This work elucidates friction in Poly-Ether-Ether-Ketone (PEEK) sliding contacts through multiscale simulations. At the nanoscale, non-reactive classical molecular dynamics (MD) simulations of dry and water-lubricated amorphous PEEK–PEEK interfaces are performed. During a short running-in phase, we observe structural transformations at the sliding interface that result in flattening of the initial nanotopographies accompanied by strong polymer chain alignment in the shearing direction. The MD simulations also reveal a linear pressure – shear stress dependence and large adhesive friction in dry conditions. This dependence, summarized in a nanoscale friction law, is of central importance for our multiscale approach, since it forms a link between MD and elastoplastic contact mechanics calculations. An integration of the nanoscale friction law over the real area of contact yields a macroscopic friction coefficient that allows for a meaningful comparison with measurements from macroscopic tribometer experiments. Severe normal loading conditions result in significant wear and high experimental friction coefficients µ≈0.5–0.7, which are in good agreement with the calculated values from the multiscale approach in dry conditions. For milder experimental loads, our multiscale model suggests that lower friction states with µ≈0.2 originate in the presence of physisorbed molecules (e.g., water), which significantly reduce interfacial adhesion.

Graphical Abstract

中文翻译：

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干聚合物接触的多尺度摩擦模拟：通过分子动力学和接触力学的耦合达到实验长度尺度

这项工作通过多尺度仿真阐明了聚醚醚酮（PEEK）滑动触点中的摩擦。在纳米级，对干燥和水润滑的无定形PEEK-PEEK界面进行非反应性经典分子动力学（MD）模拟。在短暂的磨合阶段，我们观察到滑动界面处的结构转变，导致初始纳米形貌扁平化，并伴随着剪切方向上的强聚合物链排列。MD模拟还揭示了线性压力-剪切应力依赖性以及干燥条件下较大的粘合剂摩擦。以纳米尺度的摩擦定律总结的这种依赖性对于我们的多尺度方法至关重要，因为它在MD和弹塑性接触力学计算之间形成了联系。纳米级摩擦定律在实际接触面积上的积分产生了宏观摩擦系数，可以与宏观摩擦计实验的测量结果进行有意义的比较。严重的正常载荷条件会导致严重的磨损，并且实验摩擦系数µ≈0.5-0.7高，这与干燥条件下多尺度方法的计算值非常吻合。对于较轻的实验负载，我们的多尺度模型表明，μ≈0.2的较低摩擦态源自存在物理吸附的分子（例如水），这大大降低了界面粘附力。严重的正常载荷条件会导致严重的磨损，并且实验摩擦系数µ≈0.5-0.7高，这与干燥条件下多尺度方法的计算值非常吻合。对于较轻的实验负载，我们的多尺度模型表明，μ≈0.2的较低摩擦态源自存在物理吸附的分子（例如水），这大大降低了界面粘附力。严重的正常载荷条件会导致严重的磨损，并且实验摩擦系数µ≈0.5-0.7高，这与干燥条件下多尺度方法的计算值非常吻合。对于较轻的实验负载，我们的多尺度模型表明，μ≈0.2的较低摩擦态源自存在物理吸附的分子（例如水），这大大降低了界面粘附力。

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