Fretting is caused by small, repetitive oscillatory motions between two contacting surfaces under load. Several factors contribute to the occurrence of fretting:
- Relative Motion: Micro-movements or vibrations between contact surfaces, typically in the range of micrometers to millimeters, lead to repeated contact and separation.
- High Contact Pressure: Increased contact pressure intensifies the frictional forces and wear between the surfaces.
- Environmental Conditions: Presence of oxygen and humidity can exacerbate fretting by forming abrasive oxide particles (fretting corrosion).
- Material Properties: Softer materials are more susceptible to fretting wear, and the presence of hard particles can act as abrasives.
- Surface Roughness: Rough surfaces increase the likelihood of asperity interactions, leading to higher wear rates.
- Cyclic Loading: Components subjected to cyclic or oscillatory loads, such as vibrations or thermal cycling, are more prone to fretting.
Common Examples:
- Bolted Joints: Slight movements in bolted joints due to dynamic loading.
- Bearings: Micro-movements between bearing surfaces under load.
- Electrical Contacts: Vibrations in electrical connectors leading to fretting corrosion.
Preventive measures include optimizing material selection, surface treatments, lubrication, and design modifications to minimize relative motion and contact pressure.