轴压和循环冲击次数对砂岩动态力学特性的影响

利用岩石动静组合加载SHPB试验装置，研究不同轴压的岩石在循环冲击过程中动态强度和变形特性。首先，对具有不同轴压的岩石进行循环冲击；进而考察了在循环冲击过程中岩石的典型动态应力-应变曲线；最后，研究轴压和循环冲击次数对岩石动态强度和变形特性的影响。研究结果表明：随着循环冲击次数的增加，加载段和第2卸载段的变形模量、峰值应力、恢复的应变与峰值应变之比和恢复的应力与临界卸载应力之比值逐渐降低；平均应变率、峰值应变、第1卸载段的变形模量以及单位体积吸收能逐渐增大。当轴压为其单轴抗压强度的22%，51%和65%时，岩石对外部冲击载荷的抵抗能力与冲击次数间的关系整体上呈现“平缓发展-急剧下降”，当轴压为0或为其单轴抗压强度的87%时，岩石抵抗冲击的能力随冲击次数的增加基本呈现匀速降低的趋势。当轴压为其单轴抗压强度的22%时，抵抗外部循环冲击载荷的能力最高。

Effects of axial pressure and number of cyclic impacts on dynamic mechanical characteristics of sandstone

The characteristics of dynamic strength and deformation on rock with different axial pre compressions under cyclic impacts were conducted with modified split Hopkinson pressure bar(SHPB).Firstly，the different axial pre compression stresses were loaded on sandstone specimens before the cyclic impact loadings were carried on.And then，the typical dynamic stress strain curve of specimen under cyclic impacts was investigated.Finally，the characteristics of dynamic strength and deformation of rock with different axial pre compressions were studied during cyclic impacts.The results show that，with the increase of number of cycle impacts，the deformation modulus of loading stage and the first unloading stage，transmitted wave and peak stress，the ratio of recovered strain and peak strain，the ratio of recovered stress and critical unloading stress reduce gradually.While，the average strain rate，peak strain，the deformation modulus of the first unloading stage，and specific energy absorbency increase gradually.When the axial compression of rock is 22%，51% and 65% of its uniaxial compressive strength，the relation between the ability of resistance against cyclic impacts and the cycle index is from slow development to sharp decline.When the axial compression of rock is 0 or 65% or 87% of its uniaxial compressive strength，the ability of resistance against cyclic impacts drops constantly during the whole cycle.The rock’s ability of resistance against the cyclic impacts is highest when the axial compression of rock is 22% of its uniaxial compressive strength.