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1.
制备了颗粒规则四方排列和六方排列的橡胶粘接颗粒材料试样,实验测试了所制备试样在单向拉伸载荷下的应力松弛曲线和不同应变率时的应力应变曲线.基于所测试的应力松弛曲线,采用曲线拟合方法得到了所测试材料的宏观Burger’s粘弹性本构模型参数.采用离散元模型中单元间连结模型代表颗粒间橡胶粘接剂的作用,并基于试样的宏观Burger’s模型参数与离散元模型中细观Burger’s连结模型参数间的关系,建立了橡胶粘接颗粒材料的无厚度胶结离散元分析模型.最后采用所建立的离散元模型计算了所测试试样的松弛和拉伸力学性能.离散元预测结果与实验结果的对比表明,采用无厚度胶结离散元模型能较好的计算颗粒规则排列的橡胶粘接颗粒材料松弛和拉伸力学性能,但基于应力松弛实验拟合而来参数不能准确反应橡胶粘接剂在高应变率条件下其力学性能的应变率相关性. 相似文献
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《应用力学学报》2017,(4)
利用有限元分析软件,建立基于随机分布的EPS混凝土细观力学模型。对EPS混凝土的受压损伤破坏过程进行数值模拟,分析EPS颗粒面积占有率、排列方式、形状对EPS混凝土力学性能的影响。结果表明:当EPS颗粒面积占有率较小时,EPS混凝土的破坏表现出明显的脆性破坏,随面积占有率的增加,EPS混凝土破坏逐渐由脆性破坏转化为延性破坏;EPS颗粒含量较低时,规则分布与随机分布对混凝土应力-应变关系影响较小;随着EPS颗粒面积占有率的增加,规则分布较随机分布具有更大残余应力;相同面积占有率下,规则分布较随机分布脆性指数更小,规则分布表现出更好的延性;当EPS颗粒形状为三角形时,EPS混凝土应力最大延性最好,正方形时应力最小延性最差,形状为圆形和五角形时,EPS混凝土应力-应变关系与脆性指数相接近。 相似文献
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应用大规模分子动力学方法,采用粗粒化聚乙烯醇模型,模拟了晶区与非晶区随机交杂的半晶态聚合物模型系统,研究了半晶态聚合物在单轴拉伸变形过程中的应力-应变行为和微观结构演变.应力-应变曲线表现出4个典型变形阶段:弹性变形、屈服、应变软化和应变强化.在拉伸变形过程中,主要存在晶区折叠链之间的滑移、晶区破坏、非晶区的解缠结,以及分子链沿拉伸方向重新取向等4种主要的微结构演变形式.在屈服点附近,晶区分子链之间排列紧密程度减小而发生滑移,之后晶区变化需要的应力变小,从而形成应变软化现象.随着应变的增大,经各分子链段协同作用使非晶区分子链的解缠结和重新取向行为扩展到相对宏观尺度,导致拉伸应力增大而形成应变强化现象. 相似文献
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动态压缩荷载作用下,脆性岩石内部动态细观裂纹扩展特性,对岩石宏观动态力学特性有着重要的影响。然而,对岩石内部动态细观裂纹扩展与宏观动态力学特性的关系研究较少。基于准静态裂纹扩展作用下的应力-应变本构模型、准静态与动态裂纹扩展断裂韧度关系、裂纹速率与应变率关系模型及应变率与动态断裂韧度关系,提出了一种基于细观力学的动态应力-应变本构模型。其中裂纹速率与应变率关系,是根据裂纹长度与应变关系的时间导数推出;应变率与动态断裂韧度关系,是根据推出的裂纹速率及应变率关系,与裂纹速率及断裂韧度关系相结合而得到。研究了应变率对应力-应变本构关系及动态压缩强度影响。并通过试验结果验证了模型的合理性。讨论了岩石初始损伤、围压、模型中参数m、ε0和R对应力-应变关系、动态压缩强度和动态弹性模量的影响。研究结果可为动态压缩荷载作用下深部地下工程脆性围岩稳定性分析提供了一定的理论支持。 相似文献
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单轴拉伸过程中双相不锈钢局部微观变形行为的细观力学有限元分析 总被引:1,自引:0,他引:1
针对双相不锈钢中奥氏体相和铁素体相分别展开了纳米压痕实验,并通过有限元反演得到两相各自的拉伸应力-应变关系,利用Voronoi Tessellation法生成代表性的微结构体积单元,对双相不锈钢的单轴拉伸行为进行了有限元仿真和模拟,研究了双相不锈钢在拉伸过程中的局部应力、应变分布和演化规律.结果表明,利用Voronoi Tessellation法建立单元模型,结合本文通过纳米压痕实验获取的两相力学性能参数,可以很好地模拟双相不锈钢的整体单拉行为,奥氏体比铁素体软,拉伸载荷下双相不锈钢的应变集中在奥氏体中,应力集中在铁素体中;局部应力应变的分布特征与两相分布特征和晶粒形状有关,最大应变值主要集中在奥氏体晶粒狭长且尖锐的区域,而最大应力则主要发生在铁素体晶粒狭长和尖锐的区域;对于奥氏体和铁素体晶粒占比相当的双相不锈钢,其虽然可以具有较为综合的宏观力学性能,但是其微观应力集中的区域和应力最大值相对较大.研究成果为进一步揭示双相不锈钢局部失效机理奠定了基础. 相似文献
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采用?75 mm大口径SHPB系统进行了钢纤维体积率为0%、0.75%、1.5%三种混凝土材料动态性能实验,得出了不同钢纤维含量、不同应变率下的材料应力-应变关系曲线,实验结果表明:随着纤维含量及应变率的增加,钢纤维混凝土材料的峰值应变、峰值应力都随之提高,并在峰值应力之后出现应力的应变软化现象。以此实验结果为基础,提出了一种依赖于应变和应变率相关函数的新型非线性黏塑性动态本构关系,并通过对实验曲线的三步逐次最小二乘优选模拟,得到了相应的材料参数。结果表明,该本构关系对实验数据的模拟效果较好。 相似文献
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J. Jäger 《Archive of Applied Mechanics (Ingenieur Archiv)》1999,69(3):181-203
Summary Mechanical behavior of dense packing spheres with small irregularities is investigated in this paper. A generalization of
the hertzian contact model for surfaces of the form x
k
yields a normal contact force F
n
, which is proportional to ζ1+1/
k
, with the normal displacement ζ. For oblique forces, the frictional force can be calculated, [10]. Different load cases are
explained in detail. It is shown that the stress-strain curve during initial loading of the packing is identical with the
force-displacement relation at the contact point, using an appropriate constant. The results for uniaxial loading, unloading
and reloading are illustrated. As experimentally observed, the axial pressure in unloading is smaller than during loading,
while the lateral pressure increases. The stress-strain relation is compared with well-known empirical relations of rock and
