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Institut for Mekanisk TeknologiDanmarks Tekniske Universitet
Slidmekanismer og slidforebyggelse
Niels Bay
DTU-Mekanik
FMV Temadag om Slid på Metaller
Scandic Hotel, København
15. november 2012.
Institut for Mekanisk TeknologiDanmarks Tekniske Universitet
Mechanisms of wear
Primary mechanisms
1. Adhesive wear
2. Abrasive wear
3. Corrosive wear
4. Fatigue wear
Secondary mechanisms
5. Fretting
6. Erosive wear
7. Cavitation wear
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Institut for Mekanisk TeknologiDanmarks Tekniske Universitet
Adhesive wear
Adhesive wear is due to strong attractive forces appearing when the atoms approach each other.
.
Arises when two rather smooth surfaces slide against each other and particles from one surface are torn out adhering to the other one.
Institut for Mekanisk TeknologiDanmarks Tekniske Universitet
Adhesive wearSize of wear particles
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Institut for Mekanisk TeknologiDanmarks Tekniske Universitet
Abrasive wear
Arises from the cutting action of a hard surfacesliding on a softer material (2-body abrasivewear)
or
when loose debris particles trapped betweenthe sliding surfaces are penetrating the softersurface and scratching a wear groove in the harder one (3-body abrasive wear)
Institut for Mekanisk TeknologiDanmarks Tekniske Universitet
Abrasive wear
Severe journal wear
Severe wear of bronze shaft due to failing soft packing
Severe tearing of bearing surface
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Institut for Mekanisk TeknologiDanmarks Tekniske Universitet
2-body abrasive wear 3-body abrasive wear
Institut for Mekanisk TeknologiDanmarks Tekniske Universitet
Corrosive wear
If sliding did not take place, the corrosiveproducts would form a protective film on the surface impeding further corrosion, but the slidingwears out the corrosive film thus allowing the corrosion to continue.
(Corrosion is the degradation of a surface by chemical reaction with the environment)
Corrosive wear arises when two surfaces slide against each other in a corrosive environment.
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Institut for Mekanisk TeknologiDanmarks Tekniske Universitet
Corrosive wearRemoval of lead phase from lead-bronze slide bearing
Institut for Mekanisk TeknologiDanmarks Tekniske Universitet
Fatigue wear
Arises when a surface is loaded cyclically due to repeated sliding, rolling or impacts.
The repeated loading and unloading causes crack formation in the surface or subsurface and subsequent breaking off fragments from the surface resulting in pit formation.
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Institut for Mekanisk TeknologiDanmarks Tekniske Universitet
Fatigue wear Shear stresses in the subsurface layer
Institut for Mekanisk TeknologiDanmarks Tekniske Universitet
Fatigue wear
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Institut for Mekanisk TeknologiDanmarks Tekniske Universitet
Fretting
Fretting occurs when two surfaces in contact under load and nominally at rest with respect to each other are subjected to slight oscillating tangentialmovement with small amplitude.
Typical examples are vibrations in:
Poorly aligned spline coupling
Loosely bolted machine parts
Riveted joints
Press fits
Surgical implants
Initial adhesive wear forms wear debris which may oxidize to form abrasivewear particles, which cannot readily escape due to close fit of the surface.
Often surprisingly large wear rates.
Institut for Mekanisk TeknologiDanmarks Tekniske Universitet
FrettingScavenge pump failed
by fretting fatigue at centre
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Institut for Mekanisk TeknologiDanmarks Tekniske Universitet
Fretting
Riveted joint
Screw joint
Institut for Mekanisk TeknologiDanmarks Tekniske Universitet
Erosive wear
Damage experienced by a solid body, when a fluid or gas containing solid particles impinges on to the surface of the body.
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Institut for Mekanisk TeknologiDanmarks Tekniske Universitet
Erosive wear
Compressor blade in Ti-alloyErosive wear of leading edgesdue to sand particles
Institut for Mekanisk TeknologiDanmarks Tekniske Universitet
Cavitation wearCavitation wear arises when a solid and a fluid are in relative motion, and bubbles formed in the fluid become unstable and implode against the surface of the solid.
Cavitation wear is closely related to fatigue wear and as such materialswhich are hard and ductile are resistive to cavitation wear.
The implosion creates a chock wave which can tear out particles from the surface.
