冲击荷载作用下岩石破碎分形特征

为探究冲击荷载作用下岩石破碎分形特征,选取花岗岩和砂岩开展分离式霍普金森压杆(SHPB)岩石动力学试验,得到了不同应变率下岩石的应力-应变曲线、破碎特性、强度参数和能量参数;利用标准筛对破碎后的岩块进行筛分,获取了岩石破碎块度分布曲线,并基于碎块粒径分布的质量分形模型计算出分形维数D;最后分析了分形维数与加载参数、破碎特性和耗能特性之间的关系。结果表明,岩石在冲击荷载作用下的破碎块度分布符合分形规律;动态抗压强度随应变率增大而增大,两者满足乘幂函数关系;加载过程中岩石应变率越大,岩石破碎程度越深,分形维数越大;分形维数与岩石破碎耗能密度之间满足乘幂函数关系。采用分形维数可实现对岩石在冲击荷载作用下的破碎特性、力学特性和破碎耗能特性的定量研究。

Fractal characteristics of rock fragmentation under impact load

In order to study fractal characteristics of rock fragmentation under impact load, rock dynamic tests with separated Hopkinson pressure bar (SHPB) were conducted for granite and sandstone to obtain rock stress-strain curves, broken characteristics, strength parameters and energy ones under different strain rates. The standard sieve was used to screen and classify broken rocks to gain rock fragmentation distribution curves. The fractal dimension D was calculated based on the mass fractal model of fragments’ particle size distribution. Finally, relations among fractal dimension, loading parameters, broken characteristics and energy-dissipating were analyzed. The results showed that the fragmentation distribution of rock under impact load accords with the fractal law; rock dynamic compressive strength increases with increase in strain rate, both of them satisfy a power function relation; the greater the rock strain rate during loading, the deeper the degree of rock fragmentation and the larger the fractal dimension; the relation between fractal dimension and rock fragmentation energy- dissipating density satisfies a power function relation; fractal dimension can be used to realize quantitatively studies among rock broken characteristics, mechanical properties and energy-dissipating characteristics under impact loading.