共查询到20条相似文献，搜索用时 125 毫秒
1.
There exists a critical cyclic stress ratio when sand or clay is subjected to cyclic loading. It is an index distinguishing stable state or failure state. The soil static and dynamic universal triaxial and torsional shear apparatus developed by Dalian University of Technology in China was employed to perform different types of tests on saturated soft marine clay in the Yangtze estuary. Undisturbed samples were subjected to undrained cyclic vertical and torsional coupling shear and cyclic torsional shear after three-directional anisotropic consolidation with different initial consolidation parameters. The effects of initial orientation angle of major principal stress, initial ratio of deviatoric stress, initial coefficient of intermediate principal stress and stress mode of cyclic shear on the critical cyclic stress ratio were investigated. It is found that the critical cyclic stress ratio decreases significantly with increasing initial orientation angle of major principal stress and initial ratio of deviatoric stress. Compared with the effects of the initial orientation angle of major principal stress and initial ratio of deviatoric stress, the effect of initial coefficient of intermediate principal stress is less evident. Under the same consolidation condition, the critical cyclic stress ratio from the cyclic coupling shear test is lower than that from the cyclic torsional shear test, indicating that the stress mode of cyclic shear has an obvious effect on the critical cyclic stress ratio. The main reason is that the continuous rotation in principal stress directions during cyclic coupling shear damages the original structure of soil more than the cyclic torsional shear does. 相似文献
2.
颗粒材料力学性质的离散元数值模拟 总被引：2，自引：0，他引：2
基于颗粒离散元法对二维颗粒体进行了双轴压缩数值模拟.将离散系统中的变形与连续体中相应的变形联系起来,应用于颗粒离散元方法中平均应力的计算,比较了不同颗粒形状、颗粒间摩擦系数对颗粒体的微观-宏观力学性能的影响,并分别考虑了不同摩擦系数下,颗粒颗粒间接触力的法向分量和切向分量对剪切应力的贡献.本文的计算结果表明颗粒的形状和表面性质对颗粒体的力学性能有显著的影响. 相似文献
3.
The mechanical behavior of sand is very complex, and depends on factors including confining pressure, density, and drainage condition. A soil mass can be contractive or dilative when subjected to shear loading, and eventually reaches an ultimate state, referred to as the critical state in soil mechanics. Conventional approach to explore the mechanical behavior of sand mainly relies on the experimental tests in laboratory. This paper gives an alternative view to this subject using discrete element method （DEM）, which has attracted much attention in recent years. The implementation of the DEM is carried out by a series of numerical tests on granular assemblies with varying initial densities and confining pressures, under different test configurations. The results demonstrate that such numerical simulations can produce correct responses of the sand behavior in general, including the critical state response, as compared to experimental observations. In addition, the DEM can further provide details of the microstructure evolutions during shearing processes, and the resulting induced anisotropy can be fully captured and quantified in the particle scale. 相似文献
4.
利用灰色关联分析方法研究粉煤灰的粒度分布对水泥性能的影响．结果表明：O～5μm、5～10μm粉煤灰颗粒分别是水泥3d、28d抗压强度的最强影响因子;水泥3d、28d强度随小于33μm的粉煤灰颗粒含量增大而提高,随大于33pm的粉煤灰颗粒含量增大而降低;可以通过优化粉煤灰的粒度分布来改善水泥性能． 相似文献
5.
Xue-cheng Wu Qin-hui Wang Chen Tian Zhong-yang Luo Meng-xiang Fang Ke-fa Cen 《浙江大学学报(A卷英文版)》2008,9(7):922-931
Particle rotation plays an important role in gas-solid flows. This paper presents an experimental investigation on the spatial distribution of average rotation speed for glass beads in the upper dilute zone of a cold circulating fluidized bed （CFB） riser. It is shown that in the horizontal direction, the average rotation speed in the near-wall area is larger than that in the center area, while in the vertical direction, it decreases as the height increases. The reason resulting in this distribution is analyzed by considering several factors including particle size, particle shape, particle number density, particle collision behavior, and the surrounding flow field, etc. The effects of CFB operation conditions on the spatial distribution of average rotation speed are also studied. The results show that the increasing superficial gas velocity increases the average rotation speed of particles in the near wall area but takes nearly no effect on that in the center area. The external solids mass flux, however, takes the opposite effect. It is found that the average rotation speeds of particles in both areas are increased as the total amount of bed material increases. 相似文献
6.
