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Luftfahrzeugtechnik
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
Luftfahrzeugtechnik
Contents
Introduction
Simulating Sandwich Structures
Impact damage behaviour of honeycomb sandwich
Investigation of NOMEX® paper
Impact simulation on honeycomb sandwich
Conclusions
COMPTEST 2006 10.-12. April 2006, Porto, Portugal
Luftfahrzeugtechnik
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
COMPTEST 2006 10.-12. April 2006, Porto, Portugal
Luftfahrzeugtechnik
Contents
Introduction
Simulating Sandwich Structures
Impact damage behaviour of honeycomb sandwich
Investigation of NOMEX® paper
Impact simulation on honeycomb sandwich
Conclusions
COMPTEST 2006 10.-12. April 2006, Porto, Portugal
Luftfahrzeugtechnik
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
COMPTEST 2006 10.-12. April 2006, Porto, Portugal
Luftfahrzeugtechnik
Contents
Introduction
Simulating Sandwich Structures
Impact damage behaviour of honeycomb sandwich
Investigation of NOMEX® paper
Impact simulation on honeycomb sandwich
Conclusions
COMPTEST 2006 10.-12. April 2006, Porto, Portugal
Luftfahrzeugtechnik
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
COMPTEST 2006 10.-12. April 2006, Porto, Portugal
Luftfahrzeugtechnik
Contents
Introduction
Simulating Sandwich Structures
Impact damage behaviour of honeycomb sandwich
Investigation of NOMEX® paper
Impact simulation on honeycomb sandwich
Conclusions
COMPTEST 2006 10.-12. April 2006, Porto, Portugal
Luftfahrzeugtechnik
Investigation of NOMEX® paper
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
COMPTEST 2006 10.-12. April 2006, Porto, Portugal
Luftfahrzeugtechnik
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
COMPTEST 2006 10.-12. April 2006, Porto, Portugal
Luftfahrzeugtechnik
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
COMPTEST 2006 10.-12. April 2006, Porto, Portugal
Luftfahrzeugtechnik
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
COMPTEST 2006 10.-12. April 2006, Porto, Portugal
Luftfahrzeugtechnik
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
COMPTEST 2006 10.-12. April 2006, Porto, Portugal
Luftfahrzeugtechnik
Contents
Introduction
Simulating Sandwich Structures
Impact damage behaviour of honeycomb sandwich
Investigation of NOMEX® paper
Impact simulation on honeycomb sandwich
Conclusions
COMPTEST 2006 10.-12. April 2006, Porto, Portugal
Luftfahrzeugtechnik
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
COMPTEST 2006 10.-12. April 2006, Porto, Portugal
Luftfahrzeugtechnik
Impact simulation on honeycomb sandwichexample: 10J impact
NDTvisible
face damage
damaged area top face
simulation
core damage
simulation
damagedhoneycomb
experiment
COMPTEST 2006 10.-12. April 2006, Porto, Portugal
Luftfahrzeugtechnik
Contents
Introduction
Simulating Sandwich Structures
Impact damage behaviour of honeycomb sandwich
Investigation of NOMEX® paper
Impact simulation on honeycomb sandwich
Conclusions
COMPTEST 2006 10.-12. April 2006, Porto, Portugal
Luftfahrzeugtechnik
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
COMPTEST 2006 10.-12. April 2006, Porto, Portugal
Luftfahrzeugtechnik
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