摘要
采用红砂岩制作中心直裂纹半圆盘弯曲试样(Notched semi-circular bend, NSCB),设置不同的负温温度对岩石试样预处理,随后利用改进后的分离式霍普金森杆(SHPB)实验系统开展动态试验.结果表明:岩石的断裂韧度存在明显的加载率效应,断裂韧度试验值随加载率的增加近似呈指数型增大;当加载率一定时,岩石断裂韧度由常温进入负温后先缓慢后快速增加,在–20℃时达到最大值,随着温度进一步降低,岩石断裂韧度快速减小.进一步对岩石破裂过程分析发现,不同温度下岩石的断裂过程基本一致,且裂纹扩展速度受温度影响较小.基于岩石断面的扫描电子显微镜结果分析岩石断裂模式为:负温下红砂岩的断裂以沿晶破裂和胶结物的撕裂为主,伴有少量的穿晶破裂现象,同时当温度降低至–25℃时,岩石内部微裂隙数量明显增多,说明负温对岩石具有劣化作用.最后探讨了温度对岩石内部结构的影响机制,对分析岩石断裂特性的低温效应具有一定参考意义.
Considering that fluctuations in temperature can cause variations in both the internal structure as well as the mineral composition of rocks,their fracture characteristics must be impacted accordingly.With the exponential development of geotechnical engineering in cold regions,it is urgent to study the influence of the sub-zero temperature environment on the mechanical properties and dynamic properties of rocks.In order to investigate the influence of sub-zero temperature gradient on the dynamic fracture characteristics of rocks,red sandstone was used for the preparation of notched semi-circular bend specimens.First,a water-saturated machine and a sub-zero temperature incubator were utilized to pretreat the rock for 48 h,conducive for both satiation and freezing processes.Subsequently,the dynamic tests were carried out utilizing an improved split Hopkinson bar experimental system with a cryogenic sub-system.Concurrently,the striker velocity was modulated by setting distinctive air pressures,following which the rock was loaded at various loading rates.The test results demonstrate that the fracture toughness of the rock has an evident loading rate effect,and the fracture toughness proliferates exponentially with the increase in the loading rate.In the event that the loading rate is certain,the fracture toughness of the rock primarily increases gradually and then expeditiously over the course of advancement from room temperature to-20℃.Contradictorily,the rock fracture toughness diminishes abruptly with plummeting temperature.Analysis of the rock fracture process,accommodated by a high-speed camera,revealed that the fracture process of the rock at distinctive temperatures is fundamentally equivalent,and the crack propagation speed is negligibly influenced by the temperature.Furthermore,the rock fracture mode was analyzed by employing a scanning electron microscope(SEM)system.The SEM images of the rock depicted that the fracture of red sandstone at sub-zero temperature is predominantly intergranular fracture and cement tearing,accompanied by a trace of transgranular fracture.Meanwhile,the experimentation also revealed that the number of micro-cracks in the rock significantly multiplied when the temperature declined to-25℃,illustrating that sub-zero temperature has a deteriorating effect on the rock.Conclusively,the influence mechanism of temperature on the internal structure of the rock is discussed,and it is assumed that the change in the internal structure of the rock is the collaborative effect of thermal expansion-cold contraction and ice-water phase transition.The interpretation of this study has substantial reference significance for the further consequential analysis of frigidity on the fracture properties of the rock.
作者
方士正
杨仁树
李炜煜
李永亮
杨阳
FANG Shizheng;YANG Renshu;LI Weiyu;LI Yongliang;YANG Yang(School of Civil and Resource Engineering,University of Science and Technology Beijing,Beijing 100083,China;School of Safety Science and Engineering,Anhui University of Science and Technology,Huainan 232000,China;School of Energy and Mining Engineering,China University of Mining and Technology Beijing,Beijing 100083,China)
出处
《工程科学学报》
EI
CSCD
北大核心
2023年第10期1704-1715,共12页
Chinese Journal of Engineering
基金
国家自然科学基金重点资助项目(51934001)。