共查询到20条相似文献，搜索用时 958 毫秒
1.
The ISA-plasticity is a mathematical platform which allows to propose constitutive models for soils under a wide range of strain amplitudes. This formulation is based on a state variable, called the intergranular strain, which is related to the strain recent history. The location of the intergranular strain can be related to the strain amplitude, information which is used to improve the model for the simulation of cyclic loading. The present work proposes an ISA-plasticity-based model for the simulation of saturated clays and features the incorporation of a viscous strain rate to enable the simulation of the strain rate dependency. The work explains some aspects of the ISA-plasticity and adapts its formulation for clays. At the beginning, the formulation of the model is explained. Subsequently, some comments about its numerical implementation and parameters determination are given. Finally, some simulations are performed to evaluate the model performance with two different clays, namely a Kaolin clay and the Lower Rhine clay. The simulations include monotonic and cyclic tests under oedometric and triaxial conditions. Some of these experiments include the variation of the strain rate to evaluate the viscous component of the proposed model. 相似文献
2.
The analysis of geotechnical problems involving saturated soils under cyclic loading requires the use of advanced constitutive models. These models need to describe the main characteristics of the material under cyclic loading and undrained conditions, such as the rate of the pore water pressure accumulation and the stress attractors. When properly doing so, the models are expected to be reliable for their use in boundary value problems. In this work, an extension of the widely implemented intergranular strain model by Niemunis and Herle (Mech Cohes Frict Mater 2(4):279–299, 1997) is proposed. The modification is aimed to improve the capabilities of the model when simulating a number of repetitive cycles, where a proper reduction of the strain accumulation is expected. For validation purposes, the reference model and proposed improvement are compared against some monotonic and cyclic triaxial tests. The results indicate that the intergranular strain improvement model provides a more realistic prediction of the accumulation rates under cyclic loading, without spoiling the advantages of the original formulation.
相似文献3.
A hypoplastic constitutive model for clays 总被引：3，自引：0，他引：3
D. Ma&#x;ín 《国际地质力学数值与分析法杂志》2005,29(4):311-336
This paper presents a new constitutive model for clays. The model is developed on the basis of generalized hypoplasticity principles, which are combined with traditional critical state soil mechanics. The positions of the isotropic normal compression line and the critical state line correspond to the Modified Cam clay model, the Matsuoka–Nakai failure surface is taken as the limit stress criterion and the non‐linear behaviour of soils with different overconsolidation ratios is governed by the generalized hypoplastic formulation. The model requires five constitutive parameters, which correspond to the parameters of the Modified Cam clay model and are simple to calibrate on the basis of standard laboratory experiments. This makes the model particularly suitable for practical applications. The basic model may be simply enhanced by the intergranular strain concept, which allows reproducing the behaviour at very small strains. The model is evaluated on the basis of high quality laboratory experiments on reconstituted London clay. Contrary to a reference hypoplastic relation, the proposed model may be applied to highly overconsolidated clays. Improvement of predictions in the small strain range at different stress levels is also demonstrated. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
4.
5.
A constitutive model for dry metamorphosed snow is proposed, within the framework of elasto‐viscoplasticity, which is able to reproduce the most relevant features of the macroscopic behaviour of snow, particularly its time and rate dependency. The basic ideas for modelling stem from the conceptual forms proposed for bonded geomaterials, such as cemented soils or soft rocks. The high viscosity of snow is accounted for by adopting an overstress approach, suitably modified. An evolution law for the curvature‐driven process of sintering, by which intergranular ice necks form and grow, is established. The system of constitutive equations is then numerically integrated via a fully implicit time stepping scheme. Selected results from finite element simulations of laboratory tests, available in the literature, are presented. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
6.
