【作者】 杨荣伟；

【导师】 程晓辉；

【作者基本信息】 清华大学 ， 土木工程， 2009， 硕士

【摘要】 众多学者认为,进一步促进岩土力学发展和变革的关键在于,从颗粒尺度来重新认识这门学科。众多的研究均表明,颗粒材料中平均强度力链和几何结构对材料宏观的力学和变形性质均起着重要的作用。本文借助光弹实验手段和数字图像处理方法,通过研制的直剪仪,初步探讨了颗粒材料在直剪作用下,颗粒几何结构和平均强度力链分布之间的关系。本文设计研制了直剪仪,并进行了光弹材料的制备和退火等前期准备工作,得到了本实验光弹颗粒的退火曲线。通过引入的平均彩色梯度的算法,实验拟合得到了,颗粒的平均接触力F和平均彩色梯度<G2>的关系曲线,该关系曲线是颗粒材料中平均强度力链识别的重要力学基础。本文对光弹实验拍摄得到的数码图像进行处理,识别得到了颗粒材料的几何位置信息,在此基础上,结合彩色梯度算法获取得到的光弹颗粒材料力学信息,最终识别得到颗粒材料中的接触向量角度分布图和平均强度力链分布图。基于数字图像处理获得的结果,建立平均配位数和剪切变形的关系,解释了直剪过程中的剪胀和剪缩现象;对直剪作用下的接触向量角度分布进行统计分析,并定义了“极化角区间”等概念,结果表明:初始阶段,颗粒材料的几何结构基本上呈现各向异性。在直剪过程中,随着剪应力的增大,其各向异性越来越明显,当达到峰值强度时,其各向异性最为明显。颗粒材料初始状态固有的各向异性对加载过程中几何结构的各向异性有较大的影响。同时,颗粒材料直剪过程中的接触向量角度分布,受到颗粒材料的初始状态固有的各向异性影响。本文还对接触向量初始极化角和平均强度力链分布进行分析,结果表明:当颗粒材料施加剪应力后,剪切力的逐渐增大诱发了几何结构的各向异性,出现了极化角区间,而几何结构的各向异性则导致了平均强度力链在这些极化角度区间内大量分布,从而引起平均强度力链分布的局部化。本文仅对平均强度力链和几何结构的关系进行初步的探讨,更加深入的研究仍在继续。更多还原

【Abstract】 It is agreed among many researchers that the approach of granular geo-mechanics is the key to the better understanding of fundamentals of geo-materials. The force chain and fabric of photo-elastic granular assemblies as crucial to the phenomenological properties of geo-materials were studied in a direct shear box in the present thesis using photo-elastic and digital image analysis techniques.First, a direct shear box filled with the photo-elastic bi-disperse discs was made transparent to the polarized light. The residual stress of discs due to manufacturing was removed with the specified anneal treatment preceding the tests. The so-called average color gradient <G2> of each disc was calculated to analyze the force information captured in the photo-elastic images during the direct shearing followed with the obtained correlation of <G2> with the average contact force of each disc.In parallel, the digital image analysis was also performed to extract the kinetic information of each disc during the direct shearing. The kinetic and force information extracted from the sequence of photos enabled the quantitative description of contact network and force chain developed in the granular assembly due to slow direct shearing.The well known phenomenon of dilatancy and compression were eventually impetrated as the variance of the average coordination number of whole granular assembly. The statistics of the inclinations of branching vectors revealed the strong inherent anisotropy which even enhanced in the following shearing. The anisotropy becomes more and more obvious as the increasing of the shear strength. Having analyzed both the characteristics of contact vector and force chain induced suggested that the anisotropy of contact vector induced by the increasing shear force results in the localization of the force chains.更多还原