Mechanics of Cohesive-frictional Materials最新文献_第3页

Multiscale simulations of the mechanical behaviour of an ensiled granular material 青贮颗粒材料力学行为的多尺度模拟

Mechanics of Cohesive-frictional Materials

Pub Date : 2000-08-01 DOI: 10.1002/1099-1484(200008)5:6<425::AID-CFM103>3.0.CO;2-V

S. Masson, J. Martínez

Discrete simulations by the distinct element method are performed for modelling an ensiled granular material. Starting from the material microstructure on a microscopic scale, two procedures are considered in order to simulate the mechanical behaviour of the material within a silo on a megascopic scale. On the one hand, a direct discrete simulation from the microscopic scale to the megascopic scale is carried out. On the other hand, a two-step simulation procedure is performed: the determination of the macroscopic behaviour from the microscopic scale, followed by a continuum analysis from the macroscopic scale to the megascopic scale. The macroscopic parameters are derived from discrete simulations of usual rheological tests. An experimental validation of the distinct element method is presented by simulating a biaxial compression test. The macroscopic parameters of the ensiled material are then identified and introduced into a finite element analysis with an elastic–plastic constitutive model using the Mohr–Coulomb criterion. The results of the two above procedures are compared and in this way the relevance of the discrete simulation is demonstrated. Copyright © 2000 John Wiley & Sons, Ltd.

采用离散元法对青贮颗粒材料进行离散模拟。从微观尺度上的材料微观结构出发，考虑了两种程序，以便在宏观尺度上模拟筒仓内材料的力学行为。一方面，进行了从微观尺度到宏观尺度的直接离散模拟。另一方面，执行两步模拟过程:从微观尺度确定宏观行为，然后从宏观尺度到宏观尺度进行连续分析。宏观参数来源于通常流变试验的离散模拟。通过模拟双轴压缩试验，对不同单元法进行了实验验证。然后确定了青贮材料的宏观参数，并采用Mohr-Coulomb准则将其引入弹塑性本构模型的有限元分析中。对上述两种方法的结果进行了比较，并以此方式证明了离散模拟的相关性。版权所有©2000约翰威利父子有限公司

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引用次数: 19

An implicit constitutive algorithm for finite strain Cam-clay elasto-plastic model 有限应变Cam-clay弹塑性模型的隐式本构算法

Mechanics of Cohesive-frictional Materials

Pub Date : 2000-08-01 DOI: 10.1002/1099-1484(200008)5:6<469::AID-CFM105>3.0.CO;2-9

M. Rouainia, D. Wood

This work is directed toward the formulation and analysis of the modified Cam-clay critical state model within the framework of isotropic multiplicative finite strains. A suitable energy function, in which the shear modulus is made to depend on the mean pressure, is chosen allowing the hyperelastic response to be energy conserving. As a result of the use of Eulerian logarithmic stretches as strain measures in conjunction with an exponential approximation of the plastic flow rule, the small strain integration algorithms, and the corresponding consistent tangent operators, automatically extend to the finite strain regime. Numerical simulations are provided to demonstrate the stability and good performance of the proposed formulation. Copyright © 2000 John Wiley & Sons, Ltd.

引用次数: 30

Dynamic behaviour of concrete: the structural effects on compressive strength increase 混凝土的动力特性:结构对抗压强度增加的影响

Mechanics of Cohesive-frictional Materials

Pub Date : 2000-08-01 DOI: 10.1002/1099-1484(200008)5:6<491::AID-CFM106>3.0.CO;2-R

H. L. Nard, P. Bailly

Many concrete structures may be submitted to high rate dynamic loadings (impacts, explosions, etc.). So, it is necessary to know the behaviour of this material in order to predict the response of the structure. Under dynamic loading an increase of apparent compressive strength is observed. This may be due to a rheological effect or to a structural effect. Dynamic compression tests are available using the split Hopkinson pressure bars. Forces and velocities are obtained on each face of the specimen. A simulation of these tests is carried out using two different models. The first, based on plasticity theory, is a non-associated model with a failure surface of the Ottosen type. This model is independent of the strain rate. The second model is an elasto-viscoplastic model with a damage law. It only takes into account the main features of the behaviour, the sliding phenomena, the damage and the softening. The comparison of experimental results and simulations leads us to consider the structural effect as an inertial confinement responsible for the apparent increase in strength. Copyright © 2000 John Wiley & Sons, Ltd.