通过将Perzyna过应力理论与临界状态理论相结合,并引入Wheeler旋转硬化法则,提出一个能描述土体初始各向异性及应力诱发各向异性的三维弹黏塑性本构模型。模型考虑流变发生的下限,在三维应力空间,模型存在形状相似的静屈服面及动态加载面。采用缩放形式的幂函数。本构模型数值算法采用回映算法,借助ABAQUS软件UMAT子程序接口实现。并通过对三轴不排水蠕变试验的模拟,确定合适的积分步长。此后,分别对三轴不排水蠕变试验及常应变率三轴不排水剪切试验进行了模拟。模拟中通过设置不同参数值,可将模型退化为各向同性模型,并对这两种模拟结果进行了比较。模拟结果表明：(1) 对于三轴不排水蠕变,在低剪应力水平下,各向同性模型和各向异性模型模拟的结果相差不大,而在高剪应力水平下,各向异性模型模拟结果更接近试验结果;(2) 对于常应变率加载试验的模拟,模型合理反映了土体不排水强度随着加载速率的增大而增大现象。 相似文献
7.
In finite element calculations the constitutive model plays a key role. The evaluation of the stress response of the constitutive relation for a given strain increment, which is a time integration in the case of models of the rate type, is a typical sub task in such calculations. Adaptive behaviour of the time integration is essential to assure numerical stability and to control the accuracy of the solution. An adaptive second order semi-implicit method is developed in this paper. Its numerical behaviour is compared with an adaptive second order explicit scheme. The two proposed methods control the local error and guarantee numerical stability of the time integration. We include several numerical geotechnical element tests using hypoplasticity with intergranular strain. The element tests simulate the behaviour of a finite element method based on the displacement formulation. 相似文献
8.
为了描述软黏土一维应力-应变关系的时效特性,基于Bjerrum的等时间线体系,提出等黏塑性应变率线概念,推导了黏塑性应变率与黏塑性应变增量的关系,建立了软黏土的一维弹黏塑性模型;从理论上分析了新建模型与3种典型的一维弹黏塑性时效本构模型的内在联系,表明新建模型与其他3种模型在本质上是等效的,且形式更简洁,物理意义更明确;利用新建模型对软黏土的固结-蠕变耦合效应、应变率效应、应力松弛效应等时效特性进行了理论分析,并得到了相应的解析解;结合宁波软黏土的一维固结试验,阐述了模型参数的确定方法,并用新建模型对宁波软黏土的固结-蠕变试验、温州软黏土的一维多级等应变率试验、香港海相软黏土的一维应力松弛试验进行模拟,验证了新建模型的有效性。研究结果表明,新建模型能很好地模拟软黏土的一维时效特性。 相似文献
9.
A hypoplastic macroelement model for shallow foundations under monotonic and cyclic loads 总被引：3，自引：3，他引：0
In this work, a macroelement for shallow foundations on sands has been developed based on the theory of hypoplasticity. The
incrementally nonlinear constitutive equations of the macromodel are defined in terms of generalized forces and displacements
and are constructed based on the general approach proposed by Niemunis (Extended Hypoplastic Models for Soils. Habilitation
Thesis, Bochum University, 2002). A suitable vectorial internal variable—mimicking the concept of intergranular strain introduced
by Niemunis and Herle (Mech Cohes Frict Mater 2:279–299, 1997) for continuum hypoplasticity—is employed to provide the model
sufficient memory of past displacement history to be able to reproduce the observed behavior under cyclic loading paths. As
compared to similar macroelements formulated within the framework of the theory of elastoplasticity, the proposed approach
has the advantage of a much simpler mathematical structure, which allows a straightforward implementation in existing structural
analysis FE codes. The model performance has then been evaluated by comparing the model predictions with available experimental
results from a series of small-scale model tests reported by Nova and Montrasio (Géotechnique 41:243–256, 1991). Overall,
the model captures reasonably well the observed response under nonproportional, complex loading paths. A series of simulations
reproducing the tests performed by di Prisco et al. (Shallow footing under cyclic loading: experimental behaviour and constitutive
modelling. Patron, Bologna, 2003) has also demonstrated the potential of the proposed model to simulate the observed behavior
of footings under cyclic loading paths, at least from a qualitative point of view. 相似文献
10.
