Study On Dynamic Characteristics And Numerical Simulation Of Thermally Damaged Granite

As the most common material on Earth,rock materials are widely used in practical engineering,especially in major projects such as deep rock mass engineering,storage of nuclear waste,and large amounts of geothermal development and utilization.In these engineering works,not only dynamic loads but also temperature effects are required.Dynamic load and temperature together cause varying degrees of damage to granite.Therefore,it is particularly important to study the dynamic mechanical properties of thermally damaged granite.This paper focuses on the Hopkinson compression bar test,supplemented by LS-DYNA numerical experiments,to study the dynamic characteristics and fractal fragmentation of thermally damaged granite.The main work and related conclusions are as follows:Firstly,a series of dynamic and static combined tests were conducted on thermally damaged granite using an improved Hopkinson compression bar(SHPB).The test results show that with 400 ℃ as the boundary,the strength and elastic modulus of rock mass significantly decrease after 400 ℃.The relationship between temperature and peak stress as well as the number of cycles presents a reverse trend.Before 400 ℃,axial pressure can increase the peak stress,which proves that axial pressure can improve the resistance of rock samples to external impact loads.However,with the increase of temperature,the peak stress shows a downward trend,which proves that the impact of temperature(especially under high temperature conditions)on rock mechanical properties is greater than the impact of external stress.The change of peak strain shows an upward trend with the increase of temperature,showing a phenomenon of temperature ladder.Under different axial pressures,the higher the axial pressure,the lower the peak strain,indicating that axial pressure has a certain inhibitory effect on strain,further reflecting that axial pressure can enhance the ability of rock specimens to resist external impact loads.Secondly,research on the failure morphology and fractal dimension of granite after impact crushing is carried out.The test results show that the morphology is different under different temperatures and axial pressures,which proves that the two factors have significant differences in the impact on the interior of rocks.Under low temperature and low axial pressure,rock fragmentation presents splitting failure,while when the axial pressure increases,the shape of the rock presents a state of flat ends and thin middle,resulting in a typical "end effect".After that,the distribution statistics of rock fragments were conducted,and it was found that under low temperatures,the fragmentation of rocks was mainly concentrated on the bulk size,while under high temperatures,the fragmentation release of rocks was significantly different,with the fragmentation mainly concentrated on the small size.In terms of fractal dimension,axial pressure has an important impact on the distribution of rock fragmentation.The fractal dimension under high temperature and high axial pressure is significantly higher than that under other conditions.It has been proved that under the action of high temperature and axial pressure,the formation of impact fracture of granite has different effects.Finally,a numerical simulation study of rock was carried out using LS DYNA finite element software.JOHNSON was given at the beginning＿HOLMQUIST＿A method for determining the parameters of the CONCRETE(HJC)model.After that,the simulation of the experimental process was started to obtain the stress-strain curve,failure process,and final failure results of the rock.The simulation results obtained are basically consistent with the experimental results,and the shape of the stress-strain curve and the description of mechanical conditions are consistent.Thereby verifying the feasibility of defining the mechanical behavior of rocks using HJC model parameters.