Fretting wear is a type of wear that is caused due to many cycles of the short amplitude reciprocating sliding movement at the interface of the material. The fretting wear causes severe damage causing material disintegration and surface fatigue. The wear mechanism is unique which is neglected mostly. In case of significantly fewer sliding conditions the wear is comparatively less, however, at a certain point, the sliding is sufficient to affect the microscopic changes on the surface due to changes in normal and tangential loads, these changes cause fretting wear . The schematic figure of fretting wear and the stress distribution in the interface is shown in the Fig- 1.
Fig-1 The micrograph of the fretting wear on Ti-Al-V material .
Mechanism of fretting wear:
The fretting wear is mainly because of the repeated cyclic failure on the surface when the surface is at reciprocating sliding conditions. The mechanism of fretting on a surface can be explained by three steps.
- Step-1 The initial stage of the surface fretting occurs at the asperity levels. This is supported by the oxidation and the adhesion at the surface where the disintegration of the material occurs mainly at the extended asperities on the surface.
- Step-2 The second stage of the fretting wear is by oxidation generating the wear debris, however the gap between the interface is less which does not let the debris to escape.
- Step-3 The third stage of the fretting wear is severe which is caused due to the initiation of the cracks at the edges of the loaded area. These stresses are due to the repeated loading which further creates the fretting fatigue.
The variation in the fretting wear mechanism can also depend on the type of contact, the Fig- 2, shows the fretting wear for different loading conditions. The distribution of the forces on the surface of the materials at different loading conditions can also be seen in the Fig-2.
Fig-2 The fretting wear mechanism for different loading conditions 
The characteristics of the fretting wear:
The fretting wear is characterised by various factors influencing the material disintegration and the severe fretting fatigue on the surface. The factors such as the slip amplitude, contact load and frequency at the interface are the most vital factors that would affect the wear rate in the fretting conditions. This factors are discussed individually in this section.
- Slip amplitude: The variations in the slip amplitude determines the fretting wear rate on the material surface. If the slip is lower then this would cause the nucleation and the crack initiation at the surface undetected. If the slip amplitudes are increased then this causes the effects similar to the direct abrasion and the fretting wear rates are increased. The fretting rate v/s slip amplitude of the mild-steel interface with duralumin and mild-steel are shown in the Fig- 3.
Fig-3 The fretting rate v/s slip amplitude 
- Contact load: The contact load on a material interface plays an important role in affecting any kind of wears, in case of fretting wear it is believed that the contact wear would normalise the fretting wear without increasing it further. But it is known that when the contact load is increased then the contact area at the interface is increased which causes the increase in the fretting wear. This effect is shown in the Fig- 4.
Fig-4 The weight loss v/s the unit load 
- Frequency: Frequency is another factor that is one of the influencing factors affecting the fretting wear rate. However the frequency variation mainly depends on the contact geometry at the interface. If the interface is in non conformal contacts then the increase in frequency increases the fretting wear directly. This effect of variation of fretting rate with frequency is shown in the Fig- 5.
Fig-5 Effect of Frequency on Fretting Damage of Mild Steel 
Types of fretting wear:
The fretting wear can be differentiated by the type of effect that has caused the material disintegration on the surface of the material. Based on this it can be differentiated into two types which is the corrosion fretting wear and fatigue fretting wear.
- Corrosion fretting wear: This is one of the most common type of the fretting wear, the corrosion is caused at the surface during the fretting wear because of favourable conditions. During fretting the ruptured material gets oxidised on the surface by reacting with the atmospheric air. This depends on the type of material in contact and since the disintegrated materials are trapped at the contact interface this cycle repeats. The corrosion fretting is shown in the Fig- 6.
Fig-6 The fretting corrosion on the material 
- Fatigue fretting wear: The surfaces at fretting are caused due to the cyclic friction stresses on the surface which causes the fatigue on the surface. This frictional stresses are maximum at the surface which decreases inside the material therefore the fatigue is high on the surface of the material. The initiation of the cracks takes place on the surface and extends across the material causing the failure. The fatigue fretting is shown in the Fig- 7.
Fig-7 The fretting fatigue on the material 
Fretting wear research:
The researchers have studied the fretting wear on various aspects such as the mechanisms of the fretting, the formation of the wear debris, the simulation studies on predicting the fretting wear etc. M. Varenberg et.al., studied the role of wear debris in fretting wear by texturing the surface of materials which provided the path for the debris to escape from the contact region. The presence of wear debris at the contact helps in reducing if the mechanism is adhesive wear and it harms the surface when the mechanism is abrasive wear . In a study based on predicting the fretting wear using the finite element simulation, I.R. McColl et.al., showed the wear simulation technique is incremental in nature and it can be optimised by altering the mech size .
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I am currently working as a Postgraduate Researcher at the University of Leeds. Previously I completed my master's under the prestigious Erasmus Mundus joint master's degree program (Master's in Tribology). I have also completed my bachelor's in Mechanical engineering from VTU, Belgaum, India. I am working as the social media manager for Tribnet and also I have my youtube channel Tribo Geek.