New Tool May Boost Dreamliner Safety

Doug Smock, Contributing Editor -- Design News, September 22, 2008

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."