峰前和峰后循环荷载下岩石断裂损伤特征

Fracture Damage Characteristics of Rock Under Pre-Peak and Post-Peak Cyclic Loading Condition

在岩体开挖过程中,循环荷载可能发生在峰值前,也可能发生在峰值后.为获得岩石在峰前和峰后循环作用下的断裂损伤演化特征,采用数字图像相关法和声发射技术,进行了三点弯曲开口花岗岩梁的断裂试验.采用割线模量、声发射能量、有效裂缝长度分别构建了岩石断裂损伤指数D_(E)、D_(AE)和D_(L),并对岩石的断裂损伤过程进行了定量分析.结果表明:岩石试样的损伤指数存在明显的率效应,在相同循环次数下,加载速率越大,其损伤指数越小.对于峰前循环加载条件,采用D_(E)可以较好地反映岩石由弹性阶段向弹塑性阶段的断裂变化过程.而在峰后循环加载条件下,采用D_(L)可以更好地表现岩石从阶梯上升到持续破坏的断裂损伤过程.

In the process of rock excavation,cyclic loading may occur before or after the peak value.In order to obtain the fracture damage evolution characteristics of rock under the pre-peak and the post-peak cyclic loading condition,the fracture tests of three-point bending granite beams were conducted by using the digital image correlation method and the acoustic emission technology.Based on the secant modulus,the acoustic emission energy and effective crack length,the rock fracture damage indexes D_(E),D_(AE),and D_(L) were constructed respectively,and the rock fracture damage process was quantitatively analyzed.The results show that the damage index of the rock sample has an obvious rate effect.At the same number of cycles,as the loading rate increases,the damage index decreases.For the pre-peak cyclic loading condition,the fracture process of rock from elastic stage to elastic-plastic stage can be well reflected by D_(E).Under the condition of post-peak cyclic loading,D_(L) can better represent the fracture damage process of rock from step up to continuous failure.