Development of thin-ply composites in the last decade has opened up new possibilities for designing
high-performance lightweight and flexible structural components with increased damage resistance,
ductility and multifunctionality. In addition to improved mechanical properties thin-ply hybrid
laminates can be simultaneously utilized as multifunctional materials owing to beneficial physical
properties of constituents. For example, glass fibers have good electrical insulation properties and
carbon fibers have good thermal conductivity properties. Such multifunctional hybrid composites have
great potential for application in structural electronics, structural batteries, aerospace and
automotive industry among others. In the present work carbon/glass thin-ply laminates with various
lay-ups and different layer thicknesses were studied experimentally. Laminate specimens were
subjected to cyclic mechanical loading with relatively high frequency, which causes self-heating of
composite and accelerates the fatigue failure. A detailed investigation of self-heating within the
laminate was performed in the present work using high-resolution thermal imaging camera.
Carbon/glass thin-ply laminates were manufactured using Textreme carbon fiber plain weave fabrics
from Oxeon (Sweden) with areal weight of 100g/m2 and glass fiber plain weave fabrics from Interglas (Germany) with an areal weight of 80g/m2. Epoxy resin LY1564 from Huntsman (USA) with XB3404-1 hardener was used as the matrix. Fabrics were hand stacked into 6 different lay-ups and two
reference materials (purely carbon fiber/epoxy and purely glass fiber/epoxy composites). Vacuum
infusion technique was used for epoxy infusion into the stacked dry fabrics. Composite plates were
cured in an oven at 80°C temperature for 8 hours. Hybrid carbon/glass laminates with various
combinations of single, double and quadruple carbon and glass fiber layers were manufactured for the
purpose of parametric analysis regarding their self-heating and heat transfer behavior. All plates
including the reference material plates consisted of 16 layers.
The main objective of the present work is to parametrically investigate self-heating of hybrid
carbon/glass thin-ply laminates subjected to cyclic mechanical loading. Mechanical loading was
performed on Instron E10000 dynamic testing machine, equipped with a ±10 kN load cell. The tests
were carried out in tension-tension cyclic loading regime with fixed maximum and minimum strain
levels. In order to observe a clearly measurable self-heating effect during the cyclic loading, relatively
large loading frequencies (20 – 30Hz) were applied. Maximum applied tensile strain levels were in the
range from 0.4% up to 0.9%. Heat generation and temperature distribution within laminate layers were
measured using a high-performance and high-resolution thermal imaging camera FLIR A6752sc. In
order to perform a detailed temperature change monitoring in thin laminate layers, the camera was
equipped with FLIR 1X microscope lens. All cyclic loading tests were started at room temperature and
the cyclic loading of specimens was conducted until reaching steady state thermal conditions at which
no significant further temperature increase was observed. After reaching the steady state temperature
(typically within 7-8 minutes) the cyclic loading was stopped but the specimen was kept in the tensile
machine grips until complete cool-down back to room temperature. The temperature distribution and
change in the force was also recorded during the cool-down step.
The results for reference carbon/epoxy laminates (CR) were analyzed first. As expected, it was found
that higher applied maximum strain level leads to larger self-heating and higher temperatures recorded
during the test. The effect of loading frequency (20-30 Hz) on self-heating for CR laminates was found
to be relatively small. Results for glass fiber reference laminates (GR) subjected to 20 Hz
cyclic loading frequency at different maximum strain levels. Relative
increase of average temperature (ΔT) in test specimens with respect to initial (room) temperature is
plotted on the vertical axis. In general, self-heating increases significantly with
increased maximum strain level. Compared to CR laminates, results indicated higher self-heating of
GR laminates when subjected to equal loading conditions. Finally, the work also investigated and
compared the self-heating of various carbon/glass hybrid laminates. A clear dependency of self-
heating on laminate lay-up and maximum strain level was observed. Notably, the hybrid laminate lay-
up with the most distributed layer configuration and with carbon/epoxy external layers demonstrated
the highest self-heating compared to other studied hybrid laminate lay-ups
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