| Rock is one of the main components of the earth’s lithosphere.It is usually composed of one or more minerals and has a high strength and stable shape.In addition,in many fields such as energy,civil engineering and geology,such as deep-layer disposal of high-level nuclear waste,exploitation and utilization of geothermal resources,coal and gas explosion in underground mines,underground gasification of coal seams and repair and reinforcement of rock mass engineering after fire inevitably involve the strength and damage characteristics of rocks after high temperature.Therefore,it is of great significance to study the dynamic mechanical properties of granite and their variation with temperature field and loading rate.The research work and conclusions of this paper mainly include the following aspects:Firstly,static splitting and tensile tests were carried out on the granite subjected to9 different temperatures(25℃～800℃).The results show that the basic physical and mechanical properties of granite change obviously with the increase of temperature,the static compressive strength increases first and then decreases with the increase of heat treatment temperature,and the static tensile strength decreases first,then increases and then decreases.The failure mode of granite is complex,and the failure mode at most temperatures is a comprehensive failure mode composed of multiple failure modes.Secondly,the modified SHPB device was used to carry out dynamic compression experiments at three loading rates(8.1m/s,12.5m/s and 16.8m/s)on granite samples subjected to nine different temperatures.The results show that with the increase of loading rate,the stress-strain curves of the specimens treated at 25°C～700°C change from "type II" to "type I",while those treated at 800°C all show "type I" characteristics.At the same temperature,the peak stress,peak strain and average strain rate of granite increase with the increase of loading rate,but the elastic modulus does not change much,and the failure mode changes from radial splitting tensile failure mode to crushing failure mode.The dynamic mechanical properties of granite samples reach the optimal value at 300℃,and gradually deteriorate at 500℃.The properties are weakest at 800℃ and the damage degree is the most serious.Meanwhile,based on the energy principle of rock instability failure,the energy dissipation law of rock in the crushing process of impact test is analyzed.The results show that: the energy time-history curve of granite sample mainly presents four stages,and the energy increases with the increase of time,and finally tends to be stable.The dynamic failure state of granite specimens is closely related to incident energy and temperature.The variation trend of dissipated energy is controlled by loading rate and temperature.The utilization rate of energy decreases with the increase of temperature.The peak stress of dynamic compression is proportional to the transmitted energy.Finally,the numerical simulation software ANSYS/LS-DYNA and the RHT constitutive model were used to simulate the SHPB test of heat-treated granite.The results show that the numerical simulation results are in good agreement with the laboratory test results.The dynamic compression failure process is divided into four parts.With the increase of loading rate,the final failure form of the sample is obviously aggravated.Figure 75 Table 14 Reference 91... |
