共查询到20条相似文献，搜索用时 875 毫秒
1.
基于Wheeler土体各向异性旋转硬化法则,结合边界面理论,构造一个能够反映土体初始各向异性及加载后应力诱发各向异性的边界面本构模型,并借助ABAQUS软件提供的UMAT子程序接口,采用隐式积分算法--图形返回算法实现。通过对正常固结状态下（OCR=1）高岭土试样三轴不排水剪切试验进行模拟,并将模拟结果与ABAQUS自带的修正剑桥模型模拟结果进行了比较分析,表明本模型的模拟结果能够反映土体在偏压加载过程中产生的各向异性现象。在此基础上,采用本模型对中等超固结（OCR=4）高岭土试样三轴不排水剪切试验进行模拟,并再次与ABAQUS自带的修正剑桥模型模拟结果进行比较,表明本模型能够较好地反映中等超固结土在小应变情况下的非线性特性。相比于经典弹塑性模型,如修正剑桥模型,本模型的模拟结果更符合中等超固结土的变形特性。 相似文献
2.
天然土体经历开挖卸荷应力路径后,其应力变形特性与常规加载应力路径条件下规律存在较大差异。目前常用土体本构模型大多建立在等向固结单向加载三轴试验基础上,没有考虑初始K0固结和开挖卸荷应力路径的影响。以剑桥模型为基础,借鉴关口-太田模型的建模思想,通过引入新的应力比参数,对p-q平面上屈服轨迹硬化轴进行旋转,调整弹性区范围,以反映初始K0固结的影响;再运用变换应力法将模型三维化处理,从而使模型可以描述土体三向不等向应力状态,最终得到一个能综合反映土体K0固结开挖卸荷应力-应变特性的三维弹塑性本构模型。通过和典型室内应力路径试验结果进行对比,验证了模型的合理性。 相似文献
3.
软粘土的各向异性和小应变条件下的本构模型(ASM) 总被引：12，自引：5，他引：7
以能量方程为基础推导出各向异性和小应变条件下弹塑性的本构方程,并将屈服面与修正桥模型和试验测得的屈服面进行了对比,表明新的屈服面比修正剑桥模型更接近试验结果,采用从初始应力到状态边界面的距离为参数的系数来修正硬化准则以模拟土体小应谱条件下的应力－应变特征。将新的本构模型编入有限元程序,对小应变试验进行了计算分析,计算结果表明,新的模型比修正剑桥模型能更好地反映土体的主要力学特性。 相似文献
4.
基于应力空间变换的修正剑桥模型改进 总被引：10，自引：3，他引：7
从岩土类材料极限应力状态线所致的各向异性出发,提出了应力空间变换的思想。以修正剑桥模型屈服面的中心为映射中心,给出了重塑土的应力空间变换、应力增量变换的公式, 并考虑了应力洛德角的影响。在变换应力空间中对修正剑桥模型进行了重新表述与改进,给出了基于应力空间变换的改进模型的具体应力应变计算式。通过4种应力路径的基于应力空间变换的改进模型与修正剑桥模型预测结果的对比,揭示了改进后模型的优越性：可以较好的反映各向异性的影响;可以很好地反映三轴伸长等应力路径的应力应变特性;可以反映 等路径所致的软化现象。 相似文献
5.
土体结构性的数学模型是21世纪土力学的核心问题。由于土体微观结构的变化造成了重塑土与原状土的力学特性上的差异。采用应变型和应力型结构性宏观参数来表征这种微观结构的变化,同时将应变性结构性参数引入到等向固结过程中去,用以描述常规三轴试验中剪切前的等向固结过程以及剪切时球应力对结构性土体的影响。实现应变型和应力型结构性宏观参数对整个三轴剪切过程的描述。修正剑桥模型对正常固结重塑黏土的三轴压缩试验能做出准确地描述,但对超固结黏土及原状土,即具有结构地土体,则不能给出准确地描述。将应变型和应力型结构性宏观参数引入到修正剑桥模型中,实现修正剑桥模型的结构化。该结构性修正剑桥模型参数的确定方法与常规修正剑桥模型参数的确定方法相差不多,只不过多了球应力与土体结构性体应变的关系式、偏应力与土体结构性广义剪应变的关系式。经过数值模拟比较,结构性修正的剑桥模型能较好地反映原状土的结构性演化过程,能描述原状土结构的整个破坏过程,在多种应力路径下具有很好的预测作用。 相似文献
6.
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
7.
