Tabuteau Hervé, Sikorski Darek, de Vet Simon J, de Bruyn John R
Department of Physics and Astronomy, University of Western Ontario, London, Ontario, Canada N6A 3K7.
Phys Rev E Stat Nonlin Soft Matter Phys. 2011 Sep;84(3 Pt 1):031403. doi: 10.1103/PhysRevE.84.031403. Epub 2011 Sep 16.
We study the behavior of a yield-stress fluid following the impact of a vertically falling sphere. Since the impact produces shear stresses larger than the yield stress, the material in the vicinity of the impact becomes fluidized. The sphere entrains air when it enters the fluid, and the resulting cavity pinches off below the surface. The upper part of this cavity then rebounds upward. For sufficiently fast impacts, a vertical jet is produced by the cavity collapse. While many aspects of this process are similar to that in Newtonian fluids or granular materials, the rheological properties of our target material change the scaling of the cavity pinch-off depth and have a dramatic effect on the height of the jets. The material returns to a solid-like behavior once the stresses due to the impact have relaxed to below the yield stress, leaving a crater in the surface of the material. We find that the diameter of this crater depends nonmonotonically on the impact speed. The crater shape also changes with speed, reflecting the dynamics of the impact process.
我们研究了垂直下落球体撞击后屈服应力流体的行为。由于撞击产生的剪应力大于屈服应力，撞击附近的材料会流化。球体进入流体时会夹带空气，产生的空腔在表面下方收缩。这个空腔的上部随后向上反弹。对于足够快的撞击，空腔坍塌会产生垂直射流。虽然这个过程的许多方面与牛顿流体或颗粒材料中的情况相似，但我们目标材料的流变特性改变了空腔收缩深度的标度，并对射流高度产生了显著影响。一旦撞击产生的应力松弛到屈服应力以下，材料就会恢复到类似固体的行为，在材料表面留下一个坑。我们发现这个坑的直径与撞击速度呈非单调关系。坑的形状也随速度变化，反映了撞击过程的动力学。
