fatigue analysis of short glass fiber reinforced plastics and continuous carbon fiber laminates
DESCRIPTION
Fiber reinforced plastics are the logical means to reduce weight in automotive structures or vehicles, which are more efficient when less mass has to be moved. Additionally the infinite long fibers are in use for covers, sheet structures and cabin parts - design meet functionality. All these new designs have to be approved by fatigue analyses like their metal counterparts before. How and by which technological means this can be carried out in APA product FEMFAT is shown in this presentation. Data preparation is using also Converse by PART engineering from APA.TRANSCRIPT
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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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