共查询到20条相似文献，搜索用时 15 毫秒
1.
A computational framework is presented for dynamic strain localization and deformation analyses of water‐saturated clay by using a cyclic elasto‐viscoplastic constitutive model. In the model, the nonlinear kinematic hardening rule and softening due to the structural degradation of soil particles are considered. In order to appropriately simulate the large deformation phenomenon in strain localization analysis, the dynamic finite element formulation for a two‐phase mixture is derived in the updated Lagrangian framework. The shear band development is shown through the distributions of viscoplastic shear strain, the axial strain, the mean effective stress, and the pore water pressure in a normally consolidated clay specimen. From the local stress–strain relations, more brittleness is found inside the shear bands than outside of them. The effects of partially drained conditions and mesh‐size dependency on the shear banding are also investigated. The effect of a partially drained boundary is found to be insignificant on the dynamic shear band propagation because of the rapid rate of applied loading and low permeability of the clay. Using the finer mesh results in slightly narrower shear bands; nonetheless, the results manifest convergency through the mesh refinement in terms of the overall shape of shear banding and stress–strain relations. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
2.
研究并提出一种以应变软化指标为基础的岩石非线性蠕变模型。首先,基于岩石三轴压缩试验结果,分析提出一种峰后应变软化指标R1来描述岩石峰后力学参数软化与塑性变形间的关系。接着,通过分析加速蠕变阶段与峰后段的联系,建立加速蠕变应变软化指标R2,并以此为基础构建非线性黏塑性体。然后,将其与Hook体和Kelvin元件串联,组建非线性蠕变模型,并将模型嵌入ABAQUS有限元程序。最后,针对砂岩和泥岩三轴蠕变试验建立数值模型,模拟曲线与试验曲线吻合良好,说明所建模型适用于硬岩/软岩加速蠕变现象的模拟。其中,参数 对加速蠕变曲线形态起调节作用,显示模型模拟脆性?延性流变破坏的特点。另外,模型参数均可由常规压缩破坏试验以及蠕变试验确定,易于获取。 相似文献
3.
已有震害研究表明,震后边坡会因持续变形而破坏,且伴随着土体强度逐渐降低的现象,即土的循环软化行为。因此,有必要研究考虑循环软化的非线性动力本构模型以用于复杂条件下地震边坡稳定性分析。在已有的非线性动力本构模型基础上,提出了考虑循环软化的处理方法。同时,在FLAC3D平台上实现了本构模型二次开发,并通过了理论公式与已有文献中试验数据的验证。结果表明：计算出的骨干曲线与理论公式一致,且计算出的动剪切模量比及阻尼比与试验数据吻合较好,能够克服Hardin-Drnevich模型和Davidenkov模型在较大应变处（>0.01%）过高地估算阻尼比的缺陷;考虑了循环软化后,计算出的剪切强度有明显降低,且当遇到骨干曲线剪应力可以连续地过渡到软化后的主干曲线上,模型的收敛性较好。所开发的本构模型可为大应变条件下软土场地及边坡地震灾害评估提供支持。 相似文献
4.
The aim of the present paper is to numerically analyse the behaviour of frozen sand by using a viscoplastic constitutive model with strain softening. A constitutive model has been developed introducing the stress history tensor which is a functional of the stress history, with respect to a generalized time measure. It is shown that Adachi and Oka's model is applicable to the results of triaxial tests on a frozen Toyoura sand at different strain rates. First, the instability of the model is discussed within the framework of bifurcation theory. The model is then implemented into a FEM code to numerically simulate the behaviour under plane strain conditions. From the numerical results, it is revealed that the formation of shear bands is possible and the characteristics of strain localization, such as shear banding, depend on the strain rates. 相似文献
5.
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
6.
This paper deals with numerical modeling of the compressive behavior of granite rock under high strain rate dynamic loading and wide range of confining pressure. For this end, a constitutive model based on damage mechanics and viscoplasticity for rock is formulated and implemented in explicit dynamics FEM. The viscoplastic part is based on a simple power law type yield criterion that incorporates the rate-dependency with a linear viscosity term. Moreover, a Rankine type of tensile cut-off is employed. The damage part of the model is formulated with separate scalar damage variables in tension and compression. The model is calibrated for Kuru granite and validated with the experimental data from dynamic compression tests at the strain rate of 600 1/s up to 225 MPa of confining pressure. The numerical simulations demonstrate that, despite the underlying continuum modeling approach, the model captures the correct experimental failure modes, including the transition from single-to-multiple fragmentation, as well as the dynamic compressive strengths at different confining pressures. 相似文献
7.