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Institut for Mekanisk TeknologiDanmarks Tekniske Universitet
Cavitation wearShips propellers, centrifugal pumps
Institut for Mekanisk TeknologiDanmarks Tekniske Universitet
Modelling of adhesive wear
During sliding small asperities may come into contact and during passage there is a small possibility that separation does appear in the original interface.
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Institut for Mekanisk TeknologiDanmarks Tekniske Universitet
Adhesive wearArchards model for adhesive wear
r0 ApP
All contacts assumed to have same size and diameter d. The total number of contacts N :
0
2
r pP
4d
NA
20dpP4
N
Institut for Mekanisk TeknologiDanmarks Tekniske Universitet
Adhesive wearArchards model for adhesive wear
20 dpP4
N
Every contact assumed to exist during a sliding length of d. If N contacts remain under load the number of new formed contacts per unit sliding length is:
dN
n 30 dpP4
n
Total number of contacts
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Institut for Mekanisk TeknologiDanmarks Tekniske Universitet
Adhesive wearArchards model for adhesive wear
)lengthslidingunitpercontacts
formednewofnumbern(dp
P4n
30
vnkdxdV
k: probability of formation a wear fragment
1k0
Fragment shape is assumed to be semi-spherical
12d
nkdxdV 3
12d
dpP4
kdxdV 3
30
0pP
3k
dxdV
0p3xP
kV
v: volume of wear fragment
Institut for Mekanisk TeknologiDanmarks Tekniske Universitet
Archards model for adhesive wearThe dimensionless wear coefficient k
0p3xP
kV
Combinationin dry contact
Wear constant k
Zinc on zinc 16010-3
Low carbon steel on low carbon steel 4510-3
Copper on copper 3210-3
Stainless steel on stainless steel 2110-3
Copper on low carbon steel 1.510-3
Low carbon steel on copper 0.510-3
Bakelite on bakelite 0.0210-3
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Institut for Mekanisk TeknologiDanmarks Tekniske Universitet
Archards model for adhesive wearThe dimensionless wear coefficient k
0p3xP
kV
Surface conditionMaterial combination
Like Unlike
Clean (dry contact) 510-3 210-4
Poor lubrication 210-4 210-4
Average lubrication 210-5 210-5
Excellent lubrication 210-6-10-7 210-6-10-7
Institut for Mekanisk TeknologiDanmarks Tekniske Universitet
Archards model for adhesive wearPrevention of adhesive wear
0p3xP
kV
Small normal pressures
Small sliding lengths
Hard materials
Combine materials with small interaction (small k)
Chose one material to be non-metallic
Chose materials with low mutual adhesion energy
Apply lubrication
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Institut for Mekanisk TeknologiDanmarks Tekniske Universitet
Adhesive wear in spaceProblems with cargo hatch hinges on space shuttle
Adhesive wear in spaceprevented by ion sputtering of MoS2 on clean surfaces
High duty tribo-elements likeballs and gears are Au-plated
Institut for Mekanisk TeknologiDanmarks Tekniske Universitet
Abrasive wearExperimental studies of plowingand cutting mechanisms
Plowing
Cutting
Cutting
T. Abildgaard Petersen, T. Wanheim
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Institut for Mekanisk TeknologiDanmarks Tekniske Universitet
Model for abrasive wear
20r0 d
4pApP
0
2
p
P4d
Projected area of indented cone on plane perpendicular to sliding direction:
4tand
A2
rs
d
p0
P
tan2d
z
Volume removed when sliding the distance dx:
dx4tand
dV2
1
dx
ptanP
0
Institut for Mekanisk TeknologiDanmarks Tekniske Universitet
Model for abrasive wear
d
p0
P
tan2d
zVolume removed when sliding the distance dx:
dxptanP
dV0
1
Summing up for all contact points we get:
dxp
tanPdV
0
or
0ridge p
xPtanV
Assuming that only a fraction β of the load is carried by asperities with cutting action we get:
0wear p
xPtanV
0abrwear p3
xPkV
tan3
kabr
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Institut for Mekanisk TeknologiDanmarks Tekniske Universitet
Model for abrasive wear
0abrwear p3
xPkV
tan3
kabr
2-body abrasive wear: 0.02 < kabr < 0.2
3-body abrasive wear: 0.001 < kabr < 0.01
Experimental investigations confirms the model as regards the influence of the three main parameters P, x and p0
Institut for Mekanisk TeknologiDanmarks Tekniske Universitet
Prevention of abrasive wear
0abrwear p3
xPkV
tan3
kabr
Ensure that one of the materials is harder than the abrasive particles and the other so soft, that it can bury wear particles. Since these have about the same hardness as the harder surface a hardness ratio of minimum 3 is feasible.
