Development of building block approach for crashworthiness testing of composites

Development of building block approach for crashworthiness testing of composites

1. Development of a
Building BlockApproach
for CrashworthinessTesting
ofComposites
DanAdams
University ofUtah
FAA JAMS 2018 TechnicalReview
May24,2018

2. FAA Sponsored ProjectInformation
2
•PrincipalInvestigators:
Dr. DanAdams
•Graduate StudentResearchers:
Mark Perl
Dalton Ostler
MichaelTerry
•FAA TechnicalMonitor:
AllanAbramowitz
•Collaborators:
Boeing:Mostafa Rassaian, Kevin Davis
Engenuity, LTD: Graham Barnes
Hexcel: AudreyMedford

3. Overview:
3
CMH-17 Crashworthiness WorkingGroup
•Founded in 2005
•Original focus on automotivecomposites
•Current focus on aviationapplications
•Testing, Analysis, and Certificationsubgroups
•Two previous exercises/phases in testing &analysis
•Current focus: Phase III crashworthiness building
blockexercise
–Monthlyteleconferences
–Meet at CMH-17: Charleston, SC, Tues July 31,1:30-5:45

4. FloorBeam
Stanchion#3
Frame &Skin
•Central assembly consisting
of four primarymembers
4
•Stanchion#3
(primary crushmember)
•Floorbeam
•Frame
•Skin
•Initial sizing based on 6gvertical
loadingcondition
(AltairEngineering)
•Cross sectiongeometry
•Laminate plyorientations
•Laminatethickness
Current CMH-17 ChallengeProblem:
Composite Cargo FloorStanchion

5. TraditionalDesign:Use of 0°, ±45°, and 90°plies
Material:IM7/8552 unitapeprepreg
Geometry:C-channel
Laminate:“Hard”laminate
•50%0°,25%±45°,25%90°(50/25/25)
•16 plies (@ 0.0072 in.), 0.115 in.thickness
FloorBeam
Stanchion
Frame &Skin
Primary CrushMember:
C-ChannelStanchion
5

6. Initial TestingActivities:
Laminate Design forCrashworthiness
•Flat-coupon crushtesting
•Tailor laminate to achieve stable
crush, high energyabsorption
•Miniround-robintoevaluate
proposedcrushtestfixtures
anddraftstandard
Design-value
development
Component
tests
Sub-componenttests
Structural elementstests
Allowabledevelopment
Material specification development Materialproperty
evaluation
Material screening andselection
Full-
scale
te s ts
Analysisvalidation
6

7. Flat Coupon CrashworthinessTesting:
What will these testsprovide?
Specific Energy Absorption(SEA):
Energy absorbed per unit mass of crushedmaterial
•Usefulness typically limited to material/laminate
screening and rankingpurposes
Energyabsorbed
SustainedCrushStress:Average crush load
divided by the specimen cross sectionalarea
•A measure of the crashworthiness of
a compositematerial/laminate
•Useful in the design of crushstructures
CompressionCrushRatio:Ratio of compression
strength to the sustained crushstress
•An indicator of the likelihood of the composite
material crushing in a stablemanner
7

8. Previous ResearchResults:
Crush Modes Affect EnergyAbsorption
FiberSplaying
•Long axialcracks
•Frondformation
•Delamination
dominated
Fragmentation
•Short axialcracks
•Shear failure from
compressivestresses
•Extensive fiberfracture
BrittleFracture
•Intermediate length
cracks
•Combines characteristics
from other failure modes
Energy
Absorption
8

9. Flat Coupon CrushTesting:
Unsupported andPin-Supported
UnsupportedTesting
For FlatSections
Pin-SupportedTesting
For Curved Sections &Corners
•Measure SEA and CrushStress
for both supportconditions
•For use in crush predictionsof
structuralmembers
9

10. “Hard” Laminates (50/25/25) to betested:
•[902/±45/04]S
•[902/02/±45/02]S
•[90/+45/02/90/-45/02]S
•[±45/902/04]S
•[±45/90/0/90/03]S
Stiffest plies atmidplane
High SEA in previousstudy
Plydispersionwhile maintaining SEA
45’s on outside, high SEA previousstudy
45’s on outside, greater plydispersion
Hybrid laminates –with fabriclayers
•[(0/90)f/±45/02]S
•[(±45)f/902/04]S
•[(±45)f/90/0/90/03]
0/90 Fabric layer onoutside
±45 fabric layer onoutside
Outer fabriclayer,greaterplydispersion
Stanchion#3
Laminate Design forCrashworthiness:
(50 25 25) HardLaminate
10

11. Flat Coupon Crush TestResults:
HardLaminates
•50% 0°, 25%±45°,
25%90°
•No significant
difference dueto
fabric layers in
Hybridlaminates
•Minimalvariation
betweenlaminates
investigated
•Two laminates
selected forfurther
investigation
All laminates produced good energyabsorption
80
70
60
50
40
30
20
10
0
HardLaminates HybridHard
Laminates
SEA
(kJ/kg)
Unsupported Pin‐Supported
11