Considering the effects of particle crushing and intermediate principal stress on material yielding strength, the spatial mobilization plane(SMP) yielding criterion and state parameter model including a general critical state line are selected in the analysis of cylindrical cavity expansion.Meanwhile, combining Rowe's flow rule and Bolton's simplification to stress-dilatancy relationship to reflect soil shear dilatancy and softening behavior, this paper analyzes the problem of cylindrical cavity expansion i... 相似文献
7.
Undrained anisotropy and non-coaxial behavior of clayey soil under principal stress rotation 总被引：2，自引：0，他引：2
In this study, a series of undrained tests were conducted on both intact and reconstituted clay using an automatic hollow cylinder apparatus. Monotonic shearing tests with fixed principal stress directions were carried out, pure and cyclic prin- cipal stress rotation tests were also performed. The non-coaxiality, defined as the non-coincidence of the principal plastic strain increment direction and the corresponding principal stress direction, of clayey soil was studied experimentally. The effects of the intermediate principal stress, shear stress level, and inherent anisotropy were highlighted. Clear non-coaxiality was observed during pure principal stress rotation, in both intact and reconstituted clay. The influence of the intermediate principal stress pa- rameter, shear stress level, and inherent anisotropy on the non-coaxial behavior of the clayey soil was found to be insignificant when compared with the sand. The non-coaxial behavior of the clayey soil depended more on the stress paths. Under undrained conditions, the contribution of elastic strain to the direction of the total principal strain increment cannot be ignored. 相似文献
8.
Lattice Boltzmann method was used to numerically investigate the motion and orientation distribution of cylindrical and cubic particles in pipe flow with high concentration and high particle to pipe size ratio. The transient impulse model of 3D collisions between particles and between particle and wall is proposed. The numerical results are qualitatively in agreement with and quantitatively comparable to the experiment data. The results show that the increases of both the cylindrical particle to pipe size ratio and the particle aspect ratio decrease the rotation about all axes. All rotations of cubic particles decrease with increasing the particle concentration. The cubic particles, rotating more drastically in the flow with large Reynolds number, rotate faster than the cylindrical particles with the same size. The cylindrical particles align with the flow direction more obviously with decreasing Reynolds numbers. However, the orientations of cubic particles are spread all over the range with no significant difference in magnitude, and the Reynolds numbers have no obvious effect on the orientations of cubic particles. 相似文献
9.
Richard J. Jardine 《浙江大学学报(A卷英文版)》2011,12(1):1-14
An integrated approach to geomaterial characterization is advocated that combines geology, in-situ testing, fabric studies, routine index experiments and advanced laboratory testing. It is shown that advanced laboratory testing can explore features such as kinematic yielding and anisotropy in stiffness or shear strength that would otherwise be impossible to quantify. A detailed study performed in London clay at the new Heathrow Terminal 5 site is used to illustrate the arguments made. It is shown that the London clay has strong anisotropy in stiffness, is highly non-linear over the strain range of engineering interest, has markedly anisotropic shear strength characteristics and exhibits a pronounced degree of brittleness. These features can impact significantly on the practical design and analysis of civil engineering works including shallow and deep foundations, tunnels and excavations, and the stability of slopes. 相似文献
10.
