damage tolerance and fatigue behaviour of composites
DESCRIPTION
Composites Damage Tolerance and Fatigue behaviour in a concise presentationTRANSCRIPT
28/06/2012
Kunststofftechnik an der Montanuniversität Leoben 1
Damage Tolerance and Fatigue Behaviour of Composites
Otto Glöckel-Straße 2, A-8700 Leoben, Tel.: +43 3842 402 2100
www.kunststofftechnik.at
Behaviour of Composites
Univ.-Prof. Dr. mont. Gerald Pinter
Chair of Materials Science and Testing of Polymers, Montanuniversitaet Leoben
FACC Technical Colloquium „Advances in Composites“
Salzburg, July 5-6, 2012
28/06/2012
Kunststofftechnik an der Montanuniversität Leoben 2
Scope and Content
� Introduction:Why is fatigue and fatigue damage toleranceof importance?
Topics covered
g Approaches to fatigue of composites
www.kunststofftechnik.at 2FACC Colloquium 2012, gPinter
Approaches to fatigue of composites- stress/strain based- fracture mechanics concepts
g Outlook:Methodology and testing concept for fatigue life assessment
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Kunststofftechnik an der Montanuniversität Leoben 3
Topics of Interest and Open Issues
Are we using composites to the best of their performance capacity?
Key Questions in dealing with composite fatigue problems
Over- vs.Under-Design
What is the residual lifetime or residual loading capacity (strength) if damage occurs or is present?
Fatigue DamageTolerance
www.kunststofftechnik.at 3FACC Colloquium 2012, gPinter
How do current design concepts/methods deal with these issues?
Applicability &
Limitations
of Current
Fatigue Design
Methodologies
Do we have the proper knowledge and adequate test concepts and design tools to answer these questions?
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Kunststofftechnik an der Montanuniversität Leoben 4
Stress/Strain Based Approach
Methodology
Concepts for the characterization of the fatigue
behavior of engineering plastics
Fracture Mechanics Approach
www.kunststofftechnik.at 4FACC Colloquium 2012, gPinter
Stress/Strain Based Approach
� S-N curves
� Hysteresis measurements
� Isocyclic stress-straindiagrams
Fracture Mechanics Approach
� Fatigue crack propagation
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Stress/strain based approachS-N diagram (Wöhler)
www.kunststofftechnik.at 5FACC Colloquium 2012, gPinter
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Kunststofftechnik an der Montanuniversität Leoben 6
Stress/strain based approachS-N diagram (Wöhler)
Laminate with foil defects(6.35 × 6.35 mm)
Specimen with notch(diameter: 6.35 mm)
Artificial defects in woven carbon fabric RTM laminates
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Two layers of teflon foil sealed with an adhesive tape in order to entrap air
(Felber, 2006)
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Kunststofftechnik an der Montanuniversität Leoben 7
Stress/strain based approachS-N diagram (Wöhler)
500
600
700
Effect of artificial defects on S/N curves
of woven carbon fabric RTM laminates
www.kunststofftechnik.at 7FACC Colloquium 2012, gPinter
100
101
102
103
104
105
106
107
100
200
300
400
∆σ
∆σ
∆σ
∆σ , MPa
N , 1
CF-EP qi
CF-EP qi-foil defect
CF-EP qi-notch
23 °C, 10 Hz, R=0.1
(Felber, 2006)
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Stress/strain based approachS-N diagram (Wöhler)
Residual stress after fatigue for differentlycompacted RTM laminates
1,000 � INJW
1,000 � INJW
After 106 cycles at 60% of
tensile strength
After 106 at 70% of
tensile strength
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23 °C, 10 Hz, R=0,10
100
200
300
400
500
600
700
800
900
1,000 � INJW
� INJBC1
� INJST1x8
� INJST2x4
� INJST4x2
σσ σσzB, 60% of tensile strength [MPa]
0
100
200
300
400
500
600
700
800
900
1,000 � INJW
� INJBC1
� INJST1x8
� INJST2x4
� INJST4x2
σσ σσzB, 70% of tensile strength [MPa]
(Painold, 2003)
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Kunststofftechnik an der Montanuniversität Leoben 9
Stress/strain based approachHysteresis measurements
Data Acquisition
stress σ
max
σ
E
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strain
cycles
σmin
εmax
εmin
ε
EdynES
ES= Secant Modulus
Edyn= Dynamic Modulus
Viscoelastic effects and material damage
Material damage
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Stress/strain based approachHysteresis measurements
