phase and a fluid phase, which can redistribute itself under loading, altering hydrostatic pressure within the material. Thus, articular cartilage exhibits a time-dependent viscoelastic behavior when subjected to constant loading or deformation, and will reach an equilibrium via stress relaxation and creep behavior. The objective of this study was to test a custom designed confined compression chamber. We characterize the ability of the test chamber to generate curves capable of quantifying the stress relaxation level and equilibrium state in bovine articular cartilage, and to show the preliminary results of a comparison between the equilibrium aggregate modulus (HA) obtained from pre- conditioned and non-conditioned tissues. Using fresh bovine articular cartilage samples, stress relaxation tests were conducted in compression, obtaining equilibrium stress and HA through a linear relation between the initial strain and the equilibrium stress. The test specimens were divided into two groups, one with a pre-conditioning load and the other without. The tests resulted in equilibrium stresses of 0.015 ± 0.0067 MPa for the non-conditioned and 0.067 ± 0.012 MPA for the pre-conditioned, and HA values of 0.205 ± 0.100 MPa for the unconditioned group and 0.878 ± 0.160 MPa in the pre-conditioned group. Our confined compression chamber successfully produced the stress relaxation curve characterizing the mechanical behavior of articular cartilage, defining both the equilibrium stress and HA. Our results suggest that pre-conditioning correlates with a higher equilibrium stress and aggregate modulus based on the fact that pre-loading the specimens reduces the effects of viscoelasticity.
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Ulker, Pinar, Herbert J. Meiselman y Oguz K. Baskurt. "Neither a Nitric Oxide Donor Nor Potassium Channel Blockage Inhibit RBC Mechanical Damage Induced by a Roller Pump". Open Biomedical Engineering Journal 2, n.º 1 (1 de abril de 2008): 17–21. http://dx.doi.org/10.2174/1874120700802010017.
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Red blood cells (RBC) are exposed to various levels of shear stresses when they are exposed to artificial flow environments, such as extracorporeal flow circuits and hemodialysis equipment. This mechanical trauma affects RBC and the resulting effect is determined by the magnitude of shear forces and exposure time. It has been previously demonstrated that nitric oxide (NO) donors and potassium channel blockers could prevent the sub-hemolytic damage to RBC, when they are exposed to 120 Pa shear stress in a Couette shearing system. This study aimed at testing the effectiveness of NO donor sodium nitroprussid (SNP, 10-4 M) and non-specific potassium channel blocker tetraethylammonium (TEA, 10-7 M) in preventing the mechanical damage to RBC in a simple flow system including a roller pump and a glass capillary of 0.12 cm diameter. RBC suspensions were pumped through the capillary by the roller pump at a flow rate that maintains 200 mmHg hydrostatic pressure at the entrance of the capillary. An aliquot of 10 ml of RBC suspension of 0.4 L/L hematocrit was re-circulated through the capillary for 30 minutes. Plasma hemoglobin concentrations were found to be significantly increased (~7 folds compared to control aliquot which was not pumped through the system) and neither SNP nor TEA prevented this hemolysis. Alternatively, RBC deformability assessed by laser diffraction ektacytometry was not altered after 30 min of pumping and both SNP and TEA had no effect on this parameter. The results of this study indicated that, in contrast with the findings in RBC exposed to a well-defined magnitude of shear stress in a Couette shearing system, the mechanical damage induced by a roller pump could not be prevented by NO donor or potassium channel blocker.
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Pribenszky, C., M. Molnar, S. Cseh y L. Solti. "117EFFECTS OF PREVIOUS PRESSURE TREATMENT ON THE SURVIVAL AND DEVELOPMENTAL SPEED OF EXPANDED MOUSE BLASTOCYSTS FROZEN RAPIDLY (PILOT STUDY)". Reproduction, Fertility and Development 16, n.º 2 (2004): 181. http://dx.doi.org/10.1071/rdv16n1ab117.
