热处理花岗岩循环冲击下断口形貌研究

Fractography study of heat-treated granite under action of cyclic impact loading

为了研究温度和动载对黑云母花岗岩破坏机制的影响,利用分离式霍普金森压杆对不同温度处理后的花岗岩试样进行了循环冲击试验,随后采用钨灯丝扫描电镜对岩样的断口形貌进行细观观测。结果表明:常温岩样低弹速作用后,其断口表面出现韧性疲劳裂纹,中弹速作用后则出现脆性疲劳裂纹,而在高弹速冲击作用后,断口出现典型的解理裂纹;相同冲击荷载下,低于400℃的岩样断口表面存在大量解理裂纹和瓦纳线,随着热处理温度的升高,解理裂纹减少,准解理裂纹及韧窝逐渐增多;花岗岩在循环冲击荷载作用下,加载率效应明显,弹速越高脆性断裂特征越显著;温度效应使花岗岩的韧性增强,处理温度升高会使花岗岩由脆性断裂向脆性-局部韧性断裂的耦合破坏模式转变。

In order to investigate the influences of temperature and dynamic loading on the failure mechanism of biotite granite, the cyclic impact compression tests on the granite specimens heat-treated by different temperatures were carried out using the split Hopkinson pressure bar. The tungsten-filament scanning electron microscope was used to observe the fracture morphology of the specimens. The resuhs show that at room temperature the ductile fatigue cracks appear on the fracture surface under the low impact velocity and brittle fatigue cracks are turned out under the action of the middle impact velocity. However, the typical cleavage cracks appear on the fracture surface under the high impact velocity. Under the same impact loading, there are a large number of cleavage cracks and wallner lines on the fracture surface of the rock specimens below 400℃ heat treatment temperature. With the increase of the heat treatment temperature, the number of the cleavage cracks decreases, and many quasi-cleavage fractures and dimples gradually increase. Under cyclic impact loading, the loading-rate effect of the granite is obvious, that is, the higher the impact velocity, the more obvious the brittle fracture characteristics is. Meanwhile, the temperature effect makes the ductility of the granite significantly enhanced, and an increase in the heat treatment temperature will lead to the transition of the failure mode of the granite specimens from the brittle fracture to the brittle-local ductile fracture.