温度冲击对花岗岩动态拉伸力学性能的影响

在特定情况下，岩体工程中的岩石会经历温度快速变化（温度冲击），因此研究温度冲击对岩石的影响对实际工程中岩体的稳定性分析有重要意义。通过将花岗岩试件加热至3种高温（200，400，600 ℃），并采用3种方法冷却，研究了温度冲击对花岗岩物理性质的影响；使用分离式霍普金森压杆研究了温度冲击对花岗岩动态拉伸特性的影响，发现其动态拉伸强度随加热温度和冷却速率的增大而减小；使用高速摄影仪记录试件拉伸破坏时的裂纹形态，结合碎块形态，分析温度冲击对花岗岩的损伤程度，得出200 ℃加热条件下花岗岩不产生温度冲击，而在400 ℃和600 ℃加热条件下，花岗岩损伤程度随加热温度和冷却速率的增大而增大。

Effect of Thermal Shock on the Dynamic Tensile Mechanical Behavior of Granite

Under certain conditions，such as the drilling surrounding rock cooled by drilling fluid in geothermal development，the surrounding rock rapid cooled in the process of extinguishing the fire，rock in rock mass engineering will experience rapid temperature change（thermal shock）.Therefore the study of thermal shock in rocks is of great significance for stability analysis of rock structure affected by thermal shock.Granite specimens were heated to the high temperatures of 200 ℃，400 ℃ and 600 ℃，and then cooled by three methods of water cooling，air cooling and cooling in the stove.The physical properties such as dry density，P-wave velocity，porosity of granite after distinctive thermal shock were measured.The dry density and porosity were measured with buoyancy techniques.The P-wave velocity was measured by a non-destructive ultrasonic detector.As the heating level and cooling rate rise，the dry density and P-wave velocity present a descending trend，and the porosity presents an ascending trend.The damage degree of granite increases with the increase of heating temperature and cooling rate.The dynamic tensile tests were performed on the specimens after distinctive thermal shock treatment utilizing the split Hopkinson pressure bar system.The dynamic tensile strength of granite heated at 600 ℃ is less than that of granite heated at 400 ℃ and 200 ℃，and the dynamic tensile strength of water-cooled granite is less than that of air-cooled and stove-cooled granite.The damage degree of the granite caused by thermal shock was analyzed by the crack morphology of the specimens recorded by high-speed photography during the tensile failure and the morphology of the broken pieces after failure.The results show that the damage degree of granite increases with the increase of heating level and cooling rate.Scanning electron microscopy （SEM） was used to identify the microcosmic damage and fracture characteristics of granite caused by thermal shock.There are two kinds of characteristic fracture morphology of thermal shock were observed on the specimens after heated at 400 ℃ and 600 ℃ （both air-cooled and water-cooled conditions）.However，neither fracture morphology can be found at 200 ℃ （including 3 kinds of cooling conditions）.Therefore，there is no thermal shock at 200 ℃；When the heating level reaches 400 ℃，the granite is damaged by high temperature and thermal shock.When the heating level reaches 600 ℃，the granite is badly damaged.And the damage degree of granite increases with the increase of heating temperature and cooling rate.This study can provide theoretical basis for the analysis of thermal shock damage and the evaluation of rock mass stability after high temperature disaster in practical engineering.