measuring and modeling the fatigue performance of ...– testing resources ... hyperelastic option...

© 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


Agenda

• About Endurica

• Solution Overview

• Case study: Wellhead sealing element

– Geometry

– Load History

– Materials

• Brief fe-safe/rubber tour

• Results


About Endurica LLC

Mission: Pre-prototype solutions for managing elastomer durability

Founded in 2008

100% focus - elastomers and durability


Case Study: Wellhead Sealing Element

Wellhead

Pipe

Segment

Rubber

Isometric

Top View

Side View


Sealing Element Operation


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


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


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


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


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


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


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


Fe-safe/Rubber fatigue analysis software

Material Properties Database

FE Model Results

Fatigue Analysis Setup

Execution Log


FE Analysis of sealing element


Strain History: worst element 6085

closure insertion


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


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


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


Fatigue Life of Sealing Element

N=5870

Forward paths:

- Materials A vs B

- Pipe diameter effects

- Control

recommendations for

control on ID


Mark WyattNorth American Sales, 3DS

Office: 781 810 [email protected]

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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measuring and modeling the fatigue performance of ...– testing resources ... hyperelastic option...

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