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It has been demonstrated that embryos can survive exposure to a substantial amount of pressure. (Pribenszky et al., 2003 Theriogenology 59, 329, and 2002 Theriogenology 57, 506). Other studies report that, if a biological system is challenged by certain stresses, its ability to react and survive other stresses can be improved. The aim of our present study was to examine whether the survival rate of expanded mouse blastocysts could be improved by a certain pressure treatment before the freezing procedure. Morula stage mouse embryos were collected and cultured at 37°C with 5% CO2 and maximal humidity in air in G 2.2 medium (Vitrolife, Göteborg, Sweden) to the expanded blastocyst stage. Embryos were randomly allocated to three groups. Embryos in Group I were equilibrated for 5 minutes in a solution containing 1.5M ethylene glycol (EG) and 0.25M sucrose in M2 (Sigma, St. Louis, MO, USA), supplemented with 10% FCS (Sigma), and then transferred into a vitrification solution (7M EG, 0.5M sucrose in M2 with 10% FCS) pre-loaded in a 0.25-ml plastic straw (7–9 embryos/straw). After 1-min exposure to the vitrification solution, the straw was slowly immersed in liquid nitrogen. Embryos in Group II were loaded into 0.08-mL straws (7–9 embryos/straw) with M2. Straws were placed into the chamber, filled with M2, of a special laboratory-made device that is capable of generating and precisely detecting hydrostatic pressure up to 150MPa (1500atm), and were exposed to 60MPa pressure for 30min. After the pressure treatment, embryos were frozen as described above. Straws were thawed by transfer into 30°C water for 30s and then the embryos were recovered and placed in rehydration medium (0.5M sucrose in M2 supplemented with 10% FCS) for 5min. Embryos then were cultured in medium G2.2 as described above. A total of 27, 29 and 26 embryos were assigned to Group I, Group II and the untreated control group, respectively. Embryo viability and development were assessed at 6 and 20h after culture as determined by morphological appearance and hatching. At 6h, 16% (4/27) of the non-pressurized embryos were one-half expanded, at 20 hours 37% (10/27) were two-thirds and 30% (8/27) were one-half expanded; none of them were hatching. While at the pressure treated groups 89% (26/29) of the embryos were fully expanded at 6 hours, and 68% (20/29) were hatching at 20h (untreated: 25/26 fully expanded at 6h, 24/26 hatched at 20h). Data were analyzed by chi-square test. We considered embryos which were at least two-thirds expanded. After 6 hours Group I differed from Group II and the control (P<0.01). There was no significant difference between Group II and the control (P<0.01). After 20 hours the same relations were seen. In the case of hatching, Group I differed from Group II and the control (P<0.01). There was no significant difference between Group II and the control (P<0.05). According to our results, the applied pressure treatment improved the in vitro development of the embryos after freezing. The re-expansion was faster and the survival rate was higher for those embryos that received pressure treatment before cryopreservation. Further experiments are needed to confirm and explore the in vitro and in vivo effects and benefits of pressure treatment before freezing.
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Bukotas, Gintaras y Rimantas Kačianauskas. "ANALYSIS OF AXISYMMETRIC BORE-TYPE FOUNDATION IN RESPECT OF PLASTIC DEFORMATION/AŠIAI SIMETRINIO GRĘŽININIO PAMATO ANALIZĖ ĮVERTINANT PLASTINES DEFORMACIJAS". JOURNAL OF CIVIL ENGINEERING AND MANAGEMENT 3, n.º 10 (30 de junio de 1997): 24–31. http://dx.doi.org/10.3846/13921525.1997.10531680.
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In order to design efficient foundations, it is necessary to know exact behaviour of them and surrounding soil under the load. At present various numerical methods [1–11] are used to determine such response. The behaviour of axi-symmetric bored foundation is described in this paper. The finite element method is utilized in analysis of the foundation. Linear and non-linear properties of material are taken into account. The investigation of properties of soil, predominating in Lithuania, and economical constructing of foundation gives preference to bored foundation [12]. Schematically this type of foundation can be depicted as a cylindrical body resting on soil (Fig 1). Geometrically the foundation can be described through the diameter d and the height h. F denotes the vector of the axisymmetric load. Such bored foundation has ratio h/d ≥ 2 and transmit part of the external load through their side surface to soil. It is very difficult to achieve a shear failure of soil mass for such a type of foundation, but the foundation may suffer significant deflections. It is, therefore, important to known the stress-strain state of soil for design purpose. Various stress-strain models have been proposed for representing the behaviour of soil [14]. These range from very simple linear-elastic to complex elastic-plastic models. In general, the stress vector σ is related to the strain vector ε through the elasticity matrix [C] (1) [1,2]. The linear-elastic stress-strain model is the simplest. In this case matrix [C] is constant and history independent (2) [4]. More complex is the non-linear-elastic model. Two incremental linear-elastic approaches can be used to handle this problem [4]. In the first case a tangent and in the other—secant modulus are used. The described models imply that volume changes are induced by changes in mean normal effective stress alone, while shear strains are induced by shear stress alone. Investigation shows that volumetric strains are induced by changes in shear stress as well as by changes in the mean normal stress [4, 11]. This can be