• Shi, Zhengwei
• Howie, Tucker
• Georgeson, Gary
• Flinn, Brian
• Yang, Jeffrey
• Jang, Sei-Hum

Abstract

Incipient thermal damage is a significant issue for CFRP composites because it is difficult to detect by common NDE techniques like ultrasound and it can cause fiber-matrix debonding, delamination, and matrix embrittlement which can reduce the mechanical properties of the composite. Diffuse reflectance infrared transform spectroscopy (DRIFTS) is capable of detecting incipient damage, but it has a small spot size that is not efficient for inspecting large areas for thermal damage. In our previous work a thermally activated fluorescent probe was shown to activate when the composite was thermally exposed. This "turn-on" type behavior could show that thermal exposure had occurred, but could not provide more details about the thermal event. In this study a method for estimating the time and temperature of the thermal exposure (a so-called time-temperature indicator or TTI) is presented. The basis for this method is combining two different thermally activated probes with different activation kinetics and emission wavelengths. Using ratiometric fluorescence to monitor the changes in the fluorescence spectra, time-temperature response curves can be generated that can be used for estimating the time and temperature of the thermal exposure. Copyright 2014 by Tucker Howie.

Topics

• impedance spectroscopy
• composite
• activation
• diffuse reflectance infrared Fourier transform spectroscopy