Knitted fabric is very different from woven fabric due to its more complicated knitting structures. The buckling of knitted fabric sheets subjected to simple shear in the wale direction is investigated analytically in consideration of the large deformation of fabric sheet in critical configuration. The theory on instability of finite deformation is applied to the analysis. All the stress boundary conditions of knitted fabric sheet are satisfied. An equation to determine the buckling direction angle is derived. It is shown that there are two possible buckling modes, flexural mode and barreling mode. The buckling condition equations for the flexural mode and barreling mode are also obtained respectively. Numerical illustrations reveal that only the flexural mode can actually occur and the barreling mode cannot, which agrees with the experimental observations. For a permitted buckling mode on margin boundaries, the critical value of shear amount and the buckling direction angle can be determined. 相似文献
11.
INTRODUCTION The orientation of fibers plays an important rolein determining the rheological properties of fibersuspensions and the behaviors of composite materialsproduced by various forming operations. A fiber canbe treated as a rigid cylinder with length l and di-ameter d. It is convenient to define three regimes ofconcentration: dilute, semi-concentrated and concen-trated. Dilute regime is defined when c<(d/l)2, wherec is the volume fraction of fibers. In this regime fibersare … 相似文献
12.
受沿经向简单剪切的织物屈曲分析 总被引：5，自引：0，他引：5
分析了织物受沿经向简单剪切时的屈曲 ,得到确定织物屈曲方向 (屈曲波的方向 )的方程 ,该方程表明织物屈曲方向与临界剪切值有关 .还证明了织物受沿经向简单剪切时会发生离面屈曲 ,并且只存在一种屈曲模态——弯曲屈曲模态 ,得到了该屈曲模态的屈曲条件及屈曲条件曲线 . 相似文献
13.
In-situ vane shear test is frequently performed to determine shear strength for slope stability analysis in Tianjin New Harbor. However,the soil shear strength varies with the shear plane orientation. A possible means to reduce the effect of directional dependency of shear strength is to convert the in-situ vane shear strength into undrained shear strength parameters. A method of converting in-situ vane shear strength into undrained shear strength parameters is presented. The shear strength parameters determined for all of the in-situ vane shear strengths are subjected to statistical regression analysis to take into consideration the possible effect of non-homogeneity in the soft clay deposit. Using the regressed shear strength parameters, slope stability analyses are performed for five existing soil slopes. The results of stability analyses indicate that the safety factors obtained from the converted parameters reflect the state of the slopes analyzed much better than those obtained from in-situ vane shear strength and laboratory consolidated-undrained and unconsolidated-undrained strength parameters. It is concluded that the presented methsod of determining undrained shear strength parameters for in-situ vane shear strength is effective. 相似文献
14.
Discrete element modelling approach to assessment of granular properties in concrete 总被引：1，自引：0，他引：1
This paper presents the technological relevance of a concurrent algorithm-based discrete element modelling (DEM) system, HADES.
This new system is the successor of SPACE that is limited to spherical grains only. It can realistically simulate the packing
of arbitrary-shaped particles up to the fully compacted state. Generation of families of such particles, i.e., generally representing
aggregate of fluvial origin and crushed rock, respectively, and the forming way of particulate structure are described. Similarly
shaped particles are proposed for simulation of cement paste because of conformity with experimental results obtained by the
X-ray tomography method. Technologically relevant territories inside and outside concrete technology are presently explored
in this efficient, reliable, and economic way. Some results obtained by this DEM approach are presented. 相似文献
15.
This paper is focused on the structural behavior of the single shear bolted connections with thin-walled ferritic stainless steel.The purpose of this study is to investigate the ultimate behaviors,such as ultimate strength and fracture mode of the single shear bolted connections of thin-walled ferritic stainless steel(low cost steel) rather than austenitic stainless steel(high cost steel).Bolt arrangement and end distance parallel to the direction of applied load are considered as main variables of the test specimens for bolted connections.Specimens have a constant dimension of edge distance perpendicular to the loading direction,bolt diameter,pitch,and gauge.A monotonic tensile test for specimens has been carried out and some bolted connections with long end distance showed curling(out of plane deformation) occurrence which led to strength reduction.The ultimate behaviors such as fracture mode,ultimate strength are compared with those predicted by current design codes.Further,conditions of curling occurrence and the strength reduction due to curling are investigated and modified strength equations are suggested considering the curling effect. 相似文献
16.