accounted for the dilatant-elastic stress-strain model. The incremental shear-induced volume change Δεv can be expressed in terms of a tangent dilation parameter αϵ [10] according to (4), in which Δγ is the increment of maximum shear strain [4]. The dilatant-elastic materials lead to a three parameter stress-strain model in which the increments of volumetric and shear strain are related to the corresponding stress increments according to (5). The most complex is the elastic-plastic stress-strain model. A basic assumption of elastic models is that the unloading path is identical to the loading path. This is generally not true for soils where the recoverable strain upon unloading is generally small. The recoverable strain is considered to be elastic, while the non-recoverable strain is considered to be plastic. There have been proposed various yield conditions to model those plastic properties of soils. Von Mises yield condition can be written (6) in terms of the second invariant of stress deviator J 2 and yield stress Y(κ) from uniaxial tests [2]. For soils, concrete and other ‘frictional’ materials the Drucker and Prager law (7) is frequently used [2,13]. In this law hydrostatic press σm is incorporated, while c and Φ are the cohesion and angle of friction, respectively [8]. The problem is formulated and analysed by the finite element method. The region of a model is subdivided into discrete elements. The global system of equations to be solved is described by the equation (9), where [K(U)] denotes the global non-linear stiffness matrix, U is the unknown deflection vector and F is the vector of nodal forces [1,2]. The matrix [K(U)] and the vector F can be made up by adding up the element stiffness matrices [k e(u e)] and the element nodal deflection vectors f e, respectively. Therefore the problem can be mathematically described through the governing equation of the separate element (10), where u e denotes the unknown element nodal deflection. The stiffness matrix can be determined from the principle of virtual work. This involves equating the work done by the internal stresses with that done by the nodal forces. In a non-linear analysis the matrix [k e(u e)] depends on the vector u e and solution of a problem must be obtained throughout the complete history of incremental load application [1]. Time is a convenient variable tthat denotes different intensities of load applications. Equality of virtual work is expressed through displacement increments Δu e in the time step Δt. In this case the relation of a governing equation is (11) where tpe , denotes nodal point forces corresponding to the element stresses at time t. A solution of (11) may be subject to very significant errors, it is, therefore, necessary to iterate until the solution is obtained to sufficient accuracy. The incremental equations, used in the Newton-Raphson iteration, are (12) and (13), for i= 1, 2, 3,…with the initial conditions shown in (14). The foundation and soil are considered a non-homogeneous deformable solid [2,4,9]. Two separate problems were formulated. The first problem deals with linear-elastic material properties. The other accounts for elastic-plastic properties of soil. Von Mises and Drucker-Prager yield conditions are applied. The formulation is geometrically linear and axisymmetric. The sketch of the model is depicted in Fig 2. The material properties of soil and concrete are chosen such, that predominate in Lithuania [15]. The ANSYS [5–8] computer code is used for the calculation. Another problem is to choose geometric dimensions of a soil model because it is possible to analyse the finite size model by finite element method. The width of a model D=3.75 d is chosen from the investigations of other authors [2, 9]. Some analyses were carried out in order to determine the influence of the soil depth under the foundation H = 2—4.333 h on the deflection at the top of the foundation. In this case the linear-elastic model was applied. The results are depicted in Fig 3. The depth H =2.167 h was chosen for further analysis. The generated discrete model was estimated for the quality. The model was under the circular in plane with the radius r = 0.4 m uniform distributed surface loading p = 1.989 MPa [16]. The calculated stress and strain distribution in soil under the centre of loading are compared, as shown in Fig 4 and 5, respectively. In case of non-linear analysis the load is applied in two stages. In the first stage the model is loaded by weight. The full external load p = 1.989 MPa is incrementally applied in the second stage. The history of load application is described through the time variable t. The history of the deflection at the top of the foundation is depicted in Fig 6. It seems that the deflection of linear model under the full 1 MN load and that of model, implemented with Drucker-Prager yield condition, differs by 11%. The distribution of accumulated equivalent plastic strain in the cross-section (Fig 7) of the model, utilizing the Drucker-Prager yield condition, shows that the biggest plastic deformation developed in the immediate contact with the foundation. The history of the principal stresses of the node under the foundation and Drucker-Prager and von Mises yield surfaces in principal stress space are depicted in Fig 8. Our analysis of axisymmetric bored foundation allows to know stress-strain state near the foundation. We can see that the external force of great magnitude cause significant plastic deformation, which, in turn, leads to significant deflection of the foundations.
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Yahia, L. H., G. Drouin y P. Duval. "A Methodology for Mechanical Measurements of Technical Constants of Trabecular Bone". Engineering in Medicine 17, n.º 4 (octubre de 1988): 169–73. http://dx.doi.org/10.1243/emed_jour_1988_017_044_02.
