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中。在某些应用中，力是在两个表面相互滑动时产生的，表面之间由一层薄薄的液体润滑。这一职业奖的重点是弹性流体动力润滑(EHL)，它指的是两个表面是可变形的(“弹性”)，作用在两个表面上的力取决于它们的变形和它们之间的润滑液流动(“流体动力”)。在许多令人感兴趣的情况下，表面并不光滑，而是嵌入了图案。虽然触觉工程学的目标是产生在人类手指长度尺度上施加的力，但与非常薄的润滑层上的流固摩擦相关的弹流体力的来源尚不清楚，这使得概括人类的完整触觉感知成为一个挑战。该项目包括实验和计算机模拟，将确定弹流润滑中发生的各种力，以确定包含触觉应用基本特征的定义良好的模型几何形状。这项工作的结果将有助于实践者设计更逼真地再现触觉的触觉技术。此外，该项目将包括通过公民科学互动会议、科学营参与者的虚拟感知演示以及本科生的触觉应用和软物质教学来激发公众对流体力学和软物质的兴趣的活动。将进行一系列实验，以验证两个表面的剪切、弯曲和压缩通过不同空间维度的图案分离的中心假设。这项拟议的研究将解决弹流润滑摩擦学中的三个悬而未决的问题：1)是否有可能使用表面图案来检测复杂的流变性？2)是否可能测量滑动过程中软摩擦副的膜厚？3)图案的弯曲如何影响膜厚度？将设计实验来表征弹性体和水凝胶等有图案的软材料的摩擦特性。摩擦流变仪和触觉设备将被用来将摩擦学与用手测量的力和扭矩联系起来。润滑流体力学和直接可视化将被用来模拟摩擦间的油膜厚度。采用实验、标度理论和计算流体力学模拟相结合的方法，研究滑动方向、弯曲和表面地形对流体流动剖面的影响。非牛顿流体的本构模型将用于计算应力张量，并与实验数据进行拟合。这些研究目标将为涉及液体的触觉工程提供分析基础。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。

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.