A study of the dynamics of drop impact: Impact forces, pressure and shear stress distributions

跌落冲击动力学研究：冲击力、压力和剪应力分布

• 批准号: 2017071
• 负责人: Xiang Cheng
• 金额: $ 30.15万
• 依托单位: University of Minnesota-Twin Cities
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2020
• 资助国家: 美国
• 起止时间: 2020-06-01 至 2024-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2017071&HistoricalAwards=false
• 关键词: study; dynamics; drop; impact; Impact

From raindrops battering on a windshield to coffee splashing on a table, drop impact is ubiquitous in our daily life and relevant to many important natural and industrial processes. Although the phenomenon has been studied for many decades, the understanding of drop impact is still far from complete due to the complexity associated with typical fast impact processes. Significant progress has been made on drop impact in recent years using high-speed photographic techniques. Relying on direct imaging, most experiments focused on the kinematics of drop impact, i.e., the shape of impacting drops. Few studies have probed the dynamic properties of drop impact such as its impact force, pressure and shear stress. These dynamic quantities lead to the most important outcome of an impact event and affect a wide range of phenomena, including soil erosion, impact-induced wear/damage and the survival of living organisms exposed to the elements. The goal of this research is to conduct a systematic study on mapping the dynamic aspects of drop impact under different conditions. The research will develop a new experimental technique, 3D high-speed stress microscopy, to measure the impact force, pressure, and shear stress of drop impact with high spatial and temporal resolutions. The project will provide a fundamental understanding of the dynamics of drop impact in unexplored regimes and a practical guideline to control impact forces and mitigate impact-induced damage on solid substrates. The project will also provide a unique opportunity to introduce frontier research in undergraduate curriculum and forge collaborations with coating companies. By combining traction force microscopy with high-speed photography, the research will construct a 3D high-speed stress microscope to measure the temporal variation of pressure and shear stress distributions beneath an impacting drop during a fast impact process. With the new technique, the project will verify previous theoretical predictions, including the singular dynamics of off-center pressures, the scaling relation of drag forces, and the propagation of boundary layers in spreading drops. As such, the study will reveal the dynamics of drop impact in spatiotemporal regimes, inaccessible to conventional kinematic measurements. Moreover, the research will examine the influence of different surface properties such as stiffness, wettability, and micro-textures on the stress distributions. The study aims to seek optimal surface designs, which can substantially reduce impact-induced wear and damage.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

从雨滴敲打挡风玻璃到咖啡飞溅在桌子上，跌落冲击在我们的日常生活中随处可见，与许多重要的自然和工业过程有关。虽然这一现象已经被研究了几十年，但由于典型的快速碰撞过程的复杂性，对跌落碰撞的理解仍然很不完整。近年来，利用高速摄影技术在跌落撞击方面取得了重大进展。依靠直接成像，大多数实验都集中在液滴撞击的运动学上，即液滴撞击的形状。很少有研究探讨液滴撞击的动力学特性，如冲击力、压力和剪应力。这些动态量导致了撞击事件的最重要的结果，并影响了广泛的现象，包括土壤侵蚀、撞击引起的磨损/破坏以及暴露在元素中的生物的生存。本研究的目的是对不同条件下跌落碰撞的动力学特征进行系统的研究。这项研究将开发一种新的实验技术--3D高速应力显微镜，以高空间和时间分辨率测量跌落碰撞的冲击力、压力和剪应力。该项目将提供对未探索区域中跌落撞击动力学的基本了解，并为控制撞击力和减轻撞击对固体衬底造成的损害提供实用指南。该项目还将提供一个独特的机会，在本科课程中引入前沿研究，并与涂料公司建立合作关系。通过将牵引力显微镜与高速摄影相结合，该研究将构建一个3D高速应力显微镜，以测量快速撞击过程中撞击液滴下压力和剪应力分布的时间变化。利用这项新技术，该项目将验证之前的理论预测，包括偏心压力的奇异动力学，阻力的标度关系，以及扩展液滴中边界层的传播。因此，这项研究将揭示落点撞击在时空区域的动力学，这是传统运动学测量无法获得的。此外，研究还将考察不同的表面属性，如硬度、润湿性和微观结构对应力分布的影响。这项研究旨在寻求最优的表面设计，以大幅减少冲击引起的磨损和损害。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。