亚塑性模型为模拟颗粒材料的非线性力学行为提供了一条新途径,特别是CLoE亚塑性模型在模拟应变局部化时具有一定的优势。然而该模型在模拟小幅应力-应变循环时表现出一定的锯齿效应。为了克服该效应,基于颗粒间应变张量的概念发展了修正的CLoE亚塑性模型以正确模拟循环荷载下密砂的力学行为。此外,为保证单调荷载作用下修正模型与原模型预测结果的一致性,改进了颗粒间应变率及颗粒间最大应变的定义。数值算例表明:（1）修正模型保留了克服锯齿效应的优点。（2）修正模型能够反映不同振幅条件下的卸载刚度。（3）在大振幅循环条件下,滞回圈的面积随着循环次数增加而增大。（4）修正模型能够保证单调加载条件下所得结果与原模型的一致性。（5）修正模型可以反映材料的疲劳破坏机制。 相似文献
11.
The paper begins with a discussion of the phenomenon of small‐strain stiffness and presents the small‐strain overlay model, a simple model that takes into account the non‐linear stiffness of soils at small strains. The new model can enhance already established elastoplastic formulations for non‐linear stiffness variation at small strains in a similar way that intergranular strain enhances the hypoplastic model. The overlay model is driven by the material's strain history and only two additional material constants, both with clear physical meaning. Therefore, the proposed model is a step towards the incorporation of small‐strain stiffness into routine design. In this paper, the new small‐strain overlay model is formulated. Its ability to take into account the influence of various strain histories on soil stiffness is illustrated in several examples. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
12.
The theory of fractional calculus has been successfully applied to model the triaxial behaviour of soils under static loading conditions. However, limited work has been carried out in using the fractional calculus to describe the cyclic behaviour of granular soils. In this paper, a fractional order constitutive model for granular soils under drained cyclic loading is proposed by incorporating the concept of fractional rate for strain accumulation. The fractional rate for strain accumulation is obtained from the analysis of the experimental data by utilizing the fractional calculus. Comparison between the test results and model predictions is presented. The key feature of the proposed model is that it can reasonably characterise the cyclic deformation of granular soils under both low and high loading cycles. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
13.
中低应变率下的岩石损伤本构模型研究 总被引：2，自引：0，他引：2
深部岩石的破碎与钻探中,岩石主要处在中低应变率的载荷作用下,而目前的研究还沿用中高应变率推导的动态损伤本构关系。从工程背景和试验角度分析了中低应变率下的岩石动力学特性,提出Maxwell体、Bingham体和损伤体的并联模型,借助拉普拉斯变换,引入基于岩石孔隙、裂隙劣化的损伤变量,导出了中低应变率下的岩石动态损伤本构模型。利用该模型对泥质砂岩和花岗岩在应变率为87 s-1、382 s-1、673 s-1时的应力-应变试验数据进行拟合,并将拟合结果与实测数值、原文献拟合曲线对比,结果表明该理论模型适用性较好。分析拟合参数可知,该动态损伤本构模型能够主动适应中低应变率两类情况,本构曲线和损伤变量的变化符合实际情况。 相似文献
14.
黏土的应力路径本构模型 总被引：2，自引：0，他引：2
根据黏土应力-应变曲线的特点及其应力路径的相关特性,将作者所建立的砂土应力路径本构模型扩展用于黏土,建立了黏土的应力路径本构模型,利用变换应力方法将SMP准则用于黏土的应力路径本构模型,使模型得到了合理的三维化。黏土的应力路径模型与修正剑桥模型相比,在双向加载A区和卸载D区二者完全相同;在单向加载B区和F区,两种模型均可计算塑性应变;特别是在C区和E区,黏土的应力路径模型可计算塑性应变,而修正剑桥模型的塑性应变为0。通过与修正剑桥模型比较和对藤森黏土试验结果的预测,反映了黏土应力路径本构模型描述黏土在不同应力路径条件下应力-应变特性的优越性。 相似文献
15.
16.
