Detection of Exposure Damage in Composite Materials Using Fourier Transform Infrared Technology

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1 Detection of Exposure Damage in Composite Materials Using Fourier Transform Infrared Technology Randy Duvall Dennis Roach Sandia National Labs FAA Airworthiness Assurance Center Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy s National Nuclear Security Administration under contract DE-AC04-94AL85000.

2 Goals of Composite NDI & FTIR Program Goal: to detect the subtle changes in laminate composite structures brought about by thermal, chemical, ultraviolet, and moisture exposure Compare sensitivity of an array of NDI methods, including FTIR, to detect subtle differences in composite materials due to deterioration Inspection methods applied: ultrasonic pulse echo, through transmission ultrasonics, thermography, resonance testing, mechanical impedance analysis, eddy current, low frequency bond testing & FTIR Comparisons between the NDI methods are being used to establish the potential of FTIR to provide the necessary sensitivity to non-visible, yet significant, damage in the resin and fiber matrix of composite structures Comparison of NDI results with short beam shear tests are being used to relate NDI sensitivity to reduction in structural performance

3 Fourier Transform Infrared Spectroscopy Chemical analyses technique, which measures the infrared intensity versus wavelength of light reflected on the surface of a structure (chemical and physical information via this signature) Advances in instrumentation have resulted in hand-held portable devices that allow for field use (few seconds per scan) Shows promise for production quality assurance and in-service applications on composite aircraft structures (scarfed repairs) Statistical analysis on frequency spectrums produced by FTIR interrogations are being used to produce an NDI technique for assessing material integrity A2 Technology Devices 2007: Exoscan (6 lbs) 2010: Flexscan (3 lbs)

4 Absorbance Absorbance Exoscan FTIR with Docking Station Infrared Spectra - measures specular reflectance over a frequency range ( cm-1) Determine relationship between FTIR and Short Beam Shear Background wavelength Infrared Measurement for Composites FTIR Signature Wavenumber Wavelength 1200 Infrared Spectra Calibration 1000

5 Thermal Damage Study BMS8-276 Coupons Sample of Thermal Damage Matrix of Test Specimens (24 ply laminates) On average, planes are struck by lightening once per year

6 Assessment of Heat Damage in Composite Laminates Using Conventional NDI and FTIR Several 24-ply carbon graphite laminate sets Set 2 Set 1

7 MAUS V Pulse Echo (10 MHz) Time Base Shift with Amplitude Change Good Signal - Good Laminate Signal Indicating Damaged Laminate

8 MAUS V PE C-Scan Display (Set #1) X-Plot Pristine Ref 1 Pristine Ref 2 E8.1 E8.2 E17.1 E17.2 E19.1 E19.2 C13.1 C13.2 C20.1 C20.2

9 MAUS V PE C-Scan Display (Set #2) Baseline C9-1 C Specimens E8-1 Baseline E9-1 C9-2 E14-1 C Specimens E8-2 E9-2 E14-2

10 MAUS V - Low Frequency Bond Test

11 MAUS V - Low Frequency Bond Test (Set #1, 64 KHz) Pristine Ref 1 Pristine Ref 2 X-Plot E8.1 E8.2 E17.1 E17.2 E19.1 E19.2 C13.1 C13.2 C20.1 C20.2 Only subtle differences observed

12 Bondmaster Low Frequency Bond Test (Swept Mode KHz)

13 Low Frequency Bond Test Comparison of Amplitude and C-Scan Data Typical Bad Areas C13.1 C13.2 MAUS V Low Frequency Bond Test (set #2) C20.1 C20.2 Baseline C9-1 C13-1 E8-1 E9-1 E14-1

14 MAUS V - Mechanical Impedance Analysis (26 KHz) Baseline C9-1 C13-1 MAUS V MIA Set 2 E8-1 E9-1 E14-1

15 Bondmaster - Mechanical Impedance Analysis Good C13.1 C13.2 Bad C20.1 C20.2

16 V-95 Bondtester - Mechanical Impedance Analysis Meter Shows Drop In Amplitude in Flawed Regions (Typical) C20.1 and C20.2 Bad Samples