许多混凝土结构可能承受高速率的动载荷(冲击、爆炸等)。因此，为了预测结构的响应，有必要了解这种材料的性能。在动荷载作用下，观察到表观抗压强度增加。这可能是由于流变效应或结构效应。动态压缩试验可使用分离式霍普金森压力杆。在试样的每个面上得到力和速度。使用两种不同的模型对这些试验进行了模拟。第一种是基于塑性理论的非关联模型，其破坏面为Ottosen型。该模型与应变速率无关。第二个模型是具有损伤规律的弹粘塑性模型。它只考虑了主要的行为特征、滑动现象、损伤和软化。实验结果与模拟结果的比较使我们认为结构效应是造成强度明显增加的惯性约束。版权所有©2000约翰威利父子有限公司

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引用次数: 46

Catastrophic landslides due to frictional heating of the failure plane 破坏面摩擦加热引起的灾难性滑坡

Mechanics of Cohesive-frictional Materials

Pub Date : 2000-08-01 DOI: 10.1002/1099-1484(200008)5:6<443::AID-CFM104>3.0.CO;2-W

I. Vardoulakis

In this paper catastrophic landslides on a discrete failure plane are considered, which are explained by a mechanism of frictional heat generation that gives rise to high pore-water pressures generation inside the shear band. The problem is governed by a set of coupled diffusion–generation equations for the pore pressure and the temperature inside the shear band at the base of the landslide. The thermo-poro-mechanical coupling leads to frictional softening due to effective stress reduction and explains the extremely low apparent friction angles for rapid slides documented in the literature. The analysis suggests also that the shear band thickness must scale with the geometric dimensions of the slide. Copyright © 2000 John Wiley & Sons, Ltd.

引用次数: 87

Microstructural analysis of inherent and induced anisotropy in clay 粘土固有和诱导各向异性的微观结构分析

Mechanics of Cohesive-frictional Materials

Pub Date : 2000-07-01 DOI: 10.1002/1099-1484(200007)5:5<341::AID-CFM99>3.0.CO;2-C

P. Hicher, H. Wahyudi, D. Tessier

The aim of this study was to relate the mechanical behaviour of saturated clays to their structural characteristics. Two clays were studied: a kaolinite and a bentonite. The evolution of the shape, the size, the concentration and the orientation of the elements which constitute the clay structure was examined by means of scanning and transmission electron microscopes. Particular care was taken to avoid as far as possible disturbing the micro-structure during observation. The results showed the existence of particle breakage and the creation of structural anisotropy during loading. We can conclude from this work that the mechanical behaviour to clayed materials is largely dependent on the changes which occur at the scale of the particles.

本研究的目的是将饱和粘土的力学行为与其结构特征联系起来。研究了两种粘土:高岭土和膨润土。利用扫描电镜和透射电镜研究了构成粘土结构的元素的形状、大小、浓度和取向的演变。在观察过程中，特别注意尽量避免干扰微观结构。结果表明，加载过程中存在颗粒破碎和结构各向异性的产生。我们可以从这项工作中得出结论，粘土材料的机械行为在很大程度上取决于颗粒尺度上发生的变化。

引用次数: 107

Ground movements around excavations in granular soils: a few remarks on the influence of the constitutive assumptions on FE predictions 颗粒土中开挖周围的地面运动:关于本构假设对有限元预测影响的几点评论

Mechanics of Cohesive-frictional Materials

Pub Date : 2000-07-01 DOI: 10.1002/1099-1484(200007)5:5<399::AID-CFM101>3.0.CO;2-R

G. Viggiani, C. Tamagnini

Two different approaches for modelling soil non-linearity (hardening plasticity and hypoplasticity) are compared with reference to the analysis of soil–structure interaction in an excavation in dense dry sand, supported by a propped diaphragm wall. The analysis focuses on the prediction of wall and soil movements. A commercial FE code has been used for the elastoplastic analyses, in order to assess the performance of a readily available design tool in current geotechnical engineering practice as compared to the predictions of a more advanced research tool. Although obtained for an idealized scheme, the results allow a number of more general conclusions to be drawn on the influence of the constitutive assumptions. Copyright © 2000 John Wiley & Sons, Ltd.

引用次数: 33

Experimental observations of behaviour of heterogeneous soils 非均质土特性的实验观察

Mechanics of Cohesive-frictional Materials

Pub Date : 2000-07-01 DOI: 10.1002/1099-1484(200007)5:5<373::AID-CFM100>3.0.CO;2-D

D. Wood, G. Kumar

Triaxial tests have been performed on mixtures of kaolin clay and a coarse uniform sand (d50∼2 mm). Drained and undrained compression tests have been performed on isotropically normally consolidated and overconsolidated samples. It has been found that the mechanical behaviour of the mixture is dominated by the mechanical behaviour of the clay matrix until the clay content falls below 40 per cent and the volume fraction of the granular constituent reaches about 0.45. Pore pressures in undrained tests are unaffected by the presence of the sand. Volumetric strains in the clay matrix in drained tests are virtually identical to those seen in pure clay. Calculations of mechanical response of mixtures have been made using a theoretical analysis, developed for the behaviour of composites: it is found that this analysis overestimates the effect of the granular material. Numerical analyses using a finite element program lie closer to the experimental observations but still overestimate the influence of the sand.

