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1.
为了研究煤岩和砂岩在加载过程中的损伤对岩石力学性质的影响,分别对煤岩和砂岩做单轴和三轴全应力应变加卸载实验。进而构建岩石的损伤本构方程,实验结果表明:随着岩石损伤的增大,岩石的卸载弹性模量逐渐减小,塑性应变逐渐增加,表明岩石损伤属于弹塑性损伤;同时随着围压的增大,岩石的弹性模量随损伤的增加而下降的速率减小,表明岩石损伤主要引起岩石塑性应变的增加,岩石损伤破坏逐渐由脆性破坏向塑性破坏转变。假设岩石损伤速率符合威布尔统计分布规律,在此基础上构建煤岩损伤演化方程,通过实验和相关分析构建煤和砂岩弹塑性损伤本构方程。最后用构建的本构方程对实验曲线进行拟合,验证了弹塑性损伤本构方程的正确性。 相似文献
2.
硅藻质软岩的三维弹粘塑性模型分析 总被引：3，自引：1，他引：2
基于Perzyna的弹粘塑性理论的基本假设、粘塑性流动法则及殷建华和Graham的三维弹粘塑性模型,得出了在三轴应力状态下的本构关系表达式。殷建华和Graham的模型提出了“等效时间”,“瞬时时间线”,“参考时间线”,“极限时间线”等一系列新的概念。用三轴应力状态下的本构关系表达式对软岩的固结不排水三轴剪切试验进行了模拟计算,并与试验结果进行了比较。结果表明：数值模拟计算结果与试验结果几乎一致。该模型简单、实用、精度较高,可以模拟硅藻质软岩材料与时间有关的应力-应变关系、孔隙水压力与应变的关系,以及有效应力路径等。 相似文献
3.
考虑裂隙的连通率、间距、孔隙基质和裂隙材料在表征单元（REV）中的体积分数,并假定双重孔隙-裂隙介质的等效内摩擦角保持常数,而等效黏聚力是固有黏聚力、等效塑性应变、基质吸力、溶质浓度及温度的函数,提出了一种在热-水-应力-迁移耦合条件下确定表征单元内任一平面上等效的黏聚力及内摩擦角的方法。针对一个假定的位于非饱和双重孔隙-裂隙岩体中的高放废物地质处置模型进行了数值模拟及分析。结果表明,基质吸力对于等效黏聚力的增强作用大于等效塑性应变和溶质浓度的减弱作用,使得等效黏聚力得到了提高,故减少了围岩中的塑性区;由此岩体应力、孔（裂）隙水压力及流速、孔（裂）隙溶质浓度的分布及量值也发生相应的改变。 相似文献
4.
岩石屈服之后,弹性参数随塑性变形而变化,即岩石具有弹塑性耦合特征。在弹塑性耦合框架和现有应变分类、定义、本构方程研究的基础上,主要做了以下工作：结合岩石压缩试验,从损伤和塑性变形角度分析了弹性参数随塑性演化的现象;重点研究了加载增量步的应变特征,将与加载应力增量对应的应变增量分解为符合广义Hooke定律的弹性应变增量 、不符合广义Hooke定律的弹性应变增量 和塑性应变增量 ;通过采用加载增量步之后的弹性参数将 与 构造弹性关系,分别在应变空间和应力空间中建立了适用于加载、中性变载和卸载条件的本构方程;对表征物质微观结构变化的内变量进行了讨论。所提出的应变分类和定义方法概念清晰,适合于应变强化阶段和应变软化阶段,且所建立的弹塑性耦合本构方程能够反映不同加载条件对弹性参数变化速率的影响,符合岩石的弹塑性耦合力学特性。 相似文献
5.
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
6.
