圆盘试样巴西劈裂试验的空间应力分布及破坏过程

Three-dimensional stress distribution and failure process of disc specimens in Brazilian test

利用离散元数值计算方法,研究了圆盘试样径向加载时的空间应力分布及劈裂过程的裂隙扩展情况。结果表明：1）径向加载圆盘试样横截面上的应力分布规律与二维解析计算的结果相同,中轴线上的拉应力并不是常数,而是呈两端高、中间低分布,具有明显空间效应;2）不同高径比对拉应力的分布具有重要影响,试样两端最大拉应力随高径比增加而增大,中间拉应力随高径比增加而减小,当高径比大于1以后,最大和最小拉应力数值不再变化,因空间效应引起的拉应力增高程度最大为25%左右;3）由于拉应力分布不均,圆盘试样破坏裂隙首先在试样轴向两端产生,然后向试样内部延伸,试样宏观裂隙在中轴线贯通并不代表试样失去径向承载能力;4）由于空间效应影响,试样的最大径向承载应力随高径比增加而减少,由二维圆盘计算公式得到的巴西劈裂强度明显偏小,对于试验中常用的高径比为0.5的试样,建议使用系数k=1.25～1.30进行修正。

The three-dimensional stress distribution and the initiation and propagation of fracture in disc rock specimens under diametric compression were analyzed through discrete element method. The results have shown that： 1） Stress distribution on cross section in disc specimens were in alignment with two-dimensional analytic calculation result, while the tensile stress on central axis were not constant but variable distribution of higher on the both ends and lower in the middle; 2） The ratio of high and diame- ter had significant effect on the distribution of tensile stress： the maximum tensile stresses on two ends increased and the minimum tensile stress in the middle decreased with the increase of high-diameter ra- tio, and they would no longer change when the high-diameter ratio was bigger than 1. The maximum increasing of tensile stress caused by special effect was about 25% above the result by two-dimensional analytic calculation; 3） Because of the uneven distribution of tensile stresses, the initial of macro cracks were generated on two ends of the discs, and then extended to the middle with the compression increas- ing. Another phenomenon needed to mention was that the interconnection of micro-cracks in disc did not mean it lost the bearing capacity with diametric compression; 4） Because of the spatial effect, the capacity of disc to bearing diametric compression stress decreased with the high-diameter ratio increas- ing, and Brazilian splitting strength calculated by the formula got from two-dimensional analytic calcu- lation was noticeably small. For the common used disc specimens with 0.5 high-diameter ratio, the cor- rection coefficient k=1.25-1.30 was recommended.