Dynamic Compression Characteristics and Failure Mechanism of Water-Saturated Granite

For Fangshan granite in Beijing, the static compression and dynamic compression tests have been carried out separately under natural air drying and water saturation. It was found that the dynamic compressive strength of water-saturated granite is higher than that of air-dried granite, which is contrary to the result that the strength of water-saturated rock is lower than that of air-dried granite under static load. Furthermore, under the medium strain rate condition, when the strain rate is 85 s−1, the dynamic strength of natural air-dried granite could be increased by nearly 0.5 times compared with its static state. The dynamic strength of water-saturated granite could be increased by nearly 1–2 times compared with its static strength, which shows that water-saturated granite has stronger strain rate sensitivity than natural air-dried granite. Meanwhile, under impact loading, from the perspective of water-bearing granite the Bernoulli effect of fluid, the adhesion effect of free water and the Stefan effect of fluid in water-saturated granite were revealed, and found to be the essential reasons affecting the dynamic strength of water-saturated granite. The dynamic strength in different water-bearing states in the range of medium strain rate could then be analyzed in depth, providing a certain reference value for the strength design of water-bearing rock engineering.

Numerical Modeling of Concrete Spallation at Medium Strain-rate

Dynamic tensile strength of brittle materials such as concrete is usually obtained by performing laboratory investigations such as direct tensile, Brazilian splitting, and spall tests. This research presents a study aimed to investigate numerically the dynamic behavior of concrete exposed to tensile loading at medium strain-rate. The dynamic tensile behavior of concrete is investigated using the Modified Split Hopkinson Bar (MSHB) at strain-rate ranges from 33 to 80 s-1. The commercial finite element explicit code LS-DYNA is used to perform the numerical simulations of the MSHB tests. Karagozian & Case Concrete Model (K&C) is adopted to define the mechanical properties of the investigated specimens. The employed K&C material model is verified by using the experimental results obtained in [1]. The validation of the K&C material model is carried out with the comparison of the computed and experimental pull-back velocities of the specimens free end. The results of the analysis are used to enhance the understanding of strain-rate sensitivity of the concrete tensile strength.

CFRP Reinforced Foam Concrete Subjected to Dynamic Compression at Medium Strain Rate

Carbon fiber-reinforced polymer (CFRP)-confined foam concrete can be applied in structure protection, e.g., as an impact barrier of bridge piers, in which it is used as the core of the composite impact barrier. Applying CFRP to the foam concrete exterior enhances both the CFRP and the foam concrete, leading to improved compressive performance due to their interaction. In the present study, the carbon-fiber reinforced polymer (CFRP) confining effect on the response and energy absorption of foam concrete subjected to quasi-static and medium-strain-rate dynamic compression was experimentally investigated. The confinement by CFRP changed the response and failure mode of foam concrete specimens from shear in quasi-static load and splitting in dynamic load to crushing, resulting in a significant increase in the load bearing and energy absorption capacity. The composite consisting of CFRP and foam concrete was sensitive to strain rate. In particular, the CFRP–foam concrete interaction led to the remarkably improved resistance and energy absorption capacity of CFRP-confined specimens, which were significantly higher than the sum of those of standalone CFRP and foam concrete.