砂岩方梁断裂过程区范围的实验确定方法

裂纹前端的断裂过程区是引起岩石非线性断裂及尺寸效应的主要原因。利用数字图像相关技术对砂岩开展了三点弯曲梁实验,获得观测区域高精度的全场位移和应变数据,根据断裂韧带区域水平位移和水平应变的分布特征,结合裂尖岩石颗粒变化的微观分析,提出采用裂纹尖端水平位移波动性和水平应变突变性所得到的波动系数和水平应变突变值,确定断裂过程区形状和临界尺寸的方法。结果表明:砂岩断裂过程区的形状为不规则的狭长带状区域,断裂过程区的临界长度为11~13mm,临界宽度为1.58~2.36mm。断裂过程区区域内形变在趋向裂尖时呈指数增加,但其单位区域内的形变增量呈波动状态。该方法能够更加准确判断岩石断裂过程区的范围,有助于分析岩石的非线性断裂特性。

Experimental determination method of fracture process zone of sandstone using square beam sample

The fracture process zone around crack front is the main cause of non-linear fracture and size effect of rock.In this paper,three-point bending test was carried out for beams made of sandstones,and high-precision full-field displacement and strain data are obtained by using the digital image correlation technology.According to horizontal displacement and strain distributions in the fractured ligament region as well as the microscopic change of the fractured rock particles,a method to determine the shape and critical dimension of the fracture process zone is proposed based on the fluctuation of horizontal displacement and the mutation of horizontal strain at the crack tip.The results showed that the shape of the fracture process zone is irregular and narrow striped zone with the critical length of 11~13 mm and the critical width of 1.58~2.36 mm.The deformation in the fracture process increases exponentially as it approaches the crack tip,but the deformation increment in the unit area reveals fluctuation.This method can more accurately determine the extent of the rock fracture process zone and help to analyze the nonlinear fracture characteristics of rocks.