当前,地下工程围岩蠕变问题仍然存在,蠕变理论需要进一步丰富。岩石蠕变实质上是损伤不断积累的过程,针对蠕变条件下岩石损伤演化情况,文章采用TAW-2000多功能三轴伺服试验系统对取自四川乐山依卜隧道的红砂岩进行三轴蠕变试验,分析不同围压下试样蠕变变形规律,同时以西原模型为基础,结合Weibull分布和Perzyna黏塑性理论,建立一种改进的可以描述岩石蠕变破坏全过程的黏弹塑性蠕变模型。通过划分蠕变阶段来定义临界点损伤变量,从而更为准确地确定加速蠕变启动时间。得出如下结论：（1）模型曲线与试验数据具有良好的一致性,验证了模型的准确性与合理性,说明基于Weibull分布建立的红砂岩黏弹塑性蠕变模型是可行的;（2）基于Perzyna黏塑性理论,建立了可以更加准确的描述加速蠕变的黏塑性应变表达式;（3）文章建立的基于Weibull分布和Perzyna黏塑性理论的三轴损伤蠕变模型能够较好的描述岩石蠕变全过程,克服了西原模型不能描述加速蠕变的缺点。本研究通过定义不同蠕变阶段的临界点损伤变量更好的反映了岩石蠕变变形与损伤之间关系,丰富了岩石类材料的蠕变本构理论。 相似文献
7.
基于各向同性弹塑性损伤和Prevost模型的基本理论,把弹塑性等向硬化、运动硬化和各向同性损伤结合起来,推导了循环荷载作用下不排水饱和软黏土的弹塑性动力损伤本构模型。由循环累积塑性偏应变建立损伤演化方程,以描述循环加载对软黏土结构的破坏作用,并通过对循环三轴试验的模拟验证了模型的有效性。结果表明,提出的模型能较好地描述饱和软黏土在循环荷载作用下的变形、孔压变化及模量损伤过程。 相似文献
8.
结合软土变形的大位移、大应变、渗透固结及依时性特点,采用黏弹塑（西原）模型模拟土骨架,建立了分析软土地基的大应变黏弹塑性有限元列式和迭代求解算法,并采用动态“生”“死”单元模拟路堤的施工过程,建立了软土路基双重非线性渗透固结分析模型,研制了相应的大型实用化有限元分析程序LSVEP。分别采用反分析所得参数和室内试验确定参数对路基地表沉降和地基深层沉降进行预测,并将所得结果和现场实测结果进行对比分析,结果表明：所建立的大应变黏弹塑性有限元分析方法正确;计算参数的准确选择对沉降预测精度影响很大;用反分析所得参数进行沉降预测的精度远高于正分析预测,是提高沉降预测精度的有效途径,可供类似工程借鉴。 相似文献
9.
通过对西安地区不同湿度原状Q2黄土的单轴蠕变试验和三轴蠕变试验,得到了Q2黄土的单轴、三轴蠕变曲线和应力-应变等时曲线。试验曲线分析表明,Q2黄土具有明显的非线性流变特性。Q2黄土的粘弹性特性可采用五元件广义的Kelvin模型来描述,其线性粘塑性特性可用与一滑块并联的Maxwell模型来描述,而非线性粘塑性特性可通过损伤与塑性应变的耦合作用来反映。在考虑损伤门槛值的统计损伤及黄土粘弹塑性组合模型的基础上,应用应变等效原理,建立了考虑瞬时损伤的统计损伤流变模型,并通过拟牛顿法确定了相应的模型参数。该模型能够很好地模拟黄土流变非线性特征,该模型不仅参数较少,而且适用性较广。 相似文献
10.
以连续介质不可逆热力学为基础,采用了Mohr-Coulomb屈服准则,提出混凝土塑性损伤耦合的新的本构方程。在该模型中采用了塑性应变 、各向同性损伤标量D作为内变量。这个新的本构关系模型严格满足热力学的基本方程。以不同围压作用下混凝土试件的单轴压缩行为为例,采用开发的程序进行了局部水平上本构模型数值验证。结果表明,模型损伤演化数值结果符合试验趋势。 相似文献
11.
12.
