Integration of Nanotechnology with materials for aerospace application. A hot research topic

1. NASREEN HABEEB UR RAHIMAN
M140497NS
NIT-C

2.  Introduction
 Carbon Nanotubes
 Potential role of CNTs in aeronautics
 Single-walled carbon nanotube–epoxy composites
for structural and conductive aerospace adhesives
 Need for structural and conductive aerospace
adhesives
 Why CNT based composite?
 Experimental details
 Performance evaluation
 Results and Discussions
 Conclusion
 Further scope of research
 Reference

3.  A cylinder fabricated of rolled up graphene sheet.
 Sp2 hybridized carbon- hexagonal layers with weak out-
of plane bonding (Van der Waals force) and strong in
plane bonds.
 Structure characterized by chiral vector, C = na1 + ma2
 Integer pair (n,m) gives number of unit vectors in
graphene lattice along two directions
 Carbon tube diameter is given by
,a is lattice constant of graphene
sheet

4. CNT
SWCNT
(Single walled)
Zigzag structure :
m=0
Armchair: n=m
Chiral : n≠m
MWCNT
(multi walled)
Russian doll model:
One CNT contains
another CNT inside it
Parchment model:
Single graphene sheet
wrapped around itself
PROPERTIES:
•When n-m = multiple of 3, highly conductive or
metallic CNT (e.g. armchair)
•High elasticity
•MWCNT shields inner carbon nanotubes from
chemical attacks and has higher tensile strength.
•Due to strong bonds, they are good thermal
conductors and can withstand elevated
temperature

7. NEED FOR STRUCTURAL AND CONDUCTIVE
AEROSPACE ADHESIVES
 Adhesively bonded joints pursued as alternatives
to mechanical joints in aerospace and other
engineering applications
 Advantages : lower weight, lower fabrication
cost, and improved damage tolerance
 Riveting is the only current solution for electrical
bonding. Disadvantages are:
 Corrosion risks and damage to carbon fiber reinforced
plastics (CFRP)
 additional holes and the weight of the rivets
 conductive adhesives with good structural
bonding capability is required to achieve both
structural and electrical adhesive bonding of
aircraft structures.

8.  Electrical bonding: intentional connection of all
exposed metallic items not designed to carry
electricity in a room or structure as protection
from electric shock. This creates equipotential
zone
 Electrical bonding in aircraft :
 electrical bonding prevents static electricity build up
that can interfere with radio and navigation
equipment.
 Provides lightening protection-by allowing the current
to pass through the airframe with minimum arcing.
 Prevents dangerous static discharges in aircraft tanks
and hoses.

9.  Improve mechanical properties and impart electrical
conductivity to polymers, including epoxy
 Conductivities have reached 103 Sm-1 at several wt% CNT
filler, well above the percolation threshold
 Critical volume fraction for electrical percolation of
randomly distributed nanotubes is inversely proportional
to the aspect ratio (length-to-diameter ratio)
 Hence, nanotubes reach the percolation threshold with
a very small volume fraction
 This helps to achieve good electrical conductivity
without sacrificing the high-performance structural
bonding requirements of an aerospace adhesive

10.  SWCNTs offer
 the highest intrinsic conductivity and aspect ratio
 lowest percolation threshold, which is typically less
than 0.1 wt%.
 Lower percolation threshold
higher conductivity at a fixed loading
 Thus SWCNT based epoxy composite was chosen
implies

11. MATERIALS:
 SWCNT produced by LASER ablation
 Size: average diameter= 1.34nm, length=1-10µm
 Baseline adhesive: aerospace grade epoxy resin +
amine based hardener
SYNTHESIS:

12. • for screening SWCNT dispersion at the optical level
• Sampling larger area along with showing compositional variation
 Disk shaped samples (1 mm thickness, 3–4 cm diameter)
prepared by curing between glass plates treated with a
release agent
 A silver paint was used on the top and bottom surface to
provide electrodes.
 A Keithley 2635A source-meter unit was used to measure I–V
curves, typically from 10 V to +10 V
 conductivity determined from the slope of the curve in the
Ohmic region and sample dimensions. This approach works
only for conductive composites (σ >10-7S m-1)
 for very low conductivity samples, i.e. conductivity (σ ~10-13
Sm-1) was estimated by applying a larger voltage (±100 V) and
waiting (500 s) for the current to stabilize.

