Composite Characterization By a New Non Destructive Technology (NDT): Mobile Fourier Transform Infrared Spectroscopy (FTIR)

The prospect of greater fuel economy and lower operating costs linked to sturdier and lighter airframe, has led to rapid adoption of composite materials in commercial aircraft.  The increased use of composites presents new challenges in maintaining safe flying conditions and already, calls have been made for improving inspection of composite materials.  All aircrafts are subject to environmental damages; however, composite materials are susceptible to environmental damages that are different than that for traditional aluminum materials. The resin component of the composite consists of organic molecules (most often epoxy based), which are susceptible to the affect of a number of external stressors such as heat, cold, moisture, ultraviolet light and exposure to chemicals.  Analyzing the affect of these environmental stressors on in-service composite based aircraft requires new techniques and strategies.

      Oak Ridge National Labs studied several spectroscopic techniques for the determination of extent of heat damage on composite panels.  The study found that diffuse reflectance FTIR (Fourier Transform Infrared Spectroscopy) or DRIFT spectroscopy and laser induced fluorescence had the highest degrees of success, but both techniques required development of a field unit that could be used for NDI (Non Destructive Inspection).

With recent progresses in optoelectronics, FTIR instruments have now reached a critical form factor to be used in places like aircraft hangars. Combined with easy to use interface, portable FTIR can be operated by non-technical users for composites repair of in-service parts, manufacturing QC and also composite coating QC for identification among other things. In this talk, we will focus on applications of handheld FTIR for analysis of polymers, composites/coatings and the potential to use FTIR as a quality control tool for composite bonding.  First, we will show how FTIR can be correlated to heat damage of BMI composites for aerospace applications such as the maintenance of the Boeing 787 fuselage. Subsequently, we will cover how FTIR can be used to determine composites and/or coatings curing time on large composite parts such as wind turbine blades. Finally, we will show how FTIR can be used to detect manufacturing contaminants such hydrocarbon or silicon based oil on composites parts, assess the level of preparedness of composites from work developed by the University of Washington (AMTAS) group.