17 Specimen Set #1 Ranking Temperature Effects with PE UT E19 E17 C F F F C F E F BMS8-276 Material # Calib 13: F # Eval 8: F # Eval 19: F # Eval 17: F # Calib 20: F MAUS V - Pulse-Echo UT Results

18 Specimen Set #2 Ranking Temperature Effects with PE UT E9-1 E14-1 C F F F C F E F BMS8-256 Material C13-1 and -2 : F E8-1 and -2 : F E9-1 and -2 : F E14-1 and -2 : F C9-1 and -2 : F MAUS V - Pulse-Echo UT Results

19 Absorbance FTIR Spectra MASTER Signatures CHART SET 2 Damaged and Undamaged Parts (Set #2) Wavelength Frequency Baseline- Blue C9-1- Red C13-1- Green E8-1- Orange E9-1- Pink E14-1- Purple

20 Absorbance Absorbance A2 Technology Thermal Damage Study - Changes in FTIR Spectra Data analysis uses Neural Networks (history of cal sample set) and weighting functions to produce more robust assessment of component (accurate damage detection with low false calls) High damage No damage Wavenumber Wavenumber

21 Comparison with Short Beam Shear Results (Univ. of Delaware) Short Beam Shear Test Set-Up SBS Testing Raw Data Test Specimen

22 Comparison of NDI with Short Beam Shear Results Short Beam Shear Strength Retention vs. Temp./Time Set 1 No cracks visible in micrographs Onset of crack development visible in micrographs Damage becomes visible in C-Scans

23 FTIR Predicted SBS Predicted SBS Comparison of FTIR and Short Beam Shear Results Possible to not only detect deterioration but also determine strength values for composite structure Measured SBS Measured SBS (MPa)

24 Conclusions Use of NDI to assess loss of composite laminate integrity brought about by thermal, chemical, ultraviolet, and moisture exposure Degradation trends between SBS strength and exposure levels (temperature and time) have been established for different materials Various NDI methods have been applied to evaluate damage and relate this to loss of integrity PE UT shows greatest sensitivity FTIR shows promise for damage detection and calibration to predict structural integrity (short beam shear) Detection of damage for medium exposure levels (possibly resin matrix degradation only) is more difficult and requires additional study These are initial results only - program is continuing with additional heat, UV, chemical and water exposure test specimens

25 2010 ATA NDT Forum Detection of Exposure Damage in Composite Materials Using Fourier Transform Infrared Technology Randy Duvall Dennis Roach Sandia National Laboratories FAA Airworthiness Assurance Center Infrared (IR) spectroscopy is a chemical analyses technique, which measures the infrared intensity versus wavelength of light reflected on the surface of a structure. Infrared spectroscopy has long been used in the laboratory as a means of gaining chemical and physical information about materials. Fourier Transform Infrared (FTIR) spectrometry was developed in order to overcome the limitations encountered with dispersive instruments. The main difficulty was the slow scanning process and the limitation of laboratory-based use. Recent advances in instrumentation have resulted in hand-held portable devices that allow the laboratory to be taken to the sample. The signal can be acquired very quickly such that the time element per sample is reduced to a matter of a few seconds rather than several minutes. Aircraft manufacturers are now interested in using this infrared technology to support production quality assurance and in-service applications on aircraft. The FAA Airworthiness Assurance Center at Sandia National Labs has been inspecting damaged, carbon composite panels with various nondestructive inspection processes and comparing these results with those obtained with A2 Technology s FTIR system. The inspections are intended to detect the subtle changes in carbon composite structures brought about by thermal, chemical, ultraviolet, and moisture exposure. Inspection methods applied to the solid laminate specimens include: ultrasonic pulse echo, through transmission ultrasonics, thermography, resonance testing, mechanical impedance analysis, eddy current, and low frequency bond testing. Statistical analysis on frequency spectrums produced by FTIR interrogations are being used to produce a robust NDI technique for assessing material integrity. Comparisons between the various methods are being used to establish the potential of FTIR to provide the necessary sensitivity to non-visible, yet significant, damage in the resin and fiber matrix of composite structures.