天然土体的初始各向异性通常可对其后继循环特性产生显著影响。现有考虑循环载荷作用的土体弹塑性模型,往往采用类似修正剑桥模型的椭圆形屈服面,已有研究表明,该椭圆形屈服面因其拉伸弹性区域偏大,针对天然K0固结状态的土体,其计算精度较差。基于新近提出的广义各向同性硬化准则,在边界面方程中引入初始各向异性张量,并采用空间滑动面破坏准则（SMP）的变换应力法,建立了能考虑饱和黏土初始各向异性的循环边界面塑性模型。分别针对等压和偏压固结的饱和黏土静、动三轴试验进行模拟,结果表明,该模型能合理反映土体的初始各向异性及其后继循环动力特性。 相似文献
8.
在临界状态弹塑性力学的框架内,建立了可以考虑循环荷载作用下各向异性对饱和软土力学特性影响的边界面塑性模型。该模型采用非关联的流动法则,引入了反映土体各向异性的内变量,利用该内变量的初始值描述初始各向异性,采用一种理论更为严谨、模型参数确定更为恰当的旋转硬化法则描述循环加载过程中各向异性的演化,利用更新映射中心的径向映射法则和与塑性偏应变路径长度有关的塑性模量插值规律,保证模型能够模拟循环加载时应力-应变响应的非线性、滞回性、应变累积性等基本特性,解释了模型参数的物理意义和确定方法,特别是给出了一种合理确定描述土体初始各向异性状态变量方法。通过文献中等压固结和偏压固结饱和黏土的循环三轴试验结果与模型预测结果的对比验证了模型的合理性。 相似文献
9.
剑桥模型只适用于正常固结软黏土,不能描述不等向固结土的应力-应变行为的各向异性特性。基于剑桥模型,在其椭圆屈服面中引入各向异性张量和一个形状参数,建立了一个各向异性屈服面,提出了一个适用于等向和不等向固结软黏土的本构模型。各向异性张量的初始值由初始固结应力状态确定,其演化过程由一个与塑性剪应变和塑性体应变都有关的硬化法则描述。形状参数的引入保证了各向异性屈服面的灵活性和适应性。通过对Boston Blue黏土、高岭土和Otaniemi黏土的三轴试验结果的模拟,验证了模型的模拟能力。 相似文献
10.
《岩土力学》2017,(3)
库岸边坡土体受到库水位涨落的周期性影响,其受力过程可描述为在前期固结压力范围内有效应力的多次循环加、卸载过程。通过室内应力路径三轴试验模拟土体孔隙水压力的循环加、卸载,并通过对统一硬化模型的扩展和加、卸载准则的修正,来预测土体的变形发展规律,研究结果表明:循环加、卸载过程中,土体的体积变形呈周期性弹性变化,剪应变呈螺旋上升趋势且增幅随循环次数逐渐减小;卸围压屈服阶段,土体变形呈现体积膨胀的剪胀特征和剪应变增幅加快的脆变趋势,且土体剪切变形在6%左右时即出现实测孔压骤减和峰值强度点;建立压缩曲线系数与加、卸载次数的关系,并修正超固结土的加、卸载准则,扩展后的统一硬化模型能够较好地预测特殊应力路径下岸坡饱和土体的变形特性。 相似文献
11.
A rotational kinematic hardening constitutive model with the capability of predicting the behavior of soil during three‐dimensional stress reversals has been developed. An existing elasto‐plastic constitutive model, the Single Hardening Model, utilizing isotropic hardening serves as the basic framework in these formulations. The framework of the kinematic hardening model was discussed in a companion paper. The previously proposed cross‐anisotropic Single Hardening Model is added to the present kinematic hardening mechanism to capture inherent anisotropy of sands in addition to the stress reversals. This model involves 13 parameters, which can be determined from simple laboratory experiments, such as isotropic compression, drained triaxial compression and triaxial extension tests. The results from a series of true triaxial tests with large three‐dimensional stress reversals performed on medium dense cross‐anisotropic Santa Monica Beach sand are employed for comparison with predictions. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
12.
A kinematic hardening mechanism has previously been proposed to capture the behavior of soil during large stress reversals in the triaxial plane. This mechanism is now extended to the principal stress space. It incorporates rotation and intersection of yield surfaces to achieve a consistent and physically rational fit with experimentally observed soil behavior during large three‐dimensional stress reversals. An existing elasto‐plastic model with isotropic hardening is used as the basic framework to which the rotational kinematic hardening mechanism has been added. The new combined model preserves the behavior of the isotropic hardening model under monotonic loading conditions, and the extension from isotropic to rotational kinematic hardening under three‐dimensional conditions is accomplished without introducing new material parameters. The framework of the model is presented here with some comparisons between theoretical and experimental directions of strain increment vectors to indicate the potential of the model. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
13.
