A new
testing tool holds promises to further improve the safety of carbon composite
structures, such as the Boeing 787 Dreamliner.
A2 Technologies, a member of the University of Delaware
Center for Composite Materials' Industrial Consortium, developed an
innovative handheld device that allows on-site non-destructive testing of
aircraft components.
The
analyzer, called Exoscan, is based on a characterization technology known as Fourier
Transform Infrared Spectroscopy (FTIR), which has traditionally been
carried out in a lab. The breakthrough with the Exoscan is its portability,
enabling aircraft and other large metal or composite parts to be examined in
place without destructive removal of small-scale samples.
The system
tracks changes in the resin properties or contamination on the surface,
allowing evaluation of environmental damage, such as lightning strikes. It's designed
with a high-performance optical system and an integrated
reflectance sampling interface.
"Existing nondestructive
testing tools have limited capability to assess the chemical effect of
environmental stresses on the composite," says Dirk Heider, assistant director
of the Delaware
consortium. "Environmental effects on composite properties including exposure
to UV or high temperature during lightning strike and contact with hydraulic
and deicing fluids are difficult to evaluate but knowledge about such effects
is critical to the use of these materials for aerospace applications."
The
consortium helped determine the effectiveness of the new testing device.
"Specifically, we wanted to know whether the handheld FTIR could detect changes
in the molecular structure of the composite induced by increasing exposure temperatures,"
says Alan Rein, vice president for Business Development at A2. "We then wanted
to correlate the spectral changes to the mechanical strength reduction of the
composite."
In tests
carried out on autoclave specimens fabricated using toughened epoxy,
correlation of actual to predicted values was described as very high and within
the standard deviation of the test data. "The results show that the handheld
FTIR can be used to accurately predict the reduction in strength of an epoxy
carbon composite due to high-temperature exposure," Heider says.
The company
and the Center will collaborate under a Federal Aviation Administration program
through 2011 to better understand degradation mechanisms, correlations to FTIR
measurements and the effect of surface preparation on the measurement method.
"Our goal
is to develop a robust technique to evaluate damage to composites and then to
provide a tool to enable effective repair of the damage," Rein says. "Other
applications of the handheld equipment, such as assessment of surface cleaning
methods used prior to adhesive bonding and evaluation of prepreg material for
recertification, are also being considered."
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