盐岩损伤测试中卸载模量研究

利用MTS815 Flex Test GT岩石力学试验系统,对盐岩和大理岩进行了单轴压缩下的7级加卸载试验和低周循环加卸载试验测试,对盐岩和大理岩的卸载模量进行了探讨。低周循环试验加载波形采用正弦波,频率1Hz,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。通过试验,得到了盐岩应力应变滞回环均为条带状,大理岩则均为尖叶状;盐岩在加卸载部位具有较大不可逆变形,对应弹性响应较慢,大理岩则反之;盐岩卸载模量变化趋势受加载测试方法影响较大,而大理岩在2种试验条件下得到的卸载模量变化趋势相似;加载应力幅值比加卸载循环数对盐岩不可逆变形增量影响更加显著。损伤变量研究结果表明,利用低周循环加卸载方法测试具有显著时间效应变形岩石的损伤弹性模量,能更真实反映其损伤特征。

Resarch on Unloading Modulus for Salt Rock Damage Testing

This paper studies the damage unloading modulus of salt rock with marked visco-plastic deformation based on the applicability of damage definition on hypothesis of strain equivalence, and the marble stones as the contrast stone are tested. All of the tests are realized on MTS815 Flex Test GT rock mechanics test system. The test types include the loading and unloading test and the low cyclic loading test, and the loading method is the axial load control. On the process of each test, the stress has 7 grades for reloading and unloading. Through the test, the ribbon shape of hysteresis loops for the curves of strain and stress of salt rock are obtained, and the tine lobation for marble stone; salt rock has larger irreversible deformation at reloading and unloading position where corresponding elastic deformation response is slow, but the results for the marble stone are contrary; the changing tendency of unloading modulus for salt rock is reverse by 2 test methods, while the results for marble stone are consistent each other, and the unloading modulus increase with the loading stress increasing; the effect on the increment of irreversible deformation for salt rock is more prominent for the condition of the loading stress amplitude than that of the cyclic numbers. The damage variable test results reveal that it is more authentic to describe the damage property through the damage elastic modulus which is tested by the low cyclic loading test method for rock with marked visco-plastic deformation.