采用MP-PIC (multi-phase particle in cell)方法模拟了三维多段气化炉（上部快速床,下部鼓泡床）多粒径煤粉的循环流化过程,研究了分布板不同进气方向对气化炉内颗粒分布的影响。结果表明:分布板开孔与水平方向夹角越大,物料进入快速床并形成流化状态越快,但对成形后的流化形态影响较小;分布板进气方向对分布板处的轴向颗粒浓度分布影响较大,对快速床内轴向颗粒浓度分布影响较小;随着分布板进气方向与水平夹角的减小,鼓泡床下部颗粒浓度增大,固相颗粒通量增大;分布板进气方向对旋风分离效率影响较小。因此,工程上可根据需要适当减小分布板进气方向与水平方向的夹角来增加分布板上部颗粒浓度分布。 相似文献
17.
李占福胡云霄童昕 《福建工程学院学报》2019,(6):555-559
为研究振动参数对双层等厚筛筛分效率的影响,采用离散单元法(DEM)模拟5种不同粒径的颗粒在不同振幅、筛面倾角、振动频率下的筛分过程。运用多项式逼近方法对仿真结果进行曲线拟合,得到拟合度最好时的筛分效率与振动参数关系图。最后,选出最好筛分效率下的振动参数进行正交试验。结果表明:双层等厚筛筛分效率最优的参数组合为振动幅度7mm、振动频率14Hz、筛面倾角17°。 相似文献
18.
Zhou Cheng-ti 《大连大学学报》1991,(1)
本文论述了复合材料的强度和稳定性理论中的三个近代问题:复合材料迭层板的强度准则,多层复合材料圆柱壳的非线性稳定性理论,以及复合材料板的动力稳定性理论。关于迭层板的强度准则,论述了目前以张量多项式形式所表述的唯象性破坏准则,着重讨论和比较了各种近代理论在确定耦合系数方面的特点和差别。提出了近代理论中所存在的困难和发展趋势。在多层复合材料圆柱壳的非线性稳定性理论分析中,主要的问题在于如何研究和考虑那些非线性因素,诸如由材料的剪切模量所引起的物理非线性,横向剪切变形的影响,壳体结构的初始缺陷和几何非线性,以及前屈曲变形和边界支承条件的影响等。本文指出了考虑这些因素的方法以及它们的影响程度。复合材料板的动力屈曲性能研究是一个重要的近代研究方向。本文提出了关于复合材料本身的阻尼系数,纵向和转动惯性力影响,横向剪切效应,迭层板的初始几何缺陷,以及增强纤维的铺设方向等因素对于动力屈曲性能的影响。同时提出了计算这些影响的方法,指出这些因素在复合材料板的动力稳定性分析中有着重要作用。 相似文献
19.
通过计算机仿真模拟,研究了各向异性粒种扩散沉积集团的维数与多重分形谱.研究结果表明,各向异性粒种扩散沉积集团具有随机分叉、开放的结构,明显的多重分形性质.集团的维数与质量分布非均匀性随着各向异性的增加而增加. 相似文献
20.
The effect of non-reactive powder particle properties on the detergent dry agglomeration process in a high shear mixer was investigated. Three types of micron-scale silica were chosen as the non-reactive fine powders and a semi-solid alkyl ethyl ethoxy sulfate(AES) paste with ultra-high viscosity was chosen as the binder. The granules were characterized using massbased granule size distribution, scanning electron microcopy, and bulk density tests. The results revealed that powder particle size plays a leading role in agglomeration behavior. A decrease in the median particle size results in enhanced dispersion of silica particles in the AES paste binder droplets, which leads to the formation of uniform granules that are slightly affected by compacting forces. Agglomerate quality, using silica with high oil absorption as well as optimum particle size, was satisfactory, and the product exhibited a smaller median particle size, narrower size distribution, and superior anti-caking capacity under the same liquid-to-solid ratio(L/S). 相似文献