Data Presentation
relative m
odulus
cyclic creep
damage accumulation
ES
Edyn
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� Evaluation of the stiffness decrease as a result of viscoelastic effects and material damage
� No deformation analysis� Restricted use as a material law
log (N)
relative m
odulus
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Stress/strain based approachHysteresis measurements
Evaluation of cyclic stiffness for differentlycompacted RTM laminates
Dynamic Modulus
1.0
1.1
Secant Modulus
1.0
1.1
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102
103
104
105
106
0.5
0.6
0.7
0.8
0.9
Edyn,rel [ ]
N [ ]
70% of σσσσts
INJW
INJBC1
INJST1x8
INJST2x4
INJST4x2
PRIW
102
103
104
105
106
0.5
0.6
0.7
0.8
0.9
ES,rel [ ]
N [ ]
70% of σσσσts
INJW
INJBC1
INJST1x8
INJST2x4
INJST4x2
PRIW
23 °C, 10 Hz, R=0,1(Painold, 2003)
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Kunststofftechnik an der Montanuniversität Leoben 12
σmax
103
Isocyclic σmax-εmax diagram
σσσσmax, 1
σσσσmax, 2
σσσσmax, 4
εmax
σσσσmax, 3
σσσσmax
σσσσmax, 1
σσσσmax, 2
σσσσmax, 3
σσσσmax, 4
N
Stress/strain based approachIsocyclic stress-strain diagram
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εmax
Isocyclic ∆σ-∆ε diagram
log N103
log N
∆ε
∆σ∆σ∆σ∆σ
∆σ∆σ∆σ∆σ1
∆σ∆σ∆σ∆σ2
∆σ∆σ∆σ∆σ3
∆σ∆σ∆σ∆σ4
103 ∆ε∆σ
∆σ∆σ∆σ∆σ1
∆σ∆σ∆σ∆σ2
∆σ∆σ∆σ∆σ3
∆σ∆σ∆σ∆σ4103
N
(Zahnt ,2003)
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Stress/strain based approachIsocyclic stress-strain diagram
Isocyclic σmax-εmax diagram
� accumulative material reaction up to the specified cycle
number
- Viscoelastic effects
- Material damage
Isocyclic ∆σ-∆ε diagram
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� instantaneous material reaction at a specified cycle number
- Only material damage
• Assessment and comparison of the resulting deformation contribution of viscoelastic effects and of cumulated damage
• Deformation analysis as a function of cycle number with the potential to be used as a material law for component design
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PP-SGF30
0
20
40
60
∆σ [MPa]
∆ε [1]
23 °C
10 Hz
R = 0,1 (tension)
R = 10 (compression)
PP-SGF30
longitudinal
40
60
σmax [MPa]
23 °C
10 Hz
R = 0,1 (tension)
PP-SGF30
longitudinal
40
60
σmax [MPa]
23 °C
10 Hz
R = 0,1 (tension)
PP-SGF30
longitudinal
Stress/strain based approachIsocyclic stress-strain diagram
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-0,015 -0,010 -0,005 0,000 0,005 0,010 0,015
-80
-60
-40
-20
cycle N [1]:
101
102
103
104
105
106
cyclic
damage-0,015 -0,010 -0,005 0,000 0,005 0,010 0,015
-80
-60
-40
-20
0
20
εmax [1]εmin [1]
σmin [MPa]
R = 0,1 (tension)
R = 10 (compression)
cycle N [1]:
102
101
103
104
105
106
cyclic
creep + damage
-0,015 -0,010 -0,005 0,000 0,005 0,010 0,015
-80
-60
-40
-20
0
20
εmax [1]εmin [1]
σmin [MPa]
R = 0,1 (tension)
R = 10 (compression)
cycle N [1]:
102
101
103
104
105
106
cyclic
creep + damage
(Zahnt, 2003)
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Kunststofftechnik an der Montanuniversität Leoben 15
30
40
50
60N [1] PP-SGF30 PP-LGF30
101
102
103
104
105
106
∆σ
∆σ
∆σ
∆σ [MPa]
longitudinal
cyclic
damage
50
60
cyclic
creep + damage50
60
cyclic
creep + damage50
60
50
60
cyclic
creep + damage
Stress/strain based approachIsocyclic stress-strain diagram
www.kunststofftechnik.at 15FACC Colloquium 2012, gPinter
Effect of fiber length in PP-GF30
0,000 0,002 0,004 0,006 0,008 0,010 0,012 0,014 0,016
0
10
20
23 °C
10 Hz
R = 0.1
∆σ
∆σ
∆σ
∆σ
∆ε∆ε∆ε∆ε [1]
0,000 0,002 0,004 0,006 0,008 0,010 0,012 0,014 0,0160
10
20
30
40
23 °C10 HzR = 0.1
σσ σσmax[MPa]
εεεεmax[1]
N [1] PP-SGF30 PP-LGF30
101
102
103
104
105
106
longitudinal
0,000 0,002 0,004 0,006 0,008 0,010 0,012 0,014 0,0160
10
20
30
40
23 °C10 HzR = 0.1
σσ σσmax[MPa]
εεεεmax[1]
N [1] PP-SGF30 PP-LGF30
101
102
103
104
105
106
longitudinal
0,000 0,002 0,004 0,006 0,008 0,010 0,012 0,014 0,0160
10
20
30
40
0,000 0,002 0,004 0,006 0,008 0,010 0,012 0,014 0,0160
10
20
30
40
23 °C10 HzR = 0.1
σσ σσmax[MPa]
εεεεmax[1]
N [1] PP-SGF30 PP-LGF30
101
102
103
104
105
106
longitudinal
(Zahnt, 2003)
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0
100
200
300
400
500
600
-0,01 -0,0075 -0,005 -0,0025 0 0,0025 0,005 0,0075 0,01 0,0125
σσ σσ[MPa]
102
103104
105
106
N [1] 23 °°°°C10 Hz
R = 0,1 (tension)
R = 10 (comp.)
