论文部分内容阅读
为了研究不同预静载水平下硬岩受不同扰动频率载荷的断裂特性变化规律,采用红砂岩制作中心直裂纹半圆盘三点弯曲试样(Semi-Circular Bend,SCB),利用MTS Landmark电液伺服试验机,开展“不同预静载+动力扰动”下砂岩的断裂韧度测试试验。以岩石静载断裂载荷为基础,选取4个预静载水平(60%,70%,80%和90%的静载断裂载荷)作为初始静载状态,之后分别施加扰动载荷直至试样断裂。扰动加载方式采用正弦波载荷,加载波幅值依次为静载断裂载荷的40%,30%,20%和10%,设置扰动频率分别为1,10,20,30,40和50 Hz。研究结果表明,不同预静载水平下岩石的断裂韧度值较常规加载下都有不同幅度的减小,并且随着扰动频率的增加,岩石断裂韧度呈线性减小的趋势。但不同预静载水平之间的减韧效应存在差异性,预静载水平越高,减韧幅度越大。与常规加载条件下相比,预静载水平下的断裂位移整体具有减小的趋势。岩石扰动断裂点的分布区段具有明显的集中性,当预静载水平低于90%时,断裂点位于预应力水平之上的加载段,而当预静载水平为90%时,断裂点多数位于预应力水平之上的卸载段,并且基本上没有断裂破坏发生在预应力水平之下。断裂疲劳寿命随扰动频率的增加出现先增大后减小再增大的趋势,整体呈增加趋势。断裂破坏时间跟预静载水平、扰动频率之间的相关性不明显。综合考虑认为,扰动频率为10 Hz时达到相对最优的致裂效果。
In order to study the variation regularity of the fracture characteristics of hard rock subjected to different disturbance frequency loads under different pre-static loading levels, a center-cracked semi-circular Bend (SCB) sample was made with red sandstone. MTS Landmark electro-hydraulic Servo testing machine to carry out “different pre-static + dynamic disturbance” under the sandstone fracture toughness test. Based on the static load at rock breaking, four static load levels (60%, 70%, 80% and 90% of static load) were selected as the initial static load condition, and then the disturbance loads were applied respectively until the specimen was broken. The disturbance loading method adopts the sine wave load, the amplitude of the load wave is 40%, 30%, 20% and 10% of the static load breaking load in turn, and the disturbance frequency is set as 1, 10, 20, 30, 40 and 50 Hz respectively. The results show that the fracture toughness values of rock under different pre-loading levels decrease with different amplitudes under normal loading, and the fracture toughness of rock decreases linearly with the increase of disturbance frequency. However, there are differences between the different pre-static levels of the toughness reduction effect, the higher the level of pre-static load, the greater the rate of reduction of toughness. Compared with the normal loading condition, the fracture displacement under the pre-static load level has a decreasing tendency as a whole. When the pre-static load level is lower than 90%, the fracture point is located at the loading section above the pre-stress level. When the pre-static load level is 90%, the fracture point Most of the unloading section is located above the level of prestressing and essentially no fracture failure occurs below the level of prestressing. Fracture fatigue life increases with disturbance frequency first increases then decreases then increases, the overall trend is increasing. The correlation between fracture failure time and pre-static load level and disturbance frequency is not obvious. It is considered synthetically that the relatively optimal fission effect is achieved when the disturbance frequency is 10 Hz.