SIMULATION OF THE CURE OF PASTE ADHESIVES BY INDUCTION HEATING · · 2015-12-07systems cured by...
1
BACKGROUND 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. 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. COMSOL VALIDATION 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. Temperature distribution Heating and cooling at the center of the upper CFRP plate Heating at different positions of the upper CFRP plate. 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. Alberto Sánchez Cebrián, Florian Klunker, Markus Zogg and Paolo Ermanni ETH Zurich, Centre of Structure Technologies, CH-8092 Zurich, http://www.structures.ethz.ch SIMULATION OF THE CURE OF PASTE ADHESIVES BY INDUCTION HEATING Input parameters DSC degree of cure [%] COMSOL degree of cure [%] Relative error [%] 800 s at 62.4A and 256 kHz + 500 s at 69.6 A and 256 kHz 91.7 92.2 0.55 820s at 76 A and 256 kHz 95.2 95.0 0.21 500 s at 62.4A and 256 kHz + 800 s at 69.6 A and 256 kHz 94.8 94.0 0.84 500 s at 62.4A and 256 kHz + 800 s at 76 A and 256 kHz 97.2 96.5 0.72 200 at 62.4 A and 256 kHz +600 at 76 A and 256 kHz 93.8 94.5 0.75 800 at 36.8A and 266 kHz + 800 at 47.2 A and 260 kHz 52.3 53.5 2.29 800 s at 54.4 A and 258 kHz 63.2 63.7 0.79 50 s at 47.2 and 260 kHz + 500 s at 54.4 A and 258 kHz 61.8 61.0 1.29 350 s at 64 A and 256 kHz 63.1 63.8 1.11 Heat transference Magnetic fields Curing Kinetics INPUT •Electrical current I(t) [A] •Geometry •Material properties •Curing reaction OUTPUT Degree of cure α [-] COMSOL MODEL 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. Test rig and geometry used in the COMSOL model 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 set- up, and using the temperature record to measure the curing degree according to the curing kinetics of the adhesive. Temperature distribution in the simulated test rig applying 54,4 A. APPLICATION 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. COMSOL MODEL
Transcript of SIMULATION OF THE CURE OF PASTE ADHESIVES BY INDUCTION HEATING · · 2015-12-07systems cured by...
BACKGROUND 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.
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.
COMSOL
VALIDATION 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.
Temperature distribution
Heating and cooling at the center of the upper CFRP plate
Heating at different positions of the upper CFRP plate.
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.
Alberto Sánchez Cebrián, Florian Klunker, Markus Zogg and Paolo Ermanni
ETH Zurich, Centre of Structure Technologies, CH-8092 Zurich,
http://www.structures.ethz.ch
SIMULATION OF THE CURE OF PASTE
ADHESIVES BY INDUCTION HEATING
Input parameters DSC
degree of cure [%]
COMSOL degree of cure [%]
Relative error [%]
800 s at 62.4A and 256 kHz + 500 s at 69.6 A and 256 kHz
91.7 92.2 0.55
820s at 76 A and 256 kHz 95.2 95.0 0.21 500 s at 62.4A and 256 kHz + 800 s at 69.6 A and 256 kHz
94.8 94.0 0.84
500 s at 62.4A and 256 kHz + 800 s at 76 A and 256 kHz
97.2 96.5 0.72
200 at 62.4 A and 256 kHz +600 at 76 A and 256 kHz
93.8 94.5 0.75
800 at 36.8A and 266 kHz + 800 at 47.2 A and 260 kHz
52.3 53.5 2.29
800 s at 54.4 A and 258 kHz 63.2 63.7 0.79 50 s at 47.2 and 260 kHz +
500 s at 54.4 A and 258 kHz 61.8 61.0 1.29
350 s at 64 A and 256 kHz 63.1 63.8 1.11
Heat transference
Magnetic fields
Curing Kinetics
INPUT •Electrical current I(t) [A]
•Geometry
•Material properties
•Curing reaction
OUTPUT Degree of cure α [-]
COMSOL MODEL 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.
Test rig and geometry used in the COMSOL model
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 set-up, and using the temperature record to measure the curing degree according to the curing kinetics of the adhesive.
Temperature distribution in the simulated test rig applying 54,4 A.
APPLICATION 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.
COMSOL MODEL