根据红砂岩在冲击荷载作用下应力曲线表现出的明显的分段特征,以朱王唐本构模型为基础进行改进,建立了一种非线性体、Maxwell体和基于Weibull分布的损伤体并联的本构模型;根据红砂岩动态力学特性,对朱王唐本构模型进行简化,并基于Lemaitre等效应变假设推导出一种率型损伤本构方程。对两种新建本构方程进行试验验证,讨论其适用性并对比分析各参数对试验数据拟合结果的影响,结果表明,基于Weibull分布的非线性黏弹性损伤本构方程能很好地对常温及冻结状态下红砂岩峰前以及整个应力曲线的动态力学性能进行表征,而基于Lemaitre等效应变假设的损伤本构方程只可对红砂岩峰前应力部分进行解答,对整个应力曲线的表征存在一定的局限性。 相似文献
13.
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
14.
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
15.
针对现有损伤模型的不足,提出同时反映岩石初始损伤和残余强度的岩石变形过程模拟方法.将岩石材料分为未损伤部分、损伤部分和微缺陷,未损伤部分和损伤部分共同承担岩石所受的应力.通过岩石材料几何条件及微观受力分析建立未损伤部分的应变分析.再考虑岩石的形变比能只与损伤部分材料相关,从而建立损伤部分的应变分析.然后探讨岩石损伤和耗散能的关系,提出了可以反映岩石初始损伤的损伤演化方程,基于各部分应变分析建立模拟岩石变形过程的损伤本构模型,同时给出模型各参数的确定方法.结果表明:损伤演化方程不仅表现了岩石的初始损伤特征,也可以完整地体现岩石变形破坏过程的5个阶段;与前人模型相比,提出的岩石变形模拟方法与试验曲线更加吻合,体现了岩石的变形全过程,特别是更加直观地反映了岩石的初始损伤和残余强度特征.综合体现了本文模型在模拟岩石变形全过程时的优势. 相似文献
16.
Formulation and algorithmic treatment of a rate‐dependent plastic–damage model modified to capture large tensile cracking in cyclic‐loaded concrete structures are presented in detail for a three‐dimensional implementation. The plastic–damage model proposed by Lee and Fenves in 1998 was founded based on isotropic damaged elasticity in combination with isotropic multi‐hardening plasticity to simulate cracking and crushing of concrete under cyclic or dynamic loadings. In order that the model can capture large crack opening displacements, which are inevitable in plain concrete structures, the excessive increase in plastic strain causing unrealistic results in cyclic behaviors is prevented when the tensile plastic–damage variable controlling the evolution of tensile damage is larger than a critical value. In such a condition, the crack opening/closing mechanism becomes similar to discrete cracking. The consistent tangent operator required to accelerate convergence rate is also formulated for the large cracking state including viscoplasticity. The validation and performance of the modified algorithm implemented in a special finite element program is exemplified through several single‐element tests as well as three structural applications. The last example examines the model in the seismic fracture analysis of Koyna dam as a benchmark problem and the resulting crack profile is compared with the available experiment. The numerical experimentations well demonstrate that the developed model whose modification is necessary to properly simulate the cyclic behavior of plain concrete subjected to large tensile strains is robust and reasonably accurate. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
17.
基于损伤塑性模型的地下洞室结构地震作用分析 总被引：2，自引：1，他引：1
基于损伤力学原理,通过引入损伤变量的方法,详细推导了ABAQUS中的损伤塑性本构模型,描述混凝土后继屈服阶段及其卸荷后的损伤机制和力学行为。此本构模型可考虑循环荷载条件下材料刚度退化和应变率的影响,适用于类似混凝土材料的脆性材料,如岩石等。以某水电站地下厂房洞室结构为例,进行二维动力时程非线性分析,考虑不同的刚度恢复权重因子和应变率相关性对结构损伤的影响。多个数值算例表明：洞室混凝土结构和其周围一定深度的围岩的损伤是一个渐进积累的过程;材料的率相关性效应并不是在地震动作用开始时就立即产生,而是在一段时间后,结构经历一定程度的损伤后才慢慢体现出来;此损伤塑性模型适合地震荷载等循环荷载作用下地下洞室结构的动力时程非线性分析,尤其是强震下采用此损伤塑性模型是合理和必要的。 相似文献
18.
