不同频率循环荷载作用下花岗岩细观疲劳损伤特征研究

摘要

开展花岗岩细观疲劳损伤特征的试验研究对于理解花岗岩宏观力学疲劳特性具有重要的理论价值和实践意义.首先,基于RMT-150B多功能全自动刚性岩石伺服试验机,对花岗岩试样采用幅值为10 MPa,频率分别为0.01,0.02,0.05,0.10,0.20,0.50和1.00 Hz的正弦疲劳荷载进行单轴循环加卸载试验;然后,利用扫描电镜(SEM)获取大量花岗岩细观微结构信息,来研究不同频率循环荷载作用下花岗岩细观疲劳损伤特征.结果表明:在较低频率循环荷载作用时,沿晶裂纹是3类晶体主要损伤形式;当荷载频率较高时,石英和云母仍以沿晶裂纹为主要损伤形式,而长石则表现出以沿晶裂纹为主,穿晶裂纹和晶内裂纹为辅的损伤特征;沿晶裂纹和晶内裂纹的方位角表现出趋于循环荷载轴向方向的特征,而穿晶裂纹方位角则表现出明显的无规律性;沿晶裂纹是主要的损伤发展方式,穿晶裂纹次之,晶内裂纹对损伤发展基本没有贡献.%The fatigue damage of granite under cyclic fatigue load are caused by the propagation and coalescent of cracks at mesoscale, so it is of important theoretical value and practical significance to understand the fatigue properties of rock by experimental research on meso fatigue damage of granite.The whole test scheme included two parts as follows: the uniaxial different frequencies cyclic loading and unloading tests and the meso-damage quantification tests based on SEM.The uniaxial different frequencies cyclic loading and unloading tests on granite were done on the RMT - 150B multi-function automatic rigid rock servo material testing machine.Sine wave cyclic loads with stress amplitude of 10 MPa and seven different frequencies of 0.01, 0.02, 0.05, 0.10, 0.20, 0.50 and 1.00 Hz were adopted as dynamic disturbance.A great deal of mesostructural images of granite has been obtained by means of scanning electron microscope(SEM).It is shown that when the cyclic frequency is relative low, intergranular cracks are the main forms of meso fatigue damage of crystals.When the frequency is relatively high, intergranular cracks are the main forms of meso fatigue damage of quartz and mica crystal and the forms of meso fatigue damage of feldspar are intergranular cracks, transgranular cracks and grain cracks.The azimuth of intergranular cracks and grain cracks tends to the axial direction of cyclic load.But the azimuth of transgranular cracks appeares irregular.And the major meso fatigue damage is intragranular cracks.