14. samples for tensile testing
were cut into bars
(3.5 mm wide and 30 mm
long)
tested using a micro-
tensile test frame
(Fullam sub stage test
frame) at a displacement
rate of 1 mm/min

15.  Adhesive bonding can be tested by : tensile,
shear/compression testing, peel
testing(applied when there is flexibility in a
joined layer)
 Typical peel test involve peeling two flexible
adherents from each other ,or a flexible
bonded adherent from a rigid substrate.
 Generally conducted at 900 or 1800 angles
 Peak peel load, average peel strength and
statistical measures of peel strength
variability are some parameters used to
characterize behavior under peel loading

16. Preparation of adhesive bonded panels using SWCNT–adhesive composite showing
(a)spreading of adhesive onto a peel test panels (covering half a panel)
(b–d) assembly of lap-shear test panels.

17.  Shear joints impose uniform stresses across bond area,
which results in highest possible joint strength.
 Generally uses a single lap joint specimen to
determine the shear strength of specimens
 Procedure :
measure amount of shear area in square centimeters
 load each end of specimen in the tensile grips 
apply force at controlled rate till the specimen breaks
 record the maximum force and type of joint
failure.
 Evaluating the SEM images give the type of joint
failure

21.  Darker areas are indicative higher
concentration of the SWCNT filler.
 More uniform dispersion is observed for THF-
dispersed SWCNTs in comparison to acetone-
dispersed SWCNTs.
 THF is generally a better solvent for CNTs

22. 1. ELECTRICAL PROPERTIES
curing at elevated temperature gives consistent yield

23. 1.
• Tensile tests conducted on samples with loadings of 0,
0.2, 0.5 and 1 wt% SWCNTs
2.
• ultimate tensile strength (UTS), elastic modulus (E), and
maximum strain (εmax) were maintained or improved with
up to 1 wt% SWCNTs, regardless of the solvent
3.
• UTS and εmax decreased significantly at 2 wt% SWCNTs
4.
• Therefore, based on the electrical and tensile results,
loadings of 0, 0.5 and 1 wt% SWCNTs were selected for
study with joint tests.

24.  0.5% SWCNT content shows similar strength of
baseline adhesive

26.  The resistance of bonded aluminum/CNT adhesive/aluminum
coupons was significantly higher than predicted by the bulk
conductivity
 Resistance dramatically affected by the surface preparation method
 indicates the importance of
contact effects
 Cleaned-only sample had the
lowest apparent conductivity
due to presence of oxide layer
of Aluminium.
 Post-application of electrical
current across such joints
improved electrical performance
due to localized decomposition
of the surface oxide near
CNT-adherent contacts

27.  SWCNT–adhesive composite joints were prepared containing
0.5 wt% and 1 wt% SWCNT filler and performance was
compared to that of the baseline, aerospace-grade adhesive
 The composites are conductive, with a percolation threshold
between 0.2 and 0.5 wt%.
 The joint resistance of bonded metal/SWCNT–adhesive/metal
samples was two-to-three orders of magnitude higher than
expected from the bulk electrical conductivity; owing to
surface-oxide-effects in metal bonds
 The apparent conductivity of the bonded samples could be
improved by a voltage post-treatment step such that the
bonded samples reached roughly 30% of bulk conductivity.
 Peel strength was improved with a SWCNT loading of 1 wt%.

28.  Even the most conductive CNT–polymer composites,
both in the present study and the wider literature, do
not reach the 105S m-1 achieved in silver-filled ECAs
(electrically conductive adhesives)
 But they do achieve moderate conductivity with
1/100th the amount of conductive filler required in
conventional ECAs for electronics applications, where
the structural bonding requirements are low.
 Whether some decrease in lap shear strength at 1 wt%
SWCNTs is an acceptable trade-off to improve
conductivity will depend on the detailed joint
requirements and the effect of the CNTs on other
parameters (e.g., shelf-life and viscosity).
 The conductive adhesives in this study easily exceed the
threshold cited for electrostatic discharge

29.  The best results in the present study (0.1 S m-1
for 1 wt% SWNCTs) show potential to reach
other thresholds around 1–10 S m-1, including
that to enable electromagnetic shielding, but
further improvement is required to reach
these targets.

30.  Potential and prospective implementation of
carbon nanotubes on next generation aircraft
and space vehicles: A review of current and
expected applications in aerospace sciences
Omid Gohardani, Maialen Chapartegui Elola, Cristina
Elizetxea
 Single-walled carbon nanotube–epoxy
composites for structural and conductive
aerospace adhesives :
Michael B. Jakubinek , Behnam Ashrafi , Yunfa
Zhang,Yadienka Martinez-Rubi,Christopher T. Kingston a,
Andrew Johnston b, Benoit Simard.