LEAP-HI/GOALI: Meso-Scale Mechanisms for Friction in Structured Soft Materials: Elastic Hysteresis and Dislocation Arrays

控制软材料表面的摩擦往往是至关重要的。例如，橡胶轮胎与路面之间的高滑动摩擦力可以实现快速刹车。在生物学的背景下，有时希望最小化摩擦，例如隐形眼镜和眼睛之间的摩擦。在其他情况下，需要很高的摩擦力，例如，当设计用于抓取物体的软机器人的手时。这一领先的美国繁荣、健康和基础设施工程(LEAP-HI)学术联络机会赠款(GOALI)项目将开发两种新机制，以改善软材料的摩擦，其基础是近表面结构的生物灵感设计。这项研究将由一个由来自利哈伊大学、康奈尔大学和美国米其林大学的成员组成的研究团队进行，并将其应用于轮胎。轮胎生产是美国工业概况的主要组成部分。数十家工厂每年生产超过1.5亿辆轿车、卡车、公交车和其他轮胎。这项研究将支持提高车辆安全性和帮助美国保持其领先轮胎制造商地位所需的创新。摩擦作为一种界面性质通常被理解为由界面分子间的相互作用所控制，与宏观长度尺度上的整体变形和能量耗散相耦合，例如通过粘弹性。最近在生物启发和仿生材料方面的工作表明，如何在分子(纳米)和连续体(毫米或更大)尺度之间的介观尺度(微米)上适当设计的近表面结构可以用来强烈地调节表面特性，如附着力。这为软材料界面的设计开辟了一种新的范式和机制，但在摩擦控制方面却鲜有人利用。其中一些机制是分子水平现象的中尺度版本，这些现象是首先在表面之间如何产生摩擦这一基本问题的基础。该项目的目标是研究和开发摩擦能量损失背后的两个中观机制，a)中观位错阵列：其中界面包含周期性的特征阵列，通过产生中观界面位错来适应取向偏差，可用于控制摩擦；b)弹性滞后：其中弹性模数的周期性近表面图案可用于建立周期性阻力，进而建立机械不稳定性和滞后，从而产生巨大的摩擦增强。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。

It is often crucial to control friction of soft material surfaces. For example, high sliding friction between rubber tires and the road surface enables quick braking. In the biological context, it is sometimes desirable to minimize friction, as between a contact lens and the eye. On other occasions high friction is needed, for example when designing hands of a soft robot for grasping objects. This Leading Engineering for America's Prosperity, Health, and Infrastructure (LEAP-HI) Grant Opportunity for Academic Liaison (GOALI) project will develop two novel mechanisms to improve friction of soft materials based on bio-inspired design of near-surface structures. The research will be carried out by a research team with members from Lehigh and Cornell Universities, and Michelin USA, with application to tires. Tire production is a major component of the US industrial profile. Dozens of plants produce over 150 million car, truck, bus and other tires per year. This research will support innovation that is needed to both increase vehicle safety and help the USA to maintain its position as a leading tire manufacturer. Friction as an interfacial property is usually understood to be governed by interfacial intermolecular interactions, coupled to bulk deformation and energy dissipation at macroscopic length scales, for example by viscoelasticity. Recent work on bioinspired and biomimetic materials has shown how appropriately designed near-surface structures at a meso-scale (microns) intermediate between the molecular (nm) and continuum scales (mm and larger) can be used to strongly modulate surface properties like adhesion. This has opened up a new paradigm and mechanisms for design of soft material interfaces, which however has been little exploited for control of friction. Some of these mechanisms are meso-scale versions of molecular level phenomena that underlie the fundamental question of how friction arises between surfaces in the first place. The goal of this project is to study and develop two meso-scale mechanisms underlying frictional energy loss, a) Meso-Scale Dislocation Arrays: in which the interface comprises a periodic array of features that accommodate misorientation by generating meso-scale interfacial dislocations, which can be used to control friction, and b) Elastic Hysteresis: in which periodic near-surface patterning of elastic modulus can be used to set up a periodic resisting force that, in turn, sets up mechanical instabilities and hysteresis to yield large friction enhancement.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.