soil mechanics, and the wave velocity for spherical irregularities agrees with earlier geomechanical theories for random packing
of smooth spheres.
Received 19 July 1998; accepted for publication 19 October 1998 相似文献
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This paper presents the integrated results of a series of new methods for preparing mesoporous silica spheres as high-performance liquid chromatography (HPLC) packing materials. The separation performance of the mesoporous spheres materials has also been determined. Micrometer- sized silica spheres with uniform spherical morphologies and ordered mesostructures were first successfully synthesized by the method employing a water-soluble polymer-assisted assembly. Then the templates for getting ordered mesoporous materials with high-density silanol groups were removed by using hydrothermal oxidation. Finally the silica spheres were functionalized with C8 alkyl groups by surface modification under hydrothermal conditions. The resultant functionalized silica spheres were demonstrated to be excellent oacking materials for HPLC. 相似文献
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This paper presents the integrated results of a series of new methods for preparing mesoporous silica spheres as high-performance liquid chromatography (HPLC) packing materials. The separation performance of the mesoporous spheres materials has also been determined. Micrometersized silica spheres with uniform spherical morphologies and ordered mesostructures were first successfully synthesized by the method employing a water-soluble polymer-assisted assembly. Then the templates for getting ordered mesoporous materials with high-density silanol groups were removed by using hydrothermal oxidation. Finally the silica spheres were functionalized with C8 alkyl groups by surface modification under hydrothermal conditions. The resultant functionalized silica spheres were demonstrated to be excellent packing materials for HPLC. 相似文献
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基于球形颗粒几何排列的离散元试样高效生成方法 总被引:1,自引:0,他引:1
在球体离散元数值模拟中,颗粒的初始排列状态是影响计算效率和计算结果的重要环节。本文采用前进面几何构造算法,提出了一种基于网格搜索的球形颗粒随机排列高效算法。通过求解空间三边方程,满足了粒径设置的任意大小的颗粒依次置入前进面的外侧,并与构成前进面的三个颗粒相互接触。为获得高体积分数的颗粒簇,该算法允许颗粒改变其粒径大小。采用颗粒网格化方法可以简化前进面的搜索,并由此提高排列效率。通过计算平均配位数、体积分数和二阶结构张量的特征值,对不同粒径比下得到的立方体试样进行了分析,得到试样配位数及体积分数均随着粒径比的增大而增大,且得到的试样为各向同性。此外,空间网格的大小和初始颗粒的生成点对随机排列的效率均会产生显著的影响。最后,对非规则铁路道砟进行了精细构造及压碎模拟,发现DEM模拟得到的应力-应变曲线与试验结果基本吻合,验证了该算法得到的颗粒试样在模拟道砟裂纹起裂、扩展等过程的有效性。 相似文献
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Low Reynolds number flow-induced alterations of permeability of random packing of mono-sized spheres is studied. The number of spheres is several thousands and the porosities ranges between 0.4 and 0.6. The change of permeability is obtained for elastic deformations of the positions of the spheres using either of two methods. Each sphere is elastically attached to single points or the spheres that are connected via an elastic porous network. The system of spheres is divided into smaller volumes with Voronoi diagrams and the flow is derived by usage of a dual stream function. The local saturated flow fields are approximated as for close packed spheres and the overall flow pattern is obtained by minimising the dissipation rate of energy. The results show that the permeability for large random systems increases as a function of velocity and thus the deformation. The alteration is, however, much less than for two-dimensional cases like parallel cylinders. The relative increase in permeability becomes larger as the porosity increases from 0.4 to 0.6. 相似文献