基于摩尔-库仑模型的非线性本构模型的开发及其在应变局部化中的应用 总被引：1，自引：0，他引：1
以FLAC中的Mohr-Coulomb（M-C）本构模型为基础,在C++环境下实现了考虑拉伸截断的非线性本构模型的二次开发。针对应力及位移的分布规律,将理想弹塑性的Hoek-Brown（H-B）本构模型、M-C本构模型及自定义本构模型的数值解及H-B本构模型的理论解进行了比较,验证了自定义本构模型的正确性。采用弹-脆-塑性的自定义本构模型,以先加载,后挖洞的方式模拟了圆形巷道围岩的应变局部化过程,在计算模型的边界条件对称及均质本构参数的条件下,模拟出了4个对称的V型坑,模拟结果与静水压力条件下岩爆的现场观测及试验结果吻合,而采用接近脆性的H-B应变软化模型所得结果的对称性较差 相似文献
8.
平面应变状态下土体的软化特性与本构模拟 总被引：3，自引：2，他引：1
在平面应变状态下,由于土体在应力峰值状态出现了应变局部化现象,从而变形模式失去了原有的均匀性而呈现软化特性。为此,采用常规的弹塑性本构模型模拟土体峰值前的均匀变形,对应力峰值状态则采用非共轴的分叉理论进行预测,而土样在峰值后出现不均匀变形的宏观力学特性则通过复合体理论加以描述。理论预测表明,构建这样的软化本构模型能真实反映平面应变状态下的应力-应变特性。理论分析还表明,经典的变形分叉理论中引入非共轴弹塑性模型,才能准确地预测土体的应力峰值,这是构建平面应变状态下土体软化本构模型的关键所在。 相似文献
9.
Summary This paper is intended to describe the SHELVIP (Stress Hardening ELastic VIscous Plastic) model, a new viscoplastic constitutive
law which has been developed to incorporate the most important features of behaviour observed in tunnels excavated in severe
to very severe squeezing conditions. This model couples the elastoplastic and time-dependent behaviour by using a plastic
yield surface, as frequently adopted in tunnel design analysis, and the definition of a state of overstress referred to a
viscoplastic yield surface. The model is formulated in all its detailed aspects. The related analytical closed-form solution
for representing triaxial creep deformations is developed. Also developed is an incremental numerical solution for describing
the triaxial stress–strain behaviour under constant strain rate conditions. The model is shown to fit very satisfactorily
the results of creep tests on clay shales and relaxation tests on coal specimens, as recently performed for design analysis
of tunnels in squeezing conditions.
Correspondence: D. Debernardi, Department of Structural and Geotechnical Engineering, Politecnico di Torino, Torino, Italy 相似文献
10.
岩石类材料的能量基率相关弹塑性损伤模型 总被引：2，自引：2，他引：0
岩石类材料的动态本构模型研究是岩石动力学理论研究的基础问题。相比于其他的非线性理论,损伤力学理论已证实可成功地模拟岩石类材料的应变软化和渐进破坏等特征,可用于解释其静、动态破坏机制。现有的通过理论推导得出的动态本构中大部分并未考虑损伤因素,而通过维象学试验方法建立起的动态本构则缺乏损伤力学理论基础。为此基于弹性余能等效原理和损伤力学的基本概念,并结合动态试验,推导建立了岩石类材料的率相关弹塑性损伤模型。并通过与文献中的试验资料对比,证明了模型的有效性,为岩石类材料组成的结构的动力响应研究奠定了基础。 相似文献
11.
Rate‐dependent behaviour of chalk and other porous rocks has undergone widespread study in geomechanics due to its implications on the performance of engineering structures. We present a rate‐dependent constitutive model for chalk and other porous rocks with several new features. The model formulation is based on a viscoplastic rate‐lines approach in which the axial strain rate depends on the proximity of the stress point to an elliptical reference surface. A non‐associated viscoplastic potential surface and an axial scaling algorithm are used to determine the viscoplastic strain components. The model predicts that axial yields stress varies as a power function of applied axial strain rate, as shown by published laboratory data. Comparisons with published experimental data indicate that the model is capable of reproducing observed rate‐dependent behaviour of chalk under a variety of loading conditions. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
12.
