An Introduction to Marine
Composites
Paul H. Miller
Department of Naval
Architecture and Ocean
Engineering
U. S. Naval Academy
2 May 2001
Webb Institute of Naval Architecture
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Presentation Overview
• Why use
• Design Examples
composites in the
marine
environment
• What are they
• How to analyze
them
2 May 2001
• IACC rudder
• 78’ performance
cruiser
• A marine
composites
dissertation
project
Webb Institute of Naval Architecture
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Why Marine Composites?
• Approximately 1/3
• High specific
of marine
applications are
now made of
composites
• Low maintenance
requirements (low
life-cycle costs)
material properties
• High geometric
flexibility
• Good moisture
stability
2 May 2001
Webb Institute of Naval Architecture
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Why not?
•
•
•
•
2 May 2001
High Initial Cost
Tight tolerances required
Fire/smoke toxicity
Environmental
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A “Composite”
• A combination of more than one material
with resulting properties different from the
components
• Examples:
• Reinforced concrete
• Wood
• Polymer composites (1000+ resins, 25+ fibers,
20+ cores)
• Note: a “composite ship” is not a composite
material
2 May 2001
Webb Institute of Naval Architecture
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Material Properties
• Isotropic Materials
• Transversely
(ie metals)
• E
• 
• t , c , 
Isotropic Materials
(ie one fiber in resin)
• Ex (fiber direction), E , Gxy
• 
•  xt ,  xc ,  t ,  c ,
y
xy
y
2 May 2001
Webb Institute of Naval Architecture
y
xy
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Analysis Methods
• Classical Lamination Theory –
Timoshenko’s layered
stiffness/stress approach. Uses
matrix algebra.
• “Blended Isotropic” – ABS Method
• Empirical - Gerr
2 May 2001
Webb Institute of Naval Architecture
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Methods Compared
• “Blended
• CLT
• Analytically difficult
• Accurate to within
1% if base
properties are
known.
• Possible
unconservative
inaccuracy to 15%
2 May 2001
Isotropic”
• Analytically easy
• Accuracy to within
1% if all properties
are known.
• Possible
unconservative
inaccuracy to a
factor of 4!
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Suggestions
• Use “blended isotropic” for preliminary
design (or to check for ABS
compliance) only!
• Use CLT for all final
design!
2 May 2001
Webb Institute of Naval Architecture
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Typical Material Properties
• Mostly linear stress/strain
• Brittle (0.8-2.7% ultimate strain) resins or fibers
• Stiffness and Strength Properties (ASTM tests –
Wet/Dry)
Tensile
Compressive
Shear
Flex
Fatigue
20000
15000
Stress [psi]
•
•
•
•
•
E-glass Mat/Polyester Sample #1
10000
5000
0
0
0.05
Tensile Test
2 May 2001
Webb Institute of Naval Architecture
0.1
0.15
0.2
0.25
Extension [in]
10
Moisture Absorption Results
2 .5 0 %
1.8% weight gain
for submerged
We ight G ain
1.3% for 100%
relative humidity
2 .0 0 %
1 .5 0 %
1 .0 0 %
0 .5 0 %
Equilibrium in 4
months
0 .0 0 %
0
33
66
99
132
165
198
231
D a ys
TNR
2 May 2001
TNW
Webb Institute of Naval Architecture
S NR
S NW
F ic kia n
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Example Design Problem –
IACC Rudder
• Goal: As light as possible without
breaking!
• Construction: Carbon fiber and epoxy
• Loads from Lift equations and CFD
2 May 2001
Webb Institute of Naval Architecture
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Approach
• FEA model
• Geometry
• Loads
• Fwd speed
• Backing speed
• Angle of
Attacks
• Laminate tailoring
• CFD loads
• Tsai-Wu and Hashin
failure criteria
• Preliminary
analysis from
beam
equations/CLT/
lift equation
2 May 2001
Webb Institute of Naval Architecture
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77 foot Performance Cruiser
• Carl Schumacher design
• Building at Timeless
Marine, Seattle
• To ABS Offshore Yacht
Guide
2 May 2001
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Approach
• Preliminary design using CLT
(“Laminator”), MathCad (for ABS
equivalent) and Excel (ABS Guide)
• Final design using FEA
• Nine load cases
• 15% increased in FEA over ABS
2 May 2001
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My Dissertation
• Extend the standard fatigue methods
used for metal vessels to composite
vessels
• Verify the new method by testing
coupons, panels and full-size
vessels.
