Some aspects of wedge impact on granular layers and attendant flows

摘要

We observed and measured impacts of steel wedges on layers of 200μm solid glass spheres and the subsequent response with the ultimate aim to establish the effectiveness of these materials for blast panels and energy absorption. The success of the layers to absorb and dissipate energy is quantified, especially as regards the unconfined free surface of the granular material and its ability to dissipate and redirect momentum laterally through wave-like motion. Experiments were conducted with two granular layer depths; two drop elevations; and three wedge angles. As expected, as the wedge included-angle increases the peak force increases significantly, whereas the period associated with the response is much-reduced. It was shown that with a reduction in layer thickness, the bed can be forced to vacate locally, and subsequently the wedge strikes the reservoir bottom causing a rapid rise to a very large peak force. It was seen that the included-angle 180° wedge caused predominantly solid-like response (I.e. compaction); the 102° wedge generated mostly viscous/fluid-like behavior (I.e. similar to a Newtonian fluid); and as might be expected the 141° wedge exhibited both fluid-like and solid-like behavior. High-speed imaging of the surface response for the viscous-like motion showed breaking wavelike characteristics. In addition granular material was forced upward in a thin free sheet with hexagonal structure. Lastly we quantified the peak force ratio, the impulse, and the energy dissipation in the underlying load cells for the 102° wedge impacting the 16.36 cm bed versus the same test with no bed in place. For this last comparison the peak force ratio exceeded 15; the impulse was about a third less for the granular bed; and the ratio of energy dissipation in the load cells was more than 200.