The introduction of nanoscaled reinforcement in otherwise conventional fiber reinforced composite materials has opened
an exciting new area in composites research. The unique properties of these materials combined with the design
versatility of fibrous composites may offer both enhanced mechanical properties and multiple functionalities which has
been a focus area of the aerospace technology on the last decades. Due to unique properties of carbon nanofillers such as
huge aspect ratio, extremely large specific surface area as well as high electrical and thermal conductivity, Carbon
Nanotubes have benn investigated as multifunvtional materials for electrical, thermal and mechanical applications.
In this study, MWCNTs were incorporated in a typical epoxy system using a sonicator. The volume of the
nanoreinforcement was 0.5 % by weight. Two different levels of sonication amplitude were used, 50% and 100%
respectively. After the sonication, the hardener was introduced in the epoxy, and the system was cured according to the
recommended cycle. For comparison purposes, specimens from neat epoxy system were prepared. The
thermomechanical properties of the materials manufactured were investigated using a Dynamic Mechanical Analyser.
The exposed specimens were subjected to thermal shock. Thermal cycles from +30 °C to -30 °C were carried out and
each cycle lasted 24 hours. The thermomechanical properties were studied after 30 cycles .
Furthermore, the epoxy systems prepared during the first stage of the study were used for the manufacturing of 16 plies
quasi isotropic laminates CFRPs. The modified CFRPs were subjected to thermal shock. For comparison reasons
unmodified CFRPs were manufactured and subjected to the same conditions. In addition, the interlaminar shear strength
of the specimens was studied using 3-point bending tests before and after the thermal shock. The effect of the
nanoreinforcement on the environmental degradation is critically assessed.
The remarkable mechanical and electrical properties exhibited by carbon nanotubes (CNTs) have encouraged efforts to
develop mass production techniques. As a result, CNTs are becoming increasingly available, and more attention from
both the academic world and industry has focused on the applications of CNTs in bulk quantities. These opportunities
include the use of CNTs as conductive filler in insulating polymer matrices and as reinforcement in structural materials.
The use of composites made from an insulating matrix and highly conductive fillers is becoming more and more
important due to their ability to electromagnetically shield and prevent electrostatic charging of electronic devices. In
recent years, different models have been proposed to explain the formation of the conductive filler network. Moreover,
intrinsic difficulties and unresolved issues related to the incorporation of carbon nanotubes as conductive fillers in an
epoxy matrix and the interpretation of the processing behavior have not yet been resolved. In this sense, a further
challenge is becoming more and more important in composite processing: cure monitoring and optimization. This paper
considers the potential for real-time control of cure cycle and dispersion of a modified epoxy resin system commonly
utilized in aerospace composite parts. It shows how cure cycle and dispersion control may become possible through realtime
in-situ acquisition of dielectric signal from the curing resin, analysis of its main components and identification of the
significant features.
The attainment of structural integrity of the reinforcing matrix in composite materials is of primary importance for the
final properties of the composite structure. The detailed monitoring of the curing process on the other hand is paramount
(i) in defining the optimal conditions for the impregnation of the reinforcement by the matrix (ii) in limiting the effects of
the exotherm produced by the polymerization reaction which create unwanted thermal stresses and (iii) in securing
optimal behavior in matrix controlled properties, such as off axis or shear properties and in general the durability of the
composite. Dielectric curing monitoring is a well known technique for distinguishing between the different stages of the
polymerization of a typical epoxy system. The technique successfully predicts the gelation and the vitrification of the
epoxy and has been extended for the monitoring of prepregs. Recent work has shown that distinct changes in the
properties of the propagated sound in the epoxy which undergoes polymerization is as well directly related to the gelation
and vitrification of the resin, as well as to the attainment of the final properties of the resin system.
In this work, a typical epoxy is simultaneously monitored using acoustic and dielectric methods. The system is
isothermally cured in an oven to avoid effects from the polymerization exotherm. Typical broadband sensors are
employed for the acoustic monitoring, while flat interdigital sensors are employed for the dielectric scans. All stages of
the polymerization process were successfully monitored and the validity of both methods was cross checked and verified.
The increasing use of composite materials in aerostructures has prompted the development of an effective structural
health monitoring system. A safe and economical way of inspection is needed in order for composite materials to be used
more extensively. Critical defects may be induced during the scheduled repair which may degrade severely the
mechanical properties of the structure. Low velocity impact LVI damage is one of the most dangerous and very difficult
to detect types of structural deterioration as delaminations and flaws are generated and propagated during the life of the
structure. In that sense large areas need to be scanned rapidly and efficiently without removal of the particular
components. For that purpose, an electrical potential mapping was employed for the identification of damage and the
structural degradation of aerospace materials. Electric current was internally injected and the potential difference was
measured in order to identify induced damage in Carbon Fiber Reinforced Polymer (CFRP) structures. The experimental
results of the method were compared with conventional C-scan imaging and evaluated.
The variation of the electrical properties of fiber reinforced polymers when subjected to load offer the ability of strain
and damage monitoring. This is performed via electrical resistance and electrical potential measurements. On the other
hand Carbon Nanotubes (CNTs) have proved to be an efficient additive to polymers and matrices of composites with
respect to structural enhancement and improvement of the electrical properties. The induction of CNTs increases the
conductivity of the matrix, transforming it to an antistatic or a conducting phase. The key issue of the structural and
electrical properties optimization is the dispersion quality of the nano-scale in the polymer phase. Well dispersed CNTs
provide an electrical network within the insulating matrix. If the fibers are conductive, the CNT network mediates the
electrical anisotropy and reduces the critical flaw size that is detectable by the change in conductivity. Thus, the network
performs as an inherent sensor in the composite structure, since every invisible crack or delamination is manifested as an
increase in the electrical resistance. The scope of this work is to further exploit the information provided by the electrical
properties with a view to identify strain variation and global damage via bulk resistance measurements. The
aforementioned techniques were employed to monitor, strain and damage in fiber reinforced composite laminates both
with and without conductive nanofillers.
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