A presentation on the fundamentals of Fretting wear which is a major topic of Tribology.

1. FUNDAMENTALS OF
FRETTING WEAR
CR 4102 Assignment by Rishab Agarwal
Course Instructor - Prof. Debashish Sarkar
Department- Ceramic Engineering
NIT Rourkela
Roll No.-118CR0671

2. OUTLINE :-
● Fretting Definition and Wear.
● Fretting Wear/ Vibratonal Wear.
● Stages of Vibrational Wear.
● Characteristics of Fretting Wear.

3. Fretting Definition :-
 Fretting wear is surface degradation caused by periodic motion (vibrational
tangential displacement) of low amplitude between two contacting surfaces. The
lubricant is forced out from the contact points, resulting in metal-to-metal
contact.
 Since the contact region cannot be re-lubricated due to the low amplitude motion,
significant localised wear might result. Two-body erosion , adhesion, and/or
fretting fatigue (a type of surface fatigue) wear are all accelerated by this type of
wear.

4. Fretting Wear or Vibrational Wear :-
 Fretting wear is a surface-to-surface wear that is influenced by a variety of
circumstances.
 Fretting causes fatigue fractures in shafts and other highly strained components,
which can lead to failure.
 When fretting wear occurs in a corrosive environment, both the rubbing-off of
oxide layers and the enhanced abrasiveness of the tougher oxidised wear debris
accelerate wear significantly. The process is known as fretting corrosion when
corrosion activity is clearly visible, as shown by the colour of the debris particles.

5. There is no macroscopic
slippage in fretting. In the
centre area of a contact (for a
ball on flat case), when the
normal pressure is strong, the
surfaces are theoretically in
static contact. Microslip occurs
near the perimeter, when
pressure is minimal and
tangential traction is adequate
to overcome static friction.

6. STAGES OF FRETTING WEAR :-
First Stage -
 The metallic contact between two surfaces is the initial step. Surfaces must be in close proximity to
one another. The contact happens in a few locations known as asperities (surface protrusions).
Fretting may be achieved with relatively tiny movements of 10–8 cm.
Adhesion :
 In order for the metals to be in physical contact with each other, there must be no protective oxide
layer. The breakdown of the protective layer is essential for the onset of fretting. The asperities are
bonded together at adhesion sites created by the relative slip of the surfaces. Fretting may occur at
amplitude as small as 10−8 cm. The coefficient of friction can increase from 0.2 to 0.55 within 20
cycles.

7. Protective layers on both metals in close contact will be disturbed if they are
identical; however, if one metal is soft and the other is hard, the layer on the soft
metal will be destroyed while the layer on the hard metal will not be damaged.

8. 2nd Stage -
 The oxidation and debris production step comes next. It's possible that oxidation will happen
before or after debris clearance, with each phase being governed by the conditions that cause
fretting. The debris is formed in either scenario as a result of oxidation.
Generation of Debris :
 Debris is the material that is removed from the metal surface as a result of fretting. The
majority of the debris produced by low carbon steel is ferric oxide, Fe2O3.
 In the case of non-ferrous metals, the waste may also comprise unoxidized particles. The
composition of the debris varies depending on the metal.
 The rate of wear is lowered and fretting is lessened when the oxide particles become lodged
in the softer material. Because loose particles accelerate wear, fretting occurs at a rapid pace.

9. Crack Propagation :-
 Cracks develop in the fretting area in a direction perpendicular to the applied load. Because
the impact of stress on a fretted surface only reaches to a shallow depth, some fissures may
not spread at all at low stresses. The presence of favourable compressive stresses either
restricts or prevents crack propagation.
 The fretting fatigue stage is when a crack begins to form. Crack propagation at greater
strains is important in practise because it can lead to component failure, such as shafts and
axles. The crack begins at the fretting zone's edge and spreads outward. If a corrosion
medium comes into contact with the fracture during propagation, corrosion fatigue plays a
role in crack propagation.
 The crack propagates as a fatigue crack outside the sphere of the surface contact stress, and
when it fractures, it leaves a distinctive slip.

11. Characteristics of Fretting Wear :-
 A mechanically loaded contact exposed to a tiny oscillatory motion is the most
important element in fretting wear. The amplitude of oscillation determines the wear
coefficient.
 Nucleation and propagation of fractures that lead to wear debris are too small to detect
at slips smaller than 100 micrometres. This low wear rate is apparently caused by the
wear debris rolling at that degree of oscillation.
 The gross wear rate is caused by direct abrasion of the contact by hard particles (oxide
particles) at high amplitudes. The fretting wear coefficient is nearly identical to that of
unidirectional wear at large amplitudes of oscillation.

13. With the number of cycles, the level of fretting increases. With the number of cycles, the look of the
surface varies. According to reports, there is an incubation phase during which the harm is minimal.
This is followed by a steady-state stage in which the fretting rate remains relatively constant. The
rate of fretting wear is enhanced in the last stage.

14. Fretting wear is usually affected by
changes in the normal load. Although
many equipment users believe that
greater normal loads will minimise
fretting by dampening vibration, the
increased contact area causes more
surface interaction, which tends to
balance this impact. As a result, increased
load or unit pressures causes greater wear
rates.

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