Determining Static Friction in Dry Contacts

The current report deals with the issue of static friction, which is the force acting against initiation of relative motion between two surfaces, provided they are not glued together. This report also shows a clear distinction of three different tribo-contacts measured on an Anton Paar MCR Tribometer.

The current report deals with the issue of static friction, which is the force acting against initiation of relative motion between two surfaces, provided they are not glued together. Consider a person sitting on a chair with slightly reclined back. If the static friction between the material of his trousers and the material of the chair is not high enough, the person would simply slide down the seat of the chair. And so is the case between the rubber pads underneath the computer keyboard and the surface of the table it rests on. Imagine how uncomfortable it would be if the keyboard keeps sliding away as we type. In contrast, one would not like to have a higher value of static friction between a mouse and its mousepad. Similarly, it is static frictional resistance that allows us to grip and lift objects. There are also other applications where the magnitude of static friction could determine success or failure of the system. For instance, the efficiency and functioning of a conveyer belt would be at stake if the static friction between its surface and the object it transport is too low and the latter begins to slide on the former. Another example is the static friction between tires and the road. In this case, static friction inhibits sliding of the tire on the road, and thereby facilitating rotary motion of the wheel. Accurate determination of limiting friction or the breakaway force of a given system is quite a challenging task. It involves highly precise measurement of forces and displacements with nanoscale resolution. Herein, the measuring equipment should be capable of precisely controlling the movement of one body over the other in sub-micron level, and at the same time as it involves precise measurement of forces and displacements in the nano- to micro-scale. Tribological measurement systems from Anton-Paar offer all the above features. In the following sections, a simple yet effective method to determine the break-away torque of select systems has been presented.

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