| Coal is an important part of energy composition and consumption structure in China.With the continuous exploitation of coal resources,the frequency and intensity of coal-rock dynamic disasters such as rockburst and coal and gas outburst are also increasing.The occurrence of these disasters is essentially the result of the overall failure and instability of the "coal-rock" combination system under the strong disturbance of engineering geology.However,the research on the mechanical properties of coal and rock mass at home and abroad is mainly aimed at the study of the mechanical properties of pure coal or simple rock mass under static and dynamic loads.The dynamic mechanical properties and failure and instability of coal-rock composites are rarely studied.Therefore,systematic research on the failure mechanism and mechanical behavior of coal-rock combination is of great significance for mastering the mechanism,prediction technology and treatment technology of coal mine dynamic disasters.Based on this,this paper combines theoretical analysis,impact dynamics experiment,numerical simulation,high-speed camera technology and digital image correlation method(DIC)to study the dynamic mechanical properties of different coal-rock composites under high strain rate.The mechanical behavior,damage damage and energy dissipation of coal-rock composites under load are systematically studied.The coal samples used in the experiment were taken from 13-1 coal in Zhangji Coal Mine of Huainan Mining Group.The rock samples used were taken from the top and bottom rocks of the same coal seam.The combined specimens were processed according to the experimental standards.The research contents and results are as follows:(1)In the dynamic-mechanical test of rock-coal-rock and coal-rock-coal combination,there is a good linear relationship between the impact velocity and strain rate of the bullet and the dynamic compressive strength of the composite,and the strain rate increases continuously.High,the dynamic elastic modulus of the assembly is also increasing,the strain change is more obvious,and the deformation of the composite specimen has elastic aftereffect characteristics,but this phenomenon will accelerate and decrease as the strain rate increases.(2)The change law of stress-strain curve of the composite under dynamic impact can be roughly divided into elastic phase,yield phase and failure phase.After the initial stress,the stress-strain curve rises linearly to about 50%of the peak stress.As the stress increases,the slope of the curve gradually decreases.The fracture degree of the test piece gradually develops until the stress peak is reached,and the test piece is broken.Loss of carrying capacity.(3)As the experimental strain rate increases,the impact kinetic energy increases,and the energy carried by the stress wave also increases.The energy carried in the stress wave is used to destroy the energy of the coal-rock combination,that is,the crushing work also exhibits a linear growth relationship.The degree of body fragmentation also increases rapidly,the block volume decreases rapidly,and the block fractal dimension increases linearly.However,the dispersion of energy dissipation rate is strong,and there is no obvious trend of gradually increasing or decreasing,but fluctuating within a certain range,mainly due to the pores and cracks or structures appearing in the internal structure of the coal and rock specimens.Caused by unevenness.(4)According to the DIC analysis results,after the uneven deformation of the coal-rock combination in the early stage,the internal part of the specimen passes through the wave propagation and reflection,the internal deformation tends to be uniform,the whole specimen is compressed,and the displacement tends to be consistent.When the load on the specimen continues to increase,due to the small strength of the coal in the coal-rock combination,the coal part of the specimen begins to crack first,and the crack gradually extends and expands into the rock under the continuous action of the load,forming a large The crack,and finally the overall fracture of the test piece,both combinations generally undergo three processes of deformation uniformity phase,local deformation phase and overall fracture phase.(5)The dynamic load or strain rate has a great influence on the displacement field and strain field of the specimen.As the strain rate increases,the time for the specimen assembly to reach the strain uniform is shorter,and the speed of crack evolution and expansion is higher.Fast,the greater the degree of fragmentation of the assembly.(6)As long as the plastic yield failure occurs in the coal-bearing rock mass containing confining pressure,it first occurs in the weakest coal body region,and the plastic yield failure phenomenon occurs inward from the outer surface of the coal body or rock.When the confining pressure is small,the volume expansion effect will occur in the later stage of the impact,and the smaller the confining pressure,the more significant the volume expansion effect.With the increase of confining pressure,the volume of the resulting plastic zone decreases,and the time of plastic zone in each coal rock mass area also has a hysteresis effect The body strain at each position of the test piece is gradually expanded by the impact of low confining pressure.The conversion to impact compression,and the peak value of the transmitted wave on the top surface increases,and the power shock energy consumption decreases nonlinearly.Figure 130 table 15 reference 180... |
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