We study experimentally the penetration of a projectile into a two-dimensional granular bed composed of magnetic repelling grains. The projectile can experience either repulsive, attractive or neutral interaction with the particles generating different dynamics: i) the repulsive intruder compresses the granular bed without contact and experiences rebounds before stopping; ii) the attractive intruder is first accelerated when it approaches the bed, then, some magnets attach to its surface increasing its effective diameter and the drag force acting on the intruder until it reaches the repose; and iii) the neutral projectile penetrates deeper into the granular bed than in the two previous cases because there is no magnetic interaction with the particles. In addition, we developed molecular dynamics simulations able to reproduce the experimental results and used to determine the effect of the magnetic strength and the role of friction between the particles and the container walls. The results show that the medium behaves similar to a viscoelastic micellar fluid on impact, and the projectile dynamics can be modelled by a spring-dashpot model. Our findings can be useful in the design of new magnetic granular dampers.

我们通过实验研究了弹丸对由磁性排斥颗粒组成的二维颗粒床的渗透。弹丸可能会与粒子发生排斥，吸引或中性相互作用，从而产生不同的动力学特性：i）斥力入侵者压缩颗粒床而没有接触，并在停止之前经历反弹；ii）吸引人的入侵者在接近床具时首先被加速，然后，一些磁铁附着在其表面上，从而增加了其有效直径，并且作用在入侵者上的阻力一直到它到达静止为止；iii）中性弹丸比前两种情况更深地渗透到颗粒床中，因为与颗粒之间没有磁性相互作用。此外，我们开发了分子动力学模拟，能够重现实验结果，并用于确定磁强度的影响以及颗粒与容器壁之间的摩擦作用。结果表明，该介质在撞击时的行为类似于粘弹性胶束流体，并且可以通过弹簧-阻尼器模型对弹丸动力学进行建模。我们的发现对设计新型磁性颗粒阻尼器很有用。