messy sentiments about scale issues - Luleå University of .../file/C_Courbon_2013_09_26... ·...
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C. Courbon *, S. Hernandez, J. Hardell and B. Prakash *Ph.D, Post-doctoral Researcher Luleå University of Technology Division of Machine Elements 971 87 Luleå, Sweden +46 725 661731 [email protected] Another insight into our experiments: messy sentiments about scale issues
Transcript of messy sentiments about scale issues - Luleå University of .../file/C_Courbon_2013_09_26... ·...
C. Courbon*, S. Hernandez, J. Hardell and B. Prakash*Ph.D, Post-doctoral Researcher
Luleå University of TechnologyDivision of Machine Elements
971 87 Luleå, Sweden+46 725 661731
Another insight into our experiments:
messy sentiments about scale issues
2/23
Background
One of the future trend in Tribology
Tribological
tests
• Out of the process • Simple config.• Flexible config.• Access to more data
Wear simulation in
a tribosystem
Contact/Wear
mechanisms
Contact/Wear
modelling
• Predict wear of the comp.• Predict surface defects• Opt. contacting geometry• Opt. operating cond.
• Properly model friction • Properly model heat trans. • Model at the right scale• Wear modelling strategy
• Better understanding• Identif. contact conditions • Identif. wear mechanisms •Propose a wear model
Know what we are doing/looking at
3/23
How are we usually investigating friction and wear?
Standard tribological tests
Reciprocating or unidirectional sliding
Open or closed configuration
Extracted data
Average friction coefficient
Specific wear rate
Post-mortem analysis of the samples
Tribological experiments
Open pin-on-disc
Closed pin-on-disc
Reciprocating test
4/23
Under which conditions are we effectively measuring wear?
Possible heterogeneous contact
Sliding on sticking material, oxide layers
Sliding on worn parts (material removed)
Third body always present in the contact
Low contact pressures (< 100 MPa)
Questions:
Where is the contact actually occurring?
What is the real contact area?
What is the actual contact pressure?
Where is wear actually occurring?
Tribological experiments
[Hardell et al., 2008]
[Kondratiuk & Kuhn, 2011]
5/23
Under which conditions are we effectively measuring wear?
Possible heterogeneous contact
Flat-end pin – RT – 75 N [Hernandez et al., 2013]
Many deposits, irregular surface, ploughing…
Local contact phenomena
Sliding direction
Flattened areas
Sliding direction
Pin Disc
6/23
Under which conditions are we effectively measuring wear?
Local contact phenomena
75 N
RT
7/23
Under which conditions are we effectively measuring wear?
Possible heterogeneous contact
Flat-end pin – 300°C – 75 N
Formation of a tribofilm
Local contact phenomena
Sliding direction Sliding direction
Pin Disc
8/23
Under which conditions are we effectively measuring wear?
Local contact phenomena
75 N
300°C
9/23
Under which conditions are we effectively measuring wear?
Local contact phenomena
75 N
300°C
10/23
Local contact phenomena
Let’s try to get “into the contact”…
Ultrasounds as a powerful method
[Kendall & Tabor, 1971][Marshall et al., 2005][Dwyer-Joyce, 2005]
Direct image of what is happening at the interface
Powerful technic to assess film thickness
Can be used to assess contact area, pressure, adhesion, junction growth…
Online and precise wear monitoring
100 N
RT
Time (s)
1rst reflected pulse
2x
11/23
Local contact phenomena
Let’s try to get “into the contact”…
Overview of the set-up
100 N
RT
12/23
Local contact phenomena
Let’s try to get “into the contact”…
Results – Evolution of the “real contact area”
Time (s)
100 N
RT
13/23
Under which conditions are we effectively measuring wear?
Impact of an heterogeneous contact
Increased local contact pressure and flash temperature
Wear only occurring on asperities ⇒ heterogeneous wear profile
Impairing heat transfer & heat generation across the interface
Consequences
T
P
nF
Concentrated loadingson asperities
W
nF
Artificially increased wear rate
nF
Affected heat transferFormation of TCR
14/23
Modelling scale
How should we look at the contact interface?
