Fatigue Analysis of Short Glass Fiber Reinforced Plastics and Continuous Carbon Fiber Laminates
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Transcript of Fatigue Analysis of Short Glass Fiber Reinforced Plastics and Continuous Carbon Fiber Laminates
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Fatigue Analysis of Short Glass Fiber Reinforced Plastics – a Multidisciplinary AnalysisGerhard SpindelbergerAxel WerkhausenEngineering Center Steyr
ATC EUROPE 201424th – 26th June, 2014
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Contents
• Fatigue analysis of short glass fiber reinforced plastics in multidisciplin method
− Influence Factors & Anisotropy to be considered− Work flow from CAD to fatigue life− Application Examples− Summary / Outlook
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Fatigue Analysis of Short Glass Fiber Reinforced Plastics
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Kplus-project “fatigue design methodology for autom otive applications of engineering plastics” 2004-2009, 201 0-2015
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Influence Factors on Fatigue Life
• Notch support effect• Joint Lines
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Fiber Orientation, Material Anisotropy
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Temperature and Fiber Orientation Influence on Fatigue Life
10000 100000 1000000 1E70.1
0.2
0.3
0.4
0.5
0.6
0.70.80.9
1
PA 6T/6I-GF50EMS-specimen Kt=1,6
R=0,1 f=10 Hz
1x
k1=5
k1=5
k1=6
stopped
longitudinal transversalT=23°CT=80°CT=120°C
k1=10
Nor
mal
ized
Str
ess
Am
plitu
de σ
a (lo
g.)
[-]
Number of Cycles (log.) [-]
1x
k1=14
k1=11
2x
1x
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Work Flow
11
1
3
3
2
2
1
1 =
+
++
+
+
−
−
b
i
i
b
i
i
bbb
N
n
N
n
N
n
N
n
N
nK
Damage accumulation
Fatigue Life Prediction
Injection Die Cast Simulation
MOLDFLOW
FE-Mesh
Fiber orientation / anisotropic material data
Geometry
(CAD-Data) Stress distribution
Finite Element Analysis (FEA)
STRESSES
Load
Time
Load-time-history / Load spectrum
local SN curve of component
log Sa
SN curve of material
σD
NE
k
Fiber orientation
Temperature, etc.
Stress gradient
Environment
Material data / Influence factors
log N
PART EngineeringConverse
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Improved Inter-/Extrapolation of Material Parameter s
In FEMFAT input of 2 material parameter sets for 2 different orientation degrees parallel and perpendicular to fiber orientation ⇒⇒⇒⇒ Linear/Log inter-/extrapolation
Specimen Tests performed at University of Leoben,Prof. Eichlseder
Nom
inal
End
uran
ce S
tren
gth
Sa
Average Fiber Orientation a xx [-]
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Example 1: Analysis of a Ring Spanner
Stress amplitudes
Fill simulation with MoldFlow
FEMFAT Damage distribution
FE mesh consisting of about 200.000 elements
Comparison test –FEMFAT analysis
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Example 2: BMW Motorcycle Luggage Rack
• Test of 5 components• Sinusoidal load (R=- ∞)
• Mean load = -0,75kN• Load amplitude = 0,75kN• f=10Hz
critical area
injection point
boundary conditions
Load application
0
-1,5
Fa [kN]
t0
-1,5
Fa [kN]
t
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Example 2: BMW Motorcycle Luggage Rack
Test of five components yielded load cycles between 46.000 und 96.000 until crack initiation.
Calculated lifetime 26.000 cycles
Fiber Orientation Tensor (Component a11)
• FE-Model for fill simulation:~ 1,3 Mio. Elements
• FE-Model with mapped data:~ 400.000 Elements
Analysis without considering anisotropy delivers 2.000.000 cycles ⇒ 30 times too optimistic!