Ensure filtering of lubricant
Be careful to avoid formation of large wear particles which are more dangerous than small ones. Avoid fatigue wear particles. Chose materials with good resistance against fatigue.
Apply very flexible materials like rubber as the softer material.
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Institut for Mekanisk TeknologiDanmarks Tekniske Universitet
Prevention of abrasive wear in hot forgingDiminish sliding
0abrwear p3
xPkV
tan3
kabr
Lubricated forging Unlubricated forging
Tool roughness Ra not too small
Institut for Mekanisk TeknologiDanmarks Tekniske Universitet
Abrasive wearMohs hardness scale
1. Talc
2. Gypsum
3. Calcite
4. Fluorite
5. Apatite
6. Felspar
7. Quartz
8. Topaz
9. Corundum
10. Diamond
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Institut for Mekanisk TeknologiDanmarks Tekniske Universitet
Off-line testing of new, environmentally friendly tribo-systems for sheet metal forming
Objective:
• To replace environmentally harmful lubricants such as chlorinated paraffin oils
• Sheet forming of tribologically difficult materials, e.g. AHSS, stainless steel, Al, Ti
Partners:
• Grundfos
• Uddeholm
• SSAB
• Outokumpu Stainless
Institut for Mekanisk TeknologiDanmarks Tekniske Universitet
Deep drawing in progressive tool - Grundfosa. Deep drawingb. 1st redrawingc. 2nd redrawing Tribologically the most severe operationd. Sharp pressing of flange
Step a Step b Step c Step d
Workpiece material: AISI 304
Step c E. Ceron, E. Madsen, N. Bay
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Institut for Mekanisk TeknologiDanmarks Tekniske Universitet
Simulation of deep drawing and 2 redrawings
LS-DYNA 2D implicit model
The blank is transferred from one process to the following updating flow stress and equivalent strain
E. Ceron, N. Bay
Institut for Mekanisk TeknologiDanmarks Tekniske Universitet
Distribution of radial stress in step c
workpiece
die
[MPa]
Maximum contact pressure pmax = 900 MPa
E. Ceron, N. Bay
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Institut for Mekanisk TeknologiDanmarks Tekniske Universitet
Simulation of BUT test
Round pin with radius R = 3,5Maximum contact pressure 360 MPawith maximum back tension 300 MPa
tool strip
MPa
E. Ceron, N. Bay
Institut for Mekanisk TeknologiDanmarks Tekniske Universitet
Distribution of radial stresses in BUT test
Workpiece strip
tool
[MPa]
By modifying the BUT test tool to a 45°contact instead sufficient contact pressure can bereachedMaximum contact pressure pmax = 1000 MPa with back tension 300 MPa
E. Ceron, N. Bay
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Institut for Mekanisk TeknologiDanmarks Tekniske Universitet
BUT
DBT
SRT
E. Ceron, N. Paldan, J. Gregersen, N. Bay
New, universal sheet tribo-tester
Institut for Mekanisk TeknologiDanmarks Tekniske Universitet
Universal sheet tribo-testerAutomatic PLC controlled running of repeated tests
Material feed from coil of more than 1000m
Adjustable sliding lengths, speed, cycle time and total number of strokes
Ensuring appropriate emulation of production conditions withheating and cooling cycle
Easy programming by Labview
E. Ceron, N. Paldan, J. Gregersen, N. Bay
BUT_test_running_detail.avi
BUT_test_running.avi
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Institut for Mekanisk TeknologiDanmarks Tekniske Universitet
Second screening test campaign
DP 800; Shell Ensis PQ 144• Back tension = 250 MPa; production speed = 85 stroke/min; Vanadis 4E; (test 1)
• EDS analysis of pick-upSpectrum In stats. C Si S V Cr Mn Fe Total
1 Yes 10.8 0.6 1.1 87.5 100.0
2 Yes 5.1 1.4 4.8 5.0 83.7 100.0
No Vanadium and Chromium in spectrum 1 but Manganese and Silicium.Spectrum 2 is tool surface
Institut for Mekanisk TeknologiDanmarks Tekniske Universitet
Second screening test campaign
DP 800; Fuchs PLS 100• Back tension = 300 MPa; production speed = 40 stroke/min; Vancron 40 (V40_C3); (test 26)
• Almost no pick-up on the tool surface
Exit edge Entrance threshold
Sliding direction