David Ma&#x;ín Claudio Tamagnini Gioacchino Viggiani Daniele Costanzo 《国际地质力学数值与分析法杂志》2006,30(13):1303-1336
In this paper, the performance of different advanced constitutive models for soils is evaluated with respect to the experimentally observed behaviour of a soft reconstituted clay subject to a wide range of loading directions, see (presented in the companion paper). The models considered include a three‐surface kinematic hardening elastoplastic model; the CLoE hypoplastic model; a recently proposed K‐hypoplastic model for clays, and an enhanced version of the same model incorporating the concept of intergranular strain. A clear qualitative picture of the relative performance of the different models as a function of the loading direction is obtained by means of the incremental strain response envelopes. The definition of suitable error measures allows to obtain further quantitative information in this respect. For the particular initial conditions and loading programme considered in this study, the kinematic hardening and the enhanced K‐hypoplastic models appear to provide the best performance overall. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
17.
循环加-卸载岩石本构模型是预测压气储能洞室长期稳定性的关键,但目前还没有适用的本构模型,因此,提出了一种能够描述岩石循环加载和卸载的本构模型。鉴于岩石在循环作用下损伤不断累积,将基于Weibull分布的岩石损伤软化模型进行拓展,并用内变量疲劳本构模型描述每个循环的初始模量和卸载模量的变化,进而得到循环加-卸载作用下的岩石本构模型,然后将该模型与现有的试验结果进行对比。该模型物理意义明确,涉及的参数较少,且便于拟合。提出的循环加-卸载下岩石本构模型对试验数据拟合效果较好,能较准确地反映循环荷载上、下限值对应的轴向应变,也能反映出循环内部变形模量衰减的趋势。该模型的成功建立为循环加-卸载下岩石本构模型的研究提供了新思路。 相似文献
18.
A viscoplastic constitutive model of rock is proposed for which both yield stress and viscosity undergo variation during the deformation process. The model is initially formulated for a uniaxial stress state; its extension for a general stress state is also provided. Model parameters are determined from compression tests at different values of strain rate, and its application to simulate results of such tests is given. The examples of stress redistribution in a coal seam due to progressing longwall exploitation are presented by applying the developed degradation model. The model provides good simulation of material response in both stable and post-critical stages. 相似文献
19.
在描述重塑土的统一硬化模型（UH模型）基础上,以动态地移动正常固结线（MNCL）代替静态的正常固结线（NCL）作为参考线来确定参考应力,将土的结构性衰减体现在MNCL的演化中,从而把UH模型扩展为可考虑土结构性的结构性土UH模型。结构性土UH模型可以合理地并连续光滑地描述结构性土的等向压缩规律、应变硬化、应变软化、剪切体积收缩、剪切体积膨胀、不排水剪切减压软化以及结构性和密度耦合影响等力学特性。相比于UH模型,结构性土UH模型新增3个参数,分别用于描述结构性的程度、衰减速度、以及塑性流动规律。通过3种天然土的试验结果与模型预测对比验证了结构性土UH 模型的合理性。 相似文献
20.
In the paper, we present newly developed hydro-mechanical hypoplastic model for partially saturated soils predicting small strain stiffness. Hysteretic void ratio dependent water retention model has been incorporated into the existing hypoplastic model. This required thorough revision of the model structure to allow for the hydro-mechanical coupling dependencies. The model is formulated in terms of degree of saturation, rather than of suction. Subsequently, the small strain stiffness effects were incorporated using the intergranular strain concept modified for unsaturated conditions. New features included degree of saturation-dependent size of the elastic range and an updated evolution equation for the intergranular strain. The model has been evaluated using two comprehensive data sets on completely decomposed tuff from Hong-Kong and Zenos Kaolin from Iran. It has been shown that the modified intergranular strain formulation coupled with the hysteretic water retention model correctly reproduces the effects of both the stress and suction histories on small strain stiffness evolution. The model can correctly predict also different other aspects of partially saturated soil behaviour, starting from the very small strain range up to the asymptotic large-strain response. 相似文献