G. Y. Sheu 《Geotechnical and Geological Engineering》2009,27(6):729-740
This study presents the recognition of an elastic–plastic constitutive law by a multiobjective evolutionary algorithm (MOEA).
This idea is illustrated by the identification of ellipse aspect ratio and plastic modulus of a reported bounding surface
model. Based on the multi-goals of well predicting all available drained or undrained stress–strain behaviors simultaneously,
the compromising solutions of these two parameters are found by a strength Pareto evolutionary algorithm 2 (SPEA2). Their
fittest values are then determined by additionally introducing the Akaike information criterion. Experimental data for the
Ottawa sand are used to test such processes. The results show that an MOEA is an efficient and automatic tool to identify
the fittest form of an elastic–plastic constitutive law from a large amount of experimental data. However, sufficient data
are required to determine the correct searching range of parameters to be identified. 相似文献
13.
重大建设项目对施工过程中岩土体稳定性提出了更高的要求,常以一种动态设计施工模式来应对工程体的各类突发状况与病害。流变损伤模型既能反映岩土体在施工过程中变形的时效发展,又能反映其力学性质的时效劣化,继而能较准确地掌握工程体动态稳定性。基于以上考虑,为体现卸载边坡工程在卸载回弹阶段的瞬时塑性特征和时效演化阶段的黏塑性特征,因此,在流变模型中引入加载塑性元件和黏塑性元件,建立了复合黏弹塑（弹-黏-黏弹-黏塑-塑）模型,室内岩石压缩（卸载）蠕变试验证明了该流变模型的合理性,并对其参数进行辨识。在此基础上,从几何研究方法出发,引入反映节理分布的初始损伤张量及一种等效的依据黏塑性偏应变推导出的损伤演化方程,最终建立了一种新型的节理岩体等效流变损伤模型。将此模型用于川东红层某软硬岩互层型路堑边坡的卸载分析,结果表明：随不同的开挖阶段,易损部位（软岩集中段、软岩深埋段、软硬交接硬岩段）在瞬时卸载回弹阶段的塑性损伤和时效演化阶段的黏塑性损伤逐渐积累,边坡浅表部逐渐出现卸载损伤（松弛）带,在损伤累积中边坡各部位蠕变速率呈不同程度的增长。计算结果较好地反映了边坡变形、损伤发展与动态稳定性特征,其研究结果对于指导支护时机及相应的信息化施工具有一定的意义。 相似文献
14.
A new analytical model to study the influence of weld on the vertical dynamic response of prestressed pipe pile 
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下载免费PDF全文 Wenbing Wu Guosheng Jiang Shenggen Huang Guoxiong Mei Chin Jian Leo 《国际地质力学数值与分析法杂志》2017,41(10):1247-1266
This investigation is concerned with the mathematical analysis of a viscoelastic prestressed pipe pile embedded in multilayered soil under vertical dynamic excitation. The pile surrounding soil is governed by the plane strain model, and the soil plug is assumed to be an additional mass connected to the pipe pile shaft by applying the distributed Voigt model. Meanwhile, the prestressed pipe pile is assumed to be a vertical, viscoelastic, and hollow cylinder governed by the one‐dimensional wave equation. Then, analytical solutions of the dynamic response of the pipe pile in the frequency domain are derived by means of the Laplace transform and impedance function transfer method. Subsequently, the corresponding quasi‐analytical solution in the time domain for the case of the prestressed pipe pile undergoing a vertical semi‐sinusoidal exciting force applied at the pile top is obtained by employing the inverse Fourier transform. Utilizing these solutions, selected results for the velocity admittance curve and the reflected wave curve are presented for different heights of the soil plug to examine the influence of weld properties on the vertical dynamic response of prestressed pipe pile. The reasonableness of the theoretical model is verified by comparing the calculated results based on the presented solutions with measured results. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
15.