A rotational kinematic hardening constitutive model with the capability of predicting the behavior of soil during 3-D stress-reversals has been developed. An existing elasto-plastic constitutive model, the Single Hardening Model, utilizing isotropic hardening serves as the basic framework in these formulations. To this framework is added the capability of handling cross-anisotropic behavior as well as the kinematic hardening mechanism to capture inherent anisotropy of the sand in addition to the large stress-reversals. The model involves thirteen parameters, which can be determined from simple laboratory experiments, such as isotropic compression, drained triaxial compression and triaxial extension tests. The results from a series of true triaxial tests with large stress-reversals performed on loose cross-anisotropic Santa Monica Beach sand are employed for comparison with predictions. 相似文献
14.
The results of a series of true triaxial tests with stress paths involving large reversals under 3D conditions are presented. These tests were performed on medium dense Santa Monica Beach sand to provide experimental evidence for the rotational kinematic hardening hypothesis presented in a companion paper and to provide stress–strain and volume change relations for experiments with 3D stress paths and large stress reversals to be predicted by the rotational kinematic hardening model. The experimental equipment and the testing procedures are briefly explained followed by a presentation of the experimental results and their sensitivity to unknown causes as well as effects of cross‐anisotropy on the sand behavior. The stress paths are presented in a σ3′‐plane and in an octahedral plane and the directions of experimental strain increment vectors are compared with those obtained from the rotational kinematic hardening model. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
15.
Deep clays exhibit a pronounced strain anisotropy both during mechanical loading as well as during heating and cooling at constant stress in drained isotropic conditions. During mechanical loading vertical strain is larger than the horizontal one. During heating the vertical strain is larger than the horizontal one within the elastic range; the opposite is observed in the elasto-plastic range. The above described response can be interpreted adopting a consistent rotational, kinematic hardening thermo-elasto-plastic constitutive law. 相似文献
16.
In this paper, a simple bounding surface plasticity model is used to reproduce the yielding and stress–strain behavior of the structured soft clay found at Shanghai of China. A series of undrained triaxial tests and drained stress probe tests under isotropic and anisotropic consolidation modes were performed on undisturbed samples of Shanghai soft clay to study the yielding characteristics. The degradation of the clay structure is modeled with an internal variable that allows the size of the bounding surface to decay with accumulated plastic strain. An anisotropic tensor and rotational hardening law are introduced to reflect the initial anisotropy and the evolution of anisotropy. Combined with the isotropic hardening rule, the rotational hardening rule and the degradation law are incorporated into the bounding surface formulation with an associated flow rule. Validity of the model is verified by the undrained isotropic and anisotropic triaxial test and drained stress probe test results for Shanghai soft clay. The effects of stress anisotropy and loss of structure are well captured by the model. 相似文献
17.
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
18.
19.
Compaction bands are localized failure patterns that appear in highly porous rock material under the effect of relatively high confining pressure. Being affected mainly by volumetric compression, these bands appear to be almost perpendicular to the most compressive principal stress of a stress state at the so-called “cap” of the yield surface (YS). In this study, we focus on the mechanism that leads to the onset of compaction bands by using a viscoplasticity model able to describe the post-localization response of these materials. The proposed constitutive framework is based on the overstress theory of Perzyna (1966) and the anisotropic clay plasticity model of Dafalias (1986), which provides not only the necessary “cap” of the YS, but introduces a rotational hardening (RH) mechanism, thus, accounting for the effect of fabric anisotropy. Following the analysis of Veveakis and Regenauer-Lieb (2015), we identify the compaction bands as “static” cnoidal wave formations in the medium that occur at a post-yield regime, and we study the effect of rotational and isotropic hardening on their onset. Moreover, we determine a theoretical range of confining pressures in triaxial compression tests for the compaction bands to develop. Under the assumption of coaxiality between stress and anisotropy tensors, the results show that the isotropic hardening promotes compaction localization, whereas the RH has a slightly negative effect on the onset of compaction localization. 相似文献
20.
由于加荷方式不同,土体在复杂应力状态下在各主应力方向上应力-应变关系表现出显著应力各向异性,在常规三轴试验基础上,采用经典弹塑性理论各向同性土体模型对此不能合理描述。通过真三轴试验,总结应力各向异性柔度矩阵规律,结合试验规律进行相应理论研究,用非线性各向异性弹性矩阵代替弹塑性模型的弹性矩阵,用具有各向异性屈服准则的弹塑性模型描述塑性部分,建立非线性各向异性弹性-塑性模型,可以改善柔度矩阵矩阵形态,反映复杂应力状态下土体应力各向异性特征。 相似文献