CAREER: Elastohydrodynamic lubrication of soft patterned interfaces

触觉技术通过向用户施加力来创建触摸的感知和体验。 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产生力，由表面之间的液体薄膜润滑。 这个CAREER奖项专注于弹性流体动力润滑（EHL），这是指两个表面可变形（“弹性”）的特殊情况，它们上的力取决于它们的变形和它们之间的润滑流体的流动（“流体动力”）。 在许多感兴趣的情况下，表面并不光滑，而是具有嵌入其中的图案。 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体-固体摩擦相关的EHL力的起源还没有很好地理解，这使得再现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，将确定在弹性流体动力学中发生的各种力，用于包含触觉应用的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触觉技术，更逼真地再现触觉。 此外，该项目将包括通过互动公民科学会议，通过科学营参与者的虚拟感知演示，以及通过本科生的触觉应用和软物质教学，激发公众对流体力学和软物质的兴趣的活动。并且两个表面的压缩通过具有不同空间维度的图案被解耦。这项研究将解决弹流摩擦学中的三个突出问题：1）是否有可能使用表面图案感测复杂的流变学？2)在滑动过程中，是否可以测量软摩擦副中的油膜厚度？3)图案的弯曲如何影响膜厚？实验将被设计为表征图案化的软材料，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。润滑流体动力学和直接可视化将被用来模拟摩擦对之间的膜厚度。滑动方向，弯曲和表面形貌对流体流动剖面的影响将使用实验，缩放理论和计算流体动力学模拟相结合的研究。将使用非牛顿流体的本构模型来计算应力张量，并将其拟合到实验数据。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.