基于FDEM的岩石颗粒破碎后碎片形状的统计分析

Statistical analysis of fragment shape of rock grain after crushing based on FDEM

针对碎片尺寸和形状会影响岩石强度和变形的问题,采用三维扫描技术获得真实岩石颗粒的表面点云数据,然后通过数字图像处理技术重构数字颗粒,利用连续-离散耦合方法(FDEM)模拟单个颗粒在平板压缩下的断裂破碎.识别颗粒破碎后所产生的碎片,并进行碎片形状的表征和量化,分析碎片形状与颗粒初始形状、碎片尺寸的关系.为了准确描述裂纹尖端的应力梯度和损伤演化,进行颗粒有限元网格密度的敏感性分析,结果表明,断裂过程区至少需要5、6个界面单元以减弱网格尺寸的影响.本研究关注颗粒破碎后所产生碎片的整体形态,忽略断裂引起的碎片表面局部起伏和粗糙变化.尽管所研究颗粒的初始形状存在较大差异,仍发现颗粒破碎后所产生碎片的形状指标分布具有一些共性特征.碎片的圆度、扁平率、Domokos因子和凸度对颗粒初始形状的敏感性逐渐增强,并且除了圆度外,其他形状指标分布与碎片尺寸之间并未发现显著的相关性.不同粒径组碎片的圆度分布表明,较大的碎片棱角更明显.

3D scanning technology was employed to obtain the surface point cloud data of real rock grains and these grains were reconstructed by using digital image processing technology,aiming at the influence of fragment size and shape on the strength and the deformation of crushing rock grain.The combined finite-discrete element method(FDEM)was used to simulate the fracture and fragmentation of single grain under compression of flat plates.The fragment shape was characterized and quantified,and then the relationships between fragment shape and grain shape and size were analyzed by identifying each fragment produced by single grain crushing.The sensitivity analysis of grain finite element mesh density was conducted to accurately describe the stress gradient and damage evolution along the crack tip.Results show that at least 5、6 cohesive interface elements are required in the fracture process zone to reduce the effects of the element size.The overall shape of fragments generated after grain crushing was focused on,while the local undulation and roughness changes of fragment surface caused by fracture were ignored.Although the grains shapes are different,there are some generic features of shape distribution of fragments after crushing.The sensitivity of sphericity,aspect ratio,Domokos shape descriptor,and convexity of fragments to grain shape gradually increases,and no significant correlation was found between the distribution of other shape descriptors and fragment size except sphericity.The sphericity distribution of fragments with different sizes shows that the larger size fragments tend to be more angular.