Abstract:Rocks are likely to undergo spalling failure under dynamic loading. The fracture development and rock failure behaviours were investigated during dynamic tensile loading. Tests were conducted with a split-Hopkinson pressure bar (SHPB) in four different impact loading conditions. Thin sections near failure surfaces were also made to evaluate the growth patterns of fractures observed by polarizing microscope. Scanning electron microscopy (SEM) was used to observe mineral grains on failure surfaces and to evaluate their response to loading and failure. The results indicate that the number of spalling cracks increases with increase in peak impact loads and that quartz sustains abundant intergranular fracturing. Cleavage planes and their direction relative to loading play a vital role in rock strength and fracturing. Separation along cleavage planes perpendicular to loading without the movement of micaceous minerals parallel to loading appears to be unique to the rock spalling process.

Key words: microscopic observation; dynamic loading; spalling failure; mineral properties; intercrystalline fracture