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An Introduction to Marine Composites

Paul H. MillerDepartment of Naval Architecture and Ocean Engineering

U. S. Naval Academy

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Presentation Overview

• Why use composites in the marine environment

• What are they

• How to analyze them

• Design Examples• IACC rudder• 78’ performance

cruiser

• A marine composites dissertation project

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Why Marine Composites?

• Approximately 1/3 of marine applications are now made of composites

• Low maintenance requirements (low life-cycle costs)

• High specific material properties

• High geometric flexibility

• Good moisture stability

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Why not?

• 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

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Material Properties

• Isotropic Materials (ie metals)

• E t , c ,

• Transversely Isotropic Materials (ie one fiber in resin)

• Ex (fiber direction), Ey , Gxy

xy

xt , xc , yt , yc ,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

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Methods Compared

• CLT• Analytically difficult• Accurate to within

1% if base properties are known.

• Possible unconservative inaccuracy to 15%

• “Blended 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 Use CLT for all final design!design!

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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

E-glass Mat/Polyester Sample #1

0

5000

10000

15000

20000

0 0.05 0.1 0.15 0.2 0.25

Extension [in]

Stre

ss [

psi]

Tensile Test

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Moisture Absorption Results

0.00%

0.50%

1.00%

1.50%

2.00%

2.50%

0 33 66 99 132 165 198 231Days

Weig

ht G

ain

TNR TNW SNR SNW Fickian

1.8% weight gain for submerged

1.3% for 100% relative humidity

Equilibrium in 4 months

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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

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Approach

• Geometry• Loads

• Fwd speed• Backing speed• Angle of

Attacks

• Preliminary analysis from beam equations/CLT/ lift equation

• FEA model• Laminate tailoring• CFD loads• Tsai-Wu and Hashin

failure criteria

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77 foot Performance Cruiser

• Carl Schumacher design

• Building at Timeless Marine, Seattle

• To ABS Offshore Yacht Guide

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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

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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.

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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

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Project Overview

• Material and Application Selection

• Testing (Dry, Wet/Dry, Wet)• ASTM Coupons, Panels, Full Size• Static and Fatigue

• Analysis• Local/Global FEA• Statistical and Probabilistic

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Material & Application Selection

• Polyester Resin (65%)• E-glass (73%)• Balsa Core (30%)• J/24 Class Sailboat

• 5000+ built• Many available locally• Builder support• Small crews

Ideally they should represent a large fraction of current applications!

Another day of research…

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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

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Fatigue Testing

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Fatigue Results – S/N Data

70%

80%

90%

100%

1 10 100 1,000 10,000 100,000 1,000,000

Stress Cycles

Pe

rce

nt

of

Ori

gin

al S

tiff

ne

ss

12.5%-Wet 12.5%-Dry 25%-Wet 25%-Dry 37.5%-Dry37.5%-Wet 50%-Dry 50%-Wet 75%-Dry 75%-Wet

Specimens failed when stiffness dropped 15-25%No stiffness loss for 12.5% of static failure load specimens25% load specimens showed gradual stiffness loss

Moisture decreased initial and final stiffness but the rate of loss was the same.

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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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Panel FEA Results

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 2 4 6 8 10 12 14

Pressure (psi)

De

fle

ctio

n (

in)

Wet Deflection Dry DeflectionPanel Linear Panel NonLinPanel & Frame 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!

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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

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On-The-Water Testing- Set Up

Instrument LocationStrain Gage #1 Portside shroud chainplateStrain Gage #2 Forestay chainplateStrain Gage #3 Inside hull on centerlineStrain Gage #4 Inside hull off centerlineStrain Gage #5 Outside hull on centerlineStrain Gage #6 Outside hull off centerlineAccelerometer Bulkhead aft of strain gages

Instrument Locations for Boat Tests

Location ofsink through-hull (behindfender)

Location of straingauges (underepoxy)

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Data Records

J6 TestImajinationTest

Wind0

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Inside on CL Inside off CL

Strains

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AccelAccelerations

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