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3rd INTERNATIONAL CONFERENCE ON COMPOSITE TESTING AND MODEL IDENTIFICATION

Evaluation of the Material Properties of Resin-impregnate NOMEX® Paper as Basis for the Simulation

of the Impact Behaviour of Honeycomb Sandwich

F. Hähnel, K. WolfChair of Aircraft Engineering

Institute of Aerospace EngineeringDresden University of Technology

10th, 11th and 12th April 2006Porto, Portugal

COMPTEST 2006 10.-12. April 2006, Porto, Portugal

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Contents

Introduction

Simulating Sandwich Structures

Impact damage behaviour of honeycomb sandwich

Investigation of NOMEX® paper

Impact simulation on honeycomb sandwich

Conclusions


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IntroductionBackground:

Honeycomb sandwich:- high strength- and stiffness-to-weight ratio- thin, brittle CFRP skins and weak core

susceptible to impact loading

Impact damages reduce the load carrying capability

Damage tolerant design of primary aircraft structures

- current procedure: based on experiments expensive- future approach: mainly simulation, few experiments for evaluation

Aim:Development of reliable simulation models to

- obtain the structural response- evaluate damage propagation


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Contents

Introduction





Conclusions


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Simulating sandwich structures

Investigation of damage propagation in sandwich structures (e.g. under impact load) 3D-simulation models necessary

Structural model: - skins shell-elements, - core structure

a) macro-mechanical approach b) meso-mechanical approach

-- global core behaviour implemented in brick elements

- influence of local core failure mechanism are not considered

-- honeycomb cell walls shell elements- influence of local failure mechanism of the cell walls are considered


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Contents

Introduction





Conclusions


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Impact damage behaviour of honeycomb sandwichexample: 15J impact, 1” impactor

crushed honeycomb as result of local buckling and compression failure

of the resin impregnated NOMEX® paper

visible damage of the top face

shear loaded areas - formation of shear cracks in the cell walls

Impact damage formation in the honeycomb core depends mainly on stiffness and strength of the resin impregnated NOMEX® paper


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Contents

Introduction





Conclusions


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Aim: determination of the typical material characteristic and properties (strength, stiffness) as basis for simulation

ISO standards for testing paper and board: only partial applicable development of special testing devices is necessary

Test specimen: honeycomb cell walls rather small - not useable for testing larger sheets of NOMEX® paper required

Test results:ISO standards for testing paper and board:

failure load index =

for simulation: engineering stress - strain behaviour is essential

load_______________________specimen wide · area weight


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Investigation of NOMEX® paperCharacterisation of honeycomb cell walls - example C1 4.8-64

- non-absorbent like silicon paper

NOMEX® paper

phenol resin

NOMEX® honeycomb cell walls - layered material

- coating NOMEX® paper- brittle phenol resin layer


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Investigation of NOMEX® paperTension

P P

Tensile tester: according to standard ISO 1924-2:1994 en

0

20

40

60

80

100

120

0,00 0,02 0,04 0,06 0,08strain [ ]

forc

e [N

]

direction 0° 45° 90°

phenol resin volume fraction

0.000.480.75


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Investigation of NOMEX® paperCompression

P

P

Test device derived from: standard ISO 12192:2002 en – Paper and board determination of the ring crush resistance

clampstest specimen0

100

200

300

400

500

600

0,00 0,10 0,20 0,30 0,40strain [ ]

forc

e [N

]phenol resin volume fraction

0.000.480.62


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Investigation of NOMEX® paperShear

Test device derived from: ASTM D 4255 – Standard Test Method for In-Plane Shear Properties of Polymer Matrix Composite Materials by the Rail Shear Method

P P 0

10

20

30

40

50

60

70

80

0,00 0,05 0,10 0,15 0,20shear deformation [ ]

forc

e [N

]phenol resin volume fraction

0.000.15


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Contents

Introduction





Conclusions


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Impact simulation on honeycomb sandwichExample: 10J impact

Explicit FE-code LS-DYNA

Simulation model

skins - CFRPcore - honeycomb 4.8-48impactor - rigid sphere 1”, 1.1kg

0

0,5

1

1,5

0 2 4 6 8time [ms]

cont

act f

orce

[kN

]

simulation

experiments

structural response


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Impact simulation on honeycomb sandwichexample: 10J impact

NDTvisible

face damage

damaged area top face

simulation

core damage

simulation

damagedhoneycomb

experiment


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Contents

Introduction





Conclusions


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Conclusions

Complex damage formation in honeycomb sandwich structures due to impact loads

Meso-mechanical approach for structural model is necessary to consider local failure mechanism of the honeycomb cell walls in the simulation

Material properties of the honeycomb cell walls are necessary

Special tests for the determination of the material characteristics of phenolresin impregnated NOMEX® paper carried out

The use of measured NOMEX® material data is essential to get good correlation between impact tests and simulation results


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Thank youThank you

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