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431.
A mechanistic constitutive model for fully formed cracks in geomaterials, such as concrete and rock, is presented. A three‐dimensional characterisation of the crack morphology is employed in which the crack surface is idealised as a series of conical teeth and corresponding recesses of variable height and slope. Based on this geometrical characterisation, an effective contact function is derived to relate the contact stresses that develop on the sides of the teeth to the net stresses on a crack plane. Plastic embedment and frictional sliding are simulated using a local plasticity model in which the plastic surfaces are expressed in terms of the contact surface function in cylindrical relative displacement space. Finally, the performance of the model is assessed against several sets of experimental data from direct shear tests, and it is concluded that the model is able to capture key characteristics of the behaviour of fully formed cracks in geomaterials. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
432.
The governing differential equations of unsaturated soils considering the thermo‐poro‐mechanical behaviour consist of equilibrium, moisture air and heat transfer equations. In this paper at first, following some necessary simplifications, the thermal three‐dimensional fundamental solution for an unsaturated deformable porous medium with linear elastic behaviour in Laplace transform domain is presented. Subsequently, the closed‐form time domain fundamental solutions are derived by analytical inversion of the Laplace transform domain solutions. Then a set of numerical results are presented, which demonstrate the accuracies and some salient features of the derived analytical transient fundamental solutions. Finally, the closed‐form time domain fundamental solution will be verified mathematically by comparison with the previously introduced corresponding fundamental solution. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
433.
The cyclic behaviour of slender cantilever columns in full-scale models of precast industrial buildings, designed by Eurocode
8, was studied experimentally and analytically. The shear span ratio of the columns was 12.5, which is more than allowed by
Eurocode 8 for columns in frame structures (10). High deformability and a large deformation capacity (8%~drift) of the columns
was observed. A lumped plasticity model was used in the analysis. In the paper the observed behaviour of the models has been
compared with the predicted behaviour obtained by several empirically based models and procedures. It was observed that these
models, which were developed for much lower shear span ratios (2–6), were not applicable for the analyzed very slender columns
without appropriate additional considerations and modifications. In the case of such columns the yield drift is dominated
by the flexural mode (it is practically proportional to the height of the column) and the ultimate drift under cyclic loading
conditions is only slightly dependent on the shear span (indicating that the ratio of the equivalent length of the plastic
hinge to the height of the column decreases with the increasing shear span). An appropriately modified lumped plasticity model
incorporating in-cycle and repeated-cycle strength deterioration was chosen for future use in performance-based design and
seismic risk studies. 相似文献
434.
矢量波场弹性波Kirchhoff偏移 总被引:2,自引:0,他引:2
Based on Kuo and Dai's vectorial wave-field extrapolation equations, we derive new Kirchhoff migration equations by introducing unit vectors which represent the ray directions at the imaging points of the reflected P- and PS converted-waves. Furthermore, using the slope of the events on shot records and a ray racing procedure, mirror-image reflection points are found and the reflection data are smeared along the Fresnel zone. The migration method proposed in this paper solves two troublesome imaging problems caused by limited receiving aperture and migration artifacts resulting from wave propagation at the velocities of non original wave type. The migration method is applied successfully with model data, demonstrating that the new method is effective and correct. 相似文献
435.
海洋桩基工程中的钙质土 总被引:5,自引:0,他引:5
本文在简述钙质土成因和组成的基础上,介绍分析了这种土的物理力学性质,尤其是其受力后变化的特性;说明了钙质土与桩的相互作用特性;对钙质土中导管架平台桩基设计的土工调查及其有关设计参数的选用作了论述 相似文献
436.
This paper presents a procedure for developing yield functions with consistent flow rules for granular materials from a family of two parameter dissipation functions in combination with appropriate kinematic constraints. Through a mathematical procedure described in the paper, a general formulation is developed that can, by adjusting the values of the two parameters, reproduce a wide range of yield surfaces, including the Drucker–Prager, Matsuoka–Nakai, and Lade–Duncan. Specifically, an analytical expression for the yield function is obtained in terms of a parameter that is a selected solution to a high order polynomial. The roots of this polynomial can always be found using the eigenvalues of the companion matrix and instructions on how to select the appropriate root are given in the paper. Two ways of incorporating anisotropy into the procedure are explored and the role within it of the recent history of deformation is examined. 相似文献
437.
438.
Composition, lattice parameters, and room temperature elastic constants of natural single crystal xenotime from Novo Horizonte 总被引:1,自引:1,他引:0
P. Mogilevsky E. B. Zaretsky T. A. Parthasarathy F. Meisenkothen 《Physics and Chemistry of Minerals》2006,33(10):691-698
The composition, lattice parameters, and elastic constants of natural single crystal YPO4 xenotime from Novo Horizonte (Brazil) were determined using EPMA, XRD, and the pulse-echo technique. The composition indicates a 24% substitution of Y sites with other rare-earth elements. The lattice parameters of the studied crystal deviated only slightly from those reported for synthetic YPO4 and were in a good agreement with trends obeyed by other orthophosphates with the xenotime structure. The measured elastic constants C
11, C
33, C
44, and C
66 were consistent with synthetic crystals when porosity was accounted for. C
12 and C
13 constants were evaluated based on the comparison with other materials with xenotime structure. The elastic constants could be rationalized using interionic force constants and bond energies.
相似文献
P. MogilevskyEmail: |
439.
The neuroprotective role of P-glycoprotein, a multixenobiotic resistance transporter (ABCB1/MDR1), in the blood-brain barrier in fish was examined using behavioural toxicological assays. P-glycoprotein acts as cellular efflux pump to prevent substrates from accumulating in the brain, including environmental contaminants such as ivermectin, a common aquaculture pesticide and mammalian anti-parasitic drug. The behavioural toxicological assays were developed to determine the neuropathological effect of ivermectin in killifish (Fundulus heteroclitus). P-glycoprotein function and thus blood-brain barrier integrity can be compromised by chemosensitizers that inhibit transport activity. Fish treated with ivermectin and the P-glycoprotein inhibitor cyclosporin A were significantly more sensitive and succumbed more rapidly to tilting, lethargy, slowing of pectoral-fin movement and loss of haptic-reactivity compared to fish treated with ivermectin-only. P-glycoprotein inhibition is associated with significantly earlier onset and increased mortality in ivermectin-exposed fish. Our results suggest that P-glycoprotein confers resistance against ivermectin-induced behavioural neuropathology and mortality in fish. This assay provides us with a non-invasive tool to study P-glycoprotein function in the blood-brain barrier and evaluate the behavioural effects of potential environmental neurotoxins. 相似文献
440.
Matthieu Dumont Said Taibi Jean-Marie Fleureau Nabil Abou Bekr Abdelghani Saouab 《Comptes Rendus Geoscience》2010,342(12):892-900
A simple thermohydromechanical (THM) constitutive model for unsaturated soils is described. The effective stress concept is extended to unsaturated soils with the introduction of a capillary stress. This capillary stress is based on a microstructural model and calculated from attraction forces due to water menisci. The effect of desaturation and the thermal softening phenomenon are modelled with a minimal number of material parameters and based on existing models. THM process is qualitatively and quantitatively modelled by using experimental data and previous work to show the application of the model, including a drying path under mechanical stress with transition between saturated and unsaturated states, a heating path under constant suction and a deviatoric path with imposed suction and temperature. The results show that the present model can simulate the THM behaviour in unsaturated soils in a satisfactory way. 相似文献