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© Endurica LLC 2013www.endurica.com
Measuring and Modeling the Fatigue
Performance of Elastomers for
Applications with Complex Loading
Requirements
W. V. Mars
Endurica LLC
Energy Rubber Group16 January 2014
© Endurica LLC 2013www.endurica.com
Agenda
• About Endurica
• Solution Overview
• Case study: Wellhead sealing element
– Geometry
– Load History
– Materials
• Brief fe-safe/rubber tour
• Results
© Endurica LLC 2013www.endurica.com
About Endurica LLC
Mission: Pre-prototype solutions for managing elastomer durability
Founded in 2008
100% focus - elastomers and durability
© Endurica LLC 2013www.endurica.com
Case Study: Wellhead Sealing Element
Wellhead
Pipe
Segment
Rubber
Isometric
Top View
Side View
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Sealing Element Operation
© Endurica LLC 2013www.endurica.com
Sealing Element Operation
© Endurica LLC 2013www.endurica.com
© Endurica LLC 2013www.endurica.com
© Endurica LLC 2013www.endurica.com
© Endurica LLC 2013www.endurica.com
Sealing Element Development Challenges
• Technical– How many repeats of the operating history can be endured?
– Where will part fail?
– What compound will give best life?
– Diagnostics – what specific features, loads, times are critical?
– Optimal operating procedures (ie seal ID vs pipe OD) for seal life?
• Management– Prototyping / Manufacturing Resources
– Testing Resources
– Accurate evaluation vs. limited development time and budget
– Consequences of failure at prototype or production stages
– Communication about complex problems
© Endurica LLC 2013www.endurica.com
Characterization Know Your Material
Core Fatigue TestFully Relaxing Behavior from both nucleation and fracture
mechanical perspectives
Nonrelaxing OptionQuantify Strain Crystallization, Min and Mean Strain Effects
Thermal OptionQuantify dissipative properties,
thermal properties, temperature dependence
Hyperelastic OptionSimple, Planar, and
Equibiaxial tension, Mullins Effect
Mean Strain
Str
ain
Am
plit
ude
Infinite Life
Courtesy Axel Products
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Material Definition – Stress-strain
*Hyperelastic, arruda-boyce
209.6, 3.17, 6.67e-06
5
1122
)3(i
iii
m
i IC
GW ,
673750
519,
7000
19,
1050
11,
20
1,
2
154321 CCCCC
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0 1 2 3 4 5 6 7
x 105
34
36
38
40
42
44
46
48
50
52
54
Cycles
Cra
ck L
engt
h, m
m
measured
fitted
Observed and Fitted Crack Growth
© Endurica LLC 2013www.endurica.com
Material Definition: Fatigue Behavior
1.E-10
1.E-09
1.E-08
1.E-07
1.E-06
1.E-05
1.E-04
1.E-03
1.E-02
1.E-01
100 1000 10000 100000
Cra
ck G
row
th R
ate
, m
m/c
yc
Energy Release Rate, J/m^2
c0=0.100 mmcf=1.00 mm
Rc=0.01 mm/cyc
Tc=65500 J/m^2
Tc=100 J/m^2
F0
F
cc T
Tr
dN
dc
max
)( otF
c
Ftc
TTT
TrA
)( max oTTAdN
dc
© Endurica LLC 2013www.endurica.com
Material Definition Crack Precursor Size
1.00E+02
1.00E+03
1.00E+04
1.00E+05
1.00E+06
1.00E+07
1.00E-02 1.00E-01 1.00E+00
Life
, cy
cle
s
Precursor Size, mm
0
1( , )
( , )
fc
f
c
N dcf T R
Calculated
Tested
© Endurica LLC 2013www.endurica.com
Solution Overview
Documentation
Elastomer Durability Software for Finite Element Models
Analysis Software
Pre-defined Materials
TrainingPrinciples and
Practices
CharacterizationKnow Your Material
Support / ConsultingWorld Leading
Expertise
Validation Case
powered by
© Endurica LLC 2013www.endurica.com
Fe-safe/Rubber fatigue analysis software
Material Properties Database
FE Model Results
Fatigue Analysis Setup
Execution Log
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FE Analysis of sealing element
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Strain History: worst element 6085
closure insertion
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Technology: Critical Plane Analysis
Continuum / nucleation viewpoint
Accounts for finite straining
Crack closure in compression
Failure plane identification
Crack precursor loading experience
For every material
point
For every plane
Loading History on
plane
Identification of
Events via Rainflow count
Integration of
damage law
Identification of material
point and plane with
minimum life
-1
-0.5
0
0.5
1
-1-0.8-0.6-0.4-0.200.20.40.60.81
0
0.2
0.4
0.6
0.8
1
US Patent No. 6,634,236 B1
0
1( , )
( , )
fc
f
c
N dcf T R
© Endurica LLC 2013www.endurica.com
Technology: Damage accumulation
Rainflow counting
Based on numerical
integration of crack growth
rate law
Arbitrary multiaxial, variable
amplitude loading history
Time-domain scheme enables
direct identification of
damaging events
0 0.2 0.4 0.6 0.8 1
Experienced by Crack
Fraction of Mission Profile
Cra
ck D
rivin
g F
orc
e
M
ii RTfr
1max ),(
Crack growth rate per application of
given duty cycle
fa
ada
taTrN
0 )),((
1,
Number of repeats of duty cycle
required to develop a crack
© Endurica LLC 2013www.endurica.com
Crack Precursor Driving Energy Density, worst element
0
0.5
1
1.5
2
2.5
0 0.05 0.1 0.15 0.2 0.25 0.3
Cra
ck P
recu
rso
r D
rivi
ng
En
erg
y D
en
sity
,
mJ/
mm
^3
time, min
© Endurica LLC 2013www.endurica.com
Fatigue Life of Sealing Element
N=5870
Forward paths:
- Materials A vs B
- Pipe diameter effects
- Control
recommendations for
control on ID
© Endurica LLC 2013www.endurica.com
Mark WyattNorth American Sales, 3DS
Office: 781 810 3759mark.wyatt@3ds.com
Henry GonzalezSenior Sales Representative
3DS281 827 8745
Forward Paths…
Learn More aboutPrinciples and Practices
CharacterizeYour Material
Evaluate fe-safe/Rubber
•18-20 Feb : Characterizing elastomer fatigue behavior for analysis & engineering, (Ann Arbor, USA)•22 – 24 July: Theory & Application of Rubber Fatigue Analysis (Houston, TX, USA)
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