CAREER: Elastohydrodynamic lubrication of soft patterned interfaces

触觉技术通过向用户施加力来创造触摸的感知和体验。它通常用于远程手术和机器人等应用。在某些应用中，当两个表面相互滑动时，由表面之间的液体薄膜润滑产生力。CAREER奖的重点是弹性流体动力润滑（EHL），这是一种特殊情况，两个表面是可变形的（“弹性”），作用在它们身上的力既取决于它们的变形，也取决于润滑流体在它们之间的流动（“流体动力学”）。在许多有趣的情况下，表面不是光滑的，而是嵌入了图案。虽然触觉工程的目标是产生施加在人类手指长度尺度上的力，但与非常薄的润滑层上的流固摩擦相关的EHL力的来源尚未得到很好的理解，这使得重现人类的完整触觉感知成为一项挑战。该项目包括实验和计算机模拟，将确定EHL中发生的各种力，用于定义良好的模型几何，包含触觉应用的基本特征。这项工作的结果将有助于从业者设计更真实地再现触摸感觉的触觉技术。此外，该计划将包括通过互动的公民科学会议，通过科学营参与者的虚拟感知演示，以及为本科生提供触觉应用和软物质的指导，激发公众对流体力学和软物质的兴趣。我们将进行一系列实验，以验证两个表面的剪切、弯曲和压缩被不同空间维度的模式解耦的中心假设。提出的研究将解决EHL摩擦学中的三个突出问题：1)是否有可能使用表面图案来感知复杂的流变学？2)能否在滑动过程中测量软摩擦副的膜厚？3)图案的弯曲如何影响薄膜厚度？实验将被设计来表征有图案的软材料（如弹性体和水凝胶）的摩擦。摩擦流变仪和触觉装置将用于将摩擦学与人手测量的力和扭矩相关联。润滑流体力学和直接可视化将用于模拟摩擦副之间的膜厚度。滑动方向、弯曲和表面形貌对流体流动剖面的影响将采用实验、标度理论和计算流体动力学模拟相结合的方法进行研究。非牛顿流体的本构模型将用于计算应力张量并与实验数据拟合。这些研究目的将为涉及液体的触觉工程提供分析基础。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Haptic technology creates the perception and experience of touch by applying forces to a user. It is used commonly in applications such as remote surgery and robotics. In some applications, the forces are generated as two surfaces slide over each other, lubricated by a thin film of liquid between the surfaces. This CAREER award focuses on elastohydrodynamic lubrication (EHL), which refers to the special case where the two surfaces are deformable (“elasto”) and the forces on them depend both on their deformation and the flow (“hydrodynamic”) of lubricating fluid between them. In many cases of interest, the surfaces are not smooth, but, instead, have patterns embedded in them. Although the goal of haptic engineering is to produce forces exerted on the length scale of human fingers, the origin of the EHL forces associated with fluid-solid friction on very thin lubricating layers is not well understood, which makes it a challenge to recapitulate the full haptic perception for humans. This project comprises experiments and computer simulations that will determine the various forces that occur in EHL for well-defined model geometries that contain the essential features of haptic applications. The results of the work will aid practitioners in the design of haptic technology that more realistically reproduces sensations of touch. In addition, the project will include activities to stimulate interest in fluid mechanics and soft matter among the public through interactive citizen science sessions, through virtual perception demonstrations for science camp participants, and through instruction in haptic applications and soft matter for undergraduates.A set of experiments will be conducted to test the central hypothesis that the shear, bending, and compression of two surfaces are decoupled by patterns with different spatial dimensions. The proposed research will address three outstanding questions in EHL tribology: 1) Is it possible to sense complex rheology using surface patterns? 2) Is it possible to measure film thickness in soft tribopairs during sliding? 3) How does the bending of patterns influence film thickness? Experiments will be designed to characterize the friction of patterned soft materials such as elastomers and hydrogels. Tribo-rheometry and a haptic device will be used to correlate tribology to forces and torques measured with human hands. Lubrication hydrodynamics and direct visualization will be used to model the film thickness between tribopairs. The effects of sliding orientation, bending, and surface topography on fluid flow profiles will be investigated using a combination of experiments, scaling theory, and computational fluid dynamics simulations. Constitutive models for non-Newtonian fluids will be used to compute the stress tensor and fitted to the experimental data. These research aims will provide the analytical foundation for haptic engineering involving liquids.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.