12. 80
70
60
50
40
30
20
10
0
Quasi‐Isotropic HybridQuasi‐
Isotropic
SEA
(kJ/kg)
UnsupportedPin‐Supported •No significant
difference due
to fabriclayers
in hybrid
laminates
•Minimal
variation in pin-
supportedtests
Fewer 0°plies produces lowerSEA
Flat Coupon Crush TestResults:
Quasi-IsotropicLaminates

13. 0
10
20
30
40
50
60
70
80
[
±
45/90₂/0₄]s
[90₂/
±
45/0₄]s
[
±
45/90/0/90/0₃]s[90
₂/
0
₂
/±
45/
0
₂]s
[90/+45/0₂/90/‐45/0₂]s
[(0/90)f₂/
±
45/0₄]s
[(
±
45)f₂/90/0/90/0₃]s
[(
±
45)f₂/90₂/0₄]s
[90/
±
45/0]₂s
[(
±
45)₂/90₂/0₂]s
[90₂/(
±
45)₂/0₂]s
[
±
45/90/0]₂s
[(
±
45)f₂/(
±
45)f₂/90₂/0₂]s
[(0/90)f₂/
±
45/90/
±
45/0]s
HardLaminates HybridHard
Laminates
Quasi‐Isotropic HybridQuasi‐
Isotropic
SEA
(kJ/kg)
Unsupported Pin‐Supported
Flat Coupon Crush TestResults:
LaminateComparison
13

14. •IM7/8552 unitape prepreg, 190gsm
•[902/02/±45/02]s and[90/+45/02/90/-45/02]S
•“hard”laminate
•0.25 in. cornerradius
•Layup and cure in accordance
with NCAMPspecifications
C-Channel Stanchion CrushTesting:
SpecimenManufacturing

15. CurrentFocus:
C-Channel CrushTesting
•University of Utah instrumented
drop-weight impacttower
•High-speed video of crush
process
•[902/02/±45/02]sand
15
[90/+45/02/90/-45/02]S
“hard”laminates
•Results to be used
to assessnumerical
modelingcapabilities

16. •Use of “double dog-bone”specimen
•Dynamic compression test fixture similar
to crushfixture
•Variable drop height to control strainrate
•High crosshead mass used to ensure
constant strain rate over testduration
•Digital Image Correlation used
to determine strainrate
•Used to investigatechanges
in modulus and strengthat
strain rates between 5-30ɛ/sec
Dynamic MaterialsCharacterization:
CompressionTesting
16

17. •Modification to V-Notched
Rail ShearTest,
ASTM D7078
•Compressionloaded
•Use in droptower
•Allows for testingof
variouslaminates
•Use of Digital Image
Correlation (DIC) to
measure strainsduring
testing
•Challenges with inertial
effects producing load
oscillations
Dynamic MaterialsCharacterization:
V-Notched ShearTesting
17

18. •Compression-loaded
fixture producestension
load inspecimen
•Dynamic analog toASTM
D3518
•Use of ±45°laminate
•Tensionloaded
•Load using drop tower
•Use of Digital Image
Correlation (DIC) to
measure strains during
testing
Dynamic MaterialsCharacterization:
±45°Tensile ShearTesting
18

19. Stanchion#3
•Stanchion bolted to the
upper floor and lowerframe
•Bearing failure possible at
boltedconnection
•Investigate dynamic bearing
strength and bearing crush
behavior
19
CurrentFocus:
Dynamic BearingTesting

20. •Single fastener/singleshear
bearingtest
•Use of Univ. of Utah flat coupon
crush testfixture
•0.25 in. diameter steelfastener
•Test specimen bolted to steel
block
•Compressionloaded
•Quasi-static: 0.4in/min
•Dynamic: 12 ft/sec
(drop-weightimpact)
TestProcedure:
Dynamic BearingTesting
20

21. 0
5
10
15
20
25
0 5 20
Force
(kN)
10 15
Displacement(mm)
[90/+45/0₂/90/-45/0₂]s Laminate
Dynamic Static
Avg. Dynamic Peak Force 18.0kN
Avg. Static Peak Force15.7
•Initial load peak
(bearing strength)
followed by
progressivecrush
21
•Dynamic bearing
strength 10-20%
higher thanquasi-
static
Initial TestResults:
Dynamic BearingTesting

22. Dynamic BearingTesting:
EnergyAbsorption
•Minimaldifference
inSEAvaluefrom
staticanddynamic
testing
•Significantly
higher SEAthan
obtained for
laminatecrush
22

23. Dynamic BearingTesting:
EnergyAbsorption
•Minimaldifference
inSEAvaluefrom
staticanddynamic
testing
•Significantly
higher SEAthan
obtained for
laminatecrush
•SEA based on
width offastener
(0.25 in.) and
crush
displacement
23

24. BENEFITS TOAVIATION
24
•Building block approach for composite
crashworthiness
•Development of coupon-level testing to assess
crashworthiness of composite materials and
laminates
•Documentation of building block exercise in
CMH-17
•Dissemination of research results through FAA
technical reports and conference/journal
publications

25. Thank you for yourattention!
Questions?