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The University of Delaware Center for Composite Materials’ Industrial Consortium member A2 Technologies has developed an innovative handheld device that allows on-site non-destructive testing of aircraft components.
Known as the Exoscan, the analyzer is based on a common characterization technology, Fourier Transform Infrared Spectroscopy (FTIR), which has traditionally been carried out in a lab. However, Exoscan is portable, thus 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 and/or contamination on the surface, allowing evaluation of damage due to environmental effects.
“The use of carbon composite materials has grown significantly in recent years,” says CCM Assistant Director Dirk Heider. “In particular, new aerospace designs that incorporate lightweight composites, such as the Boeing 787 Dreamliner, benefit from lower total structural weight and the potential for reduced maintenance requirements.”
“However,” he continues, “existing nondestructive testing tools have limited capability to assess the chemical affect of environmental stresses on the composite. 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.”
To test the effectiveness of the Exoscan, A2 Technologies turned to CCM for help. “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 at CCM on autoclave specimens fabricated using Cytec 977–3 toughened epoxy, correlation of actual to predicted values was very high and consistently within the standard deviation of the actual mechanical 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 continue to collaborate under a program funded by the Federal Aviation Administration over the next three years in an effort 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 NDE 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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