Introduction to Wear
Plastic deformation at the interface often leads to
wear, i.e., deformation induced wear.
Wear can also be caused by chemical processes.
There are many different kinds of wear mechanisms
We have to analyze these wear mechanisms using
mechanics, thermodynamics, etc. Tribology is a
multi-disciplinary subject.
1
Wear Mechanisms
Classification Wear Mechanisms Wear
coefficient
K (range)
Wear dominated by
mechanical Behavior
of Materials
1. Asperity deformation and removal
2. Wear caus ed by plowing
3. Delamination wear
4. Adhesive wear
5. Abrasive wear
6. Fretting wear
7. Wear by solid pa rticle impingement
10
-4
10
-4
10
-4
10
-4
10
-2
to 10
-1
10
-6
to 10
-4
Wear dominated by
chemical behavior of
1. Solut ion wear
2. Oxidat ion wear
materials 3. Diffusion wear
4. Wear by melting of the surface layer
5. Adhesive wear at high temperatu res
2
Wear Coefficient
Definition of Wear Coefficient K
K is dimensionless..
K=
(Wear volume) (Hardness)
(Normal load) (Sliding distance)
=
3VH
NS
3
4
Wear of metals
Consider the case of two metal disks sliding
against each other. Which metal will wear
faster among the following pairs?
1. AISI 1020 steel against AISI 1020 steel
2. OFHC copper against OFHC copper
3. OFHC copper against AISI 1020 steel
4. Carbon/carbon composite and OFHC copper
Sliding Wear at Low Speeds
Wear by Asperity Removal
Initial surface asperities
Smooth/Rough transition during steady state wear
Particles are expected to be small
5
Wear by Asperity Removal
1020 steel disk sliding against 52100 steel pin
(normal load 0.3 kg)
Graph removed for copyright reasons.
See Figure 5.1 in [Suh 1986]: Suh, N. P. Tribophysics. Englewood Cliffs NJ:
Prentice-Hall, 1986. ISBN: 0139309837.
6
Wear by Asperity Removal
1020 steel disk sliding against 52100 steel pin
(normal load 0.0.075 kg)
Graph removed for copyright reasons.
See Figure 5.2 in [Suh 1986].
7
Plastic deformation of original asperities for 1018 steel
(a) 2 mm CLSA, normal = 0.91 kg (After 10 passes)
(b) 3.3 mm CLA, normal load of 0.35 kg after 0.25 m of sliding
(Testing done in argon at 1.8 m/min.)
Photos removed for copyright reasons.
See Figure 5.3 in [Suh 1986].
8
Sliding Wear at Low Speeds
Wear by Plowing
Formation of grooves and furrows
Repeated deformation of the furrows
Removal of particles
Expected to be thin and small
9
Plowing at Low Sliding Speeds
Figure by MIT OCW. After Suh, N. P., and H. C. Sin. "The Genesis of Friction." Wear 69 (1981): 91-114.
10
Groove
Schematic illustration of wear particle formation due to plowing.
(A) Ridges formed along the sides of the plowed grooves. (B) Flattened ridges.
Wear particle associated
with plowing
(A)
(B)
Sliding Wear at Low Speeds
Delamination Wear
Subsurface crack nucleation and propagation
Basic steps of delamination wear
Plastic deformation of the surface layer
Subsurface crack nucleation
Subsurface crack propagation
Creation of loose wear sheets
Large particles -- thickness > 1 m, length~10 to 100
m
11
Deformation of the Surface Layer
Experimental Results: (a) copper, (b) 1020 steel
Graphs removed for copyright reasons.
12
Deformation of the Surface Layer
Analytical Results
0.1
0.3
0.5
0.75
R
e
s
i
d
u
a
l
s
h
e
a
r
s
t
r
a
i
n
p
e
r
p
a
s
s
,
x
z
/
(
p
0
/
G
)
1.0
0.2
0.4
=0.25
1.0
2.0
Depth below surface, z / a
13
Annealed iron with 1.3% Mo
Crack Nucleation -- Experimental Observation
Photos removed for copyright reasons.
See Figure 4.33 in [Suh 1986].
14
Subsurface Cracks (annealed 1020 steel)
Photos removed for copyright reasons.
See Figure 4.34 in [Suh 1986].
15
Precipitation Hardened Cu-0.81 at% Cr alloy
(a) after 5 min (b) 10,000 min of aging
Photos removed for copyright reasons.
See Figure 4.35 in [Suh 1986].
16
Subsurface deformation, void elongation, and
crack formation in steel:
(a) doped 1020 steel, (b) commercial 1020 steel
Photos removed for copyright reasons.
See Figure 5.5 in [Suh 1986].
17
Wear sheet formation in iron solid solution.
The sliding direction is always from right left since the only crack tip behind the
direction 70 degrees away from the surface.
slider can be subjected to tensile stress field which propagates the crack along the
Photos removed for copyright reasons.
See Figure 5.6 in [Suh 1986].
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