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CompositesAtSheffield.
www.sheffieldcomposites.co.uk © 2011 The University Of Sheffield
Delamination modelling in mechanicaljoints of composite laminates
Akın Ataşa,b, Constantinos Soutisa
aThe University of Sheffield, Sheffield, United KingdombBalikesir University, Balikesir, Turkey
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Contents
- Introduction- Description of the problem- FE modelling- Mixed mode delamination modelling- Results- Conclusions- Acknowledgements
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Composite materials are the preferred materials for aircraftconstruction because of their high specific properties.
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Catastrophic failure of the structure usually initiates and propagates at thehole boundary including interlaminar and intralaminar failure modes.
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There are in general 3 mainfailure types observed inmechanical joints.
Net-tension and shear-outmodes are common forrelatively small specimen sizeand they are catastrophic.
The laminate geometry ischosen to assure a progressivebearing failure mode (w/d=6,e/d=3).
w
e
d
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1st case (Pin loaded).
One SOLID185 linear brickelement per layer.
Symmetry conditions areapplied to reduce the computationtime.
Pin material is steel with E=210GPa and ν=0.3.
Perfect fit is assumed betweenthe pin & laminate.
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2nd case (Bolt loaded).
One SOLID185 8-noded linearbrick element per layer.
Symmetry conditions areapplied to reduce the computationtime.
Bolt and washers are modelledas a unique body (fastener).
Fastener material is steel withE=210 GPa and ν=0.3.
Perfect fit is assumed betweenthe bolt & laminate.
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Fully integrated elements areused in the vicinity of the holeboundary.
Reduced integration elementsare used away from the hole.
Element aspect ratio at the holeboundary is set to 1.0 in order tocapture high stress gradients.
This ratio also ensures thatenough interface elements areused within the cohesive zone.
Orthotropic unidirectional material properties, Harper and Hallett (2008)
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The cosine radial stressdistribution gives anapproximation of pin/laminatecontact stresses:
20cos4
)(
DtP
rr
(rr) is the radial stress,
P is the applied load,
D is the hole diameter,
t is the laminate thickness.
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cnn
cnnnnnn
nnnn
n
uuifuuuifduK
uuifuK
0
)1(
22
21
0
)1(
uuu
uuifuuuifduK
uuifuK
t
ctt
ctttttt
tttt
t
Bonded contact element approach is used with a bi-linear traction-separation behaviour.
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CompositesAtSheffield.
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tct
ct
ncn
cn
m
mm
t
t
n
nm
mmnn
mttt
mmnn
mnnn
uu
u
uu
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u
ifduKifuK
ifduKifuK
,1
1)1(1
1)1(1
22
The interaction of relative contact stresses in normal and tangentialdirections are taken into account.
Interfacial properties, Harper and Hallett (2008)
Mixed mode
mΔ.
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ctct
cncn
ttt
nnn
ct
t
cn
n
uG
uG
duG
duG
GG
GG
max
max
2121
1
Total fracture energy at the completion of the mixed modedelamination is the sum of both normal and tangential contactstresses.
Mixed mode
mΔ.
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CZE inserted between the90˚/0˚ layers and within the 0˚layer in a cross-ply [90˚/0˚]scomposite laminate at the notchtip where splitting anddelamination damage modes areexpected.
Figure shows the split lengthversus applied stress for FEmodel predictions andexperimental results of (Spearingand Beaumont 1992).
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www.sheffieldcomposites.co.uk © 2011 The University Of Sheffield
X-ray image of a [90˚/0˚]sspecimen subjected to amonotonic loading at 350 MPa(80% of the failure strength).
The model captures the non selfsimilar delamination growth aswell as the splitting length.
x
y
x
y
(Spearing and Beaumont 1992)
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A
B40˚
The intersection of the shear stresscomponents for both 0˚ and 90˚ layer,and the average maximum shear stressoccurs at 40˚ to the loading axis.
Pin loaded case delamination initiation (friction coefficient μ=0)
Sb=P/dt
ux=0.294 mm
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Pin loaded case delamination initiation (friction coefficient μ=0)
Mode II is the dominantdelamination mechanismfor pin loaded compositelaminates.
Contribution of Mode Iis negligible and is notshown here.
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CompositesAtSheffield.
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Pin loaded case delamination initiation and growthFriction coefficient μ=0 Friction coefficient μ=0.2
ux=0.294 mm
ux=0.4 mm
ux=0.6 mm
ux=0.33 mm
ux=0.4 mm
ux=0.6 mm
(onset)
(growth)
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www.sheffieldcomposites.co.uk © 2011 The University Of Sheffield
Bolt loaded case delamination initiation and growthFriction coefficient μ=0 Friction coefficient μ=0.2
ux=0.32 mm
ux=0.4 mm
ux=0.6 mm
ux=0.39 mm
ux=0.4 mm
ux=0.6 mm
(onset)
(growth)
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CompositesAtSheffield.
www.sheffieldcomposites.co.uk © 2011 The University Of Sheffield
Bolt loadedFriction coefficient μ=0.2
Pin loaded
ux=0.294 mm
ux=0.4 mm
ux=0.6 mm
ux=0.33 mm
ux=0.4 mm
ux=0.6 mm
(onset)
(growth)
20
CompositesAtSheffield.
www.sheffieldcomposites.co.uk © 2011 The University Of Sheffield
Thank you for your attention!
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CompositesAtSheffield.
www.sheffieldcomposites.co.uk © 2011 The University Of Sheffield
Balikesir University and the Turkish Council ofHigher Education (YOK) are acknowledged forthe PhD scholarship awarded to Mr Akin Atas.
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