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Summary / Outlook
• Summary:– Fiber orientation and temperature have a big influence on fatigue life– S-N curves have been measured for short fiber reinforced polymers– There is no endurance limit, fixation of fatigue limit at 10 million cycles– A fatigue life prediction method has been developed for orthotropic materials based on
a critical plane criterion– Different FE-meshes require mapping of material data and fiber orientation
• Outlook– Automatic detection of joint lines– Torsion– Creep, stress relaxation– Ageing– Methods for estimation of material parameter
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Fatigue Analysis of Continuous Carbon Fiber Laminates
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Workflow and Interfaces
ABAQUSStress
analysis
Lifetimeprediction
ABAQUSViewer
FE-Structure.inp or .odb FEMFAT
Results.odb
FE
MFA
TF
E-A
dapt
er
FE-Stresses.odb
FE-Stresses.fts FEMFAT
Results.fps
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Fatigue Assessment for Fiber Fracture (FF)
• Necessary material data for fatigue analysis:– S-N curve for longitudinal loading with R=-1,
defined by fatigue limit, slope and cycle limit.Endurable stress at 2e6 cycles is per definition “fatigue limit”.Measured fatigue limit for R=0
– R||t, R||
c acc. VDI 2014 … tensile and compressive strength of UD laminaparallel to fiber directionfor Haigh-diagram construction
• Rainflow counting of σ1.• Linear damage accumulation.
1σ
σA
σMR||
t-R||c
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Fatigue Assessment of Normal Stressfor Inter Fiber Fracture (IFF)
• Necessary material data for fatigue analysis:– S-N curve for transversal loading with R=-1,
defined by fatigue limit, slope and cycle limit.Endurable stress at 2e6 cycles is per definition “fatigue limit”.
– Measured fatigue limit for R=0– R⊥
t, R⊥c acc. VDI 2014 … tensile and
compressive strength of UD lamina transverse to fiber directionfor Haigh-diagram construction
• Rainflow counting of σ2.• Linear damage accumulation.
σA
σM
2σ
R⊥t-R⊥
c
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Fatigue Assessment of Shear Stressfor Inter Fiber Fracture (IFF)
• Necessary material data for fatigue analysis:– Measured S-N curve for shear loading with
R=-1, defined by fatigue limit, slope and cycle limit.Endurable stress at 2e6 cycles is per definition “fatigue limit”.
– R ⊥|| acc. VDI 2014 … in-plane shear strength of UD laminafor Haigh-diagram construction (symmetric !!!)
– Extension of FEMFAT material input and ffd-file format
• Rainflow counting of τ21.• Linear damage accumulation
21τσ
τ
σA
σMR ⊥|| R ⊥||
21τ 21τ
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Fatigue Assessment of Different Load Directions in Laminate Plane
• Necessary material data for fatigue analysis:– S-N curve is interpolated between normal and
shear– Static strength depend on load direction and
are taken from Puck’s curve– Haigh-diagram is interpolated between normal
and shear
• Input number of load directions• Rainflow counting of stress vector
projected on each load direction(red lines)
• Linear damage accumulation for each load direction.
• Additional parameters p⊥||t and p⊥||
c have to be specified, default values for CFK acc. VDI 2014:– p⊥||
t = 0.35– p⊥||
c = 0.3
σA
σM
2σ21τ
Cutting plane
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Critical Component Haigh Diagram
- Smooth transition betweentension / compression / shear
- Linear interpolation of slope of S-N curve- Linear interpolation of log(cycle limit) of S-N curve
ϕ
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Example: Commercial Vehicle Cross Member
719
142
43
Composite Cross Member Load Cases
(30/-30/03/45/-45/0)S [°]8.85 (0.8/0.8/1.2/0.6/0.6/0.85)S [mm]
LF1 (Shearing)
LF2 (Bending)
Dimensions [mm]
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Example: Commercial Vehicle Cross Member
Damage [-]
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Summary / Outlook
• Summary:– ChannelMAX– ABAQUS-interface– Assessment of shell elements with COMPOSITE property– No assessment of interlaminar stresses σ3, τ31, τ32
– The maximum damage over all plies and stress components defines the type of failure– FEMFAT visualizer: Visualization of results for each layer (damage, amplitude and
mean stress, S-N curve, failure mode, etc.)
• Outlook– Assessment of delamination by considering interlaminar stresses σ3, τ31, τ32
– Support of solid elements with composite properties– New interfaces (Nastran, Ansys, etc.)
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The future is ours to make.
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