循环荷载作用下岩石阻尼特性的试验研究

EXPERIMENTAL STUDY ON DAMPING CHARACTERISTICS OF ROCK UNDER CYCLIC LOADING

对2组红层泥质粉砂岩在MTS815 Flex Test GT岩石力学试验系统上进行单轴4级循环加卸载试验。试验加载波形采用正弦波,频率3Hz,循环应力幅值小于其平均抗压强度,单级应力幅值为30个振动循环,得到动弹性模量和阻尼比随动应变的变化规律。通过试验发现,泥质粉砂岩在循环荷载作用下的加卸载应力–应变曲线并不重合,而是形成一个封闭的滞回环,动应变相位始终滞后于动应力相位;滞回环在荷载反转处并非椭圆形,而是尖叶状,在该处岩石的塑性变形小,弹性变形响应迅速。随动应力幅值增加,泥质粉砂岩的动应变增加,动弹性模量随动应变增加线性递减,而阻尼比则线性递增。得到2组泥质粉砂岩的平均动弹性模量和阻尼比与动应变的相关表达式,其相关系数的平方R2均超过98%。岩石的不可逆塑性变形随动应变增加而增大,同时由循环荷载引起的损伤变形也逐渐增加。

The four-grade uniaxial cyclic loading and unloading tests for two groups of red argillaceous siltstones were carried out on MTS815 Flex Test GT rock mechanics test system. The sine wave is adopted in loading test, and its frequency was 3 Hz. The maximum cyclic stress was less than the value of the average intensity of compression; and the cyclic number of each level cyclic stress was 30. Through the test, the relationships of dynamic moduli of elasticity and damping ratio to dynamic strain for the two groups of rocks were gained. The test results showed that the curves of strain and stress for loading and unloading were not superposition under cyclic loading, but hysteresis loops. The strain wave location was always later than stress wave location： and the hysteresis loops were not ellipse-shaped, but tine-lobation when the cyclic loading was reversed. The dynamic strain increased with the increase of oscillation amplitude; the dynamic modules of elasticity was linearly decreasing with the dynamic strain increasing, but the damping ratio was reversed. The four relationship equations were gained, and the correlation coefficient R^2 was over 0.98. Moreover, the irreversible plastic deformation of rock increased, and at the same time, the fracture deformation of rock gradually increased, which was produced by cyclic load.