对高岭土粘土和粗均匀砂(d50 ~ 2mm)的混合物进行了三轴试验。对各向同性正常固结和超固结试样进行了排水和不排水压缩试验。研究发现，在粘土含量低于40%，颗粒成分的体积分数达到约0.45之前，混合料的力学行为主要受粘土基质的力学行为支配。不排水试验中的孔隙压力不受砂粒存在的影响。在排水试验中，粘土基质的体积应变几乎与纯粘土中所见的相同。混合力学响应的计算已经使用理论分析，为复合材料的行为发展:发现这种分析高估了颗粒材料的影响。使用有限元程序的数值分析更接近于实验观测，但仍然高估了沙的影响。

引用次数: 38

Experimental observations of behaviour of heterogeneous soils 非均质土壤特性的实验观测

Mechanics of Cohesive-frictional Materials

Pub Date : 2000-06-28 DOI: 10.1002/1099-1484(200007)5:5<373::AID-CFM100>3.0.CO;2-D

D. Muir Wood, G. V. Kumar

Triaxial tests have been performed on mixtures of kaolin clay and a coarse uniform sand (d₅₀∼2 mm). Drained and undrained compression tests have been performed on isotropically normally consolidated and overconsolidated samples. It has been found that the mechanical behaviour of the mixture is dominated by the mechanical behaviour of the clay matrix until the clay content falls below 40 per cent and the volume fraction of the granular constituent reaches about 0.45. Pore pressures in undrained tests are unaffected by the presence of the sand. Volumetric strains in the clay matrix in drained tests are virtually identical to those seen in pure clay.

Calculations of mechanical response of mixtures have been made using a theoretical analysis, developed for the behaviour of composites: it is found that this analysis overestimates the effect of the granular material. Numerical analyses using a finite element program lie closer to the experimental observations but still overestimate the influence of the sand.

对高岭土和粗粒均匀砂（d50～2mm）的混合物进行了三轴试验。对各向同性正常固结和超固结样品进行了排水和不排水压缩试验。已经发现，混合物的机械行为由粘土基质的机械行为主导，直到粘土含量降至40%以下，颗粒成分的体积分数达到约0.45。不排水试验中的孔隙压力不受沙子存在的影响。排水试验中粘土基质的体积应变与纯粘土中的体积应变几乎相同。使用为复合材料性能开发的理论分析计算了混合物的机械响应：发现该分析高估了颗粒材料的影响。使用有限元程序进行的数值分析更接近实验观测，但仍然高估了沙子的影响。

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引用次数: 38

Microstructural analysis of inherent and induced anisotropy in clay 粘土固有各向异性和诱导各向异性的微观结构分析

Mechanics of Cohesive-frictional Materials

Pub Date : 2000-06-28 DOI: 10.1002/1099-1484(200007)5:5<341::AID-CFM99>3.0.CO;2-C

P. Y. Hicher, H. Wahyudi, D. Tessier

The aim of this study was to relate the mechanical behaviour of saturated clays to their structural characteristics. Two clays were studied: a kaolinite and a bentonite. The evolution of the shape, the size, the concentration and the orientation of the elements which constitute the clay structure was examined by means of scanning and transmission electron microscopes. Particular care was taken to avoid as far as possible disturbing the micro-structure during observation. The results showed the existence of particle breakage and the creation of structural anisotropy during loading. We can conclude from this work that the mechanical behaviour to clayed materials is largely dependent on the changes which occur at the scale of the particles. Copyright © 2000 John Wiley & Sons Ltd.

本研究的目的是将饱和粘土的力学行为与其结构特征联系起来。研究了两种粘土：高岭石和膨润土。用扫描和透射电子显微镜研究了构成粘土结构的元素的形状、大小、浓度和取向的演变。特别注意在观察过程中尽可能避免干扰微观结构。结果表明，在加载过程中存在颗粒破碎和结构各向异性的产生。从这项工作中我们可以得出结论，粘土材料的力学行为在很大程度上取决于颗粒尺度上发生的变化。版权所有©2000 John Wiley&；儿子有限公司。

引用次数: 107

Ground movements around excavations in granular soils: a few remarks on the influence of the constitutive assumptions on FE predictions 颗粒土开挖周围的地面运动：关于本构假设对有限元预测的影响的几点意见

Mechanics of Cohesive-frictional Materials

Pub Date : 2000-06-28 DOI: 10.1002/1099-1484(200007)5:5<399::AID-CFM101>3.0.CO;2-R

Gioacchino Viggiani, Claudio Tamagnini

Two different approaches for modelling soil non-linearity (hardening plasticity and hypoplasticity) are compared with reference to the analysis of soil–structure interaction in an excavation in dense dry sand, supported by a propped diaphragm wall. The analysis focuses on the prediction of wall and soil movements. A commercial FE code has been used for the elastoplastic analyses, in order to assess the performance of a readily available design tool in current geotechnical engineering practice as compared to the predictions of a more advanced research tool. Although obtained for an idealized scheme, the results allow a number of more general conclusions to be drawn on the influence of the constitutive assumptions. Copyright © 2000 John Wiley & Sons, Ltd.

引用次数: 33