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Vertebral trabecular bone was tested by non-destructive uniaxial and triaxial loadings with the purpose of investigating the orthotropic properties of bone. A triaxial testing apparatus using hydrostatic pressure was developed and allowed to characterise the bony tissue in a three-dimensional stressed state. Thirty specimens, in the form of 10 mm cubes, were tested. The Young's moduli obtained in this study for the trabecular bone of human lumbar vertebrae are found to be in agreement with the values obtained by ultrasonic methods. Analyses of triaxial compressive tests provided, for the first time, the Poisson's ratios of vertebral trabecular bone. These values are found to satisfy thermodynamic restrictions established by Cowin and Van Buskirk (1986). Finally, no significant differences in the material properties were found for segment level (L3-L4).
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Kawai, M. "Constitutive Modeling of Creep and Damage Behaviors of the Non-Mises Type for a Class of Polycrystalline Metals". International Journal of Damage Mechanics 11, n.º 3 (julio de 2002): 223–45. http://dx.doi.org/10.1106/105678902026411.
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Phenomenological constitutive models to describe the creep and damage behaviors that deviate from the von Mises type for a class of polycrystalline materials are developed. Theoretical and empirical approaches are taken to the formulation. The effective stresses that govern the rates of creep and damage are scaled to describe any deviation from the response of the von Mises type. A general form of scaling parameter is proposed which can consider the hydrostatic stress and/or the third invariant of the stress deviator. A kinematic hardening model is first formulated on the basis of irreversible thermodynamics using the scaling parameters for creep and damage. Then, two kinds of empirical basis models are presented for cases of kinematic hardening and isotropic hardening, respectively. The proposed models can describe the primary, secondary and tertiary creep behaviors and distinguish between the creep and damage behaviors under different modes of loading. To illustrate the features of the proposed models, numerical simulations of the unequal creep behaviors under tension, compression, and torsion are carried out and compared with experimental results.
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"Orientation of hydraulic fractures in salt under hydrostatic and non-hydrostatic stresses". International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts 27, n.º 4 (agosto de 1990): 204. http://dx.doi.org/10.1016/0148-9062(90)90592-p.
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Chaki, T. K. "Mechanism of Stress-Enhanced Solid-Phase Epitaxy". MRS Proceedings 237 (1991). http://dx.doi.org/10.1557/proc-237-601.
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ABSTRACTEnhancement of solid-phase epitaxial growth (SPEG) due to hydrostatic pressures and bending stresses is explained by stress-enhanced mobility of point defects in the amorphous solid. The crystallization is by the adjustment of atomic positions in the vicinity of the crystallization/amorphous (c-a) interface due to self-diffusion in the amorphous phase, assisted by a free energy decrease equal to the difference in free energies between the amorphous and crystalline phases. Due to a mismatch in the bulk moduli between the amorphous and crystalline phases, the application of a hydrostatic pressure can develop tensile stresses in the amorphous layer near the c-a interface. Non-hydrostatic stresses in the amorphous layer enhance the mobility of point defects in the amorphous layer and, therefore, an enhancement of the SPEG rate. In the cases of both hydrostatic pressure and bending, the enhancement occurs in the tensile side, indicating that vacancy-like mechanism is predominant in SPEG.
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Wang, Xu, Liang Chen y Peter Schiavone. "A concentrated couple near two non-elliptical inclusions with internal uniform hydrostatic stresses". Zeitschrift für angewandte Mathematik und Physik 69, n.º 1 (11 de diciembre de 2017). http://dx.doi.org/10.1007/s00033-017-0899-0.
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Duffy, T. S., G. Shen, D. L. Heinz, Y. Ma, R. J. Hemley, H. K. Mao y A. K. Singh. "Lattice Strains in Gold and Rhenium Under Non-Hydrostatic Compression". MRS Proceedings 499 (1997). http://dx.doi.org/10.1557/proc-499-145.
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ABSTRACTLattice strains have been measured as a function of the angle, ψ, from the diamond cell stress axis in a sample of gold and rhenium at pressures of 15–37 GPa. Experiments were conducted using X-ray transparent gaskets made from beryllium. The differential stresses supported by gold and rhenium have been characterized to 37 GPa. It is also shown that proper choice of the diffraction geometry allows recovery of a quasi-hydrostatic compression curve under these highly non-hydrostatic conditions. X-ray elastic moduli have also been determined, and while good agreement with previous data is achieved for gold, there is a large discrepancy between the present results and extrapolated ultrasonic data for rhenium.
