NDI Tool for Heat Damage Detection in Composites

The incipient thermal damage (ITD) of carbon fiber reinforced plastic (CFRP) composites cannot be detected by common nondestructive evaluation (NDE) methods, such as ultrasound or visual inspection. ITD, however, can reduce matrix dominated mechanical properties of composites and, thus, requires detection and evaluation to ensure the integrity of composite structures that might be subjected to thermal exposures. Fourier transform infrared (FTIR) spectroscopy is an established technique that has shown promise for the NDE of ITDs. The purpose of this work is to develop methodologies using FTIR to detect the thermal damage of BMI carbon fiber reinforced composites with ITD. FTIR works by measuring chemical changes to the polymer matrix as a function of the time and temperature of exposure, which can be correlated with matrix dominated mechanical properties, such as short-beam strength (SBS). A method that uses FTIR spectra to predict the level of damage based on the FTIR measurements will be developed. Additionally, the complementary technique of using Fringing Electric Field Dielectrometry sensors will be integrated with FTIR scans, in order to achieve an unprecedented diagnostics capability being able to combine sensor signals from the surface and from the bulk of the material for a comprehensive damage evaluation.