Classical lubrication theory is unable to explain a variety of phenomena and experimental observations involving soft viscoelastic materials, which are ubiquitous and increasingly used in e.g. engineering and biomedical applications. These include unexpected ruptures of the lubricating film and a friction–speed dependence, which cannot be elucidated by means of conventional models, based on time-independent stress–strain constitutive laws for the lubricated solids. A new modeling framework, corroborated through experimental measurements enabled via an interferometric technique, is proposed to address these issues: Solid/fluid interactions are captured thanks to a coupling strategy that makes it possible to study the effect that solid viscoelasticity has on fluid film lubrication. It is shown that a newly defined visco-elasto-hydrodynamic lubrication (VEHL) regime can be experienced depending on the degree of coupling between the fluid flow and the solid hysteretic response. Pressure distributions show a marked asymmetry with a peak at the flow inlet, and correspondingly, the film thickness reveals a pronounced shrinkage at the flow outlet; friction is heavily influenced by the viscoelastic hysteresis which is experienced in addition to the viscous losses. These features show significant differences with respect to the classical elasto-hydrodynamic lubrication (EHL) regime response that would be predicted when solid viscoelasticity is neglected. A simple yet powerful criterion to assess the importance of viscoelastic solid contributions to soft matter lubrication is finally proposed.

中文翻译：

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软质润滑：固体粘弹性是否重要？

经典的润滑理论无法解释涉及软粘弹性材料的各种现象和实验观察，这些现象和现象普遍存在，并越来越多地用于例如工程和生物医学应用中。这些包括润滑膜的意外破裂和摩擦速度依赖性，这是无法通过常规模型基于润滑固体的与时间无关的应力-应变本构律来阐明的。为解决这些问题，提出了一种新的建模框架，该模型通过干涉测量技术支持的实验测量得到了证实：由于采用了耦合策略，因此可以研究固体粘弹性对液膜润滑的影响，从而捕获了固/液相互作用。结果表明，根据流体流动与固体滞后响应之间的耦合程度，可以采用新定义的粘弹性流体动力润滑（VEHL）方案。压力分布显示出明显的不对称性，在流量入口处出现峰值，相应地，薄膜厚度在流量出口处显示出明显的收缩。除粘滞损耗外，摩擦还受到粘弹性滞后的严重影响。这些特征相对于经典的弹性流体动力润滑（EHL）响应而言，表现出显着差异，而当忽略固体粘弹性时，可以预测这些响应。最后提出了一个简单而有效的准则，用以评估粘弹性固体对软物质润滑的重要性。