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A method for calculating the loose packing structure of polydisperse spherical particles with a predetermined size distribution function is proposed. The coordinates of the particle centers in the loose layer are determined as the result of random fall of single spheres on a substrate under the action of gravity, assuming the inelastic collision of the spheres and considering the force of their adhesive interaction, and also assuming that the motion of one sphere on the surface of the other is pure slip. Numerical simulation is used to obtain the pattern of arrangement of polydisperse spherical particles in the loose powder layer, whose porosity depends on the particle size distribution function. The results are compared with experimental data. 相似文献
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Nicos S. Martys William L. George Byong-Wa Chun Didier Lootens 《Rheologica Acta》2010,49(10):1059-1069
A smoothed particle hydrodynamics approach is utilized to model a non-Newtonian fluid with a spatially varying viscosity. In the limit of constant viscosity, this approach recovers an earlier model for Newtonian fluids of Español and Revenga (Phys Rev E 67:026705, 2003). Results are compared with numerical solutions of the general Navier–Strokes equation using the “regularized” Bingham model of Papanastasiou (J Rheol 31:385–404, 1987) that has a shear-rate-dependent viscosity. As an application of this model, the effect of having a non-Newtonian fluid matrix, with a shear-rate-dependent viscosity in a moderately dense suspension, is examined. Simulation results are then compared with experiments on mono-size silica spheres in a shear-thinning fluid and for sand in a calcium carbonate paste. Excellent agreement is found between simulation and experiment. These results indicate that measurements of the shear viscosity of simple shear-rate-dependent non-Newtonian fluids may be used in simulation to predict the viscosity of concentrated suspensions having the same matrix fluid. 相似文献
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In this paper, a discrete element simulation scheme for pebble beds in fusion blankets is presented. Each individual pebble is considered as one element obeying equilibrium conditions under contact forces. We study not only the rearrangement of particles but also the overall behaviour of an assembly under the action of macroscopic compressive stresses. Using random close packing as initial configurations, the discrete element simulation of the uniaxial compression test has been quantitatively compared to experiments. This method yields the distribution of the inter-particle contact forces. Moreover, the micro-macro relations have been investigated to relate the microscopic information, such as the maximum contact force and the coordination number inside the assembly, to the macroscopic stress variables. 相似文献
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本文依照四川大学某理论力学教学班实际教学改革的经验,通过具体举例说明计算机技术在理论力学教学中尚未开发的巨大潜力,减小数学运算使学生重点关注理论力学基本原理,批量求解使学生提前接触实际应用案例,普适性求解使学生深化对处理多变量问题的认识。同时本文还探讨了理论力学教学改革的方向和目的,即把教学重点放在普适的教学方法上,借助计算机求解多刚体、多变量问题,以期有助于理论力学教材更好地适应时代发展。 相似文献
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金属空心球结构是一种新型的超轻多孔金属材料。本文对直接堆积和胶合堆积的两球、三球金属空心球列组元进行了单轴准静态压缩实验,分析压缩过程的变形情况,得出其应力/屈曲极限、有效弹性模量、有效应力-应变曲线,并讨论了发生屈服/屈曲的原因。基于实验现象作者提出了三种边界条件,通过分析的方法导出列组元的有效弹性模量公式,其预测值与实验结果较为符合。通过对两种不同堆积模式面组元的压缩实验,研究了金属空心球结构的力学性能和垮塌规律,分析其比刚度和比体积能量吸收值,讨论了两种不同堆积模式的面组元的特点和优越性,发现HC堆积模式具有更好的力学性能。同时对比三球列组元的有效弹性模量发现,SC堆积模式的有效弹性模量只与堆积层数有关。 相似文献