cyclic
damage
RTM Laminates
500
600
N [1] 23 °C500
600
N [1] 23 °C500
600
N [1] 23 °C
Stress/strain based approachIsocyclic stress-strain diagram
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-400
-300
-200
-100
-0,01 -0,0075 -0,005 -0,0025 0 0,0025 0,005 0,0075 0,01 0,0125
∆∆ ∆∆σσ σσ
∆∆∆∆εεεε [ ]
-400
-300
-200
-100
0
100
200
300
400
500
-0,01 -0,0075 -0,005 -0,0025 0 0,0025 0,005 0,0075 0,01 0,0125
εεεεmax[ ]
σσ σσmax[MPa]
102
103104
105
106
N [1] 10 Hz
R = 0,1 (tension)
R = 10 (comp.)
cyclic
creep + damage
-400
-300
-200
-100
0
100
200
300
400
500
-0,01 -0,0075 -0,005 -0,0025 0 0,0025 0,005 0,0075 0,01 0,0125
εεεεmax[ ]
σσ σσmax[MPa]
102
103104
105
106
N [1] 10 Hz
R = 0,1 (tension)
R = 10 (comp.)
cyclic
creep + damage
-400
-300
-200
-100
0
100
200
300
400
500
-0,01 -0,0075 -0,005 -0,0025 0 0,0025 0,005 0,0075 0,01 0,0125
εεεεmax[ ]
σσ σσmax[MPa]
102
103104
105
106
N [1] 10 Hz
R = 0,1 (tension)
R = 10 (comp.)
cyclic
creep + damage
(Lintschinger, 2003)
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Kunststofftechnik an der Montanuniversität Leoben 17
Stress/Strain Based Approach
Methodology
Concepts for the characterization of the fatigue
behavior of engineering plastics
Fracture Mechanics Approach
www.kunststofftechnik.at 17FACC Colloquium 2012, gPinter
Stress/Strain Based Approach
� Generation of S-N curves
� Hysteresis measurements
� Isocyclic stress-straindiagrams
Fracture Mechanics Approach
� Fatigue crack propagation
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Fracture mechanics approachFatigue crack propagation
www.kunststofftechnik.at 18FACC Colloquium 2012, gPinter
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Kunststofftechnik an der Montanuniversität Leoben 19
Fracture mechanics approachFatigue crack propagation
Fatigue delamination growth in polymer matrix composites
Effect of polymer matrix in UD-CF Laminates
10-3
10-2
CF-EP1
CF-EP1
CF-PEEK
CF-PEEK
CF-EP2
da/dN, mm/cycle
23 °C
f=5 Hz
R=0,1
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1010
-6
10-5
10-4
1000
CF-EP2
CF-EP2
da/dN, mm/cycle
GImax,
J/m2
100
(Stelzer, 2009)
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Fracture mechanics approachFatigue crack propagation
Fatigue delamination growth in polymer matrix composites
Effect of textile technology
10-3
10-2
10-1
triaxial braid - Epoxy
45/0/-45
UD - Epoxy
5276
UD - PEEK
da/dN, mm/cycle
www.kunststofftechnik.at 20FACC Colloquium 2012, gPinter
101
102
103
10410
-8
10-7
10-6
10-5
10-4
23°C
f=5Hz
R=0,1
UD - PEEK
PEEK
da/dN, mm/cycle
GI,max
, J/m2
(Stelzer, 2009)
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Kunststofftechnik an der Montanuniversität Leoben 21
Scope and Content
� Introduction:Why is fatigue and fatigue damage toleranceof importance?
