this presentation on " SURFACE FATIGUE " -About the surface fatigue -it is in general -fatigue wear in sliding contact -It's in impact contact

1. SONAM PALJOR PES1201702403
DEPARTMENT OF MECHANICAL ENGINEERING
Presentation
On
SURFACE FATIGUE

2. SURFACE FATIGUE
 Surface : The outside part or uppermost layer of something.
 Fatigue : Type of contact/movement/loading
 Surface fatigue is a failure that occurs due to cyclic loading.
 It is different from other type of fatigue failures because it is
found solely on the top layer of a material.
 Surface fatigue usually appears in the form of micro cracks on
a material's surface. If left unchecked, the failure could spread
past the surface of the material.

3. SURFACE FATIGUE IN GENERAL
 The key to surface fatigue is in the contact type and the stresses
it creates.
 Maximum shear stresses at contacts lies beneath the surface and
especially peak values can be high in small area contacts
 Still cracks can be initiated from the surface also (surface flaws,
particles etc.)
 Contact shear stresses enables the crack growth
 Material loss mechanisms: spalling or delamination

4. FATIGUE WEAR IN SLIDING CONTACT
 In addition to surface pitting, repeated sliding contact may also cause
horizontal subsurface cracks to grow
 The surface is deformed plastically, but a compressive stresses restrains
crack growth in the surface layer
 Subsurface, where the compressive stress is lower, cracks start to
initiate around discontinuities, such as hard inclusions and voids, or
around dislocation pile-ups

5. FATIGUE WEAR IN SLIDING CONTACT
 The cracks grow horizontally under deformed layer, coalesce and
finally lead to detachment of thin sheets
 This kind of wear is also called as delamination wear
The deformation of surface layer and delamination of the deformed layer

6. SURFACE FATIGUE IN IMPACT CONTACT
 When surface fatigue is active the cracks form like in the case of
sliding contact, but now the hard white layer is the key
 Material removal by delamination (b) or spalling (c)

7. SURFACE FATIGUE IN IMPACT CONTACT
 Due to formation of white layer in impact contact the micro crack
initiation is focused within this work hardened layer and crack
propagation continues by:
Delamination:
crack propagates through weak interface of below white layer
Spalling :
crack propagates parallel to the flow lines in deformation zone

8. Thank you ! ! !