Dynamic mechanical behavior of coral rock subjected to high strain rate loading.

Coral rock of biological origin exhibits distinctive mechanical behavior compared to that of conventional mineral rocks. Quasi-static and impact loading tests were conducted to investigate the mechanical properties of coral rock using a servo-hydraulic device and a split Hopkinson pressure bar (SHPB) apparatus. The dependence of the dynamic compressive strength, elastic modulus and energy absorption were quantitatively analyzed with respect to loading strain rate. The coral rock is characterized by a high porosity of 50.99 (± 5.60)% and a low bulk density of 1.31 (± 0.07) g cm−3 because of biological sedimentary. Both the quasi-static and dynamic stress–strain curves contain more pronounced compaction portion than dense rocks due to its special porous skeleton structure. The dynamic increase factor (DIF) of strength increases from 1.88 to 3.76 with the strain rate increasing from 117 to 334 s−1, which could be expressed with a parabolic function. The dynamic elastic modulus exhibits an overall linear increasing trend with loading strain rate. The ratio of reflected energy to incident energy is positively related with the strain rate while the absorbed ratio is roughly negatively correlated with strain rate with a value less than 0.08. The specific energy absorption (SEA) is found to be proportional to the logarithm of the loading strain rate. It seems that the failure mode of coral rock under both quasi-static and dynamic compression is more dependent on inherent flaws like pre-existing pores, growth lines, weak bonding areas than loading strain rate. Nevertheless, the dominant failure mode in microscopic scale for coral rock at higher strain rate is still trans-granular fracture by means of SEM. [ABSTRACT FROM AUTHOR]