Stick-slip effect (from English stick ' to stick' and slip ' to slide') or also stick-slip effect or (self-excited) frictional vibration describes the jerk- sliding of solid bodies moving against one another . Well-known examples are the sound generation of stringed instruments , the chirping of insects, the squeaking of wall panels , creaking doors, screeching brakes or tires, rattling wiper and a latex - balloon rubbelnde or the rim of a drinking glass in vibration versetzende, wet fingertip (see glass harp ).
- for the respective force
- for the respective coefficient of friction .
At the same time, dampened, coupled parts of the surface exert a rapid sequence of movements: sticking, tensioning, separating and sliding ( see below: mechanism ).
The drive V leads to the fact that the spring R is tensioned until the spring force exceeds the static friction force of the mass M on the plate (disconnect as soon as ) and sets it in motion (sliding down for as long ).
Soon the speed of the mass exceeds the speed of the drive, whereby the spring relaxes again and the spring force decreases. Due to its inertia , the mass moves a little beyond the point at which the spring force is equal to the sliding friction force, and then stops (sticking as soon as ). After stopping, the drive first catches up this piece and then increases the spring tension again up to the static friction limit (tensioning, as long as ). Then the cycle starts all over again.
Range of variation
With a string instrument , the friction is small and the spatially distributed mass and spring - the string is both at the same time - is capable of vibrations at their natural frequency . A clean sound is created when the glide phase is relatively long.
The instability leading to the effect is increased when the deformation dynamically presses the surfaces rubbing against one another when the spring is tensioned, while the relaxation reduces the pressure. An example is pushing the fork over the plate.
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 tear and material fatigue. He can also perform the smallest movements, such. B. in precision machine tools , completely prevent.
- reducing the difference between sliding and static friction, often by reducing the overall friction, such as through lubrication
- an increase in the rigidity of the drive or the body itself
- Reduction of the masses involved
- greater attenuation
- a geometry that reduces instability.
- FP Bowden, D. Tabor: The Friction and Lubrication of Solids , Oxford University Press, 2001, 424 p, ISBN 0-19-850777-1 .
- NM Kinkaid, OM O'Reilly, P. Papaclopoulos: Automotive disc brake squeal - Journal of sound and vibration, 2003, v. 267, Issue 1, pp. 105-166.
- K. Magnus, K. Popp: Vibrations: an introduction to physical principles and the theoretical treatment of vibration problems . Stuttgart, Teubner, 2005, 400 pp.
- Bo NJ Persson: Sliding Friction. Physical Principles and Applications . Springer, 2002, ISBN 3-540-67192-7 .
- Valentin L. Popov: Contact Mechanics and Friction. A text and application book from nanotribology to numerical simulation , Springer-Verlag, 2009, 328 p., ISBN 978-3-540-88836-9 .
- Ernest Rabinowicz: Friction and Wear of Materials . Wiley-Interscience, 1995, ISBN 0-471-83084-4 .