Stick-slip phenomenon

The stick -slip effect (of English. Stick, adhere ' and slip, slide ') or stick-slip refers to the stick-slip relative motion of solid bodies. Well-known examples are creaking doors and rattling wipers.

Cause

The effect may occur when the stiction is substantially greater than the sliding friction. This practice coupled damped surface parts of a rapid movement sequence from sticking, clamping, cutting and sliding. The effect disappears when the friction partners are completely separated by the lubricant ( hydrodynamic sliding friction ).

Mechanism

V is a linear drive ( crank threaded spindle ) R symbolizes a spring constant and M is the mass located on a plate.

The drive V causes the spring R is stretched until the spring force exceeds the static friction force of mass M on the plate and this set in motion. Depending on the speed decreases the coefficient of friction, see Stribeck curve. The speed of the mass soon exceeds the speed of the drive, making the spring relaxes. The inertia of the mass, the mass moves a bit beyond the point at which the spring force is equal to the sliding friction force. After the stopping of the drive obtained in this first piece, and then increases again, the spring tension to the friction limit.

Variation

When plate tectonics relatively short gliding phases are ( the earthquake ) separated by long pauses, because the friction in relation to the stiffness of the spring is large and the drive slowly.

In a string instrument, the friction is small and the spatially distributed mass and spring - the string is both at once - able to vibrate at its natural frequency. A clean sound is produced when the sliding phase is relatively long.

Leading to the instability effect is enhanced if the deformation during tightening of the spring to each other, the surfaces rubbing against each other dynamically pressed, the relaxation, however, decreases the pressure. Example is pushing the fork on the plate.

When drawer effect dominates the influence of the geometry. In its pure form, it has nothing to do with stick-slip effect.

Effects and countermeasures

The stick -slip effect is often undesirable in technical applications. It generates noise and structure-borne noise, which is often perceived as unpleasant, see Noise, Vibration, Harshness, and can lead to increased wear and fatigue.

Countermeasures include the reduction of the difference between sliding and static friction, often by reducing the friction in total, such as lubrication, increasing the stiffness of the drive or the body itself, reducing the masses involved, greater attenuation and an instability -reducing geometry.