Highly loaded lubricated contacts may present a friction plateau on which the friction force becomes independent from the sliding velocity. Although this phenomenon has been known for a long time, its physical origin remains poorly known. The present paper aims at giving further insight on the physical mechanisms triggering the friction plateau. The study specifically focuses on the influence of pressure on the physical state of the lubricant. An uncoupled experimental approach (rheology, tribology, spectrometry) has been conducted on a model lubricant. The lubricant behavior has been probed both at rest by Brillouin light scattering spectroscopy and dynamically under stationary conditions in a lubricated contact. The first experimental approach led to evidence a transition pressure associated with the lubricant glass transition, which has then been correlated to the lubricant macroscopic response in friction. We show that the onset of the plateau behavior occurs for Hertzian pressures close to the glass transition pressure, corresponding to a very small fraction of lubricant in a “nominal glassy state” within the contact.

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关于高负载摩擦接触中相变的影响

高负载的润滑触点可能会出现摩擦平稳状态，在该摩擦状态下摩擦力变得与滑动速度无关。尽管这种现象早已为人所知，但其物理起源仍然鲜为人知。本文旨在进一步揭示引发摩擦平稳的物理机制。该研究特别关注压力对润滑剂物理状态的影响。已对模型润滑剂进行了非耦合实验方法（流变，摩擦学，光谱法）。既可以通过布里渊光散射光谱在静止状态下，也可以在润滑条件下在静止条件下动态地研究润滑剂的行为。第一种实验方法得出的证据是与润滑剂玻璃化转变相关的转变压力，然后将其与润滑剂的宏观摩擦响应相关联。我们表明，平台行为的发生是在接近玻璃化转变压力的赫兹压力下发生的，对应于接触中“名义玻璃态”的润滑剂的极小部分。