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Félix Darve Stein Sture René de Borst Andrew J. Whittle Ian M. Smith 《国际地质力学数值与分析法杂志》2009,33(3):n\a-n\a
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The mathematical structure and numerical analysis of classical small deformation elasto–plasticity is generally well established. However, development of large deformation elastic–plastic numerical formulation for dilatant, pressure sensitive material models is still a research area. In this paper we present development of the finite element formulation and implementation for large deformation, elastic–plastic analysis of geomaterials. Our developments are based on the multiplicative decomposition of the deformation gradient into elastic and plastic parts. A consistent linearization of the right deformation tensor together with the Newton method at the constitutive and global levels leads toward an efficient and robust numerical algorithm. The presented numerical formulation is capable of accurately modelling dilatant, pressure sensitive isotropic and anisotropic geomaterials subjected to large deformations. In particular, the formulation is capable of simulating the behaviour of geomaterials in which eigentriads of stress and strain do not coincide during the loading process. The algorithm is tested in conjunction with the novel hyperelasto–plastic model termed the B material model, which is a single surface (single yield surface, affine single ultimate surface and affine single potential surface) model for dilatant, pressure sensitive, hardening and softening geomaterials. It is specifically developed to model large deformation hyperelasto–plastic problems in geomechanics. We present an application of this formulation to numerical analysis of low confinement tests on cohesionless granular soil specimens recently performed in a SPACEHAB module aboard the Space Shuttle during the STS‐89 mission. We compare numerical modelling with test results and show the significance of added confinement by the thin hyperelastic latex membrane undergoing large stretching. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
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Joshua E. Colwell Stein Sture Dan Durda Tyler Goudie Daniel J. Ashcom Thomas Keohane Michael Lupton 《Icarus》2008,195(2):908-917
Collisions between planetary ring particles and in some protoplanetary disk environments occur at speeds below 10 m/s. The particles involved in these low-velocity collisions have negligible gravity and may be made of or coated with smaller dust grains and aggregates. We undertook microgravity impact experiments to better understand the dissipation of energy and production of ejecta in these collisions. Here we report the results of impact experiments of solid projectiles into beds of granular material at impact velocities from 0.2 to 2.3 m/s performed under near-weightless conditions on the NASA KC-135 Weightless Wonder V. Impactors of various densities and radii of 1 and 2 cm were launched into targets of quartz sand, JSC-1 lunar regolith simulant, and JSC-Mars-1 martian regolith simulant. Most impacts were at normal or near-normal incidence angles, though some impacts were at oblique angles. Oblique impacts led to much higher ejection velocities and ejecta masses than normal impacts. For normal incidence impacts, characteristic ejecta velocities increase with impactor kinetic energy, KE, as approximately KE0.5. Ejecta masses could not be measured accurately due to the nature of the experiment, but qualitatively also increased with impactor kinetic energy. Some experiments were near the threshold velocity of 0.2 m/s identified in previous microgravity impact experiments as the minimum velocity needed to produce ejecta [Colwell, J.E., 2003. Icarus 164, 188-196], and the experimental scatter is large at these low speeds in the airplane experiment. A more precise exploration of the transition from low-ejecta-mass impacts to high-ejecta-mass impacts requires a longer and smoother period of reduced gravity. Coefficient of restitution measurements are not possible due to the varying acceleration of the airplane throughout the experiment. 相似文献
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In this paper, the application of an efficient, transparent and accurate kinematic-cyclic constitutive model based on the fuzzy-set concepts and incremental plasticity theory is presented to show its capability in modeling cyclic mobility of saturated granular soil. The nature and kinematic mechanism of the membership functions in the fuzzy-set constitutive model are illustrated. The model’s capability of modeling soil dilatancy is investigated. Important features of volume change and pore water pressure build-up related to soil cyclic mobility are captured. The formulation of the proposed model is relatively simple and it can be readily implemented in finite element codes. The enhanced fuzzy-set model is capable of simulating ground motion problems particularly related to cyclic mobility, soil liquefaction, and spreading behavior. 相似文献
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Beach sands located above the sea water level exist in an unsaturated, rather than a fully saturated or dry state. Within the unsaturated zone, a steep excavated surface can be sustained for some unknown but finite time, and some slopes may remain stable for extended time periods due to capillary forces. These observations clearly indicate small but nonzero values for attraction strength (tensile strength and cohesion) in unsaturated beach sands, especially apparent but not confined to settings where there are low stress levels. Thus, experiments were carried out to quantify the magnitude of attraction strength in moist sands (Dr = 30%) and to examine the variation of these values as a function of moisture content and presence of a small amount of fines. Tensile strength, which is significantly different from zero, increases with increasing moisture content and fines. However, the influences of fines on the tensile strength are substantially dependent on the water content. Apparent cohesion strength is also identified in moist sands. A simple relationship between tensile strength and apparent cohesion is proposed using the obtained data. This study would help to further understand the phenomenon of stability of beach sands. 相似文献
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Elucidation of important nursery habitats for young fish can aid in the management and assessment of fish stocks. Herring (Clupea harengus) in the Baltic Sea primarily spawn in coastal areas, but larvae are also present in off-shore, open sea areas. To investigate if sheltered coastal habitats provide a better growth environment for larval herring, we compared short-term growth (as indexed by whole body RNA:DNA ratios) of larval herring from three habitat types of the northwest Baltic proper (sheltered inner bay, exposed outer bay, and open sea). In addition, we compared individual RNA content of adult female Eurytemora affinis (a common Baltic copepod) among these different habitats. High RNA levels in these copepods indicate high production of nauplii, which are important food for larval herring. Both RNA:DNA ratios of larval herring and RNA content of E. affinis were significantly greater in embayment habitats, suggesting that the sheltered coastal areas are high quality nursery habitats for young Baltic herring. 相似文献
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Stress‐driven integration strategies and m‐AGC tangent operator for Perzyna viscoplasticity and viscoplastic relaxation: application to geomechanical interfaces 
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下载免费PDF全文 The paper proposes a stress‐driven integration strategy for Perzyna‐type viscoplastic constitutive models, which leads also to a convenient algorithm for viscoplastic relaxation schemes. A generalized trapezoidal rule for the strain increment, combined with a linearized form of the yield function and flow rules, leads to a plasticity‐like compliance operator that can be explicitly inverted to give an algorithmic tangent stiffness tensor also denoted as the m‐AGC tangent operator. This operator is combined with the stress‐prescribed integration scheme, to obtain a natural error indicator that can be used as a convergence criterion of the intra‐step iterations (in physical viscoplasticity), or to a variable time‐step size in viscoplastic relaxation schemes based on a single linear calculation per time step. The proposed schemes have been implemented for an existing zero‐thickness interface constitutive model. Some numerical application examples are presented to illustrate the advantages of the new schemes proposed. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献