In this article we present closed‐form solutions for the undrained variations in stress, pore pressure, deformation and displacement inside hollow cylinders and hollow spheres subjected to uniform mechanical pressure instantaneously applied to their external and internal boundary surfaces. The material is assumed to be a saturated porous medium obeying a Mohr–Coulomb model failure criterion, exhibiting dilatant plastic deformation according to a non‐associated flow rule which accounts for isotropically strain hardening or softening. The instantaneous response of a porous medium submitted to an instantaneous loading is undrained, i.e. without any fluid mass exchange. The short‐term equilibrium problem to be solved is now formally identical to a problem of elastoplasticity where the constitutive equations involve the undrained elastic moduli and particular equivalent plastic parameters. The response of the model is presented (i) for extension and compression undrained triaxial tests, and (ii) for unloading problems of hollow cylinders and spheres through the use of appropriately developed closed‐form solutions. Numerical results are presented for a plastic clay stone with strain hardening and an argilite with strain softening. The effects of plastic dilation, of the strain softening law and also of geometry of the cavity on the behaviour of the porous medium have been underlined. Analytical solutions provide valuable benchmarks enabling various numerical methods in undrained conditions with a finite boundary to be verified. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
16.
The paper presents a simple constitutive model for the behavior of sands during monotonic simple shear loading. The model
is developed specifically to account for the effects of principal stress rotation on the simple shear response of sands. The
main feature of the model is the incorporation of two important effects of principal stress on stress–strain response: anisotropy
and non-coaxiality. In particular, an anisotropic failure criterion, cross-anisotropic elasticity, and a plastic flow rule
and a stress–dilatancy relationship that incorporate the effects of non-coaxiality are adopted in the model. Simulations of
published experimental results from direct simple shear and hollow cylindrical torsional simple shear tests on sands show
the satisfactory performance of the model. It is envisioned that the model can be valuable in modeling in situ simple shear
response of sands and in interpreting simple shear test results. 相似文献
17.
18.
基于Drucker-Prager准则的岩石弹塑性损伤本构模型研究 总被引：1，自引：0，他引：1
大多数岩石材料软化本构模型在硬化函数中引入塑性内变量来表示材料的硬化/软化性质,但并不能反映岩石微裂隙损伤对材料力学性能的影响及单轴拉伸和压缩所表现的初始屈服强度f0与屈服极限fu的差异。基于D-P准则同时考虑塑性软化及损伤软化,建立岩石类材料的弹塑性本构关系及其数值算法。塑性屈服函数采用Borja等的应力张量的硬化/软化函数,反映塑性内变量及应力状态对硬化函数的影响;由于岩石损伤软化是微裂隙扩展所导致的体积膨胀引起的,因此,提出用体积应变表征岩石损伤变量的演化,并用回映隐式积分算法编制了岩石的弹塑性损伤本构程序。对单轴压缩及拉伸荷载作用下的岩石材料试验进行数值模拟,结果表明,所提出的岩石弹塑性损伤本构模型可以较好地符合岩石材料的力学特性。 相似文献
19.
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
20.
基于Drucker-Prager（下简称D-P）准则,建立压缩载荷作用下的非贯通节理岩石的弹塑性断裂模型。针对节理岩石小范围屈服翼裂纹尖端塑性区,推导了D-P屈服准则的纯I、纯II及I、II复合型3种翼裂纹无量纲塑性区径长函数,并与Mises准则的塑性区进行对比;结果表明,D-P准则的I型和复合型塑性区较Mises屈服准则的塑性区大,且其II型及I、II复合型塑性区在翼裂纹上下表面不连续。进一步,引入断裂软化因子以表征节理岩石裂隙断裂扩展后的断裂软化规律,考虑非贯通节理岩石复合型断裂软化,是由于节理尖端翼裂纹应变能密度超过最小应变能密度导致其成核扩展引起的,提出用应变能密度的指数函数形式表征断裂软化变量的演化;塑性屈服函数采用Borja等的应力张量3个不变量的硬化/软化函数,反映塑性内变量及应力状态对硬化函数的影响;建立节理岩石的弹塑性断裂本构关系及其数值算法,并用回映隐式积分算法编制了弹塑性断裂模型的程序。以单轴压缩下非贯通节理岩石为例,分析岩石断裂韧度、节理摩擦系数和节理倾角等参数的影响,结果表明,所提出的弹塑性断裂模型与数值和试验结果比较吻合。 相似文献