Different scales can hide different phenomena
Perfect or imperfect contact?
Contact modelling
Body 1
Body 2
Vsl
yMacroscopic scale
Asperity scale
sTS1
S2
1T
2T
Con
stric
tion
area
Roughness scale
S1
S2
Heat flux lines
15/23
Modelling scale
Macroscopic scale
Neglecting the constriction area
Direct separation between surfaces in contact
Introduction of a Thermal Contact Resistance (TCR)
Possible temperature discontinuity
1T
2T
Con
stric
tion
area
Roughness scale
1T
2T
Con
stric
tion
area
Macroscopic scale
sTCR
( ) gϕαϕ ⋅−= 12
gϕαϕ ⋅=1
S1
S2
S1
S2
VslVsl
Contact modelling
16/23
Heat transfer modelling
Macroscopic Thermal Contact Resistance
Connected to the real contact area
Temperature and Pressure dependent
Contact modelling
0
0.5
1
1.5
2
2.5
3
3.5
4
0 100 200 300 400 500
Temperature (°C)
TC
R (K
.mm
²/W)
P = 80 MPa
Uncoated steel - Copper
Source: LIMATB, France
17/23
Modelling scale
Influence on “contact temperature”
Macroscopic model
0.00
20.00
40.00
60.00
80.00
100.00
120.00
140.00
0.00 0.50 1.00 1.50 2.00
Distance along the path (mm)
Tem
pera
ture
(°C
)
No_TCR
Inf_TCR
Contact modelling
S2
S1
Extraction path
µ = 0.2Vslid = 0.1 m/s
25 °C
100 °C
Macroscopic model
S1
S2
18/23
Modelling scale
But… if we look a little bit closer…
The “actual” contact temperature Ts can not be modelled
Heat generation is not occurring at the right place
Conduction
Conduction
Con
stric
tion
( ) gϕα ⋅−1
gϕα ⋅
gϕ
1T
2T
sT
1ϕ1ϕ
2ϕ 2ϕ
1T
2T
sTCR
1TCR
2TCR
S1
S2
Vsl
( ) gϕα ⋅−1
gϕα ⋅
a b
Contact modelling
19/23
Modelling scale
Modelling a contact interface at a mesoscopic scale [Rogeon et al., 2009]
Application in resistance spot welding
Conduction
Conduction
( ) gϕα ⋅−1
gϕα ⋅
gϕsT
1ϕ
2ϕ
1T
2T
1TCR
2TCR
Vsl
a b
Mesoscopic scale
gϕ
1T
2T
sT
( )111 eTCReq ,λ
( )222 eTCReq ,λ
1e
2e
Contact modelling
20/23
0.00
20.00
40.00
60.00
80.00
100.00
120.00
140.00
160.00
180.00
200.00
0.00 0.50 1.00 1.50 2.00
Distance along the path (mm)
Tem
pera
ture
(°C
)
No_TCR
Inf_TCR
MESO
Modelling scale
Influence on “contact temperature”
Mesoscopic model Extraction path
µ = 0.2Vslid = 0.1 m/s
25 °C
100 °C
+ 60 %
Eq. conductivity
Contact modelling
Mesoscopic model
S2
S1
S1
S2
21/23
Modelling scale
Influence on contact temperature [Richard et al., 2008]
Similar findings in the literature with DEM
Contact modelling
22/23
Conclusions
Summary
To keep in mind
“Proper” contact conditions in our experiments (controlled)
Measure as much data as possible
To think about the scale that needs to be considered
Importance of the scale
Temperature distribution
Effect on wear and friction
Important if we are looking from a local point of view
Needs and future trends
Let’s try to get “into the contact” !
23/23
Perspectives
24/23
Discussion
Thank you for your attention !Thank you for your attention !
Soon at:
LTDS UMR CNRS/ECL/ENISESaint-Etienne, France
+33 6 86 94 78 [email protected]