Topics covered
g Approaches to fatigue of composites
www.kunststofftechnik.at 21FACC Colloquium 2012, gPinter
Approaches to fatigue of composites- stress/strain based- fracture mechanics concepts
g Outlook:Methodology and testing concept for fatigue life assessment
28/06/2012
Kunststofftechnik an der Montanuniversität Leoben 22
Damage modes during fatigue life
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(Reifsnider, 1991)
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Stiffness reduction during fatigue life
Matrix cracking
Long period of stiffness reduction caused by additional matrix cracking in off-axis and on-axis plies, crack coupling, internal delaminations
Delamination, fibre fracture
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Stages of stiffness reduction during fatigue life of a [0/902]s graphite epoxy laminate (R=0.1)
(Reifsnider, 1991)
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Residual strength and stiffness during fatigue life
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Schematic diagram of strength change during fatigue life of an unnotched laminate (Reifsnider, 1991)
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Talreja (1987), „Fatigue of Composite Materials“
Chapter„Stiffness Based Fatigue Damage Characterisation of Fibrous Composites“
� 2 approaches: Strength degradation and stiffness changes
� Quote: „It is generally accepted now that the strength degradation does not always reflect the fatigue damage“
www.kunststofftechnik.at 25FACC Colloquium 2012, gPinter
not always reflect the fatigue damage“
„Stiffness properties change continously with fatigue cycles and could provide basis for nondestructive procedure for fatigue damage characterization“
„A complete characterization of fatigue damage would require measuring changes in all stiffness components relating to these damage mechanics“
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Kunststofftechnik an der Montanuniversität Leoben 26
1. Cyclic loading on-axis2. Load axis with angle of
15° to longitudinal axis3. Poisson‘s ratio measured
with a vice
Talreja (1987) „Stiffness Based Fatigue Damage Characterisation of Fibrous Composites“
Steel
Specimen with Al-tabs
Specimen
On-axis
Off-axis
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� E11, E22, G12, ν12, ν21
for UD-ply
(Talreja, 1987)
Specimen
On-axis
Off-axis
(transverse isotropic)
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Kunststofftechnik an der Montanuniversität Leoben 27
Leoben 2012: Extended test-set up for orthotropic materials
Steel
Specimen with Al-tabs
Specimen
On-axis
Off-axis
Off-axis
Cycle dependent determination of
stiffness components with modern methods of deformation analysis
(online optical)
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E11, E22, E33G12, G13, G23,
ν12, ν13, ν23
(orthotropic)
Off-axis
On-axis
Off-axis
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Stiffness tensors
1. Correlation between components of stiffness tensor with failure mechanisms
2. Cycle-dependent stiffnesses for law of elasticity (not available up to now)
Strengths
� Residual strengths(single value)
� Information about load capacity of material
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Complete material characterisation
3. Physically based stiffness degradation model for material/component simulation
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Acknowledgements
� Colleagues from the Leoben Composite Team− Markus Wolfahrt (PCCL)− Steffen Stelzer (WPK-MUL)− Julia Brunbauer (WPK-MUL)
� Scientific Partners− Institute of Lightweight Design and Structural
Biomechanics, Technical University Vienna
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Biomechanics, Technical University Vienna− Chair Carbon Composites, Technical University
Munich− Polymer Competence Center Leoben GmbH
� Company Partners− FACC AG− Airbus Deutschland GmbH− Toho Tenax Europe GmbH
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Kunststofftechnik an der Montanuniversität Leoben 30
6 Chairs – 6 Full Professors
From Molecules
over Processing Technology
to Polymer-based Materials
and Components and Products
Department Polymer Engineering and Science Montanuniversitaet Leoben, A
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and Components and Products
Polymer
Chemistry
Polymer
Processing
Materials Science
of Polymers
Designing of Plastics
& Composites
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Kunststofftechnik an der Montanuniversität Leoben 31
Polymer Competence Center Leoben, GmbH
� founded in 2002
� currently 85 employees
� non-university research company
with two sites (Leoben und Graz)
� scientific, pre-competitive and
LEOBEN
Graz
About us
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� scientific, pre-competitive and
applied research in polymer
engineering and science
� project partner for the national and
international plastics industry
� close cooperation with university
research and education (bachelor
and master theses, dissertations)Headquarters of PCCL (Leoben, Austria)
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Polymer Center Leoben
Thank youfor
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foryour attention