| dc.description.abstract | Carbon fiber reinforced polymer (CFRP) laminates are currently used in commercial aircrafts
replacing their metallic counterparts. Epoxy is used as matrix in CFRPs in the primary structures
of aircrafts such as fuselage, wings and tail parts, due to its superior properties. However, there
are many disadvantages in CF/Epoxy (CFRE) laminates such as, slow production rate due to
curing, lack of recyclability, brittleness, and susceptibility to catastrophic failure. Additionally,
epoxy requires rivets for joining, have a limited pot life, and pose challenges in damage repair.
Their sensitivity to high temperatures also restricts their use in applications near engine
components. To overcome these problems, high temperature thermoplastics such as PEEK can be
used instead of epoxy as matrix. It does not require curing and the presence of phenyl groups in
the main backbone chain provides high strength, thermal stability and rigidity to the polymer, and
it can be used at high temperatures (150-200oC) for prolonged time without losing structural
integrity. However, the surface energy of CF and PEEK are very different. The lack of functional
groups and smooth surface of CF increases the difficulty in wetting of PEEK over CF. The poor
interface between PEEK and CF will give rise to poor mechanical properties such as interlaminar
shear strength (ILSS), Flexural strength (FS), fracture toughness etc. This work endeavors to
achieve good mechanical properties as well as functional properties such as, deicing and
electromagnetic shielding, in CF/PEEK laminates.
Chapter 1 is introduction giving a holistic view of thermoplastic based laminates in aerostructures.
Current challenges in CFRE laminates and state-of-the-art literature, which provides approaches
to overcome those challenges. It also discusses the outlook and perspective of the literature
review, and the objectives of the thesis. Chapter 2 contains information about the materials, experimental techniques and characterization
methods used in the thesis.
Chapter 3 aims to optimize the processing parameters, pressure, temperature and residence time,
in compression molding to produce CF/PEEK laminates. The results show that 410oC
temperature, 5+10+15+20MPa pressure cycle and 30minutes at each pressure produced the best
laminate with 67MPa ILSS and 658MPa FS, which are much superior to the commercial CFRE
laminates currently being used. The deicing time was 120s in electrothermal heating at 2V to melt
frozen droplets of 10μL water and EMI shielding effectiveness was 47.5dB.
Chapter 4 aims to improve the deicing and EMI shielding performance by incorporating stainless
steel (SS) mesh at the top and bottom of the CF/PEEK laminate. To improve the bonding with
PEEK matrix, SS mesh was coated with Polyetherimide (PEI). ILSS, FS and storage modulus
showed an improvement of 9%, 16% and 44% after the incorporation of PEI coated SS mesh.
The deicing time was reduced from 120s to 45s. EMI shielding effectiveness also improved from
47.5dB to 60dB. The dominant mechanism of EMI shielding changed from absorption to
reflection.
Chapter 5 aims to improve Mode I fracture toughness (GIC) and ILSS by electrospraying graphene
oxide (GO) and then growing ZnO nanorods by SILAR technique on CF surface. GIC and ILSS
showed an increase of 19% and 13% for ZnO+GO-CF/PEEK laminates. The SEM fractographs
showed the interfacial debonding was suppressed and the major mode of failure changed to matrix
deformation. A minor increment in EMI shielding effectiveness was also observed from 47.5dB
to 48.7dB.
Chapter 6 explores the shockwave damage of the neat CF/PEEK laminates and ZnO+GOCF/
PEEK laminates. The damaged laminates were then healed using appropriate temperature and
pressure to recover the loss in mechanical properties. The neat CF/PEEK laminate lost 35% and 66% ILSS at 367bar and 545bar damaging pressure, whereas these losses were 29% and 37% for
ZnO+GO-CF/PEEK laminate. After the healing treatment, the neat CF/PEEK laminate recovered
100% and 74% of original ILSS value at 367bar and 545bar respectively, whereas these values
were 82% and 75% for ZnO+GO-CF/PEEK laminate. Thus, the interfacial strengthening by
ZnO+GO reduced the damage. However, the recovery is similar because the broken ZnO or GO
nanoparticles could not be repaired by healing treatment.
In summary, this thesis contributes to enhance the current knowledge on improving the important
structural and functional properties of CF/PEEK laminates, which is highly desirable as an
aerostructure material in the current scenario. It also explores the damage aspects and recovering
the properties after damage. | en_US |
