SIMULATION OF THE CURE OF PASTE
ADHESIVES BY INDUCTION HEATING
Alberto Sánchez Cebrián, Florian Klunker, Markus Zogg and Paolo Ermanni
ETH Zurich, Centre of Structure Technologies, CH-8092 Zurich,
http://www.structures.ethz.ch
BACKGROUND
COMSOL MODEL
VALIDATION
This study, part of the European JTI ‘Clean sky’,
presents a simulation tool designed to predict time
and temperature dependent evolution of the degree
of cure of the paste adhesives used in CFRP bonded
systems cured by induction heating. The simulation
combines induced Eddy currents in electrical
conductive materials, which cause the heating of the
CFRP adherents by Joule effect, and the consequent
chemical reaction which gives the relation between
temperature, time and degree of cure of the
adhesive.
The setup used considered for the design of the simulation tool
is an AC power supply that provides high current and high
frequency (maximum of 385 A and 400 kHz). The model used is
the EASYHEAT 2.4W by AMBRELL. The inductor head is
composed of a single-turn copper coil and a magnetic field
concentrator attached on the lower part of the coil made of
‘Ferrotron’ by Fluxtrol. The equipment is used to bond SLS
composite structures, supporting the CFRP plates on a sandwich
structure made of GFRP with a cardboard core used as base.
Additionally, wood is used to fix the plates to be bonded and
support the sandwich structure.
For the validation of the model, different
measurements are carried out.
• First of all, the temperatures at different
locations of the model are compared with the
real test rig, validating the predicted
temperature distribution over one of the CFRP
plates as a result of the induction. Additionally,
heating and cooling stages at different points are
measured and compared with the simulation
values.
SIMULATION
APPROACH
COMSOL Multiphysics is the software used to
simulate the behavior of the induction equipment
and the curing process of the paste adhesive used in
the bonded joint. This tool permits to calculate the
theoretical curing degree of the adhesive after
applying certain intensity I (t) [A], dividing the
simulation in three modules: magnetic fields, heat
transfer and the kinetics of the chemical reaction.
INPUT
Temperature distribution
Test rig and geometry used in the COMSOL model
•Electrical current I(t) [A]
•Geometry
•Material properties
•Curing reaction
The simulation is carried out in 2-D in order to reduce the
degrees of freedom and reduce the computational time for the
solution.
The solution provides the temperature distribution of the setup, and using the temperature record to measure the curing
degree according to the curing kinetics of the adhesive.
COMSOL MODEL
Heat
transference
COMSOL
Heating and cooling at the center of the upper CFRP plate
Heating at different positions of the upper CFRP plate.
Magnetic
fields
Curing
Kinetics
Temperature distribution in the simulated test rig applying 54,4 A.
OUTPUT
APPLICATION
Degree of cure α [-]
The model can be used to consider non-isothermal curing
processes, taking on account heating and cooling stages due to
the change of intensity applied to the equipment.
The CFRP plate heats
up from 100 °C to 160
°C when increasing the
electrical
current
applied
by
the
induction equipment,
in this case from 54,4
A to 74 A .
The
increase
of
temperature will lead
to an acceleration of
the curing process,
which will shorten the
overall process, in this
case from 1 hour to
less than 28 minutes.
Cooling at different positions of the upper CFRP plate.
• To complete the validation of the entire model
including the modeling of the curing reaction,
several plates bonded by induction under
different conditions and its degree of cure are
measured by DSC. Finally, obtained results are
compared with the predicted values from the
simulations.
Input parameters
800 s at 62.4A and 256 kHz +
500 s at 69.6 A and 256 kHz
820s at 76 A and 256 kHz
500 s at 62.4A and 256 kHz +
800 s at 69.6 A and 256 kHz
500 s at 62.4A and 256 kHz +
800 s at 76 A and 256 kHz
200 at 62.4 A and 256 kHz
+600 at 76 A and 256 kHz
800 at 36.8A and 266 kHz +
800 at 47.2 A and 260 kHz
800 s at 54.4 A and 258 kHz
50 s at 47.2 and 260 kHz +
500 s at 54.4 A and 258 kHz
350 s at 64 A and 256 kHz
DSC
degree of
cure [%]
COMSOL
Relative
degree of
error [%]
cure [%]
91.7
92.2
0.55
95.2
95.0
0.21
94.8
94.0
0.84
97.2
96.5
0.72
93.8
94.5
0.75
52.3
53.5
2.29
63.2
63.7
0.79
61.8
61.0
1.29
63.1
63.8
1.11