Abstract
The sliding of a solid object on a solid substrate requires a shear force that is larger than the maximum static friction force. It is commonly believed that the maximum static friction force is proportional to the loading force and does not depend on the apparent contact area. The ratio of the maximum static friction force to the loading force is called the static friction coefficient µM, which is considered to be a constant. Here, we conduct experiments demonstrating that the static friction force of a slider on a substrate follows a novel friction law under certain conditions. The magnitude of µM decreases as the loading force increases or as the apparent contact area decreases. This behavior is caused by the slip of local precursors before the onset of bulk sliding and is consistent with recent theory. The results of this study will develop novel methods for static friction control.
Highlights
The sliding of a solid object on a solid substrate requires a shear force that is larger than the maximum static friction force
We experimentally investigate the precursor dynamics and the macroscopic static friction coefficient of a PMMA slider loaded on a PMMA base block using the transmission of a laser sheet
Prior to the large drop in the shear force corresponding to the onset of bulk sliding, there is a sequence of small drops, which are shown by black arrows
Summary
The sliding of a solid object on a solid substrate requires a shear force that is larger than the maximum static friction force. It is commonly believed that the maximum static friction force is proportional to the loading force and does not depend on the apparent contact area. The magnitude of mM decreases as the loading force increases or as the apparent contact area decreases This behavior is caused by the slip of local precursors before the onset of bulk sliding and is consistent with recent theory. When Amontons’ law holds, this ratio is a constant that does not depend on the loading force or the apparent contact area. The friction force is proportional to the loading force, does not depend on the apparent contact area, and Amontons’ law holds.
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