2 May 2001
Webb Institute of Naval Architecture
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Simplified Metal Ship Fatigue Design
1. Predict wave encounter ship “history”
2. Find hull pressures and accelerations
using CFD for each condition
3. Find hull stresses using FEA
•
•
Wave pressure and surface elevation
Accelerations
4. Use Miner’s Rule and S/N data to get
fatigue life
2 May 2001
Webb Institute of Naval Architecture
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Project Overview
•
•
Material and Application Selection
Testing (Dry, Wet/Dry, Wet)
•
•
•
ASTM Coupons, Panels, Full Size
Static and Fatigue
Analysis
•
•
2 May 2001
Local/Global FEA
Statistical and Probabilistic
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Material & Application Selection
Ideally they should represent a large
fraction of current applications!
•
•
•
•
Polyester Resin (65%)
E-glass (73%)
Balsa Core (30%)
J/24 Class Sailboat
•
•
•
•
5000+ built
Many available locally
Builder support
Small crews
Another day of research…
2 May 2001
Webb Institute of Naval Architecture
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Finite Element Analysis
• Coupon, panel, global
• Element selection
•
•
•
•
Linear/nonlinear
Static/dynamic/quasi-static
CLT shell
Various shear deformation theories used
(Mindlin and DiScuiva)
• COSMOS/M software
• Material property inputs from coupon
tests
2 May 2001
Webb Institute of Naval Architecture
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Fatigue Testing
2 May 2001
Webb Institute of Naval Architecture
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Fatigue Results – S/N Data
Percent of Original Stiffness
Moisture
decreased initial
and final stiffness
but the rate of
loss was the
same.
100%
90%
80%
70%
1
10
100
1,000
10,000
100,000
1,000,000
Stress Cycles
12.5%-Wet
37.5%-Wet
12.5%-Dry
50%-Dry
25%-Wet
50%-Wet
25%-Dry
75%-Dry
37.5%-Dry
75%-Wet
Specimens failed when stiffness dropped 15-25%
No stiffness loss for 12.5% of static failure load specimens
25% load specimens showed gradual stiffness loss
2 May 2001
Webb Institute of Naval Architecture
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Panel Analysis
• Responds to
•
•
•
•
USCG/SNAME
studies
Solves edge-effect
problems
Hydromat test
system
More expensive
Correlated with FEA
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Webb Institute of Naval Architecture
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Panel FEA Results
1
0 .9
0 .8
De fle ction (in)
0 .7
0 .6
0 .5
0 .4
0 .3
0 .2
0 .1
0
0
P re s s u re (p s i)
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2
4
6
W et Deflec tion
Panel Linear
Panel & Frame NonLin
8
10
12
14
Dry Deflec tion
Panel NonLin
Panel & Frame Linear
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Impact Testing
• The newest boat had the lowest stiffness.
• Did the collision cause significant
microcracking?
Yes, there was
significant
microcracking!
2 May 2001
Webb Institute of Naval Architecture
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Global FEA
• Created from plans and boat checks
• Accurately models vessel
• 8424 quad shell elements
• 7940 nodes
• 46728 DOF
• Load balance with accelerations
2 May 2001
Webb Institute of Naval Architecture
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On-The-Water Testing- Set Up
Instrument Locations for Boat Tests
Instrument
Location
Strain Gage #1 Portside shroud chainplate
Strain Gage #2 Forestay chainplate
Strain Gage #3 Inside hull on centerline
Strain Gage #4 Inside hull off centerline
Strain Gage #5 Outside hull on centerline
Strain Gage #6 Outside hull off centerline
Accelerometer Bulkhead aft of strain gages
2 May 2001
Location of
sink throughhull (behind
fender)
Webb Institute of Naval Architecture
Location of strain
gauges (under
epoxy)
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A ccel
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Wind
0 .1 2
0 .1
0 .0 8
Webb Institute of Naval Architecture
Inside on CL
Inside off CL
Strains
0 .0 6
0 .0 4
0 .0 2
0
-0 .0 4
Accelerations
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Imajination
Test
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J6 Test
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Data Records
0.0016
0.0014
0.0012
0.0008
0.001
0.0006
0.0004
0.0002
0
2 May 2001
Webb Institute of Naval Architecture
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