Ground motion records obtained in recent major strong earthquakes have provided evidence that ground motions recorded near the near-fault regions differ in many cases from those observed further away from the seismic source. As the forward directivity and fling effect characteristics of the near-fault ground motions, they have the potential to cause more considerable damage to structures during an earthquake. Therefore, understanding the influence of near-fault ground motions on the performance of structures is critical to mitigate damage and perform effective response. This paper presents results of a study aimed at evaluating the effects of near-fault and far-fault ground motions on seismic performance of concrete gravity dams including dam-reservoir-foundation interaction. Koyna gravity dam is selected as a numerical application. Four different near-fault ground motion records with an apparent velocity pulse are used in the analyses. The earthquake ground motions recorded at the same site from other events that the epicenter far away from the site are employed as the far-fault ground motions. The seismic performance evaluation method based on the demand-capacity ratio, the cumulative overstress duration and the spatial extent of overstressed regions is presented. The concrete damaged plasticity model including the strain hardening or softening behavior is employed in nonlinear analyses. Nonlinear seismic damage analyses of the selected concrete dam subjected to both near-fault and far-fault ground motions are performed. The results obtained from the analyses show the effects of near-fault ground motions on seismic performance of concrete gravity dams and demonstrate the importance of considering the near-fault ground excitations. 相似文献
19.
In quasi‐brittle material the complex process of decohesion between particles in microcracks and localization of the displacement field into macrocracks is limited to a narrow fracture zone, and it is often modelled with cohesive crack models. Since the anisotropic nature of the decohesion process in separation and sliding is essential, it is particularly focused in this paper. Moreover, for cyclic and dynamic loading the unloading, load reversal (including crack closure) and rate dependency are essential features that are included in a new model. The modelling of degradation is based on a ‘localized’ version of anisotropic continuum damage coupled to inelasticity. The concept of strain energy equivalence between the states in the effective and nominal settings is adopted in order to define the free energy of the interface. The proposed fracture criterion is of the Mohr type, with a smooth transition of the failure and kinematics (slip and dilatation) characteristics between tension and shear. The chosen potential, of the Lemaitre‐type, for evolution of the dissipative processes is additively decomposed into plastic and damage parts, and non‐associative constitutive equations are obtained. The constitutive equations are integrated by applying the backward Euler rule and by using Newton iteration. The proposed model is assessed analytically and numerically and a typical calibration procedure for concrete is proposed. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
20.
The effect of reservoir length on seismic performance of gravity dams to near- and far-fault ground motions 总被引：1，自引：1，他引：0
In this article, the effect of reservoir length on seismic performance of gravity dams to near- and far-fault ground motions
is investigated. For this purpose, four finite element models of dam–reservoir–foundation interaction system are prepared
by using the Lagrangian approach. In these models, the reservoir length varies from H to 4H (H: the height of dam). The Folsom gravity dam is selected as a numerical application. Two different ground motion records of
1989 Loma Prieta earthquake are used in the analyses. One of ground motions is recorded in near fault; the other is recorded
in far fault. Also, the two records have the same peak ground acceleration. The study mainly consists of three parts to assess
the effects of reservoir length on the seismic performance of the concrete gravity dam. In the first part, the linear time-history
analyses of the four finite element models prepared for the Folsom gravity dam are performed. In the second part, the seismic
performance of the dam is evaluated according to demand–capacity ratio and cumulative inelastic duration. Finally, the nonlinear
time-history analyses of the finite element models of the dam are carried out by using Drucker–Prager yield criteria for dam
concrete. It is seen from the analyses results that the seismic behavior of the concrete gravity dams is considerably affected
from the length of the reservoir. The reservoir length of 3H is adequate for concrete gravity dams. The selection of ground motion is on of the important parts of seismic evaluation
of gravity dams. Also, the frequency characteristics of the ground motion having the same peak ground acceleration affect
the seismic performance of the dam. The near-fault ground motions are generally creates more stress on the dam body than far-fault
ground motions. The used performance approach provides a systematic methodology for assessment of the seismic performance
and necessity of nonlinear analyses for dam systems. 相似文献