Determination of attenuation effects of coral sand on the propagation of impact-induced stress wave

A new methodology for determining the attenuation effects of stress wave in granular media was proposed based on an unproved hollow-aluminum split Hopkinson pressure bar (SHPB) testing system. A total of 156 impact tests were conducted on "long" cylindrical dry coral sand and silica sand specimens confined by a steel sleeve. The primary advantage of this configuration is that a state of stress equilibrium is not required in the specimen; this is not the case for normal SHPB tests. The results showed that an approximate 30% greater wave attenuation effect was evident in coral sand than in silica sand. A systematic parametric study was also performed to determine the influence of key parameters on the attenuation effects of stress wave; these parameters, include wave duration, wave amplitude, as well as relative density and particle size of coral sand. It is concluded that the attenuation effect of coral sand is independent of the wave amplitude, whereas it is inversely correlated to both wave duration and relative density. There exists a critical stress zone between 1.98 MPa and 0.32 MPa, which indicates the crushing of coral particle. When the peak stress is beyond this stress zone, coral sand of large particle size exhibits a better attenuation effect than that of small particle size. Conversely, when the peak stress is below this stress zone, coral sand of small particle size exhibits a better attenuation effect than that of large particle size. A series of explicit formulae on determining the attenuation effect of stress wave in coral sand were proposed; parameters include peak stress, wave velocity and peak stress velocity could be calculated.