From water balloons to cells and various organs, thin elastic shells enclosing liquid cores or capsules are ubiquitous. Although such capsules are rampant in nature and in engineering, the physics of their deformation upon rapid impact is virtually unexplored. Here we perform experiments and develop formal models to rationalize the deformation and possible bursting of elastic capsules impacting rigid walls. We discover an analogy to the impact of liquid drops, where the shell surface modulus plays the role of the drop surface tension. On the basis of this analogy, we propose an energy balance that quantitatively predicts the maximal deformation of the capsule in the inviscid limit, and for liquids with viscosities up to 1,000 cP (Reynolds numbers ≳10). Unlike drops, however, capsules can be pre-stretched and burst. Experiments show a substantial influence of the pre-stretch on the critical burst velocity, a feature also captured by our model. While we focus on macroscopic objects, our model could potentially be extended to account for the deformations of microcapsules in microfluidic channels. In addition, this work could have practical implications from the optimized detonation of fire-extinguishing balls to fight domestic fires and wildfires to the prevention of organ bursting in car crashes.

从水囊到细胞和各种器官，包裹着液芯或胶囊的薄弹性壳无处不在。尽管这样的胶囊在自然界和工程学上都很猖ramp，但它们在快速撞击时变形的物理原理实际上尚未得到探索。在这里，我们进行实验并开发形式化的模型，以合理化弹性胶囊的变形和可能破裂的冲击刚性壁。我们发现一个类似于液滴冲击的现象，其中壳表面模量起着液滴表面张力的作用。在这种类比的基础上，我们提出了一种能量平衡，可以定量地预测胶囊在无粘性极限内的最大变形，并且对于粘度高达1,000 cP的液体（雷诺数≳10）。但是，与液滴不同，胶囊可以预先拉伸并破裂。实验表明，预拉伸对临界爆破速度有重大影响，我们的模型也捕获了这一特征。当我们专注于宏观物体时，我们的模型可能会扩展为考虑微流体通道中微胶囊的变形。此外，这项工作可能具有实际意义，包括为扑灭家庭火灾和野火而对灭火球进行优化的爆炸，以及防止车祸中的器官爆裂。