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Desser
Tire and Rubber Company, Inc., and its affiliate
repair station, Aero Wheel and Brake Service uses
state of the art Laser Shearography testing testing
for advanced interferometry non-destructive testing
of aircraft and motorcycle tire carcasses.
Although
this NDT measurement principle is not required
by the FAA or the DOT, we feel such a system significantly
contributes to the safety and quality features
of our retreaded aircraft tires. Michelin and
Goodyear Aircraft retread tire divisions use this
same method for testing on heavy turboprop and
jet transport tires.
As
a matter of fact....our motorcycle tires may be
more thoroughly tested than a new tire. Since
most new tires are not subject to Laser Shearography,
we can find areas of concern that have not ever
been looked for by the original manufacturer.
Shearography
Measuring System
Shearography
was originally designed for strain analysis and
inspection and evaluation of honeycomb and bonded
composites. Laser Shearography is very sensitive
to slight changes in surface strain due to subsurface
flaws, and it is able to detect imperfections
and defects such as belt-edge separations, bead
blisters, undercure, liner separation and broken
cord and ply construction in aircraft tires.
Our
new system accommodates aircraft tires up to 49" in diameter, incorporating the latest computer
imaging analysis software, electronic Phase-Shearing-Interferometry
methods, integrated laser-diode CCD camera, and
adapted optic illumination image analysis in real
time. The system will store the recorded test
on disc for accurate traceability by work order
and serial number.
The
benefits of this system are:
1.
Dramatically increased carcass abnormality detection
2. Immediate carcass fatigue detection
3. Immediate internal damage of carcass detection
4. 100% validation of used carcass
5. Increased detectability of carcass deterioration
Desser
Tire and Rubber Company, Inc., is the only aircraft
tire retreader (excluding OEM's) that has taken
this action to support the safety and reliability
of our retreaded aircraft tire products for our
valued customers. We will continue to look for
ways to improve on the quality and processes in
the products we provide. We look forward to supporting
the needs of corporate and commuter aircraft operators
worldwide.
Below is the technical aspect
of laser shearography:
Basics
of Interferometry
The following are Non Destructive
Testing methods typically used for the
inspection of new tires and casings for retreading:
Ultra Sonics -
low resolution
X-Ray -
other anomalies
Interferometry - interferometry
is the core technology in our applications
and therefore it is declared in more detail now
Interferometric Methods
In the past:
film-based Holographic Interferometry
and Shearography
Today:
film-less "Speckle-Interferometry"
and "Speckle-Shearing"
- Compact sealed optical
setup with an
- integrated interferometer
with CCD-camera
- integrated laser
laser diodes
- Standard PC
with an image analysis system
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Principle of Measurement
the basic effect is the interference
of light waves
- fast and sensitive
(~ 0,0004 mm fringe to fringe)
- safe, no radiation (machine
setup is laser class1)
to get this interference effect the
light source has to meet the following main requirements:
- single frequency
and constant over the time (coherent)
the measuring technique is
based on:
- Michelson Interferometer
for the Shearing-Setup
- Classic Phase-Shifting
Method for Image Analysis
- Multiple Laser-Diodes
(US Patent,
No. US 6,417,916 B1)
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Test-Setup for tire testing:
the measuring setup is positioned
relative to the
tire inside or/and outside
the inspection of the tire is in
sections
of circumference
the whole setup is within a chamber
to stress
the tire with a pressure differential
Measuring:
the surface is illuminated with
coherent light
and simultaneously observed with
the
shearing setup
two phase shifted images
- before and after stress load
- are superposed
and preprocessed
Courtesy
of SDS Systemtechnik GmbH.
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