Induction Heating and Health Monitoring using Adapted ... · Induction Heating and Health...
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Induction Heating and Health Monitoring Solutions for Smart Aircraft Maintenance using Adapted Composite Patches - INDUCERINDUCERINDUCERINDUCER
Induction Heating and Health Monitoring
Solutions for Smart Aircraft Maintenance
using Adapted Composite Patches
INDUCERINDUCERINDUCERINDUCER
Project No: SP1-JTI-CS-2009-01-255770-GRA-01-010
Topic Manager: Alenia Aeronautica
Bonded composite repaired areas of aircraft structures frequently suffer from a variety of factors that
may influence their structural integrity, on either a short or long term basis. In order to overcome
these drawbacks, an advanced aircraft repair and maintenance concept of “smart patches” has been
developed, both for composite to composite and composite to metal repairs, combining “smart curing”
of the repair by induction heating and “smart sensing” using magnetostrictive sensors. One of the main
innovations of this project is that the same element which will be used within the repair for induction
heating (i.e. magnetostrictive sensors array), will be consequently used for lifetime structural health
monitoring of the repaired area, providing accurate mapping of strain development and evolution.
Smart Curing:Smart Curing:Smart Curing:Smart Curing: Induction heating occurs in ferromagnetic materials when they are exposed to a varying magnetic field. This
is the result of the development of “eddy currents” in the material, which means that heat generation is
mainly the consequence of the Joule effect. Heat is no more produced remotely and then transferred to the
repair by conduction (as in the case of “heating blankets”), but is internally generated by means of induced
electrical eddy currents, through a coil placed on top of the patch, that creates a rapidly alternating
electromagnetic field within conductive elements of the repair (susceptors).
Induction heating principle Different susceptor placement options Generation of heat in the repair
The developed induction system within INDUCER consists of a low power generator adapted to the process
needs, a specially designed induction coil and a susceptor in the form of a magnetostrictive materials mesh .
Initial prototype equipment used for
development of the induction principle
“Butterfly” coil configuration
used for heat generation
Final portable induction heating equipment
for in field applications
The induction heating methodology achieves better temperature homogeneity and process efficiency
compared to conventional conduction heating equipment and methods, resulting in direct improvement of the
repair quality, due to the minimization of thermal losses, as heat is generated within or extremely close to the
repair area to be heated. Moreover, the area to be heated is much smaller compared to conventional heating
using thermal blankets, leading to a significant improvement in power consumption compared to current
technology. Finally, being a non-contact process, equipment and consumables requirements are minimized
(cables exiting vacuum bagging etc.), making induction heating more robust, reliable, faster, cheaper and
easier to apply, compared to conventional conduction heating techniques, leading to an environmentally
friendly, low-energy, low-cost and easily interfaced solution for operational field bonding.
Aluminium
Composite
Induction Coil
Susceptor
Induction Heating and Health Monitoring Solutions for Smart Aircraft Maintenance using Adapted Composite Patches - INDUCERINDUCERINDUCERINDUCER
Smart sensingSmart sensingSmart sensingSmart sensing When a magnetic material carrying a low intensity & high frequency alternating current is subjected to an
external magnetic field, it exhibits a sharp change in its electrical impedance, called Magneto-Impedance
(MI) effect. Magnetostrictive Materials (MGSM) change shape when subjected to a magnetic field, due to the
fact that magnetic domains in the material align with the magnetic field, while the magnetic energy changes
when the material is strained (stretched or compressed). This phenomenon is reversible and is simplified into
two reversible energy conversion steps: Electric ⇔ Magnetic & Magnetic ⇔ Mechanical. It was
demonstrated that tensile and torsion stresses modify this domain structure, by introducing circular magnetic
anisotropy and/or helically magnetized interface between both areas, therefore changing the spatial
magnetization distribution close to the surface. Within INDUCER, the change of the MI response under the
effect of stresses was measured using appropriate magnetic flux sensors (i.e. co-centric induction coils) in
order to produce an image of the strains developed in repaired areas, for structural health monitoring
purposes.
Specimens with incorporated
MGSM used for
characterization of properties
Typical diagrams of ∆V
versus strain retrieved for
MGSM (Fe77.5Si7.5B15)
MGSM wires mesh produced
within INDUCER for smart
sensing and heating
Achieved performances
Strain Sensitivity: 0.02%
Spatial Sensor Resolution: 10µm
Overall method resolution: 2mm (depending on the MGSM mesh pitch)
Very good repeatability of
measurements.
Very good stability in time.
MGSM like Fe77.5Si7.5B15 and Co68.25Fe4.5Si12.25B15 were used in the form of wire of approximate diameter
0.125 mm (i.e. equivalent to the thickness of UD prepregs), produced according to the INDUCER
specifications in order to comply with composite repair health monitoring requirements.
Co-centric magketic fluc
sensors and MGSM wire
MGSM and magnetic
flux model setup
MGSM and magnetic flux
simulation results
Magnetic sensor equipped with
IR LED to record scanning
Apart from the hardware design and manufacturing, the appropriate algorithms and software have been
developed to support the MGSM sensing. Main achievements included specially designed software to (a)
Support the magnetic flux scanning by recording the sensor position and indicating successful area scanning
(b) Convert magnetic flux to strain measurements, (c) Visualize results using chromatic codes and (d)
Compare current to previous strain readings, to enable identification of areas where damage may exist.
Scanning progress
supporting software
Visualization of measurements
along MGSM wire
Measurements of
crossing MGSM
Overview of experimental set up for structural
health monitoring technology development
The combination of “smart heating” with “smart sensing” using magnetostrictive wires meshes
developed within INDUCER is expected to result in reduction of overall aircraft maintenance costs,
through (a) increase of repair and maintenance process reliability, (b) achievement of better repair
quality, (c) reduction of aircraft downtime during inspection intervals and (d) enabling certification of
larger and more complex bonded composite repairs, both to composite and to metallic structures.