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Wang, Huaning, Fei Song, Tao Zhao y Mingjing Jiang. "Solutions for lined circular tunnels sequentially constructed in rheological rock subjected to non-hydrostatic initial stresses". European Journal of Environmental and Civil Engineering, 6 de mayo de 2020, 1–33. http://dx.doi.org/10.1080/19648189.2020.1737576.
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Vassiliou, John K., J. W. Otto, G. Frommeyer, J. J. Davis y P. Pinto. "Plastic Deformation and the Role of Fault Formation in the Equation of State of Micron Size Intermetallic Alloys Under Non-Hydrostatic Pressure". MRS Proceedings 791 (2003). http://dx.doi.org/10.1557/proc-791-q5.25.
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ABSTRACTThe elastic and plastic deformation of micron size anisotropic polycrystals of Ni3Al and Cu3Au intermetallic alloys have been studied under non-hydrostatic conditions by energy-dispersive X-ray diffraction (EDX) in a diamond-anvil cell. Compression was achieved by confining the samples in a viscous fluid or directly between the diamond anvils. Deviatoric forces are introduced in the samples as a result of the increasing viscosity with pressure and the eventual glassification of the pressurizing medium or by the contact forces of the diamond anvils. Line shifts and line profiles were used to analyze elastic and plastic strains. Plastic deformation is due to the onset of non-hydrostatic stresses and the introduction of stacking faults and dislocations. A volume incompressibility due to plastic deformation and the saturation of the stacking fault probability is followed by an elastic compression of a fully plastically deformed state. The compression of this state is isotropic and independent of the presence and type of the pressurizing medium. From the measured strains at different crystallographic orientations, the uniaxial stress and the stacking fault probability as a function of the confining pressure are derived and their role in the equation of state is examined. Using finite elasticity, the equation of state is derived in the presence of uniaxial stresses causing stacking faults, defects and dislocations.
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Vassiliou, John K., J. W. Otto, G. Frommeyer, A. J. Viescas, K. Bulusu y H. Bellumkonda. "Deformation of Ni3Al Polycrystals at Extremely High Pressures". MRS Proceedings 646 (2000). http://dx.doi.org/10.1557/proc-646-n5.47.1.
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ABSTRACTThe compression behavior in a multi-anvil apparatus of a foil of Ni3Al embedded in a pressure medium of NaCl has been studied by energy-dispersive X-ray diffraction (EDX). At ambient temperature, the pressure and stresses, determined from line positions of NaCl, were constant throughout the sample chamber. Line positions and line widths of NaCl reflections were reversible on pressure release. Ni3Al polycrystals, in contrast, undergo extensive (ductile) plastic deformation above 4 GPa due to the onset of high non-hydrostatic stresses and the introduction of stacking faults and dislocations. Plastic deformation due to stacking faults leads to a volume incompressibility followed by elastic compression of a fully plastically deformed state. The compression of a fully plastically deformed material is elastic and isotropic, independent of the presence and type of pressure medium. A discontinuity in the compressibility at the transition back from plastic to elastic compression is due to the yield strength of the plastically deformed material and corresponds to the Hugoniot elastic limit.
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Chen, Gang, Dileep Singh, Osman Eryilmaz, Ali Erdemir, Jules Routbort y Wenjun Liu. "Depth-dependent defect and residual stress distribution in magnetron sputtered MoN:Cu nanocomposite films by x-ray microdiffraction". MRS Proceedings 977 (2006). http://dx.doi.org/10.1557/proc-977-0977-ff08-05.
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AbstractWe have developed a synchrotron-based x-ray microdiffraction technique for measuring depth-resolved residual stress distribution in nanocrystalline films with submicron resolution [1]. In this study, we further refined this technique and applied it to low-friction and high-hardness Cu-doped MoN films. These magnetron sputtered nanocomposites films consist of MoN, Mo2N, and Cu phases, whose ratio depends on Cu concentration. By using the microdiffraction technique, we discovered that both the deviatoric and the hydrostatic components of the residual stresses depend on the film depth (Fig.1). The former indicates depth-dependent distribution of biaxial stresses, while the latter implies depth-dependent defect distribution, which also depends on Cu concentration. Thermal annealing of the nanocomposite film partially relives the stress, significantly reduces the lattice spacing, and eliminates the defect gradients. These results suggest that interstitial N may play an important role in the lattice expansion and the defect gradients formed during the non-equilibrium sputtering process. Our study provides fresh insights into understanding the structure-property relations in the magnetron sputtered MoN:Cu nanocomposites films.